JPH06302516A - Vapor growth method - Google Patents

Abstract

PURPOSE:To uniform the thickness of thin films by specifying the total number of susceptor rotations. CONSTITUTION:A susceptor with a substrate held thereon is rotated, and further material gas is fed along the surface of the substrate to grow a crystal thin film. The total number R of susceptor rotations for a period from the start to the end of the growth of the crystal thin film is determined by an equation of R>=L/2x-0.5, where L (%) is the variability of the thickness of the thin film when the susceptor is at a standstill, and x (%) is the one when it is rotated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vapor phase growth method for forming a thin film on a substrate while rotating a susceptor, and more particularly to finding a suitable total number of rotations of the susceptor to improve thin film characteristics.

[0002]

2. Description of the Related Art The vapor phase growth method is a method of rotating a susceptor in a reaction furnace and flowing a source gas over a substrate supported by the susceptor to form a thin film, which is a thin film of a compound semiconductor such as GaAs or AlGaAs. Suitable for growing single crystals. High-purity organic metal, hydride, and carrier gas are used as the source gas, and it does not require ultra-high vacuum such as molecular beam epitaxy, so it is excellent in mass productivity.

In a typical horizontal vapor phase growth apparatus, a raw material gas is flowed in parallel with a substrate to form a thin film while rotating a susceptor supporting the substrate. The reason why the thin film is formed while rotating the susceptor is that when the susceptor is stationary, the film thickness of the crystal growing on the substrate varies in the flow direction of the source gas. Is reduced.

[0004]

As described above, in the conventional lateral vapor phase growth apparatus, when the susceptor is stationary, the film thickness of the crystal grown on the substrate varies in the flow direction of the source gas. There is. Therefore, the susceptor is rotated to make the film thickness distribution of the thin film grown on the substrate uniform.

When rotating the susceptor, if the susceptor is rotated at a constant speed, a thin crystal thin film that grows on the substrate requires a long time from the growth start time to the growth end time if the film thickness is large. Therefore, the total number of rotations of the susceptor increases. On the contrary, if the film thickness is thin, the total number of rotations is small. Also, when the total number of rotations of the susceptor during the growth of the thin film on the substrate is large, the film thickness is large and the influence of the variation is small, but when the total number of rotations of the susceptor is small, the film thickness is thin. The influence of the variation on the thickness becomes large.

In this respect, in the past, even when the total number of revolutions of the susceptor is small and the film thickness is thin, the susceptor is rotated at a constant speed without being distinguished from when it is thick. When the total number of revolutions R of the susceptor is not an integer, there is a problem that the film thickness of the crystal layer becomes non-uniform within the substrate, resulting in a decrease in performance and yield of various semiconductor elements. This problem becomes more remarkable as the thickness of the thin film becomes smaller.

An object of the present invention is to provide a vapor phase growth method capable of eliminating the above-mentioned drawbacks of the prior art and making the thickness of a thin film uniform by defining the total number of revolutions of the susceptor. is there.

[0008]

The vapor phase growth method of the present invention comprises:
In the vapor phase epitaxy method in which a source gas is introduced into a reaction furnace and a thin film is formed on a substrate supported by the susceptor while rotating the susceptor in the reaction furnace, the film thickness variation of the thin film when the susceptor is stationary is measured. L (%), the total number of rotations of the susceptor from the start to the end of thin film growth when the susceptor is rotated to grow a thin film is R (times), and the film thickness variation of the thin film when the susceptor is rotated is x (%). Then, the relationship of R ≧ L / 2x−0.5 is satisfied. Here, the total rotation speed R of the susceptor means not the rotation speed but the number of times the susceptor actually rotates during the growth of the thin film, and the unit is times.

In this case, in order to further improve the uniformity of the thin film, it is preferable that the total rotational speed R of the susceptor be an integer. Further, a suitable thin film targeted by the method of the present invention may be not only a single layer of a compound semiconductor but also a multi-layered thin film.

[0010]

Since the rotation speed R of the susceptor is performed to make the film thickness of the thin film formed on the substrate uniform, it is closely related to the film thickness variation L of the thin film when the susceptor is stationary. . The present invention has found the relationship between R and L.

