A method for improving the film thickness uniformity of a lithium tantalate bonding sheet

Abstract

The present invention belongs to the field of semiconductor materials, and particularly relates to a method for improving the film thickness uniformity of a lithium tantalate bonding wafer, which includes: thinning the lithium tantalate bonding wafer; performing stepped pressure on different regions of the polished bonding wafer according to the film thickness distribution of the thinned lithium tantalate bonding wafer, and fitting a polishing rate model based on the real-time measured film thickness, and adjusting the pressure application formula for polishing. Among them, the polishing rate model is used to judge whether the final stop thickness is reasonable and obtain compensation, and then secondary polishing is carried out. The thinning process ensures the consistency of the incoming material before polishing, providing a basis for improving the polishing film thickness uniformity; the stepped pressure on different regions ensures the film thickness uniformity within the bonding wafer; the polishing rate model ensures the film thickness uniformity between the bonding wafers.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor materials, and particularly relates to a method for improving the film thickness uniformity of a lithium tantalate bonding sheet. Background Art

[0002] With the rapid development of the mobile communication industry, as an important part of the radio frequency system, filters are gradually developing towards the directions of high frequency, compound, miniaturization, and integration. Traditional surface acoustic wave (SAW) filters have problems such as low frequency and poor temperature stability, and cannot meet the performance requirements of new-generation devices; while the wafer bonding process can achieve new structures, high-efficiency and low-cost manufacturing, and heterogeneous integration of materials.

[0003] Lithium tantalate (LiTaO3) crystals have excellent piezoelectric, acousto-optic, ferroelectric, and pyroelectric effects, and have advantages such as a large piezoelectric coefficient, a small frequency temperature coefficient, and a high electromechanical coupling coefficient. They are basic functional materials in the fields of surface acoustic wave devices, optical communication, lasers, and optoelectronics. In order to improve the performance of surface acoustic wave filters, bonding technology is required to bond lithium tantalate wafers with other material wafers together to meet the requirements of low insertion loss, high bandwidth, and good thermal stability of surface acoustic wave filters. However, for existing thin-film and thick-film products of lithium tantalate bonding sheets, the lithium tantalate bonding sheets need to be thinned and polished by mechanical processing. During the processing of large-size lithium tantalate bonding sheets, as the film layer becomes thinner, the thin film is extremely prone to bending deformation and even generates defective fragments; during the polishing process, the temperature, internal stress during the processing, and uneven distribution of the polishing liquid may all cause uneven film thickness of the thin film, and it is not easy to correct the polished film thickness. Therefore, there is an urgent need to develop a method for improving the film thickness uniformity of lithium tantalate bonding sheets.

[0004] The invention patent with the publication number CN118081603A discloses a bonding sheet polishing method. This method controls the polishing removal amount of the top silicon layer by providing a matching carrier, placing the bonding sheet in the carrier to perform a double-sided polishing process, improving the thickness uniformity of the top silicon layer after double-sided polishing, and reducing the wear of the carrier. However, this method is only applicable to the polishing of silicon-silicon bonding sheets. For lithium tantalate-silicon bonding sheets, due to the different hardnesses of the two, under double-sided polishing conditions, even if the carrier is suitable, the removal rates of the lithium tantalate surface and the silicon surface are very different, and it is impossible to uniformly control the thickness of the lithium tantalate thin film.

[0005] The invention patent with the publication number CN104779143A discloses a thin film disposed on a substrate and a preparation method thereof. In this invention, a thin film layer on a substrate of the same material is first prepared, and there is a sacrificial layer between the thin film layer and the substrate of the same material. Then, the thin film layer is bonded to the target substrate, the sacrificial layer is removed to separate the thin film from the substrate of the same material, or the substrate of the same material is removed by grinding or etching, and then the sacrificial layer is removed, finally obtaining the thin film layer on the target substrate. Its advantage lies in that it is not restricted by the difference in the thermal expansion coefficients of the original substrate and the target substrate, can realize the overall transfer of the thin film between the original substrate and the target substrate, and the formed thin film layer has a low defect density and a uniform thickness, with the thickness reaching the nanoscale. However, this method is only applicable to thin film products. When the thickness of the thin film exceeds 1 μm or even reaches 30 μm, the ion implantation technology cannot efficiently prepare the thin film, and the corresponding defects will be generated during the too long implantation time, reducing the yield rate.

