CN110640552B - Processing method of easily-cleaved semiconductor crystal - Google Patents

Abstract

The present invention discloses a method for processing semiconductor crystals that are easy to cleave. The method adopts a method of controlling grinding force and workpiece rotation to grind gallium oxide wafers that are easy to cleave. The steps are as follows: fixing the gallium oxide wafer on a workbench, under which a force sensor is arranged; using diamond grinding wheels with coarse and fine grains to perform rough grinding and fine grinding on the gallium oxide wafer respectively; setting the initial feed speed, feed amount, and maximum grinding force _Fcoarse and Ffine during rough grinding and _fine grinding respectively, and ensuring that the grinding force is within the range of Fcoarse ±0.1N and _Ffine ±0.1N during _rough grinding and fine grinding respectively. The data processor collects the grinding force signal measured by the force sensor in real time, amplifies it, processes it, and transmits it to the negative feedback system. The negative feedback system controls the feed speed in real time to achieve a grinding force less than the gallium oxide cleavage stress threshold. This solution solves the dissociation phenomenon that is easy to occur in gallium oxide machining and achieves a high yield.

Description

A kind of processing method of easily cleavable semiconductor crystal

technical field

The invention belongs to the technical field of ultra-precision processing of hard and brittle semiconductor wafers, and in particular relates to a processing method for easily cleavable semiconductor crystals.

Background technique

Gallium oxide (β-Ga ₂ O ₃ ) is a new type of ultra-wide bandgap oxide semiconductor material with very stable physical and chemical properties, high breakdown field strength and strong radiation resistance, which is more suitable for the development of high-power semiconductors . Gallium oxide (β-Ga ₂ O ₃ ) is expected to produce high withstand voltage and low loss at low cost compared to the other two as next-generation power semiconductor materials such as silicon carbide (SiC) and gallium nitride (GaN) of power semiconductor components. In addition, the UV cut-off edge of β-Ga ₂ O ₃ crystal can reach 260nm, and the transmittance in the ultraviolet band is high, which can meet the requirements of the new second-generation optoelectronic materials for short-wavelength working range, which makes the photodetector can operate at a shorter wavelength ( UV light). Therefore, gallium oxide (β-Ga ₂ O ₃ ) will have great application prospects in the fields of high-performance optoelectronics and power electronic devices.

At present, the difficulty of ultra-precision processing technology of gallium oxide crystal lies in its high hardness, high brittleness, anisotropy, and easy cleavage, which is a typical extremely difficult material to process. In conventional crystal processing, a certain amount of pressure must be applied to the wafer in order to increase the material removal rate. However, gallium oxide crystals are prone to cleavage and fragmentation under the action of stress, and the machining accuracy and surface quality are unstable. In recent years, the processing technology of β-Ga ₂ O ₃ substrate is similar to the processing of silicon wafer. It is necessary to slice the well-grown gallium oxide single crystal rod first. After the gallium oxide crystal is cut, the surface of the wafer will leave cutting marks Usually, the free abrasive grinding process is used to quickly eliminate the tool marks, reduce the thickness of the damaged layer and improve the surface accuracy, and then use the diamond grinding wheel to carry out ultra-precision grinding and mechanical polishing, and finally use the CMP polishing process to obtain damage-free flatness. surface. Therefore, in view of the fact that gallium oxide crystals are easily cleavage and broken under the action of stress, the grinding process effect of gallium oxide crystals is not ideal.

In the field of ultra-precision machining of hard and brittle semiconductor wafers, the quality of processing is very high. Surface and subsurface damage caused by gallium oxide production or processing may significantly affect the mechanical, optical and electrical properties of semiconductor materials. The acquisition of high-quality wafers is Fundamentals of semiconductor device fabrication, especially in the machining of hard brittle gallium oxide crystals with strong cleavage properties. In terms of ultra-precision machining, gallium oxide wafers are mostly processed by grinding. Although β-Ga ₂ O ₃ is easily cleavable, cracks and pits will occur during the grinding process, reducing the yield, but compared with grinding process, the grinding process is easier to control. In addition, the current research on ultra-precision machining of easily cleavable gallium oxide single crystal substrates at home and abroad is only in the initial stage of exploration. Therefore, a high-efficiency processing method for easily cleavable semiconductor crystals is urgently needed to fill the current vacancy.

