JP4199014B2 - Semiconductor impurity doping method and apparatus therefor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a semiconductor impurity doping method and apparatus, and more particularly, to a semiconductor impurity doping method and apparatus suitable for use in producing a semiconductor material having high conductivity.
[0002]
[Prior art]
Conventionally, when a semiconductor material is produced, a plurality of types of crystal raw materials and a plurality of types of impurity raw materials are used in a predetermined crystal growth apparatus etc. A semiconductor impurity doping method is known in which impurities are doped into a crystal layer formed on a substrate by a raw material.
[0003]
By the way, in this conventional semiconductor impurity doping method, the plurality of types of crystal raw materials and the plurality of types of impurity raw materials are continuously supplied, so that the crystal atomic layer formed on the substrate by the crystal raw materials. A plurality of types of impurities are randomly taken into the inside.
[0004]
For this reason, when the plurality of types of impurity materials are a p-type impurity material and an n-type impurity material, respectively, the p-type impurity material and the n-type impurity material cancel each other (compensation effect), and the carrier The concentration is a difference in concentration between the p-type impurity material and the n-type impurity material, and there is a problem that the carrier concentration of the semiconductor material to be produced is reduced and the conductivity is reduced.
[0005]
In addition, when a p-type semiconductor material is produced by continuously supplying a plurality of types of crystal raw materials and a plurality of types of impurity raw materials by a conventional semiconductor impurity doping method, the p-type semiconductor material is in a forbidden band. Since the impurity level is deep and the activation energy is large, there is a problem in that high density holes cannot be obtained and the conductivity becomes low.
[0006]
In view of these problems, even when the p-type impurity material and the n-type impurity material are doped in the crystal layer, a semiconductor material having a high conductivity can be formed by increasing the carrier concentration. Semiconductor impurity doping method and apparatus therefor, semiconductor impurity doping method and apparatus capable of producing a high-conductivity p-type semiconductor material having high-density holes, and high conductivity A semiconductor material has been proposed by the present inventor (see Patent Document 1).
[0007]
[Patent Document 1]
JP 2002-75879 A
By the way, in recent years, in order to produce optical devices and electronic devices in the ultraviolet wavelength region, development of p-type AlGaN having high conductivity and high conductivity is required. In particular, a p-type AlGaN high-conductivity material having a high Al composition ratio was indispensable for the production of light-emitting diodes (LEDs) and laser diodes (LDs) in the ultraviolet region.
[0008]
However, conventionally, it has been extremely difficult to produce a p-type crystal having high conductivity with AlGaN having a high Al composition ratio.
[0010]
[Problems to be solved by the invention]
  The present invention has been made in view of the problems of the prior art as described above.An object of the present invention is to provide a semiconductor impurity doping method and apparatus capable of producing a p-type semiconductor material having a high hole concentration and high conductivity.
[0011]
Another object of the present invention is to produce a semiconductor material having high conductivity so that the carrier concentration is increased even when the p-type impurity material and the n-type impurity material are doped into the crystal layer. It is an object of the present invention to provide a semiconductor impurity doping method and apparatus capable of achieving the above.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, when a semiconductor crystal is grown, a plurality of types of crystal raw materials are alternately supplied in a pulse shape to perform the crystal growth.
[0014]
For example, when AlGaN is grown by using a metalorganic chemical vapor phase epitaxy (MOVPE) method, a group III element of Al and Ga and a group V element of N are pulsed as crystal raw materials. AlGaN crystals are grown by alternately supplying them.
[0015]
Further, in the present invention, when doping impurities into a semiconductor, crystal growth is performed by alternately supplying a plurality of types of crystal raw materials in a pulsed manner, and the impurity raw materials are supplied in a pulsed manner by controlling the timing. Thus, the semiconductor is doped with impurities.
[0016]
Here, the impurity source for doping the semiconductor may be a single impurity source or a plurality of types of impurity sources. In the case of a single impurity source, either a p-type impurity source or an n-type impurity source may be used. In the case of a plurality of types of impurity sources, both the p-type impurity source and the n-type impurity source are used. There may be.
[0017]
For example, when Mg and Si are doped as impurity raw materials while growing AlGaN using the MOVPE method, Group III elements of Al and Ga and Group V elements of N are alternately supplied in a pulse manner as crystal raw materials. In addition to crystal growth of AlGaN, impurity raw materials Mg and Si are also supplied with pulse timing controlled to perform impurity doping in AlGaN.
[0018]
  That is, the invention according to claim 1 of the present invention isIn a semiconductor impurity doping method for doping a crystal layer formed of a crystal raw material with impurities, TMGa, TMAl and Cp at a first timing ₂ Mg supply started, Cp ₂ At the second timing when Mg is supplied for a predetermined time, Cp ₂ A first step of terminating the supply of Mg; and Cp ₂ A second step of starting the supply of TESi immediately after or after the second timing at which the supply of Mg is terminated, and ending the supply of TMGa, TMAl, and TESi at a third timing at which TESi is supplied for a predetermined time; , Immediately after or after the third timing when the supply of TMAl and TESi is terminated. ₃ Started to supply NH ₃ At the fourth timing when the gas is supplied for a predetermined time. ₃ The cycle consisting of the third step of ending the supply of is repeated a predetermined number of timesIt is what I did.
[0019]
  The invention according to claim 2 of the present invention is the invention according to claim 1 of the present invention.In order to suppress the desorption of nitrogen from the AlGaN surface, it does not degrade the crystal quality.A small amount of N is continuously supplied.
[0020]
  The invention according to claim 3 of the present invention is a semiconductor impurity doping apparatus for doping impurities into a crystal layer formed of a crystal raw material, and a reaction tube in which a substrate is disposed, A plurality of tubes for supplying gaseous materials Ga, Al, and N in gaseous form into the reaction tube and supplying Mg and Si as impurity materials in gaseous form, respectively, and disposed in each of the plurality of tubes. A gas valve, flow rate setting means for setting the flow rates of the crystal raw material gas and the impurity raw material gas flowing in the plurality of tubes to predetermined values, and heating the substrate disposed in the reaction tube, respectively. Heating means for controlling, opening and closing control of the gas valve, control of the flow rate set by the flow rate setting means, and control of heating of the substrate by the heating means, the Al and Ga of the crystal raw material And the supply of N gas of the crystal raw material are alternately performed in a pulsed manner, at the same time as or after the start of supply of the Al and Ga gases of the crystal raw material, and Prior to the start of supplying the N gas of the crystal material, control is performed so that the Mg and Si gases of the impurity material are supplied at close timings.Control meansIn the semiconductor impurity doping apparatus, the Ga gas of the crystal material is TMGa, the Al gas of the crystal material is TMAl, and the N gas of the crystal material is NH.₃And the impurity source Mg gas is Cp.₂Mg, and the impurity source Si gas is TESi, and the control means is configured to transmit TMGa, TMAl, and Cp at the first timing.₂Mg supply started, Cp₂At the second timing when Mg is supplied for a predetermined time, Cp₂A first step of terminating the supply of Mg; and Cp₂A second step of starting the supply of TESi immediately after or after the second timing at which the supply of Mg is terminated, and ending the supply of TMGa, TMAl and TESi at a third timing at which TESi is supplied for a predetermined time; , Immediately after or after the third timing when the supply of TMAl and TESi is terminated.₃Started to supply NH₃At the fourth timing when the gas is supplied for a predetermined time.₃Is controlled so as to repeat a cycle consisting of the third step of ending the supply of a predetermined number of times.
[0040]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, embodiments of a semiconductor impurity doping method and apparatus according to the present invention will be described in detail with reference to the accompanying drawings. In the following description and the drawings, the same or corresponding configurations and contents are indicated by the same reference numerals.
