JPH0265124A - Compound semiconductor crystal growth method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for growing compound semiconductor crystals by organometallic vapor phase epitaxy.

[Conventional technology] Organic metal vapor deposition method (organic metal vapor deposition method)
- Phase epitaxy (OMVPE method) is a method of growing a thin single crystal film on a substrate by thermally decomposing an organometallic compound and a metal hydride compound in a reactor. This method facilitates the formation of an ultra-thin multilayer structure and is highly suitable for mass production, so it is used for manufacturing substrates for heterojunction devices using compound semiconductors. Among the heterojunction devices, the hetero bipolar transistor (H
BT) operates at ultra-high speed and is therefore being actively developed.

FIG. 2 is a sectional view showing the structure of an example of the HBT. To explain this HBT with reference to FIG. 2, the semi-insulating G
a A s J&ff1lE60 has n”-G
An aAs layer 61 is formed on which an n-GaAs layer 6 is formed.
2 is formed. A p''-GaAs layer 63 is formed on this n-GaAs layer 62.
An nAILGaAs layer 64 is formed on the -GaAs layer 63, and an n-GaAs layer 65 is formed thereon. A collector electrode 66 is formed on the n-GaAs layer 62, a base electrode 67 is formed on the p+-GaAs layer 63, and an emitter electrode 68 is formed on the n-GaAs layer 65. The characteristics of the HBT are greatly influenced by the steepness of the pn junction between the base layer 63 and the emitter layer 64, and the steeper the interface of the pn junction, the better the characteristics can be obtained.

Conventionally, Zn has been used as a p-type dopant in the OMVPE method, but since Zn has a large diffusion coefficient, it diffuses from the base region to the emitter region during growth, resulting in the formation of a steep p-n junction. The problem was that I couldn't do it. On the other hand, in the molecular beam epitaxy (MBE method), Be is generally used due to its small diffusion coefficient, but in the OMVPE method, it is difficult to use Be due to safety issues. It is. Therefore, Mg element, which has a diffusion coefficient about five orders of magnitude lower than that of Zn, is being considered as a dopant.

As the raw material E1 of such Mg dopant, biscyclopentagenylmagnesium (CpoMg) or
Bismethylcyclopentadienyl magnenium (M2
Cp2 Mg) is used. These raw materials are liquid or solid white metals, and are introduced into the reaction tube together with organic metals and metal hydrides, which are the raw materials for compound semiconductors, using hydrogen as a carrier gas, thermally decomposed on the substrate, and crystallized. taken inside.

FIG. 3 is a schematic diagram showing a manufacturing apparatus using such an OMVPE method. A susceptor 2 is provided within the reaction tube 1, and a substrate 3 is placed on the susceptor 2. An RF coil 4 is provided around the reaction tube 1. Hydrogen gas, which is a carrier gas, is introduced through piping 51.

A pipe 52 connected to the reaction tube 1 and a pipe 53 connected to five exhaust pipes are connected to the pipe 51. A flowmeter 22 is attached to the pipe 52, and a flowmeter 21 is attached to the pipe 53. A, a raw material for group V elements in compound semiconductors
sH, is contained in the AsH, container 11, and is connected to the pipe 56 via the pressure regulator 31 and the flow r:Li+ 23.
It is connected to the. The pipe 56 is connected to the pipe 53 via three valves and to the pipe 52 via a valve 38.

Trimethyl gallium (TMG), which is a raw material for group Ⅰ elements of compound semiconductors, is placed in a TMG container 12 .

Hydrogen gas, which is a carrier gas, is introduced into the TMG container 12 from a pipe 54 connected to a pipe 51 via a mW meter 24 and a valve 32 . Gas from the TMG container 12 is led to a pipe 57 via a valve 33.

A valve 34 is provided between the valve 32 and the valve 33. The pipe 57 is connected to the pipe 53 via the valve 41 and to the pipe 52 via the valve 40.

Cp2Mg, which is the raw material for the Mg element of the dopant, is Cp
Hydrogen, which is a carrier gas, is introduced into the C92Mg container 13 from a pipe 55 connected to a pipe 51 via a flow m + i I' 25 and a valve 35. . C92Mg container 1
The compound gas from 3 is led to piping 58 via valve 36. A valve 37 is provided between the valve 35 and the valve 36. The pipe 58 is connected to the pipe 53 via the valve 43 and to the pipe 52 via the valve 42. The piping 52 is connected to the reaction tube 1 and
Exhaust air is provided by a pipe 60.

