JPS63939B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vapor phase growth method for obtaining a high quality vapor phase growth film.

As a method for forming high-quality vapor-phase grown films during vapor-phase growth, it is effective and important to auto-dope impurities from the sample substrate to the grown film during vapor-phase growth and to reduce out-diffusion. Therefore, it is necessary to lower the growth temperature or shorten the growth time. However, lowering the growth temperature lowers the crystallinity of the grown film, so generally a method is used to shorten the growth time without lowering the growth temperature too much. Therefore, from the relational expression t=T _G ×R _G among the grown film thickness (t), growth time (T _G ), and growth rate (R _G ), in order to obtain a grown film of a constant thickness in a short time, It is necessary to increase the speed. However, shortening the growth time presents various problems in supplying the reaction gas to the reaction chamber.

FIG. 1 shows an outline of the gas system of a conventional vapor phase growth apparatus. A conventional method of growing a silicon single crystal on a single-crystal sapphire substrate using this apparatus, so-called SOS crystal growth, will be explained. Hydrogen gas that has been purified to a high degree by passing through a palladium membrane is introduced into the carrier gas line 1 as a carrier gas, and the carrier gas flowmeter (FM-1) 2 having a flow rate adjustment device is used to measure, for example, 100%
After adjusting the flow rate to 1/min, the gas is injected into the reaction chamber 4 from a gas injection device 5 disposed within the reaction chamber 4 via the reaction chamber gas line 3. A disc-shaped susceptor 6 is disposed in the reaction chamber 4, and is supported by a support having a rotation mechanism, and heated to a suitable growth temperature, for example, 950 to 1020°C, depending on the heating position. A sapphire substrate is placed on the susceptor 6. On the other hand, an impurity gas (dopant gas; for example, phosphine (PH ₃ )) and monosilane gas (SiH ₄ ) are introduced into an impurity gas line 7 and a monosilane gas line 8 as reaction system gases, respectively. The impurity gas introduced into the impurity gas line 7 is passed through an impurity gas flow meter (FM--) equipped with a gas flow rate adjustment device.
2) After adjusting the flow rate at step 9 and diluting the impurity gas to an appropriate concentration with hydrogen gas introduced through the impurity gas dilution line 10 branched from the carrier gas line 1, the first automatic gas flow rate adjustment device (AFC) An appropriate amount of impurity gas is introduced into the reaction system gas mixing line 14 by introducing it into the diluent gas flowmeter (FM-3) 12 equipped with the added impurity gas flow rate adjustment device 11 and the gas flow rate adjustment device consisting of It is introduced through the valve (V ₇ ) 13.

On the other hand, the monosilane gas introduced into the monosilane gas line 8 is adjusted to an appropriate flow rate (for example, 1/min) by a monosilane gas flow rate adjustment device 15 consisting of a second automatic gas flow rate adjustment device (AFC-2), and the reaction system gas is mixed. It is introduced into line 14 via an eighth valve (V ₈ ) 16 . The reaction system gas mixing line 14 is connected to the primary side of a first valve (V ₁ ) 17 and a second valve (V ₂ ) 18, and the secondary side of the first valve 17 is connected to the reaction chamber gas. The secondary side of the second valve 18 in the line 3 is connected to a reaction system gas discharge line 19, respectively. The first valve (V ₁ ) 17 and the second valve (V ₂ ) 18 have an interlocking mechanism in which the opening and closing operations are reversed, and in the state before the start of the vapor growth reaction, the first valve 17 Since the second valve 18 is closed and the second valve 18 is open, the mixed gas of the reaction system flows from the reaction system gas mixing line 14 to the reaction system gas discharge line 1.
introduced in 9. The reaction system gas discharge line 19 is arranged so as to discharge the reaction system gas and the impurity-containing gas from the dilution gas flowmeter 12 to the outside of the vapor phase growth apparatus. The vapor phase growth reaction starts at the first valve 1.
7 opens and the second valve 18 closes due to the interlocking operation. That is, reaction system gas mixing line 1
It can be considered that the process starts from the time when the reaction system gas No. 4 is introduced into the reaction chamber gas line 3. Since hydrogen gas is introduced into the reaction chamber gas line 3 as a carrier gas as described above, the reaction system gas introduced into the reaction chamber gas line 3 is mixed with hydrogen gas when the gas injection device in the reaction chamber 4 A silicon single crystal containing an appropriate amount of impurity elements is grown on a sapphire single crystal substrate on a susceptor 6 which is heated to an appropriate temperature by introducing the silicon single crystal into the reaction chamber 4 via the susceptor 5 . The reaction gases such as hydrogen gas and reaction system gas introduced into the reaction chamber 4 are then introduced into the reaction chamber gas exhaust line 20 through the gas exhaust port provided below the reaction chamber 4, and are then introduced into the gas phase. It is discharged outside the growth equipment.

