A cutting method of an ultra-thick cadmium zinc telluride crystal

Abstract

The application discloses a cutting method of an ultra-thick CdZnTe crystal, and comprises the following steps: S1, taking CdZnTe wafers and two pieces of carriers, and after cleaning treatment, using melted paraffin as a binder to form a sandwich combination structure in the order of carrier-wafer-carrier; S2, fixing the sandwich combination structure on a UV film, adsorbing the UV film on a workbench, using a blade to perform multiple step cutting along the thickness direction, completing the cutting of the wafer, and obtaining a wafer with a required size. The cutting method can obviously reduce the edge collapse of the cut product, improve the perpendicularity, and has good surface quality, and effectively improves the yield of the product and the utilization rate of raw materials.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of crystal processing, and particularly relates to a cutting method of super-thick cadmium zinc telluride crystal. BACKGROUND

[0002] The cadmium zinc telluride detector is the third generation detector after the gas glow discharge detector and the scintillation crystal detector, is internationally recognized as the best room temperature detector for detecting rays with an energy range of 20-800 keV, and is the best alternative material for the detection material of the future high-energy ray detector.

[0003] However, the cadmium zinc telluride is soft and brittle, and needs a relatively thick thickness as a detector, and the thickest crystal is as high as about 7 mm, so that the edge collapse is prone to occur in the cutting process, causing damage and destruction of the crystal. At present, for the cutting of the crystal for the detector, the traditional process usually adopts a resin diamond soft knife for processing. However, the knife is prone to breakage in the processing process, and the cutting process is prone to cause the edge collapse of the crystal, and the products are often unqualified in perpendicularity and surface quality, so that the yield of the products is low, and the utilization rate of raw materials is low, and therefore it is particularly important to develop a cutting process for the cadmium zinc telluride crystal with a thickness of 1-7 mm. SUMMARY

[0004] In view of the problems in the prior art, the purpose of the present application is to provide a cutting method of super-thick cadmium zinc telluride crystal, which can significantly reduce the edge collapse of the product, improve the perpendicularity, and improve the surface quality, and effectively improve the yield of the product and the utilization rate of raw materials.

[0005] A cutting method of super-thick cadmium zinc telluride crystal, comprising:

[0006] S1, taking cadmium zinc telluride wafers and two pieces of carrier films, cleaning and treating, and then using melted paraffin as an adhesive to form a sandwich combination structure according to the carrier film-wafer-carrier film;

[0007] S2, fixing the sandwich combination structure on a UV film, fixing the UV film on a workbench by adsorption, and cutting the wafer along the thickness direction by using a blade to complete the cutting of the wafer and obtain a wafer with a required size.

[0008] If the cutting depth is too deep, the heat dissipation cannot be effectively and quickly conducted, the sparking (temperature is too high, and the surface is scorched) is prone to occur, the cutting resistance is large, and the blade is prone to breakage; if the cutting depth is too shallow, the processing efficiency is reduced. As preferred, in step S2, the cutting depth is 0.3-0.5 mm, and the cutting speed is 0.8-1.2 mm / s in the multiple step cutting process, and the cutting speed is too high, and the edge collapse is prone to occur.

[0009] Preferably, in step S2, the blade is provided with a cutout for chip discharge and heat dissipation; the blade comprises an integrally formed cutting blade body and a support part, the cutting blade body is made of resin-bonded sintered diamond, the support part is made of rigid material, and the rigidity of the rigid material is greater than that of sintered diamond.

[0010] Preferably, in step S1, the sandwich structure is further subjected to a pressurization treatment.

[0011] Preferably, in step S1, the sandwich structure made of molten paraffin as a binder and in the form of a wafer-carrier wafer-carrier is prepared by heating the first carrier, melting the paraffin, uniformly spreading the molten paraffin, and then placing the back of the wafer on the carrier, and then performing the same treatment on the second carrier and placing it on the front of the wafer, and then obtaining the sandwich structure and performing a pressurization treatment, and then cooling the wafer and ending the pressurization.

[0012] Preferably, the rigid material is stainless steel, which not only ensures sufficient rigidity, but also plays a rust-proof role in the process of continuously spraying water to cool the blade and workpiece during cutting.

[0013] Preferably, in step S2, after the wafer is cut, the wafer is cleaned, the UV film is removed, the wafer is heated and taken out, and finally the wafer is cleaned.

