Wafer double-side polishing thickness precision control method

Abstract

The application discloses a wafer double-face grinding thickness precision control method, which comprises the following steps: preparation, suspension configuration, polishing liquid configuration, disc repairing, frequency setting, feeding, grinding processing, frequency returning and unloading. When Z-cut wafers which cannot be detected in frequency are processed, AT-cut wafers which can be detected in frequency are put in as frequency detection wafers, and the fixed thickness difference of the two types of wafers when processed to a certain thickness is utilized, so that the processing thickness precision of the Z-cut wafers can be controlled within the range of ±0.001 mm.

Description

Technical Field

[0001] This invention relates to the field of wafer grinding and processing, and specifically to a method for precise control of thickness during double-sided wafer grinding. Background Technology

[0002] Artificial quartz crystal wafers, or simply "wafers," are processed in different ways, resulting in different characteristics. Some wafers have detectable frequencies, while others do not. During the double-sided grinding process, for wafers with detectable frequencies, the thickness can be precisely controlled within a range of approximately ±0.001 mm. However, for wafers with undetectable frequencies, traditional processing methods can only control the thickness tolerance within ±0.01 mm, a difference of an order of magnitude. Therefore, for wafers with undetectable frequencies, traditional processing methods are not precise enough in controlling their thickness. Summary of the Invention

[0003] To address the aforementioned technical problems, the main objective of this invention is to provide a method for precisely controlling the thickness of double-sided wafer grinding. When processing Z-cut wafers where the frequency cannot be detected, an AT-cut wafer where the frequency can be detected is placed as a frequency measuring chip. By utilizing the fixed thickness difference between the two types of wafers when they are processed to a certain thickness, the processing thickness accuracy of the Z-cut wafer is controlled within ±0.001mm. Adding a frequency measuring chip in the middle of the wafer reduces the amount of frequency measuring chip used.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a method for precise control of wafer double-sided grinding thickness, comprising the following steps:

[0005] S1: Select a cruise ship according to the specifications of the wafers being processed, and conduct a spot check on the double-sided polishing machine;

[0006] S2: Preparation of suspension: Sodium nitrite, triethanolamine and deionized water are mixed to form a solution, wherein the mass ratio of sodium nitrite, triethanolamine and deionized water is 5:7:88;

[0007] S3: Preparation of grinding fluid: Mix and stir the diamond abrasive, suspension and deionized water to prepare a grinding fluid for double-sided grinding. The diamond abrasive is GC3000# green silicon carbide. The mass ratio of GC3000# green silicon carbide, suspension and deionized water is 9:2:20.

[0008] S4: Dressing: Based on the flatness of the grinding disc and the end runout of the grinding machine, place the dressing wheel on the lower grinding disc and select the dressing method of forward or reverse rotation of the grinding machine according to the principle of "dressing the inside in the forward direction and the outside in the reverse direction".

[0009] S5: Frequency setting: Based on the correspondence between thickness and frequency, convert the required thickness into a frequency point.

[0010] S6: Loading: Place the cruise ship onto the lower grinding disc of the double-sided grinding machine, and simultaneously place the wafer to be processed and the frequency measuring chip into the square hole of the cruise ship;

[0011] S7: Grinding process: Lower the upper grinding disc of the double-sided grinding machine, turn on the sand pump to draw out the grinding fluid, turn on the main unit start button of the double-sided grinding machine, and slowly rotate the speed regulator knob to adjust the speed to 30 rpm to start the double-sided grinding process.

[0012] S8: Frequency Response: During the grinding process, an automatic frequency meter is used to continuously detect the frequency value of the frequency measuring plate. Once the automatic frequency meter detects the preset frequency point, the double-sided grinding machine will automatically stop.

[0013] Restart the double-sided grinding machine, observe the frequency value displayed on the automatic frequency meter, and confirm whether the displayed value is consistent with the preset value. Stop the machine after confirming that the preset value has been reached.

[0014] S9: Unloading: Raise the upper platen of the double-sided grinding machine, remove the roller first, and then remove the wafer;

[0015] S10: Move the polished wafer obtained in step S9 to the next process, take out the next batch of wafers to be processed, and repeat S6-S9 until all wafers are processed.

