JP3018763B2 - GaAs single crystal, method of manufacturing the same, and method of controlling ion implantation of GaAs wafer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a GaAs single crystal grown by a liquid sealing pulling method, a method of manufacturing the same, and a method of controlling ion implantation of a GaAs wafer, and more particularly to a method of controlling a carbon concentration in a crystal.

[0002]

2. Description of the Related Art GaAs single crystals are widely used as substrates for ICs and LSIs. One of the manufacturing methods of the GaAs single crystal is a liquid sealing pulling method (hereinafter referred to as LEC method). A method for producing a GaAs single crystal by the LEC method will be described. A GaAs melt as a raw material and B ₂ O ₃ as a liquid sealing material are accommodated in a pBN crucible and placed in a pressure vessel filled with an inert gas. A GaAs seed crystal is brought into contact with the melt while adjusting the temperature of the GaAs melt with a heater arranged on the outer periphery of the crucible, and the seed crystal is gradually pulled up while rotating. A GaAs single crystal is obtained by pulling up the diameter of the crystal grown following the seed crystal while controlling it to a predetermined value.

[0003] GaAs single crystals manufactured by the LEC method include:
Carbon is contained as an impurity. Carbon in the GaAs crystal becomes a shallow acceptor and has a large effect on the electrical characteristics of the crystal. The carbon content required for the GaAs crystal varies depending on the purpose of use of the crystal substrate, and is not necessarily good if it is generally small. Therefore, a technique for uniformly distributing a predetermined concentration of carbon in a crystal is required for the production of a GaAs single crystal.

[0004] Carbon mixed into a GaAs single crystal manufactured by the LEC method is supplied from carbon monoxide in an atmosphere gas.
It is described in the following document 1 that carbon monoxide is generated from a graphite member in a pressure vessel.

Reference 1: "Carbon in Undoped LEC Semi-i
nsulating GaAs; Origin and MeltComposition Dependen
ce ": T.Kikuta et.al., J.Crystal Growth 76 (1986) 517-
520 Further, an experiment in which the concentration of carbon monoxide in a crystal is changed by intentionally controlling the concentration of carbon monoxide in a pressure vessel during crystal growth is described in the following Reference 2.

Reference 2: "Growth of Semi-insulating Ga
As Crystals with Low Carbon Concentration Using Pyr
olytic Boron Niteride Coated Graphite ": T.Inada et.
al., Applied Physics Letter 50 (3), 19 Jan. 1987 Recently, in order to control the concentration of carbon monoxide in the pressure vessel during crystal growth within a predetermined range, carbon dioxide was added to the inert gas in the pressure vessel. A method of growing a GaAs single crystal by mixing a predetermined amount of carbon monoxide (Reference 3), a method of replacing a gas in a pressure vessel with a pure inert gas or a mixed gas of carbon monoxide and an inert gas. A method of growing a crystal (Reference 4) is also performed.

Reference 3: JP-A-1-192793 Reference 4: The Carbon and Boron Concentration Control
in Crystals Grownby Liquid Encapsulated Czochrals
ki Method ": N.Sato et.al., Semi-insulating III-V M
aterials, 1990 Chapter3 p.211

[0008]

SUMMARY OF THE INVENTION GaAsIC and LSI
Has formed an active layer by implanting ions into a wafer and applying heat treatment to activate the implanted ions. The activation rate of the wafer largely depends on the impurity concentration in the crystal, particularly the carbon concentration. Needless to say, the carbon concentration in the crystal should be uniformly distributed at a constant concentration in the crystal. The above gas in the pressure vessel is mixed with carbon dioxide or the like, and the gas in the pressure vessel is replaced with GaAs.
Although the development of methods for growing s single crystals (References 3 and 4) has made it possible to control the carbon concentration in crystals within a predetermined range, the distribution still varies within the crystal. is there. For this reason, at the time of ion implantation, the electrical characteristics such as the carbon concentration or the specific resistance reflecting the carbon concentration are measured in advance at the wafers located at both ends (head and tail) of the crystal into which the ion is implanted. Is estimated to adjust the ion implantation conditions.