[0041]
  FIG. 1 shows a semiconductor crystal growth method andAccording to the inventionFIG. 2 is a schematic configuration explanatory view of a main part of a crystal growth apparatus that realizes a semiconductor impurity doping method. FIG. 2 shows an example of timing at which a crystal material is supplied by a semiconductor crystal growth method, that is, a material supply pulse. FIG. 3 is an explanatory diagram schematically showing a crystal structure of a semiconductor crystal formed by a semiconductor crystal growth method. FIG. 4 and FIG. FIG. 6 is a timing chart showing an example of the timing at which the crystal material and the impurity material are supplied by the semiconductor impurity doping method according to the present invention, that is, an example of the sequence of the material supply pulse. FIG. 7 is an explanatory diagram schematically showing the crystal structure of the semiconductor material formed by the semiconductor impurity doping method according to the present invention. To have.
[0042]
In the following description, as the crystal raw material A, for example, a group III element and a group II element such as Al, Ga, In, B, Zn, Cd can be used. As the crystal raw material B, for example, Al , Ga, In, B, Zn, Cd and other Group III elements and Group II elements can be used. Examples of the crystal raw material C include group V elements such as N, As, P, S, Se, Te, and the like. Group VI elements can be used. For example, Mg, Be, Si, O or the like can be used as the impurity raw material D. For example, Mg, Be, Si, O or the like can be used as the impurity raw material E. Can do.
[0043]
However, the crystal raw material A, the crystal raw material B, and the crystal raw material C are different from each other. Further, the crystal raw material A, the crystal raw material B, and the crystal raw material C are not limited to one kind of element, and two or more kinds of elements can be used.
[0044]
When a group III element is used as the crystal material A and the crystal material B, a group V element is preferably used as the crystal material C, and a group II element is used as the crystal material A and the crystal material B. In this case, it is preferable to use a group VI element as the crystal raw material C.
[0045]
The impurity source D and the impurity source E use different elements, one of them is a p-type impurity source for forming a p-type semiconductor, and the other is for forming an n-type semiconductor. An n-type impurity material is used.
[0046]
  First, in order to facilitate understanding of a semiconductor crystal growth method (hereinafter referred to as “first method” where appropriate), a reaction tube of a crystal growth apparatus having a substrate disposed therein will be described. (For example, composed of quartz glass), each of the crystal materials is supplied in a pulsed manner at a predetermined timing via a tube (for example, composed of quartz glass), and the supplied crystal materials react. In this case, a crystal structure is formed on the substrate by reacting in the tube (see FIG. 1. Note that when only the first method is performed, the impurity raw material D and the impurity raw material E are not supplied. The configuration relating to the supply of the impurity raw material D and the impurity raw material E may be deleted from the configuration shown in FIG.
[0047]
More specifically, when crystal formation is performed using the crystal raw material A, the crystal raw material B, and the crystal raw material C by the first method, all of the crystal raw material A, the crystal raw material B, and the crystal raw material C are continuously supplied. In this case, the supply is performed for a predetermined time, and the supply is stopped and supplied in a pulse shape except for the predetermined time.
[0048]
The crystal raw material A and the crystal raw material B are supplied at the same time, but the crystal raw material C is not supplied at the same time as the crystal raw material A and the crystal raw material B.
[0049]
FIG. 2 shows a timing chart showing an example of the first technique. In this timing chart, the crystal raw material A and the crystal raw material B are set to a predetermined time T._AJust after that, the crystal raw material C is supplied immediately after that for a predetermined time T._BThis cycle is repeated with this as one cycle. That is, the supply of the crystal material A and the crystal material B and the supply of the crystal material C are time T_A, T_BTherefore, the supply of the crystal raw material A and the crystal raw material B and the supply of the crystal raw material C are not performed at the same timing.
[0050]
Specifically, the supply of the crystal raw material A and the crystal raw material B is started at the timing T1.
[0051]
Then, the crystal raw material A and the crystal raw material B are changed to a time T_AOnly at the timing T2, the supply of the crystal raw material A and the crystal raw material B is completed.
[0052]
Then, immediately after the timing T2 at which the supply of the crystal raw material A and the crystal raw material B is finished, the supply of the crystal raw material C is started,_BOnly at the timing T3, the supply of the crystal raw material C is finished.
[0053]
One cycle of processing is completed as described above, and the next cycle is started with this timing T3 as timing T1.
[0054]
By repeating such a cycle a desired number of times, a crystal having a desired film thickness can be obtained as a semiconductor crystal.
[0055]
That is, as described above, the crystal raw material A, the crystal raw material B, and the crystal raw material C are all supplied once, that is, by repeating one cycle from timing T1 to timing T3 as one cycle. A crystal having a desired thickness is formed.
[0056]
Note that the supply timing of the crystal raw material C is not limited to immediately after the timing T2 when the supply of the crystal raw material A and the crystal raw material B is completed, and even after a predetermined time has elapsed after the arrival of the timing T2. Good.
[0057]
The crystal structure formed according to the timing shown in FIG. 2 has a time T from timing T1, as shown in FIG._ABy supplying the crystal raw material A and the crystal raw material B, a layer 102 composed of the crystal raw material A and the crystal raw material B is formed on the substrate 100.
[0058]
Then, time T from timing T2_BBy supplying the crystal raw material C, the layer 104 made of the crystal raw material C is laminated on the layer 102 made of the crystal raw material A and the crystal raw material B.
[0059]
Further, when the above-described one cycle (see FIG. 2) is repeated a desired number of times, the layer 102 composed of the crystal raw material A and the crystal raw material B and the layer 104 composed of the crystal raw material C are changed according to the number of repeated cycles. Lamination is repeated to form a crystal having a desired thickness W, and this crystal can be used as a semiconductor crystal.
[0060]
Next, in order to facilitate understanding of the first method (hereinafter referred to as “second method” as appropriate) of the semiconductor impurity doping method according to the present invention, an outline thereof will be described. A crystal raw material and one kind of impurity raw material are pulsed through a tube (for example, composed of quartz glass) or the like in a reaction tube (for example, composed of quartz glass) of the provided crystal growth apparatus. The crystal raw material and the impurity raw material react with each other in a reaction tube to form a crystal structure on the substrate (see FIG. 1; see the second example). When only the method is performed, the impurity raw material E is not supplied, so the configuration relating to the supply of the impurity raw material E may be deleted from the configuration shown in FIG.
[0061]
More specifically, when crystal formation is performed using crystal raw material A, crystal raw material B, crystal raw material C and impurity raw material D by the second method, crystal raw material A, crystal raw material B, crystal raw material C and impurity raw material are used. D is not continuously supplied, but is supplied only for a predetermined time, and the supply is stopped and supplied in a pulse shape except for the predetermined time.
[0062]
Here, the crystal raw material A, the crystal raw material B, and the crystal raw material C are supplied at the same timing as the first method described above.
[0063]
On the other hand, the impurity source D is synchronized with the supply of the crystal source A and the crystal source B, or after the start of the supply of the crystal source A and the crystal source B and before the start of the supply of the crystal source C. Supplied in pulses.
[0064]
FIG. 4 shows a timing chart showing an example of the second method. In this timing chart, the supply of the crystal raw material A and the crystal raw material B is started at the timing T1, and the impurity raw material D is supplied. Start supplying.
[0065]
Then, the crystal raw material A and the crystal raw material B are changed to a time T_AOnly while supplying the impurity material D for a time T_ATime T equal to_COnly at the timing T2, the supply of the crystal raw material A and the crystal raw material B is finished and the supply of the impurity raw material D is finished.
[0066]
Then, immediately after the timing T2 when the supply of the crystal raw material A, the crystal raw material B, and the impurity raw material D is finished, the supply of the crystal raw material C is started,_BOnly at the timing T3, the supply of the crystal raw material C is finished.
[0067]
One cycle of processing is completed as described above, and the next cycle is started with this timing T3 as timing T1.
[0068]
By repeating such a cycle a desired number of times, a crystal having a desired film thickness can be obtained as a semiconductor material.
[0069]
That is, as described above, the crystal raw material A, the crystal raw material B, the crystal raw material C, and the impurity raw material D are all supplied once, that is, one cycle from timing T1 to timing T3. By repeating the process, a crystal having a desired thickness can be formed.