[0006] Therefore, in the prior art, there is a lack of a method for improving the film thickness uniformity of lithium tantalate bonded wafers that is efficient, not prone to fragmentation, and has few defects in the thin film. Summary of the Invention

[0007] The present invention provides a method for improving the film thickness uniformity of lithium tantalate bonded wafers to solve the deficiencies of the prior art. The processing process of this method is stable, and it solves the problem of poor film thickness uniformity during the batch preparation of thin films of existing lithium tantalate bonded wafers.

[0008] The present invention discloses a method for improving the film thickness uniformity of lithium tantalate bonded wafers, which includes the following steps:

[0009] Step a: Thinning the lithium tantalate bonded wafer, including:

[0010] Performing rough thinning on the lithium tantalate bonded wafer to remove a first removal amount; and

[0011] Performing fine thinning on the lithium tantalate bonded wafer to remove a second removal amount;

[0012] Step b: Pressurize the bonded wafer to be polished according to the film thickness distribution of the thinned lithium tantalate bonded wafer, and fit the polishing rate model based on the real-time measured film thickness, and adjust the pressurization formula for polishing.

[0013] In the above step a, in the rough thinning process, the first removal amount needs to be greater than 50 μm, the grinding wheel used is 3000 - 4000 mesh, the rotational speed of the grinding wheel is 1500 - 2000 rpm, the rotational speed of the carrier table is 100 - 500 rpm, the slow lift time for rough thinning is 5 - 10 s, and the slow lift rate is 0.5 - 0.8 μm / s; among them, the grinding wheel preferably used for rough thinning is 3000 mesh;

[0014] In the thinning process, the second removal amount is 10 - 15 μm, the grinding wheel used is 8000 mesh, the rotational speed of the grinding wheel is 1000 - 1500 rpm, and the rotational speed of the stage is 100 - 300 rpm;

[0015] The thinning needs to be carried out in three steps. The removal amount in the first step is 7 - 12 μm, and the removal rate is 0.3 - 0.5 μm / s; the removal amount in the second step is 2 μm, and the removal rate is 0.1 - 0.3 μm / s; the removal amount in the third step is 1 μm, and the removal rate is 0.05 - 0.1 μm / s. The slow lift time for thinning is 5 - 15 s, and the slow lift rate is 0.1 - 0.5 μm / s;

[0016] In the above step a, after the rough and fine thinning processes on the lithium tantalate bonded wafer, the spark time is 5 - 10 s, and the spark time is positively correlated with the film thickness range;

[0017] In the above step a, the thinned lithium tantalate bonded wafer is cleaned and spin - dried. The cleaning time is 5 - 10 s, and the spin - dry blowing time is 5 - 10 s;

[0018] Before polishing the thinned lithium tantalate bonded wafer, a polishing dressing wheel is used in combination with pure water to dress the polishing pad. The rotational speed of the dressing wheel is 50 - 100 rpm, the pressure of the dressing wheel is 0.5 - 2 psi, and the scanning time is 5 - 10 s;

[0019] In the above step b, the maximum pressure of the wafer ≤ 6 psi, the maximum pressure of the retainer ring ≤ 6 psi, the maximum rotational speed of the polishing head ≤ 100 rpm, the maximum rotational speed of the polishing platen ≤ 100 rpm. Among them, the rotational speed of the polishing head must be greater than the rotational speed of the polishing platen, and the difference between the two needs to be 3 - 5 rpm;

[0020] In the above step b, the left - right swing amplitude of the polishing head during polishing is 30 - 50 cm, and the swing rate is 5 - 10 cm / min;

[0021] In the above step b, the lithium tantalate bonded wafer is divided into a circular area and three adjacent concentric circular - ring areas successively surrounding the circular area. From the inside out, they are denoted as Area 4 (Zone4) / Area 3 (Zone3) / Area 2 (Zone2) / Area 1 (Zone1);

