JPH039516A - Epitaxial growth method of compound semiconductor mixed crystal - Google Patents

Abstract

PURPOSE:To reduce dislocation density when a mixed crystal epitaxial layer having different lattice constant is grown on a compound semiconductor substrate, by interrupting the growth of the mixed crystal for a while, and growing a layer of uniform composition after a gradient composition layer whose composition ratio changes is formed on a substrate. CONSTITUTION:When a epitaxial layer of mixed crystal whose lattice constant is different from substrate crystal is vapor-grown on a semiconductor single crystal substrate 5, the growth of the mixed crystal is interrupted for a while after a gradient composition layer 52 whose composition ratio gradually changes is formed on the substrate 5, and then a constant composition layer 53 is grown. That is, by the growth interruption the dislocation generated in the gradient composition layer 52 can be restrained from vanishing or propagating to the growth layer thereon. Thereby dislocation density on the surface of the mixed crystal epitaxial layer 53 of constant composition can be reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an epitaxial growth technique on a semiconductor wafer, particularly on a compound semiconductor single crystal wafer.
6. Related to effective techniques for vapor phase growth of group mixed crystals [Prior Art] Mixed crystal epitaxial wafers are sometimes used as substrates for compound semiconductor devices such as light emitting diodes. In this case, the properties of the wafer affect the characteristics of the device. In particular, a compound semiconductor device is desired to have a low dislocation density because if the dislocation density in the crystal is high, the device life will be shortened or the emission intensity will be weakened.

Conventionally, when growing an epitaxial layer of a mixed crystal whose lattice constant is significantly different from that of the substrate crystal on a compound semiconductor substrate, a composition gradient layer in which the composition ratio gradually changes is formed between the substrate and the mixed crystal. The lattice mismatch was alleviated and the generation of dislocations was suppressed.

On the other hand, a technique has been proposed in which a region in which the composition ratio changes discontinuously is provided in a composition gradient layer for the purpose of reducing variations in luminance of a light emitting diode (Japanese Patent Laid-Open No. 61
-291491).

[Problems to be Solved by the Invention] However, when growing a GaAsP mixed crystal epitaxial layer on a GaAs substrate, even if a composition gradient layer is provided or a gradient discontinuous region is provided in this composition gradient layer, It was found that it was not possible to obtain an epitaxial layer in which the dislocation density was reduced to the same extent as that of a binary compound.

The present invention was made against the above-mentioned background, and its purpose is to sufficiently reduce dislocation density when growing mixed crystal epitaxial layers with different lattice constants on a compound semiconductor substrate. Our goal is to provide a vapor phase growth technology that is effective.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a method for vapor phase growing an epitaxial layer of a mixed crystal having a lattice constant different from that of the substrate crystal on a semiconductor crystal substrate. After forming a composition gradient layer on top of which the composition ratio gradually changes, the growth of the mixed crystal is temporarily interrupted, and then a constant composition layer is grown, or the growth of the mixed crystal is interrupted and the growth of the constant composition layer is continued. I tried to do it at least once at a time. The growth interruption time is a time that does not decompose the grown mixed crystal (several minutes to several tens of minutes).
Set.

Furthermore, when epitaxial growth is interrupted, the introduction of raw material gas into the reaction tube is stopped and only the carrier gas is allowed to flow, so that the temperature within each reaction tube is kept the same as during growth.

Furthermore, when the mixed crystal to be grown contains volatile elements such as phosphorus and arsenic, it is preferable to keep a hydride gas containing these elements flowing during the growth interruption.

In order to improve surface smoothness, it is desirable to use a growth substrate whose plane orientation is tilted by 0.5 to 10 degrees from the (001) plane or an equivalent plane.

Furthermore, in order to prevent dislocations of the growth substrate itself from propagating to the mixed crystal epitaxial layer, it is preferable to provide a buffer layer having the same composition as the substrate between the substrate and the composition gradient layer.

[Example 3] FIG. 3 shows an example of a vapor phase growth apparatus used in the vapor phase epitaxial growth method according to the present invention.

This vapor phase growth apparatus consists of a cylindrical quartz reaction tube 1 and an electric furnace 2 that heats the reaction tube 1 from the outside.The electric furnace 2 can control the axial temperature distribution of the reaction tube 1. It is configured as follows. With this vapor phase growth apparatus, Ga
When performing vapor phase epitaxial growth of A s P, a raw material boat 4 containing gallium 3, which is a material source, is placed on the upstream side (left side in the figure) in the reaction tube 1, and vapor phase growth is performed on the downstream side. A GaAs substrate 5 is placed.

On the other hand, a first gas introduction pipe 6a is connected to the upstream end of the reaction tube 1 to bypass the raw material boat 4 and supply gas upstream of the substrate 5. Also.

A second gas introduction pipe 6b and a third gas introduction pipe 6C for supplying gas to the raw material boat 4 are connected to the upstream end of the reaction tube 1.

