JPS636835A - Manufacture of semiconductor thin film - Google Patents

Abstract

PURPOSE:To reduce the cost of a high performance transistor by increasing the density or flow rate of a gas material at the start of feeding the material different from a gas material grown on a first type semiconductor to abruptly vary the material composition in a boundary of hetero junction. CONSTITUTION:Non-doped GaAs is grown on a semiconductor substrate by TMG or AsH3 before time t1. TMA is fed at flow rate of l2=1500cc/min as H2 base, TMH and AsH3 flow rates are always constant during crystal growth at 10cc/min and 240cc/min at H2 base from time t1 to time t3. Only TMA is reduced at its flow rate from the time t3 to time t4 at flow rate l1=7cc/min. and the thickness of nondoped GaAlAs at 100Angstrom from the time t3 to time t4. Dopant Si2H6 is fed at flow rate of 14cc/min to a reaction furnace to set the thickness of So-doped GaAlAs at 500Angstrom from time t4 fo time t2. Thus, the abrupt variation in the material composition occurs in the boundary of the hetero junction to reduce the cost of a high performance transistor.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a semiconductor thin film using vapor phase growth, and in particular to a method for manufacturing a thin film for a high electron mobility transistor using a semiconductor heterojunction. Regarding the method.

[Conventional technology]

I of compound semiconductor heterojunction crystal using vapor phase growth
As a second production method, a growth method by thermal decomposition of effective metals (M
OCVD method) is used. In this method, during crystal growth, all raw materials are transported to the growth chamber in the form of gas, so it is difficult to form a heterojunction.

When switching the source gas, the flow rate changes slowly, so we need to form a steep hetero interface that can fully utilize the high-speed performance of high electron mobility 1 to transistors using the two-dimensional electron gas formed at the hetero interface. was difficult. This will be explained with reference to the drawings. Figure 3 is a diagram schematically showing a GaΔs/GaAQAs epitaxial growth system by the MOCVD method. In Figure 3, 1 is a substrate, 2 is a susceptor, 3 is a high frequency coil (RF coil), 4 is a reactor, 5 is a raw material gas transfer pipe, 6 is a bypass pipe, 7 and 8 are organometallic trimethyl, respectively. Aluminum A
('rM^), trimethyl gallium ('I'MG)
, 9 and 10 are monosilane gas and arsine gas respectively, 11 is a gas opening/closing valve, valves A, B, C,
D is connected to reactor 4, and valves E, F, G, H
is connected to bypass 6. 12 is a mass flow controller used for flow control of Hz gas and raw material gas. 1
3 is a gas backflow prevention trap.

In this system, the M material gas is transported through a pipeline using H2 gas as a carrier gas and is injected into one reactor 4. However, the horns: (feed gas release valves A, B, C,
Between D and $ and the substrate 1 in the reactor 4, 1 is usually a number 1o
Since there is a distance several meters from an, valves A, B, C, D
The stepwise concentration change (flow rate change) of the raw material gas released from the reactor becomes dull before it reaches one reactor. This will be explained with reference to FIG. 4th to 1 is a diagram schematically plotting the concentration (flow rate) of the raw material gas introduced into the reactor versus time and position. Here, 'I' MA is taken as an example of the M source gas. Note that since the a degree of the π material gas is proportional to the flow rate, hereinafter, a change in flow rate will mean a change in concentration. In FIG. 4, if raw material gas 1'MA is blown out from the raw material gas outlet in a step-like flow rate change curve 14 from time t1 to tZ, the flow rate change of TMA immediately before the substrate in one reactor is as follows. It becomes like the curve 16 with a delay of time ΔL, and does not become like the steep flow rate change curve 15, which maintains the original shape of the step rise.

Figure 5 shows GaA! , /G, JAQ This is a schematic diagram of the energy band of an As heterojunction. (a) is the case where the composition change of AQ at the interface of a heterojunction is steep.
While two-dimensional electron gas accumulates at the heterojunction interface, A
(b) is a case where the composition change of Q is gradual.

