JPH0628246B2 - Method for producing silicon-germanium alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a material for directly converting heat energy and electric energy, that is, to manufacture a silicon-germanium alloy among thermoelectric materials, and to use the alloy. The present invention relates to a method suitable for element processing.

[Prior Art] As a method for producing a thermoelectric material silicon-germanium alloy, for example, R.I. A. Referer, Gee. Elle. Macbe and R. J. Baumann: ”
Preparation of Hot Pressed Silicon Germanium Ingot; Part III Vacuum Hot Pressing ”, Materials Research Brachin, 9863 (1974) (Lefever, GLMcVay and RJBaugh
man: ”Preparation of Hot-Pressed Silicon-Germanium
Ingot: Part III-Vacuum HotPresing ”, Mat.Res.Bul
l. 9 863 (1974)) and its series (Part I and Part II). According to this document, the powder sintering method is a process of melting metallic silicon, metallic germanium and a doping material.

 The step of cooling the melt obtained in the step of.

The step of crushing the silicon-germanium alloy obtained in the step of to about 10 mesh.

The step of further finely grinding (grinding) the silicon-germanium alloy particles obtained in the step of.

The silicon-germanium alloy powder obtained in the step of
Hot pressing in a vacuum container of 10 ^-5 torr or less at a high pressure of approximately 1300 ° C. and approximately 2000 kg / cm ² .

And the like.

In addition, Japanese Patent Application Laid-Open No. 58-190077 discloses an invention relating to a thermoelectric material composed of a multi-element non-single crystal body. In the examples therein, a method for producing SixGeyBz (x + y + z = 1) is disclosed. Has been deferred. According to this, SiH ₄ , GeH ₄ , and B ₂ H ₆ are used as a source gas and introduced into a vacuum container by a H ₂ carrier gas and decomposed to obtain a ternary amorphous crystal composed of Si, Ge and B at 50 Å / min. Is gaining at the growth rate of. There is also a method of obtaining a thermoelectric material by using a gaseous compound as a raw material in this manner and vapor-decomposing this as a raw material.

When the thermoelectric material thus obtained is used as a pair of PN elements, conventionally, P-type silicon-germanium and N-type silicon-germanium were processed and molded according to the intended use, and a hot shoe and a cold shoe were bonded.

[Problems to be Solved by the Invention] Among the conventional methods for producing a thermoelectric material, the former powder sintering method has a complicated process as described above, and a high temperature of 1400 ° C. or higher in the melting step of the raw material. , In the process of hot pressing 13
Special manufacturing conditions such as high temperature near 00 ℃, high pressure of about 2000 kg / cm ² , high vacuum degree of 10 ^-5 torr or less, or high technical level to achieve it were required.

Also, as in the latter example of JP-A-58-190077,
A film-forming method using SiH ₄ , GeH ₄ , and B ₂ H ₆ as raw materials and introducing them into a vacuum container has a slow growth rate of 50 Å / min., Which is still problematic for industrial success.

Furthermore, when the silicon-germanium alloy thus produced is used as a thermoelectric element, it must be processed into a structure as shown in FIG. 6, for example.
To form a bridge with the mold, generally a so-called adhesion process such as metallization process and brazing must be performed. However, in this method, the process is complicated and it is difficult to select an appropriate brazing agent for adhesion in terms of melting point and adhesiveness.

[Means for Solving Problems] The present invention provides a method for solving the problems of the above-mentioned conventional method, that is, special manufacturing conditions such as high temperature, high pressure, and high vacuum degree, and provides a means for easy industrialization. Provided is a novel thermoelectric element forming method which enables production at a high yield and a high growth rate and does not require a separate step for forming a bridge between opposite conductivity types as in the conventional device formation.