However, in the conventional GaAs crystal growth method according to References 3 and 4, in order to keep the concentration of carbon monoxide in the container at a constant value, a predetermined amount of carbon dioxide and carbon monoxide is mixed in the container, or Since the control for replacing the gas in the container is performed, the concentration of carbon monoxide in the container during the crystal growth is increasing or decreasing. For this reason, the carbon concentration in the crystal varies from a certain concentration to the center value, the distribution does not have a certain regularity, and it is necessary to accurately grasp the internal carbon concentration distribution only by evaluating the characteristics at both ends of the crystal. Was difficult. As a result, the variation in the activation rate when heat treatment is performed by implanting ions is large, which causes a reduction in the manufacturing yield of the device.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to measure the carbon concentration at both ends of a GaAs crystal or the electrical characteristics reflecting the same to obtain a carbon concentration distribution in the crystal between them. It is an object of the present invention to provide a GaAs single crystal that can easily estimate the GaAs single crystal.

Another object of the present invention is to produce a GaAs single crystal capable of easily producing a GaAs single crystal in which the distribution of carbon concentration in the crystal monotonically increases or decreases from the head to the tail of the crystal. It is to provide a method.

Another object of the present invention is to provide a method for controlling ion implantation of a GaAs wafer capable of making the electrical characteristics of a series of wafers cut from the head to the tail of the crystal uniform.

[0013]

In a semi-insulating GaAs single crystal containing carbon as an impurity in the crystal of the present invention, the distribution of carbon concentration in the crystal is changed from the head (starting end) to the tail (ending end) of the crystal. Are distributed so as to monotonically increase or decrease, so that the distribution of the carbon concentration inside the crystal can be easily grasped.

Further, according to the method for producing a GaAs single crystal of the present invention, a crucible containing a GaAs melt and a liquid sealing material for covering the upper surface of the melt is placed in a container filled with an inert gas.
In a method for producing a GaAs single crystal by bringing a seed crystal into contact with the upper surface of a GaAs melt and rotating and pulling the seed crystal, before growing the crystal, carbon monoxide or carbon monoxide is added to an inert gas in a container. introducing the resulting carbon dioxide gas, to set the concentration of carbon monoxide in the container to a predetermined value, to start crystal growth thereafter, during crystal growth, the container
Of carbon monoxide concentration in carbon dioxide using a carbon monoxide detector
And the concentration of carbon monoxide in the inert gas increases monotonically or
The gas in the container so reduced was replaced with a pure inert gas, a gas such as carbon dioxide produces carbon monoxide with carbon monoxide or container, or a mixed gas thereof, a single crystal is grown It is like that. The gas to be introduced into the container includes, besides carbon monoxide or carbon dioxide, a mixed gas of carbon monoxide and carbon dioxide, methane gas, ethane gas and the like.

Further, according to the method for controlling ion implantation of a GaAs wafer of the present invention, a method of controlling the ion implantation of a GaAs single crystal in which the carbon concentration in the GaAs crystal is monotonously increased or decreased from the head to the tail of the crystal. From the part to the tail, a wafer is cut out, and the carbon concentration [C] of each cut out wafer is obtained from the following equation, and [C] = ([C _T ] − [C _S ]) × m / L + [C _S ] where [ [C _T ] is the carbon concentration in the crystal measured at the tail of the crystal [C _S ] is the carbon concentration in the crystal measured at the head of the crystal m is the distance from the head of the crystal from which the sample whose carbon concentration was measured was taken L is the distance from the head to the tail of the crystal from which the carbon concentration was measured. From this, the ion implantation dose φ was obtained from the following equation using [C] obtained for each wafer, and φ = φ ₀ + ([C] - [C S]) × a proviso phi ₀ are those coefficient determined by the dose a is implantation conditions as a reference ion this dose was so driven into the corresponding wafer.

[0016]

The carbon concentration required for the GaAs crystal varies depending on the type of device to be manufactured, the manufacturing conditions, and the like, and cannot be specified unconditionally. The correlation between the carbon concentration in the GaAs crystal and the carbon monoxide concentration in the vessel during crystal growth varies greatly depending on the vessel, crystal size, crystal growth conditions, etc., and defines the carbon monoxide concentration in the vessel. You can't.

