JPH0637024A - Compound semiconductor single-crystal substrate - Google Patents

Abstract

PURPOSE:To prevent a substrate from sliding during transportation by measuring surface roughness for a point of a specific length in every specified area on a substrate surface and limiting the measured values on a line of a specified measuring length to a specified range of values. CONSTITUTION:A GaAs single-crystal ingot, grown by a boat method, is sliced to obtain wafers of 530 pro in thickness. Each wafer is processed into a circular substrate in 76mm in dia. for liquid phase epitaxial growth. An inner diameter saw wheel having ordinary diamond abrasive grains electrodeposited is used for the slicing; however, the surface roughness is improved by improving the mechanical accuracy of each part of the slicer and further optimizing the size and shape of diamond grain. The surface roughness of a sliced wafer is measured on a line of 1mm in length in almost every area of 1cm<2> on the wafer surface. The surface roughness shall be within the range of from 1-4mum to 20mum at 50% or more of the measured points.

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, a substrate having a mirror-polished surface has been used as a substrate for epitaxial growth of compound semiconductors. The surface roughness is generally less than 1 μm per 1 mm line. Such a mirror-like or near-mirror-like substrate can be obtained by slicing a single crystal ingot, then circularly processing if necessary, and lapping the surface thereof and polishing if 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, thickness uniformity, and stability of electro-optical characteristics of the epitaxial layer grown thereon are not impaired.

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

[0004]

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

[0005]

The compound semiconductor single crystal substrate for liquid phase epitaxial growth according to the present invention has a surface roughness of 1 μm or more and 20 μm or less per 1 mm line, preferably 1 μm or less.
It is characterized in that it is 1 μm or more and 10 μm or less for each mm line. The substrate is GaAs. Furthermore, it is characterized by being used as a substrate of an epitaxial wafer for infrared or visible light emitting diodes. 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 a line having a length of 1 mm is measured, the height difference is between the highest part and the lowest part.

The surface roughness is measured on the surface of the substrate at a point of about 1 cm ² and 50% of the values measured at each point are measured.
% Or more is 1 μm or more and 20 μm or less, preferably 1 μm or more and 10 μm or less.

[0007]

[Function] Substrate surface roughness is 1 μm or more per 1 mm line 2
Since it is 0 μm or less, preferably 1 μm or more and 10 μm or less, lapping and polishing are unnecessary in the manufacturing process. Therefore, the time and effort required for manufacturing can be reduced, and the substrate can be obtained at a relatively low cost. Further, since the surface is rougher than that of the mirror-like substrate, the problem of slippage during transportation is reduced. INDUSTRIAL APPLICABILITY The semiconductor single crystal substrate of the present invention is useful as an infrared or visible light emitting diode epitaxial wafer, particularly a GaAs single crystal substrate.

The epitaxial layers used in these light emitting diodes usually have a thickness of 10 μm or more. The present inventor has found that when the epitaxial layer having such a thickness is grown by the liquid phase epitaxy method, the surface of the substrate crystal does not need to be a mirror surface or a state close to a mirror surface. The substrate of the present invention can be effectively used by setting appropriate growth conditions in the liquid phase epitaxial growth method. By the way, the thickness of an epitaxial layer for an electronic device or the like grown by a vapor phase growth method or a molecular beam epitaxial growth method is generally less than 10 μm. 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 GaAs single crystal ingot grown by the boat method was sliced to cut a wafer having a thickness of 530 μm. Each wafer was processed into a circle having a diameter of 76 mm to obtain a substrate for liquid phase epitaxial growth. For the slicing, an inner peripheral edge grindstone in 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 sliced wafer was measured on a line having a length of 1 mm, one point for each approximately 1 cm ^{2 of the} wafer surface. The surface roughness was 1 to 4 μm at 50% or more of the measurement points. An example of the measurement results of the surface roughness is shown in FIG.

An Si-doped GaAs epitaxial layer for an infrared light emitting diode was formed on this GaAs single crystal substrate by a liquid phase growth method. The total thickness of the epitaxial layer was 180 μm for the p-type layer and the n-type layer, and the thickness uniformity 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. Before the growth is started, it is preferable to melt back the surface of the substrate (partially dissolve the surface of the substrate in the raw material solution). By optimizing the meltback conditions, 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
Sliced aAs single crystal ingot and thickness 370μm
The wafer 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 the slicing, an inner peripheral edge grindstone in 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 sliced wafer was measured on a line having a length of 1 mm, one point for each approximately 1 cm ^{2 of the} wafer surface. The surface roughness was 5 to 13 μm at 50% or more of the measurement points.