[0022] The centers of Zone4 / Zone3 / Zone2 / Zone1 coincide with the center of the lithium tantalate bonded wafer. The radius of the circular area Zone4 is 20% of the radius of the bonded wafer. The inner and outer radii of the circular - ring area Zone3 are 20% and 60% of the radius of the bonded wafer respectively. The inner and outer radii of the circular - ring area Zone2 are 60% and 90% of the radius of the bonded wafer respectively. The inner and outer radii of the circular - ring area Zone1 are 90% and 100% of the radius of the bonded wafer respectively;

[0023] Measure the film thickness distribution of the thinned Zone4 / Zone3 / Zone2 / Zone1 areas with a film thickness gauge. The number of measurements by the film thickness gauge is greater than 30 and evenly distributed within each area. Calculate the average film thickness of each area based on the film thickness measurement results in each area.

[0024] In step b above, according to the film thickness distribution of the thinned bonding wafer, polish the thinned lithium tantalate bonding wafer by a step-by-step pressure application method in different areas.

[0025] For the above-mentioned zoned pressure application, usually, since the outermost circular ring area of the bonding wafer contacts the polishing liquid the most and has the largest polishing removal amount, taking Zone1 as the reference area, determine the set pressure according to the percentage that the average film thickness of Zone2 / Zone3 / Zone4 is greater than or less than the average film thickness of Zone1, and apply pressure.

[0026] For the above-mentioned step-by-step pressure application, the pressure increase or decrease between adjacent steps of the pressure application program does not exceed 1.5 psi. And in the polishing program, the polishing head speed and the stage speed can only be adjusted to the maximum after reaching the maximum first, to avoid the generation of polishing debris.

[0027] In step b above, use spectroscopic analysis measurement method to measure the film thickness in real time. The number of measurement points is 400 - 700 and evenly distributed in each area. The refractive index of lithium tantalate is 2.18. When the processed film thickness is greater than 5 μm, it is necessary to filter out the measurement clutter at 2 μm.

[0028] During batch processing, on the one hand, consumables such as the polishing pad, the retaining ring, and the halogen lamp for film thickness measurement will be worn out as the polishing progresses, resulting in differences in the processing environment for different lithium tantalate bonding wafers, and there are also differences in the measurement points for different lithium tantalate bonding wafers. On the other hand, there are problems of less data volume and measurement accuracy in the early stage of film thickness measurement, resulting in distorted measurement data. Then, using the real-time measurement data as the polishing stop data will result in deviations.

[0029] Further, in step b above, fit the polishing rate model at different stages of polishing for use as the stop thickness compensation. On the premise of the same polishing program, divide the usage stages of the polishing pad, the retaining ring, and the halogen lamp for film thickness measurement into intervals of 1000 min, record the polishing thickness and polishing time to calculate the polishing rate every 40 s, and fit the polishing rate curve.

[0030] The total effective polishing duration of the above-mentioned polishing rate model is within 200 s. Calculate whether the final stop thickness is reasonable based on this model and obtain the compensation.

[0031] If the required polishing amount cannot be achieved according to the existing polishing rate model, secondary polishing is required to ensure the consistency of the average film thickness of lithium tantalate bonding wafers during batch processing.

[0032] The secondary polishing includes horizontal polishing and step-by-step pressure application polishing in zones, which are carried out successively:

[0033] First, polish for 200 s in a horizontal manner (i.e., the set pressures in the four zones of Zone1, Zone2, Zone3, and Zone4 are equal). Since the surface of the wafer is the polished surface during secondary polishing, the polishing rate is relatively lower than that of the thinned wafer. After horizontal polishing, polish the remaining polishing amount by step-by-step pressure application in zones at 80% of the polishing rate calculated by the primary polishing rate model.

[0034] Brush the polished lithium tantalate bonded wafer for 60 - 120 s, spin-dry for 60 - 120 s, and then measure the film thickness.

