WO2022121012A1 - Method for processing large-size ultra-thin high-precision lithium niobate wafer - Google Patents

Abstract

The present invention relates to the technical field of semiconductor material processing, and in particular to a method for processing a large-size ultra-thin high-precision lithium niobate wafer. The method comprises the steps of slicing, chamfering, grinding 800, blackening, grinding 2000 and polishing; a double-sided grinder is used in the steps of grinding 800 and grinding 2000, and a grinding pressurization mode uses a slow segmented pressurization mode at 22±2°C; a double-sided polisher is used in the step of polishing, the maximum rotational speed of a device is 6-10 rpm at 22±2°C, a SiO22 polishing solution is used, the specific gravity is 1.06-1.20, and a polishing pressurization mode uses a slow segmented pressurization mode. Since a slow and gradual pressurization mode is used during pressurization, the conditions such as scratching, fragmentation, and cracking are greatly reduced, and moreover, the conditions such as edge collapse, edge explosion, and insufficient grinding can be effectively reduced in conjunction with a fixture of the present invention, thereby greatly increasing the yield of production, and getting rid of the restriction of manufacturer semiconductor machine devices on products.

Description

Large-size, ultra-thin and high-precision lithium niobate wafer processing method technical field

The invention relates to the technical field of semiconductor material processing, in particular to a processing method of a lithium niobate crystal substrate.

Background technique

Lithium niobate (LiNbO ₃ ) is a compound of niobium, lithium and oxygen, and is a negative crystal (n0>ne). The relative density of lithium niobate is 4.30, lattice constant a=0.5147μm, c=1.3856μm, melting point 1240℃, Mohs hardness 5, refractive index n0=2.297, ne=2.208 (λ=600μm), dielectric constant ε=44 , ε=29.5, ε=84, ε=30. Lithium niobate is a ferroelectric crystal with a Curie point of 1140°C, a spontaneous polarization of 50×10C/cm', and a thermal conductivity of 0.056 (W/cm·K). The distorted lithium niobate crystal has piezoelectric, ferroelectric, optoelectronic, nonlinear optics, pyroelectric and other multi-performance materials, and also has photorefractive effect. Its single crystals are important materials for optical waveguides, mobile phones, piezoelectric sensors, optical modulators and various other linear and nonlinear optical applications. Lithium niobate crystal is one of the most widely used new inorganic materials. It is a good piezoelectric transducer material, ferroelectric material and electro-optical material. As an electro-optical material, lithium niobate plays an optical modulation role in optical communication.

High-performance electronic components have extremely high requirements on the surface lattice integrity of lithium niobate wafers, not only high flatness, but also damage-free, ultra-smooth and no crystal orientation deviation. Ordinary wafers have the phenomenon of electrostatic accumulation on the surface. This problem can be solved by the blackening process. The blackening process can also make the wafers have the effect of low pyroelectricity, which is more in line with the laws and needs of the development of the semiconductor industry.

At present, with the rapid development of the semiconductor industry, the demand for lithium niobate wafers is gradually increasing. In order to increase the output and reduce the cost, the wafer needs to develop in the direction of large size. On the one hand, it can improve the general process platform for large-size lithium niobate wafers, and on the other hand, it can get rid of the constraints of the manufacturer's semiconductor machine equipment on the product. Since 8-inch lithium niobate wafers are larger than conventional wafers, greater processing stress will be generated during processing, which may easily lead to defects such as edge bursts, fragments, and cracks. And the larger the wafer size, the more difficult it is for TTV, WARP, BOW, PLTV and other indicators to reach the same level as the conventional size during processing.

Chinese patent application CN111230598A discloses a preparation method of an 8-inch lithium niobate wafer. The three-time etching method solves the problem of severe internal stress and deformation of the lithium niobate wafer and the resulting wafer is easily broken during the production process; Porous ceramic disc adsorption solves the problem that TTV is not easy to control caused by the traditional wax sticking process; however, the acid used for corrosion in actual operation poses a safety hazard to the environment and human body, and the use of porous ceramic disc adsorption to equipment and accessories High precision is required, and only one-side polishing can be achieved.