An Si-doped GaAs epitaxial layer for an infrared light emitting diode was formed on this GaAs single crystal substrate by liquid phase epitaxy. The total thickness of the epitaxial layer was 180 μm for the p-type layer and the n-type layer, and the thickness uniformity 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. Before the growth is started, it is preferable to melt back the surface of the substrate (partially dissolve the surface of the substrate in the raw material solution). By optimizing the meltback conditions, 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 a wafer having a thickness of 600 μm. Each wafer has a diameter of 76
A substrate for liquid phase epitaxial growth was obtained by processing into a circle of mm. The surface roughness of the wafer was measured on a line having a length of 1 mm, one point for each approximately 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 this substrate by liquid phase epitaxy. 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.

(Example 4) Z grown by the boat method
An n-doped GaAs single crystal ingot was sliced to cut a wafer having a thickness of 370 μm. 50 for each wafer
A substrate for liquid phase epitaxial growth was obtained by processing into a circle of mm. The surface roughness of the wafer was measured on a line having a length of 1 mm, one point for each approximately 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 this substrate by liquid phase epitaxy. Epitaxial layer thickness uniformity is within ± 3% between wafer surfaces
It was within. The surface of the epitaxial layer was in a good state without abnormal growth.

In the above four examples, it was found that the surface roughness of the substrate may be slightly rougher when growing AlGaAs than when epitaxially growing GaAs. It can be inferred that the growth surface of AlGaAs is flatter than that of GaAs.

(Comparative Experimental Example 1) The surface roughness of the substrate is 1 μm.
With respect to various wafers of less than m, the number of wafers dropped during transportation was examined. 1000 wafers each of 6 levels having a surface roughness of 0.2 μm to 2 μm were held and transported by tweezers having a resinous tip. The results are as shown in FIG. 2. When the surface roughness was less than 1 μm, 3 to 6 sheets were dropped, but when the surface roughness was 1 μm or more, the wafer was not dropped.

(Comparative Experimental Example 2) The surface roughness is 1 μm to 3 μm.
Using various types of 0 μm wafers as substrates, a thickness of about 20
A μm GaAs epitaxial layer was grown. 10 for each of 10 levels of surface roughness between 1 μm and 30 μm
Using 0 substrates, the relationship between the surface roughness of the substrate and the degree of occurrence of surface abnormality in the grown epitaxial layer was investigated. The results are shown in FIG. 3. When the surface roughness was 20 μm or less, the occurrence of abnormalities on the surface of the epitaxial layer was small, but when the surface roughness exceeded 20 μm, the occurrence of abnormalities increased rapidly. 1 μm
In the above range of less than 10 μm, the occurrence of abnormalities was particularly small.

[0018]

The compound semiconductor single crystal substrate of the present invention is
Surface roughness is 1 μm or more and 20 μm or less, preferably 1 μm
Since it is 10 μm or less, the steps of lapping and polishing are unnecessary in the manufacturing process. Therefore, it is possible to prevent the substrate from dropping due to slippage during transportation,
It is possible to provide a liquid phase epitaxial growth substrate at a relatively low cost.

[Brief description of drawings]

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

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

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

Claims (4)

[Claims] 1. The surface roughness is measured on a line of 1 mm at every 1 cm ^{2 of the} substrate surface, and 50% or more of the measured values at each measurement point are in the range of 1 μm or more and 20 μm or less. A compound semiconductor single crystal substrate for liquid phase epitaxial growth, characterized by: 2. The surface roughness is measured on a line of 1 mm for each approximately 1 cm ^{2 of the} substrate surface, and 50% or more of the measured values at each measurement point are in the range of 1 μm or more and 10 μm or less. A compound semiconductor single crystal substrate for liquid phase epitaxial growth, characterized by: 3. The compound semiconductor single crystal substrate according to claim 1, wherein the substrate is GaAs. 4. A substrate for an epitaxial wafer for an infrared or visible light emitting diode.
The compound semiconductor single crystal substrate according to [4].