[0035] The present invention discloses a method for improving the film thickness uniformity of a lithium tantalate bonded wafer, and also involves a method for calculating the set pressures in different zones during zone-by-zone pressure application, specifically:

[0036] Taking Zone1 as the reference zone, determine the set pressure of the reference zone as the reference pressure P Wafer , and determine the set pressures of the remaining zones according to the percentage by which the average film thickness of each of the remaining zones is greater than or less than the average film thickness of the reference zone. The calculation method for the polishing set pressure of any one of the remaining zones follows formula (1):

[0037] ----(1);

[0038] where P i is the set pressure of any one of the remaining zones, D i is the average film thickness of the zone, i = 2, 3, 4; D1 is the average film thickness of the reference zone; P Wafer is the reference pressure, α is a coefficient. The values of P Wafer and α vary according to the range of the average film thickness in the Zone1 / Zone2 / Zone3 / Zone4 zones, specifically:

[0039] When the range of the average film thickness is less than 600 nm, P Wafer = 4.0 psi, α = 1.0;

[0040] When the range of the average film thickness is greater than or equal to 600 nm and less than 1000 nm, P Wafer = 3.0 psi, α = 1.3;

[0041] When the range of the average film thickness is greater than or equal to 1000 nm, P Wafer = 3.0 psi, α= 1.5;

[0042] The calculation result of the set pressure follows the rounding principle and takes one decimal place.

[0043] If the average film thickness of Zone 1 is not the thinnest, that is, in the remaining regions, there is at least one region where the calculated value of the set pressure is less than the reference pressure P Wafer When this is the case, the actual set pressure of all regions is increased by the same value above the original set pressure, so that the minimum value of the actual set pressure in the remaining regions is equal to the reference pressure P Wafer . For example, taking Zone 1 as the reference region, when the range of the average film thickness is less than 600 nm, P Wafer = 4.0 psi, and the calculated values of the set pressures for Zone 1 / Zone 2 / Zone 3 / Zone 4 are 4.0 / 3.9 / 3.9 / 4.1 psi respectively, then the actual set pressures are 4.1 / 4.0 / 4.0 / 4.2 psi;

[0044] If the calculated value of the set pressure exceeds 6 psi, then the actual set pressure is 6 psi.

[0045] Preferably, the wafer material bonded to the lithium tantalate wafer is one of sapphire, silicon, silicon carbide, and quartz, and the shape and size of the sapphire, silicon, silicon carbide, and quartz are the same as those of the lithium tantalate wafer;

[0046] Preferably, a terrace needs to be processed on the edge of the lithium tantalate bonded wafer, the width of the terrace needs to be 2 - 3 mm, and the terrace angle is 40 - 50°;

[0047] Preferably, during the polishing process, the ambient temperature is 20 - 25 °C, the relative humidity level is 50 ± 10%, and there is no external vibration and noise;

[0048] Preferably, the thickness of the holding ring used for polishing is the thickness of the lithium tantalate bonded wafer to be processed minus 50 - 150 mm.

[0049] To improve the film thickness uniformity of the lithium tantalate bonded wafer, compared with the prior art, the present invention has the following beneficial effects:

[0050] First, in terms of the incoming material control before polishing, by precisely regulating the thinning removal amount, the thinning process is optimized to ensure the uniformity of the incoming material for polishing the lithium tantalate bonded wafer; at the same time, the spark time parameter is optimized to control the film thickness range, providing a prerequisite for improving the polishing uniformity;

[0051] Second, through the single - wafer polishing process, according to the film thickness distribution within the wafer, a zoning and step - by - step pressure application strategy is adopted for polishing, significantly reducing the film thickness range within the lithium tantalate bonded wafer, thereby effectively improving the film thickness uniformity of the single - wafer lithium tantalate bonded wafer;

[0052] Thirdly, the polishing rate of the lithium tantalate bonded wafer at different polishing stages is calculated based on the real-time measured film thickness, and is used to fit the polishing rate model. This model can first be used for real-time measurement of film thickness compensation. Secondly, when the real-time measured film thickness is used as the stop condition, if there is still a film thickness deviation, secondary polishing can be performed according to this model to correct the film thickness, reducing the film thickness difference between lithium tantalate bonded wafers during batch processing, thereby effectively improving the film thickness uniformity between lithium tantalate bonded wafers during batch polishing. Description of the Drawings