[0016] S11: Equipment cleaning: Rinse the upper and lower grinding discs and the inside of the machine cavity thoroughly.

[0017] Furthermore, the selected cruise ship is one that can place the frequency measurement chip in the center and the chip to be processed around the perimeter.

[0018] Furthermore, the selected cruise ship has a square hole for a frequency measurement chip at its center.

[0019] Furthermore, the selected cruise ship has multiple sand-flowing holes for the passage of abrasive fluid.

[0020] Furthermore, each cruise ship can hold 3 chips that need to be processed, along with 1 frequency measurement chip.

[0021] Furthermore, by adding an electrode to the center of the upper grinding disc of the grinding machine, the processing frequency of the frequency measuring plate on the cruise ship plate can be detected.

[0022] Furthermore, the speed adjustment process in step S7 is as follows: the motor rotates at a low speed of 2-3 rpm, the counter jumps 5-10 revolutions, and after the operation is normal, it is gradually and slowly accelerated to 30 rpm.

[0023] Furthermore, in step S7, the pressure of the grinder is set to 55 kg.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] 1. In the present invention, when processing Z-cut wafers whose frequencies cannot be detected, AT-cut wafers whose frequencies can be detected are placed as frequency measuring wafers. By utilizing the fixed thickness difference between the two types of wafers when they are processed to a certain thickness, the processing thickness accuracy of the Z-cut wafers is controlled within the range of ±0.001mm.

[0026] 2. This invention adds a frequency measuring chip in the middle of the cruise ship, reducing the amount of frequency measuring chips used. Only one frequency measuring chip is needed to process three Z-cut wafers.

[0027] 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 to make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the cruise ship used in an embodiment of the present invention.

[0029] In the diagram: 1. Frequency measurement chip placement hole; 2. Wafer to be processed placement hole; 3. Sanding hole. Detailed Implementation

[0030] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following describes in detail, with reference to the accompanying drawings and preferred embodiments, a method for precise control of wafer double-sided grinding thickness according to the present invention, including its specific implementation, structure, features and effects.

[0031] A method for precise thickness control during double-sided wafer grinding includes the following steps:

[0032] (1) Preparatory work

[0033] Select the appropriate roller based on the specifications of the wafer being processed. The roller's aperture should be 0.5-1.0 mm larger than the wafer's diameter, and the roller's thickness should be 0.01 mm thinner than the wafer's thickness. Perform routine inspections on the double-sided polishing machine.

[0034] (2) Preparation of suspension

[0035] To prevent the equipment from rusting and to prevent the precipitation of diamond powder, a mixed solution of sodium nitrite, triethanolamine and deionized water is prepared, wherein the mass ratio of sodium nitrite, triethanolamine and deionized water is 5:7:88.

[0036] (3) Preparation of grinding fluid

[0037] A grinding slurry for double-sided grinding is prepared by mixing and stirring the diamond abrasive, suspension and deionized water. The diamond abrasive is GC3000# green silicon carbide, and the mass ratio of GC3000# green silicon carbide, suspension and deionized water is 9:2:20.

[0038] (4) Repairing the plate

[0039] Based on the flatness of the grinding disc and the end runout of the grinding machine, place the correction wheel on the lower grinding disc and select the grinding machine's forward or reverse rotation correction method according to the principle of "correcting the inside in the forward direction and the outside in the reverse direction".

[0040] (5) Frequency setting

[0041] Based on the correspondence between thickness and frequency, the required thickness is converted into frequency points.

[0042] (6) Feeding

[0043] Place the cruise ship on the lower grinding disc of the double-sided grinding machine, place the wafer to be processed into the wafer placement hole 2, and at the same time place the frequency measuring chip into the frequency measuring chip placement hole 1.