[0014] Preferably, the thickness of the UV film is 0.25-0.35mm; and the UV film is vacuum adsorbed on the workbench. If the thickness of the UV film is too thin, the perpendicularity of the side of the crystal after cutting cannot be guaranteed, and if the thickness is too thick, the wafer cannot be expanded after cutting, which increases the risk of wafer edge collapse. Vacuum adsorption is beneficial to improve the fixing effect and improve the cutting effect.

[0015] Preferably, in step S1, the cleaning treatment is: flushing the CdZnTe wafer and the two carriers with pure water, wiping them with alcohol after flushing, and then blowing them dry with nitrogen.

[0016] Preferably, in step S2, the sandwich structure is fixed on the UV film by adhesion; and the UV film is vacuum adsorbed on the workbench.

[0017] As preferred, the diameter of the blade is different according to the thickness of the product, the effective cutting thickness of the blade is blade exposure amount = (blade outer diameter-flange outer diameter) / 2, the cutting thickness refers to the maximum thickness that the blade can theoretically cut, the blade exposure amount is slightly larger than the thickness of the cut product, about 0.3-0.5mm larger than the product thickness, that is, the cutting thickness = (blade outer diameter-flange outer diameter) / 2-(0.3-0.5mm), if the outer diameter is increased, although the exposure amount and the cutting thickness can be increased, part of the rigidity will be lost.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] 1. The cutting method can cut ultra-thick crystals with a thickness of up to 7mm, and can well guarantee the cutting quality and reliability of large-thickness crystals, the crystal surface quality and perpendicularity obtained by cutting are good, the yield is high, the reliability is high, the edge collapse is smaller, the utilization rate of the crystal can be effectively improved, and the cost is reduced.

[0020] 2. The cutting method adopts the "sandwich" structure of carrier sheet+crystal+carrier sheet, is bonded by wax, and is fixed by a UV film before being processed multiple times in steps, which not only can effectively absorb vibration and the first impact, reduce the occurrence of edge collapse and angle collapse, but also can avoid surface damage and contamination of the crystal during cutting processing, and the wax layer is easy to remove. The "sandwich" structure of carrier sheet+crystal+carrier sheet is also applicable to diamond wire cutting and ultra-high pressure water cutting processing.

[0021] 3. The cutting method adopts an integrated blade of rigid+flexible combined material, which can not only guarantee the cutting quality, but also can avoid the loss of rigidity caused by large depth; by optimizing the thickness of the UV film, the adhesion during cutting processing can be ensured, vibration can be reduced, and processing quality can be further improved; by adopting the integrated blade of rigid+flexible combined material and optimizing the thickness of the UV film, not only the edge collapse can be further reduced, but also the perpendicularity of large-thickness crystal cutting can be improved, the utilization rate of the crystal and the product quality can be improved.

[0022] 4. The perpendicularity of the crystal cut by the cutting method is less than 0.05mm; compared with the yield of the traditional cutting process which is only 20% or less, the yield of the cutting method is 80% or more. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0024] Figure 1 Cutting process flow chart of super-thick CdZnTe crystal.

[0025] Figure 2 "Sandwich" structure of crystal and carrier sheet.

[0026] Figure 3 "Sandwich" structure state before cutting.

[0027] Figure 4 "Sandwich" structure state after cutting.

[0028] Figure 5 Schematic diagram of cutting blade.

[0029] Figure 6 State diagram of crystal after cutting in Example 1.

[0030] Figure 7 State diagram of crystal after cutting in Comparative Example 1.

[0031] Reference signs:

[0032] 1, upper carrier sheet; 2, CdZnTe wafer; 3, lower carrier sheet; 4, iron ring; 5, UV film. DETAILED DESCRIPTION

[0033] In order to facilitate the understanding of the present application, the present application will be described in more detail and in a more comprehensive and detailed manner below in combination with the drawings of the specification and the preferred embodiments, but the protection scope of the present application is not limited to the following specific embodiments.