[0070]
The supply timing of the impurity source D is not limited to being synchronized with the timing T1 when the supply of the crystal source A and the crystal source B is started, and the supply of the crystal source A and the crystal source B is started. It may be after the timing T1.
[0071]
In short, the impurity raw material D is supplied at the same time as or after the start of the supply of the crystal raw material A and the crystal raw material B and before the start of the supply of the crystal raw material C.
[0072]
The crystal structure formed in accordance with the timing shown in FIG. 4 has a predetermined time T from timing T1, as shown in FIG._ABy supplying the crystal raw material A and the crystal raw material B, a layer 502 composed of the crystal raw material A and the crystal raw material B is formed on the substrate 100.
[0073]
At this time, by supplying the impurity material D, the impurity material D is doped in the layer 502 made of the crystal material A and the crystal material B.
[0074]
Then, time T from timing T2_BBy supplying the crystal raw material C, the layer 504 made of the crystal raw material C is laminated on the layer 502 made of the crystal raw material A and the crystal raw material B doped with the impurity raw material D.
[0075]
Further, when the above-described one cycle (see FIG. 4) is repeated a desired number of times, the layer 502 composed of the crystal raw material A and the crystal raw material B doped with the impurity raw material D and the crystal raw material according to the number of repeated cycles. Lamination with the layer 504 made of C is repeated to form a crystal having a desired thickness W, and this crystal can be used as a semiconductor material.
[0076]
Next, in order to facilitate understanding of a semiconductor impurity doping method according to the present invention (hereinafter, referred to as “third method” where appropriate), an outline thereof will be described. Crystal growth with a substrate disposed therein Crystal raw material and impurity raw material (p-type impurity raw material and n-type impurity raw material) through a tube (eg made of quartz glass) in a reaction tube (eg made of quartz glass) of the apparatus Are supplied in pulses at predetermined timings, and the supplied crystal material and impurity material react in a reaction tube to form a crystal structure on the substrate (see FIG. 1).
[0077]
More specifically, the crystal raw material A, the crystal raw material B, the crystal raw material C, the impurity raw material D (for example, a p-type impurity raw material) and the impurity raw material E (for example, an n-type impurity raw material) are obtained by the third method. ) (See FIG. 6), the crystal raw material A, the crystal raw material B, the crystal raw material C, the impurity raw material D, and the impurity raw material E are not continuously supplied, but for a predetermined time. The supply is performed only, and the supply is stopped and supplied in a pulse shape except for the predetermined time.
[0078]
Here, the crystal raw material A, the crystal raw material B, the crystal raw material C, and the impurity raw material D are supplied at the same timing as in the second method. FIG. 6 shows a timing chart showing an example of the third technique. Unlike the timing chart shown in FIG. 4, the timing chart shown in FIG. The supply of the raw material D is not completely synchronized with the supply of the crystal raw material A and the crystal raw material B. That is, the supply start timing of the impurity raw material D coincides with the supply start timing of the crystal raw material A and the crystal raw material B, but the time T during which the impurity raw material D is supplied._CTime T for supplying crystal raw material A and crystal raw material B_ATherefore, the timing of the end of the supply of the impurity source D is earlier than the timing of the end of the supply of the crystal source A and the crystal source B.
[0079]
In this third method, the impurity material E is also synchronized with the supply of the crystal material A and the crystal material B, or after the start of the supply of the crystal material A and the crystal material B, as with the impurity material D. In addition, before the start of the supply of the crystal raw material C, it is supplied in a pulse shape, and the impurity raw material D and the impurity raw material E are supplied at close timing.
[0080]
The timing chart shown in FIG. 6 will be specifically described. At timing T1, the supply of the crystal material A, the crystal material B, and the impurity material D is started.
[0081]
Then, the crystal raw material A and the crystal raw material B are changed to a time T_AIn addition to supplying the impurity raw material D for time T_AShorter time T_CThen, the supply of the impurity material D is finished at the timing T1 '.
[0082]
Next, immediately after the timing T1 'at which the supply of the impurity material D is finished, the supply of the impurity material E is started, and the impurity material E is supplied for a predetermined time T1._DThen, the supply of the crystal raw material A, the crystal raw material B, and the impurity raw material E is finished at timing T2.
[0083]
Then, the supply of the crystal material C is started immediately after the timing T2 when the supply of the crystal material A, the crystal material B, and the impurity material E is finished._BThen, the supply of the crystal raw material C is finished at the timing T3.
[0084]
One cycle of processing is completed as described above, and the next cycle is started with this timing T3 as timing T1.
[0085]
That is, as described above, a unit in which the supply of the crystal raw material A, the crystal raw material B, the crystal raw material C, the impurity raw material D and the impurity raw material E are all performed once, that is, one cycle from timing T1 to timing T3, By repeating this one cycle, a crystal having a desired thickness is formed.
[0086]
Note that the supply start timing of the impurity source E is not limited to immediately after the timing T1 'at which the supply of the impurity source D ends, but may be the timing T1 at which the supply of the impurity source D is started.
[0087]
That is, the time T between the timing at which the supply of the impurity source D is started (see timing T1 in FIG. 6) and the timing at which the supply of the impurity source E is started (see timing T1 'in FIG. 6)._cdIs 0 or more time T_cThe period during which the impurity raw material D and the impurity raw material E are simultaneously supplied may be generated.
[0088]
Further, the supply of the impurity raw material D is not limited to being synchronized with the timing T1 when the supply of the crystal raw material A and the crystal raw material B is started, and the supply of the crystal raw material A and the crystal raw material B is started. It may be after the timing T1.
[0089]
In short, the impurity material D and the impurity material E are supplied at the same time as or after the start of the supply of the crystal material A and the crystal material B, and at a timing close to the start of the supply of the crystal material C. is there.
[0090]
The crystal structure formed in accordance with the timing shown in FIG. 6 has a time T from timing T1, as shown in FIG._ABy supplying the crystal raw material A and the crystal raw material B, a layer 702 composed of the crystal raw material A and the crystal raw material B is formed on the substrate 100.
[0091]
At this time, the impurity source D and the impurity source E are doped in the layer 702 composed of the crystal source A and the crystal source B by the supply of the impurity source D and the impurity source E. It is considered that a kind of impurity pair (DE) due to E is formed.
[0092]
Then, time T from timing T2_BThe layer 704 made of the crystal material C is stacked on the layer 702 made of the crystal material A and the crystal material B doped with the impurity material D and the impurity material E.
[0093]
Further, when the above-described one cycle (see FIG. 6) is repeated a desired number of times, the crystal material A and the crystal material B are doped with the impurity material D and the impurity material E according to the number of repeated cycles. Lamination of the layer 702 and the layer 704 made of the crystal raw material C is repeated to form a crystal having a desired thickness W, and this crystal can be used as a semiconductor material.
[0094]
In the first method, the second method, and the third method described above, gallium (Ga) is used as the crystal material A, aluminum (Al) is used as the crystal material B, and nitrogen (N) is used as the crystal material C. When forming a layer of AlGaN crystal on the substrate using magnesium (Mg) as the impurity source D and silicon (Si) as the impurity source E, the supply of N as the crystal source C is stopped. In order to suppress desorption of N from the AlGaN surface in the inside, it is preferable to continuously supply a small amount of N that does not deteriorate the crystal quality.
[0095]
Next, with reference to FIG. 8 to FIG. 16, a case where an AlGaN crystal layer is formed as a semiconductor crystal (semiconductor material) on a substrate by the first method, the second method, and the third method described above. I will explain.
[0096]
FIG. 8 shows metal organic chemical vapor deposition (MOCVD) that can be used as an apparatus for forming a layer of an AlGaN crystal as a semiconductor material by the first method, the second method, and the third method described above. A schematic configuration explanatory diagram of the Vapor Deposition apparatus is shown.