[0044] (7) Grinding process

[0045] Lower the upper grinding disc of the double-sided grinder, turn on the sand pump to draw up the grinding fluid, turn on the start button of the double-sided grinder, and slowly rotate the speed controller knob: the motor will rotate at a low speed of 2-3 rpm, the counter will jump 5-10 revolutions, and after there is no abnormality in operation, you can gradually and slowly accelerate to 30 rpm to start the double-sided grinding process.

[0046] (8) Reciprocal frequency

[0047] During the grinding process, an automatic frequency meter is used to continuously detect the frequency value of the frequency measuring plate. The displayed frequency value is stable. After the automatic frequency meter detects the preset frequency point, the double-sided grinding machine will automatically stop. Restart the double-sided grinding machine, observe the frequency value displayed on the automatic frequency meter, and confirm whether the displayed value is consistent with the preset value. Stop the machine after confirming that the preset value has been reached.

[0048] (9) Feeding

[0049] Raise the upper platen of the double-sided polishing machine, remove the roller first, and then remove the wafer;

[0050] (10) Repeat (6)-(9) until the processing is complete.

[0051] The polished wafers obtained in step (9) are moved to the next process, and the next batch of wafers to be processed is taken out for processing. Steps (6)-(9) are repeated until all wafers are processed.

[0052] (11) Equipment cleaning

[0053] Clean the upper and lower grinding discs and the inside of the machine cavity.

[0054] Furthermore, the selected cruise ship is one that can place the frequency measurement chip in the center and the chip to be processed around the perimeter.

[0055] Furthermore, the selected cruise ship has a square hole for a frequency measurement chip at its center.

[0056] Furthermore, the selected cruise ship has multiple sand-flowing holes 3 for passing abrasive fluid.

[0057] Furthermore, by adding an electrode to the center of the upper grinding disc of the grinding machine, the processing frequency of the frequency measuring plate on the cruise ship plate can be detected.

[0058] Furthermore, each cruise ship can hold 3 chips that need to be processed, along with 1 frequency measurement chip.

[0059] Furthermore, in step (7), the pressure of the grinder cannot be adjusted arbitrarily; the pressure is set to 55 kg and the rotation speed is set to 30 rpm.

[0060] The principle of this processing method is to insert an AT-cut wafer, which can detect frequencies, as a frequency measuring wafer when processing a Z-cut wafer where frequencies cannot be detected. By utilizing the fixed thickness difference between the two wafer types when they are processed to a certain thickness, the processing thickness accuracy of the Z-cut wafer is controlled within ±0.001mm. This rule has been verified through long-term experiments. The following are the verification experiments:

[0061] Three wafer reels were tested. Five Z-cut wafers were taken from each reel to measure thickness, and five AT-cut wafers were taken to measure frequency. The data are as follows: Reel 1

[0062] Film 1 Second film The 3rd film The 4th piece 5th piece average value Z-cut wafer thickness (unit: mm) 0.1211 0.1231 0.1222 0.1218 0.1233 0.1223 AT-cut wafer thickness (unit: KHz) 13700 13653 13685 13710 13721 13693.8

[0063] Thickness difference: 0.1223 - 1660 / 13693.8 = 0.001077 ≈ 0.0011

[0064] Second round

[0065] Film 1 Part 2 The 3rd film The 4th piece The 5th film average value Z-cut wafer thickness (unit: mm) 0.1189 0.1181 0.1152 0.1163 0.1191 0.11752 AT-cut wafer thickness (unit: KHz) 14240 14257 14251 14277 14281 14261.2

[0066] Thickness difference: 0.11752 - 1660 / 14261.2 = 0.00112 ≈ 0.0011

[0067] 3rd round

[0068] Film 1 Part 2 The 3rd film The 4th piece The 5th film average value Z-cut wafer thickness (unit: mm) 0.1265 0.1273 0.1294 0.1288 0.1276 0.12792 AT-cut wafer thickness (unit: KHz) 13098 13108 13092 13077 13069 13088.8

[0069] Thickness difference: 0.12792 - 1660 / 13088.8 = 0.001094 ≈ 0.0011

[0070] Therefore, when both Z-cut and AT-cut wafers are processed to approximately 0.12 mm, their thickness difference is a fixed value, approximately 0.0011.