SUMMARY OF THE INVENTION

In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a processing method for easily cleavable semiconductor crystals. The entire processing process of the present invention is based on a negative feedback system to effectively control the maximum grinding force to ensure real-time grinding during the entire grinding process. The cutting force is less than the critical grinding force for the cleavage of the gallium oxide crystal; secondly, the fine-grained diamond grinding wheel is used to reduce the fluctuation of the grinding force and reduce the cleavage phenomenon. The combination of the two effectively controls the traditional crystal processing technology ( Especially the cleavage phenomenon in the grinding stage) improves the yield of the product and improves the surface quality of the product.

The technical means adopted in the present invention are as follows:

A processing method for easily cleavable semiconductor crystals, comprising the following steps:

S1. Fix the gallium oxide wafer on the worktable, and there is a force sensor under it;

S2. Start the rotation of the coarse-grained diamond grinding wheel and the worktable;

S3. Feed the coarse-grained diamond grinding wheel to the top of the gallium oxide wafer, stop feeding until the force sensor shows the indicated value, set the initial feed speed of rough grinding, the maximum grinding force F _rough and the feed amount to reduce the oxidation The gallium wafer is subjected to rough grinding until the set feed is reached, and the grinding force is guaranteed to fluctuate within the range of F _rough ±0.1N during rough grinding;

S4. Stop the feed and continue to perform no-feed grinding on the gallium oxide wafer after rough grinding. After that, lift the coarse-grained diamond grinding wheel, and stop the coarse-grained diamond grinding wheel and the rotation of the worktable;

S5. Replace the coarse-grained diamond grinding wheel with a fine-grained diamond grinding wheel, and start the fine-grained diamond grinding wheel and the worktable to rotate;

S6. Feed the fine-grained diamond grinding wheel to the top of the gallium oxide wafer after no feed grinding, stop feeding until the force sensor shows the value, set the initial feed speed for fine grinding, and the maximum grinding force F _fine After adjusting the feed rate, the gallium oxide wafer is finely ground until the set feed rate is reached. During the fine grinding process, the grinding force is guaranteed to fluctuate within the range of F _fine ±0.1N.

The gallium oxide wafer is a circular wafer 7, which is adsorbed on the vacuum chuck of the worktable or fixed on the worktable, as shown in Figure 2(b);

Or, the gallium oxide wafer is a plurality of small-sized gallium oxide wafers 6 evenly distributed on the disk in the circumferential direction, and the disk is adsorbed on the vacuum suction cup of the worktable or fixed on the worktable, as shown in Figure 2 (a ) shown;

The rough grinding, the non-feed grinding and the fine grinding are all cooled by cooling liquid, the flow rate of the cooling liquid is 4-6 L/min, and the cooling liquid is deionized water.

In the step S2, the rotational speed of the coarse-grained diamond grinding wheel is 600-1000 r/min, and the rotational speed direction is clockwise;

The rotational speed of the worktable is 200-400 r/min, and the rotational speed direction is counterclockwise.

In the step S3, the coarse-grained diamond grinding wheel is fed to the top of the gallium oxide wafer, and the specific steps of stopping feeding until the force sensor shows a value are as follows:

Feed the coarse-grained diamond grinding wheel close to the top of the gallium oxide wafer, and then slowly feed it to the gallium oxide wafer at a feed speed of 10 μm/min, until the force sensor shows a value and stop feeding;

In the step S3, the initial feed rate is 0.5-1 μm/min, the maximum grinding force F is _roughly 20-30 N, and the feed amount is 10-20 μm;

In the step S3, the negative feedback system is used to ensure that the grinding force fluctuates within the range of F _rough ±0.1N during the rough grinding process;

The data processor collects the grinding force signal measured by the force sensor in real time, and amplifies it and sends it to the negative feedback system. The negative feedback system compares it with the set maximum grinding force and continuously feeds it back to the control system. Control the feed speed of the coarse-grained diamond grinding wheel. The increase or decrease of the feed speed is related to the difference between the real-time grinding force and the set maximum grinding force. As shown in the flowchart in Figure 3, m and V _n , V _m has a certain relationship to ensure that the grinding force fluctuates within the range of F _rough ± 0.1N during rough grinding;

The abrasive grain size of the coarse-grained diamond grinding wheel is W10-W14.

During the rough grinding process, the data processor is used to analyze the grinding force data, and feedback control the feed rate of the coarse-grained diamond grinding wheel, and continuously control the maximum grinding force to keep it within a certain fluctuation range ( F _coarse ±0.1N). Achieve constant force grinding to control the probability of cleavage of gallium oxide crystals.

The parameters of the no-feed grinding are the same as the parameters of the rough grinding except the feed speed is zero;

The grinding time of the no-feed grinding was 3 min.