In this way, the Ga element, which is a group I element of a compound semiconductor, and hydrogen gas are introduced into the reaction tube 1, and the As element, which is a group V element of a compound semiconductor, is introduced into the reaction tube 1 in the form of a hydride. These raw materials are thermally decomposed on the heated substrate 3 in the reaction tube 1, and a compound semiconductor crystal is grown on the substrate 3. To form a p-type layer in this compound semiconductor crystal, Cp2Mg gas is introduced into the reaction tube 1. M
Before doping with the g element, the valve 43 is open and the valve 42 is closed. Therefore, the Cp2Mg gas passes through the valve 36, the pipe 58, and the valve 43, and is discharged from the pipe 53 to the five exhaust pipes. When doping with the Mg element, the compound gas from the Cp2Mg container 13 is guided into the pipe 52 and into the reaction tube 1 by closing the valve 43 and opening the valve 42. After growing the p-type compound semiconductor layer to a predetermined thickness, the valve 42 is closed;
The valve 43 is opened and the compound gas is discharged from the pipe 53 to the exhaust pipe 59 again.

[Problems to be Solved by the Invention] However, the organic metal used as a raw material for the Mg element has the property of being adsorbed on the inner walls of piping and reaction tubes. For this reason, even if raw material gas containing Mg element is introduced into the reaction tube, the compound gas containing Mg element is adsorbed on the inner wall of the piping and the inner wall of the reaction tube, and until this adsorption is saturated, doping to the compound semiconductor occurs. The amount was not constant. Also, M
Even after switching the raw material gas of the Mg element from being supplied to the reaction tube to exhausting it to the exhaust pipe, the raw material gas of the Mg element is still adsorbed on the inner wall of the piping and the inner wall of the reaction tube, and this adsorbed gas gradually Since it is desorbed and supplied to the reaction tube, M
Doping of the g element continued. As a result, when attempting to form a P layer by doping with Mg element, there is a problem in that a steep doping profile cannot be obtained.

In order to solve these problems, J.Cryst,G.
rowth, Vol, 77 P, 37-41 (19
86), M. I. Timmons et al.
The source gas switching valve is moved closer to the reaction tube. However, with such a method, although the rise of the doping profile can be slightly improved, the fall of the doping profile cannot be improved. This improvement in falling is due to H
This becomes a big problem when stacking an n layer on a p layer like in BT.

An object of the present invention is to provide a method for growing compound semiconductor crystals that can obtain a steep doping profile in doping with Mg element.

[Means for Solving the Problems] In the compound semiconductor crystal growth method of the present invention, Mg element is doped by crystal growth by organometallic vapor phase epitaxy using a compound semiconductor raw material gas and a compound gas containing Mg element. A compound semiconductor layer that has been doped with the Mg element and a compound semiconductor layer that is not doped with the Mg element are stacked, and while a compound gas containing the Mg element is supplied at a constant flow rate, crystal growth is achieved in which the Mg element is not doped at such a flow rate of the compound gas. By increasing the growth rate to
A feature of this method is that a compound semiconductor layer is formed without doping with Mg element.

In the present invention, as a method for switching between forming a compound semiconductor layer doped with Mg element and forming a compound semiconductor layer not doped with Mg element, the following two methods can be mentioned, for example.

Taking AILGaAs as an example, one method is to prepare two lines each of TMG (trimethylgallium) and TMA (1-lmethylaluminum), and set one set at a flow rate that provides a growth rate that does not dope Mg. However, the other set of lines is set at a flow rate that provides a growth rate that provides a desired doping amount, and the doping is controlled by switching between these two sets of lines. Another method is to use -dan TMG before and after doping.
In this method, growth is temporarily interrupted by discharging the respective gases of TMA and TMA to the outside of the reaction tube, and after adjusting the flow rates, growth is started. In this invention, no matter which method is used,
The steepness of the interface of the doped layer can be several tens of angstroms or less.

Note that the compound semiconductor crystal-grown according to the present invention is not particularly limited, but includes, for example, GaAs and Al.
Examples include compound conductors such as GaAs, InP, and GaInAs.

