WO2021088126A1

WO2021088126A1 - Double-sided polishing method for large-size ultrathin lithium niobate substrate

Info

Publication number: WO2021088126A1
Application number: PCT/CN2019/119601
Authority: WO
Inventors: 沈浩; 王勤峰; 徐秋峰; 朱海瀛; 丁孙杰; 曹焕; 汤卓伦
Original assignee: 天通控股股份有限公司
Priority date: 2019-11-06
Filing date: 2019-12-20
Publication date: 2021-05-14
Also published as: CN110744364A; CN110744364B

Abstract

Disclosed is a double-sided polishing method for a large-size ultrathin lithium niobate substrate, comprising the following steps: a) grinding the cut large-size ultrathin lithium niobate wafer to obtain a large-size ultrathin lithium niobate double-sided grinding sheet having a rough structure on the surface; b) and then performing double-sided thinning and ultrasonic cleaning to obtain a large-size ultrathin lithium niobate double-sided thinning sheet having a rough structure on the surface; c) directly performing chemical corrosion in a closed container containing nitric acid, hydrofluoric acid, and a sustained release agent which are uniformly mixed to obtain a large-size ultrathin lithium niobate corroded sheet having a random disordered depression structure on the surface; and d) performing double-sided polishing by using a double-sided polishing machine and polishing solution, and then performing ultrasonic cleaning to obtain the final large-size ultrathin lithium niobate double polished sheet. According to the present invention, one-time polishing and mass production are achieved, the polishing efficiency is high, and the produced lithium niobate substrate has a high surface flatness. This characteristic determines that the lithium niobate substrate is not easy to break in the device application, the material utilization rate is high, and the processing yield is high.

Description

Double-sided polishing method for large-size ultra-thin lithium niobate substrate

Technical field

The invention relates to the field of semiconductor materials, in particular to a double-sided polishing method for a lithium niobate substrate as a semiconductor substrate material.

Background technique

Lithium niobate (LiNbO ₃ , hereinafter referred to as LN) is a multifunctional material integrating piezoelectric, ferroelectric, pyroelectric, nonlinear, optoelectronic, photoelastic, and photorefractive functions. LN has received more and more attention due to its excellent physical properties, and has been widely used in aviation, aerospace, and civil optoelectronic products. The LN substrate after double-sided polishing is widely used in sensors, acousto-optic devices, optical gyroscopes, etc. Unlike silicon crystals and sapphire crystals, it is characterized by extremely low fracture toughness and hardness. For example, its fracture toughness is actually one-third of silicon and one-tenth of sapphire. Large-size ultra-thin lithium niobate wafers are easily damaged during processing, which not only has a high rejection rate, but also has extremely low processing efficiency, leading to high production costs for enterprises.

With the development and advancement of IC design technology and manufacturing technology, the integration of integrated circuit chips is continuously improving, the chip density is increasing exponentially, the line width is constantly shrinking, the line density is continuously increasing, the depth of focus is continuously becoming shallower, and the device is becoming smaller. , The development of the direction of the chip, which requires the substrate material to be large-sized and ultra-thin, and the roughness and flattening requirements of the substrate material continue to increase. Polishing technology has always been an important method in ultra-precision machining. It is a final machining method to reduce surface roughness, remove damage layers, and obtain a smooth, non-damaged surface. Ultra-precision CMP has been recognized by the industry as the most effective global planarization technology in semiconductor manufacturing technology.

Under normal polishing conditions, the material removal rate is proportional to the polishing speed, polishing pressure, and polishing temperature. The higher the relative polishing speed, the higher the pressure, and the higher the temperature, the higher the material removal rate and the greater the surface roughness obtained. The unevenness of the positive polishing pressure will cause uneven polishing wear, worsen the polishing quality, and deteriorate the roughness and flatness.

Summary of the invention

The technical problem to be solved by the present invention is to provide a double-sided polishing method for large-size ultra-thin lithium niobate substrates, which can be polished once, mass-produced, with high polishing efficiency and high flatness of the surface of the produced lithium niobate substrates. The characteristics determine that the lithium niobate substrate is not easy to be broken in device applications, the material utilization rate is high, and the processing yield is high.

