A polishing jig and a surface polishing method for large-size CdZnTe substrates

Abstract

This invention discloses a polishing fixture and a method for surface polishing large-size cadmium zinc telluride substrates. The polishing fixture is a ceramic disc with a central convex shape, and the polishing fixture transitions smoothly from the center to the periphery. The micro-convex fixture effectively controls the "edge collapse" phenomenon of the substrate, solving the problem of "thick in the middle and thin around the edges" surface shape that is easily formed during traditional polishing. This improves the surface flatness of the substrate, especially solving the problem of poor surface flatness in the processing of large-size cadmium zinc telluride substrates. This lays a good foundation for improving the yield of high-quality mercury cadmium telluride epitaxy, device interconnection, and detector performance consistency.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and in particular to a polishing fixture and a method for surface polishing large-size cadmium zinc telluride substrates. Background Technology

[0002] Cadmium zinc telluride (CZD) substrates, as compound semiconductors widely used in infrared detectors, are the preferred substrate material for high-performance mercury cadmium telluride (HCd) epitaxial films. The surface finish of the CZD substrate directly affects the quality of the HCd epitaxial film, which in turn affects the subsequent device fabrication process and performance. In particular, the surface flatness of the CZD substrate significantly affects the consistency of HCd infrared detector performance. On one hand, the surface flatness directly affects the thickness uniformity of the HCd epitaxial film, thus affecting the connectivity of device / circuit interconnects. Poor surface flatness can lead to some photosensitive elements and readout circuits failing to connect, and can also cause excessive stress and large deformation in some indium pillars, resulting in defect proliferation and performance degradation in the PN junction due to excessive stress. On the other hand, poor surface flatness can also alter the transmission characteristics of optical signals on the device, affecting the device's responsivity and optical crosstalk. Therefore, obtaining CZD substrates with high surface flatness is of great significance for improving the performance of infrared detectors. Especially with the continuous increase in the number of pixels and the continuous reduction in pixel size of infrared detectors, the integration density is becoming increasingly higher, making large-size, high-surface-quality mercury cadmium telluride (HCd) epitaxial films a key foundation. As the substrate material for HCd epitaxial films, zinc cadmium telluride (ZZC) places even higher demands on its surface flatness. Ensuring uniform thickness of HCd material to meet the application requirements of next-generation megapixel, highly integrated, high-performance, ultra-large-scale infrared focal plane array detectors has become an urgent problem to be solved. Summary of the Invention

[0003] This invention provides a polishing fixture and a method for surface polishing large-size zinc zinc cadmium substrates to solve the problem of "collapsed edges" on the substrate surface after polishing in the prior art, which makes it difficult to ensure high surface flatness.

[0004] In a first aspect, the present invention provides a polishing fixture for polishing the surface of a large-size cadmium zinc telluride substrate, comprising: the polishing fixture being a ceramic disc with a central protrusion, and the polishing fixture having a gentle transition from the central protrusion to the periphery; the height and diameter of the protrusion are both set according to the size of the cadmium zinc telluride substrate being polished.

[0005] Optionally, the height of the protrusion is 6 micrometers, and the diameter of the polishing fixture is 100-150 millimeters.

[0006] Optionally, when the size of the cadmium zinc telluride substrate is smaller than a preset threshold, the polishing fixture further includes: a circular carrier; the circular carrier is vacuum adsorbed onto the polishing fixture, and the cadmium zinc telluride substrate is bonded to the circular carrier.

[0007] Optionally, the preset threshold is 2.5 inches.

[0008] Optionally, the circular slide is a glass circular slide or a sapphire circular slide.

[0009] Secondly, the present invention provides a method for polishing a large-size cadmium zinc telluride substrate using any of the polishing fixtures described above, comprising:

[0010] The cadmium zinc telluride substrate to be polished is placed on the polishing fixture;

[0011] The cadmium zinc telluride substrate is polished according to a preset polishing process to obtain a cadmium zinc telluride substrate with a smooth surface.