In the middle of the gas introduction pipes 6b and 6c, there are bubblers 8a containing AsCR and PCQ3, respectively.

8b is interposed. The gas introduction pipes 6b and 6c have H
By introducing H2 gas into the bubblers 8a and 8b, a mixed gas of AsCQ and PCQ3 can be supplied into the reaction tube 1 using H as a carrier. Further, the bubblers 8a and 8b are placed in a constant temperature bath (not shown) whose temperature can be controlled, and by controlling the temperature, the amount of evaporation of AsCQ, PCQ, is controlled.

Note that 7a, 7b, and 7c are mass flow controllers for flow rate control, and 9 is an exhaust pipe connected to the downstream end of the reaction tube 1.

FIG. 4 shows the temperature distribution in the reaction tube 1. The temperature of the raw material boat section 4 is controlled by the electric furnace 2 so that the temperature of the 870'C1 GaAS substrate 5 is 790°C.

Using the above apparatus, a GaAs substrate with a plane orientation tilted 2" from (100) is set in the reaction tube 1, and then the mass flow controllers 7b and 7c control AsCQ, PCQ,
The molar ratio of PCQ, /CPCQ.

+AsCQ, ) was gradually changed from 0 to 0.38 and supplied into the reaction tube 1, and as shown in FIG. 50 μm GaAs P
A composition gradient layer 52 was formed.

Then, switch the valves 10a to 10d to AsCQ, □
and pcI2. The supply of the GaAsP mixed crystal layer was stopped, and instead only H2 gas, which is a carrier gas, was flowed to grow the GaAsP mixed crystal layer for about 10 min.
It was stopped for a minute. After that, G is applied on top of the composition gradient layer 52.
A constant composition layer 53 of a Aso, 2 PG, . . . was grown to a thickness of 50 μm.

During the growth of the constant composition layer 53, A s CQ and PCQ were flowed at a rate of 1 and 7×10-' mol/min and 1°I×10-' mol/min, respectively.

As a result of measuring the dislocation density of the epitaxial growth layer of the wafer obtained by the above method, the dislocation density was 9
10' (1m-2), and it was found that the dislocation density was significantly reduced compared to the dislocation density of 2X10' to 3X10'am arch when the present invention was not applied. Figure 1 shows a mixed crystal. FIG. 2 shows the cross-sectional structure of the process in which the epitaxial layer was grown, and also shows changes in the thickness of the epitaxial layer during vapor phase growth.

In the above embodiment, the growth was temporarily interrupted at the boundary (symbol A) between the composition gradient layer 52 and the constant composition layer 53, but the growth and interruption were repeated once or twice or more during the growth of one constant composition layer. (See symbols B and C in FIGS. 3 and 4). Note that the term "during the growth of the constant composition layer" includes the time immediately before the growth of the constant composition layer (time point A).

Furthermore, the present invention can be used for epitaxial growth of ternary and quaternary mixtures other than GaAsP.

[Effects of the Invention] As explained above, in the present invention, in vapor phase growing an epitaxial layer of a mixed crystal having a lattice constant different from that of the substrate crystal on a semiconductor single crystal substrate, the composition ratio is gradually changed on the substrate. After forming the changing composition gradient layer, the growth of the mixed crystal is temporarily interrupted, and then a constant composition layer is grown, or the growth of the mixed crystal is interrupted at least once during the growth of the constant composition layer. As a result, the dislocations generated in the one-composition gradient layer are eliminated or prevented from propagating to the growth layer above it due to growth interruption, and the dislocation density on the surface of the mixed crystal epitaxial layer with a constant composition is significantly reduced. There is.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an example of the structure of a process for growing a mixed crystal epitaxial layer. FIG. FIG. 3 is a longitudinal sectional front view showing an example of a vapor phase growth apparatus used in the vapor phase epitaxial growth method of compound semiconductors according to the present invention, and FIG. 4 is a graph showing the temperature distribution of the reaction tube. 1...Reaction tube, 2...Electric furnace, 4...Raw material boat, 5...Substrate.

Claims (2)

[Claims] (1) In vapor phase growing an epitaxial layer of a mixed crystal having a lattice constant different from that of the substrate crystal on a semiconductor single crystal substrate, a composition gradient layer whose composition ratio gradually changes is formed on the substrate, and then a mixed crystal layer is formed on the substrate. 1. A method for epitaxial growth of a compound semiconductor mixed crystal, characterized in that the growth of the crystal is temporarily interrupted, and then a layer having a constant composition is grown. (2) When forming a mixed crystal composition gradient layer in which the composition ratio gradually changes on a semiconductor single crystal substrate, and growing a constant mixed crystal composition layer on top of the layer in a vapor phase, the growth of the mixed crystal is interrupted when the composition remains constant. 1. A method for epitaxial growth of a compound semiconductor mixed crystal, characterized in that the epitaxial growth method is performed at least once during the growth of a layer.