That is, first, SiH ₄ gas, GeCl ₄ gas, and one conductivity type doping gas are introduced into the reaction vessel, and
A silicon-germanium alloy is deposited on a substrate heated to 0 ° C. or higher, and SiH ₄ gas and GeCl ₄ gas and a doping gas having a conductivity type opposite to that of the doping gas are introduced onto the silicon-germanium alloy. Then, a series of steps of depositing another silicon-germanium alloy so as to have a conductivity type opposite to that of the previously deposited silicon-germanium alloy is repeated one or more times.

Further, in the present invention, the material of the substrate is composed of a silicon-germanium alloy of one conductivity type from the beginning, and a silicon-germanium alloy of the conductivity type opposite to the substrate is deposited thereon, and a series of steps similar to those described above is performed. It can also be adopted and manufactured.

Hereinafter, the present invention will be described in detail with reference to FIG.

Of the gases used in the present invention, nitrogen (N ₂ ) gas, SiH ₄
Gas, doping gas, and hydrogen (H ₂ ) gas are supplied through line 1, line 2, line 3, and line 4, respectively. 11, 12, and 13 are flow controllers for each gas.
The H ₂ supplied by line 4 is used for replacement of the device and the container 4
Used as a carrier gas for GeCl ₄ stored at 0.

First, the base 31 is set in the reaction container 32. Prior to the growth, the inside of the reaction vessel is evacuated by a vacuum pump 23 and then replaced with H ₂ , and then a predetermined amount of H ₂ is flown. This H ₂ is discharged at a predetermined pressure by the pressure keeping device 24. In parallel with this operation, the same amount of SiH ₄ , one conductivity type doping gas, and GeCl _{4 of} H ₂ carrier as in the initial growth conditions are flown into the abatement device 27 through the purge line 50. Base is power supply 35
More power is supplied and the temperature is raised to a predetermined temperature. Peep window
The substrate 31 is controlled at a constant temperature by a temperature control pyrometer 34 through 33. The growth is carried out by stopping the H ₂ and at the same time introducing the raw material gas flowing through the purge line into the reaction vessel. Then, the deposition of the silicon-germanium alloy of the opposite conductivity type is started. This is because once the first deposition is finished, the raw material gas is once stopped and H ₂ is flown to purge it, and then the opposite conductivity is obtained by the above operation. The mold silicon-germanium alloy is deposited.

Alternatively, GeCl ₄ and SiH ₄ are kept flowing as they are, only the doping gas is once stopped, and after a while, the doping gas of the opposite conductivity type is used to deposit.

Further, by repeating these operations, a silicon-germanium alloy composed of a plurality of layers alternately having opposite conductivity types can be obtained.

After the growth is completed, the source gas is stopped and only H ₂ is supplied. After a lapse of a predetermined time, the temperature of the substrate is lowered, and after the temperature is completely lowered, N ₂ is flown into the reaction vessel to replace the inside with N ₂ . Further, in order to complete the replacement, the inside of the reaction vessel is replaced with N ₂ using a vacuum pump, and the product is taken out.

[Operation] According to the method for producing a thermoelectric material silicon-germanium alloy of the present invention, a homogeneous silicon-germanium alloy can be obtained by the following operations.

That is, first, a gaseous compound is used as a raw material,
Since this raw material is sufficiently agitated by natural convection in the reaction vessel, the gas in the reaction vessel becomes homogeneous. Next, these raw material gases reach the surface of the substrate and are decomposed by receiving the thermal energy of the substrate there, and the desired silicon-germanium alloy is successively deposited on the surface of the substrate. At this time, since the silicon-germanium alloy does not go through a molten state, it is not subjected to the segregation action, and as a result, a silicon-germanium alloy having a homogeneous composition can be obtained. When the pressure in the reaction container is particularly higher than atmospheric pressure, natural convection is likely to occur in the reaction container, so that the raw material gas is effectively consumed and a high growth rate and a high yield can be achieved.