The carbon concentration in the crystal is generally determined by the LVM method (Lo
cal Vibration Mode method), which is obtained by measuring the absorption coefficient of infrared rays.
It is about 0 ¹⁴ cm ^-3 . In the present invention, even in a crystal in which the carbon concentration distribution in the crystal monotonically increases or decreases,
It is necessary to consider that the carbon concentration at each measurement point has a measurement error of about ± 5 × 10 ¹⁴ cm ⁻³ . That is, there is a possibility that the carbon concentration measured at any two points appears to be reversed from the increasing tendency or the decreasing tendency within a range of 1 × 10 ¹⁵ cm ^{−3 at} the maximum due to a measurement error. Therefore, the monotonous increase or decrease in the carbon concentration distribution in the crystal as referred to in the present invention means a true increase or decrease that does not include an increase or decrease due to such an error.

[0018]

【Example】

(Example 1) A GaAs single crystal was grown by using a GaAs crystal pulling apparatus having a structure as shown in FIG. 1 and controlling the concentration of carbon monoxide in an inert gas to monotonously increase the concentration of carbon monoxide in a container.

In a crucible 11 made of pBN, 4000 g of GaAs polycrystalline raw material and a water content 20
700 g of 0 ppm B ₂ O ₃ was placed in the crystal growth vessel 1. This was melted using a heater 2 under an atmosphere of 20 kg / cm ² of argon gas to form a GaAs melt 5. After the melt was formed, the pressure in the container was reduced to 3 kg / cm ² and left for 1 hour to remove bubbles in B ₂ O ₃ . And when pressurizing again to 20 kg / cm ² ,
Argon gas mixed with carbon monoxide was introduced into the vessel 1 through the gas introduction pipe 8, and before the crystal growth, the carbon monoxide in the vessel 1 was set to 3000 ppm. Thereafter, the GaAs seed crystal 1 attached to the lower end of the upper shaft 12
3 is brought into contact with the surface of the GaAs melt 5, and the seed crystal 13 is pulled up at a speed of 10 mm / hr while rotating the crucible 11 attached to the upper end of the lower shaft 14 at a relative speed of 20 rpm. , 3 inch diameter Ga
As single crystal 3 was grown.

The concentration of carbon monoxide in the vessel during the crystal growth is determined by detecting the atmospheric gas in the vessel collected through the gas collection pipe 7 using the carbon monoxide concentration detector 10 and detecting the concentration of carbon monoxide from 3000 ppm. The mass flow controller 9 installed on the pure argon gas introduction side of the gas introduction pipe 8, the mass flow controller 9 installed on the carbon monoxide mixed argon gas introduction side, and the gas exhaust pipe 6 so as to monotonically increase to 4000 ppm. The gas in the container 1 was replaced at a constant speed through the mass flow controller 9.

The carbon concentration in the crystal thus obtained is determined by F
5 at room temperature by TIR (Fourier transform infrared spectrometer)
An absorption coefficient of 18 cm ^-1 was measured, and a conversion coefficient of 1.18 × 1
^Multiplied by 0 ¹⁶ cm ^-3 . FIG. 2 shows the obtained distribution of the carbon concentration in the crystal. The carbon concentration in the crystal was 6.1 at the head.
It changes monotonically from × 10 ¹⁵ cm ^-3 to 8.5 × 10 ¹⁵ cm ^-3 at the tail, and the carbon concentration in the crystal can be easily estimated only by measuring the carbon concentration at both ends of the crystal.

A series of wafers were collected from this crystal,
Ions were implanted and activated, and the sheet carrier concentration was measured. At this time, the carbon concentration in the crystal was estimated from the carbon concentrations measured at the head and tail of the crystal, and the dose of ions to be implanted was changed so that the sheet carrier concentration when activated was equalized. That is, the carbon concentration [C] of the wafer collected from a distance of mcm from the seed is [C] = ([C _T ] − [C _S ]) × m / L + [C _S ] (1) Can be estimated. Where [C _S ],
[C _T ] is the carbon concentration in the crystal measured at the head and tail of the crystal, and L is the distance between the head and tail of the crystal from which the carbon concentration was measured.