A qualitative explanation of R ≧ L / 2 × −0.5 will be given. In order to improve the film thickness variation x of the thin film when the susceptor is rotated to be suppressed to a predetermined value, if the film thickness variation L of the thin film when the susceptor is stationary is large, the variation is uniformized. In order to do so, it is necessary to increase the total number of rotations. Conversely, when L is small, the total number of rotations may be small.

Since the lower limit of the total rotation speed of the susceptor is defined so that x can be suppressed to a predetermined value, even when the total rotation speed R of the susceptor from the start to the end of the growth of the crystal thin film is not an integer, The thickness of the crystal thin film can be made uniform within the substrate.

[0013]

EXAMPLE FIG. 3 is a vertical sectional view showing an example of a horizontal vapor phase growth apparatus for carrying out the vapor phase growth method of the present invention.
A chamber 8 communicating with the inside of the furnace is provided at the center of the horizontal reactor 1 having a gas introduction pipe 2 at one end and a gas exhaust pipe 3 at the other end. One substrate 4 is placed in the chamber 8 by the susceptor 5.
Are supported parallel to the furnace axis with the substrate surface facing up. The susceptor 5 is rotatably supported by a motor 9 via a susceptor support shaft 7. Substrate 4 is susceptor 5 by heater 6.
Is heated through.

In such a horizontal vapor phase growth apparatus, a raw material organic metal (for example, trimethylgallium: Ga (C
H ₃ ) ₃ , trimethylaluminum: Al (C
H _{3) 3),} hydrides (e.g., arsine; AsH3
) And a carrier gas (for example, hydrogen H2) are introduced into the reaction furnace 1 through the gas introduction pipe 2. The introduced raw material is thermally decomposed, and a compound semiconductor crystal (eg, GaAs, AlGaA) is formed on the substrate 4 on the susceptor 5 heated by the heater 6.
s) grows. The reacted gas is discharged from the gas exhaust pipe 9.

By the way, when the susceptor is stationary,
It has already been described that the film thickness becomes non-uniform with some variation L (%) in the flow direction of the source gas. Figure 4
Shows the film thickness distribution of the thin film when such a susceptor is stationary. Although the film thickness can be made uniform by rotating the susceptor 5, the thin film is extremely thin,
Alternatively, if the variation L is large, the film thickness may become non-uniform when the total number of rotations R of the susceptor 5 from the start to the end of growth of the thin film is not an integer. That is, the film thickness becomes uniform after the susceptor completes one rotation, but when the rotation is stopped for half a rotation, the variation cannot be absorbed, so that the film thickness becomes uneven.

For example, assuming that a crystal grows by a thickness d during one rotation of the susceptor 5, the crystal has a thickness dR when the susceptor 5 rotates R times. In particular, the thickness when the susceptor 5 is rotated half a turn is d /
It becomes 2. It is known that the variation in the film thickness due to the half rotation of the susceptor 5 is approximately (d / 2) (L / 100) = dL / 200 (1). That is, the film thickness d (R
With respect to +0.5, x = (dL / 200) × 100 / d (R + 0.5) = L / 2 (R + 0.5) (%) (2) occurs.

Therefore, in order to make the film thickness distribution uniform, it is necessary to set the total rotational speed R of the susceptor 5 of the formula (2) to R ≧ L / (2x−0.5) (3).

In this equation (3), the relationship between L and R when the variation when the susceptor 5 is rotated is set to x = 1 (%) is shown in the form of a graph in FIG. In the figure, when L = 1 (%), x = 1 without rotation.
(%) Means that it can be secured.

According to the present embodiment, the total number of rotations of the susceptor is set to R so as to satisfy the expression (3), so that when the thin film is extremely thin or the variation L is large, the crystal layer Even if the total rotation speed R of the susceptor from the start to the end of growth is not an integer, the film thickness of the crystal layer can be made uniform in the substrate.

Next, in order to confirm that the above equation (3) is actually correct, H is measured by using the horizontal vapor phase growth apparatus of FIG.
A thin film crystal having an EMT (High Electron Mobility Transistor) structure was vapor-grown and its electrical characteristics were examined. The thickness variation of the thin film when the susceptor 5 is stationary is L = 20
(%)Met. Therefore, the total number of revolutions R of the susceptor 5 in which the variation in the film thickness of the thin film when the susceptor 5 is rotated is x = 1 (%) should be R ≧ 9.5 in the calculation from the equation (3). .

Therefore, the total rotational speed R of the susceptor when the thinnest thin film (spacer layer) of the HEMT structure crystal is grown is changed as follows so as to include the above calculation result, and the variation of the electrical characteristics is changed. , That is, the variation Δn (%) in the sheet carrier concentration n _s corresponding to the variation in film thickness
I checked.

R = 2.5, R = 5.0, R = 9.5 When R = 2.5, Δn = 4.5 (%), When R = 5.0, Δn = 1.1 (%), When R = 9.5 Δn = 1.2
It became (%).

As calculated, Δn is small at R = 9.5. At R = 2.5, Δn is large because the total rotational speed R is small. When R = 5.0, R ≧ 9.5
However, Δn is small because R is an integer.

Thus, in this example, it was proved that the equation (3) was correct, and by determining the total number of revolutions of the susceptor for obtaining the desired thin film thickness variation from the equation (3), the HEMT structure was obtained. The yield could be improved by reducing the variation in the electrical characteristics of the crystal.

In the above embodiment, the case where the number of substrates supported by the susceptor is one has been described, but the present invention is not limited to this, and as in the modification shown in FIG. A plurality of substrates 4 may be set on top. Also in this case, if the total number of rotations of the susceptor is defined so as to satisfy the expression (3), the film thickness distribution of the thin layers of all the substrates 4 set on the susceptor 15 can be made the same. Further, it is needless to say that the present invention can be applied to a vapor phase growth method in which a substrate is supported downward.

[0026]

【The invention's effect】

(1) According to the vapor phase growth method of claim 1, the total number of revolutions of the susceptor is specified based on the variation when the susceptor is stationary and the variation when the susceptor is stationary. Unlike the conventional case of rotating, the film thickness in the substrate can be made uniform even when the total number of rotations of the susceptor from the start to the end of growth of the crystal thin film is not an integer. By making the film thickness uniform, the yield of the device can be improved. In particular, the present invention is effective when growing an extremely thin crystal thin film such as a spacer layer of a HEMT structure crystal.

(2) According to the vapor phase growth method of the second aspect, since the specified total number of revolutions of the susceptor is set to be an integer, the film thickness in the substrate can be made largely uniform.

(3) Since the vapor phase growth method according to the third aspect is applied to a thin film of a compound semiconductor, the performance and the yield of various semiconductor devices made of the compound semiconductor should be improved.

[Brief description of drawings]

FIG. 1 is a graph showing the magnitude L of variation in film thickness when the susceptor is stationary and the total number of revolutions R of the susceptor when the variation in film thickness due to rotation of the susceptor according to the embodiment of the present invention is set to 1%. The characteristic diagram which shows a relationship.

FIG. 2 is a plan view of a susceptor that supports a plurality of substrates according to a modification of the present invention.

FIG. 3 is a vertical sectional view showing an embodiment of a horizontal vapor phase growth apparatus for carrying out the method of the present invention.

FIG. 4 is a characteristic diagram showing the film thickness distribution in the substrate in the flow direction of the source gas when the susceptor is stationary.

[Explanation of symbols]

 1 Reactor 2 Gas Inlet Pipe 3 Gas Exhaust Pipe 4 Substrate 5 Susceptor 6 Heater 7 Susceptor Support Shaft 8 Chamber 9 Motor

Claims (3)

[Claims] 1. A vapor phase growth method in which a raw material gas is introduced into a reaction furnace and a thin film is formed on a substrate supported by the susceptor while rotating the susceptor in the reaction furnace, when the susceptor is stationary. Is L (%), the total number of rotations of the susceptor from the start to the end of thin film growth when the thin film is grown while rotating the susceptor is R (times), and the thin film thickness when the susceptor is rotated A vapor phase growth method characterized in that the relation of R ≧ L / 2x−0.5 is satisfied, where the variation is x (%). 2. The vapor phase growth method according to claim 1, wherein the total rotational speed R of the susceptor is an integer. 3. The vapor phase growth method according to claim 1, wherein the thin film is a single-layer or multi-layer thin film of a compound semiconductor.