In this figure, the change in the composition of AQ is too gradual, and no accumulation of two-dimensional electron gas is formed. As shown in Figure 4, if there is no frequency change in the number of TMA cores immediately before the substrate in the reactor, it is possible to create a steep AQ composition change at the hetero interface as shown in Figure 5 (a). It is obvious that this is difficult and results in a situation like that shown in Fig. 2(b), and it is impossible to explode a high-mobility transistor. One way to achieve this is to provide a container for impurity gas immediately before the raw material gas discharge valve, as described in Japanese Patent Publication No. 58-38929.

[Problem that the invention seeks to solve]

As described above, with the conventional technology, it is difficult to account for instantaneous concentration changes in the raw material gas immediately before the substrate in the reactor. Furthermore, the method described in Japanese Patent Publication No. 58-18929, in which a raw material gas container is provided immediately before the gas release valve, is as follows:
When the raw material gas stored under pressure in the container is released from the release valve, the vapor pressure decreases as the pressure decreases, and it liquefies or solidifies and adheres to the vicinity of the valve outlet and enters one reactor. It may become difficult to transport. In particular, in the case of organic metals such as 1゛MΔ and TMG, this possibility is large, and consideration must be given to the possibility that the valve will become clogged.

One object of the present invention is to provide a novel vapor phase growth method for producing a sharp change in material composition in a heterojunction.

[Means for solving problems]

The configuration of the present invention to achieve the above object [1] is to control the flow rate using a mass flow controller, for example, to control the pulsed flow rate change (a degree change) of the raw material gas in the stepwise blowing of the raw material gas at the beginning of the blowing. or 2 similar raw material containers.
By using the above, the change in gas composition on the sample is made steeper.

[Effect]

FIG. 1 takes TMA as an example of the raw material gas and schematically shows changes in TMA flow rate with respect to time and position when the present invention is implemented. In FIG. 1, at the position of the source gas blow-off valve, the flow rate is 11 from time t1 to t8.
2, and thereafter the flow rate is reduced to a flow rate Q5 from t4 to t and z.1 The flow rate change immediately before the substrate in the reactor has a steep rise. In addition, the raw material TMA
container.

Another organometallic bubbler tank 'tlj shown in Fig.
MA flow rate control is performed, and the flow rate f4I as shown in Figure 2 (a) and (L) is performed for each 'r~IA, and the sum is shown in Figure 2 (c). It is possible to add jAδN changes in T M A as shown. In this way, by controlling the mass flow controller 1~roller and valve, it is possible to realize a steep change in the AQJul formation at the pedero contact ?1 interface by changing the flow time of the raw gas in a pulsed manner. .

[Embodiments of the invention]

Example l TM in the formation of GaAs/GaAQAs heterojunctions
I tried changing the A flow rate over time as shown in Figure 1.

Here, the mass flow controller 1-roller is used to change the flow rate of TMA to vary the concentration of the raw material. TMA is placed in a bubbler container maintained at a constant temperature of 20°C, H2 gas is bubbled into the TMA liquid, 1'M A is included in the Hz gas, and it is transported through a pipeline to the reactor. In FIG. 1, before time L1, T
Undoped GaAs was deposited on a semi-insulating substrate using MG (-10°C) and AsH3 (diluted with H2 to a concentration of 10%).
After growing 1 μm at 0°C, open MA for 10 seconds from t1 to t3 for 1 hour at H2 base flow rate Q2 = 15cc/
min, TMH and AsHa flow rate during crystal growth,
Always constant flow rate, 10cc/ll each on H2 basis
6th order with l1n and 240 cc/min,
During the 10 seconds from t3 to t4, the flow rate of only TMA was reduced to Q l = 7 cc/mjn, and non-doped Ga
The PI of Al2As was set to 100 people. For 60 seconds from t4 to t2, dopant Si zHo (4pp
diluted with H2 to a degree of m) into the reactor at 14 cc/m
The flow rate of Si-doped GaAQAs was introduced at a flow rate of 500 in. Note that the growth humidity of GaAQAs was 700'C. Next, we investigated the compositional change of Al1 at the interface of the heterojunction after growth, as shown in Figure 6(b).
As shown in , it was found that the interface was extremely steep. FIG. 6(a) schematically depicts the energy band near the heterojunction interface based on the composition change of AQ at the interface.