The conventional vapor phase growth method described above has the following drawbacks. That is, since the gas flow rates between the reaction chamber gas line 3 and the reaction system gas discharge line 19 are significantly different, a pressure difference is generated between the respective lines. For this reason, the internal pressure of the reaction system gas mixing line 14 fluctuates before and after the start of the reaction. This is an added impurity gas flow rate adjustment device 11 consisting of an automatic gas flow rate adjustment device.
This changes the pressure on the secondary side of the monosilane gas flow rate adjustment device 15. Since pressure fluctuations on the secondary and primary sides of the automatic gas flow rate adjustment device change the gas flow rate for 40 to 60 seconds, the flow rate of the reaction system gas maintained at the predetermined flow rate before the start of the reaction was maintained for 60 seconds. The following ideal vapor phase growth cannot be performed.
In other words, when performing short-term vapor phase growth under high-speed growth conditions, for example, when growing at a growth rate of 5 to 15 μm/min and a growth time of about 4 to 10 seconds, it is possible to reproduce the thickness of the vapor phase grown film and the impurity concentration in the grown film. It was difficult to control it effectively.

The present invention provides a vapor phase growth method that improves these drawbacks.

The basics of the serious vapor phase growth method are to eliminate fluctuations in the flow rate of gas flowing through the reaction chamber gas line and reactive gas discharge line before and after the start of vapor phase growth, and to almost maintain the internal pressure of the reaction chamber gas line and reactive gas line. Adjust them equally and then start vapor phase growth.

Hereinafter, a description will be given of FIG. 2, which schematically shows a gas control system of a vapor phase growth apparatus for performing SOS crystal growth as an embodiment of the present invention.

