JPS61136993A - Method for growing semiconductor crystal - Google Patents

Abstract

PURPOSE:To obtain an interface having excellent sharpness by increasing or decreasing the flow rate of a diluent gas free of a raw gas when the raw has is changed in the formation of a multilayered thin film of a semiconductor by a vapor phase growth method. CONSTITUTION:A raw gas such as AsH3, trimethylgallium, trimethylaluminum, diethyllead, and hydrogen selenide and a carrier gas (e.g., hydrogen) are prepared. The raw gases are introduced in the desired order into a crystal growth chamber 18 by switching valves 7, 8, 9, 10, etc., and a multilayered thin film of a semiconductor is formed on a substrate 19 arranged in the crystal growth chamber 18. At this time, the flow rate of a carrier gas is increased or decreased along with the switching of the raw gas by the operating of valves 31 and 32 to keep the total flow rate of the gases flowing into the crystal growth chamber 18 constant. Consequently, interfacial sharpness of less than several Angstrom can be provided to the boundary between each layer.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for growing semiconductor epitaxial crystals.

(Prior art and its problems) There is a vapor phase growth method as a method for growing semiconductor crystals.

In this method, a gaseous raw material is sent into a crystal growth chamber to grow a semiconductor crystal from the gaseous raw material.

In particular, vapor phase growth (M
The O-CVD (O-CVD) method is attracting attention as a method that can perform high-quality crystal growth in a wide range of applications and is excellent in mass productivity. In the MO-CVD method, control of the composition and doping of the epitaxial crystal is shown in Figure 3.
This is an example of a GaAs epitaxial growth apparatus. Raw material gas arsine (AsH3), )limethyl gallium (TMG)
a),) The flows of remethylaluminum (TMAI), diethylzinc (DBZn), and hydrogen selenide (Ht8e) are indicated by numbers 1 to 5 in the figure, respectively. These source gases are switched between the flow to the main stream 23 and the flow to the bypass line 24 by switching the stop valves 6, 11t7, 12j8, 13t9, ttt 10 and 15 to open and close, respectively. . The main stream 23 flows into the reaction tube 18 via the needle valve 16 . Reaction tube 1
In the chamber 8 , crystal growth occurs on the substrate 19 placed on the susceptor 20 due to the reaction of the flowing source gas.

The waste gas after the reaction is taken out to the outside through the exhaust port 26.

On the other hand, the gas flowing into the bypass line 24 passes through the needle valve 17 and is discarded to the outside through the bypass outlet 25.

The bypass line 24 is provided to maintain a constant flow even when the raw material gas is not introduced into the reaction tube. However, when the pulp at the outlet of the source gas is opened only when it is needed for growth, it takes a certain amount of time to obtain a stable and constant flow of the source gas. In order to prevent this phenomenon, a bypass line is provided to maintain a constant flow. For example, in the apparatus shown in FIG. 3, GaAs doped with selenium (8e) 1 AILj Ga doped with zinc (Zn)
6. A case will be described in which two layers of yAs are successively grown in order. During Se-doped GaAs growth, stop pulp 6s7plO113y14 is open and stop pulp 89911,12715 is closed. Thus A
8Hs p TMGa s Ho5e flows into the main stream 23 and flows into the reaction tube 18, and Se-doped Ga A
s growth, TMAI and DEZn flow into the bypass line 24, bypass the reaction tube, and are discarded to the outside. Subsequently, Zn-doped A 1 o, s Ga O
，? When moving on to the growth of A', stop pulp 1 (1
1114 is closed, 15 and 8.9 are opened, H2Se is switched from the main flow to the bypass line, and TMAI and DEZn are switched from the bypass line to the main flow. In this way, Zn
We now turn to the growth of doped Al 6.3 Ga 6,7 As. This is to minimize fluctuations in the gas flow rate when adjusting the needle valves 16, 17 and switching the hydrogen flow 27,28. However, even with this method, when switching gases, the total flow rate of gas flowing into the main flow 23 and the total flow rate of gas flowing into the bypass line 24 fluctuate, so the pressure in each line fluctuates temporarily. It is inevitable that a transition layer of composition and dopant concentration will occur at the interface of the epitaxially grown layer. In Figure 4,
Profile of the A1 composition near the boundary and the dopant growth direction when the 8e-doped GaAs and Zn-doped AlxGa1-xAs layers are successively grown in this order in the configuration shown in Figure 3. shows. The thickness of the transition layer reaches several 100K when the growth rate is a practical growth rate of 10X or more per second, which is a major obstacle when forming an ultra-thin film that requires an interface steepness of several degrees or less. As described above, the conventional method has the disadvantage that when a multilayer thin film of semiconductor is formed by MOCVD, a transition layer of composition and dopant concentration is formed at the interface between each layer with a thickness of several hundred degrees.

