Cd-Zn-Te wafer double-sided chemical mechanical polishing method

Abstract

The invention discloses a cadmium zinc telluride wafer double-sided chemical mechanical polishing method, which relates to a semiconductor material processing technology, and comprises the following steps: forming a diversion trench in a polishing pad in advance so as to improve the flowability of a polishing solution on the upper and lower surfaces of a wafer based on the diversion trench, and bonding the polishing pad to a polishing disk; preparing a polishing solution comprising an abrasive, water, a moistening agent and an oxidizing agent according to a set ratio; selecting a loose pulley sheet with a proper material and thickness, and placing a batch of tellurium-zinc-cadmium wafers on the porous loose pulley sheet; before polishing, a moistening agent is sprayed on the surface of the tellurium-zinc-cadmium wafer so as to reduce the fragment probability of the wafer at the earlier stage of polishing; a polishing program is set, so that the flow of the polishing solution and the polishing pressure in each stage are increased in a gradient manner; in the polishing process, the dry-wet condition of the polishing pad is judged according to the condition of the polishing liquid overflowing between the upper polishing disc and the lower polishing disc, and adjustment is conducted through a polishing program; and cleaning and testing after polishing to finish polishing. The method is used for realizing batch double-sided chemical mechanical polishing of the cadmium zinc telluride wafer.

Description

Technical Field

[0001] This application relates to the field of semiconductor material processing technology, and in particular to a double-sided chemical mechanical polishing method for cadmium zinc telluride wafers. Background Technology

[0002] Cadmium zinc telluride (CZN) substrates are the preferred material for growing mercury cadmium telluride (HCd) thin films. Poor surface geometry can lead to inconsistent device performance or even failure, affecting overall product yield and performance stability. Therefore, a smooth surface without mechanical damage, low surface roughness, and high surface flatness are required. After mechanical grinding and polishing, CZN wafers undergo chemical mechanical polishing (CMP) to remove surface damage and achieve a smooth, flat surface. Thus, controlling wafer flatness is crucial during CMP.

[0003] Currently, chemical mechanical polishing (CMP) of cadmium zinc telluride (CZD) wafers is generally a single-sided process. This involves attaching the CZD wafer to a carrier made of glass, quartz, or ceramic using methods such as wax bonding, and then polishing a single surface using a polishing fixture to achieve a smooth, flat epitaxial surface. However, existing CMP processes for CZD wafers mostly employ single-wafer polishing. Factors such as the uniformity of the bonding medium, the consistency of polishing pressure distribution, and the wafer surface shape can lead to instability in pressure transmission and material removal rates during polishing, thus affecting surface flatness. Furthermore, single-sided polishing can only process one surface of the wafer at a time, and the wafer must be bonded to the carrier before polishing and removed afterward, resulting in low processing efficiency and unsuitability for mass production.

[0004] Double-sided polishing can polish both surfaces of a wafer simultaneously, avoiding the bonding and dielectric removal steps before and after polishing, thus significantly shortening the mass production cycle. Furthermore, double-sided polishing results in more uniform stress and processing conditions on both sides of the wafer, which is more conducive to controlling the wafer surface flatness. While double-sided chemical mechanical polishing (CMP) is a mature process for processing semiconductor materials such as silicon wafers, it cannot be directly applied to cadmium zinc telluride (CZD) wafers due to their brittle nature and susceptibility to chipping or microcracks during polishing. CZD also exhibits high chemical reactivity, readily undergoing strong chemical corrosion in the acidic or alkaline polishing solutions commonly used for polishing silicon wafers, making it impossible to form a uniform polished layer. Summary of the Invention

[0005] This application provides a double-sided chemical mechanical polishing method for cadmium zinc telluride wafers, which differs from the traditional single-sided chemical mechanical polishing process. This application is used to achieve mass production of double-sided chemical mechanical polishing for cadmium zinc telluride wafers.