[0097]
Further, FIG. 9 shows a schematic configuration explanatory diagram of the main part of FIG. 8, FIG. 10 shows a schematic configuration explanatory diagram of the reaction tube shown in FIG. 8, and FIG. FIG. 12 is a timing chart showing an example of timing for supplying a crystal raw material when forming AlGaN as a semiconductor crystal by the technique 1, that is, an example of a sequence of raw material supply pulses when forming AlGaN. FIG. 13 is an explanatory diagram schematically showing the crystal structure of AlGaN formed by the raw material supply pulse sequence when forming the AlGaN shown in FIG. 11 by the first method. An example of timing for supplying a crystal raw material and an impurity raw material when forming an AlGaN crystal as a semiconductor material by the method 2, that is, a sequence of a raw material supply pulse when forming AlGaN A timing chart showing an example is shown, and FIG. 14 schematically shows the crystal structure of AlGaN formed by the sequence of raw material supply pulses when forming AlGaN shown in FIG. 13 by the second method. FIG. 15 shows an explanatory diagram, and FIG. 15 shows an example of timing for supplying a crystal raw material and an impurity raw material when forming an AlGaN crystal as a semiconductor material by the third technique, that is, a raw material for forming AlGaN. A timing chart showing an example of a supply pulse sequence is shown, and FIG. 16 shows an AlGaN crystal structure formed by a raw material supply pulse sequence when forming the AlGaN shown in FIG. 15 by the third method. The explanatory view which shows typically is shown.
[0098]
In the following description, when AlGaN is grown by the first method, trimethylgallium (TMGa) is used as a source gas for gallium (Ga) as a crystal source, and aluminum (Al) source as a crystal source. Trimethylaluminum (TMAl) is used as a gas, and ammonia (NH) is used as a source gas for nitrogen (N) as a crystal source.₃) Shall be used.
[0099]
Further, when forming an AlGaN crystal as a semiconductor material by the second method, in addition to the crystal material used in the first method, magnesium (Mg) as an impurity material for doping (p-type impurity material) As a raw material gas, biscyclopentadienylmagnesium (Cp₂Mg) is used.
[0100]
That is, biscyclopentadienyl magnesium (Cp) is used as a magnesium (Mg) raw material as an impurity of p-type AlGaN.₂Mg) is used.
[0101]
Further, when forming an AlGaN crystal as a semiconductor material by the third method, in addition to the crystal material used in the first method and the impurity material used in the second method, doping impurities Tetraethylsilane (TESi) is used as a source gas of silicon (Si) which is a material (n-type impurity source).
[0102]
That is, tetraethylsilane (TESi) is used as a silicon (Si) raw material as an impurity of n-type AlGaN.
[0103]
First, the outline of the MOCVD apparatus (AlGaN crystal growth MOCVD apparatus) 10 shown in FIG. 8 will be described. A bubbler 14 for storing, a bubbler 15 for storing trimethylaluminum (TMAl), and ammonia (NH₃) NH storing gas₃Cylinders 16-1, 16-2 and biscyclopentadienylmagnesium (Cp₂A bubbler 18 for storing Mg), a bubbler 20 for storing tetraethylsilane (TESi), and hydrogen (H₂) H to store gas₂Cylinder 22 and nitrogen (N₂N) to store gas₂The cylinder 24 and various controls (for example, control of opening and closing various gas valves and pressure reducing valves described later, and various mass flows described later for setting the flow rates of various gases flowing into the reaction tube 12 to predetermined values) A control device 26 for controlling the controller, controlling the temperature of the substrate 200 by controlling energization of a high-frequency current to the substrate heating high-frequency coil 32, which will be described later, and an exhaust device for exhausting the reaction tube 12 The rotary pump 28 and an exhaust gas treatment device 30 for treating the exhaust gas from the rotary pump 28 are provided.
[0104]
Here, a high frequency coil 32 for substrate heating is wound around the outer periphery of the reaction tube 12. In addition, a carbon susceptor 34 that supports the substrate 200 is disposed inside the reaction tube 12, and a thermocouple 36 that is attached to the carbon susceptor 34 is disposed.
[0105]
That is, in the MOCVD apparatus 10, the carbon susceptor 34 is heated by passing a high-frequency current through the substrate heating high-frequency coil 32, thereby heating the substrate 200 disposed on the carbon susceptor 34 to a predetermined temperature. To do.
[0106]
Then, the temperature of the carbon susceptor 34 is monitored by the thermocouple 36, and the high frequency current supplied to the high frequency coil 32 for substrate heating is controlled by the control device 26 based on this monitor, and the substrate 200 is heated to a predetermined temperature. Thus, the temperature of the substrate 200 is controlled.
[0107]
Further, the reaction tube 12 includes NH in the reaction tube 12.₃From cylinders 16-1 and 16-2 to NH₃A quartz tube 40 for supplying gas, and H₂H as carrier gas from cylinder 22₂A quartz tube 42 for supplying gas, and N₂N as carrier gas from cylinder 24₂A quartz tube 43 for supplying gas is disposed.
[0108]
And NH₃NH stored in cylinders 16-1 and 16-2₃When the gas valves 57, 59, 60, 61 are opened, the gas flows at a gas flow rate set to a predetermined value by the mass flow controllers (MFC) 50, 51, respectively.₂The gas is supplied into the reaction tube 12 through the quartz tube 40 together with the gas.
[0109]
H₂H stored in the cylinder 22₂The gas is sent from the hydrogen purifier 70 through the gas valve 80 and the pressure reducing valve 81, and the gas valves 67, 77, 68, 69 are opened at a gas flow rate set to a predetermined value by the MFCs 54, 75, 55, 56. As a result, it is supplied to the bubblers 14, 15, 18, and 20.
[0110]
Here, the bubblers 14, 15, 18, and 20 are provided with thermostats 72, 73, 74, and 76, respectively, and are stored in the bubblers 14, 15, 18, and 20 and maintained at predetermined temperatures, respectively. TMGa, TMAl, Cp₂When the gas valves 64, 65, 66, 91, and 92 are opened and the gas valve 62 is opened, Mg and TESi have a gas flow rate of H set to a predetermined value by the MFC 52.₂Along with the carrier gas, each is supplied into the reaction tube 12 via the quartz tube 42.
[0111]
On the other hand, N₂N stored in cylinder 24₂When the gas valve 63 is opened, the gas is supplied into the reaction tube 12 through the quartz tube 43 at a gas flow rate set to a predetermined value by the MFC 53.
[0112]
The gas flow rate is controlled by the MFCs 50, 51, 52, 53, 54, 75, 55, 56, and the gas valves 57, 59, 60, 61, 62, 63, 64, 65, 66, 67, 77, 68, 69 are used. , 80, 91, 92 and control of opening / closing of the pressure reducing valve 81 are performed by the control device 26.
[0113]
In the above configuration, in order to form an AlGaN crystal by the first method, the second method, and the third method in the MOCVD apparatus 10, the pressure (internal pressure) in the reaction tube 12 is set to 76 Torr (0.1 atm). ) And a mixed gas obtained by mixing hydrogen at a flow rate of 5 slm and nitrogen at a flow rate of 2 slm is used as a carrier gas, and the source gas of each of the above-described raw materials is introduced into the reaction tube 12 by the carrier gas. Crystal growth is performed.
[0114]
The substrate 200 uses a sapphire substrate (0001) surface, and will be described as a sapphire substrate 200 hereinafter.
[0115]
Hereinafter, each of the first method, the second method, and the third method will be described in detail.
[0116]
First, the first method will be described. In order to clean the sapphire substrate 200 disposed on the carbon susceptor 34 before crystal growth, the sapphire substrate 200 is heated in hydrogen gas at 1200 ° C. for 10 minutes to obtain sapphire. Cleaning such as removing the oxide film on the surface of the substrate 200 is performed.
[0117]
Next, an AlN low-temperature buffer layer (LT-AlN buffer) 202 is deposited on the sapphire substrate 200 disposed on the carbon susceptor 34 by a known technique at 600 ° C. for 3 minutes, and then heated to 1130 ° C. Then, a non-doped AlGaN buffer layer (AlGaN buffer) 204, which is not doped with magnesium and silicon as impurity materials, is grown by continuously supplying crystal materials by a known technique (see FIG. 12).
