JPH0547519B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to a method for manufacturing a single crystal thin film, and more particularly to a method for forming an n-type silicon single crystal thin film at a low temperature. [Background Art] Low-temperature formation of single crystal thin films is attracting attention as a very important technology for achieving high integration of semiconductor devices. Various approaches have been taken for this purpose. For example, thermal CVD ( C
chemical vapor deposition )
The method requires high temperatures of approximately 1000-1100°C. Furthermore, according to our studies, the photo-CVD method using fluorosilane or disilane requires a temperature of approximately 600 to 700°C. As described above, the conventional techniques still require high temperatures, and a satisfactory low-temperature formation technique has not yet been developed. The present inventors have demonstrated that photolysis of fluorosilane (photodegradation of fluorosilane)
It was first proposed to obtain a low-resistance amorphous thin film using the CVD method (Japanese Patent Application No. 49231/1983;
No. 49232). As a result of further investigation, we surprisingly found that by using a mixed gas of fluorosilane and silane as the raw material gas, an n-type single crystal silicon thin film could be grown at a substrate temperature of 300°C or less. It is to be disclosed. [Disclosure of the Invention] The present invention is a method for producing an n-type single crystal thin film, which is characterized in that it is formed by photodecomposing (photo-CVD) a mixed gas consisting of fluorosilane, silane, a Group V compound, and preferably hydrogen. . As the fluorosilane used in the present invention, SiH _4-o Fn (n=an integer of 1 to 3) or Si ₂ F ₆ is particularly useful. Also, as a silane, Si _n H _2n+2 (m
= an integer of 1 to 3), monosilane, disilane, and trisilane are effectively used. Further V
PH ₃ (phosphine) and AsH ₃ (arsine) are used as group compounds. Further, in the present invention, as a particularly preferable embodiment, n
In a particularly preferred embodiment, the monocrystalline thin film is epitaxially grown on a monocrystalline substrate, and the substrate is a silicon wafer, sapphire, or the like. In the present invention, photolysis using ultraviolet rays is particularly preferred, but a sensitizing reaction of photolysis can also be used. That is, the present invention is a method of photolyzing a mixed gas consisting of fluorosilane, silane, V group compound, and preferably hydrogen by irradiation with ultraviolet rays to form an n-type single crystal thin film on a crystalline substrate heated to a low temperature. be. In the present invention, it is essential to perform photoCVD in a state where fluorosilane and silane coexist in the V group compound, and more preferably, a gas mixed with hydrogen is irradiated with ultraviolet rays. The mixed gas ratio can be expressed as the raw material gas supply flow rate (capacity) ratio to a thin film forming apparatus that forms an n-type single crystal thin film. In terms of this ratio, the preferred range is as follows: That is, the ratio of group V compound/silane is appropriately determined depending on the desired resistance value of the formed n-type single crystal thin film. For normal semiconductor device applications, a range of 1×10 ⁻⁷ to 1×10 ⁻³ is sufficient for this ratio, and even if the ratio is smaller than this, the resistance can be sufficiently low. Also, fluorosilane/silane ratio = 0.5 to 50,
Particularly preferably 1 to 20. On the other hand, for hydrogen, the hydrogen/fluorosilane ratio is preferably at least 2 times, particularly preferably at least 5 times. Note that if the amount of hydrogen added is too large, the growth rate of the n-type single crystal will decrease, so the preferred hydrogen/fluorosilane mixing ratio is 2 to 20 times, particularly preferably 5 to 20 times.
It is 15 times more. The method of forming the mixed gas is not a critical factor and is not particularly limited. For example, it is useful to introduce a premixed gas outside the forming apparatus, or to mix hydrogen within the forming apparatus so as to satisfy the above dilution degree. Note that Group V compounds are toxic and are usually preferably used in a diluted state. It is particularly convenient to use Group V compounds, fluorosilanes, silanes, etc. diluted with hydrogen. In the present invention, the light source that generates the ultraviolet light used for photolysis is not a critical condition and is not particularly limited. Specific examples include a mercury lamp, a rare gas lamp, a mercury-rare gas lamp, and a hydrogen discharge tube. Among these light sources, it is practically convenient to use a low-pressure mercury lamp, which is a type of mercury lamp. Photolysis can be carried out directly or indirectly via a sensitizer, if desired.
From a practical standpoint, a mercury sensitization method using mercury as a sensitizer is effectively used. When using a monosilane with m=1 in the general formula as the silane, only an intermittent mercury sensitization method is useful. m=2 and m=
Disilanes and trisilanes of No. 3 are useful both directly and indirectly. Trisilane has a boiling point of 53
Since it exists in liquid form at room temperature, it must be gasified by some means. Therefore, from the viewpoint of the photodecomposition reaction of the mixed gas, disilane (m=2) is a preferable raw material for the silane. Furthermore, one of the excellent features of the present invention is that the temperature at which the n-type single crystal thin film is formed is extremely low compared to the conventional optical CVD method. conventional light
In the CVD method, a temperature of 600°C or higher is required, but in the present invention, surprisingly, epitaxial growth can be sufficiently performed at a substrate temperature of 300°C or lower, or even 200°C, as shown in the examples. The growth temperature can be further reduced, but in this case the growth rate needs to be reduced accordingly. When the growth rate is a practical value of about 0.1 Å/sec or more, the substrate temperature may be about 100° C. or more. In the present invention, there are no particularly critical conditions for the mixed gas pressure or irradiation light intensity during photolysis. Furthermore, when mercury is used as a sensitizer, there are no particular limitations on the temperature of the mercury reservoir, the flow rate of the carrier gas for transferring mercury vapor to the thin film forming apparatus, etc.
These conditions affect the growth rate of the n-type single crystal thin film, and as mentioned above, by appropriately changing the substrate temperature according to the desired growth rate, the n-type single crystal thin film can be grown effectively epitaxially. can be done. [Preferred Modes for Carrying Out the Invention] Next, embodiments of the present invention will be described. A substrate made of a single crystal material whose surface has been cleaned by cleaning and/or etching is placed in a thin film forming apparatus having at least a light transmission window, a substrate introduction means, a substrate holding means, a substrate heating means, a gas introduction means, and a vacuum evacuation means. Heat the substrate to 100-400°C under exhaust gas. When introducing the raw material gas, a part of it is introduced into the apparatus via a mercury reservoir as necessary. The raw material gas has a flow rate ratio of group V compound to silane of 1×10 ^-7 ~
1×10 ^-3 , the flow rate ratio of fluorosilane to silane is set to 0.5 to 50, and the flow rate ratio of hydrogen to fluorosilane is doubled to be supplied to the apparatus.
The pressure inside the apparatus is reduced to 10 Torr or less using a vacuum evacuation means, and a low-pressure mercury lamp is turned on to start film formation.
Formation of a thin film begins when the lamp is turned on, so the lamp is turned off when the required film thickness is reached, taking into consideration the film formation rate. Further, the film forming time can be determined while measuring the film thickness using a film thickness monitor. Synthetic quartz is suitable for the light transmitting window of the device, but by applying high boiling point oil to this window, film formation on the light transmitting window can be suppressed. [Effects of the Invention] The n-type single crystal thin film obtained in the present invention can be formed even when the substrate temperature is as low as 300°C or lower. The present invention provides an extremely useful technology for the field of manufacturing semiconductor devices, where low-temperature formation technology for semiconductor thin films and semiconductor devices is eagerly awaited for higher integration. [Example] The present invention will be described in more detail below with reference to Examples. Example 1 A thin film forming apparatus 7 having an ultraviolet transmitting window 1, a substrate introduction means 2, a substrate holding means 3, a substrate heating means 4, a gas introduction means 5, and a vacuum evacuation means 6 as shown in FIG. 1 is used. Using the substrate introduction means 2, a p-type silicon wafer (100), which is the substrate 8 for film attachment, is placed on the substrate holding means. The cleaned substrate was heated to 200° C. by the substrate heating device while being evacuated by the vacuum pumping device. Note that 6' and 9' are exhaust means for the substrate introduction/takeout chamber 15. Then 4x phosphine/disilane/difluorosilane/hydrogen
It is introduced at a flow rate ratio of 10 ^-5 /1/15/150 and maintained at a pressure of 2 Torr by a control valve 9 installed in the evacuation means. A part of the difluorosilane introduced through the conduit 10 is heated to about 40°C in the mercury reservoir 11.
Introduce it by passing it over it. Note that 13, 14, and 16 are pipes for disilane, phosphine, and hydrogen. When the temperature of the substrate and the pressure inside the thin film forming apparatus become constant, the low pressure mercury lamp 12 is turned on,
The light turns off when the film thickness reaches approximately 6000 Å. The average film formation rate obtained by dividing the film pressure by the film formation time was about 0.95 Å/s. After cooling, the substrate was taken out and observed, and it was found that the surface of the substrate was a mirror surface with no clouding at all. The surface was observed using a reflection electron diffraction (RHEED) device, and Laue spots identical to those of the substrate were observed, confirming that a p-type single crystal thin film was epitaxially grown from the substrate surface. The specific resistance of this p-type single crystal thin film is approximately 0.025Ω・cm
It was hot. Examples 2 to 9, Comparative Examples 1 and 2 The procedure of Example 1 was repeated except that the type and amount of fluorosilane were changed. The conditions and results are listed in Table 1. Table 1 also shows examples for comparison.