[Function] The present inventors focused on the fact that the doping of Mg element depends on the growth rate, and changed the growth rate of GaAs while flowing a constant amount of Mg compound gas such as 092Mg. We have discovered a phenomenon in which the Mg element is no longer doped at all when the growth rate exceeds this. This invention is based on such knowledge.

The lower limit of the growth rate at which the Mg element is not doped changes depending on the flow rate of the compound gas containing the Mg element.
The lower limit growth rate increases as the flow rate of the compound gas containing the element increases. At growth rates less than the lower limit growth rate, the amount of Mg doping increases inversely with the growth rate.

Conventionally, when controlling the doping of the Mg element by introducing and extracting a compound gas containing the Mg element into and out of the reaction tube, as described above, it is necessary to
Due to the adsorption of compounds of elements, the doping profile is not steep.

However, when changing the growth rate as in the present invention, it is sufficient to keep the amount of Mg element compound gas constant and change only the tMQ of the compound semiconductor raw material gas. For example, in the crystal growth of GaAs, the flow rate of TMG, which is the raw material for Ga, may be changed. TMG is M
Since it does not adsorb to the inner wall of piping or the like like a compound gas of the g element, it is possible to form a steep doping profile. In the case of TMA, which is the AQ raw material for AQGaAs, it does not adsorb to the inner walls of pipes or the like like TMG, so such control of the doping of the Mg element is also possible in the compound semiconductor of AQGaAs. Furthermore, in the case of TMI (trimethylindium), which is a raw material for In, adsorption to the inner walls of piping etc. similarly does not occur, so this invention can also be applied to compound semiconductor crystals such as InP and Ga InAs. It is possible to create a doping profile.

[Example] Hereinafter, as an example of the present invention, a case where GaAs is doped with Mg element will be described.

FIG. 1A is a diagram showing changes in substrate temperature over time in an embodiment of the present invention. FIG. 1B is a diagram showing changes in AsH and flow rate over time in an embodiment of the present invention. FIG. 1C also shows T in an embodiment of the present invention.
It is a figure showing a change in MG flow rate over time. FIG. 1D is a diagram showing a change in C12Mg flow rate over time in an embodiment of the present invention. As shown in Figures 1A to 1D,
First, AsH, which is a raw material for As element, is placed in a reaction tube.

The GaAs substrate is heated to a temperature of 650° C. while flowing (arsine) gas at a flow rate of 10 rrlj/min.

Next, after setting the flow rate of AsH3 to 300 mfl/min, TMG, which is a Ga source material, was introduced into the reaction tube, and G
Started aAs crystal growth.

At this time, the flow rate of TMG was set to 7 ml/min so that the growth rate of GaAs was 2 μm/hr.

After 30 minutes, 092Mg, which had been previously flowed into the exhaust pipe, was introduced into the reaction tube. The flow rate of 092Mg is 2.5mα/
It was set to min. After 30 minutes, the TMG was switched from the reaction tube to the exhaust tube to stop the growth and reduce the growth rate to 1.
Adjust the TMG flow rate to 3.5r+l so that it becomes μm/hr.
! After changing the temperature, TMG was introduced into the reaction tube again and the growth of the P layer was started. After growing the P layer in this way for 10 minutes, T
The MG was switched to the exhaust pipe, the growth was interrupted, the flow rate of TMG was changed again to 7 mfl/min, and the TMG was introduced into the reaction tube again. After growing in this state for 30 minutes, the TMG was switched to the exhaust pipe, and the substrate temperature was returned to room temperature, and the growth was completed. Regarding the carrier density in the thickness direction of the grown crystal layer, C-
(2) Measurements were made and the results are shown in Figure 1E.

For comparison, FIG. 4E shows the results of a C-■ measurement of the carrier density in the thickness direction of a Compound 16 conductor layer grown by a conventional method. Note that FIGS. 4A to 4D show the substrate temperature, AsH, flow rate, TMG flow rate, and C1 in this comparative example.
2 shows the respective changes over time in the flow rate of Mg. 4th C
As shown in the figure, in this comparative example, the TMG flow rate was set at 3°5.
C92M was maintained at a constant flow rate of ml/min, and only during the crystal growth of the part corresponding to the p layer, as shown in Figure 4D.
g is introduced into the reaction tube.