[0118]
On the AlGaN buffer layer 204 thus formed, AlGaN crystal growth was performed by alternately supplying crystal raw materials by the first method (see FIG. 12).
[0119]
Specifically, the pressure in the reaction tube 12 (internal pressure) is reduced to 76 Torr (0.1 atm), and the temperature of the sapphire substrate 200 disposed on the carbon susceptor 34 is heated to 1100 ° C.
[0120]
Further, the control device 26 controls the MFCs 50, 51, 52, 53, and NH₃NH supplied from the cylinder 16-1.₃The gas flow rate is controlled to 1 liter / min (L / min), NH₃NH supplied from cylinder 16-2₃The gas flow rate is controlled to 50 cc / min (cc / min), and H₂H supplied from cylinder 22₂Control the gas flow rate to 2-5 liters / min, N₂N supplied from cylinder 24₂The gas flow rate is controlled to 1 to 3 liters / minute.
[0121]
That is, the source gas on the sapphire substrate 200 in the reaction tube 12 (TMGa gas supplying Ga as a crystal source, TMAl gas supplying Al as a crystal source, and NH supplying N as a crystal source)₃The internal pressure in the reaction tube 12 is reduced to 0.1 atm to make the gas) switching time 0.1 seconds or less, and the flow rates of various source gases may be several meters / second. preferable.
[0122]
Note that at high temperatures, NH₃NH from cylinder 16-1₃In order to prevent nitrogen atoms from re-evaporating from the formed AlGaN crystals and deteriorating the quality of the formed crystals while the gas supply is stopped.₃NH with small flow rate (50cc / min) from cylinder 16-2₃Gas shall be supplied continuously.
[0123]
Then, as shown in FIG. 11, TMGa and TMAl supply and NH₃Are alternately performed for 2 seconds (sec) to form an AlGaN crystal. The control device 26 controls the MFCs 58 and 77, and the flow rate of TMGa supplied from the bubbler 18 is 1 × 10.^-5The flow rate of TMAl supplied from the bubbler 15 is controlled to 1 mol / min (mol / min).^-6Control to mol / min (mol / min).
[0124]
More specifically, first, supply of TMGa and TMAl is started at timing T1.
[0125]
Then, TMGa and TMAl are set for 2 seconds (time T_A) And the supply of TMGa and TMAl is terminated at timing T2.
[0126]
Then, NH immediately after the timing T2 when the supply of TMGa and TMAl is finished.₃From cylinder 16-1 to NH₃Started to supply NH₃For 2 seconds (time T_B) Supply, NH at timing T3₃The supply of is terminated.
[0127]
One cycle of processing is completed as described above, and the next cycle is started with this timing T3 as timing T1.
[0128]
By repeating such a cycle a desired number of times, an AlGaN crystal having a desired film thickness can be obtained as a semiconductor material.
[0129]
Then, the structure of the AlGaN crystal formed according to the timing shown in FIG. 11 is 2 seconds (time T1) from timing T1, as shown in FIG._A) Of TMGa and TMAl, a layer 206 made of Ga and Al is formed on the AlGaN buffer layer 204 formed on the sapphire substrate 200.
[0130]
Then, from time T2 (time T_B) NH₃, The layer 208 made of N is laminated on the layer 206 made of Ga and Al.
[0131]
And as described above, TMGa, TMAl and NH₃1 cycle (see FIG. 11) is performed for 4 seconds. When the one cycle is repeated a desired number of times, the layers 206 and N made of Ga and Al are formed according to the number of repeated cycles. Lamination with the layer 208 is repeated to form an AlGaN crystal having a desired thickness W, and this AlGaN crystal can be used as a semiconductor material.
[0132]
When forming the AlGaN crystal by the first method described above, the gas valves other than the gas valves 65, 66, 68, 69 are kept open, but the gas valves 65, 66, 68, 69 are closed to react. Cp to room 12₂The supply of Mg and TESi is stopped.
[0133]
FIG. 17 shows the evaluation results of the AlGaN crystal created by the inventors of the present invention using the apparatus configuration and conditions (first method) shown in FIGS. 8 to 11. As an evaluation method, the AlGaN crystal (Al composition 0.5) prepared by the present inventors as described above was caused to emit light by photoexcitation, and the emission spectrum was measured to evaluate the crystallinity.
[0134]
FIG. 17 is an emission spectrum measured at a temperature of 77 K, the solid line shows the emission spectrum of AlGaN grown by alternating supply of crystal raw material by the first method, and the broken line shows continuous supply of crystal raw material by the conventional technique. The emission spectrum of AlGaN crystal-grown by is shown.
[0135]
Compared with AlGaN prepared by continuous supply of a known crystal material, the emission intensity from AlGaN prepared by alternating supply of crystal material by the first method is twice as large and the spectrum width is narrow. This result shows that the crystal quality of AlGaN by the alternate supply of crystal raw materials prepared by the first method is superior to the crystal prepared by continuous supply of conventionally known crystal raw materials.
[0136]
Compared with the case where the crystal raw materials are alternately supplied using the first method to grow GaN crystals, the case where the crystal raw materials are supplied alternately using the first method to grow AlGaN crystals. Crystals relatively better than GaN were obtained. That is, in the case of crystal growth of AlGaN, since the bonding force between Al and N is larger than Ga, desorption of nitrogen from the AlGaN crystal can be suppressed. Therefore, NH can be obtained by alternately supplying crystal raw materials.₃Even if the supply of is stopped for a short time, it is considered that the deterioration of the crystal quality due to the desorption of nitrogen is less than that of GaN.
[0137]
However, NH₃In order to suppress the desorption of nitrogen from the AlGaN surface during the supply stop of nitrogen, a small amount (50 sccm) of NH that does not deteriorate the crystal quality₃Is preferably supplied continuously.
[0138]
Next, a second method will be described. The supply of TMGa and TMAl as crystal raw materials and NH₃Since the AlGaN crystal is formed by alternately supplying for 2 seconds each time, it is the same as the above-mentioned first method, so the explanation about the processing is omitted, and is different from the above-mentioned first method. Will be described.
[0139]
When forming the AlGaN crystal by the second method, the gas valves 66 and 69 are closed and the supply of TESi to the reaction chamber 12 is stopped, but the gas valves 65 and 68 are opened and the reaction chamber 12 is opened. Cp to₂Allow supply of Mg. Cp₂The flow rate of Mg is 3.2 × 10 5 by MFC55.^-8Control to mol / min (mol / min).
[0140]
That is, in the second method, as shown in FIG. 13, the supply of TMGa and TMAl and NH₃Are alternately carried out for 2 seconds each to form an AlGaN crystal. At this time, Cp of the p-type impurity raw material₂Mg is supplied at the same time as TMGa and TMAl.
[0141]
More specifically, first, at timing T1, TMGa, TMAl and Cp₂Start supplying Mg.
[0142]
Then, TMGa and TMAl are set for 2 seconds (time T_A) Supply and Cp₂Mg for time T_AEqual to 2 seconds (time T_C) And supply TMGa, TMAl and Cp at timing T2.₂The supply of Mg is terminated.
[0143]
Then, immediately after timing T2, NH₃Started to supply NH₃For 2 seconds (time T_B) Supply, NH at timing T3₃The supply of is terminated.
[0144]
One cycle of processing is completed as described above, and the next cycle is started with this timing T3 as timing T1.
[0145]
By repeating such a cycle a desired number of times, an AlGaN crystal having a desired film thickness can be obtained as a semiconductor material.
[0146]
Then, the structure of the AlGaN crystal formed according to the timing shown in FIG. 13 is 2 seconds (time T1) from timing T1, as shown in FIG._A) Of TMGa and TMAl, a layer 1406 made of Ga and Al is formed on the AlGaN buffer layer 204 formed on the sapphire substrate 200.