[0071] The following examples further illustrate the double-sided grinding process of the artificial quartz crystal wafer described in this invention, hereinafter referred to as "wafer".

[0072] Example:

[0073] Taking a Z-cut wafer of 75*75*0.12±0.001mm processed by double-sided grinding as an example, the steps of a method for precise thickness control in double-sided grinding of a wafer are explained in the following order:

[0074] (1) Preparatory work

[0075] Wear personal protective equipment correctly. Equipment inspection includes: checking if the lubricating oil level in the grinding machine's gearbox reaches the center of the observation hole; checking if the air pressure of the air supply triple unit is 0.4MPa~0.6MPa, ensuring that the water in the triple unit's oil cups has been drained, and that the oil level in the other oil cup is centered; and checking if the sand pump's grounding wire is properly connected. Select the appropriate roller blade according to the specifications of the wafer being processed, choosing a 76*76*0.11mm roller blade with a 14*12 square hole in the center; the thickness tolerance of the same set of roller blades should be controlled within ±0.002mm.

[0076] (2) Preparation of suspension

[0077] To prevent the equipment from rusting and to prevent the precipitation of corundum, a mixed solution of sodium nitrite, triethanolamine, and deionized water is prepared, wherein the mass ratio of sodium nitrite, triethanolamine, and deionized water is 5:7:88.

[0078] (3) Preparation of grinding fluid

[0079] Mix and stir the diamond abrasive, suspension, and deionized water to prepare a grinding slurry for double-sided grinding. The diamond abrasive is GC3000# green silicon carbide. The mass ratio of GC3000# green silicon carbide, suspension, and deionized water is 9:2:20. (Take precautions during preparation to avoid inhaling GC2000# silicon carbide dust.)

[0080] (4) Repairing the plate

[0081] The flatness of the grinding disc must be checked every shift, and the end runout of the grinding machine can be inspected periodically. Check that the grinding disc meets the following requirements: ① Flatness ≤ 0.01mm; ② Inner ring end runout ≤ 0.05mm, outer ring end runout ≤ 0.15mm; ③ No scratches or bright spots on the upper and lower grinding discs.

[0082] Overhauling the grinding disc: After taking over the shift, the grinding disc should be overhauled according to the principle of "overhauling the inside, overhauling the outside". Generally, the number of grinding disc rotations should not be less than 700, and 1000 rotations with new abrasive (one replacement of diamond abrasive can be used for 5 shifts, the first shift uses new abrasive, so more grinding disc rotations are needed, which is 1000 rotations), which takes about 20 minutes. After grinding, the grinding disc should also be overhauled for 300-500 revolutions before cleaning the machine (the grinding disc rotation speed is 25 rpm).

[0083] (5) Frequency setting

[0084] Based on the correlation between thickness and frequency, the required thickness is converted into a frequency point, and the frequency point during processing is monitored by an automatic frequency meter. Specifically, the method for converting thickness to frequency is as follows: A portion of wafers are processed experimentally, with a thickness approximately 0.12mm. About 20 Z-cut wafers are measured using a height gauge with an accuracy of 0.0001mm, and the measured thickness values ​​are recorded. The frequency values ​​of approximately 10 AT-cut wafers are measured using a network frequency meter, and the frequency values ​​are recorded. The thickness of the AT-cut wafers is calculated using the frequency constant value. The calculation constant for the frequency-to-thickness conversion of the AT-cut wafers is 1660. Dividing 1660 by the frequency value yields the thickness value, and vice versa. The difference between the two wafer thicknesses is obtained by subtracting the average of the measured thickness values ​​of the Z-cut wafers from the average of the calculated thickness values ​​of the AT-cut wafers.

[0085] If the measured average thickness of the Z-cut wafer is A, the calculated average thickness of the AT-cut wafer is B, AB = C, the target thickness is 0.12 mm, and the value of the monitoring frequency point is set to 1660 / (0.12-C).