The technical solution adopted by the present invention to solve the technical problem is: a double-sided polishing method for a large-size ultra-thin lithium niobate substrate, which specifically includes the following steps:

a) Grind the cut large-size ultra-thin lithium niobate wafer with abrasives with a particle size of 1-16um, so that the roughness of the large-size ultra-thin lithium niobate wafer is less than 200nm and the flatness is less than 10um, and then ultrasonically cleaned. Obtain a large-size ultra-thin lithium niobate double-sided grinding sheet with a rough structure on the surface;

b) The large-size ultra-thin lithium niobate wafer after grinding is thinned on both sides with a special thinning grinding wheel with a grain size of 2000#～10000#, so that the roughness of the large-size ultra-thin lithium niobate wafer is less than 100nm and flat When the temperature is less than 2um, ultrasonic cleaning is performed to obtain a large-size ultra-thin lithium niobate double-sided thinning sheet with a rough structure on the surface;

c) The large-size ultra-thin lithium niobate double-sided reduced flakes are directly chemically corroded in a closed container containing nitric acid, hydrofluoric acid and a slow-release agent uniformly mixed, the corrosion temperature is 20 ℃ ~ 25 ℃, and the corrosion time is 12 ～48 hours, make the roughness of the large-size ultra-thin lithium niobate wafer <50nm and flatness <2um, and then perform ultrasonic cleaning to obtain the large-size ultra-thin lithium niobate corrosion wafer with random and disordered pit structure on the surface;

d) The large-size ultra-thin lithium niobate corroded sheet is polished on both sides with a double-sided polishing machine and a polishing liquid. The polishing unit surface pressure is 200g/cm ² ～1400g/cm ² , and the polishing temperature is 20～25℃ to make the big The roughness of ultra-thin lithium niobate wafers of size <0.50nm, flatness <1um, the lateral dimension of the pits and depressions are 0.10～0.30um, the longitudinal depth is 0.10nm～0.50nm, and the surface area of the recesses accounts for the surface area of the large ultra-thin niobium 20%-80% of the surface area of the lithium oxide substrate is then ultrasonically cleaned to obtain the final large-size ultra-thin lithium niobate double-thinning film.

As a preference, in the step a, the thickness of the lithium niobate cutting sheet is 200-250um, the thickness of the double-sided polishing sheet is 170-220um, and the thickness of the double-sided thinning sheet is 160-210um.

As a preference, the abrasive is a mixture of one or more of boron carbide, diamond, aluminum oxide or silicon carbide. The roughness of the lithium niobate abrasive sheet depends on the particle size of the silicon carbide abrasive used. Generally speaking, the larger the particle size, the greater the roughness.

In the above step b), the double-sided thinning refers to the large-size ultra-thin lithium niobate substrate double-sided polishing sheet through the two-sided small particle size grinding wheel thinning method for flatness control, warpage control, and reduction of double-sided polishing sheet Damaged layer, reducing polishing time.

In the above step c), chemical etching refers to etching and leveling the polishing sheet of the lithium niobate substrate in a mixed acid to remove surface impurities, repair surface damage, and control the degree of warpage.

In the above step c), the corrosive liquid can be selected from a mixture of one, two or three of HNO3, HF, and slow-release agents.

In the above step c), the corrosion time is determined according to the flatness and warpage after polishing with lithium niobate, which can be several minutes to several tens of hours, preferably 12 to 48 hours. After corrosion, the warpage is less than 25μm, the roughness is less than 50nm, and the flatness is less than 2um, the chemical corrosion can be ended. The surface of the substrate after chemical etching is locally planarized, and a random and disordered pit structure is formed on the surface.

In the above step d), the formation process of the polished surface is more complicated. The initial stage is mainly to remove the tiny protrusions left by the previous process. The actual polishing area at this stage is extremely small, and the polishing pressure per unit area is relatively large. Therefore, the formation rate of the polished surface at this stage is high. As the polishing process progresses, the polished surface area of the wafer becomes larger and larger, the pressure per unit area is gradually reduced, and the formation rate of the polished surface area is gradually reduced. This stage is mainly to polish the entire surface. The third stage is the stage that takes the longest time in the polishing process. Most of the polished surface has been formed in the second stage. The main task of this stage is to remove individual large defects on the surface of the wafer, at least twice as long as the first and second stages to remove these large defects.

