JPS6233784A - Method for processing compound crystal - Google Patents

Abstract

PURPOSE:To obtain a strain-free mirror finished surface having superior flatness by polishing with high work efficiency when the surface of a crystal of a compound such as CdTe or HgCdTe is polished, by carrying out mechanochemical polishing with an aqueous NaOCl soln. as an etchant on the surface of polishing cloth. CONSTITUTION:When the surface of a crystal of a compound such as CdTe or HgCdTe is polished, a (111) face wafer of the crystal is sliced off beforehand with a wire and both surfaces of the wafer are lapped by about 100mum to remove slicing strain layers and unevenness in shape and to obtain satin finished surfaces having 1mum surface roughness. Mechanochemical polishing is then carried out with an aqueous NaOCl soln. on the surface of polishing cloth having the structure of foamed polyurethane to lower the surface roughness and to relieve the working strain. Thus, a smooth mirror finished surface having <=20Angstrom surface roughness and a strain-free mirror finished surface having <=2mum planeness are obtd.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is directed to compound crystals used as detector materials for infrared rays and gamma rays, such as cadmium tellurium (CdT).
e) Crystals and mercury cadmium telluride ("'1""XCdx
The present invention relates to a processing method for finishing the surface of a (Te,

(Prior art) Ca're crystals and HgCdTe crystals are exposed to infrared rays and gamma
For use as a line detector, for example, the dimensions should be 1@60
It is required to process the thin plate into a thin plate with a length of about 800 μm and a thickness of about 10 am, and to finish the processed surface into a flat, distortion-free mirror surface that does not interfere with the incidence of infrared rays or gamma rays. However, CdTe crystals and H+zCdTe crystals have only recently been artificially developed, and the elements forming the crystals are all harmful substances, making them difficult to handle. There has been very little research on this, and even if it has been studied, not only are dangerous processing operations performed, but the accuracy is also quite poor.

For example, the Academic Press in New York, USA (
Semiconductors and Semi Metals, published by Acadnomic Press.
After mechanically lapping the surface of a wafer cut from a π, HgCdTe crystal as described on page 246 of ``Torsand Semimetals'', bromine (Br) and methanol (C1 (
, OH) (volume ratio of 1220% Br) is used to obtain a distortion-free mirror surface.

(Problems to be solved by the invention) In this method, processing is performed only by the chemical action of the etching solution, which impairs the flatness of the processed surface, and the bromine in the etching solution is a highly toxic substance. Moreover, since tutanol is a flammable organic solvent, it has drawbacks such as poor workability and extremely complicated waste liquid treatment after use.

An object of the present invention is to provide a method for processing a compound crystal, which eliminates such conventional drawbacks and enables distortion-free mirror processing with excellent workability and good flatness.

(Another means to solve the problem) According to the present invention, mechanochemical boring is carried out on the surface of the polishing cloth by using a weakly alkaline sodium hypochlorite (N, 10 (J)) aqueous solution as the etching solution. By carrying out this process, a method for processing a compound crystal is obtained, which is characterized in that deterioration in the flatness of the processed surface and inconvenience in the workability of the etching solution are eliminated.

(Function) The present invention solves the problems of the prior art by adopting the above-described configuration. By pressing the crystal wafer onto the surface of the polishing cloth, making a relative sliding movement, and processing while supplying an Na0C1-based aqueous solution as a polishing liquid between the two, it is possible to perform etching using a conventional mixed solution of bromine and methanol. The inconvenience caused by poor flatness of the machined surface and the use of dangerous chemicals is eliminated, and a flat, distortion-free mirror surface and safe polishing are achieved.