(Objective of the Invention) The present invention eliminates the drawbacks of such conventional methods, and even when forming a multilayer semiconductor thin film at a growth rate that is practical for production, the boundary between each layer has a thickness of several λ or less. The object of the present invention is to provide a crystal growth method that makes it possible to provide a steep interface.

(Structure of the Present Invention) The present invention provides a method for flowing a raw material gas into a crystal growth chamber and growing a semiconductor crystal on a substrate installed in the crystal growth chamber, in which the raw material gas is switched and at the same time diluted without containing the raw material gas. The method is characterized in that the total amount of gas flowing into the crystal growth chamber is kept constant by increasing or decreasing the gas flow rate.

(Embodiment) The present invention solves the problems of the prior art by adopting the above-described configuration.

The present invention will be described in detail using a diagram for realizing an embodiment of the present invention shown in FIG. Figure 1 shows Zn or S
In order to form a multilayer thin film of GaAs or AlGaA3 doped with e.
The structure is the same as that of the conventional example shown in FIG. 3, except that an inlet pipe for hydrogen 2) is provided. The same components are given the same numbers as in FIG. 3. Raw material gas AsH8p
TMGa-TMAI p DF! Zn p Hl
The flow of Se is indicated by arrows 1 to 5 in the figure. These raw material gases are stop pulp 6, 11 schiff, 12p8 and 13#9.
14 and 10 and 15, respectively, to connect the flow to the main stream 23 and the bypass line 24.
You can switch between the flow to and from. The main flow 23 passes through the needle pulp 16 and then into the reaction tube 18 which is a crystal growth chamber.
flows into. In the reaction tube 18, a substrate 19 is placed on a susceptor 20, and crystal growth occurs on the substrate 19 due to the reaction of the raw material gas flowing therein. The waste gas after the reaction is taken out to the outside through the exhaust port 26. On the other hand, the flow in the bypass line 24 passes through the needle valve 17, bypasses the reaction chamber 18 which is a crystal growth chamber, and is guided to the outside through the bypass outlet 25. As described in the description of the prior art, this bypass line 24 is provided to maintain a constant flow even when the raw material gas is not introduced into the reaction tube 18. Pressure gauges 21 and 22 measure the pressure of the main flow 23 and bypass line 24, respectively. The main flow 23 and the bypass line 24 have a hydrogen flow 27 as a diluent gas.
and 28. By adjusting the flow rate of the hydrogen flow 27, 28 and the contactance of the needle pals 7/16 and 17, the main flow 23 is adjusted using the pressure gauge 21122.
and the pressure in the bypass line 24 is kept equal. 29 and 30 represent hydrogen streams 1 and 2, respectively. These hydrogen flows are also switched between the flow to the main stream 23 and the flow to the bypass line 24 by opening and closing the stop pulps 31 and 33 and 32 and 34. With the configuration shown in FIG. 1, 8e doped n fiAl 6.3Ga
6. yAs N undoped GaAs, Znn doped type A
An example will be described in which the present invention is applied to a case where each layer of l 6,3 GaAs is grown in this order. 8e doped n-type A16,3Ga6. When growing yAs, open stop pulp 697p8-10j14 and
, 13, 9, and 15, and AsH3p T in the main stream 23.
MGa p TMAI p Hl Se is poured into the reaction tube 18 and DEzn and vice line 24 are poured to bypass the reaction tube 18 .

In this example, the gas flow rate including the carrier gas (dilution gas mixed with the raw raw material gas and sent, hydrogen in this example) for each raw material gas is A s Hs of 300 Ce per minute.

TMGa is 400 CC per minute, TMAI is 300 CC per minute
C.C.

Ho5e is 20cc. Undoped Ga As
During growth, stop pulp 6p7p13-14-15
Open 8,9ν10111,12, main stream 23
Pour AsH3-TMGap into TMAI IDB
Zn=Ho5e is passed through the bypass line 24. The gas flow rate of each source gas including the carrier gas is 300 cc/min for AsH3 and 400 cc/min for ITMGa.

Furthermore, when growing Znn-doped A16,3Ga6,7As, the stop pulp 6y7y8t9t15 is opened and 1
1112. Close the 13th 14th 10 and As to the main stream 23
H3pTMGa pTMAI pDEZn is poured in, and Ho5e is poured into the bypass line 24. The flow rate of each raw material gas including the carrier gas is A s Hs of 300 per minute.
cc.