By the way, in the case of producing polycrystalline silicon for semiconductors by thermal decomposition of SiH ₄ , the substrate surface is said to be suitable at 750 to 850 ° C. This is the smoothness of the surface of the deposited layer (hereinafter referred to as morphology). ) Is believed to worsen with increasing temperature. Therefore, the substrate temperature cannot be raised so much due to a problem such as a yield at the time of outer shape processing.
However, in the method for producing a silicon-germanium alloy according to the present invention, by using GeCl ₄ gas, it has been confirmed by experiments that the morphology is very good even at a temperature higher than the substrate surface temperature at the time of thermal decomposition of SiH ₄ simple substance. . Therefore, the growth rate could be increased by further raising the substrate temperature.

Example 1 In a reaction vessel having an inner diameter of about 200 mm and a height of 1300 mm, 23 × 20 × 940
87 mm graphite substrate 60 is directly energized and heated to 87
Hold at 0 ° C. Phosphine as a doping gas (P
H ₃₎ and chose diborane (B ₂ H _6).

First, monosilane (SiH ₄ ) and germanium tetrachloride (Ge
Cl ₄ ) and B ₂ H ₆ respectively at 210 Nml / min., 620 mg / mi
n., 0.10 Nml / min. was introduced into the reaction vessel. GeC
Since l ₄ is a liquid at room temperature, the flow rate was adjusted by the flow rate of carrier gas (H ₂ ) and the vapor pressure of GeCl ₄ . After that, silicon-silicon generated by the deposition of germanium-
This SiH ₄ , in the same proportion as the surface area of the germanium alloy,
The flow rates of GeCl ₄ and B ₂ H ₆ were increased. 18 hours after starting the introduction of gas into the reaction vessel, the supply of B ₂ H ₆ was stopped and the supply of PH ₃ was started. PH ₃ was supplied at a rate 1.8 times that of B ₂ H ₆ . During this time, the pressure inside the reaction vessel was maintained at 1.4 atm. The total reaction time was 36 hours. Growth rate is 2.4 μm
It was / min.

The obtained alloy has a P-type inner layer (B: 5.2 × 10 ¹³ atoms / cc)
Si _0.83 Ge _0.17 , N-type outer layer (P: 4.8 × 10 ¹⁹ atoms / c
c) Si _0.83 Ge _0.17 .

From the alloy obtained here, a pair of PN elements were cut out in the process shown in FIG. 2 and, as shown in FIG. 3, a test module 83 was produced by connecting 17 elements to the low temperature side, and the performance was examined. However, the output was 2.4 W at a temperature difference of 600 ° C.

Example 2 In a reaction vessel having an inner diameter of about 200 mm and a height of 1300 mm, 23 × 3 × 940
87 mm mm of graphite substrate 61 is directly energized and heated to
Hold at 0 ° C. Phosphine as a doping gas (P
H ₃₎ and chose diborane (B ₂ H _6).

First, monosilane (SiH ₄ ) and germanium tetrachloride (Ge
Cl ₄ ) and B ₂ H ₆ respectively at 210 Nml / min., 620 mg / mi
n., 0.10 Nml / min. was introduced into the reaction vessel. GeC
Since l ₄ is a liquid at room temperature, the flow rate was adjusted by the flow rate of carrier gas (H ₂ ) and the vapor pressure of GeCl ₄ . After that, silicon-silicon generated by the deposition of germanium-
This SiH ₄ , in the same proportion as the surface area of the germanium alloy,
The flow rates of GeCl ₄ and B ₂ H ₆ were increased. 18 hours after starting the introduction of gas into the reaction vessel, the supply of B ₂ H ₆ was stopped and the supply of PH ₃ was started. PH ₃ was supplied at a rate 1.8 times that of B ₂ H ₆ for 18 hours.

By repeating the series of steps described above, silicon-germanium alloys having opposite conductivity types were alternately deposited to obtain a multilayer structure. The total reaction time was 144 hours. During this time, the pressure inside the reaction vessel was maintained at 1.4 atm. Growth rate is 2.4
It was μm / min.