[0053] Figure 1 It is the processing flow chart of the present invention;

[0054] Figure 2 It is a schematic diagram of the pressure application zones during the polishing of the lithium tantalate bonded wafer;

[0055] Figure 3 It is a schematic diagram of the film thickness after polishing in Example 1;

[0056] Figure 4 It is a scatter plot of the film thickness versus the polishing time in Example 2, showing the reference curve of the film thickness change during polishing;

[0057] Figure 5 It is a schematic diagram of the film thickness after polishing in Comparative Example 1. Detailed Embodiments

[0058] The present invention will be further described below in conjunction with embodiments, but the protection scope of the present invention should not be limited thereby.

[0059] Example 1

[0060] (1) Coarse thinning is performed on the lithium tantalate bonded wafer. The removal amount of coarse thinning is 200 μm, the grinding wheel speed is 1800 rpm, and the stage speed is 300 rpm; The coarse thinning is divided into 2 steps. In the first step, the removal amount is 195 μm and the removal rate is 1 μm / s; In the second step, the removal amount is 5 μm and the removal rate is 0.5 μm / s; The slow lift time is 5 s and the slow lift rate is 0.5 μm / s;

[0061] Fine thinning is performed on the lithium tantalate bonded wafer. The removal amount of fine thinning is 10 μm, the grinding wheel speed is 1300 rpm, and the stage speed is 300 rpm; The fine thinning is divided into 3 steps. In the first step, the removal amount is 7 μm and the removal rate is 0.4 μm / s; In the second step, the removal amount is 2 μm and the removal rate is 0.2 μm / s; In the third step, the removal amount is 1 μm and the removal rate is 0.1 μm / s; The slow lift time is 10 s and the slow lift rate is 0.2 μm / s;

[0062] The spark time after thinning is 8 s; The cleaning time after thinning is 10 s, and the spin-drying and purging time is 10 s;

[0063] (2) Use a polishing correction wheel to trim the polishing pad. The rotation speed of the correction wheel is 80 rpm, the pressure of the correction wheel is 1.5 psi, and the scanning time is 5 s;

[0064] (3) Adsorb the bonding wafer to be polished onto the polishing head retaining ring and press it down to the stage;

[0065] (4) According to the film thickness distribution of the thinned lithium tantalate bonding wafer, determine the reference pressure P of the reference area Zone1 Wafer , and calculate the set pressure of the Zone2 / Zone3 / Zone4 areas according to formula (1). Press the bonding wafer to be polished step by step in different areas, and measure the film thickness waveform in real time, and adjust the pressing formula by fitting the model; the maximum pressure of the wafer is 4 psi, the maximum pressure of the retaining ring is 4 psi, the maximum rotation speed of the polishing head is 75 rpm, and the maximum rotation speed of the polishing disc is 70 rpm. The specific procedure is shown in Table 1:

[0066] Table 1 Polishing process parameters

[0067]

[0068] (5) Brush the polished lithium tantalate bonding wafer for 120 s and spin-dry it for 120 s. The final measured film thickness of the lithium tantalate bonding wafer prepared in Example 1 is shown in Table 2 and Figure 3 as follows:

[0069] Table 2 Film thickness of the polished lithium tantalate bonding wafer

[0070]

[0071] Example 2

[0072] (1) Coarsely thin the lithium tantalate bonding wafer. The removal amount of coarse thinning is 200 μm, the rotation speed of the grinding wheel is 1800 rpm, and the rotation speed of the stage is 300 rpm; The coarse thinning is divided into 2 steps. In the first step, the removal amount is 195 μm, and the removal rate is 1 μm / s; in the second step, the removal amount is 5 μm, and the removal rate is 0.5 μm / s; the slow lift time is 5 s, and the slow lift rate is 0.5 μm / s;