【table】

[Table] *Values when the disilane flow rate of Example 1 is set to 1 Example 10 In Example 1, monosilane (SiH ₄ ) was used instead of disilane. The deposition rate is 0.14Å/
Epitaxial growth was confirmed by electron beam diffraction, although the growth rate decreased to s. The resistivity was approximately 1.6×10 ⁻² Ω·cm. As is clear from the examples above, the present invention, which allows the growth of an n-type single crystal thin film at a substrate temperature as low as 200° C., is an extremely effective invention for lowering the manufacturing temperature of semiconductor devices.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a longitudinal section of a thin film forming apparatus useful for carrying out the present invention.

Claims (1)

[Scope of Claims] 1. A method for producing an n-type single crystal thin film, characterized in that it is formed by photodecomposing a mixed gas consisting of fluorosilane, silane, and a Group V compound. 2. The method for producing an n-type single crystal thin film according to claim 1, wherein the fluorosilane is SiH _4-o F _o (n=1 to 3) or Si ₂ F ₆ . 3. The method for producing an n-type single crystal thin film according to claim 1, wherein the silane is Si _n H _2n+2 (m=1 to 3). 4. The method for producing an n-type single crystal thin film according to claim 1, wherein the V group compound is PH ₃ or AsH ₃ . 5. A method for producing an n-type single crystal thin film according to claim 1, which is formed on a crystalline substrate. 6. The method for producing an n-type single crystal thin film according to claim 1, wherein the photodecomposition is performed by irradiation with ultraviolet rays. 7. The n-type single crystal thin film according to claim 1, which is formed on a crystalline substrate heated to a low temperature by photodecomposing a mixed gas consisting of fluorosilane, silane, a Group V compound, and hydrogen by irradiation with ultraviolet rays. manufacturing method.