The obtained alloy has a P-type layer (B: 5.2 × 10 ¹³ atoms / cc)
Si _0.83 Ge _0.17 , N-type layer, (P: 4.8 × 10 ¹⁹ atoms / c
c) Si _0.83 Ge _0.17 .

In the process shown in FIG. 4, a pair of PN elements are cut out from the alloy obtained here, and the test module 84 shown in FIG.
Was manufactured, and the performance was examined, and the output was 540 mW at a temperature difference of 600 ° C.

[Effects of the Invention] The following effects are brought about by the method for producing a thermoelectric material silicon-germanium alloy of the present invention.

1) Because of vapor phase growth, the conductivity type can be easily changed by changing the supplied doping gas. Therefore, when the element is processed, steps such as metallization of the high temperature side electrode and adhesion for so-called bridging processing between PNs are not required, the element can be easily manufactured, and the element is contaminated with an adhesive or the like. It will not happen.

2) Since it is not affected by the segregation effect, it is extremely homogeneous silicon.
A germanium alloy can be obtained.

3) Since there is no crushing or crushing process or no melting process, there is no contamination from a crushing or crushing jig or crucible.

4) It does not require special conditions such as high temperature, high pressure, and high vacuum degree, or advanced technology to obtain it, so the manufacturing equipment can be small scale and the consumable parts can be reduced.

5) The manufacturing process is simplified, so that the control items such as inspection items and manufacturing conditions in each process can be reduced.

6) Especially under a pressure of atmospheric pressure or higher, natural convection can be effectively utilized, so that a high growth rate and a high yield can be obtained. Therefore, it is particularly useful as a method for producing a silicon-germanium alloy for thermoelectric power generation using a bulk.

7) During production, by monitoring the exhaust gas with a gas chromatograph or the like, the production conditions of the silicon-germanium alloy can be easily controlled.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an apparatus for carrying out the present invention. FIG. 2 is a silicon-germanium alloy produced according to the present invention. FIG. 3 is a silicon-germanium alloy thermoelectric device manufactured according to the present invention. FIG. 4 is another silicon-germanium alloy made according to the present invention. FIG. 5 shows another silicon-germanium alloy thermoelectric element manufactured according to the present invention. FIG. 6 shows a conventional thermoelectric element. 1 …… N ₂ gas 2 …… SiH ₄ gas 3 …… Doping gas 4 …… H ₂ gas 11 …… Flow controller 12 …… Flow controller 13 …… Flow controller 21 …… Pressure gauge 23 …… Vacuum pump 24 …… … Pressure-retaining device 27 …… Detoxification device 31 …… Substrate 32 …… Reaction vessel 33 …… Viewing window 34 …… Radiation thermometer 35 …… Power supply 40 …… Vessel 41 …… Heater 50 …… Purge line 60, 61 …… Substrate 64 …… Hot shoe 65 …… Cold shoe 71,72,73 …… P-type silicon-germanium alloy 77,78,79 …… N-type silicon-germanium alloy 83,84 …… Test module

Claims (2)

[Claims] 1. A SiH ₄ gas, a GeCl ₄ gas, and a doping gas of one conductivity type are first introduced into a reaction vessel, and a silicon-germanium alloy is deposited on a substrate heated to 750 ° C. or higher in the reaction vessel. Then, SiH ₄ gas and GeCl ₄ gas and a doping gas having a conductivity type opposite to that of the doping gas are introduced onto the silicon-germanium alloy to deposit a silicon-germanium alloy having a conductivity type opposite to the silicon-germanium alloy. A method of manufacturing a silicon-germanium alloy, characterized in that the series of steps is performed once or more. 2. The material of the base is one conductivity type silicon.
The method for producing a silicon-germanium alloy according to claim 1, wherein the germanium alloy is a silicon-germanium alloy initially deposited on the substrate and has a conductivity type opposite to that of the substrate.