[0073] Finely thin the lithium tantalate bonding wafer. The removal amount of fine thinning is 10 μm, the rotation speed of the grinding wheel is 1300 rpm, and the rotation speed of the stage is 300 rpm; The fine thinning is divided into 3 steps. In the first step, the removal amount is 7 μm, and the removal rate is 0.4 μm / s; in the second step, the removal amount is 2 μm, and the removal rate is 0.2 μm / s; in the third step, the removal amount is 1 μm, and the removal rate is 0.1 μm / s; the slow lift time is 10 s, and the slow lift rate is 0.2 μm / s;

[0074] The spark time after thinning is 8 s; the cleaning time after thinning is 10 s, and the spin-dry and purge time is 10 s;

[0075] (2) Use a polishing correction wheel to trim the polishing pad. The rotation speed of the correction wheel is 80 rpm, the pressure of the correction wheel is 1.5 psi, and the scanning time is 5 s;

[0076] (3) Adsorb the bonding wafer to be polished onto the polishing head retaining ring and press it down onto the stage;

[0077] (4) According to the film thickness distribution of the thinned lithium tantalate bonding wafer, determine the reference pressure P of the reference area Zone1 Wafer , and calculate the set pressure of the Zone2 / Zone3 / Zone4 areas according to formula (1). Pressurize the bonding wafer to be polished step by step in different areas, and measure the film thickness waveform in real time, and adjust the pressurization formula based on this fitting model; the maximum pressure of the wafer is 4 psi, the maximum pressure of the retaining ring is 4 psi, the maximum rotation speed of the polishing head is 75 rpm, and the maximum rotation speed of the polishing platen is 70 rpm. The specific procedure is shown in Table 3:

[0078] Table 3 Polishing process parameters

[0079]

[0080] (5) Brush the polished lithium tantalate bonding wafer for 120 s and spin-dry it for 120 s.

[0081] Divide the usage stages of the polishing pad, retaining ring, and halogen lamp for film thickness measurement into intervals of 1000 min. Record the polishing thickness and polishing time to calculate the polishing rate every 40 s, and fit the polishing rate curve. As Figure 4 can be seen, except when the polishing time is less than 20 s, due to the amount of data and polishing stability, there are large fluctuations in the polishing rate curve. The rest of the rate curve can be fitted. And since the relationship between the removal amount and the polishing time is not linear, this fitting is very meaningful for mass production operations.

[0082] The lithium tantalate bonding wafer prepared in the embodiment of the present invention is inspected and has no scratches and no surface defects, meeting the requirements for subsequent device processing.

[0083] Comparative example

[0084] (1) Coarsely thin the lithium tantalate bonding wafer. The removal amount of coarse thinning is 200 μm, the rotation speed of the grinding wheel is 1800 rpm, and the rotation speed of the stage is 300 rpm; The coarse thinning is divided into 2 steps. The removal amount in the first step is 195 μm, and the removal rate is 1 μm / s; the removal amount in the second step is 5 μm, and the removal rate is 0.5 μm / s; the slow lift time is 5 s, and the slow lift rate is 0.5 μm / s;

[0085] The lithium tantalate bonded wafer is precisely thinned. The removal amount for precise thinning is 10 μm, the grinding wheel speed is 1300 rpm, and the stage speed is 300 rpm. The precise thinning is divided into 3 steps. In the first step, the removal amount is 7 μm and the removal rate is 0.4 μm / s. In the second step, the removal amount is 2 μm and the removal rate is 0.2 μm / s. In the third step, the removal amount is 1 μm and the removal rate is 0.1 μm / s. The final slow lift time is 10 s and the slow lift rate is 0.2 μm / s.

[0086] The spark time after thinning is 8 s; the cleaning time after thinning is 10 s, and the spin-drying and purging time is 10 s.

[0087] (2) Use a polishing dressing wheel to dress the polishing pad. The dressing wheel speed is 80 rpm, the dressing wheel pressure is 1.5 psi, and the scanning time is 5 s.

[0088] (3) Adsorb the bonded wafer to be polished onto the polishing head retaining ring and press it down onto the stage.

