JPH03193699A - Wafer cutting pretreatment method for gallium phosphide single crystal - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a pretreatment method for cutting out a wafer of gallium phosphide single crystal, which serves as a substrate for a light emitting diode.

(Prior art) Light emitting diodes (hereinafter abbreviated as LED) have characteristics as solid-state devices such as small size, light weight, low voltage operation, high reliability, and long life.They also come in a variety of colors such as red, orange, yellow, and green. Therefore, they are used in all fields from home appliances to information industry equipment as small display lamps and numeric character display devices.

Gallium phosphide (hereinafter abbreviated as GaP) single crystal is used as a substrate for LED elements. GaP LED elements are usually produced by slicing a single crystal ingot grown by the liquid encapsulation drawing method (hereinafter abbreviated as LEC method) into wafers to form a substrate, making the surface of the substrate mirror-like by etching, etc., and then epitaxially growing it. A thin film is deposited on the surface of the substrate using a method.

The product is manufactured by assembling it in several more steps.

By the way, when a wafer is made to have a mirror surface by etching or the like, a problem may arise in that the center of the wafer is concave and the mirror surface cannot be obtained. This is thought to be because macroscopic strain due to internal stress remaining inside the single crystal ingot after growth is released during wafer fabrication.

For example, a GaP single crystal ingot grown by the normal LEC method can be directly oriented with orientation <
A wafer having a flat surface of 111> is cut out, and this wafer is coated with aqua regia (HCI:HNO).

= 3:1) at 60°C for 12 minutes, 50 μm from the top surface of the wafer is etched off, and the surface (
111) is in a mirror state. However, during the same process, the central part of the mirror surface of most wafers is etched approximately 20 μm more than the peripheral part, resulting in a depressed state. This is due to the fact that during GaP single crystal growth, strain occurs due to the temperature gradient between the center and the periphery, and although some of the strain generates dislocations and releases the strain, other parts of the strain become urethane-like. Even after cutting, distortion due to residual stress remains. Therefore, when etching a wafer, there is a difference in the etching rate between the center and the periphery, which is thought to cause a depression near the center.

In order to solve the above problems, known methods to alleviate the residual internal stress in GaP single crystal ingots include increasing the single crystal growth time and slowing down the cooling rate after single crystal growth as much as possible. Ta.

(Problem to be solved by the invention) However, in this method of increasing the time to grow a single crystal or slowing down the cooling rate after growth, the pulling furnace is restricted for a long time to obtain one single crystal ingot. There was a problem in that the operating rate of the furnace deteriorated.

An object of the present invention is to provide a pretreatment that solves the above problems and efficiently improves the quality characteristics of GaP single crystals.

(Means for Solving the Problems) In order to achieve the above object, the present inventors conducted heating and cooling at a temperature of 900 to 1000° C. for 50 hours or more before cutting a wafer from the produced gallium phosphide single crystal ingot. This discovery led to the present invention.

In the examples described later, the heat treatment was performed in a nitrogen gas atmosphere, but the heat treatment may be performed in a gas of a compound containing phosphorus, a simple phosphorus gas, another inert gas, or the atmosphere.

(effect) Hereinafter, the effects of the present invention will be explained.

As is clear from Table 1 below, if the heat treatment temperature of the GaP single crystal ingot is less than 900°C, there is no effect of releasing residual stress (Comparative Example 2.3), and on the other hand, if it exceeds 1000°C, the GaP single crystal ingot The surface of the ingot decomposes, which is unfavorable for obtaining a high-quality product (Comparative Example 4).

If the heat treatment time is less than 50 hours, there is no effect of releasing residual stress (Comparative Examples 1 and 3).

The surface of the gallium phosphide single crystal ingot used in the present invention is preferably ground into a cylindrical shape (Example 2), but may be left as it is grown (Example 1).

(Example 1) Diameter 5 grown by pulling in direction <111> by LEC method
A single crystal ingot of 6nn, length 84mm, and weight 812g was heated to 1.7Q of nitrogen gas without grinding it into a cylindrical shape.
Heat treatment is performed at 990° C. for 51 hours in a heating furnace with separate flow. After the heat treatment is completed, the single crystal ingot is slowly cooled to room temperature and taken out.

Next, the outer periphery of the single crystal ingot was cylindrically ground, and then wafers with a thickness of 300 μm having a plane orientation of <111> were cut out using a diamond blade inner peripheral blade cutting device. :llN0
．． =3: Etching was performed by soaking in 1) for 12 minutes. After the etched wafers were washed with water and dried, the surface condition was visually inspected under fluorescent light.
The test results are for 49 out of 49 gold wafers (11
In case 1), a mirror-like product without a depression near the center was obtained.

(Example 2) Diameter 5 grown by pulling in direction <111> by LEC method
A single crystal ingot with a length of 6 Fm, a length of 84 Mn, and a weight of 810 g was ground into a cylindrical shape, and heat treated at 905°C for 50 hours in a heating furnace where nitrogen gas was flowed at 1°7Q/minute, and the heat treatment was completed. Thereafter, the single crystal ingot was slowly cooled to room temperature and taken out. After cylindrical grinding the outer periphery of the single crystal ingot taken out again, a diamond blade inner circumferential blade cutting device was used to cut the single crystal ingot to a thickness of 300 μm with the plane in the direction <111> as a plane.
The wafer was cut out. These wafers were etched in the same manner as in Example 1, and the surface condition was visually inspected. The inspection results showed that the surface (111) of all of the 49 wafers was a mirror surface with no depression near the center. .

(Comparative Example 1) Diameter 5 grown by pulling in direction <111) by LEC method
A single crystal ingot with a diameter of 6 nn, a length of 85 rrn, and a weight of 820 g was heat treated at 990°C for 24 hours in the same manner as in Example 1. After the heat treatment was completed, it was shaped into a wafer and etched in the same manner as in Example 1. Visually inspected. The inspection results showed that 16 out of 49 wafers, or 32.7%, were
The area near the center of (111) was depressed compared to the periphery and was not in a mirror state. The depth was measured with a micrometer and was 20 to 29 μm.

Table 1 shows the results of Comparative Examples 2 to 4, in which wafers were prepared in the same manner with different heat treatment temperatures and times, and the wafer surfaces were observed after etching.

The results of Comparative Example 5 without heat treatment are also shown in the same table.

(Left below) From the table above, it is seen that in Examples 1 and 2, which were subjected to the heat treatment of the present invention, there was no occurrence of depressions on the wafer surface, whereas in Comparative Examples 1 to 5, excluding Comparative Example 4, Occurrence of dents was observed. Comparative Example 2 compared to Comparative Example 1 shows that the occurrence rate of this depression is more affected by heating temperature than heating time.
, 3. In the case of Comparative Example 4, in which the heating temperature was 100° C. higher than the range of the present invention and the heating time was within the range of the present invention, it was found that there was a problem with the quality of the product itself, not just the problem of depressions. It can be seen that depressions are generated on the wafer surface of the conventional method in which no heat treatment is performed.

(Effects of the Invention) According to the present invention, in order to remove the residual strain in the GaP single crystal, GaP
The residual strain in the single crystal can be removed and its quality characteristics can be efficiently improved, so it has a great practical effect.

-And more-

Claims (1)

[Claims] 1. A wafer cutting pretreatment method for gallium phosphide single crystal, which comprises heating and cooling a gallium phosphide single crystal ingot at a temperature of 900 to 1000° C. for 50 hours or more prior to wafer cutting.