[0006] This application provides a method for double-sided chemical mechanical polishing of cadmium zinc telluride wafers, including: Pre-drill flow channels in the polishing pad to improve the flowability of the polishing slurry on the upper and lower surfaces of the wafer, and then adhere the polishing pad to the polishing disk. Prepare a polishing slurry containing abrasive, water, lubricant, and oxidant according to the set ratio; Select cruise ship plates and place a batch of cadmium zinc telluride wafers into the porous cruise ship plates; Before polishing, a lubricant is sprayed on the surface of the zinc zinc cadmium wafer to reduce the probability of wafer fragmentation in the early stage of polishing by utilizing the lubricating film formed by the lubricant on the surface of the zinc zinc cadmium wafer. The lubricant has a different composition than the polishing liquid. Set up a polishing program so that the flow rate and polishing pressure of the polishing fluid increase in a gradient at each stage. During polishing, the dryness or wetness of the polishing pad is determined by the amount of polishing fluid overflowing between the upper and lower polishing pads, and the polishing program is used to adjust it accordingly. After polishing, the surface is cleaned and tested to complete the polishing process.

[0007] Optionally, pre-cutting drainage channels in the polishing pad includes: A flow channel is created in the polishing pad. The width of the flow channel is 200~5000μm and the depth is 0.5~2mm, so as to improve the flowability of the polishing slurry on the upper and lower surfaces of the wafer.

[0008] Optionally, the abrasive particle size in the prepared polishing slurry is 20~100μm; During the mixing process, after the abrasive, water, lubricant, and oxidant are thoroughly mixed, a pH adjuster is added dropwise to adjust the polishing solution to a weakly acidic or weakly alkaline state.

[0009] Optionally, cruise ship laminations are selected, and a batch of cadmium zinc telluride wafers is placed onto the porous cruise ship laminations, including: Select cruise ship plates. The cruise ship plates should be made of a relatively soft polymer material. The thickness of the cruise ship plates should be slightly less than the thickness of the zinc zinc cadmium wafers, and the thickness difference should be ≤30μm. Optionally, the polishing procedure can be configured as follows: The polishing process is designed in stages, so that the flow rate and pressure of the polishing slurry increase gradually in each stage, with the maximum polishing pressure for a single batch being... for: , It is a constant between 80 and 150. This represents the total area of ​​the cadmium zinc telluride wafer.

[0010] Optionally, after polishing, the polishing fluid flow rate and polishing pressure can be gradually reduced, and the polishing time during the low-pressure phase can be extended.

[0011] Optionally, cleaning and testing are performed after polishing. Polishing is completed by including: After polishing, the wafer surface is cleaned with deionized water and ethanol, and then dried. After drying, the thickness is measured. If the predetermined thickness range is not reached, the polishing process is repeated.

[0012] This application embodiment achieves high-quality chemical mechanical polishing of cadmium zinc telluride wafers through a chemical mechanical polishing process, thereby solving the problems of inconsistent upper and lower surfaces, poor surface flatness, and low processing efficiency in single-sided chemical mechanical polishing. In addition, it solves the problems of cadmium zinc telluride wafers being fragile and easily corroded during processing, and achieves high-quality batch polishing of cadmium zinc telluride wafers.

[0013] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0014] 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 scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a schematic diagram of the overall process of the double-sided chemical mechanical polishing method for cadmium zinc telluride wafers according to an embodiment of this application. Detailed Implementation

[0015] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0016] Surface defects and damage to cadmium zinc telluride (CZD) wafers need to be removed through chemical mechanical polishing (CMP). However, traditional single-sided CMP processes struggle to guarantee consistent surface quality, surface flatness, and processing efficiency on both sides of the wafer after polishing. Furthermore, CZD wafers are prone to fragmentation and corrosion during double-sided polishing. Therefore, a double-sided polishing technology that meets the requirements for high-quality and mass production of CZD wafers needs to be developed. Based on this, this application provides a double-sided CMP method for CZD wafers to address the problems of inconsistent upper and lower surfaces, poor surface flatness, and low processing efficiency associated with single-sided CMP. It also addresses the fragility and corrosion issues of CZD wafers during processing, achieving high-quality mass production polishing of CZD wafers. The CMP method of this application includes pre-process preparation steps, a polishing step, a cleaning step, and a testing step. The CMP method of this application includes the following steps: In step S101, flow channels are pre-formed in the polishing pad to improve the flowability of the polishing slurry on the upper and lower surfaces of the wafer. In some embodiments, pre-forming flow channels in the polishing pad includes: A flow channel is opened in the polishing pad. The width of the flow channel is 200~5000μm and the depth is 0.5~2mm. The flow channel is used to improve the flow of polishing slurry on the upper and lower surfaces of the wafer and prevent the polishing slurry from being discharged in time and corroding the surface of the cadmium zinc telluride wafer.

