JP3078927B2 - Method for growing compound semiconductor thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a method for growing a Group-V compound semiconductor thin film, and more particularly, to a method for growing a Group-III compound semiconductor thin film having good crystallinity and surface morphology. In recent years, group 3-5 compound semiconductor thin films such as GaAs have been used in high-speed devices such as high-speed FETs and have attracted attention. When growing a group III-V compound semiconductor thin film on a silicon substrate, a method of growing a compound semiconductor thin film capable of obtaining a group III-V compound semiconductor thin film having good crystallinity and surface morphology is required. I have.

[0002]

2. Description of the Related Art Conventionally, GaAs or the like has been
The method of growing a group-V compound thin film was performed as follows. First, as shown in FIG. 3A, a hydrogen gas and a Group 5 source gas are introduced to form an atmosphere of a hydrogen gas and a Group 5 source gas, and the temperature of the silicon substrate is raised to about 1000 ° C. The substrate is subjected to a high-temperature heat treatment (pre-bake) to perform a surface treatment for removing contamination such as a natural oxide film. Thereafter, by lowering the temperature of the silicon substrate to a low temperature of 450 ° C. in a state where the group V source gas is introduced, a group 3-5 compound semiconductor thin film serving as an initial layer is grown on the silicon substrate. Then, the temperature of the silicon substrate is raised to 600 to 750 ° C. in a state where the group V source gas is introduced, and a group 3-5 compound semiconductor thin film serving as an epi layer is further grown on the initial layer. Through the above steps, a Group 3-5 compound semiconductor thin film was grown on the silicon substrate.

[0003]

However, in the above-described conventional method for growing a compound semiconductor thin film, as shown in FIG. 3A, all steps of high-temperature treatment before the growth of the initial group III-V compound semiconductor thin film are performed. In addition to the hydrogen gas, the group 5 source gas was also introduced, so that the reduction reaction of the hydrogen gas proceeded, and the high temperature also caused the group 5 source gas to undergo a decomposition reaction, causing active hydrogen to attack the silicon substrate. Thus, the surface morphology of the silicon substrate has deteriorated. For this reason, since the group 3-5 compound semiconductor thin film of the initial layer and the epi layer was grown with the surface morphology deteriorated, the obtained 3-5
There is a problem that the crystallinity and surface morphology of the group III compound semiconductor thin film are significantly deteriorated.

[0004] Therefore, in order to improve the problem that the surface morphology of the silicon substrate is deteriorated, a conventional method of growing a compound semiconductor thin film reported in, for example, Japanese Patent Application Laid-Open No. 2-175690 discloses a group 5 source gas. Is not performed during the entire process of the high-temperature heat treatment before the initial layer, but reaches the epi-layer growth temperature of 600 to 750 ° C. or less during the temperature decrease after the pre-bake as shown in FIG. 3B. Group 5 source gas has been introduced since that time.

In this method of growing a compound semiconductor thin film, the introduction of the group V source gas before the growth of the initial layer is delayed as compared with the case of FIG. 3A, and the maximum temperature after introduction is lower than that of FIG. Therefore, the surface morphology of the silicon substrate is improved to some extent as compared with the case of FIG. 3A, and although the crystallinity of the obtained group III-V compound semiconductor thin film is improved to some extent, the obtained 3-5 There is a problem that the surface morphology of the group III compound semiconductor thin film is still deteriorated.

[0006] Accordingly, the present invention provides a method for fabricating a silicon substrate on a silicon substrate.
It is an object of the present invention to provide a method for growing a compound semiconductor thin film that can obtain a group 3-5 compound semiconductor thin film having sufficiently excellent crystallinity and surface morphology when growing a group V compound semiconductor thin film.

[0007]

According to the present invention, there is provided a method for growing a compound semiconductor thin film according to the present invention, wherein the silicon substrate is grown at a first temperature. Heat treating at 150 ° C. and subjecting the silicon substrate to 150 ° C. or more and 400 ° C.
A step of starting supply of a group V source gas to the surface of the silicon substrate after lowering the temperature to the following second temperature; and a step of growing a first group 3-5 compound semiconductor thin film on the silicon substrate. At a third temperature higher than the second temperature, the first 3
A second group III-V compound semiconductor thin film is grown on the group III-V compound semiconductor thin film.