The applicant disclosed in CN107665813A a method for processing a lithium tantalate crystal substrate, which includes the steps of slicing, chamfering, blackening, grinding, rough polishing and fine polishing, and diamond polishing is used in the rough polishing and fine polishing steps. Liquid, the diamond polishing liquid is composed of diamond micropowder, ethylene glycol, glycerin, ethanol ammonia and deionized water, and its pH value is between 9 and 11, wherein the content of diamond micropowder is 20% to 25%, and the content of ethylene glycol is 20% to 25%. It is 8% to 15%, the glycerin content is 3% to 5%, the ethanol ammonia content is 0.1% to 0.3%, and the deionized water content is 60% to 65%. The invention can greatly improve the surface smoothness of the lithium tantalate wafer, reduce the surface roughness, eliminate stress, and achieve mirror polishing effect, thereby reducing production cost and improving product qualification rate. However, the physical properties of lithium tantalate and lithium niobate are very different, and the processing method of lithium tantalate is not suitable for lithium niobate.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a large-size, ultra-thin and high-precision lithium niobate wafer processing method, which can mass-produce 8-inch lithium niobate wafers, can realize double-sided processing, greatly improve production efficiency, is safe and reliable, and can ensure the quality of the wafers at the same time. Performance and quality, to achieve the purpose of saving production costs, improving product qualification rate, reducing the stress problem of large-sized wafers, and getting rid of semiconductor manufacturers' equipment constraints on products.

To achieve the above object, the present invention provides the following technical solutions:

A large-size, ultra-thin, high-precision lithium niobate wafer processing method, comprising the steps of slicing, chamfering, grinding 800, blackening, grinding 2000, and polishing;

Both the grinding 800 steps and the grinding 2000 steps use a double-sided grinder, and at 22°C ± 2°C, the grinding and pressing method adopts a segmented slow pressing method;

Among them, the segmented and slow pressurization mode of grinding 800 is: the first segment is 1min, no pressurization; the second segment is pressurized for 3min, and the pressurization rate is 2g/cm ² per minute; the third segment is pressurized for 2min, and the pressurization rate is 3g/cm ² per minute, the fourth stage is pressurized for 2 minutes, the pressurizing rate is 4g/cm ² per minute, and the total pressure is 20g/cm ² ;

The segmental slow pressurization mode of grinding 2000 is: the first segment is 1min, no pressurization; the second segment is pressurized for 3min, and the pressurization rate is 4g/cm ² per minute; the third segment is pressurized for 2min, and the pressurization rate is per minute 6g/cm ² ; the fourth stage is pressurized for 2 minutes, the pressurizing rate is 8g/cm ² per minute, and the total pressure is 40g/cm ² ; the mortar flow is 5L/cm ² -15L/cm ² , and the maximum speed of the equipment is 6rpm -10rpm;

In the polishing step, a double-sided polishing machine is used. At 22°C ± 2°C, the maximum rotating speed of the equipment is 6rpm-10rpm, and the polishing liquid adopts the Compol 403 polishing liquid of FUJIMI. The main component is SiO ₂ , and the specific gravity is 1.06-1.20. The pressurization method adopts the stepwise slow pressurization method. The pressurization method is: the first stage is 1min, no pressurization; the second stage is pressurized for 4min, and the pressurization rate is 10g/cm ² per minute; the third stage is pressurized for 4min, and the pressure is The pressure rate is 15g/cm ² per minute; the fourth stage is pressurized for 5 minutes, the pressure rate is 20g/cm ² per minute, and the total pressure is 200g/cm ² ; The polishing fluid flow is 10L/cm ² -12L/cm ² .

The step-by-step slow pressurization method means that before the grinding disc is pressed against each other, the lower disc is started first, so that the mortar is evenly distributed, and it can be checked whether the wafer and the fixture are fixed well, and then pressurized after running for a period of time. way of pressurization.

Figure 2-4 is a comparison chart of the relationship between the direct pressure method and the segmented pressure method in grinding 800, grinding 2000, and polishing process pressure and time. It can be seen from the figure:

The direct pressure mode of grinding 800 is pressurized for 5 minutes at a pressure rate of 4g/cm ² per minute to 20g/cm ² ; the direct pressure method of grinding 2000 is pressurized at a pressure rate of 8g/cm ² per minute for 5min Pressurize to 40 g/cm ² ; pressurize to 200 g/cm ² for 10 min at a pressing rate of 20 g/cm ² per minute in the direct pressing mode of the polishing step.