As shown in FIG. 4E, in the compound semiconductor layer grown by the conventional method, the profile of the P layer is not steep, and especially after doping, the layer remains P type and has a high carrier density. In comparison, as shown in FIG. 1E, in the compound semiconductor layer grown by the method according to the present invention, the profile of the P layer is steep, and even after doping, the carrier density returns to the level before doping. . Furthermore, it can be seen that when the growth rate is high, the carrier density does not change at all even if the raw material of Mg element is introduced into the reaction tube.

In addition, by increasing the growth rate in this way, Mg
The electron mobility at liquid nitrogen temperature for a GaAs layer that is not doped with elements is the same as that of a GaAs layer that is not doped with Mg by not flowing the Mg source
It was the same as the s layer.

Therefore, it was confirmed that the crystal layer which was not doped with Mg by such removal had the same high purity as the crystal layer grown by the conventional method.

[Effects of the Invention] As explained above, the present invention utilizes the phenomenon that even when a compound gas containing the Mg element is flowing, Mg is not doped at all at a growth rate higher than the above, and the growth rate can be increased. The doping of Mg element is controlled by changing the ratio.

This eliminates the effect of absorption of Mg compound gas into the inner walls of pipes, reaction tubes, etc., which was a problem with conventional methods, and makes it possible to form a steep doping profile of the P layer. .

[Brief explanation of the drawing]

FIG. 1A is a diagram showing changes in substrate temperature over time in an embodiment of the present invention. FIG. 1B is a diagram showing the change over time of AsH3am in an example of the present invention. FIG. 1C also shows T in an embodiment of the present invention.
It is a figure showing a change in MG style Yu over time. FIG. 1D is a diagram showing the change over time of Cp2MgaH in an example of the present invention. FIG. 1E is a diagram showing the carrier density in the thickness direction of a compound semiconductor layer grown according to an embodiment of the present invention. FIG. 2 is a sectional view showing the structure of the HBT. FIG. 3 is a schematic diagram showing a general manufacturing apparatus using the metal vapor phase growth method. FIG. 4A is a diagram showing changes in substrate temperature over time in an example of a conventional method. FIG. 4B shows the same A in an example of the conventional method.
FIG. 3 is a diagram showing changes over time in sH and flow rate. FIG. 4C is a diagram showing a change in TMG flow rate over time in an example of the same conventional method. FIG. 4D is a diagram showing the change in C22Mg flow rate over time in an example of the same conventional method. Fourth
Diagram E is a diagram showing the carrier density distribution in the thickness direction of a compound semiconductor layer grown by an example of a conventional method. In the figure, 1 is a reaction tube, 2 is a susceptor, 3 is a substrate, and 4
is an RF coil, 1] is an AsH container, 12 is a TMG container, 13 is a Cp2Mg container, 21 to 25 are flow meters, 31 is a pressure regulator, 32 to 43 are valves, 51 to 58 are piping,
59 is an exhaust pipe, and 60 is an exhaust pipe from the reaction tube. Thickness from the substrate (μl) Thickness from the substrate (μm)

Claims (3)

[Claims] (1) A compound semiconductor layer doped with Mg element by crystal growth by organometallic vapor phase epitaxy using a compound semiconductor raw material gas and a compound gas containing Mg element;
In a compound semiconductor crystal growth method in which a compound semiconductor layer is laminated with a compound semiconductor layer that is not doped with the g element, while supplying the compound gas containing the Mg element at a constant flow rate, crystal growth is performed in which the Mg element is not doped at the flow rate of the compound gas. A method for growing a compound semiconductor crystal, the method comprising: forming a compound semiconductor layer that is not doped with the Mg element by increasing the growth rate to a maximum growth rate. (2) Crystal growth of the compound semiconductor according to claim 1, characterized in that crystal growth is interrupted between formation of the compound semiconductor layer doped with the Mg element and formation of the compound semiconductor layer not doped with the Mg element. How to grow. (3) The compound semiconductor is GaAs, AlGaAs,
2. The method for growing a compound semiconductor crystal according to claim 1, wherein the compound semiconductor is one or more compound semiconductors selected from the group consisting of InP and GaInAs.