[0089] (4) Polish according to the film thickness of the lithium tantalate bonded wafer after thinning, and measure the film thickness waveform in real time. The maximum pressure of the wafer is 4 psi, the maximum pressure of the retaining ring is 4 psi, the maximum speed of the polishing head is 75 rpm, and the maximum speed of the polishing platen is 70 rpm. The specific procedure is shown in Table 4 below:

[0090] Table 4 Polishing procedure parameters

[0091]

[0092] (5) Brush the polished bonded wafer for 120 s and spin-dry it for 120 s. The final measured film thickness of the lithium tantalate bonded wafer prepared in this comparative example is shown in Table 5 and Figure 5 as follows:

[0093] Table 5 Film thickness of the lithium tantalate bonded wafer after polishing

[0094]

[0095] Comparing Table 2 and Table 5, Figure 3 and Figure 5 , it can be seen that the range of the film thickness σ after polishing in Example 1 (73.963 - 152.464) is significantly smaller than the range of the film thickness σ after polishing in the comparative example (159.688 - 234.966), which proves that the technical solution of the present invention significantly improves the uniformity of the film thickness of the lithium tantalate bonded wafer and the process is stable.

[0096] The embodiments described in this specification are only exemplary embodiments for explaining the technical solutions of the present invention, and do not constitute a limiting interpretation of the claims. For those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for improving the film thickness uniformity of a lithium tantalate bonding sheet, characterized in that It includes the following steps: Step a: Thinning the lithium tantalate bonded wafer, including: Performing rough thinning on the lithium tantalate bonded wafer in sequence to remove the first removal amount; and Performing fine thinning on the lithium tantalate bonded wafer to remove the second removal amount; Step b: Pressurized polishing the bonded wafer according to the film thickness distribution of the thinned lithium tantalate bonded wafer, fitting a polishing rate model based on the real-time measured film thickness, and adjusting the pressurization formula for polishing. The pressurization method is zone-by-step pressurization; The zone pressurization method is: taking the outermost circular ring area of the lithium tantalate bonded wafer as the reference area, determining the set pressure of the remaining areas according to the percentage that the film thickness mean value of the remaining areas is greater than or less than the film thickness mean value of the reference area, and performing pressurization; The calculation method of the set pressure is to determine the set pressure of the reference area as the reference pressure P Wafer , and calculate the set pressure of any one of the remaining areas according to the percentage that the average film thickness of each of the remaining areas is greater than or less than the average film thickness of the reference area: ； Among them, P i is the set pressure of any one of the remaining regions, D i is the average film thickness of the region, where i = 2, 3, 4; D1 is the average film thickness of the reference region; When the range of the film thickness mean value is less than 600 nm, P Wafer = 4 psi, α = 1.0; When the range of the film thickness mean value is greater than or equal to 600 nm and less than 1000 nm, P Wafer = 3 psi, α = 1.3; When the range of the film thickness mean value is greater than or equal to 1000 nm, P Wafer = 3 psi, α = 1.

5.

2. The method for improving the film thickness uniformity of a lithium tantalate bonding sheet according to claim 1, wherein In the said step a, the first removal amount is greater than 50μm, the grinding wheel used for rough thinning is 3000 - 4000 mesh, the grinding wheel rotation speed is 1500 - 2000 rpm, the stage rotation speed is 100 - 500 rpm, the slow lift time is 5 - 10 s, and the slow lift rate is 0.5 - 0.8μm / s; Among them, the grinding wheel used for rough thinning is 3000 mesh; The second removal amount is 10 - 15μm, the grinding wheel used for fine thinning is 8000 mesh, the grinding wheel rotation speed is 1000 - 1500 rpm, the stage rotation speed is 100 - 300 rpm, the slow lift time is 5 - 15 s, and the slow lift rate is 0.1 - 0.5μm / s; Among them, the fine thinning is divided into three steps. The removal amount of the first step is 7 - 12μm, and the removal rate is 0.3 - 0.5μm / s; the removal amount of the second step is 2μm, and the removal rate is 0.1 - 0.3μm / s; the removal amount of the third step is 1μm, and the removal rate is 0.05 - 0.1μm / s.

