JPH0547518B2 - - 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 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, for example, thermal CVD (Chemical Vapor Deposition ) of monosilane requires high temperatures of about 1000 to 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 a single crystal silicon thin film can be grown at a substrate temperature of 300°C or less by using a mixed gas of fluorosilane and silane as the raw material gas, which we will disclose here. It is something. [Disclosure of the Invention] The present invention is a method for producing a single crystal thin film, which is characterized in that it is formed by photodecomposing (photo-CVD) a mixed gas consisting of fluorosilane, silane, and preferably hydrogen. Particularly useful as the fluorosilane used in the present invention are SiH _{4-o Fo} (n=1 to 3 integer) or Si ₂ F ₆ . Also, as a silane, Si _n H _2n+2 (m=
Monosilane, disilane, and trisilane represented by (an integer from 1 to 3) are effectively used. Furthermore, in the present invention, a particularly preferred embodiment is to grow the single crystal thin film epitaxially on a single crystal substrate, and the substrate may be a silicon wafer, a 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, and preferably hydrogen, preferably by irradiation with ultraviolet light, to form a single crystal thin film on a crystalline substrate heated to a low temperature. In the present invention, it is essential to carry out photoCVD in a state where fluorosilane and silane coexist.
More preferably, a gas mixed with hydrogen is irradiated with ultraviolet rays. The mixed gas ratio can be expressed as a raw material gas supply flow rate (capacity) ratio to a thin film forming apparatus that forms a single crystal thin film. In terms of this ratio, the preferred range is as follows. That is, the fluorosilane/silane ratio is from 0.5 to 50, particularly preferably from 1 to 20. Regarding hydrogen, the hydrogen/fluorosilane ratio is preferably at least 2 times, particularly preferably at least 5 times. If the amount of hydrogen added is too large, the growth rate of the single crystal will decrease, 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. Of course, 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 the mercury sensitization method is effective. Disilanes and trisilanes with m=2 and m=3 are useful both directly and indirectly. Trisilane has a high boiling point of 53°C, and since it exists as a liquid at room temperature, it must be gasified by some means. Therefore, from the viewpoint of photodecomposition reaction of mixed gas, disilane (m
=2) is a preferred raw material. Furthermore, one of the excellent features of the present invention is that the temperature for forming a single crystal thin film is extremely low compared to conventional optical CVD methods. In the conventional optical CVD method, a temperature of 600°C or higher is required, but surprisingly, in the present invention, epitaxial growth can be performed at a substrate temperature of 300°C or lower, or even 200°C, as shown in the examples. be. The growth temperature can be further reduced, but in this case the growth rate must 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 regarding 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 or the flow rate of the carrier gas for transferring mercury vapor to the thin film forming apparatus. These conditions affect the growth rate of the single crystal thin film, and as described above, by appropriately changing the substrate temperature according to the growth rate, the single crystal thin film can be effectively epitaxially grown. [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 fluorosilane to silane of 0.5~
50, and the flow rate ratio of hydrogen to fluorosilane is at least twice as high as that of fluorosilane. Using vacuum evacuation means to reduce the pressure inside the device to 10 Torr or less,
Turn on the low-pressure mercury lamp and start film formation. Formation of a thin film begins as soon as the lamp is turned on, so the lamp is turned off when the required film thickness is reached, taking into account 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 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, and even as low as 200°C or lower. For the field of manufacturing high-conductor devices, where low-temperature formation technology for semiconductor thin films and semiconductor devices is eagerly awaited for optical integration,
The present invention provides extremely useful technology. [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 introducing means 2, a substrate holding means 3, a substrate heating means, a gas introducing 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. Next, disilane/difluorosilane/hydrogen are introduced at a flow rate ratio of 1/15/150, and the pressure is maintained at 2 Torr by a control valve 9 provided in the evacuation means. A portion of the difluorosilane introduced through conduit 10 is heated to approximately 40°C.
The mercury is introduced by passing it over a mercury reservoir 11 heated to . In addition, 13 is a disilane introduction pipe, and 14 is a hydrogen introduction pipe. When the temperature of the substrate and the pressure inside the thin film forming apparatus are constant, the low pressure mercury lamp 12 is turned on,
The light turns off when the film thickness reaches approximately 6000 Å. The average deposition rate was 1.0 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 obtained, confirming that a single crystal thin film was epitaxially grown from the substrate surface. This single crystal thin film is extremely weak n-type, and its specific resistance is 50~
It was 70Ω・cm. 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 shown 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 0.15Å/
Epitaxial growth was confirmed by electron beam diffraction, although the growth rate decreased to s. The resistivity was 90 to 120 Ω·cm. As is clear from the examples above, the present invention, which allows single crystal thin films to be grown at a substrate temperature as low as 200° C., is extremely effective 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 a single crystal thin film, characterized in that it is formed by photodecomposing a mixed gas consisting of fluorosilane and silane. 2. The method 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 according to claim 1, wherein the silane is Si _n H _2n+2 (m=1 to 3). 4. The method according to claim 1, which is formed on a crystalline substrate. 5. The method according to claim 1, wherein the photolysis is carried out by irradiation with ultraviolet light. 6. The method according to claim 1, wherein a gas mixture consisting of fluorosilane, silane, and hydrogen is photodecomposed by irradiation with ultraviolet rays and formed on a crystalline substrate heated to a low temperature.