The constituent materials of the first and second Group III-V compound semiconductor thin films according to the present invention include GaAs, AlAs, and Al.
GaAs, GaAsP and the like are preferable, and a preferable combination thereof is a second group III-V compound semiconductor (epi layer) /
As the first group III-V compound semiconductor (initial layer), Ga
As / GaAs, GaAs / AlAs, GaAs / Al
GaAs, GaAs / GaAsP and the like can be mentioned. In addition, it is preferable that Al is contained as the first group III-V compound semiconductor to be the initial layer because two-dimensional growth can be performed stably. The group 5 source gas includes arsine, tertiary butyl arsine, ethyl arsine and the like.

In the present invention, the lower limit of the silicon substrate for growing the first group III-V compound semiconductor thin film is set at 15 or less.
The reason why the temperature is set to 0 ° C. is that if the temperature is lower than 150 ° C., the growth rate is remarkably reduced, which is not preferable for practical use. The upper limit temperature of the silicon substrate is set to 400 ° C. This is because irregularities are generated and the surface is significantly roughened, which is not preferable for practical use.

In the present invention, it is preferable that the high-temperature heat treatment of the silicon substrate is performed in a hydrogen gas atmosphere. In this case, a natural oxide film or the like generated on the substrate surface by further raising the substrate temperature to about 1000 ° C. Dirt can be removed. In the present invention, the group 5 source gas is introduced after the silicon substrate is surface-treated by a high-temperature heat treatment at about 1000 ° C., and then the temperature is lowered to 150 ° C. or more and 400 ° C. or less. The reason that the Group 5 source gas is not introduced during the high-temperature heat treatment is that if the Group 5 source gas is introduced during the high-temperature heat treatment, the active hydrogen generated by decomposition degrades the substrate surface and grows on the substrate. This is because the crystallinity and surface morphology of the group III compound semiconductor thin film deteriorate.

In the present invention, it is preferable that the substrate temperature at the time of growing the second group III-V compound semiconductor thin film is not lower than 600 ° C. and not higher than 750 ° C. In this case, the lower limit temperature of the substrate is 600 ° C. The reason for this is that if the temperature is lower than 600 ° C., it is not preferable that the single crystal film is not completely crystallized but polycrystallized, and it is difficult to form a single crystal film having good film quality. 750 ° C
The reason for this is that if the temperature is higher than 750 ° C., the growth rate is lowered, and in particular, the surface is roughened and the surface morphology deteriorates, which is not preferable.

[0012]

According to the present invention, before the growth of the group III-V compound semiconductor thin film as the initial layer, the silicon substrate is subjected to high-temperature treatment in a hydrogen gas atmosphere without introducing a group V source gas, and in a hydrogen gas-only atmosphere. The surface roughness of the silicon substrate surface can be prevented without causing the decomposition reaction of the group V source gas accompanying the introduction of the group V source gas as in the related art. In addition, since the temperature of the silicon substrate is lowered to a lower temperature of 400 ° C. or lower than before, the morphology of the surface of the silicon substrate can be improved. Since the group V source gas is introduced again to the surface of the silicon substrate which has been lowered to a temperature of 400 ° C. or less and has a good surface morphology, the growth temperature of the initial layer and the group V source The gas can be introduced at a low temperature of 400 ° C. or less, so that a dense initial layer can be obtained. For this reason, a dense epitaxial layer can be obtained, and as a result, a group III-V compound semiconductor thin film having a sufficiently excellent crystal quality and surface morphology can be obtained.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a growth temperature sequence in a method for growing a compound semiconductor thin film according to one embodiment of the present invention. In this embodiment, GaAs is formed on a silicon substrate by MOCVD.
This is a case where an s film is grown. The silicon substrate is (00
1) Use one that is turned off twice from the surface in the [110] direction.
Trimethyl gallium (TMG) is used as a Group 3 raw material, and arsine (AsH ₃ ) or tertiary butyl arsine (TBAs, (CH ₃ ) ₃ CAsH ₂ ) is used as a Group 5 raw material.
The growth is based on a two-step growth method often used for GaAs growth or the like on a Si substrate as shown in FIG.