[0034] The cutting method of super-thick CdZnTe crystal, the process flow chart is as shown in Figure 1 , comprising:

[0035] (1) The CdZnTe wafer and the upper carrier sheet 1 and the lower carrier sheet 2 (glass sheet can be used, the surface is smooth and flat) are washed with pure water, and then wiped with alcohol after washing, and then dried with nitrogen to ensure that the surface is free of impurities;

[0036] (2) For CdZnTe crystals of different thicknesses, considering the material properties (soft and brittle), customize diamond sintered blades of different outer diameters, and use stainless steel to fix the non-cutting area to improve the stability of the blade and avoid vibration during cutting. The blade has a specific notch to facilitate the discharge of debris and heat dissipation, and the cutting thickness is (blade outer diameter-flange diameter) / 2+100um. In order to increase the depth of the cutting blade into the film and improve the perpendicularity of the cutting surface, a 0.3mm UV film is used. The diamond sintered blade includes an integrally formed cutting blade body and a support part, the material of the cutting blade body is sintered diamond, and the material of the support part is stainless steel, such as Figure 5As shown, the lower part of the blade is a stainless steel material, which is a support for the blade and is not used for cutting, mainly to improve the rigidity of the blade. The black part on the outside of the blade is a cutting blade body combined with diamond and resin, mainly used for cutting crystals. The two are integrally formed by sintering method. The width of the upper and lower blades is consistent, which improves the exposure of the blade and increases the thickness of the cut crystal. The specific processing includes: first, the annular support part of the stainless steel blade is processed, then it is placed in the mold, and the diamond and resin are placed in it. By heating and pressing, the two are organically combined to form a cutting blade body wrapped around the support part of the annular blade. The cutting surface of the annular blade is provided with a notch for debris discharge and heat dissipation. The resin acts as a binder that can bond the diamond together.

[0037] (3) Place the lower blade on the heating platform and heat it. After the temperature reaches 90°C, melt a certain amount of high-melting-point paraffin. After the paraffin is melted into a liquid, spread it evenly and continue to heat for a period of time. After the internal gas is completely discharged, place the back of the crystal on the lower blade. Reduce the temperature. After the temperature of the front of the crystal reaches 50°C, melt a certain amount of low-melting-point paraffin and spread it evenly. Place the upper blade on the front of the crystal, and then press the upper blade with a pressing block. After cooling, remove the pressing head to obtain a sandwich structure, as shown in Figure 2 The use of pressure cooling ensures the flatness and internal pore-free of the "sandwich" structure. In this step, two types of paraffin are used. The melting point of the first paraffin is about 50°C, and the melting point of the second paraffin is about 90°C. Since both the upper and lower surfaces need to be bonded with paraffin, first heat the heating platform to 90°C, place the blade on one side, and then reduce the temperature to 50°C. Wait for the temperature to stabilize and the blade to be bonded on one side. Then use low-melting-point paraffin to bond the other side. This can effectively prevent the crystal from sliding due to the inability to fix one side.

[0038] (4) Stick the "sandwich" combination structure to the UV film 5, and fix the UV film 5 to the workbench by vacuum adsorption, as shown in Figure 3 to ensure no pores.

[0039] (5) For different thicknesses of products, a distributed cutting method is used, with a cutting depth of 0.3-0.5mm each time. This ensures that the blade and crystal temperature rise during cutting will not be too high, and the cutting debris can be smoothly discharged, the heat can be timely discharged, avoiding the generation of crystal firing phenomenon, making the crystal surface have a burnt paste phenomenon, affecting the performance of the crystal, and also avoiding the secondary impact damage to the crystal caused by the generation of debris, improving the cutting quality. Because the debris will be rolled up by the blade again and impact the crystal in the opposite direction, and secondly, the debris will also cause damage to the blade, causing the blade to break.

[0040] (6) After cutting is completed, as shown in Figure 4As shown, cleaning is performed, and the cleaning uses water mist to remove dirt and impurities on the surface and in the cutting path. The dirt is removed by atomizing water and using the flow and mist under high-speed rotation. After cleaning, the cleaned sandwich structure and the UV film 5 are placed under the ultraviolet lamp for irradiation, so that the UV glue loses adhesion to release the UV glue. Then, the melted paraffin is removed by heating, the upper loading plate is removed, and finally, the paraffin is removed and cleaned. Then, characterization detection is performed.

[0041] Example 1

[0042] 2.3mm thick cadmium zinc telluride crystal cutting method, comprising:

[0043] (1) The cadmium zinc telluride wafer and the upper loading plate (glass plate can be used, the surface is smooth and flat) are washed with pure water, and then wiped with alcohol. After washing, the surface is blown dry with nitrogen to ensure that there is no impurity on the surface.