The large-size ultra-thin lithium niobate substrate of the present invention is polished on both sides, and the polished surface roughness is less than 0.50nm, and the flatness is less than 1um, and the polished surface has a random and disordered pit structure. In the random and disordered pit structure on the surface of the lithium niobate substrate of the present invention, the lateral dimension of the pit recess is 0.10～0.30um, the longitudinal depth is 0.10nm～0.50nm, and the surface area of the recess part accounts for the surface area of the lithium niobate substrate. 20% to 80%.

The polishing pressure of the present invention has a great influence on the polishing rate and the polishing surface quality. Generally, the polishing pressure increases, the mechanical action is enhanced, and the polishing rate also increases. However, using too high polishing pressure will cause uneven polishing rate and increased wear of the polishing pad. Elevated and difficult to control, so that the large-size ultra-thin wafers have scratches, fragments, and chipped corners, which increase the probability of occurrence of scratches, chips, and corners, thereby reducing polishing quality and high production costs.

Compared with the traditional global flattened lithium niobate substrate, on the one hand, compared with the traditional double-sided rough polishing and fine polishing technology, because the lithium niobate substrate of the present invention is polished on both sides at one time and is large in size and ultra-thin, The lithium niobate substrate greatly reduces the product defect rate and processing cost. At the same time, the present invention adopts chemical polishing technology when polishing large-size and ultra-thin lithium niobate substrates on both sides, which can simultaneously polish a large amount of lithium niobate double-sided thinning flakes at one time, greatly increasing the polishing efficiency.

In the second aspect, the surface roughness of the lithium niobate substrate of the present invention is small. Such a lithium niobate substrate can be directly applied to optical devices; on the other hand, the internal stress caused by lattice mismatch in the subsequent process is reduced, stress concentration is reduced, the dislocation density is reduced, and the quality of the subsequent process is improved. Because the lithium niobate substrate of the present invention has a random and disordered pit structure. Such a substrate enhances the adhesion during the coating process and prevents the coating from cracking; on the other hand, it reduces the internal stress caused by the lattice mismatch between the coating and the lithium niobate substrate, relieves stress concentration, and reduces dislocation density , Improve the quality of optical devices.

In the third aspect, due to the high surface flatness of the lithium niobate substrate of the present invention, this feature determines that the lithium niobate substrate is not easily broken in device applications, has high material utilization and high processing yield.

Fourthly, because the lithium niobate substrate of the present invention is large in size and ultra-thin, this feature determines that the lithium niobate substrate has a higher single input utilization rate in device applications, and meets the requirements of miniaturization and chipization. .

Description of the drawings

FIG. 1 is a schematic diagram of the horizontal and vertical depth changes of pits under different processing pressures in the embodiment of the present invention.

Fig. 2 is a schematic diagram of roughness changes under different processing pressures in the embodiment of the present invention.

Fig. 3 is a schematic diagram of flatness changes under different processing pressures according to the embodiment of the present invention.

The present invention will be further described below in conjunction with the drawings.

Detailed ways

Specific examples are listed below to further illustrate the present invention. It should be understood that the examples are not used to limit the protection scope of the present invention.

Example 1:

a) Grind the cut large-size ultra-thin lithium niobate wafer with an abrasive with a grain size of 5um, so that the roughness of the large-size ultra-thin lithium niobate wafer is less than 200nm and the flatness is less than 10um, and then ultrasonic cleaning is performed to obtain the surface Large-size ultra-thin lithium niobate double-sided grinding sheet with rough structure;

b) The large-size ultra-thin lithium niobate wafer after grinding is thinned on both sides with a special thinning grinding wheel with a grain size of 6000#, so that the roughness of the large-size ultra-thin lithium niobate wafer is less than 100nm and the flatness is less than 2um. , And then perform ultrasonic cleaning to obtain a large-size ultra-thin lithium niobate double-sided thinning sheet with a rough structure on the surface;