[0017] The selected polishing pad is bonded to the upper and lower polishing discs of the double-sided polishing machine and slowly pressed with a roller to ensure a tight bond between the polishing pad and the polishing disc without air bubbles.

[0018] In step S102, a polishing slurry comprising abrasive, water, lubricant, and oxidant is prepared according to a set ratio. In some examples, the abrasive particle size in the prepared polishing slurry is 20~100μm; the abrasive types include nano-sized silicon dioxide, aluminum oxide, cerium oxide, etc., powders or suspensions. During the preparation process, after the abrasive, water, lubricant, and oxidant are stirred evenly, a pH adjuster is added dropwise to adjust the polishing slurry to a weakly acidic or weakly alkaline state, preventing corrosion of the wafer surface due to excessive acidity or alkalinity of the polishing slurry.

[0019] In step S103, cruise ship wafers are selected, placed at equal intervals on the surface of the lower polishing pad, and a batch of cadmium zinc telluride wafers are placed onto the porous cruise ship wafers. In some embodiments, selecting cruise ship wafers and placing a batch of cadmium zinc telluride wafers onto the porous cruise ship wafers includes: The polishing wheel is selected and the material is a relatively soft polymer. In some examples, the polymer material has a hardness of 30~100 Shore A to avoid fragmentation during the collision between the cadmium zinc telluride wafer and the polishing wheel. The thickness of the polishing wheel should be slightly less than the thickness of the cadmium zinc telluride wafer, and the thickness difference should be ≤30μm. This design can reduce the deformation and shaking of the polishing wheel during polishing and allow it to share the pressure brought by the weight of the polishing pad.

[0020] After placing a batch of cadmium zinc telluride (CZD) wafers onto a porous wafer lathe, a wetting agent is sprayed onto the CZD wafer surface before polishing. This wetting agent forms a lubricating film on the CZD wafer surface, and its composition differs from that of the polishing slurry. This embodiment uses a wetting agent different from the polishing slurry. This wetting agent has good adhesion and film-forming properties, and can form a uniform lubricating film on the CZD wafer surface, effectively reducing the breakage rate due to insufficient lubrication in the early stages of polishing.

[0021] In step S104, the prepared polishing slurry is poured into the supply device and continuously stirred. During the polishing process, a peristaltic pump is used for a steady-speed supply of the slurry, with a drip rate of 10~100mL / min. A polishing program is set so that the flow rate and polishing pressure of the polishing slurry increase gradually at each stage. Specifically, the maximum polishing pressure is calculated based on the total area of ​​each group of wafers, the polishing program is input, the polishing disc speed and polishing pressure are set, and the process is carried out according to the operating steps of the double-sided polishing machine.

[0022] In step S105, polishing is performed. During the polishing process, the dryness or wetness of the polishing pad is determined based on the amount of polishing fluid overflowing between the upper and lower polishing pads, and adjusted using the polishing program. If the polishing pad is too dry, the friction between the wafer and the polishing pad will be too high, causing damage, scratches, or even cracks on the wafer surface. If the polishing pad is too wet, the removal rate of material from the wafer surface will be lower than the oxide formation rate, and corrosion may occur on the wafer surface. Based on the aforementioned steps, this application selects a grooved fine polishing pad (polishing pad) to improve the conductivity of ordinary polishing pads, avoid the accumulation of polishing fluid on the wafer surface causing corrosion, and wets the wafer with a wetting agent before polishing to avoid excessive friction between the wafer and polishing pad surfaces at the beginning of polishing. This has an important impact on maintaining the balance between mechanical and chemical actions during the polishing process.

[0023] In step S106, the polishing process is completed by cleaning and testing after polishing.