TMGa is 400 per minute cclTMAI is 300 per minute
cclDEZn is 300□cc per minute. n-type AI6
．． During the growth of 30a6, 7As, the total flow rate of the raw material gases including the carrier gas flowing into the vehicle flow 23 from the respective raw material gas lines is 1020 cc per minute. Undoped Ga
The total flow rate of raw material gas during A s growth is 700 cc/min,
P-type AtoJGa6. The total flow rate of raw material gas during yA♂ growth is 13 oOCC per minute. In addition to the flow of these raw material gases, 320 cc/min of hydrogen is allowed to flow into the 2-in 29 of hydrogen 1, and 280 cc/min of hydrogen is allowed to flow into the hydrogen 2 line 30. n-type AI. , 5oao, tAs#As, when the stop pulp 32ν33 is opened and 31ν34 is closed, hydrogen flows into the main flow 23 from the life 30 of the hydrogen 2 at a flow rate of 280 cc/min. Undoped Ga As
During growth, open the stop pulp 31.32 and 33.
When 34 is closed, 320 cc and 280 cc of hydrogen per minute flow into the main stream 23 from hydrogen 1 line 29 and hydrogen 2 line 30. p-type A1゜J GAG,? ”
During layer growth, the stop pulp 31132 is closed and the 33
．． 34, all hydrogen in hydrogen 1 line 29 and hydrogen 2 line 30 flows into bypass line 24. In this way, the total gas flow rate flowing into the main stream 23 is always maintained at 1300 cc per minute during the growth of n-type A 16.3 Ga OJ As % undoped GaAs % p-type A 10.3 Ga 0.7 As. In this way, mainstream 2
By always keeping the sum of the gas flow rates equal to each other, when the raw material gas is switched between the main flow 23 and the bypass line 24, which maintain the same pressure, the fluctuations in pressure in each line can be completely suppressed. As a result, the transient phenomenon of gas flow rate can be minimized, and as a result,
Composition switching and impurity doping switching can be performed extremely sharply. FIG. 2 shows the composition profile and doping concentration profile in the layer thickness direction obtained in this example. n-type Alo, 3Ga0. The boundary between the yAs layer and the undoped GaAs layer, or the boundary between the undoped GaAs layer and the p-type k16.3 Ga6. ? The composition and doping concentration at the boundary with the As layer are extremely small, less than a few degrees, and are improved by more than two orders of magnitude compared to the conventional example. This value is obtained for a practical value where the growth rate does not reduce productivity on the order of 20X per second (7.2 μm per hour). If the growth rate is further reduced to about 5X per second, an interface with a steepness of one atomic layer can be obtained. As a result, the layer structure of quantum well structures with a thickness of several tens of times or less and modulation doped structures has been significantly improved.
The characteristics of quantum well structure lasers and high electron mobility transistors using these materials have been improved.

In this example, Se-doped A 16.3 Ga 6.7
A case has been described in which undoped GaAs and Zn-doped Al@, 3Ga(1,yAs) are grown in this order, but the present invention can be applied regardless of the composition of AI X Ga@-, cA8 or the type of dopant. Needless to say, the number of layers is also arbitrary.Furthermore, the present invention can be applied to other semiconductors such as Gap I n)xPyAsl-y system and (Al
I-■ compounds such as F series, Zn8xSe1-z series and H
[-VI compounds such as gxCdt-x Te, Pd
It can be applied to the vapor phase growth method of IV-VI compounds such as X S n 1-z Te type and all other semiconductors.

(Effects of the Invention) By applying the present invention, when forming a multilayer thin film of semiconductor, it is possible to provide an interface steepness of several x or less at the boundary of each layer even at a growth rate that is practical for production. A crystal growth method that makes it possible can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a device for realizing an embodiment of the present invention, FIG. 2 is a diagram showing the improvement effect of the present invention, FIG. 3 is a diagram showing an example according to the prior art, and FIG. The figure shows the drawbacks of the prior art. 1 to 5 are raw material gases, 18 is a reaction tube, and 19 is a substrate 29.3
0 is dilution gas. The director of the Agency of Industrial Science and Technology

Claims (1)

[Claims] In a method of flowing a raw material gas into a crystal growth chamber and growing a semiconductor crystal on a substrate installed in the crystal growth chamber, the crystal growth is performed by increasing or decreasing the flow rate of a dilution gas that does not contain the raw material gas at the same time as switching the raw material gas. A method for growing semiconductor crystals characterized by keeping the total amount of gas flowing into the chamber constant.