[0012] Optionally, when the size of the zinc-cadmium telluride substrate is smaller than a preset threshold, the zinc-cadmium telluride substrate is bonded to a circular carrier, and the circular carrier is adsorbed onto the polishing fixture to polish the zinc-cadmium telluride substrate.

[0013] Optionally, the preset threshold is 2.5 inches.

[0014] Optionally, the circular slide is a glass circular slide or a sapphire circular slide.

[0015] Optionally, the cadmium zinc telluride substrate is less than 4 inches in size.

[0016] The beneficial effects of this invention are as follows:

[0017] The polishing fixture in this invention is a ceramic disc with a central convex shape, and the polishing fixture transitions smoothly from the central convex shape to the outer edge. The micro-convex fixture can effectively control the "edge collapse" phenomenon of the substrate, solving the problem of "thick in the middle and thin around the edges" surface shape that is easy to form during traditional polishing. This improves the surface flatness of the substrate, especially solving the problem of poor surface flatness in the processing of large-size zinc cadmium telluride substrates. This lays a good foundation for improving the yield of high-quality mercury cadmium telluride epitaxy, device interconnection, and detector performance consistency.

[0018] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0019] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0020] Figure 1 This is a schematic diagram of polishing a cadmium zinc telluride substrate using a micro-convex fixture provided in an embodiment of the present invention. Detailed Implementation

[0021] Cadmium zinc telluride (CZT) is a typical soft and brittle material with a Mohs hardness of approximately 0.8–1.5 and a critical shear stress of 0.1 MPa. These parameters are 6 and 19 times higher than those of Si substrates, respectively. This low hardness and critical shear stress result in CZT being both soft and brittle, making its machining difficult and complex. The low hardness of CZT leads to severe edge effects during polishing, resulting in a "bun-like" surface after polishing. This phenomenon worsens with increasing substrate size, leading to significant edge collapse and making it difficult to ensure surface flatness. To address this, this invention provides a polishing fixture with a centrally micro-convex structure to ensure surface flatness after polishing. The invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and do not limit the scope of the invention.

[0022] The first embodiment of the present invention provides a polishing fixture for polishing the surface of large-size cadmium zinc telluride substrates, see [link to relevant documentation]. Figure 1 The polishing fixture is a ceramic disc with a central protrusion, and the polishing fixture transitions smoothly from the central protrusion to the outer periphery; the height and diameter of the protrusion are set according to the size of the cadmium zinc telluride substrate being polished.

[0023] Specifically, through extensive experiments, this invention demonstrates that a polishing fixture with a protrusion height of 6 micrometers and a diameter of 100-150 millimeters can effectively achieve high surface flatness polishing on cadmium zinc telluride substrates up to 4 inches in size. Of course, in practice, those skilled in the art can make any adjustments according to actual needs, and this invention does not impose specific limitations in this regard.

[0024] In other words, the micro-convex fixture and corresponding polishing control in this embodiment of the invention effectively improve the overall stress distribution of the substrate during the polishing process, effectively control the "edge collapse" phenomenon of the substrate, and solve the problem of "thick in the middle and thin around the edges" surface shape that is easy to form during traditional polishing. This improves the surface flatness of the polished substrate, especially solving the problem of poor surface flatness of large-size zinc cadmium telluride substrates. This lays a good foundation for improving the yield of high-quality mercury cadmium telluride epitaxy, device interconnection, and detector performance consistency.

[0025] In specific implementation, when the size of the zinc cadmium telluride substrate is smaller than a preset threshold, the substrate is bonded by a circular carrier, and then the circular carrier is vacuum adsorbed onto the polishing fixture to achieve high surface flatness polishing of the substrate.

[0026] In other words, because the substrate size is smaller than the threshold, it is not easy to directly adsorb and fix the substrate onto the polishing fixture. Furthermore, if the substrate is placed directly on the polishing fixture, the entire substrate is located in the middle of the micro-convex fixture, resulting in excessively concentrated polishing pressure that cannot be evenly distributed on the substrate. Therefore, this invention innovatively proposes to first use a circular carrier to support the substrate, and then fix the circular carrier with the substrate attached to it onto the polishing fixture. Through the buffering and dispersing effect of large-sized circular carriers of different thicknesses, the polishing pressure is axially symmetrically and evenly distributed, and then evenly transmitted to the polishing substrate, thereby achieving a high surface flatness polishing treatment for the substrate.