[0024] This application embodiment achieves high-quality chemical mechanical polishing of cadmium zinc telluride wafers through a chemical mechanical polishing process, thereby solving the problems of inconsistent upper and lower surfaces, poor surface flatness, and low processing efficiency in single-sided chemical mechanical polishing. In addition, it solves the problems of cadmium zinc telluride wafers being fragile and easily corroded during processing, and achieves high-quality batch polishing of cadmium zinc telluride wafers.

[0025] In some embodiments, setting the polishing procedure includes: The polishing process is designed in stages, so that the flow rate and pressure of the polishing slurry increase gradually in each stage, with the maximum polishing pressure for a single batch being... for: , It is a constant between 80 and 150, with units of g / cm³. 2 , The total area of ​​the cadmium zinc telluride wafer is expressed in cm². 2 .

[0026] In some embodiments, after polishing is completed, the flow rate and polishing pressure of the polishing fluid are gradually reduced, and the polishing time of the low-pressure stage is extended. In this way, the internal stress generated during high-pressure polishing can be slowly released from the wafer, gradually correcting the uneven areas of wafer thickness and surface roughness, and improving the flatness and surface consistency of the cadmium zinc telluride wafer after polishing.

[0027] In some embodiments, cleaning and testing after polishing to complete the polishing process includes: After polishing, the wafer surface is cleaned with deionized water and ethanol, and then dried. After drying, the thickness is measured. If the predetermined thickness range is not reached, the polishing process is repeated.

[0028] This application also provides implementation examples of a double-sided chemical mechanical polishing method for cadmium zinc telluride wafers, such as... Figure 1 As shown, it includes: (1) First, the preparation work before polishing is to attach the selected fine polishing pad to the upper and lower polishing discs of the double-sided polishing machine and press it slowly with a roller to make the fine polishing pad and the polishing disc tightly bonded without air bubbles.

[0029] (2) Place the five round-hole wheel plates at equal intervals on the lower polishing pad and wet the upper and lower polishing pads with pure water.

[0030] (3) Select zinc cadmium telluride wafers from the same batch and place them on the cruise ship, and drip a lubricant onto the surface of all wafers to wet them.

[0031] (4) Secondly, the polishing liquid needs to be prepared before polishing. According to the proportion, the abrasive, water, lubricant and oxidant are poured into the beaker in sequence under stirring. After stirring evenly, the pH of the polishing liquid is adjusted to 3~5 by pH adjuster and poured into the polishing liquid supply device of the double-sided polishing machine. Stirring is turned on and the polishing liquid dripping rate is set.

[0032] (5) Calculate the polishing pressure based on the total area of ​​each group of wafers, input the polishing program, set the polishing disk speed and polishing pressure, and carry out the process according to the operating steps of the double-sided polishing machine.

[0033] (6) During the polishing process, the dryness or wetness of the polishing pad needs to be judged at any time based on the amount of polishing fluid overflowing between the upper and lower pads. If the polishing pad is too dry, the friction between the wafer and the polishing pad will be too large, which will cause damage, scratches or even cracks on the wafer surface. If the polishing pad is too wet, the removal rate of the material on the wafer surface will be lower than the formation rate of oxides, and corrosion may occur on the wafer surface. Therefore, a grooved fine polishing pad is selected to improve the conductivity of ordinary polishing pads, avoid the accumulation of polishing fluid on the wafer surface and cause corrosion, and wet the wafer with a wetting agent before polishing to avoid excessive friction between the wafer and the polishing pad surface at the beginning of polishing. This has an important impact on maintaining the balance between mechanical and chemical actions during the polishing process.

[0034] (7) After polishing, clean the wafer surface with cleaning solution and blow dry. Measure the thickness of each wafer and calculate the material removal rate. If the predetermined thickness range is not reached, return the wafers of this batch and repeat steps (3)-(7), adjusting the polishing time as needed. If the wafer reaches the predetermined thickness, observe its surface for cracks, damage, or corrosion using an optical microscope, and test each polished wafer separately.