In contrast, the direct pressure method is too rigid and mechanized, which is easy to cause problems such as scratches and splinter, and is not conducive to the discovery and remediation of the problem. The segmented pressure method allows time for observation and adjustment, and the pressure speed is slow. And mild, it can effectively ensure the processing quality and reduce the possibility of scratches and splits.

Wherein, the composition of the mortar ground in the grinding step 800 is: silicon carbide sand GC800#: water: mortar dispersant = 13.5KG: 30L: 1.7L; the composition of the mortar ground in the grinding step 2000 is: silicon carbide sand GC2000#: Water: Mortar dispersant = 13.5KG: 30L: 1.7L.

Wherein, the main component of the polishing liquid is SiO ₂ , and the specific gravity is 1.06-1.20.

Wherein, the grinding effect of the 800 grinding steps reaches TTV≤5 μm, Bow≤30 μm, and the grinding effect of the 2000 grinding steps reaches TTV≤4 μm, Bow≤25 μm.

Wherein, the polishing effect of the polishing step requires wafer TTV≤3μm, Bow≤20μm, WARP<40μm, PLTV>95%, mirror effect, no stress.

Wherein, the lithium niobate wafer is an 8-inch lithium niobate wafer.

The jig used in the grinding 800, grinding 2000 and polishing steps is a freewheel, and the wafer placement position in the freewheel adopts an eccentric design;

The wafer placement position is circular, and its edge is provided with a rubber ring with a diameter of 200.2 mm and a width of 5 mm;

There are five circular drainage holes distributed around the wafer placement position, with diameters of one of 60mm, two of 40mm, and two of 20mm. Taking the center of the star wheel as the center of the circle, a circle with a diameter of 290mm is made. The wafer placement circle and drainage The holes are all inscribed with the circle, the wafer placement circle and the center of the 60mm drainage hole are on the same diameter line and on both sides, the center of the 40mm drainage hole is the center of the star wheel as the center of the circle, and the radius of the 60mm drainage hole is the reference edge. Deflect 60° to the left and right, respectively, the center of the 20mm drainage hole is the center of the star wheel, and the radius of the 60mm drainage hole is the reference edge, which is deflected to the left and right by 110°. The appearance of the cruise star wheel is shown in Figure 1 .

Wherein, the slicing step is specifically: at a wire speed of 400m/min-1000m/min, at 22°C±2°C, using wire cutting equipment to cut the lithium niobate crystal rod into wafers with a thickness of 250μm-300μm, the wafers TTV≤10μm;

The chamfering step is specifically as follows: using a T-shaped grinding wheel for chamfering, and at a grinding wheel speed of 600rpm/min-1000rpm/min, at 22°C±2°C, the right angle of the lithium niobate wafer is inverted into a circle of about R0.1 Angle, can effectively reduce the probability of edge burst, fragments, splinter.

The blackening step is specifically as follows: placing the wafer in a blackening furnace for blackening treatment, the temperature is 300°C-380°C, the protective gas flow is 3L-11L, and the reduction time is 4 hours-24 hours, which can effectively Decreases the chance of warping and splintering.

A lithium niobate wafer prepared by the above-mentioned large-size, ultra-thin and high-precision lithium niobate wafer processing method.

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

The large-size, ultra-thin, high-precision lithium niobate wafer processing method and the fixture of the invention have excellent processing effects on 8-inch lithium niobate wafers, and greatly improve the production efficiency. The grinding and polishing pressurization method adopts a new segmental pressurization method, and the pressurization method adopts a slow and gradual pressurization method, which greatly reduces the scratches, fragments, cracks, etc. Effectively reduce edge slump, edge burst, insufficient grinding, etc., greatly improve the yield of production, and get rid of the constraints of semiconductor manufacturers' equipment on products.

Description of drawings

Fig. 1 is the schematic diagram of the fixture adopted in the present invention;

Fig. 2 is the pressure mode contrast graph of direct pressurization and segmental pressurization in grinding 800 steps;

Fig. 3 is the pressure mode contrast graph of direct pressurization and segmental pressurization in grinding 2000 steps;

Fig. 4 is the pressure mode contrast graph of direct pressurization and segmental pressurization in the polishing step;

Fig. 5 is the test result of the fixture of the present invention and the segmented pressurization mode;

Figure 6 shows the test results of the traditional star wheel and the segmented pressurization method;

Fig. 7 is the test result of the fixture of the present invention and direct pressurization mode;

Figure 8 shows the test results of the traditional star wheel and the direct pressurization method.