[0147]
At this time, Cp as a p-type impurity material₂By supplying Mg, Mg, which is a p-type impurity material, is doped in the layer 1406 made of Ga and Al.
[0148]
Then, from time T2 (time T_B) NH₃, The layer 1408 made of N is laminated on the layer 1406 made of Ga and Al doped with Mg.
[0149]
And as described above, TMGa, TMAl, NH₃And Cp₂One cycle (see FIG. 13) in which Mg is supplied is 4 seconds, and when the one cycle is repeated a desired number of times, it consists of Ga and Al doped with Mg according to the number of repeated cycles. Lamination of the layer 1406 and the layer 1408 made of N is repeated to form an AlGaN crystal having a desired thickness W, and this AlGaN crystal can be used as a semiconductor material.
[0150]
FIG. 18 shows the evaluation results of the AlGaN crystal created by the inventors of the present invention using the apparatus configuration and conditions (second method) shown in FIGS. 8 to 10 and FIG.
[0151]
That is, FIG. 18 shows the hole concentration of Mg-doped AlGaN in the temperature range of 20 ° C. to 400 ° C.
[0152]
Here, (1) in FIG. 18 shows the temperature dependence of the hole concentration when crystals are grown by alternate supply of raw materials by the second method, and (2) in FIG. 18 shows the prior art. This shows the temperature dependence of the hole concentration when crystals are grown by continuous supply of the raw material.
[0153]
Regarding the hole concentration in the vicinity of room temperature, the hole concentration of AlGaN grown by alternating supply of raw materials by the second method is 4 × 10.¹⁸cm^-3The hole concentration of AlGaN grown by continuous supply of raw materials according to the conventional technique is 2.5 × 10¹⁷cm^-3About 16 times larger than
[0154]
In addition, when comparing the hole mobility near room temperature, the hole mobility in AlGaN grown by alternating supply of raw materials by the second method is 1.5 cm.²V^-1s^-1The hole mobility of AlGaN grown by continuous supply of raw materials according to the conventional technique is 0.5 cm.²V^-1s^-13 times larger than
[0155]
Therefore, regarding the electrical conductivity, which is the product of the hole concentration and the hole mobility, AlGaN grown by alternating supply of raw materials by the second method is grown by continuous supply of raw materials by the conventional technique. Compared to AlGaN, it is about 48 times larger.
[0156]
Further, the activation energy of the Mg acceptor was obtained from the temperature change of the hole concentration shown in FIG. 18, and the activation energy of AlGaN grown by alternating supply of the raw material by the second method was 75 meV.
[0157]
On the other hand, for AlGaN crystal grown by continuous supply of raw materials according to the conventional technique, the activation energy of Mg is determined to be 410 meV, which is almost the same as a conventionally known value.
[0158]
As a result of measuring Mg in AlGaN by SIMS analysis, AlGaN grown by crystal by alternately supplying raw materials by the second method has an Mg density of about 5 × 10 5.¹⁸cm^-3The Mg density is about one digit lower than that of AlGaN grown by continuous supply of raw materials according to the conventional technique. However, since the activation energy of Mg is small, most of the introduced Mg is activated and a high hole concentration is obtained.
[0159]
When doping GaN with Mg, NH₃, TMG and Cp₂Mg could be doped by supplying Mg in pulses, but when doping AlGaN with Mg, NH₃Cp is stopped₂The alternate supply of raw materials by the second method of supplying Mg is effective.
[0160]
Next, the third method will be described. When an AlGaN crystal is formed by the third method, the gas valves 65, 66, 68, and 69 are opened and the Cp to the reaction chamber 12 is opened.₂Allow supply of Mg and TESi. Cp₂The flow rate of Mg is 3.2 × 10 5 by MFC55.^-8The flow rate of TESi is controlled to 7 mol / min by MFC56.^-9Control to mol / min (mol / min).
[0161]
Also in this third method, the supply of TMGa and TMAl and NH are performed in the same manner as in the first method.₃As shown in FIG. 15, specifically, the supply of TMGa and TMAl for 3 seconds and the NH for 2 seconds are performed.₃Are alternately supplied to form an AlGaN crystal. At this time, Cp of the p-type impurity raw material₂Mg is supplied at the same time as TMGa and TMAl, and is supplied for 2 seconds. The n-type impurity source TESi is Cp.₂Supply only for 1 second after supplying Mg.
[0162]
More specifically, first, at timing T1, TMGa, TMAl and Cp₂Start supplying Mg.
[0163]
Then, TMGa and TMAl are used for 3 seconds (time T_A) Supply and Cp₂Mg for time T_AShorter 2 seconds (time T_C) Supply. At time T1 ', Cp₂The supply of Mg is terminated.
[0164]
Then Cp₂The supply of TESi is started immediately after the timing T1 'at which the supply of Mg ends, and the TESi is turned on for 1 second (time t1)._D) To supply TESi and TMGa and TMAl at timing T2.
[0165]
Also, NH immediately after the timing T2₃Started to supply NH₃For 2 seconds (time t_B) Supply, NH at timing T3₃The supply of is terminated.
[0166]
One cycle of processing is completed as described above, and the next cycle is started with this timing T3 as timing T1.
[0167]
By repeating such a cycle a desired number of times, an AlGaN crystal having a desired film thickness can be obtained as a semiconductor material.
[0168]
Then, as shown in FIG. 16, the structure of the AlGaN crystal formed according to the timing shown in FIG. 15 is 2 seconds from the timing T1 (predetermined time t_A) Of TMGa and TMAl, a layer 1606 made of Ga and Al is formed on the AlGaN buffer layer 206 formed on the sapphire substrate 200.
[0169]
At this time, Cp as a p-type impurity material₂By supplying Mg of Mg and TESi of n-type impurity material, Mg and Si are doped in the layer 1606 made of Ga and Al, and Mg of p-type impurity material and Si of n-type impurity material As a result, a kind of impurity pair (Mg—Si) is formed.
[0170]
Then, from time T2 (time t_B) NH₃As a result, the layer 1608 made of N is stacked on the layer 1606 made of Ga and Al doped with Mg and Si.
[0171]
Then, as described above, TMGa, TMAL, NH₃, Cp₂One cycle (see FIG. 15) in which Mg and TESi are supplied is 5 seconds. When the one cycle is repeated a desired number of times, Mg and Si are doped according to the number of repeated cycles. Lamination of the layer 1606 made of Ga and Al and the layer 1608 made of N is repeated to form an AlGaN crystal having a desired thickness W, and this AlGaN crystal can be used as a semiconductor material.
[0172]
More specifically, as described above, simultaneously with or after the start of the supply of the Ga source gas TMGa as the crystal source material and the Al source gas TMAl as the crystal source material, and the N source gas NH as the crystal source material₃Prior to the start of supply of Mg, Mg source gas Cp as a p-type impurity source₂When Mg and the Si source gas TESi, which is an n-type impurity source, are supplied in a pulsed manner at close timing, Mg and Si are disordered in the layer 1606 made of Ga and Al doped with Mg and Si. Without being incorporated, it will be doped at an appropriate ratio.
[0173]
For this reason, the position of Mg and Si in the layer 1606 made of Ga and Al doped with Mg and Si is controlled, and Mg and Si in the layer 1606 made of Ga and Al doped with Mg and Si are controlled. Si and Si are arranged close to each other at a predetermined ratio so that Mg and Si form a kind of impurity pair, and the energy level of the impurity, that is, the activation energy is reduced.
[0174]
As a result, in the AlGaN crystal, the carrier concentration is increased, and a semiconductor material having a high conductivity can be obtained.
[0175]
FIGS. 19 to 10 show the evaluation results of the AlGaN crystal created by the inventors of the present invention using the apparatus configuration and conditions (third method) shown in FIGS. 8 to 10 and FIG.
[0176]
That is, FIG. 19 shows the hole concentration of p-type AlGaN doped with Mg and Si in a temperature range of 20 ° C. to 400 ° C.