c) The large-size ultra-thin lithium niobate double-sided thinning flakes are directly chemically corroded in a closed container containing nitric acid, hydrofluoric acid and a slow-release agent in a certain proportion, and the corrosion temperature is 20℃～25℃. The time is 12 to 48 hours, so that the roughness of the large-size ultra-thin lithium niobate wafer is less than 50nm, and the flatness is less than 2um, and then ultrasonic cleaning is performed to obtain a large-size ultra-thin lithium niobate corrosion wafer with a random and disordered pit structure on the surface ；

d) The large-size ultra-thin lithium niobate corroded sheet is polished on both sides with a double-sided polishing machine and polishing liquid. The polishing unit surface pressure is 300g/cm ² , and the polishing temperature is 20-25 ℃, so that large-size ultra-thin niobic acid The roughness of the lithium wafer is less than 0.5nm, the flatness is less than 1um, the lateral dimension of the pit and recess is 0.18um, the longitudinal depth is 0.39nm, and the surface area of the recessed part accounts for 20%～80 of the surface area of the large-size ultra-thin lithium niobate substrate %. Then ultrasonic cleaning is carried out to obtain the final large-size ultra-thin lithium niobate double-thin film.

Example 2:

b) The large-size ultra-thin lithium niobate wafer after grinding is thinned on both sides with a special thinning wheel with a grain size of 6000#, so that the roughness of the large-size ultra-thin lithium niobate wafer is less than 100nm and the flatness is less than 2um. , And then perform ultrasonic cleaning to obtain a large-size ultra-thin lithium niobate double-sided thinning sheet with a rough structure on the surface;

d) The large-size ultra-thin lithium niobate corrosion film is polished on both sides with a double-sided polishing machine and a polishing liquid. The polishing unit surface pressure is 400g/cm ² , and the polishing temperature is 20-25 ℃, so that large-size ultra-thin niobic acid The roughness of the lithium wafer is less than 0.5nm, the flatness is less than 1um, the lateral dimension of the pit and recess is 0.15um, and the longitudinal depth is 0.21nm. The surface area of the recessed part accounts for 20%～80 of the surface area of the large-size ultra-thin lithium niobate substrate %. Then ultrasonic cleaning is carried out to obtain the final large-size ultra-thin lithium niobate double-thin film.

Example 3:

d) The large-size ultra-thin lithium niobate corroded sheet is polished on both sides with a double-sided polishing machine and polishing liquid. The polishing unit surface pressure is 500g/cm ² , and the polishing temperature is 20-25 ℃, so that large-size ultra-thin niobic acid The roughness of the lithium wafer is less than 0.5nm, the flatness is less than 1um, the lateral dimension of the pits and recesses is 0.11um, the longitudinal depth is 0.13nm, and the surface area of the recesses accounts for 20% to 80% of the surface area of the large-size ultra-thin lithium niobate substrate %. Then ultrasonic cleaning is carried out to obtain the final large-size ultra-thin lithium niobate double-thin film.

Example 4:

b) The large-size ultra-thin lithium niobate wafer after grinding is thinned on both sides with a special thinning grinding wheel with a grain size of 6000#, so that the roughness of the large-size ultra-thin lithium niobate wafer is less than 100nm and the flatness is less than 2um. , And then carry out ultrasonic cleaning to obtain large-size ultra-thin lithium niobate double-sided thinning sheet with rough structure on the surface;

c) The large-size ultra-thin lithium niobate double-sided thinning flakes are directly chemically corroded in a closed container containing nitric acid, hydrofluoric acid and a slow-release agent in a certain proportion, and the corrosion temperature is 20℃～25℃. The time is 12 to 48 hours, so that the roughness of the large-size ultra-thin lithium niobate wafer is less than 50nm, and the flatness is less than 2um, and then ultrasonic cleaning is performed to obtain a large-size ultra-thin lithium niobate corrosion wafer with random and disordered surface pits structure ；