Detailed ways

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 are only a part of the embodiments of the present invention, but not all of the 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.

Embodiment 1 adopts the clamp (star wheel) of the present invention and segmented pressurization

As shown in FIG. 1 , the clamp used in this embodiment is a freewheel 1, and the wafer placement position 2 in the freewheel 1 adopts an eccentric design; the entire wafer can be processed to the maximum extent, and the processing accuracy can be ensured at the same time. .

The wafer placement position 2 is circular, and its edge is provided with a rubber ring 4 with a diameter of 105mm and a thickness of 5mm; it can effectively protect the wafer, greatly reduce edge burst, slump, splinter, debris, collapse and other phenomena, greatly improving Yield and stability.

There are five circular drainage holes 3 around the wafer placement position 2, one with a diameter of 60mm, two with a diameter of 40mm, and two with a diameter of 20mm. Taking the center of the star wheel as the center, a circle with a diameter of 290mm is made. The wafer placement circle and drainage The holes are all inscribed with the circle, the wafer placement circle and the center of the 60mm drainage hole are on the same diameter line and on both sides, the center of the 40mm drainage hole is the center of the star wheel as the center of the circle, and the radius of the 60mm drainage hole is the reference edge. Deflect 60° to the left and right, respectively, the center of the 20mm drainage hole is the center of the star wheel, and the radius of the 60mm drainage hole is the reference edge, which is deflected to the left and right by 110°.

A large-size, ultra-thin, high-precision lithium niobate wafer processing method, comprising the following steps:

1) Slicing: Under the condition that the wire speed of the steel wire is 600m/min and the temperature is 22°C, the lithium niobate crystal rod is cut into wafers with a thickness of 290μm by wire cutting equipment, and the TTV of the wafer is less than or equal to 10μm;

2) Chamfering: use a T-shaped grinding wheel for chamfering, and under the condition that the grinding wheel speed is 800rpm/min and the temperature is 22°C, the right angle of the lithium niobate wafer is poured into a rounded corner of about R0.1;

3) Grinding 800: Grinding with a double-sided grinding machine, under the condition of a temperature of 22 °C, the composition of the mortar is: silicon carbide sand GC800#: water: mortar dispersant = 13.5KG: 30L: 1.7L, the grinding pressure method adopts Staged and slow pressurization mode, the pressurization mode is the first stage of 1min, no pressurization, the second stage of pressurization for 3min, the pressurization rate is 2g/cm ² per minute, the third stage of pressurization is 2min, the pressurization rate is 3g/min cm ² , the fourth stage is pressurized for 2 minutes, the pressurization rate is 4g/cm ² per minute, the total pressurization is 20g/cm ² , the mortar flow is 10L/cm ² , and the maximum speed of the equipment is 8rpm; the grinding fixture adopts a planetary wheel , the grinding effect reaches TTV≤5μm, Bow≤30μm;

4) Blackening: place the wafer in a blackening furnace for blackening treatment, the temperature is 340°C, the flow rate of the protective gas is 7L, and the reduction time is 16 hours;

5) Grinding 2000: Grinding by double-sided grinding machine, under the condition of temperature of 22 ℃, the composition of the mortar is: silicon carbide sand GC2000#: water: mortar dispersant=13.5KG: 30L: 1.7L, the grinding pressure method adopts Staged and slow pressurization mode, the pressurization mode is the first stage pressurization for 3min, the pressurization rate is 4g/cm ² per minute, the second stage pressurization is 2min, the pressurization rate is 6g/cm ² per minute, the third stage pressurization 2min, the pressure rate is 8g/cm ² per minute, the total pressure is 40g/cm ² , the mortar flow rate is 11L/cm ² , the maximum speed of the equipment is 8rpm, and the grinding jig adopts a star wheel (the same as the one in the grinding step of 800). Star wheel), the grinding effect reaches TTV≤4μm, Bow≤25μm;

6) Polishing: use a double-sided polishing machine for polishing, the temperature is 22 ° C, the maximum speed of the equipment is 9 rpm, the polishing liquid is FUJIMI's Compol 403 polishing liquid, the main component is SiO ₂ , the specific gravity is 1.12, and the polishing pressure method is segmented. Slow pressurization mode, pressurizing mode is the first stage of pressurization for 4min, the pressurization rate is 10g/cm ² per minute, the second stage is pressurized for 4min, the pressurization rate is 15g/cm ² per minute, the third stage is pressurized for 5min, The pressurization rate was 20 g/cm ² per minute to a total of 200 g/cm ² . The flow rate of the polishing liquid is 11L/cm ² , the polishing fixture adopts the star wheel (the same as the star wheel in the grinding step of 800), and the polishing effect is the wafer TTV≤3μm, Bow≤20μm, WARP<40μm, PLTV>95%, mirror effect , No stress.

