JP2642031B2 - Liquid phase epitaxial growth method of compound semiconductor and compound semiconductor single crystal substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compound semiconductor single crystal substrate used for liquid phase epitaxial growth.

[0002]

2. Description of the Related Art Conventionally, as a substrate for epitaxial growth of a compound semiconductor, a substrate having a mirror-polished surface has been used. The surface roughness is generally less than 1 μm per 1 mm line. Such a mirror-like or near-mirror-like substrate is obtained by slicing a single crystal ingot, processing it as necessary into a circular shape, lapping the surface, and polishing as necessary. It has been common knowledge in the art to finish the surface of the substrate to a mirror surface or a surface close to the mirror surface. The reason is that important characteristics such as flatness, uniformity of thickness and stability of electric and optical characteristics of the epitaxial layer grown thereon are not impaired.

There are various methods of epitaxial growth, such as vapor phase growth, liquid phase growth, and molecular beam epitaxial growth. Conventionally, in any growth method, a substrate having a mirror surface or a surface close to the mirror surface is used. In fact, it can be said that there has not been an idea of using a substrate having a rough surface as a substrate of a liquid phase epitaxial wafer for a light emitting diode.

[0004]

Such a conventional mirror-like or near-mirror substrate requires processing steps such as slicing, wrapping and polishing, so that it takes a lot of time and labor to manufacture, and the cost is high. was there. Also, Ga
When the size of the As substrate is about 76 mm in diameter and about 600 μm in thickness, the weight is about 14 g per sheet. If the surface is mirror-like, there is also a problem that it slips and drops easily during transportation. An object of the present invention is to solve the above-mentioned problems and to provide a practically excellent compound semiconductor single crystal substrate for liquid phase epitaxial growth which is relatively inexpensive and has little slip during transportation.

[0005]

According to the present invention, the surface roughness of one point per 1 cm ^{2 of} the substrate surface is within a range of 1 μm or more and 20 μm or less of 50% or more of the measured values on a 1 mm line. A liquid phase epitaxial growth method for a compound semiconductor, characterized in that after slicing a single crystal ingot, an epitaxial layer is formed on the substrate surface without polishing the substrate surface to a mirror surface. In addition, the present invention measures the surface roughness on a 1 mm line at one point every 1 cm ^{2 of} the substrate surface, and 50% or more of the measured values at each measurement point is in a range of 1 μm or more and 10 μm or less, A semiconductor single crystal substrate for liquid phase epitaxial growth, wherein the substrate is GaAs, and the epitaxial layer on the substrate is GaAs. Further, the substrate is used as a substrate of an epitaxial wafer for an infrared or visible light emitting diode. Here, the surface roughness means that the radius of curvature of the tip is 1 to
When a 50 μm stylus is applied to the surface of the substrate and measured on a line having a length of 1 mm, the difference between the height of the highest portion and the height of the lowest portion is measured.

The surface roughness is measured on the substrate surface one point at a time approximately every 1 cm ² , and 50% of the measured values at each measurement point is measured.
% Is 1 μm or more and 20 μm or less, preferably 1 μm or more and 10 μm or less.

[0007]

The surface roughness of the substrate is at least 1 μm per 1 mm line.
Since it is 0 μm or less, preferably 1 μm or more and 10 μm or less, lapping and polishing are not required in the manufacturing process. Therefore, the time and labor required for manufacturing can be reduced, and the substrate can be obtained relatively inexpensively. Further, since the surface is rougher than that of a mirror-like substrate, the problem of slippage during transportation is reduced. INDUSTRIAL APPLICABILITY The semiconductor single crystal substrate of the present invention is useful for an epitaxial wafer for an infrared or visible light emitting diode, particularly a GaAs single crystal substrate.