This is because the time change in the TMA flow rate at the substrate 11 in the reactor was in the form of a pulse with a steep rise.6 The GaAs/GaA
When the electron mobility of the QAs heterojunction crystal was determined from Hall effect measurements, it was 8000 d/V·S at room temperature, 77° go, oooαt/V−8. - On the other hand, when the TMA flow rate changes in concentration as shown by curve 16 in FIG. 4, the electron mobility is 3000a
+f/V・S, 77 Kte 15,000ffl/V
-S,! : It was found to be low and insufficient for high mobility transistors.

Example 2 In Example 1, only one TMA bubbler container was used, but this time, two TMA bubbler containers were used, each TMA was controlled by a mass flow controller and an air valve, and TMA was introduced into the reaction tube. Crystal growth was performed by providing gas lines in two zero value rows. Figure 2 shows two TMA
The figure depicts the time variation of the TMA flow rate at the position of the bubbler hemostatic blow-off valve, where (a) shows the time from 6 to 0.
The first TMA was flowed at a flow rate of 5 cc/min for 10 seconds, and (b) the second TMA was flowed at a flow rate of 7 cc/win for 70 seconds from t6 to t7.

(c) shows the sum of the flow rates of (a) and (b). As in Example 1, the flow rates of '1' MG and ΔsHa were always constant, L Q cc / min and 240 faces/min, respectively, and 5 izH as Dovan 1-.
Using e, 20 c for 60 seconds from time 1 to 7.
The flow rate was c/win. Before time t6, 'I' M O and A s Hs are each 16 functions/
Win and 240 cc/win for 20 minutes.

GaAs/GaP Q grown in the above manner
When we measured the AQ composition at the heterointerface of the As heterojunction crystal, we found that it was almost the same as the AQ composition shown in Figure 6(b).
When the electron mobility of the As/GaAQAs heterojunction crystal was determined, it was 8200 ad/V S at room temperature and 90,0 O Offl/V S at 77°C, indicating an extremely high mobility.
It turned out that the crystals showed a temperature of 1 degree.

In the above embodiments, the case of GaAs/Gξ]AQAs was shown, but InP/InGaAs and Ga/G3As.

Similar effects were confirmed for heterojunctions such as GaSb/AQ Sb and GaAs/GaP.

〔Effect of the invention〕

As explained in the above embodiments, according to the present invention, it is possible to cause a sharp change in material composition at the interface of a heterojunction, and a high mobility transistor using two-dimensional electron gas can be produced with a high yield of 1+ ), the economic effect of lowering the price of high-performance transistors is enormous.

[Brief explanation of the drawing]

1 and 2 are schematic diagrams showing flow rate control of source gas according to the present invention, FIG. 3 is a schematic diagram showing the configuration of a vapor phase growth system by MOCVD method, and FIG. 4 is a schematic diagram showing the flow rate control of source gas according to the prior art. FIGS. 5 and 6 are schematic diagrams illustrating the flow rate control system, and are schematic diagrams illustrating the energy holding structure and composition changes of the 0aAs/GaAQAs heterojunction. 1...Substrate, 2...Susceptor, 3...Crystal frequency (R
F) Coil, 4... Reactor, 5... Conveyance pipe, 6
... Bypass pipe, 7... Trimethyl aluminum (TMA), 8... Trimethyl gallium (TMG)
, 9... Monosilane (S i H4), 10-
Arsine (Asl-1g), 11... valve, 12...
...mass flow controller, 13...1-lap,
14, 1.5.16...Time change curve of raw material gas concentration (flow rate), 17...Undoped Ga As, 18
-...Undoped GaAuAs, 19-...Si-doped G rr A QΔS, 20 - 2-dimensional 7[fi-son gas.

Claims (1)

[Claims] 1. In a method of forming a second type of semiconductor thin film on a first type of semiconductor thin film by introducing a gaseous semiconductor material into a reaction furnace through piping, the first type of gaseous material for growing the second type of semiconductor is A method for manufacturing a semiconductor thin film, characterized in that the concentration or flow rate of a gaseous material different from that used to grow the seed semiconductor is increased in a pulsed manner at the beginning of the flow.