A polishing method for a cadmium zinc telluride wafer

Abstract

The application belongs to the technical field of wafer processing, and discloses a polishing method of a cadmium zinc telluride wafer. The method comprises the following steps: cutting a crystal bar into a wafer; etching a single crystal area on a 111B surface of the cut wafer, and recording the position of the single crystal area; rough polishing the 111B surface and a 111A surface of the etched wafer; first fine polishing the 111B surface of the rough polished wafer; using a wafer scriber to cut out the single crystal area of the first fine polished wafer according to the recorded position of the single crystal area; second fine polishing the 111B surface of the single crystal area of the wafer; and cleaning. The polishing method is simple in process and convenient to operate, and the edge collapse and TTV problems of the prepared cadmium zinc telluride wafer are obviously improved.

Description

Technical Field

[0001] This invention belongs to the field of wafer processing technology and relates to a polishing method for cadmium zinc telluride wafers. Background Technology

[0002] Cadmium zinc telluride (Cd) 1-x Zn x Te (CZT) is a novel group II-VI compound semiconductor material, synthesized and grown from high-purity Cd, Zn, and Te materials through high-temperature chemical synthesis and growth. Due to its unique physical properties (high resistivity and a large bandgap: the bandgap continuously varies from 1.4 eV to 2.26 eV with varying zinc doping content), it exhibits excellent detection capabilities for X-rays and gamma rays at room temperature. CZT has broad application prospects in radiation detection and imaging fields such as medicine, nuclear detection, security inspection, nuclear industry, and astronomical detection. Furthermore, in infrared detection, CZT is the most suitable epitaxial substrate material for MCT (methyl-Dextrinsic coulombic radiometer).

[0003] Current research on CZT wafer fabrication is limited. When using CZT wafers as detector substrates, the commonly used process involves first directional slicing, chamfering, grinding, polishing, and cleaning of the CZT, followed by subsequent processing. Surface flatness is a key indicator of substrate performance. Currently, this process commonly suffers from edge collapse and poor TTV (Transient Tolerancing Value) in CZT wafers. Therefore, there is an urgent need to develop a polishing process to alleviate edge collapse and improve wafer quality. Summary of the Invention

[0004] In view of the above-mentioned problems in the prior art, the purpose of the present invention is to provide a polishing process for cadmium zinc telluride wafers that can effectively alleviate wafer edge collapse and improve wafer quality.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A polishing method for cadmium zinc telluride wafers includes the following steps: (1) Cut the crystal rod into wafers; (2) Etch the 111B surface of the wafer cut in step (1) to form a single crystal region, and record the position of the single crystal region; (3) Rough polishing is performed on both the 111B and 111A surfaces of the wafer after etching in step (2); (4) Perform a first fine polishing on the 111B surface of the wafer after rough polishing in step (3); (5) According to the position of the single crystal region recorded in step (2), use a dicing machine to dice out the single crystal region of the wafer after the first fine polishing in step (4); (6) Perform a second fine polishing on the 111B surface of the single crystal region obtained in step (5); (7) Cleaning.

[0006] Preferably, in step (1), the wafer is cut out and ground into round or square pieces using a chamfering machine. Cutting the wafer into uniform sizes helps improve polishing efficiency and saves costs.

[0007] Preferably, a mixed etching solution is used to etch single-crystal regions onto the wafer surface; the mixed etching solution is a mixture of lactic acid, nitric acid, and hydrofluoric acid; the volume ratio of lactic acid, nitric acid, and hydrofluoric acid in the mixed etching solution is 15~25:1~8:1~8; wherein the mass concentration of lactic acid used in the preparation is 85.0~90.0%, the mass concentration of nitric acid is ≥90.0%, and the mass concentration of hydrofluoric acid is 40.0~50.0%.

[0008] Preferably, in step (2), the location of the single crystal region is recorded by taking pictures after etching.

[0009] Preferably, in step (3), a double-sided grinding and polishing machine is used for rough polishing.

[0010] More preferably, during the rough polishing process: the polishing speed is 30~60 rpm, the polishing pressure is 500~1000 N, and the rough polishing time is 90~120 min.

[0011] Preferably, in step (4), a single-sided grinding and polishing machine is used for the first fine polishing.

[0012] More preferably, in step (4), during the first fine polishing process: the polishing speed is 30~60rpm, the polishing pressure is 500~1000N, and the polishing time for the first fine polishing is 5~10min.

[0013] Preferably, in step (5), the spindle speed of the dicing machine is 26000r~30000r and the feed speed is 0.04~0.06mm / s.

[0014] Preferably, in step (6), a single-sided grinding and polishing machine is used for a second fine polishing.

[0015] More preferably, in step (6), during the second fine polishing process: the polishing speed is 30~60rpm, the polishing pressure is 500~1000N, and the polishing time for the second fine polishing is 1~5min.