[0177]
Here, (1) in FIG. 19 shows the temperature dependence of the hole concentration when crystals are grown by alternately supplying raw materials according to the third method. 50 meV was determined.
[0178]
On the other hand, (2) of FIG. 19 shows the temperature dependence of the hole concentration of Mg-doped AlGaN grown by continuous supply of raw materials according to the prior art, and activation of the Mg acceptor from this temperature change. The energy was determined to be 410 meV.
[0179]
Thus, the activation energy of the AlGaN acceptor doped simultaneously with Mg and Si by the third method is compared with the activation energy of the Mg-doped AlGaN acceptor prepared by continuous supply of raw materials according to the conventional technique. And very small. That is, in the AlGaN doped with Mg and Si at the same time by the third method, the activation energy is smaller than that when only Mg is doped.
[0180]
FIG. 20 shows Cp₂Mg supply amount is 3.2 × 10^-8It shows the carrier density of AlGaN at room temperature when the supply amount of TESi is changed at a constant mol / min (mol / min). The hole concentration of p-type AlGaN in which the supply amount of TESi is 0 and only Mg is 4.2 × 10¹⁸cm^-3And mobility is 2.4 cm²V^-1s^-1Met. By supplying TESi, the hole concentration slightly decreases. However, when the TESi supply amount is further increased, the hole concentration increases and becomes 6.3 × 10 6.¹⁸cm^-3The maximum value is 1.0cm and the mobility is 1.0cm²V^-1s^-1showed that.
[0181]
Here, when the TESi supply amount was further increased, the hole concentration of p-type AlGaN decreased. That is, 8 × 10^-9When the amount of TESi supplied is at least mol / min (mol / min), it changes to n-type AlGaN as shown by the black circle, and the electron density is 8 × 10 8.¹⁷cm^-3The mobility is 31cm²V^-1s^-1Met. TESi supply amount is 9 × 10^-9In mol / min (mol / min), the electron density is 6.7 × 10 6.¹⁸cm^-3The mobility is 1.5cm²V^-1s^-1Met.
[0182]
The electron density of Si-doped n-type AlGaN is 4.2 × 10¹⁸cm^-3And mobility is 9.7 cm²V^-1s^-1Therefore, in n-type AlGaN in which Mg and Si are mixed, a decrease in mobility was observed.
[0183]
Thus, by simultaneously doping Si in addition to Mg, an increase in hole concentration was observed in a narrow range of TESi supply amount.
[0184]
As described above, in the first method, the second method, and the third method, the semiconductor crystal (semiconductor material) having a high conductivity as described above, particularly the conductivity having high-density holes. Since a p-type semiconductor material having a large thickness can be produced, it is possible to realize a highly efficient pn junction, improving the characteristics of the semiconductor device, for example, increasing the injection efficiency of the pn junction, reducing the contact resistance of the electrode, and series This can contribute to a reduction in resistance.
[0185]
Further, in the second method and the third method, even if the p-type semiconductor material has a deep impurity level in the forbidden band and a large activation energy, the activation energy can be reduced and the high density can be obtained. A p-type semiconductor material having holes and high conductivity can be produced.
[0186]
Further, in the third method, when a plurality of types of crystal raw materials are alternately supplied in a pulse shape, simultaneously with or after the start of supply of one crystal raw material and before the start of supply of the other crystal raw material Since each of the plurality of types of impurity materials is supplied in a pulsed manner at close timing, the plurality of types of impurities are not randomly taken into the atomic layer of the crystal formed on the substrate by the crystal materials, and an appropriate ratio is obtained. Even when a p-type impurity material and an n-type impurity material are used, the carrier concentration is increased and a semiconductor material having high conductivity can be formed.
[0187]
Furthermore, in the third method, since a plurality of types of impurity materials are supplied in pulses at close timing without continuously supplying them, each impurity material is formed on the substrate by a crystal material. It becomes possible to control the amount taken into the atomic layer of the crystal, and impurities can be doped into the atomic layer at an appropriate ratio to obtain a semiconductor material having an increased carrier concentration.
[0188]
For this reason, according to the third method, it is possible to realize the theory that the impurity level is changed by supplying two kinds of impurities at an appropriate ratio, thereby increasing the activation rate.
[0189]
The embodiment described above can be modified as described in the following (1) to (4).
[0190]
(1) In the above-described embodiment, the case of forming an AlGaN crystal has been described. However, the present invention is not limited to this, and the above-described MOCVD apparatus 10 or other crystal growth apparatus is used. The semiconductor material may be created by forming various crystals such as InGaN crystal, InAlGaN crystal, or GaN crystal by the first method, the second method, or the third method.
[0191]
At this time, for example, when forming an InGaN crystal, TMIn may be used instead of TMAl stored in the bubbler 15, and when forming an InAlGaN crystal, TMIn similar to the bubbler 15 is stored. In order to form a GaN crystal, various conditions may be changed as appropriate, such as stopping the supply of Al.
[0192]
(2) In the above-described embodiment, Ga is used as the crystal material A, Al is used as the crystal material B, N is used as the crystal material C, Mg is used as the impurity material D, and Si is used as the impurity material E. Although the case where it did in this way was demonstrated, it is as above-mentioned that it is not restricted to this.
[0193]
For example, as the crystal raw material A, in addition to Ga, Group III elements and Group II elements such as Al, In, B, Zn, and Cd can be used. As the crystal raw material B, in addition to Al, Ga, Group III and Group II elements such as In, B, Zn, and Cd can be used. As the crystal raw material C, in addition to N, Group V elements such as As, P, S, Se, and Te and Group VI An element can be used. As the impurity source D, Be can be used in addition to Mg. As the impurity source E, O can be used in addition to Si.
[0194]
Furthermore, the crystal raw material A, the crystal raw material B, and the crystal raw material C are not limited to one kind of material, and two or more kinds of substances can be used. For example, the crystal raw material A and the crystal raw material A ′ Even when a mixed crystal composed of the crystal raw material B, the crystal raw material B ′, the crystal raw material C, and the crystal raw material C ′ is formed, a semiconductor crystal can be formed by the present invention by making appropriate changes.
[0195]
When a group III element is used as the crystal material A, a group III element is used as the crystal material B, a group V element is used as the crystal material C, and a group II element is used as the crystal material A. It is preferable to use a group II element as the crystal raw material B and a group VI element as the crystal raw material C.
[0196]
(3) In the above-described embodiment, the p-type impurity raw material D (Cp₂The supply of the n-type impurity material E (TESi) is started immediately after the timing T1 ′ at which the supply of (Mg) is completed. However, the present invention is not limited to this. D (Cp₂After the supply of Mg) is finished, the supply of the n-type impurity source E (TESi) may be started through a predetermined purge time.
[0197]
Further, immediately after the timing T2 when the supply of the n-type impurity source E (TESi) is finished, the crystal source C (NH₃However, the present invention is not limited to this. After the timing T2 when the supply of the n-type impurity source E (TESi) is completed, a predetermined purge time is passed. Crystal raw material C (NH₃) May be started.
[0198]
(4) You may make it combine the above-mentioned embodiment and the modification shown in said (1) thru | or (3) suitably.
[0200]
【The invention's effect】
  Since the present invention is configured as described above, there is an excellent effect that a p-type semiconductor material having a high hole concentration and a high conductivity can be produced.
[0201]
In addition, since the present invention is configured as described above, even when doping a crystal layer with a p-type impurity material and an n-type impurity material, the carrier concentration is increased so that the conductivity is high. There is an excellent effect that a semiconductor material can be created.
[Brief description of the drawings]
FIG. 1 shows a semiconductor crystal growth method andAccording to the inventionIt is principal part schematic structure explanatory drawing which shows the crystal growth apparatus which implement | achieves the impurity doping method of a semiconductor.
FIG. 2 is a timing chart showing an example of a timing at which a crystal material is supplied by a semiconductor crystal growth method, that is, an example of a sequence of material supply pulses.