[0027] In this embodiment of the invention, the preset threshold may be 2.5 inches, etc.

[0028] It should be noted that the circular substrate used in the embodiments of the present invention is a glass circular substrate or a sapphire circular substrate, etc.

[0029] This invention also provides a method for polishing a larger-sized cadmium zinc telluride substrate using any of the polishing fixtures described in the above embodiments, the method comprising:

[0030] The large-sized zinc-cadmium telluride substrate to be polished is directly adsorbed and placed on the polishing fixture;

[0031] The cadmium zinc telluride substrate is polished according to a preset polishing process to obtain a cadmium zinc telluride substrate with a smooth surface.

[0032] Specifically, in this embodiment of the invention, when the size of the zinc-cadmium telluride substrate is smaller than a preset threshold, the zinc-cadmium telluride substrate is bonded to a circular carrier, and the circular carrier is adsorbed onto the polishing fixture to polish the zinc-cadmium telluride substrate.

[0033] In this embodiment of the invention, the preset threshold is 2.5 inches. In this embodiment, the size of the cadmium zinc telluride substrate is less than 4 inches, and the diameter of the polishing fixture is 4 to 6 inches. Of course, those skilled in the art can set the substrate size and the diameter of the polishing fixture as needed during implementation, and this invention does not impose specific limitations on these settings.

[0034] See Figure 1 This invention employs a specially designed micro-convex polishing fixture and a corresponding polishing control method for polishing large-size cadmium zinc telluride (CZN) substrates. First, the CZN substrate to be polished is bonded to a circular carrier (2-6mm thick sapphire sheet or glass plate). The circular carrier is then adsorbed onto the micro-convex surface of the polishing fixture using vacuum adsorption. CZN substrates of 2.5 inches and larger can be directly adsorbed onto the micro-convex surface of the polishing fixture. The polishing fixture with the substrate adsorbed is placed vertically on the polishing disc of the polishing machine, and polishing parameters are set for surface polishing. During the transmission of polishing pressure to the CZN substrate, the central part experiences higher force, while the periphery experiences lower force, i.e., σ... c >σ e By using a micro-convex fixture, the force distribution on the substrate during the polishing process is adjusted, which can effectively improve the formation of new convex parts after polishing and further improve the thickness reduction rate and surface flatness of the original intermediate convex parts in the previous process. On the one hand, it improves the surface flatness of the substrate after polishing and effectively controls the "collapse" phenomenon that exists in the traditional polishing process. On the other hand, it can efficiently meet the performance index requirements and improve the polishing efficiency.

[0035] The following three specific examples will be used to illustrate the method described in the embodiments of the present invention in detail:

[0036] Example 1: First, a 25mm × 30mm cadmium zinc telluride (CZN) substrate to be polished is bonded to a 6mm thick circular glass substrate. The circular glass substrate is then adsorbed onto the micro-convex surface of the polishing fixture using vacuum adsorption. Before polishing, it is confirmed that the adsorption on the surface of the polishing fixture is intact. The polishing fixture with the substrate adsorbed is placed vertically on the polishing plate of the polishing machine, and polishing parameters are set for surface polishing. After polishing, the surface is cleaned and inspected. Inspection results show that using the micro-convex fixture with appropriate polishing control, large-size CZN substrates can achieve a high-flatness surface with a TTV ≤ 2μm after polishing. This significantly improves the surface flatness of CZN substrates, enhances the quality of subsequent mercury cadmium telluride (HCd) epitaxial films and the yield of device interconnects, and improves the uniformity of detector performance.