Comparative example 1 uses traditional star wheel and segmented pressurization

A large-size, ultra-thin, high-precision lithium niobate wafer processing method, comprising the following steps:

1) Slicing: Under the condition that the wire speed of the steel wire is 600m/min and the temperature is 22°C, the lithium niobate crystal rod is cut into wafers with a thickness of 290μm by wire cutting equipment, and the TTV of the wafer is less than or equal to 10μm;

2) Chamfering: use a T-shaped grinding wheel for chamfering, and under the condition that the grinding wheel speed is 800rpm/min and the temperature is 22°C, the right angle of the lithium niobate wafer is poured into a rounded corner of about R0.1;

3) Grinding 800: Grinding with a double-sided grinding machine, under the condition of a temperature of 22 °C, the composition of the mortar is: silicon carbide sand GC800#: water: mortar dispersant = 13.5KG: 30L: 1.7L, the grinding pressure method adopts Staged and slow pressurization mode, the pressurization mode is the first stage of 1min, no pressurization, the second stage of pressurization for 3min, the pressurization rate is 2g/cm ² per minute, the third stage of pressurization is 2min, the pressurization rate is 3g/min cm ² , the fourth stage is pressurized for 2 minutes, the pressurization rate is 4g/cm ² per minute, the total pressurization is 20g/cm ² , the mortar flow is 10L/cm ² , the maximum speed of the equipment is 8rpm, and the grinding fixture adopts the traditional rotary star Wheel, the grinding effect reaches TTV≤9μm, Bow≤35μm;

4) Blackening: place the wafer in a blackening furnace for blackening treatment, the temperature is 340°C, the flow rate of the protective gas is 7L, and the reduction time is 16 hours;

5) Grinding 2000: Grinding by double-sided grinding machine, under the condition of temperature of 22 ℃, the composition of the mortar is: silicon carbide sand GC2000#: water: mortar dispersant=13.5KG: 30L: 1.7L, the grinding pressure method adopts Staged and slow pressurization mode, the pressurization mode is the first stage for 1min, no pressurization, the second stage is pressurized for 3min, the pressurization rate is 4g/cm ² per minute, the third stage is pressurized for 2min, and the pressurization rate is 6g per minute /cm ² , the fourth stage is pressurized for 2 minutes, the pressurization rate is 8g/cm ² per minute, the total pressurization is 40g/cm ² , the mortar flow is 11L/cm ² , the maximum speed of the equipment is 8rpm, and the grinding fixture adopts traditional swimming Star wheel, the grinding effect reaches TTV≤8μm, Bow≤30μm;

6) Polishing: use a double-sided polishing machine for polishing, the temperature is 22 ° C, the maximum speed of the equipment is 9 rpm, the polishing liquid is FUJIMI's Compol 403 polishing liquid, the main component is SiO ₂ , the specific gravity is 1.12, and the polishing pressure method is segmented. Slow pressurization mode, the pressurization mode is the first stage for 1min, no pressurization, the second stage is pressurized for 4min, the pressurization rate is 10g/cm ² per minute, the third stage is pressurized for 4min, and the pressurization rate is 15g/cm per minute ^2. The fourth stage is pressurized for 5 minutes, the pressurization rate is 20g/cm ² per minute, the total pressure is 200g/cm ² , the flow rate of the polishing liquid is 11L/cm ² , the polishing fixture adopts a traditional star wheel, and the polishing effect is wafer TTV≤6μm, Bow≤20μm, WARP<40μm, PLTV>95%, thickness 250±15μm, mirror effect, no stress.

Among them, compared with the freewheel of Example 1, the conventional freewheel lacks the rubber ring at the edge of the wafer placement position.