The epitaxial layer used in these light emitting diodes usually has a thickness of 10 μm or more. The present inventor has found that when an epitaxial layer having such a thickness is grown by the liquid phase growth method, the surface of the substrate crystal does not need to be a mirror surface or a state close to the mirror surface. By setting appropriate growth conditions in the liquid phase epitaxial growth method, the substrate of the present invention can be used effectively. Incidentally, the thickness of an epitaxial layer for an electronic device or the like grown by a vapor phase epitaxy method or a molecular beam epitaxy method is generally less than 10 μm, and in these growth methods, the unevenness of the substrate surface is faithful to the epitaxial growth layer. It tends to reflect on the surface. Therefore, a substrate having a rough surface cannot be used for the vapor phase growth method or the molecular beam epitaxial growth method.

[0009]

【Example】

Example 1 A 530 μm thick wafer was cut out by slicing a GaAs single crystal ingot grown by the boat method. Each wafer was processed into a circle having a diameter of 76 mm to obtain a substrate for liquid phase epitaxial growth. For slicing, an inner peripheral grindstone on which ordinary diamond abrasive grains were electrodeposited was used. However, the surface roughness was improved by improving the mechanical accuracy of each part of the slicer and optimizing the grain size and shape of the diamond abrasive grains. The surface roughness of the wafer after slicing was measured on a line having a length of 1 mm, one point approximately every 1 cm ^{2 of the} wafer surface. At 50% or more of the measurement points, the surface roughness was 1-4 μm. FIG. 1 shows an example of the measurement results of the surface roughness.

On this GaAs single crystal substrate, a Si-doped GaAs epitaxial layer for an infrared light emitting diode was formed by a liquid phase growth method. The thickness of the epitaxial layer was 180 μm in total for the p-type layer and the n-type layer, and the uniformity of the thickness was within ± 5% within the wafer surface and between the wafers. The surface of the epitaxial layer was in a good state without abnormal growth or the like. Before starting the growth, it is preferable to melt back the surface of the substrate (partially dissolve the substrate surface in the raw material solution). By optimizing the conditions for melt back, an epitaxial layer having a flat surface and a uniform thickness can be obtained. The light emitting diode manufactured from this epitaxial wafer had good electrical and optical characteristics.

(Example 2) G grown by the boat method
aAs single crystal ingot sliced to 370μm thick
Was cut out. Each wafer was processed into a circle having a diameter of 50 mm to obtain a substrate for liquid phase epitaxial growth. For slicing, an inner peripheral grindstone on which ordinary diamond abrasive grains were electrodeposited was used. However, the surface roughness was improved by improving the mechanical accuracy of each part of the slicer and optimizing the grain size and shape of the diamond abrasive grains. The surface roughness of the wafer after slicing was measured on a line having a length of 1 mm, one point approximately every 1 cm ^{2 of the} wafer surface. The surface roughness was 5 to 13 μm at 50% or more of the measurement points.

On this GaAs single crystal substrate, a Si-doped GaAs epitaxial layer for an infrared light emitting diode was formed by a liquid phase growth method. The thickness of the epitaxial layer was 180 μm in total for the p-type layer and the n-type layer, and the uniformity of the thickness was within ± 5% within the wafer surface and between the wafers. The surface of the epitaxial layer was in a good state without abnormal growth or the like. Before starting the growth, it is preferable to melt back the surface of the substrate (partially dissolve the substrate surface in the raw material solution). By optimizing the conditions for melt back, an epitaxial layer having a flat surface and a uniform thickness can be obtained. The light emitting diode manufactured from this epitaxial wafer had good electrical and optical characteristics.

(Example 3) Z grown by the boat method
An n-doped GaAs single crystal ingot was sliced to cut out a wafer having a thickness of 600 μm. Each wafer has a diameter of 76
This was processed into a circular shape of mm to obtain a substrate for liquid phase epitaxial growth. The surface roughness of the wafer was measured on a line having a length of 1 mm, one point approximately every 1 cm ^{2 of the} wafer surface. The surface roughness was 5 to 7 μm at 50% or more of the measurement points. An Al _0.65 Ga _0.35 As epitaxial layer having a thickness of 10 μm was formed on the substrate by a liquid phase growth method. The uniformity of the thickness of the epitaxial layer was within ± 3% within the wafer surface and between the wafers. The surface of the epitaxial layer was in a good state without abnormal growth or the like.