The apparatus for realizing vapor phase growth of the present invention includes a first gas line for supplying a carrier gas to a reaction chamber, a second gas line for supplying a predetermined amount of one or more reactive gases, A third gas line supplies a carrier gas in an amount approximately equal to the flow rate of the gas supplied by the second gas line. When hydrogen gas that has been highly purified by passing through a palladium membrane is introduced into the carrier gas line 1, the introduced carrier gas is passed through a main carrier gas flow meter (equipped with a flow rate control device) on the first gas line. FM
-1) Sub carrier gas flowmeter (FM-4) 22 on the third gas line and the dilution gas flowmeter (FM-4) via the impurity gas dilution line 10.
3) Introduced on the primary side of 12. Hydrogen gas whose gas flow rate has been adjusted is injected into the reaction chamber 4 from the secondary side of the main carrier gas flowmeter 2 through the reaction chamber gas line 3 from the gas injection device 5 disposed in the reaction chamber 4. . A disk-shaped susceptor 6 made of carbon graphite coated with silicon carbide is disposed as a sample mounting table in the reaction chamber 4, and the susceptor 6 is held by a support table having a rotating mechanism and the gas injection It rotates horizontally around the device 5. Further, the temperature of the susceptor 6 is raised to the growth temperature by high frequency heating. on the other hand,
Impurity gas (Dopant) and monosilane gas (SiH ₄ ) as reaction system gases are led to an impurity gas line 7 and a monosilane gas line 8, respectively. The impurity gas introduced into the impurity gas line 7 is passed through an impurity gas flow meter 9 equipped with a gas flow rate adjustment device.
After the flow rate is adjusted by the carrier gas line 1, the impurity gas concentration is diluted by mixing with the hydrogen gas introduced from the carrier gas line 1 through the dilution line 10, and then the first automatic gas flow rate adjustment device (AFC-1)
The degree of dilution of the impurity gas introduced into the primary side of the added impurity gas flow rate adjustment device 11 and the dilution gas flowmeter (FM-3) 12 equipped with the gas flow rate adjustment device is determined by the impurity gas flowmeter 9. It is determined by the ratio between the impurity gas flow rate and the dilution gas flow rate of the dilution gas flow meter 12. The impurity gas adjusted to an appropriate impurity concentration flows from the secondary side of the added impurity gas flow rate adjustment device 11 into an appropriate amount of impurity gas, and passes through the seventh valve (V ₇ ) 13 to the reaction system gas mixing line. 14 will be introduced. On the other hand, the monosilane gas introduced into the monosilane gas line 8 is introduced into the primary side of the monosilane gas flow rate adjustment device 15 consisting of a second automatic gas flow rate adjustment device (AFC-2), and the monosilane gas adjusted to an appropriate flow rate from the secondary side is introduced into the 8th line. is introduced into the reaction system gas mixing line 14 through the valve (V ₈ ) 16. The reaction system gas mixing line 14 collects the introduced impurity gas and monosilane gas, and then connects the first valve (V ₁ ) 17, the second valve (V ₂ ) 18 and the third valve
is supplied to the primary side of the valve (V ₃ ) 23. The secondary side of the first valve 17 is connected to the reaction chamber gas line 3. Further, the secondary side of the second valve 18 is connected to a reaction system gas discharge line 19. The reaction system gas discharge line 19 is connected to the secondary side of the diluent gas flow meter 12.
Impurity gas from 2 and reaction system gas discharge line 19
After the reaction system mixed gases are mixed, they are discharged to the outside of the vapor phase growth apparatus via the exhaust gas pressure regulating valve 25. The secondary side of the third valve 23 is connected to the gas pressure gauge (PG) 26 and the secondary side of the fourth valve (V ₄ ) 24, and the primary side of the fourth valve 24 is connected to the reaction chamber gas line. Connected to 3. On the other hand, the hydrogen carrier gas introduced into the sub-carrier gas flow meter 22 is adjusted to a flow rate equal to the sum of the impurity gas flow rate introduced into the reaction system gas mixing line and the monosilane gas flow rate by the gas flow rate adjustment device of the sub-carrier gas flow meter. It is regulated and introduced into the primary side of the fifth valve (V ₅ ) 27 and the sixth valve (V ₆ ) 28 . The secondary side of the fifth valve 27 is connected to the reaction chamber gas line 3. Further, the secondary side of the sixth valve 28 is connected to the reaction system gas discharge line 19. The opening and closing operations of the fifth valve 27 and the sixth valve 28 are reversed, so that one of the valves is always open. For example, in a state before vapor phase growth, the fifth valve 27 is open and the flow rate of the reaction gas introduced into the reaction gas mixing line 3, that is, the added impurity gas flow rate adjustment device 11
Hydrogen gas equal to the sum of the gas flow rates flowing through the and monosilane gas flow rate adjusting device 15 flows into the reaction system gas line 3.
It is introduced into the reaction chamber 4 through. Further, the opening and closing operations of the first valve 17 and the second valve 18 are reversed, and in the state before vapor phase growth, the first valve 17 is closed and the second valve 18 is open. That is, before vapor phase growth, the first valve 17 and the sixth valve 28 are closed, and the second valve 18 and the fifth valve 27 are open. Furthermore, during vapor phase growth, the opening and closing states of each valve are reversed to those before vapor phase growth. Each of these valves is adapted to operate simultaneously. The sub-carrier gas functions to keep the gas flow rates in the reaction chamber gas line 3 and reaction system gas discharge line 19 constant before and during vapor phase growth. As described above, the gases introduced into the reaction chamber system gas line 3 before vapor phase growth are only hydrogen gas as the main carrier gas and the subcarrier gas. After being injected, the gas is introduced into the reaction chamber gas exhaust line 20 through a gas exhaust port provided below the reaction chamber 4, and then discharged to the outside of the vapor growth apparatus. The gas pressure gauge 26 is for measuring the gas pressure in the reaction chamber gas line 3 and the reaction system discharge line 19. The opening and closing operations of the third valve 23 and the fourth valve 24 connected to the gas pressure gauge 26 are such that both valves are not open at the same time, and both valves are closed or closed. It is now possible for either one of the valves to be in a closed state. The reason for measuring the pressure of both lines with one gas pressure gauge is to almost eliminate the pressure difference between the two lines and prevent measurement errors due to variations between the pressure gauges, but this should be ignored. If so, a separate gas pressure gauge may be used for each. If a pressure difference occurs between the reaction chamber gas line 3 and the reaction system gas discharge line 19 measured by the gas pressure gauge 26, the exhaust gas pressure adjustment valve 2
5 allows adjustment to eliminate the pressure difference between both lines. The sapphire substrate is placed on the susceptor 6 and heated to the vapor growth temperature, and the main carrier gas flow rate (FM-2), sub-carrier gas flow rate (FM-4), impurity gas flow rate ( FM-2), dilution gas flow rate (FM-3), flow rate adjustment of added impurity gas flow rate (AFC-1), monosilane gas flow rate (AFC-2), etc., and pressure adjustment of reaction chamber gas line 3 and reaction system gas discharge line 19. In the state where the process has been completed, the preparation for vapor phase growth is completed. The start of vapor phase growth begins at the time when the second valve 18 and the fifth valve 27 are closed and the first valve 17 and the sixth valve 28 are opened at the same time in the vapor phase growth preparation completion state. That is, from the time when the reaction gas in the reaction gas mixing line 14 changes from the reaction gas discharge line 19 to the reaction chamber gas line 3 and the subcarrier gas changes from the reaction chamber gas line 3 to the reaction gas discharge line 19, the gas phase changes. Growth begins. The reaction gas added to the reaction chamber gas line 3 is mixed with hydrogen gas as the main carrier gas, and is injected into the reaction chamber 4 from the gas injection device 5 in the reaction chamber 4 to reduce the amount of impurities on the sapphire substrate and susceptor 6. controlled growth of silicon. Thereafter, the gas is introduced into the reaction chamber gas discharge line 20 through a gas discharge port provided below the reaction chamber 4, and then discharged to the outside of the vapor phase growth apparatus.