(Example) Example 1゜) TgCdTe crystal aggregate (diameter 10fi, length 2Q
**) to a thickness of 1. O
Cut out a wafer with dimensions H. The cutting strain layer and the irregularities on both surfaces of this wafer were removed by roughing for approximately 10 minutes.
0.11m is removed to create a flat matte surface with a surface roughness of 1μm. This lapping is performed on the Sn plate using a lapping agent that is a mixture of SiC abrasive grains with a particle size of 5 μm and water, for example. The surface roughness and processing distortion caused by lapping are removed using a Na0C1 aqueous solution (for example, a solution prepared by diluting approximately 36 g of Insec NIBJ, a product of Fujimi Abrasive Industries Co., Ltd., in 1 liter of pure water) to form a polyurethane foam structure. Polishing cloth (
For example, the product name of Fujimi Abrasive Industry Co., Ltd. [Surfing 0
Approximately 20μ by mechanochemical boriding on the 18J) surface.
m remove. This mechanochemical boring surface had a smooth mirror surface with a surface roughness of 20 or less and a flatness of 2 μm or less, and the entire surface of the wafer could be sufficiently used as a manufacturing surface for an infrared detector. HgCdTe crystals do not have an etchant to check processing strain, so we prototyped an infrared detector and evaluated the electrical characteristics. As a result, the mechanochemical boring surface was found to have the same performance as the etched surface. It is thought that there are.

Note that etching using only the Na0C1 aqueous solution has the disadvantage that an oxide film is completely formed on the surface, resulting in a poor interface.

On the other hand, when a roughened wafer processed in the same manner was etched using a conventional mixed solution of bromine and methanol (bromine:methanol = 1:4) with a gold piece and about 20 μm removed, the surface had a surface roughness of 0.01 μtn or less. A smooth mirror surface and a distortion-free surface with little processing distortion were obtained, but the flatness was as large as about 10 μm. This processed surface can be used for a local area, but cannot be used for the entire wafer, and is therefore unsuitable for manufacturing a detector.

Example 2 After cutting a (111)-plane wafer with a thickness of 1 female from a CdTe crystal material (diameter 10, length 20 fl) using a wire saw, the cutting strain layer remaining on both surfaces and the shape Approximately 100 μm of unevenness is removed by lapping to create a flat pear-grain surface with a surface roughness of 1 μm. This lapping is performed on a glass plate using, for example, a lapping agent that is a mixture of WA abrasive grains with a particle size of 5 μm and water. Processing distortion and surface irregularities caused by lapping are removed by about 20 μm by carboriding using a combination of Na0C1-based aqueous solution and foamed polyurethane cloth. This mechanochemically polished surface has a smooth mirror surface with a surface roughness of 20^ or less and a flatness of 2 μm or less.
, :H, O = 2:2:3 was used for etching at room temperature for 1 minute. As a result, no defects due to processing were observed. Therefore, this processed surface could be sufficiently used as a substrate for a gamma ray detector or for growing an HgCdTe thin film.

In the above example, no mention was made of the plane orientation of the HgCdTe crystal, but (100) and (010).

A distortion-free mirror surface has been achieved not only for the (111) plane but also for other planes.

Furthermore, in the above embodiment, the cases where the composition was x=0.2 and x=1 were described, but the crystal force in the range of x=0 to 1.0, that is, the crystals from HgTe to CdTe, is the same. Needless to say, a distortion-free mirror surface can be achieved.

It is thought that this processing method can also be applied to II-VI group compounds other than the above-mentioned crystals, such as Zn5e, CdSe, and HgSe, and ■-V group compounds having the same crystal structure, such as InP and GaP.

(Effect of the invention! 1:) According to the compound crystal processing method of the present invention, a NaCl-based aqueous solution that is easy to handle and safe at 4V is used as the polishing liquid, and by sliding it on the polished Y cross surface, This eliminates the deterioration of flatness and dangerous operations that occur when etching with a mixed solution of bromine and methanol, resulting in safe polishing operations and high-precision wafers. Extremely effective for processing.

Claims (1)

[Claims] In a method of processing a workpiece by pressing the workpiece onto the surface of an abrasive cloth and supplying a polishing liquid to the surface of the workpiece while causing the two to slide relative to each other, an abrasive cloth having a foamed polyurethane structure and hypochlorous acid are used. A method for processing compound crystals, characterized by distortion-free mirror polishing using a combination of sodium-based aqueous solutions.