First, about 12 SLM of hydrogen gas is introduced into the reaction chamber to form a hydrogen gas atmosphere, and the silicon substrate is heated to a high temperature of about 1000 ° C.
By subjecting the silicon substrate to a high-temperature heat treatment at a high temperature of about 10 minutes, a natural oxide film or the like generated on the surface of the silicon substrate is removed. At this time, the atmosphere in the reaction chamber is only H ₂ gas, and the supply of Group 5 source gas is not performed. Next, when the temperature of the silicon substrate was lowered to a low temperature of 350 to 450 ° C., a Group V source gas was introduced into the reaction chamber at about 50 sccm,
After 5 to 15 minutes, the group V source gas is increased to about 400 sccm and TMG is further supplied at about 18 sccm to grow a GaAs initial layer having a thickness of about 50 to 200 ° at low temperature. Subsequently, when the supply of TMG was stopped and the group V source gas was reduced to about 50 sccm and the temperature of the silicon substrate was raised to about 650 ° C., the group V source gas was reduced to 2%.
While increasing to about 00 sccm, TMG is supplied at about 2.5 sccm to grow a GaAs epi layer having a thickness of 3 μm.

Next, in the case of the present invention and the comparative example, Ga
FIG. 2 shows the dependence of the crystallinity and surface flatness of the As film on the group V source gas, its introduction temperature, and the growth (substrate) temperature of the low-temperature initial layer. The crystallinity is evaluated by the half width (FWHM) of the X-ray rocking curve by the X-ray double crystal method, and the smaller the value is, the better the crystallinity is. The surface flatness was evaluated by a root-mean-square roughness (visual field 50 μm □) by an atomic force microscope (AFM), and the smaller the value, the better the surface flatness.

As apparent from FIG. 2, in Comparative Examples 1 and 2 in which the low-temperature initial layer is grown at 450 ° C., the temperature of introducing the group 5 source gas is lowered from 1000 ° C. in FIG. In contrast, the crystallinity was improved, but the surface flatness was deteriorated.
It has been found that by growing at a low temperature of 0 ° C. or lower and by introducing the group V gas at a low temperature of 400 ° C. or lower, the crystallinity can be improved and the surface flatness can be sufficiently improved. .

It is understood from FIG. 2 that the group V source gas used is preferably TBAs rather than AsH ₃ , because the crystallinity and surface flatness can be further improved.

[0018]

According to the present invention, according to the present invention, a 3-
When growing a group V compound semiconductor thin film, there is an effect that a group 3-5 compound semiconductor thin film having sufficient film quality in crystallinity and surface morphology can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a growth temperature sequence in a compound semiconductor thin film growth method according to one embodiment of the present invention.

FIG. 2 is a diagram showing results of crystallinity and surface flatness in the case of the present invention and a comparative example.

FIG. 3 is a diagram showing a growth temperature sequence in a conventional method for growing a compound semiconductor thin film.

[Explanation of symbols]

Claims (3)

(57) [Claims] 1. A method for growing a group III-V compound semiconductor thin film on a silicon substrate, comprising: a step of subjecting the silicon substrate to a heat treatment at a first temperature to perform a surface treatment; A step of starting supply of a group V source gas to the surface of the silicon substrate after lowering the temperature to the following second temperature; and a step of growing a first group 3-5 compound semiconductor thin film on the silicon substrate. Growing a second group III-V compound semiconductor thin film on the first group III-V compound semiconductor thin film at a third temperature higher than the second temperature. Method. 2. The method according to claim 1, wherein the heat treatment of the silicon substrate at the first temperature is performed in a hydrogen gas atmosphere. 3. The compound semiconductor thin film according to claim 1, wherein a third temperature at which the second group III-V compound semiconductor thin film is grown is set to 600 ° C. or more and 750 ° C. or less. Growth method.