FIG. 3 is an explanatory view schematically showing a crystal structure of a semiconductor crystal formed by a semiconductor crystal growth method.
FIG. 4 is a timing chart showing an example of a timing at which a crystal material and an impurity material are supplied by the semiconductor impurity doping method according to the present invention, that is, an example of a sequence of a material supply pulse.
FIG. 5 is an explanatory view schematically showing a crystal structure of a semiconductor material formed by a semiconductor impurity doping method according to the present invention.
FIG. 6 is a timing chart showing an example of a timing at which a crystal material and an impurity material are supplied by the semiconductor impurity doping method according to the present invention, that is, an example of a sequence of a material supply pulse.
FIG. 7 is an explanatory view schematically showing a crystal structure of a semiconductor material formed by a semiconductor impurity doping method according to the present invention.
FIG. 8 is a metal organic chemical vapor deposition (MOCVD) that can be used as an apparatus for forming a layer of AlGaN crystal as a semiconductor material by the first method, the second method, and the third method. It is a schematic structure explanatory drawing of an apparatus.
FIG. 9 is a schematic configuration explanatory diagram of a main part of FIG. 8;
10 is a schematic structural explanatory diagram showing the reaction tube of FIG. 8. FIG.
FIG. 11 is a timing chart showing an example of timing for supplying a crystal material when forming AlGaN as a semiconductor crystal by the first technique, that is, an example of a sequence of a material supply pulse when forming AlGaN.
12 is an explanatory view schematically showing a crystal structure of AlGaN formed by a sequence of raw material supply pulses when forming AlGaN shown in FIG. 11 by the first technique.
FIG. 13 shows an example of timing for supplying a crystal material and an impurity material when forming an AlGaN crystal as a semiconductor material by the second method, that is, an example of a sequence of a material supply pulse when forming AlGaN.・ It is a chart.
14 is an explanatory view schematically showing a crystal structure of AlGaN formed by a sequence of raw material supply pulses when forming AlGaN shown in FIG. 13 by the second method.
FIG. 15 shows an example of timing for supplying a crystal material and an impurity material when forming an AlGaN crystal as a semiconductor material by the third method, that is, an example of a sequence of a material supply pulse when forming AlGaN.・ It is a chart.
16 is an explanatory view schematically showing a crystal structure of AlGaN formed by a sequence of raw material supply pulses when forming AlGaN shown in FIG. 15 by the third method.
17 is a graph showing an evaluation result of an AlGaN crystal created by the inventor of the present application according to the apparatus configuration and conditions (first method) shown in FIGS. 8 to 11; It is a graph which shows the photo-luminescence spectrum with AlGaN produced by the technique.
18 is a graph showing an evaluation result of an AlGaN crystal created by the inventors of the present invention according to the apparatus configuration and conditions (second method) shown in FIGS. 8 to 10 and FIG. 13, and Mg produced by the second method; 5 is a graph showing the temperature dependence of the hole concentration of AlGaN doped with Mg and AlGaN doped with Mg prepared by a conventional technique.
FIG. 19 is a graph showing the evaluation results of an AlGaN crystal created by the inventors of the present invention using the apparatus configuration and conditions (third method) shown in FIGS. 8 to 10 and FIG. 15, and Mg produced by the third method; 5 is a graph showing the temperature dependence of the hole concentration of AlGaN doped with Si and Si and AlGaN doped with Mg prepared by a conventional technique.
FIG. 20 is a graph showing the dependency of the hole concentration of AlGaN doped with Mg and Si on the Si supply amount.
[Explanation of symbols]
10 MOCVD equipment
12 reaction tubes
14, 15, 18, 20 Bubbler
16-1, 16-2 NH₃Cylinder
22 H₂Cylinder
24 N₂Cylinder
26 Control device
28 Exhaust system
30 Exhaust gas treatment equipment
32 High frequency coil for substrate heating
34 Carbon susceptor
36 Thermocouple
40, 42, 43 quartz tube
50, 51, 52, 53, 54, 55, 56, 75 MFC
57, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 77, 80, 91, 92 Gas valve
70 Hydrogen Purifier
72, 73, 74, 76 constant temperature bath
81 Pressure reducing valve
100 substrates
102 Layer composed of crystal raw material A and crystal raw material B
104 Layer made of crystal raw material C
200 substrate (sapphire substrate)
202 AlN low temperature buffer layer (LT-AlN buffer)
204 AlGaN buffer layer (AlGaN buffer)
206 Ga and Al layer
208 N layer
502 Layer made of crystal raw material A and crystal raw material B doped with impurity raw material D
504 Layer made of crystal raw material C
702 A layer comprising crystal raw material A and crystal raw material B doped with impurity raw material D and impurity raw material E
704 Layer made of crystal raw material C
1406 Layer made of Ga and Al doped with Mg
1408 N layer
1606 A layer made of Ga and Al doped with Mg and Si
1608 N layer

Claims (3)

In a semiconductor impurity doping method of doping impurities into a crystal layer formed of a crystal raw material,
A first step of starting the supply of TMGa, TMAl and Cp ₂ Mg at a first timing and ending the supply of Cp ₂ Mg at a _second timing of supplying Cp ₂ Mg for a predetermined time;
A _{second step} of starting the supply of TESi immediately after or after the second timing when the supply of Cp ₂ Mg is ended, and ending the supply of TMGa, TMAl, and TESi at a third timing of supplying TESi for a predetermined time; ,
TMGa, a third step of starting the supply of the NH ₃ in the third or after immediately after the timing the completion of the supply of TMAl and TESi, terminates the supply of the NH ₃ in the fourth timing where the NH ₃ supplying a predetermined time A semiconductor impurity doping method that repeats a predetermined number of cycles. The semiconductor impurity doping method according to claim 1,
A semiconductor impurity doping method in which a small amount of N is continuously supplied so as not to deteriorate the crystal quality in order to suppress desorption of nitrogen from the AlGaN surface . A semiconductor impurity doping apparatus for doping impurities into a crystal layer formed of a crystal raw material,
A reaction tube in which a substrate is disposed;
A plurality of tubes for supplying crystal raw materials Ga, Al, and N in a gaseous state into the reaction tube and supplying impurity raw materials Mg and Si in a gaseous state;
A gas valve disposed in each of the plurality of pipes;
Flow rate setting means for setting the flow rates of the crystal raw material gas and the impurity raw material gas flowing in the plurality of pipes to a predetermined value;
Heating means for heating the substrate disposed in the reaction tube;
Control of opening and closing of the gas valve, control of the flow rate set by the flow rate setting means, and control of heating of the substrate by the heating means, supply of Al and Ga gas of the crystal raw material, and control of the crystal raw material The supply of N gas is controlled so as to be alternately performed in pulses, and at the same time or after the start of supply of the Al and Ga gases of the crystal raw material, and the N gas supply of the crystal raw material Prior to the start of supply, a semiconductor impurity doping apparatus comprising: control means for controlling the gas of Mg and Si of the impurity material to be supplied at close timings, respectively.
The crystal raw material Ga gas is TMGa, the crystal raw material Al gas is TMAl, the crystal raw material N gas is NH ₃ , and the impurity raw material Mg gas is Cp ₂ Mg. The impurity raw material Si gas is TESi,
The control means includes
A first step of starting the supply of TMGa, TMAl and Cp ₂ Mg at a first timing and ending the supply of Cp ₂ Mg at a _second timing of supplying Cp ₂ Mg for a predetermined time;
A _{second step} of starting the supply of TESi immediately after or after the second timing when the supply of Cp ₂ Mg is ended, and ending the supply of TMGa, TMAl, and TESi at a third timing of supplying TESi for a predetermined time; ,
TMGa, a third step of starting the supply of the NH ₃ in the third or after immediately after the timing the completion of the supply of TMAl and TESi, terminates the supply of the NH ₃ in the fourth timing where the NH ₃ supplying a predetermined time A semiconductor impurity doping apparatus that is controlled to repeat a predetermined cycle a number of times.

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