Comparative example 2 adopts the fixture (plane wheel) of the present invention and direct pressurization

A large-size, ultra-thin, high-precision lithium niobate wafer processing method, comprising the following steps:

1) Slicing: Under the condition that the wire speed of the steel wire is 600m/min and the temperature is 22°C, the lithium niobate crystal rod is cut into wafers with a thickness of 290μm by wire cutting equipment, and the TTV of the wafer is less than or equal to 10μm;

2) Chamfering: use a T-shaped grinding wheel for chamfering, and under the condition that the grinding wheel speed is 800rpm/min and the temperature is 22°C, the right angle of the lithium niobate wafer is poured into a rounded corner of about R0.1;

3) Grinding 800: Grinding with a double-sided grinding machine, under the condition of a temperature of 22 °C, the composition of the mortar is: silicon carbide sand GC800#: water: mortar dispersant = 13.5KG: 30L: 1.7L, the grinding pressure method adopts Direct pressurizing method, pressurizing method is pressurized at a pressurizing rate of 4g/ ^cm2 per minute to 20g/ ^cm2 for 5 minutes, the mortar flow rate is 10L/ ^cm2 , the maximum speed of the equipment is 8rpm, and the grinding fixture adopts Example 1 The star wheel, the grinding effect reaches TTV≤9μm, Bow≤35μm;

4) Blackening: place the wafer in a blackening furnace for blackening treatment, the temperature is 340°C, the flow rate of the protective gas is 7L, and the reduction time is 16 hours;

5) Grinding 2000: Grinding by double-sided grinding machine, under the condition of temperature of 22 ℃, the composition of the mortar is: silicon carbide sand GC2000#: water: mortar dispersant=13.5KG: 30L: 1.7L, the grinding pressure method adopts Direct pressurizing method, pressurizing method is pressurized at a pressurizing rate of 8g/ ^cm2 per minute to 40g/ ^cm2 for 5min, the mortar flow rate is 11L/ ^cm2 , the maximum speed of the equipment is 8rpm, and the grinding fixture adopts Example 1 The star wheel, the grinding effect reaches TTV≤8μm, Bow≤30μm;

6) Polishing: use a double-sided polishing machine for polishing, the temperature is 22 ° C, the maximum speed of the equipment is 9 rpm, the polishing liquid is FUJIMI's Compol 403 polishing liquid, the main component is SiO ₂ , the specific gravity is 1.12, and the polishing pressure method is segmented. Slow pressurization mode, pressurization mode is direct pressurization mode, pressurize to 200g/ ^cm2 for 10min at a pressurization rate of 20g/ ^cm2 per minute, the flow rate of polishing liquid is 11L/ ^cm2 , and the polishing fixture adopts Example 1 The polishing effect is wafer TTV≤6μm, Bow≤20μm, WARP<40μm, PLTV>95%, thickness 250μm±15μm, mirror effect, no stress.

Comparative example 3 uses a traditional star wheel and direct pressurization

A large-size, ultra-thin, high-precision lithium niobate wafer processing method, comprising the following steps:

1) Slicing: Under the condition that the wire speed of the steel wire is 600m/min and the temperature is 22°C, the lithium niobate crystal rod is cut into wafers with a thickness of 290μm by wire cutting equipment, and the TTV of the wafer is less than or equal to 10μm;

2) Chamfering: use a T-shaped grinding wheel for chamfering, and under the condition that the grinding wheel speed is 800rpm/min and the temperature is 22°C, the right angle of the lithium niobate wafer is poured into a rounded corner of about R0.1;

3) Grinding 800: Grinding with a double-sided grinding machine, under the condition of a temperature of 22 °C, the composition of the mortar is: silicon carbide sand GC800#: water: mortar dispersant = 13.5KG: 30L: 1.7L, the grinding pressure method adopts Direct pressurizing method, pressurizing method is pressurized at a pressurizing rate of 4g/ ^cm2 per minute to 20g/ ^cm2 for 5 minutes, the flow rate of mortar is 10L/ ^cm2 , the maximum speed of the equipment is 8rpm, and the grinding fixture adopts the traditional roller Wheel, the grinding effect reaches TTV≤15μm, Bow≤40μm;

4) Blackening: place the wafer in a blackening furnace for blackening treatment, the temperature is 340°C, the flow rate of the protective gas is 7L, and the reduction time is 16 hours;