The purpose of the no-feed grinding is to eliminate the elastic deformation caused by the feeding and the amount of the knife, improve the surface finish, and prepare for fine grinding.

In the step S5, the rotational speed of the fine-grained diamond grinding wheel is 1000-2400 r/min, and the rotational speed direction is clockwise;

The rotational speed of the worktable is 300-400 r/min, and the rotational speed direction is counterclockwise.

In the step S6, the fine-grained diamond grinding wheel is fed to the top of the gallium oxide wafer after no-feed grinding, and the specific steps of stopping feeding until the force sensor shows a value are as follows:

Feed the fine-grained diamond grinding wheel close to the top of the gallium oxide wafer after no-feed grinding, and then slowly feed it to the gallium oxide wafer at a feed rate of 10 μm/min until the force sensor shows a value and stops feeding;

In the step S6, the initial feed rate is 0.5-1 μm/min, the maximum grinding force F is 30-60 N, and the feed amount is 5-10 μm;

In the step S6, the negative feedback system is used to ensure that the grinding force fluctuates within the range of F fine ±0.1N during the fine grinding process;

The data processor collects the grinding force signal measured by the force sensor in real time, and amplifies it and sends it to the negative feedback system. The negative feedback system compares it with the set maximum grinding force and continuously feeds it back to the control system. Control the feed speed of the fine-grained diamond grinding wheel. The increase or decrease of the feed speed is related to the difference between the real-time grinding force and the set maximum grinding force. As shown in the flow chart in Figure 3, m and Vn, Vm A certain relationship is required to ensure that the grinding force fluctuates within the range of F fine ±0.1N during the fine grinding process;

The abrasive grain size of the fine-grained diamond grinding wheel is W1-W5.

During the fine grinding process, the data processor is used to analyze the grinding force data, and the feed rate of the fine-grained diamond grinding wheel is fed back and controlled, and the maximum grinding force is continuously controlled to keep it within a certain fluctuation range (F fine ±0.1N). Achieve constant force grinding to control the probability of cleavage of gallium oxide crystals.

Compared with the prior art, the beneficial effects of the present invention are:

The invention controls the feed speed based on the feedback of the force sensor to control the grinding force, and at the same time adopts the ultra-precision machining method of the fine-grained diamond grinding wheel, which effectively solves the cleavage of gallium oxide in the machining stage, especially the grinding stage. In addition, the fine-grained abrasive particles can reduce the damage degree and thickness of the damaged layer, shorten the time of the subsequent chemical mechanical polishing process and reduce its removal amount.

The negative feedback system receives the grinding force signal measured by the force sensor collected and amplified by the data processor in real time, and continuously feeds it back to the control system to control the feed speed in real time, so as to realize that the grinding force is less than the cleavage stress threshold of gallium oxide. The dissociation phenomenon that is easy to occur in the machining of gallium oxide is eliminated, the surface quality of the gallium oxide crystal is improved, and a high yield is achieved.

Based on the above reasons, the present invention can be widely promoted in the fields of ultra-precision machining of hard and brittle semiconductor wafers.

Description of drawings

In order to illustrate the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without any creative effort.

FIG. 1 is a schematic diagram of preventing cleavage of a method for processing an easily cleavable semiconductor crystal according to an embodiment of the present invention.

Figure 2 (a) is a schematic diagram of the arrangement of the small-sized gallium oxide wafer fixing disk on the worktable of the present invention; Figure 2 (b) is a schematic diagram of the arrangement of the circular wafer of the present invention on the worktable.

FIG. 3 is a flow chart of the control system of the present invention.

In the figure: 1 is a diamond grinding wheel; 2 is a gallium oxide wafer; 3 is a vacuum chuck; 4 is a force sensor; 5 is a workbench; 6 is a small-sized gallium oxide wafer; 7 is a circular wafer;

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments These are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

As shown in Fig. 1, a processing method of easily cleavable semiconductor crystal has the following steps:

S1. Turn on the ultra-precision grinder, and adsorb a cut 2-inch gallium oxide wafer 2 on the vacuum suction cup 3 on the table 5 of the ultra-precision grinder. The position on the workpiece is shown in Figure 2(b). When the gallium oxide wafer 2 is clamped, the center of the worktable 5 is coincident with the center of the gallium oxide wafer 2;