[0016] Preferably, step (3) rough polishing is performed to a flatness of 3~5μm; step (4) first fine polishing is performed to a flatness of 2~4μm; and step (6) second fine polishing is performed to a flatness of 1~3μm.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The polishing method of this invention is simple and easy to operate, and the edge collapse and TTV problems of the prepared cadmium zinc telluride wafers are significantly improved. Detailed Implementation

[0018] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments in the specification, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0019] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0020] Example 1 This embodiment discloses a polishing method for cadmium zinc telluride wafers, including the following steps: (1) Roll the crystal rod into a standard 4-inch size, attach the crystal rod to the graphite strip with soft glue, cut it into slices with a multi-wire cutter, and then bevel the edges of the 4-inch wafer.

[0021] (2) A single crystal region is etched out on the 111B facet of the crystal using a mixed etching solution; the mixed etching solution is a mixture of lactic acid, nitric acid and hydrofluoric acid; the volume ratio of lactic acid, nitric acid and hydrofluoric acid in the mixed etching solution is 22:4:3; wherein the mass concentration of lactic acid used for preparation is 85.0~90.0%, the mass concentration of nitric acid is ≥90.0% and the mass concentration of hydrofluoric acid is 40.0~50.0%.

[0022] After etching, the location of the single crystal region is recorded by taking pictures.

[0023] (3) Use a double-sided grinding and polishing machine to rough polish the 111B and 111A surfaces of the wafer. The polishing speed is 60 rpm, the polishing pressure is 1000 N, the rough polishing time is 120 min, and the flatness is 4 μm. (4) Use a single-sided polishing machine to perform the first fine polishing on the 111B side of the wafer after rough polishing. The polishing speed is 40 rpm, the polishing pressure is 600 N, the polishing time is 120 min, the polishing speed ratio is 2:1, and the polishing speed ratio is the comparison value of the upper and lower disk speeds during the polishing process, until the flatness is 2 μm.

[0024] (5) Use a dicing machine to dic the single crystal region of the wafer. The spindle speed of the dicing machine is 26000r and the feed speed is 0.06mm / s.

[0025] (6) Use a single-sided polishing machine to perform a second fine polishing on the 111B surface of the single crystal area marked out on the wafer. The polishing speed is 40 rpm, the polishing pressure is 600 N, the polishing time is 2 min, and the flatness is 1 μm.

[0026] (7) Cleaning.

[0027] Example 2 This embodiment discloses a polishing method for cadmium zinc telluride wafers, including the following steps: (1) Roll the crystal rod into a standard 3-inch size, attach the crystal rod to the graphite strip with soft glue, cut it into slices with a multi-wire cutter, and then bevel the edges of the 3-inch wafer.

[0028] (2) A single crystal region is etched out on the 111B facet of the crystal using a mixed etching solution; the mixed etching solution is a mixture of lactic acid, nitric acid and hydrofluoric acid; the volume ratio of lactic acid, nitric acid and hydrofluoric acid in the mixed etching solution is 25:4:1; wherein the mass concentration of lactic acid used for preparation is 85.0~90.0%, the mass concentration of nitric acid is ≥90.0% and the mass concentration of hydrofluoric acid is 40.0~50.0%.

[0029] After etching, the location of the single crystal region is recorded by taking pictures.

[0030] (3) Use a double-sided grinding and polishing machine to rough polish the 111B and 111A surfaces of the wafer. The polishing speed is 50 rpm, the polishing pressure is 800 N, the rough polishing time is 100 min, and the flatness is 4 μm.

[0031] (4) Use a single-sided polishing machine to perform the first fine polishing on the 111B side of the wafer after rough polishing. The polishing speed is 50 rpm, the polishing pressure is 800 N, the polishing time is 100 min, the polishing speed ratio is 3:1, and the polishing speed ratio is the comparison value of the upper and lower disk speeds during the polishing process, until the flatness is 3 μm.

[0032] (5) Use a dicing machine to dice the single crystal region of the wafer. The spindle speed of the dicing machine is 27000r and the feed speed is 0.05mm / s.

[0033] (6) Use a single-sided polishing machine to perform a second fine polishing on the 111B surface of the single crystal area marked out on the wafer. The polishing speed is 50 rpm, the polishing pressure is 800 N, the polishing time is 3 min, and the flatness is 2 μm.

[0034] Example 3 This embodiment discloses a polishing method for cadmium zinc telluride wafers, including the following steps: (1) Roll the crystal rod into a standard 4-inch size, attach the crystal rod to the graphite strip with soft glue, cut it into slices with a multi-wire cutter, and then bevel the edges of the 4-inch wafer.