5) Grinding 2000: Grinding by double-sided grinding machine, under the condition of temperature of 22 ℃, the composition of the mortar is: silicon carbide sand GC2000#: water: mortar dispersant=13.5KG: 30L: 1.7L, the grinding pressure method adopts Direct pressurization method, pressurization method is pressurized at a pressurization rate of 8g/ ^cm2 per minute to 40g/ ^cm2 for 5 minutes, the mortar flow rate is 11L/ ^cm2 , the maximum speed of the equipment is 8rpm, and the grinding fixture adopts a traditional ballast Wheel, the grinding effect reaches TTV≤13μm, Bow≤30μm;

6) Polishing: use a double-sided polishing machine for polishing, the temperature is 22 ° C, the maximum speed of the equipment is 9 rpm, the polishing liquid is FUJIMI's Compol 403 polishing liquid, the main component is SiO ₂ , the specific gravity is 1.12, and the polishing pressure method is segmented. Slow pressurizing method, pressurizing method is direct pressurizing method, pressurize to 200g/ ^cm2 for 10 minutes at a pressurizing rate of 20g/ ^cm2 per minute, the flow rate of polishing liquid is 11L/ ^cm2 , and the polishing fixture adopts traditional oscillating star Wheel, the polishing effect is wafer TTV≤10μm, Bow≤20μm, WARP<40μm, PLTV>95%, thickness 250μm±15μm, mirror effect, no stress.

Various tests were performed on the 8-inch lithium niobate wafers prepared in the above Example 1 and Comparative Examples 1-3 using a TROPEL flatness tester, and the test results are shown in Figures 4-8.

The data of Example 1 and Comparative Examples 1-3 are summarized, as shown in Table 1.

Table 1

test group	TTV	thickness	WARP	BOW
Embodiment 1: star wheel of the present invention + segmented pressurization	1.247μm	242.033μm	8.612μm	7.268μm
Comparative example 1: traditional cruise ship + segmented pressurization	5.015μm	237.400μm	16.424μm	13.663μm
Comparative example 2: the present invention's star wheel + direct pressurization	5.524μm	238.531μm	14.745μm	12.249μm
Comparative example 3: traditional cruise ship + direct pressurization	9.665μm	241.362μm	19.242μm	13.426μm

It can be seen from the above results that the use of the star wheel and segmented slow pressure method of the present invention can ensure the effect of grinding and polishing by adjusting parameters within a controllable range, TTV<3μm, BOW≤10μm. Using the star wheel of the present invention + direct pressure method and using the traditional star wheel + segmented slow pressure method, TTV>5μm, BOW>10μm. Using the traditional star wheel + direct pressure method, the TTV reached 9.665μm, which is far greater than the best processing effect of 1.247μm.

The number of experimental pieces involved in the above Example 1 and Comparative Examples 1-3 and the proportion of relevant defective pieces are shown in Table 2.

Table 2

test group	Number of experimental pieces	TTV exceeded	Insufficient grinding	slump	burst edge	Fragments	Pass rate
Embodiment 1:	120	4	1	0	0	2	94.166%
Comparative Example 1:	120	8	2	2	3	4	84.166%
Comparative Example 2:	120	7	3	2	1	3	86.666%
Comparative Example 3:	120	10	5	5	3	6	75.833%

From the above results, it can be seen that Example 1 can effectively reduce the defect rate in terms of TTV, grinding sufficiency, sag, and edge burst, and improve the production yield.

Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, and substitutions can be made in these embodiments without departing from the principle and spirit of the invention and modifications, the scope of the present invention is defined by the appended claims and their equivalents.

Claims (10)

1. A method for processing large-size, ultra-thin, high-precision lithium niobate wafers, characterized in that it comprises the steps of slicing, chamfering, grinding 800, blackening, grinding 2000, and polishing;

   Both the grinding 800 steps and the grinding 2000 steps use a double-sided grinder, and at 22°C ± 2°C, the grinding and pressing method adopts a segmented slow pressing method;

   Among them, the pressurization mode of grinding 800 is: the first section is 1min, no pressurization; the second section is pressurized for 3min, and the pressurization rate is 2g/cm ² per minute; the third section is pressurized for 2min, and the pressurization rate is 3g per minute /cm ² , the fourth stage is pressurized for 2 minutes, the pressurization rate is 4g/cm ² per minute, and the total pressurization is 20g/cm ² ;

   The pressurization mode of Grinding 2000 is: the first section is 1min without pressurization; the second section is pressurized for 3min, and the pressurization rate is 4g/cm per minute; the third section is pressurized for ^2min , and the pressurization rate is 6g/cm per minute ² ; the fourth stage is pressurized for 2min, the pressurization rate is 8g/cm ² per minute, and the total pressure is 40g/cm ² ; the mortar flow is 5L/cm ² -15L/cm ² , and the maximum speed of the equipment is 6rpm-10rpm;