Using [C] obtained by this equation, the dose φ can be calculated as follows: φ = φ ₀ + ([C] − [C _S ]) × a (2) φ ₀ is the reference dose,
a is a coefficient determined by the driving conditions. Here, φ ₀ = 2.0 × 10 ¹² cm ⁻¹ and a = 0.05. The implantation energy was constant at 150 KeV for all wafers. The ion-implanted wafer is arsine gas 1
%, And heat-treated in an atmosphere of 850 ° C. for 30 minutes to activate the ions. The sheet carrier concentration was determined by Hall measurement. FIG. 4 shows the measurement results. The sheet carrier concentration was 5.9 ± 0.1 × 10 ¹⁵ over the entire length of the crystal
It could be distributed uniformly within the cm ^-3 range.

(Example 2) In the same manner as in Example 1, a GaAs single crystal was manufactured by monotonically decreasing the concentration of carbon monoxide in the vessel during crystal growth from 3000 ppm to 2000 ppm. When the carbon concentration was measured at the head and tail of the crystal, they were 6.2 × 10 ¹⁵ cm ⁻³ and 4.1 × 10 5 cm ⁻³ , respectively.
It was ¹⁵ cm ^-3 . From this measurement result, the carbon concentration in the crystal was estimated in the same manner as in Example 1, and the dose was changed and Si ions were implanted and activated to measure the sheet carrier concentration. We have succeeded in obtaining equally uniform results.

Comparative Example 1 A GaAs single crystal was grown by a conventional method for controlling the concentration of carbon monoxide in a container. That is, under the same conditions as in Example 1, the concentration of carbon monoxide in the vessel in the crystal was 3%.
The concentration was set to 000 ppm, and crystals were grown. The concentration of carbon monoxide in the container during the crystal growth is determined by detecting the atmospheric gas in the container collected through the gas collection pipe 7 using the carbon monoxide concentration detector 10, and the detected carbon monoxide concentration is 3%.
When it exceeds 000 ppm, the mass flow controller 9 installed on the pure argon gas introduction side of the gas introduction pipe 8
The gas in the container is replaced with a pure gas through the mass flow controller 9 installed in the gas exhaust pipe 6 to 300
The solution was diluted to 0 ppm or less.

FIG. 3 shows the carbon concentration distribution in the crystal thus obtained. The carbon concentration in the crystals tended to increase initially, then decrease and then increase. Looking at only the measured carbon concentration at the head and tail of the crystal, there is almost no difference, and it makes a false judgment as if it is a good crystal with very uniform control of carbon concentration in the crystal .

Si wafers were implanted into the wafers collected from the crystals, activated, and the sheet carrier concentration was measured.
Assuming that only the carbon concentration measurements at the head and tail of the crystal were known, and as a result that the carbon concentration in the crystal was assumed to be almost uniformly distributed, the ion implantation conditions were In both cases, the implantation energy was constant at 150 keV and the dose was 2.0 × 10 ¹² cm ⁻² . The heat treatment conditions for activation and the method of measuring the sheet carrier concentration are the same as in Example 1. FIG. 5 shows the measurement results. The sheet carrier concentration has an inverse correlation with the distribution of the carbon concentration in the crystal, and its variation is 5.05 to 6.45 ×.
It was very large at 10 ¹¹ cm ^-2 .

(Other Embodiments) The correlation between the concentration of carbon incorporated in a crystal and the concentration of carbon monoxide in a growth vessel varies depending on the vessel and the progress of growth.
If the concentration of carbon monoxide in the container is not intentionally controlled, the concentration of carbon monoxide may increase spontaneously depending on the container.
Some exhibit the opposite behavior. When controlling the carbon concentration in the crystal, knowing these characteristics of each container, if it is actively used, the desired crystal according to the present invention is manufactured without performing gas replacement in the container. It is also possible.

[0029]

【The invention's effect】

(1) According to the GaAs single crystal according to the first aspect, since the carbon concentration in the crystal is monotonously changed from the head to the tail, the carbon concentration at both ends of the crystal or an electrical characteristic reflecting the carbon concentration. And the like, it is possible to easily estimate the carbon concentration distribution in the crystal during the measurement.