[0086] (6) Feeding

[0087] Place the wafers evenly on the lower grinding disc of the double-sided grinding machine in sequence, and place them hole by hole. Place the 75*75 wafer (the wafer to be processed) in the 76*76 wafer placement hole 2, and place the 13*11 wafer (frequency measurement wafer) in the 14*12 frequency measurement wafer placement hole 1. After placing the wafers, check and confirm that there are no errors.

[0088] (7) Grinding process

[0089] First, press the upper plate quick-lift button and remove the safety ring. Then, press the upper plate quick-descent button. When the plate descends to about 10mm below the workpiece, press the slow-descent button to avoid impacting the workpiece. Turn on the sand pump and rotate the sand pipe one revolution to ensure the sand fully covers the wafers. Turn on the main motor and slowly rotate the adjustment knob to keep the motor running at a low speed of 2-3 rpm. The counter will jump 5-10 revolutions. After confirming normal operation, gradually increase the speed to 30 rpm. Set the grinding pressure to 55 kg (the pressure can be reduced proportionally when grinding a small number of wafers. For example, if 15 wafers are normally processed per plate, and only 10 wafers remain to be processed, adjust the pressure to 55 ÷ 15 * 10 = 36 kg).

[0090] (8) Reciprocal frequency

[0091] When grinding with an automatic frequency meter, the machine will automatically stop when the set frequency is reached. After resetting the speed controller to zero and turning on the main motor, slowly rotate the speed controller knob and observe the frequency fluctuation of the automatic frequency meter. Confirm that the displayed frequency value matches the set frequency value. One shift consists of 15 trays. After grinding the first 3 trays of material in each shift, the frequency should be checked against the manual frequency meter.

[0092] (9) Feeding

[0093] After releasing the pressure and restoring the counter to zero, the upper plate can be raised, the safety ring engaged, and the lower plate adjusted to the raised position. The scroll plate is then removed and placed flat on the plate holder. The scroll plate is checked for any wafers. The 75*75 wafers (processed wafers) are removed and placed in a cleaning rack. The cleaning rack is then immersed in water to prevent the wafers from drying out. The 13*11 wafers (frequency measurement wafers) are removed and placed in a plastic box for centralized storage.

[0094] (10) Repeat (6)-(9) until the processing is complete.

[0095] After grinding, the wafers obtained in step (9) are placed in an ultrasonic cleaner for initial cleaning and then transferred to a wafer washing chamber. A batch of wafers to be processed is then taken out and processed. Steps (6)-(9) are repeated until all wafers are processed.

[0096] (11) Equipment cleaning

[0097] The cleaning areas include the sand-washing tank, the upper plate surface, the upper and lower grinding plate sand-washing tanks, and the equipment surface. After rinsing the equipment, add suspension (when adding suspension, turn the speed controller to 2 rpm for 3-5 revolutions); when rinsing the lower grinding plate, the water pipe should be used to rinse the grinding plate vertically, not at an angle, to prevent water from entering the central shaft and increasing wear; the lower grinding plate should be in a descending state; check the tools and fixtures to ensure no wafers remain. Place them in the designated locations as required, and clean the site and assigned area.