[0044] (1) For a 2.3mm thick cadmium zinc telluride crystal, considering its material properties (soft and brittle), a diamond sintered blade with an outer diameter of 44.5mm is customized, and stainless steel is used to fix the non-cutting area to improve the stability of the blade and avoid vibration during cutting. The blade has a specific notch to facilitate the removal of debris and heat dissipation. The cutting thickness is (blade outer diameter-flange diameter) / 2+100um. At the same time, in order to increase the depth of the cutting blade into the film and improve the perpendicularity of the cutting surface, a 0.3mm UV film is used.

[0045] (2) Place the loading plate on the heating platform and heat it to 90℃. Then melt a certain amount of high-melting-point paraffin. After the paraffin is melted into a liquid, spread it evenly and continue to heat for a period of time. After the internal gas is completely discharged, place the back of the crystal on the loading plate. At the same time, when the temperature of the front surface of the crystal reaches 50℃, melt a certain amount of low-melting-point paraffin and spread it evenly. Place the upper loading plate on the front surface of the crystal, and then press the upper loading plate with a pressing block. After cooling, remove the pressing head. The use of pressure cooling ensures the flatness of the "sandwich" structure and the absence of air holes inside.

[0046] (3) Stick the "sandwich" combination structure on the UV film to ensure no air holes.

[0047] (4) Use a distributed cutting method with a cutting speed of 1mm / s and a cutting depth of 0.3-0.5mm each time. Use a five-step cutting method of 2mm (first step cutting 0.3mm)-1.5mm (second step cutting 0.5mm)-1mm (third step cutting 0.5mm)-0.5mm (fourth step cutting 0.5mm)-0.07mm (fifth step cutting 0.43mm) to avoid sparking and improve cutting quality.

[0048] After cutting, cleaning is performed, and the cleaning is performed by water mist two-step washing. After cleaning, debonding, heating, wafer taking, and finally wax removal and cleaning are performed. After that, characterization detection is performed. The cut wafer is as shown in Figure 6 Figure 1. As can be seen from the figure, the size of the cutting edge can meet the process requirements, and the yield of the finished product is 86.67% after detection. The data is shown in Table 1. Four samples are measured. The verticality of the cut crystal is within 0.01 mm. The data is shown in Table 3.

[0049] Example 2

[0050] 7.3mm thick CdZnTe crystal cutting method, comprising:

[0051] (1) The CdZnTe wafer and the upper and lower wafers (glass wafers can be used, and the surface is smooth and flat) are washed with pure water. After washing, they are wiped with alcohol, and then nitrogen is blown dry to ensure that the surface is free of impurities.

[0052] (2) For a 7.3mm thick CdZnTe crystal, considering its material properties (soft and brittle), a 55mm diameter diamond sintered blade is customized, and stainless steel is used to fix the non-cutting area to improve the stability of the blade and avoid vibration during cutting. The blade has a specific notch to facilitate the removal of debris and heat dissipation. The cutting thickness is (blade outer diameter-flange diameter) / 2+100um. At the same time, in order to increase the depth of the cutting blade into the film and improve the perpendicularity of the cutting surface, a 3mm UV film is used.

[0053] (3) Place the lower wafer on the heating platform and heat it to 90℃. Then melt a certain amount of high-melting-point paraffin. After the paraffin is melted into a liquid, spread it evenly and continue to heat for a period of time. After the internal gas is completely escaped, place the back of the crystal on the lower wafer. At the same time, when the temperature of the front surface of the crystal reaches 50℃, melt a certain amount of low-melting-point paraffin and spread it evenly. After heating for a period of time, place the upper wafer on the front surface of the crystal, and then press the upper wafer with a pressing block. After cooling, remove the pressing head. The use of pressure cooling ensures the flatness of the "sandwich" structure and the absence of internal pores.

[0054] (4) Stick the "sandwich" combination structure on the UV film to ensure no air holes.

[0055] (5) Use a distributed cutting method with a cutting speed of 1mm / s and a cutting depth of 0.3-0.5mm each time. Use 7.3-7-6.5-6-5.5-5-4.5-4-3.5-3-2.5-2-1.5-1-0.5-0.07 sixteen-step cutting to avoid sparking and improve cutting quality.