(2) According to the method of manufacturing a GaAs single crystal according to the second aspect, the carbon concentration distribution in the crystal can be adjusted without changing the conventionally used crystal manufacturing apparatus. A GaAs single crystal monotonically increasing or decreasing from to the tail can be easily manufactured.

(3) According to the method for controlling ion implantation of a GaAs wafer according to the third aspect, since a target is a series of wafers cut out of a crystal having a monotonous carbon concentration from the head to the tail. The carbon concentration distribution in the crystal can be easily estimated only by measuring the carbon concentration at both ends of the crystal. Therefore, when the active layer is formed by implanting ions into the wafer, it is possible to optimally adjust the ion implantation conditions in accordance with the carbon concentration in the crystal, thereby greatly reducing the variation in the activation rate and the wafer. Can have uniform electrical characteristics. As a result, GaAs
Elements such as ICs can be manufactured stably, and yield can be improved and manufacturing costs can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an apparatus for pulling up a GaAs single crystal while controlling the concentration of carbon monoxide for implementing the method of manufacturing a GaAs single crystal of the present invention.

FIG. 2 is a characteristic diagram showing an example of a carbon concentration distribution in a crystal according to an embodiment of the present invention.

FIG. 3 is a characteristic diagram showing an example of a conventional carbon concentration distribution in a crystal.

FIG. 4 is a characteristic diagram showing a distribution of a sheet carrier concentration when ions are implanted into a crystal and activated according to an embodiment of the present invention.

FIG. 5 is a characteristic diagram showing the distribution of sheet carrier concentration when ions are implanted into a conventional crystal and activated.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Crystal growth container 2 Heater 3 GaAs crystal 4 Liquid sealant 5 GaAs melt 6 GaAs exhaust pipe 7 GaAs sampling pipe 8 GaAs introduction pipe 9 Mass flow controller 10 Carbon monoxide concentration detector 11 Crucible 12 Upper shaft 13 Seed crystal 14 Lower axis

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C30B 15/00-15/36 C30B 27/00-27/02

Claims (3)

(57) [Claims] In a semi-insulating GaAs single crystal containing carbon as an impurity in the crystal, the distribution of carbon concentration in the crystal monotonically increases or decreases from the head (starting end) to the tail (ending end) of the crystal. A GaAs single crystal, characterized in that: 2. A crucible containing a GaAs melt and a liquid sealing material for covering the upper surface of the melt is placed in a container filled with an inert gas, and the seed crystal is brought into contact with the upper surface of the GaAs melt and rotated. In the method of manufacturing a GaAs single crystal by pulling while growing, before the crystal growth, a gas of carbon monoxide or carbon dioxide that produces carbon monoxide in the container is introduced into the inert gas in the container, and The concentration of carbon monoxide is set to a predetermined value, and after that, crystal growth is started. During the crystal growth, the concentration of carbon monoxide in the container is measured using a carbon monoxide detector.
Detected, and the concentration of carbon monoxide in the inert gas increases monotonically.
The gas in the container is replaced with a gas such as pure inert gas, carbon monoxide or carbon dioxide that produces carbon monoxide in the container, or a mixed gas thereof, so that the single crystal is added or reduced, so that the single crystal is changed. A method for producing a GaAs single crystal, characterized by growing. 3. In the GaAs single crystal according to claim 1, a wafer is cut out from its head to its tail, and the carbon concentration [C] of each cut out wafer is obtained from equation (1), and [C] = ([ C _T ]-[C _S ]) × m / L + [C _S ] (1) where [C _T ] is the carbon concentration in the crystal measured at the tail of the crystal [C _S ] is the head of the crystal M is the distance from the head of the crystal from which the sample for which the carbon concentration was measured is taken L is the distance between the head and the tail of the crystal from which the sample for which the carbon concentration was measured is taken from this The ion implantation dose φ is calculated from the equation (2) using [C] obtained every time, and φ = φ ₀ + ([C] − [C _S ]) × a (2) where φ ₀ is a reference dose amount a is a coefficient determined by implantation conditions Ion of this dose amount is implanted into the corresponding wafer A method for controlling ion implantation of a GaAs wafer.