[0098] The above description is merely an embodiment of the present invention and is not intended to limit the present invention in any way. The present invention can also have other embodiments based on the above structure and function, which will not be listed hereafter. Therefore, any simple modifications, equivalent changes, and alterations made by those skilled in the art to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for thickness precision control of double side polishing of a wafer, characterized by, The method comprises the following steps: S1: selecting a runner according to the wafer specification to be processed, and checking the double-sided grinding machine; S2: preparing a suspension: preparing a mixed solution of sodium nitrite, triethanolammonium and deionized water, wherein the mass ratio of sodium nitrite, triethanolammonium and deionized water is 5:7:88; S3: preparing a grinding liquid: mixing and stirring corundum, the suspension and deionized water to prepare a grinding liquid for double-sided grinding processing, wherein the corundum is GC3000# green silicon carbide, and the mass ratio of GC3000# green silicon carbide, the suspension and deionized water is 9:2:20; S4: dressing: according to the flatness of the grinding disc and the end jump of the grinding machine, placing a dressing wheel on the lower grinding disc, and selecting the dressing mode of the grinding machine in the principle of "dressing inside and dressing outside"; S5: frequency setting: converting the required thickness into a frequency point according to the corresponding relationship between the thickness and the frequency, and monitoring the frequency point during processing by using an automatic frequency meter; specifically, the method for converting the thickness into the frequency is as follows: processing part of wafers, processing the thickness to 0.12 mm, detecting 20 Z-cut type wafers by using a height gauge with an accuracy of 0.0001 mm to record the measured thickness values; detecting the frequency values of AT-cut type wafers processed simultaneously by using a network frequency meter to record the frequency values of 10 AT-cut type wafers, calculating the thickness of the AT-cut type wafers by using the frequency constant value, and the calculation constant value of the conversion between the frequency and the thickness of the AT-cut type wafers is 1660; subtracting the average value of the calculated thickness values of the AT-cut type wafers from the average value of the measured thickness values of the Z-cut wafers to obtain the difference between the thicknesses of the two types of wafers, wherein the average value of the measured thickness values of the Z-cut type wafers is A, the average value of the calculated thickness values of the AT-cut type wafers is B, A-B=C, the target thickness is 0.12 mm, and the value of the monitored frequency point is set to be 1660 / (0.12-C); S6: loading: placing the runner on the lower grinding disc of the double-sided grinding machine, and simultaneously placing the wafers to be processed and the frequency measuring wafers into the square hole of the runner; S7: grinding processing: lowering the upper grinding disc of the double-sided grinding machine, starting the sand pump to extract the grinding liquid, starting the main machine of the double-sided grinding machine, slowly rotating the speed regulator knob to 30 rpm, and starting the double-sided grinding processing; S8: frequency returning: continuously detecting the frequency value of the frequency measuring wafer during the grinding processing by using the automatic frequency meter, and stopping the double-sided grinding machine automatically after the automatic frequency meter monitors the preset frequency point; restarting the double-sided grinding machine, observing the frequency value displayed on the automatic frequency meter, confirming whether the displayed value is consistent with the preset value, and stopping after confirming that the preset value is reached; S9: unloading: raising the upper disc of the double-sided grinding machine, and then taking out the runner and the wafers; S10: moving the wafers obtained in step S9 to the next process, taking the next batch of wafers to be processed, and repeating S6-S9 until the processing of all wafers is completed; S11: cleaning the equipment: rinsing the upper and lower grinding discs and the inside of the machine cavity.

2. The method of claim 1, wherein the thickness of the wafer is controlled by adjusting the thickness of the polishing pad. The selected runner is a runner capable of centrally placing the frequency measuring wafer and peripherally placing the wafers to be processed.

3. The method of claim 1 or 2, wherein the thickness of the wafer is controlled by the thickness of the polishing pad. The selected cruise ship center position is provided with a square hole for placing the frequency measuring sheet.

4. The method of claim 3, wherein the thickness of the wafer is controlled by adjusting the thickness of the polishing pad.

5. The method of claim 3, wherein the thickness of the wafer is controlled by adjusting the thickness of the polishing pad. The selected cruise ship is provided with a plurality of quicksand holes.

5. The method of claim 3, wherein the thickness of the wafer is controlled by adjusting the thickness of the polishing pad. 5 Each cruise ship is placed with 3 wafers to be processed and 1 frequency measuring sheet.

6. The method of claim 1, wherein the thickness of the wafer is controlled by adjusting the thickness of the polishing pad. 5 The selected grinding machine is provided with an electrode at the center of the upper grinding disc.

7. The method of claim 1, wherein the thickness of the wafer is controlled by adjusting the thickness of the polishing pad.

8. The method of claim 1, wherein the thickness of the wafer is controlled by adjusting the thickness of the polishing pad. The speed regulation process in step S7 is that the motor rotates at a low speed of 2-3 rpm, the counter jumps 5-10 times, and after the operation is normal, it is gradually accelerated to 30 rpm.

8. The method for precise thickness control in double-sided wafer grinding as described in claim 1, characterized in that, The pressure of the grinding machine in step S7 is set to 55 kg.

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