[0056] (6) After cutting, cleaning is performed, water mist is used for cleaning, after cleaning, glue is removed, heating is performed, the wafer is taken out, finally, wax is removed, and then characterization detection is performed, the size of the cutting edge can meet the process requirements, the verticality of the cut crystal is within 0.05mm, and the yield is more than 80%.

[0057] Comparative Example 1

[0058] 2. The cutting method of the 2.3mm thick CdZnTe crystal, comprising:

[0059] (1) The CdZnTe wafer and the lower wafer (glass wafer can be used, and the surface is smooth and flat) are washed with pure water, and then alcohol is used for wiping, and then nitrogen is used for drying, so that the surface is free of impurities;

[0060] (2) The crystal is adhered to the UV film, and the sintered diamond blade bonded by resin is used for cutting the crystal.

[0061] (3) After cutting, cleaning is performed, water mist is used for cleaning, after cleaning, glue is removed, heating is performed, the wafer is taken out, finally, wax is removed, and then characterization detection is performed, the yield data is shown in Table 2, the wafer after cutting is shown in Table 2, 2 samples are taken for testing, and the verticality data is shown in Table 4. Figure 7

[0062] Table 1

[0063]

[0064] Table 2

[0065]

[0066] Table 3

[0067]

[0068] Table 4

[0069]

[0070] The above only describes the preferred embodiments of the present application, and it should be pointed out that for ordinary skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should be considered as the protection scope of the present application.​

Claims

1. A method of cutting an ultrathick CdZnTe crystal, characterized in that, The application relates to a method for cutting a CdZnTe wafer, comprising the following steps: S1, taking a CdZnTe wafer and two pieces of carrier, performing cleaning treatment, taking molten paraffin as an adhesive, and making a sandwich structure according to the carrier wafer-carrier; S2, fixing the sandwich structure on a UV film, fixing the UV film on a workbench through adsorption, using a blade to perform multiple step-by-step cutting along the thickness direction, completing the cutting of the wafer, and obtaining a wafer with a required size; The blade is provided with a cutout for chip discharge and heat dissipation; the blade comprises an integrally-formed cutting blade body and a supporting part; the material of the cutting blade body is sintered diamond bonded with resin; the material of the supporting part is rigid material, and the rigidity of the rigid material is greater than that of the sintered diamond; In step S2, the depth of each cutting in the multiple step-by-step cutting process is 0.3-0.5 mm, and the cutting speed is 0.8-1.2 mm / s; The thickness of the UV film is 0.25-0.35 mm.

2. The method of cutting an ultrathick CdZnTe crystal according to claim 1, wherein In step S1, the sandwich structure is further subjected to pressure treatment.

3. The method of cutting an ultrathick CdZnTe crystal according to claim 1, wherein In step S1, the molten paraffin is taken as the adhesive to make the sandwich structure according to the carrier-wafer-carrier, specifically comprising the following steps: heating the first carrier, melting the paraffin, uniformly spreading the paraffin after the paraffin is changed into liquid, continuing to heat until the internal gas is discharged, placing the back surface of the wafer on the carrier, performing the same treatment on the second carrier as that on the first carrier, placing the second carrier on the front surface of the wafer, obtaining the sandwich structure, performing pressure treatment, and ending the pressure treatment after the wafer is cooled.

4. The method of cutting an ultrathick CdZnTe crystal according to claim 1, wherein The rigid material is stainless steel.

5. The method of cutting an ultrathick CdZnTe crystal according to claim 1, wherein In step S2, after the wafer is cut, cleaning is further performed, the UV film is removed after the wafer is cleaned, the wafer is heated and taken out, and finally, the paraffin is removed and cleaned.

6. The method of cutting an ultrathick CdZnTe crystal according to claim 1, wherein In step S1, the cleaning treatment comprises the following steps: using pure water to rinse the CdZnTe wafer and the two carriers, wiping the carriers with alcohol after the rinsing, and then blowing dry with nitrogen.

7. The method of cutting an ultrathick CdZnTe crystal according to claim 1, wherein In step S2, the sandwich structure is fixed on the UV film through adhesion; and the UV film is adsorbed on the workbench through vacuum adsorption.

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