[0035] (2) A single crystal region is etched out on the 111B facet of the crystal using a mixed etching solution; the mixed etching solution is a mixture of lactic acid, nitric acid and hydrofluoric acid; the volume ratio of lactic acid, nitric acid and hydrofluoric acid in the mixed etching solution is 20:6:1; wherein the mass concentration of lactic acid used for preparation is 85.0~90.0%, the mass concentration of nitric acid is ≥90.0% and the mass concentration of hydrofluoric acid is 40.0~50.0%.

[0036] After etching, the location of the single crystal region is recorded by taking pictures.

[0037] (3) Use a double-sided grinding and polishing machine to rough polish the 111B and 111A surfaces of the wafer. The polishing speed is 45 rpm, the polishing pressure is 600 N, the rough polishing time is 90 min, and the flatness is 5 μm.

[0038] (4) Use a single-sided polishing machine to perform the first fine polishing on the 111B side of the wafer after rough polishing. The polishing speed is 60 rpm, the polishing pressure is 1000 N, the polishing time is 100 min, the polishing speed ratio is 5:1, and the polishing speed ratio is the comparison value of the upper and lower disk speeds during the polishing process, until the flatness is 3 μm.

[0039] (5) Use a dicing machine to dic the single crystal region of the wafer. The spindle speed of the dicing machine is 29000r and the feed speed is 0.04mm / s.

[0040] (6) Use a single-sided polishing machine to perform a second fine polishing on the 111B surface of the single crystal area marked out on the wafer. The polishing speed is 60 rpm, the polishing pressure is 1000 N, the polishing time is 5 min, and the flatness is 3 μm.

[0041] Comparative Example 1 This comparative example is basically the same as Example 1, except that: There is no step (3).

[0042] Comparative Example 2 This comparative example is basically the same as Example 1, except that: There is no step (4).

[0043] Comparative Example 3 This comparative example is basically the same as Example 1, except that: There is no step (6).

[0044] Experimental data The polished cadmium zinc telluride wafers obtained in Examples 1-3 and Comparative Examples 1-3 were tested, and the data are shown in Table 1.

[0045] Table 1 As can be seen from Table 1, the surface polishing effect of Examples 1-3 is better than that of Comparative Examples 1-3. Regarding edge condition, Comparative Example 1 shows obvious edge chipping, while Examples 1-3 show only slight edge collapse or no edge collapse, and Comparative Examples 2 and 3 show edge collapse. Regarding thickness deviation (TTV), the embodiments of the present invention control it better, while the comparative examples show poorer results. Regarding surface condition, Examples 1-3 have no surface damage points and only a few scratches, while Comparative Examples 1-3 have surface damage points and multiple scratches.

[0046] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of the present invention.

Claims

1. A polishing method for cadmium zinc telluride wafers, characterized in that, Includes the following steps: (1) Cut the crystal rod into wafers; (2) Use a mixed etching solution to etch a single crystal region on the 111B surface of the wafer cut in step (1), and record the position of the single crystal region; the mixed etching solution is a mixed solution of lactic acid, nitric acid and hydrofluoric acid; in the mixed etching solution, the volume ratio of lactic acid, nitric acid and hydrofluoric acid is 15~25:1~8:1~8; wherein, the mass concentration of lactic acid used for preparation is 85.0~90.0%, the mass concentration of nitric acid is ≥90.0%, and the mass concentration of hydrofluoric acid is 40.0~50.0%; (3) The 111B and 111A surfaces of the wafer after etching in step (2) are rough polished to a flatness of 3~5μm; during the rough polishing process: the polishing speed is 30~60rpm, the polishing pressure is 500~1000N, and the rough polishing time is 90~120min. (4) Perform a first fine polishing on the 111B surface of the wafer after rough polishing in step (3) until the flatness is 2~4μm; (5) According to the position of the single crystal region recorded in step (2), use a dicing machine to dice out the single crystal region of the wafer after the first fine polishing in step (4); (6) Polish the 111B surface of the single crystal region obtained in step (5) for the second time until the flatness is 1~3μm; during the second polishing process: the polishing speed is 30~60rpm, the polishing pressure is 500~1000N, and the polishing time for the second polishing is 1~5min; (7) Cleaning.

2. The polishing method as described in claim 1, characterized in that, In step (3), a double-sided grinding and polishing machine is used for rough polishing.

3. The polishing method as described in claim 1, characterized in that, In step (4), a single-sided grinding and polishing machine is used for the first fine polishing.

4. The polishing method as described in claim 3, characterized in that, In step (4), during the first fine polishing process: the polishing speed is 30~60rpm, the polishing pressure is 500~1000N, and the polishing time for the first fine polishing is 5~10min.

5. The polishing method as described in claim 1, characterized in that, In step (5), the spindle speed of the dicing machine is 26,000 rpm to 30,000 rpm, and the feed rate is 0.04 to 0.06 mm / s.

6. The polishing method as described in claim 1, characterized in that, In step (6), a second fine polishing is performed using a single-sided grinding and polishing machine.

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