3. The method for improving the film thickness uniformity of the lithium tantalate bonding sheet according to claim 1, wherein In the said step a, after thinning the lithium tantalate bonded wafer, the spark time is 5 - 10 s, and the spark time is positively correlated with the film thickness range.

4. The method for improving the film thickness uniformity of the lithium tantalate bonding sheet according to claim 1, wherein In the said step b, the maximum wafer pressure ≤ 6 psi, the maximum retainer ring pressure ≤ 6 psi, the maximum polishing head rotation speed ≤ 100 rpm, the maximum polishing pad rotation speed ≤ 100 rpm. Among them, the polishing head rotation speed must be greater than the polishing pad rotation speed, and the difference between the two is 3 - 5 rpm.

5. The method for improving the film thickness uniformity of the lithium tantalate bonding sheet according to claim 1, characterized in that In the said step b, when polishing, the left - right swing amplitude of the polishing head is 30 - 50 cm, and the swing rate is 5 - 10 cm / min.

6. The method for improving the film thickness uniformity of the lithium tantalate bonding sheet according to claim 1, characterized in that In the said step b, the bonded wafer is divided into a circular area and three adjacent concentric circular ring areas that successively surround the circular area. The centers of the circular area and the concentric circular ring areas coincide with the center of the lithium tantalate bonded wafer, and the film thickness distribution of each area after thinning is measured by a film thickness gauge.

7. The method for improving the film thickness uniformity of the lithium tantalate bonding sheet according to claim 1, wherein The step - by - step pressurization method in the said step b is: the pressure increased or decreased by adjacent pressurization programs does not exceed 1.5 psi.

8. The method for improving the film thickness uniformity of the lithium tantalate bonding sheet according to claim 1, wherein When performing step - by - step pressurization in the said step b, the wafer pressure and the retainer ring pressure must be adjusted to the maximum after the polishing head rotation speed and the stage rotation speed reach the maximum first.

9. The method for improving the film thickness uniformity of the lithium tantalate bonding sheet according to claim 1, wherein In the said step b, the real - time film thickness measurement method is spectroscopic analysis measurement method. The refractive index of lithium tantalate is 2.

18. When the processed film thickness is greater than 5μm, the measurement clutter at 2μm needs to be filtered out.

10. The method for improving the film thickness uniformity of a lithium tantalate bonding sheet according to claim 1, wherein In step b, the polishing rate models are respectively fitted at different stages of polishing for use in compensating the stopping thickness. On the premise of consistent polishing procedures, the polishing pad, the retaining ring, and the halogen lamp for film thickness measurement are divided into usage stages at intervals of 1000 minutes. The polishing thickness and polishing time are recorded to calculate the polishing rate every 40 seconds, and the polishing rate curve is fitted to calculate whether the final stopping thickness is reasonable and obtain the compensation; then secondary polishing is carried out.

11. The method for improving the film thickness uniformity of the lithium tantalate bonding sheet according to claim 10, characterized in that, The total effective polishing duration of the polishing rate model is within 200 seconds.

12. The method for improving the film thickness uniformity of the lithium tantalate bonding sheet according to claim 10, wherein The secondary polishing includes horizontal polishing and partitioned step-by-step pressure polishing carried out in sequence.

13. The method for improving the film thickness uniformity of the lithium tantalate bonding sheet according to claim 10, wherein In the secondary polishing, the horizontal polishing time is 200 seconds, and the polishing rate of the partitioned step-by-step pressure polishing is 80% of the rate calculated by the primary polishing rate model.

14. The method for improving the film thickness uniformity of a lithium tantalate bonding sheet according to claim 1, wherein In the remaining regions, there is at least one region where the calculated set pressure is less than the reference pressure P Wafer When this occurs, the actual set pressure of all regions is increased by the same value above the original set pressure, so that the minimum value of the actual set pressure in the remaining regions is equal to the reference pressure P Wafer .

15. The method for improving the film thickness uniformity of a lithium tantalate bonding sheet according to claim 1, wherein When the calculated value of the set pressure is greater than 6 psi, the actual set pressure is 6 psi.

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