   In the polishing step, a double-sided polishing machine is used. At 22°C ± 2°C, the maximum rotating speed of the equipment is 6rpm-10rpm, _SiO2 polishing liquid is used, the specific gravity is 1.06-1.20, and the polishing pressure method adopts a segmented slow pressure method. , the pressurization method is: the first section is 1min, no pressurization; the second section is pressurized for 4min, and the pressurization rate is 10g/cm ² per minute; the third section is pressurized for 4min, and the pressurization rate is 15g/cm ² per minute; The fourth stage is pressurized for 5 minutes, the pressurizing rate is 20g/cm ² per minute, and the total pressure is 200g/cm ² ; the flow rate of the polishing liquid is 10L/cm ² -12L/cm ² .
2. The method for processing large-size, ultra-thin, and high-precision lithium niobate wafers according to claim 1, wherein the mortar ground in the grinding step 800 is composed of: silicon carbide sand GC800#: water: mortar dispersant=13.5KG: 30L: 1.7L; the composition of the mortar ground in the grinding step 2000 is silicon carbide sand GC2000#: water: mortar dispersant=13.5KG: 30L: 1.7L.
3. The method for processing large-size, ultra-thin and high-precision lithium niobate wafers according to claim 2, wherein the grinding effect of the 800 grinding steps reaches TTV≤5 μm, Bow≤30 μm, and the grinding effect of the 2000 grinding steps reaches TTV≤4 μm , Bow≤25μm.
4. The method for processing large-size, ultra-thin, and high-precision lithium niobate wafers according to claim 1, wherein the polishing effect of the polishing step is: wafer TTV≤3μm, Bow≤20μm, WARP<40μm, PLTV>95% , mirror effect, no stress.
5. The method for processing a large-size, ultra-thin, and high-precision lithium niobate wafer according to claim 1, wherein the lithium niobate wafer is an 8-inch lithium niobate wafer.
6. The method for processing large-size, ultra-thin, and high-precision lithium niobate wafers according to claim 1, wherein the clamp used in the grinding 800, grinding 2000 and polishing steps is a star wheel, and the The wafer placement position adopts eccentric design;

   The wafer placement position is circular, and its edge is provided with a rubber ring with a diameter of 200.2 mm and a width of 5 mm;

   There are five circular drainage holes distributed around the wafer placement position, with diameters of one of 60mm, two of 40mm, and two of 20mm. Taking the center of the star wheel as the center of the circle, a circle with a diameter of 290mm is made. The wafer placement circle and drainage The holes are all inscribed with the circle, the wafer placement circle and the center of the 60mm drainage hole are on the same diameter line and on both sides, the center of the 40mm drainage hole is the center of the star wheel as the center of the circle, and the radius of the 60mm drainage hole is the reference edge. Deflect 60° to the left and right, respectively, the center of the 20mm drainage hole is the center of the star wheel, and the radius of the 60mm drainage hole is the reference edge, which is deflected to the left and right by 110°.
7. The method for processing large-size, ultra-thin, and high-precision lithium niobate wafers according to claim 1, wherein the slicing step is as follows: at a steel wire speed of 400m/min-1000m/min, 22°C±2°C Next, the lithium niobate crystal rod is cut into wafers with a thickness of 250 μm-300 μm by wire cutting equipment, and the wafer TTV is less than or equal to 10 μm.
8. The method for processing large-size, ultra-thin, and high-precision lithium niobate wafers according to claim 1, wherein the chamfering step is specifically: using a T-shaped grinding wheel to perform chamfering, and the grinding wheel rotating speed is 600rpm/min-1000rpm/ min, at 22℃±2℃, pour the right angle of the lithium niobate wafer into a rounded corner of about R0.1.
9. The method for processing large-size, ultra-thin, and high-precision lithium niobate wafers according to claim 1, wherein the blackening step is specifically: placing the wafer in a blackening furnace for blackening treatment at a temperature of 300°C - 380℃, the protective gas flow is 3L-11L, and the reduction time is 4 hours-24 hours.
10. A lithium niobate wafer prepared by the large-size, ultra-thin, high-precision lithium niobate wafer processing method according to any one of claims 1-9.

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