[0037] Example 2: A 36mm × 42mm cadmium zinc telluride (CZN) substrate to be polished was bonded to a 4mm thick sapphire circular wafer. The sapphire wafer was then adsorbed onto the micro-convex surface of the polishing fixture using vacuum adsorption. Before polishing, it was confirmed that the surface of the polishing fixture was well-adsorbed. The polishing fixture with the substrate adsorbed was placed vertically on the polishing plate of the polishing machine, and polishing parameters were set for surface polishing. After polishing, the surface was cleaned and inspected. The results showed that using the micro-convex fixture with appropriate polishing control, the polished large-size CZN substrate could achieve a high-flatness surface with a TTV ≤ 2μm. This significantly improves the surface flatness of the CZN substrate, enhances the quality of subsequent mercury cadmium telluride (HCd) epitaxial films and the yield of device interconnects, and improves the uniformity of detector performance.

[0038] Example 3: A 3-inch cadmium zinc telluride (CZD) substrate to be polished was directly adsorbed onto the micro-convex surface of a polishing fixture using vacuum adsorption. Before polishing, it was confirmed that the surface of the polishing fixture was well-adsorbed. The polishing fixture with the adsorbed substrate was placed vertically on the polishing plate of the polishing machine, and polishing parameters were set for surface polishing. After polishing, the surface was cleaned and inspected. Inspection showed that using a micro-convex fixture with appropriate polishing control, large-size CZD substrates could achieve a high-flatness surface with a TTV ≤ 2μm after polishing. This significantly improves the surface flatness of CZD substrates, enhances the quality of subsequent mercury cadmium telluride (HCD) epitaxial films and the yield of device interconnects, and improves the uniformity of detector performance.

[0039] Table 1 Comparison of surface smoothness of cadmium zinc telluride polished substrates before and after application

[0040]

[0041]

[0042] In summary, the polishing fixture in this invention is a ceramic disc with a central convex shape, and the polishing fixture transitions smoothly from the central convex shape to the outer edge. The micro-convex fixture can effectively control the "edge collapse" phenomenon of the substrate, solving the problem of "thick in the middle and thin around the edges" surface shape that is easy to form during traditional polishing. This improves the surface flatness of the substrate, especially solving the problem of poor surface flatness in the processing of large-size zinc cadmium telluride substrates. This lays a good foundation for improving the yield of high-quality mercury cadmium telluride epitaxy, device interconnection, and detector performance consistency.

[0043] Although preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will recognize that various modifications, additions, and substitutions are possible, and therefore the scope of the invention should not be limited to the embodiments described above.

Claims

1. A polishing fixture for polishing the surface of large-size cadmium zinc telluride substrates, characterized in that, include: The polishing fixture is a ceramic disc with a central protrusion, and the polishing fixture transitions smoothly from the central protrusion to the outer periphery. The height of the protrusion and the diameter of the polishing fixture are both set according to the size of the cadmium zinc telluride substrate being polished. The height of the protrusion is 6 micrometers, and the diameter of the polishing fixture is 100-150 millimeters; When the size of the zinc zinc cadmium telluride substrate is smaller than a preset threshold, the polishing fixture further includes: a circular carrier sheet; The circular carrier is vacuum-adsorbed onto the polishing fixture, and the cadmium zinc telluride substrate is bonded to it through the circular carrier.

2. The polishing fixture according to claim 1, characterized in that, The preset threshold is 2.5 inches.

3. The polishing fixture according to claim 1, characterized in that, The circular substrate is a glass circular substrate or a sapphire circular substrate.

4. A method for polishing a large-size cadmium zinc telluride substrate using the polishing fixture described in any one of claims 1-3, characterized in that, include: The cadmium zinc telluride substrate to be polished is directly adsorbed and placed on the polishing fixture; The cadmium zinc telluride substrate is polished according to a preset polishing process to obtain a cadmium zinc telluride substrate with a smooth surface.

5. The method according to claim 4, characterized in that, When the size of the zinc-cadmium telluride substrate is smaller than a preset threshold, the zinc-cadmium telluride substrate is bonded to a circular carrier, and the circular carrier is adsorbed onto the polishing fixture to polish the zinc-cadmium telluride substrate.

6. The method according to claim 5, characterized in that, The preset threshold is 2.5 inches.

7. The method according to claim 5, characterized in that, The circular substrate is a glass circular substrate or a sapphire circular substrate.

8. The method according to claim 4, characterized in that, The tellurium zinc cadmium substrate is less than 4 inches in size.

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