[0035] The method described in this application is used for high-quality chemical mechanical polishing of cadmium zinc telluride wafers. It can effectively reduce the fragmentation rate and corrosion probability, balance internal stress, and achieve higher parallelism between the top and bottom surfaces of the wafer, thereby achieving better surface flatness. In addition, in terms of processing efficiency, double-sided chemical mechanical polishing can polish both surfaces of the wafer simultaneously and can process multiple wafers in a single batch (5 to 20 wafers per batch). It can directly polish the ground surface to a mirror finish with a surface roughness as low as 1 nm without mechanical polishing, simplifying the process steps and showing significant advantages in engineering and large-scale production.

[0036] It should be noted that, in the embodiments of this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0037] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0038] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) and includes several instructions to cause a terminal (which may be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods described in the various embodiments of this application.

[0039] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims. All of these forms are within the protection scope of this application.

Claims

1. A method for double-sided chemical mechanical polishing of cadmium zinc telluride wafers, characterized in that, include: Pre-drill flow channels in the polishing pad to improve the flowability of the polishing slurry on the upper and lower surfaces of the wafer, and then adhere the polishing pad to the polishing disk. Prepare a polishing slurry containing abrasive, water, lubricant, and oxidant according to the set ratio; Select cruise ship plates and place a batch of cadmium zinc telluride wafers into the porous cruise ship plates; Before polishing, a lubricant is sprayed on the surface of the zinc zinc cadmium wafer to reduce the probability of wafer fragmentation in the early stage of polishing by utilizing the lubricating film formed by the lubricant on the surface of the zinc zinc cadmium wafer. The lubricant has a different composition than the polishing liquid. Set up a polishing program so that the flow rate and polishing pressure of the polishing fluid increase in a gradient at each stage. During polishing, the dryness or wetness of the polishing pad is determined by the amount of polishing fluid overflowing between the upper and lower polishing pads, and the polishing program is used to adjust it accordingly. After polishing, the surface is cleaned and tested to complete the polishing process.

2. The double-sided chemical mechanical polishing method for cadmium zinc telluride wafers as described in claim 1, characterized in that, Pre-cutting guide grooves in the polishing pad includes: A flow channel is created in the polishing pad. The width of the flow channel is 200~5000μm and the depth is 0.5~2mm, so as to improve the flowability of the polishing slurry on the upper and lower surfaces of the wafer.

3. The double-sided chemical mechanical polishing method for cadmium zinc telluride wafers as described in claim 1, characterized in that, The abrasive particles in the prepared polishing slurry have a particle size of 20~100μm; During the mixing process, after the abrasive, water, lubricant, and oxidant are thoroughly mixed, a pH adjuster is added dropwise to adjust the polishing solution to a weakly acidic or weakly alkaline state.

4. The double-sided chemical mechanical polishing method for cadmium zinc telluride wafers as described in claim 1, characterized in that, Select cruise ship laminations and place a batch of cadmium zinc telluride wafers into porous cruise ship laminations, including: The cruise ship laminations are selected, and the material used is a relatively soft polymer with a hardness of 30~100 Shore A. The thickness of the cruise ship laminations should be slightly less than that of the cadmium zinc telluride wafers, and the thickness difference should be ≤30μm.

5. The double-sided chemical mechanical polishing method for cadmium zinc telluride wafers as described in claim 1, characterized in that, Setting up the polishing procedure includes: The polishing process is designed in stages, so that the flow rate and pressure of the polishing slurry increase gradually in each stage, with the maximum polishing pressure for a single batch being... for: , It is a constant between 80 and 150. This represents the total area of ​​the cadmium zinc telluride wafer.

6. The double-sided chemical mechanical polishing method for cadmium zinc telluride wafers as described in claim 5, characterized in that, After polishing, the polishing fluid flow rate and polishing pressure are gradually reduced, and the polishing time during the low-pressure phase is extended.

7. The double-sided chemical mechanical polishing method for cadmium zinc telluride wafers as described in claim 6, characterized in that, After polishing, cleaning and testing are performed. Polishing is completed by: After polishing, the wafer surface is cleaned with deionized water and ethanol, and then dried. After drying, the thickness is measured. If the predetermined thickness range is not reached, the polishing process is repeated.

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