(Example 4) Z grown by the boat method
An n-doped GaAs single crystal ingot was sliced to cut out a 370 μm thick wafer. Each wafer has a diameter of 50
This was processed into a circular shape of mm to obtain a substrate for liquid phase epitaxial growth. The surface roughness of the wafer was measured on a line having a length of 1 mm, one point approximately every 1 cm ^{2 of the} wafer surface. The surface roughness was 9 to 16 μm at 50% or more of the measurement points. An Al _0.65 Ga _0.35 As epitaxial layer having a thickness of 10 μm was formed on the substrate by a liquid phase growth method. Epitaxial layer thickness uniformity is ± 3% within wafer plane and between wafers
Was within. The surface of the epitaxial layer was in a good state without abnormal growth or the like.

In the above four examples, it was found that the surface roughness of the substrate may be slightly larger when AlGaAs is grown than when GaAs is epitaxially grown. It can be estimated that AlGaAs has a property that the growth surface is more likely to be flatter than GaAs.

Comparative Example 1 The surface roughness of the substrate was 1 μm.
The number of wafers dropped during transportation was examined for various wafers less than m. 1000 wafers were held and transported with tweezers having a resinous tip for six levels of surface roughness between 0.2 μm and 2 μm. The results are as shown in FIG. 2. When the surface roughness was less than 1 μm, 3 to 6 sheets dropped, but when the surface roughness was 1 μm or more, no wafer dropped.

(Comparative Experimental Example 2) Surface roughness of 1 μm to 3
Using various types of wafers having a thickness of about 20 μm,
A μm GaAs epitaxial layer was grown. 10 levels for each of 10 levels with a surface roughness between 1 μm and 30 μm.
Using zero substrates, the relationship between the surface roughness of the substrate and the degree of occurrence of surface abnormality of the grown epitaxial layer was examined. The results are as shown in FIG. 3. When the surface roughness was 20 μm or less, the occurrence of abnormalities on the epitaxial layer surface was small, but when it exceeded 20 μm, the occurrence of abnormalities increased rapidly. 1 μm
Above the range of less than 10 μm, the occurrence of abnormalities was particularly small.

[0018]

The compound semiconductor single crystal substrate of the present invention
Surface roughness of 1 μm or more and 20 μm or less, preferably 1 μm
Since it is not less than 10 μm, lapping and polishing steps are unnecessary in the manufacturing process. Therefore, it is possible to prevent falling due to slip when transporting the substrate,
It is possible to provide a substrate for liquid phase epitaxial growth relatively inexpensively.

[Brief description of the drawings]

FIG. 1 is a graph showing an example of the surface roughness of a compound semiconductor single crystal substrate of the present invention.

FIG. 2 is a graph showing experimental results of the surface roughness of a substrate and the number of dropped substrates.

FIG. 3 is a graph showing the relationship between the surface roughness of a substrate and the number of abnormalities on the surface of an epitaxial layer.

Claims (3)

(57) [Claims] 1. The surface roughness of one point per 1 cm ^{2 of the} substrate surface is 1 μm at least 50% of the measured value on a 1 mm line.
After slicing the single crystal ingot so as to be in the range of 20 μm or less, an epitaxial layer is formed on the substrate surface without polishing the substrate surface to a mirror-like shape. Liquid phase epitaxial growth method. 2. The surface roughness is measured on a 1 mm line at one point for each 1 cm ^{2 of the} substrate surface.
A semiconductor single crystal substrate for liquid phase epitaxial growth, wherein 0% or more is in the range of 1 μm to 10 μm, the substrate is GaAs, and the epitaxial layer on the substrate is GaAs. 3. The compound semiconductor single crystal substrate according to claim 2, which is used as a substrate for an epitaxial wafer for an infrared or visible light emitting diode.