According to the above configuration, the following effects are produced.

That is, there is no change in the gas flow rates in the reaction chamber gas line 3 and the reaction system gas discharge line 19 before and during vapor phase growth. In other words, the gas flow rate (F _RL ) in the reaction chamber gas line 3 before vapor phase growth is the main carrier gas flow rate (F _Cn ) and the sub-carrier gas flow rate (F _CS ).
is the added amount (F _RL = F _Cn + F _CS ), and the gas flow rate in the reaction chamber gas line 3 during vapor phase growth (F _RL ′)
is the amount obtained by adding the reaction system gas flow rate F _R to the main carrier gas flow rate (F _Cn ) (F _RL '=F _Cn + F _R ).
Here, the sub-carrier gas flow rate (F _CS ) is adjusted by the sub-carrier gas flow meter 22 so that it is the same as the reaction system gas flow rate F _R (F _CS = F _R ), so F _RL = F _RL ′ becomes. Therefore, immediately after the start of vapor phase growth, vapor phase growth can be performed while maintaining the state of completion of preparation for vapor phase growth, that is, without changing each gas flow rate and scepter temperature. Also, in the reaction system gas discharge line 19, there is no change in the gas flow rate before and during vapor phase growth. In other words, since no pressure fluctuation occurs on the secondary side of the dilution gas flowmeter 12, the dilution gas flow rate is also stable, and the impurity gas concentration supplied to the added impurity gas flow rate adjustment device 11 is also stable.

As described above, according to the vapor phase growth method according to the present invention, stable vapor phase growth can be performed. For this reason, the growth rate is particularly large, for example, 5 to 15 μm/
The controllability and reproducibility of the impurity concentration of the grown film and the thickness of the grown film have been dramatically improved in short-term growth (about 10 seconds), where a film of about 0.5 to 1.0 μm can be grown under conditions of about 1 minute.

Although the above embodiments have described SOS crystal growth, it goes without saying that the present invention is not limited to high-speed growth of silicon and can be applied to other types of vapor phase growth. Furthermore, stable growth can be achieved even in short-term vapor phase growth under low-speed growth conditions.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a gas system of a conventional vapor phase growth apparatus, and FIG. 2 is a schematic diagram of a gas system for realizing a vapor phase growth method according to the present invention. 1...Carrier gas line, 2...Carrier gas flow meter, 3...Reaction chamber gas line, 4...
Reaction chamber, 5... Gas injection device, 6... Susceptor, 7... Impurity gas line, 8... Monosilane gas line, 9... Impurity gas flow meter, 10...
Dilution line, 11... Added impurity gas flow rate adjustment device, 12... Dilution gas flow meter, 13... Seventh valve, 14... Reaction system gas mixing line, 15...
Monosilane gas flow rate adjustment device, 16...Eighth valve, 17...First valve, 18...Second valve, 19...Reaction system gas discharge line, 20...
Reaction chamber gas discharge line, 22...Sub-carrier gas flow meter, 23...Third valve, 24...Fourth
Valve 25...Exhaust gas pressure adjustment valve.

Claims (1)

[Claims] 1. Before vapor phase growth, main carrier gas and subcarrier gas are added and flowed into the reaction chamber gas line, and at the same time, the same amount of reactive gas as the subcarrier gas is flowed into the exhaust gas line, and during vapor phase growth, By switching the sub-carrier gas and the reactive gas, the main carrier gas and the reactive gas are added and flowed into the reaction chamber gas line, and at the same time, the sub-carrier gas in the same amount as the reactive gas is allowed to flow into the exhaust gas line. A vapor phase growth method characterized by: