JPH01290220A - Compound semiconductor layer growth method - Google Patents

Abstract

PURPOSE:To flatten the surface of a growth layer to be grown on a second buffer layer by growing the second buffer layer on a first buffet layer at an intermediate temperature between a growth temperature of the first buffer layer and an ordinary growth temperature of a compound semiconductor layer. CONSTITUTION:When a two-stage growth operation is executed, an Si substrate 10 is heat-treated; after that, a first buffer layer 12 of a compound semiconductor is grown on this substrate at a first temperature which is sufficiently lower than this heat-treatment temperature. In succession, a growth operation of this first buffer layer 12 is stopped once; a second buffer layer 16 is grown at an intermediate second temperature of a halfway value to raise a temperature to an ordinary growth temperature of this compound semiconductor. In succession, a growth operation of this second buffer layer 16 is stopped once; a temperature is raised to an ordinary growth temperature of this compound semiconductor; a compound semiconductor layer is grown on the second buffer layer 16 at this temperature. By this setup, even when a film thickness of the first buffer layer 12 is irregular, the surface of the compound semiconductor layer to be grown after that at the ordinary growth temperature becomes a good specular or a face close to this state.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention provides a method for forming a compound semiconductor layer having a different lattice constant from that of a silicon (Si) substrate, in particular a ■-V group compound semiconductor layer, into a heterogeneous and taxial layer. Regarding how to grow.

(Prior Art) Techniques for producing large, high-quality wafers by growing a ■-v group compound semiconductor layer such as GaAs on a Si substrate have been developed and put into practical use. As a method of heterotaxially growing these compound semiconductor layers on a Si substrate, for example, refer to the literature: rJAPANESE
JOυRNAL OF APPLIED PHYSI'C
S, Vol, 23. NO, 11, (1984)
A two-step growth method is used, as disclosed in Glp, L843-L845J. First, this conventional method will be briefly explained.

FIG. 2 is an explanatory diagram of growth temperature to explain this conventional two-step growth method, with time on the horizontal axis and temperature (°C) on the vertical axis.
)l & plotted as shown. Further, FIG. 3 is a cross-sectional view of a wafer used to explain the conventional method.

As shown in FIGS. 2 and 3, the Si substrate 10 is
Heat treated at a temperature of about 'C (indicated by mark in Figure 2)
In the first stage, GaAs was produced at a low temperature of about 400'C.
A thin layer of , that is, a buffer layer 12, is grown as the first growth layer (indicated by ■ in FIG. 2), and then, in the M2 stage, a GaAs layer + 41Fr is grown as the second growth layer (indicated by ■ in FIG. 2). ), the growth of the second Ga43 layer in the second stage (III in Figure 2) is the same as the growth of the first layer in the first stage (■ in Figure 2). The growth of the GaAs layer is temporarily stopped, and the temperature is set to the normal GaAs growth temperature, e.g.
This is a method in which the growth of the GaAs layer 14 is restarted after the temperature is raised to about 00°C.

According to this two-step growth method, a polar crystal can be grown on a non-polar crystal to obtain a growth layer of a single domain. Furthermore, it is possible to grow a crystal even if there is lattice mismatch between the substrate and the growth layer, and therefore, the above-mentioned two-step growth method can be used to grow a crystal with lattice mismatch of a compound semiconductor such as GaAs on a Si substrate. This is an effective way to grow.

(Problem to be Solved by the Invention) By the way, the wafer obtained by forming a compound semiconductor growth layer on the Si substrate 10 in this way can be used as a wafer on which various electronic device elements are fabricated, as in the past. However, for this purpose, it is naturally desirable that the surface of the growth layer be a mirror surface.

However, in the case of this two-step growth method, the surface state of this growth layer is determined by the thickness of the first growth layer (buffer layer) grown at a low temperature and the subsequent growth by increasing the temperature. Since it is affected by the growth temperature of the second growth layer, it is not always possible to obtain a surface of the growth layer that provides good characteristics as expected when an electronic device element is fabricated.

In particular, if the first layer is thin and the second layer is grown at a high temperature, even if a single domain growth layer is obtained, the surface of the growth layer will be rough. For example, a thin film grown at a low temperature is annealed while the temperature is raised to the growth temperature of the second growth layer, and the atoms that make up the thin film are annealed. acts as a buffer layer, but if the first growth layer is too thin and the annealing temperature is high, the film will condense and the growth layer will have many irregularities. In extreme cases, the Si surface may be exposed, and the surface of the second grown layer above it may become rough.

In order to prevent the occurrence of surface roughness on the growth layer,
It is sufficient to increase the thickness of the first growth layer, but if the film is too thick, the rearrangement of atoms will not be sufficient even after annealing, so it will not be a good buffer layer.

Therefore, when using this two-step growth method, in order to make the surface of the growth layer a mirror-like surface or a mirror-like surface, the thickness of the first growth layer must be adjusted accurately to about 100 to 200%. It is necessary to control this, but this control has been difficult. Furthermore, even if the thickness of the second layer can be controlled, if the growth temperature of the second growth layer is higher than the normal growth temperature, it will be difficult to suppress the roughness of the growth surface. Ta.

This invention has been made in view of the above-mentioned conventional problems, and therefore, an object of the invention is to make the growth layer grow regardless of the state of the first growth layer and the growth temperature of the growth layer. A method for growing a compound semiconductor layer that can achieve a good surface condition of the grown layer, that is, a so-called mirror surface, with good reproducibility so that good characteristics can be obtained when an electronic device element is fabricated, and that is easy to implement. Our goal is to provide the following.

(Means for Solving the Problem) In order to achieve this object, according to the method for growing a compound semiconductor layer of the present invention, a compound semiconductor layer having a lattice constant different from that of the substrate is formed on a silicon (Si) substrate by a hetero-layer. In performing the taxial growth, after heat treatment of this substrate, a step of growing a first buffer layer of a compound semiconductor as a thin film at a first temperature sufficiently lower than this heat treatment temperature, and a step of growing a compound semiconductor layer at a normal growth temperature. Prior to this, a second buffer layer of a compound semiconductor is grown on the first buffer layer at a second temperature higher than the first temperature and at which the atoms constituting the first buffer layer are sufficiently rearranged. It is characterized by including a process.

In carrying out the present invention, preferably, the heat treatment temperature of this substrate is within the range of about 900 to 1000°C, the aforementioned first temperature is within the range of approximately 400 to 450°C, and the aforementioned second temperature is preferably within the range of approximately 400 to 450°C. is within the range of about 550-600'C, and the normal growth temperature mentioned above is set at 650-750'C.
It is best to keep the temperature within a certain range.

(Operation) According to the configuration of the present invention, when performing the two-step growth method,
After the Si substrate is heat-treated, a first buffer layer of a compound semiconductor is grown on the substrate at a first temperature that is sufficiently lower than the heat treatment temperature. Subsequently, the growth of the first buffer layer is temporarily stopped and a second buffer layer is grown at a second temperature midway through the temperature rising to the normal growth temperature of this compound semiconductor. Subsequently, the growth of the second buffer layer is temporarily stopped, and the temperature is raised to a normal growth temperature for compound semiconductors, and a compound semiconductor layer is grown on the second buffer layer at this temperature. This second temperature is a temperature at which the atoms constituting the first buffer layer are sufficiently rearranged to form a single domain, and which is lower than the normal growth temperature.

By growing this second buffer layer at the second temperature mentioned above, even if there are variations in the thickness of the first buffer layer, the surface of the compound semiconductor layer that is subsequently grown at the normal growth temperature will be good. It becomes a mirror surface or a surface close to this.

Therefore, there is no need to strictly control the growth conditions of the first buffer layer, and the range of growth conditions can be widened, making this method simple and easy to implement.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

In this embodiment, a case will be described in which a wafer is obtained by growing a GaAs layer as an example of a -v group compound semiconductor on a Si substrate by the tMOcVD method.

FIG. 1 is an explanatory diagram of the growth temperature used in the compound semiconductor layer growth method of the present invention, with time on the horizontal axis and temperature (on the vertical axis).
℃) is shown. FIG. 4 is a partial cross-sectional view of a wafer used to explain the growth method of the present invention. It should be noted that these drawings are only schematic representations to the extent that the present invention can be understood, and hatchings and the like representing cross sections are omitted. Further, in these figures, the same components and the like as those shown in FIGS. 2 and 3 are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

Further, since the embodiment described below is merely a preferred example, it should be understood that the numerical conditions and other conditions are not limited to the examples given in this embodiment.

First, a Si substrate 101Fr is prepared, and its surface is cleaned by heat treatment at a suitable temperature within the range of about 900 to 1000° C. as in the conventional method (indicated by a mark in FIG. 1). Next, GaA is grown on this substrate 10 by a two-step growth method.
Grow the s-layer. Therefore, in the first stage, as in the past, the temperature inside the furnace is lowered to a growth temperature sufficiently lower than the substrate heat treatment temperature, that is, the low first temperature of about 400 to 450 °C. For example, trimethylgallium (Ga(CHs)s) is used as a raw material gas at low temperature.
) and arsine (AsH3) and hydrogen (H2) gas as a carrier gas under arbitrary suitable growth conditions, Si
A film thickness of 200A or less, preferably 1oO
Grow a GaAs layer 12 with a thickness of ~200.8 cm (
This GaAs layer (indicated by ■ in FIG. 1) corresponds to the conventional -th layer (indicated by 12 in FIG. 3) and functions as a first buffer layer.

Note that if the film is thicker than 200A, it may not function as a good buffer layer.

Next, in the present invention, a second buffer layer 16 is grown before the second step of growing the GaAs layer.

In growing the second buffer layer 16, first, stop the supply of raw material gas, etc., temporarily stop the growth of the first buffer layer 12, and then gradually lower the temperature in the furnace from this first temperature. The temperature is increased to a suitable second temperature within the range of about 550-600°C. This second temperature is the normal 650°C for GaAs.
By increasing the temperature to this second temperature, which is lower than the growth temperature of ~750'C, the first buffer layer 1
The first buffer layer 12 becomes an effective buffer layer because the atoms constituting the first buffer layer 12 are rearranged to form a single domain. Note that at this temperature, the surface irregularities caused by the movement of atoms are not so large, so even if the first buffer layer 12 is thin, the surface of the underlying Si substrate 10 is exposed. Things will disappear.

Then, in the present invention, the supply of the raw material gas etc. is restarted at this second temperature, and the second buffer layer 161Fr of GaAs is grown on the first buffer layer 12 to a thickness of, for example, 1000 to 5000 A (see FIG. 1). ), even if the underlying first buffer layer 12 has irregularities, the second buffer layer 16 has very few irregularities, and even if the temperature is further increased, the surface of the second buffer layer 16 is There is no change in the flatness of

After growing the second buffer layer 16 with good flatness,
The temperature inside the furnace is raised again to an appropriate temperature within the range of 650 to 750 degrees, which is the normal growth temperature for GaAs, and at that temperature, raw material gas, etc. is caused to flow, and the second buffer is heated as before. On the layer 16, a normal growth layer 14 of GaAs (corresponding to the conventional second growth layer) for manufacturing electronic device elements is grown to an appropriate thickness (marked with ■ in FIG. 1). ), this normally grown layer 14 is a high quality crystal with few irregularities on the surface, and when an electronic device element is built into this grown layer 14, its good characteristics can be ensured.

Incidentally, various growth conditions not specifically mentioned in the above-described embodiments can be set as arbitrary suitable conditions depending on the design.

It is clear that the invention is not limited only to the embodiments described above, but that many variations and modifications can be made.
For example, the present invention can be applied to other materials such as -V group compound semiconductor materials other than GaAs, such as InP, GaP, mixed crystals thereof, and other materials.

Furthermore, the growth method of the present invention is suitable for application to non-legal growth of the compound semiconductor layer using a method other than MOCVD.

(Effects of the Invention) As is clear from the above description, according to the method for growing a compound semiconductor layer of the present invention, in addition to the first buffer layer of the first layer, a layer corresponding to the conventional second layer is formed. Before performing the growth of the compound semiconductor layer, a second buffer layer is grown on the first buffer layer at a temperature intermediate between the growth temperature of this first buffer layer and the normal growth temperature of the compound semiconductor layer. Therefore, even if the thickness of the first buffer layer varies greatly or is thin, the surface of the normal growth layer grown on the second buffer layer will be flat and have a so-called mirror surface or It is possible to obtain a surface close to this.

Furthermore, according to the present invention, the range of buffer layer growth conditions for obtaining such a good growth layer is widened.
The growth method of this invention is simple and easy.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of growth temperature to explain the compound semiconductor layer growth method of the present invention, FIG. 2 is an explanatory diagram of growth temperature to explain the conventional method, and FIG. 3 is a wafer diagram to explain the conventional method. Cross-sectional view FIG. 4 is a cross-sectional view of a wafer used to explain the method for growing a compound semiconductor layer of the present invention. 10.-8i substrate, +2-..first buffer layer 14.-normal growth layer, +6-..second buffer layer. Patent applicant Kozo Iizuka, Director General of the Agency of Industrial Science and Technology ('
C) Temperature ('C) N he (h clo mic;＞ (:) 'S＞ mo()q
z cb () c) Cross-sectional view of a conventional wafer (Fig. 3) Cross-sectional view of a wafer used to explain the present invention (Fig. 4)

Claims (2)

[Claims] (1) When heteroepitaxially growing a compound semiconductor layer having a lattice constant different from that of the substrate on a silicon (Si) substrate, after heat treatment of the substrate, the first layer of the compound semiconductor is grown at a first temperature sufficiently lower than the heat treatment temperature. growing a buffer layer as a thin film, and prior to growth of the compound semiconductor layer at a normal growth temperature, a second temperature higher than the first temperature and at which the atoms constituting the first buffer layer are sufficiently rearranged; A method for growing a compound semiconductor layer, comprising the step of growing a second buffer layer of a compound semiconductor on the first buffer layer at a temperature. (2) The heat treatment temperature of the substrate is within a range of about 900 to 1000°C, and the first temperature is 400 to 450°C.
The second temperature is within a range of 550 to 60°C.
The temperature is within the range of about 0°C, and the normal growth temperature is 6°C.
2. The method for growing a compound semiconductor layer according to claim 1, wherein the temperature is within a range of approximately 50 to 750°C.