JPH0549637B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to a method for producing a single crystal thin film, and more particularly to a method for forming a p-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. However, 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 of fluorosilane or disilane requires a temperature of about 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, a p-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 provides photolysis (photolysis) of a mixed gas consisting of fluorosilane, a silane group compound, and preferably hydrogen.
This is a method for manufacturing a p-type single crystal thin film, characterized in that it is formed by CVD). In the present invention, _SiH4 - _oFo (n=an integer of 1 to _{3 )} or _Si2F6 is useful as the fluorosilane used. Also, as a silane, Si _n H _2n+2 (m=1
Monosilane, disilane, and trisilane represented by (an integer of 3 to 3) are effectively used. Furthermore, B ₂ H ₆ (diborane) is used as a group compound. Furthermore, in a particularly preferred embodiment of the present invention, a p-type single crystal thin film is epitaxially grown on a single crystal substrate, and a silicon wafer, a sapphire, or the like is used as the substrate. 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 provides a method for forming a p-type single crystal thin film on a crystalline substrate heated to a low temperature by photolyzing a mixed gas consisting of fluorosilane, silane, a group compound, and preferably hydrogen, preferably by irradiation with ultraviolet rays. It is. In the present invention, it is essential to carry out photoCVD in a state where fluorosilane and silane coexist in the 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 the thin film forming apparatus that forms the p-type single crystal thin film. In terms of this ratio, the preferred range is as follows: That is, the ratio of group compound/silane is appropriately determined depending on the resistance value of the p-type single crystal thin film. In normal semiconductor device applications, this ratio is 1
A range of ×10 ⁻⁷ to 1×10 ⁻³ is sufficient, and even if the resistance is small, the resistance is sufficiently low. Also, the ratio of fluorosilane/silane = 0.5 to 50, particularly preferably 1
~20. The hydrogen/fluorosilane ratio is at least 2 times, particularly preferably at least 5 times. On the other hand, if the amount of hydrogen added is too large, the growth rate of the p-type single crystal decreases, so the preferred hydrogen/fluorosilane mixing ratio is 2 to 20 times, particularly preferably 5 to 15 times. 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.
Since the group compounds are unstable, they are usually used diluted with hydrogen. There is no problem in using fluorosilane or silane 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. In 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 monosilane with m=1 in the general formula as the silane, only indirect mercury sensitization is effective. 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 p-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 surprisingly in the present invention, as shown in the examples, sufficient epitaxial growth can be achieved at a substrate temperature of 300°C or lower, or even 200°C. 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 p-type single crystal thin film, and as mentioned above, by appropriately changing the substrate temperature according to the desired growth rate, the p-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, and the substrate is vacuum evacuated. Heat the lower substrate to 100-400℃. 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 compound to silane of 1×10 ^-7 to 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 at least twice as high. 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 p-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, an n-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 of the exhaust means 15 of the substrate introduction/extraction chamber 15.
Then diborane/disilane/difluorosilane/
Hydrogen was introduced at a flow rate of 4×10 ^-5 /1/15/150,
2 Torr with the control valve 9 installed in the vacuum evacuation means
Hold at a pressure of A portion of the difluorosilane introduced through conduit 10 is passed over mercury reservoir 11 heated to about 40°C. In addition, 1
3, 14, and 16 are disilane, diborane, and hydrogen introduction pipes. When the temperature of the substrate and the pressure within the thin film forming apparatus become constant, the low pressure mercury lamp 12 is turned on and turned off when the film thickness reaches about 6000 Å. The average film formation rate calculated by dividing the film thickness by the film formation time was approximately 1.2 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 0.068Ω・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. Deposition rate is 0.17Å/
Although the S value decreased, epitaxial growth was confirmed by electron beam diffraction. The resistivity was approximately 0.035Ω·cm. The present invention, which is capable of growing a p-type single crystal thin film at a substrate temperature as low as 200° C., is extremely effective in 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 a p-type single crystal thin film, characterized in that the film is formed by photodecomposing a mixed gas consisting of fluorosilane, silane, and group compounds. 2. The method for producing a p-type single crystal thin film according to claim 1, which is fluorosilane _{SiH4 - oFo} (n=1 to ₃ ) or _Si2H6 . 3. The method for producing a p-type single crystal thin film according to claim 1, wherein silane Si _n H _2n+2 (m=1 to 3) is used. 4. The method for producing a p-type single crystal thin film according to claim 1, wherein the Group ₄ compound is _B2H6 . 5. A method for producing a p-type single crystal thin film according to claim 1, which is formed on a crystalline substrate. 6. The method for producing a p-type single crystal thin film according to claim 1, wherein the photodecomposition is performed by irradiation with ultraviolet rays. 7. A p-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 compound, and hydrogen by irradiation with ultraviolet rays. Production method.