d) The large-size ultra-thin lithium niobate corrosion film is polished on both sides with a double-sided polishing machine and a polishing liquid. The polishing unit surface pressure is 600g/cm ² , and the polishing temperature is 20-25 ℃, which makes the large-size ultra-thin niobic acid The roughness of the lithium wafer is less than 0.5nm, and the flatness is less than 1um. The lateral dimension of the pit and recess is 0.20um, and the longitudinal depth is 0.32nm. The surface area of the recessed part accounts for 20% to 80% of the surface area of the large ultra-thin lithium niobate substrate. %. Then ultrasonic cleaning is carried out to obtain the final large-size ultra-thin lithium niobate double-thin film.

Claims

A double-sided polishing method for a large-size ultra-thin lithium niobate substrate includes the following steps:

a) Grind the cut large-size ultra-thin lithium niobate wafer with abrasives with a particle size of 1-16um, so that the roughness of the large-size ultra-thin lithium niobate wafer is less than 200nm and the flatness is less than 10um, and then ultrasonically cleaned. Obtain a large-size ultra-thin lithium niobate double-sided grinding sheet with a rough structure on the surface;

b) The large-size ultra-thin lithium niobate wafer after grinding is thinned on both sides with a special thinning grinding wheel with a grain size of 2000#～10000#, so that the roughness of the large-size ultra-thin lithium niobate wafer is less than 100nm and flat When the temperature is less than 2um, ultrasonic cleaning is performed to obtain a large-size ultra-thin lithium niobate double-sided thinning sheet with a rough structure on the surface;

c) The large-size ultra-thin lithium niobate double-sided reduction flakes are directly chemically corroded in a closed container containing nitric acid, hydrofluoric acid and a slow-release agent uniformly mixed, the corrosion temperature is 20 ℃ ~ 25 ℃, and the corrosion time is 12 ～48 hours, make the roughness of the large-size ultra-thin lithium niobate wafer <50nm and flatness <2um, and then perform ultrasonic cleaning to obtain the large-size ultra-thin lithium niobate corrosion wafer with random and disordered pit structure on the surface;

d) The large-size ultra-thin lithium niobate corroded sheet is polished on both sides with a double-sided polishing machine and a polishing liquid. The polishing unit surface pressure is 200g/cm 2 ～1400g/cm 2 , and the polishing temperature is 20～25℃ to make the big The roughness of ultra-thin lithium niobate wafers of size <0.50nm, flatness <1um, the lateral dimension of the pits and depressions are 0.10～0.30um, the longitudinal depth is 0.10nm～0.50nm, and the surface area of the recesses accounts for the surface area of the large ultra-thin niobium 20%-80% of the surface area of the lithium oxide substrate is then ultrasonically cleaned to obtain the final large-size ultra-thin lithium niobate double-thinning film.
The method for polishing a large-size ultra-thin lithium niobate substrate according to claim 1, wherein the diameter of the large-size ultra-thin lithium niobate substrate is ≥150mm, the surface roughness is less than 0.5nm, and the flatness is less than 1um, the thickness is 150～200um.
The method for polishing a large-size ultra-thin lithium niobate substrate according to claim 1, wherein in step a, the thickness of the large-size ultra-thin lithium niobate wafer after cutting is 200-250um; The thickness of the ultra-thin lithium niobate double-sided polishing sheet is 170-220um.
The method for polishing a large-size ultra-thin lithium niobate substrate according to claim 1, wherein in step a, the abrasive is one or more of boron carbide, diamond, aluminum oxide or silicon carbide. Kind of mixture.
The method for polishing a large-size ultra-thin lithium niobate substrate according to claim 1, wherein in step b, the thickness of the large-size ultra-thin lithium niobate double-sided thinning sheet is 160-210 μm.
The method for polishing a large-size ultra-thin lithium niobate substrate according to claim 1, wherein in step c, the warpage of the large-size ultra-thin lithium niobate corroded sheet after etching is less than 25 μm.
The method for polishing a large-size ultra-thin lithium niobate substrate according to claim 1, wherein in the step d, the polishing solution is alkaline silica or alumina.