S2, use the coarse-grained diamond grinding wheel 1, the abrasive grain size of the coarse-grained diamond grinding wheel 1 is W10-W14, adjust the end face of the abrasive layer of the coarse-grained diamond grinding wheel 1 to the center position of the workbench 5, then turn on the coolant, cool down The liquid is deionized water, and the cooling liquid flow is 4-6L/min; then start the coarse-grained diamond grinding wheel 1, its speed is 600-1000r/min, and the rotation direction is clockwise; then start the workbench 5, and the speed of the workbench 5 is 200-400r/min, the rotation direction is counterclockwise;

S3. Turn on the force sensor 4, manually feed the coarse-grained diamond grinding wheel 1 to 1 mm above the gallium oxide wafer 2, turn on the automatic feeding, and the feeding speed is 10 μm/min, until the force sensor 4 shows the value, and then turn off the automatic feeding Then turn on the negative feedback system, and at the same time set the initial feed rate Vi for rough grinding to 0.5μm/min, the maximum grinding force F _rough to be 30N, and the feed rate to be 20μm. After that, roughen the gallium oxide wafer 2. Grinding until the set feed rate is reached, during rough grinding, the negative feedback system receives in real time the signal of the grinding force measured by the force sensor 4 collected and amplified by the data processor, and continuously feeds it back to the control system Control the feed speed of the coarse-grained diamond grinding wheel 1 to ensure that the grinding force fluctuates within the range of F _coarse ± 0.1N during the rough grinding process, as shown in Figure 3, to control the probability of cleavage of the gallium oxide crystal. After rough grinding, carry out 3min no-feed grinding to prepare for the next fine grinding;

S4, lift the coarse-grained diamond grinding wheel 1, and stop the coarse-grained diamond grinding wheel 1 and the table 5 from rotating, and replace the coarse-grained diamond grinding wheel 1 with a fine-grained diamond grinding wheel 1. The abrasive grain size of the fine-grained diamond grinding wheel 1 is W1-W5, adjust the end face of the abrasive layer of the fine-grained diamond grinding wheel 1 to the center of the worktable 5, then turn on the coolant, the coolant is deionized water, and the coolant flow rate is 4-6/min; then start the fine-grained diamond Grinding wheel 1, its rotational speed is 1000-2400r/min, and the rotational speed direction is clockwise; then start worktable 5, the rotational speed of worktable 5 is 300-400r/min, and the rotational speed direction is counterclockwise;

S5. Turn on the force sensor 4, manually feed the fine-grained diamond grinding wheel 1 to 1 mm above the gallium oxide wafer 2 after no feed grinding, turn on the automatic feeding, and the feeding speed is 10 μm/min until the force sensor 4 appears After indicating the value, turn off the automatic feed, and then turn on the negative feedback system. At the same time, set the initial feed speed Vi for fine grinding to 0.5μm/min, the maximum grinding force F fine to 60N, and the feed rate to 10μm. The gallium oxide wafer 2 is finely ground until the set feed amount is reached. During the fine grinding process, the negative feedback system receives the signal of the grinding force measured by the force sensor 4 collected and amplified by the data processor in real time. , and continuously feedback to the control system to control the feed speed of the fine-grained diamond grinding wheel 1 to ensure that the grinding force fluctuates within the range of F fine ± 0.1N during the fine grinding process, as shown in Figure 3, to control the formation of gallium oxide crystals. The probability of cleavage, to achieve ultra-precision grinding lower than the cleavage grinding force;

After finishing the fine grinding, the gallium oxide wafer 2 can be removed and cleaned, and the ultra-precision grinding process of the gallium oxide wafer 2 is completed. In the final measurement, Ra≤1 nm and TTV≤5 μm of the obtained gallium oxide wafer 2 .

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: The technical solutions described in the foregoing embodiments can still be modified, or some or all of the technical features thereof can be equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present invention. scope.

Claims (5)

1. a processing method of easily cleavable semiconductor crystal is characterized in that having the following steps: S1. Fix the gallium oxide wafer on the worktable, and there is a force sensor under it; S2. Start the rotation of the coarse-grained diamond grinding wheel and the worktable; S3. Feed the coarse-grained diamond grinding wheel to the top of the gallium oxide wafer, stop feeding until the force sensor shows the indicated value, set the initial feed speed of rough grinding, the maximum grinding force F rough and the feed amount to reduce the oxidation The gallium wafer is subjected to rough grinding until the set feed rate is reached. During the rough grinding process, the grinding force is guaranteed to fluctuate within the range of F coarse ±0.1N. The abrasive grain size of the coarse-grained diamond grinding wheel is W10-W14; S4. Stop the feed and continue to perform no-feed grinding on the gallium oxide wafer after rough grinding. After that, lift the coarse-grained diamond grinding wheel, and stop the coarse-grained diamond grinding wheel and the rotation of the worktable; S5. Replace the coarse-grained diamond grinding wheel with a fine-grained diamond grinding wheel, and start the fine-grained diamond grinding wheel and the worktable to rotate; S6. Feed the fine-grained diamond grinding wheel to the top of the gallium oxide wafer after no feed grinding, stop feeding until the force sensor shows the value, set the initial feed speed for fine grinding, and the maximum grinding force F fine After adjusting the feed rate, the gallium oxide wafer is finely ground until the set feed rate is reached. During the fine grinding process, the grinding force is guaranteed to fluctuate within the range of F fine ±0.1N; the abrasive of the fine-grained diamond grinding wheel The particle size is W1-W5; In the step S3, the coarse-grained diamond grinding wheel is fed to the top of the gallium oxide wafer, and the specific steps of stopping feeding until the force sensor shows a value are as follows: Feed the coarse-grained diamond grinding wheel close to the top of the gallium oxide wafer, and then slowly feed it to the gallium oxide wafer at a feed speed of 10 μm/min, until the force sensor shows a value and stop feeding; In the step S3, the initial feed rate is 0.5-1 μm/min, the maximum grinding force F is roughly 20-30 N, and the feed amount is 10-20 μm; In the step S3, the negative feedback system is used to ensure that the grinding force fluctuates within the range of F rough ±0.1N during the rough grinding process; The data processor collects the grinding force signal measured by the force sensor in real time, and amplifies it and sends it to the negative feedback system. The negative feedback system compares it with the set maximum grinding force and continuously feeds it back to the control system. Control the feed speed of the coarse-grained diamond grinding wheel. The increase or decrease of the feed speed is related to the difference between the real-time grinding force and the set maximum grinding force, so as to ensure that the grinding force is within the range of F coarse ± ± during the rough grinding process. Fluctuate within the range of 0.1N; The parameters of the no-feed grinding are the same as the parameters of the rough grinding except the feed speed is zero; The grinding time of the no-feed grinding is 3 minutes; In the step S6, the fine-grained diamond grinding wheel is fed to the top of the gallium oxide wafer after no-feed grinding, and the specific steps of stopping feeding until the force sensor shows a value are as follows: Feed the fine-grained diamond grinding wheel close to the top of the gallium oxide wafer after no-feed grinding, and then slowly feed it to the gallium oxide wafer at a feed rate of 10 μm/min until the force sensor shows a value and stops feeding; In the step S6, the initial feed rate is 0.5-1 μm/min, the maximum grinding force F is 30-60 N, and the feed amount is 5-10 μm; In the step S6, the negative feedback system is used to ensure that the grinding force fluctuates within the range of F fine ±0.1N during the fine grinding process; The data processor collects the grinding force signal measured by the force sensor in real time, and amplifies it and sends it to the negative feedback system. The negative feedback system compares it with the set maximum grinding force and continuously feeds it back to the control system. Control the feed speed of the fine-grained diamond grinding wheel, and the increase or decrease of the feed speed is related to the difference between the real-time grinding force and the set maximum grinding force, so as to ensure that the grinding force is within F fine ± ± Fluctuates in the range of 0.1N. 2. The processing method according to claim 1, wherein the gallium oxide wafer is a circular wafer, which is adsorbed on the vacuum chuck of the workbench or fixed on the workbench; Or, the gallium oxide wafers are a plurality of small-sized gallium oxide wafers uniformly distributed on a disk in the circumferential direction, and the disks are adsorbed on the vacuum suction cup of the worktable or fixed on the worktable. 3. The processing method according to claim 1, wherein the rough grinding, the no-feed grinding and the fine grinding are all cooled by cooling liquid, and the flow rate of the cooling liquid is 4- 6L/min, the coolant is deionized water. 4. The processing method according to claim 1, wherein in the step S2, the rotational speed of the coarse-grained diamond grinding wheel is 600-1000 r/min, and the rotational speed direction is clockwise; The rotational speed of the worktable is 200-400 r/min, and the rotational speed direction is counterclockwise. 5. The processing method according to claim 1, wherein in the step S5, the rotational speed of the fine-grained diamond grinding wheel is 1000-2400 r/min, and the rotational speed direction is clockwise; The rotational speed of the worktable is 300-400 r/min, and the rotational speed direction is counterclockwise.

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