Piezoelectric crystal photoetching corrosion process

Abstract

The invention relates to a piezoelectric crystal photoetching corrosion process, which belongs to the technical field of quartz micromachining, and comprises the following steps of quartz substrate cleaning, barrier film plating, double-sided etching, wet etching, boss photoetching, boss corrosion and frequency fine tuning. The method comprises the following steps of: measuring a quartz wafer obtained after processing a quartz substrate by using a quartz wafer size measuring instrument to obtain a wafer length standard deviation sigma of 1.10 microns and a wafer width standard deviation sigma of 1.52 microns, and enabling the above indexes to reach the processing size precision sigma < lt >; and the process target requirements of the product are 2 microns.

Description

Technical Field

[0001] The invention belongs to the technical field of quartz micro-machining, and relates to a piezoelectric quartz wafer processing method, in particular to a piezoelectric crystal photolithography etching process. Background Art

[0002] Quartz crystal is the core component of all frequency control devices (filters, oscillators, etc.). Because quartz material is the only material that has piezoelectric properties, low loss value, high Q value, and stable physical and chemical properties, the AT cut of quartz crystal has the characteristic of zero temperature coefficient. In addition, the artificial growth technology of quartz crystal is mature and can be produced in batches at low cost. It is now widely used in resonator or oscillator components. By packaging quartz crystals, various types of quartz crystal oscillator products can be manufactured, which are used for signal frequency sources and time bases, as well as frequency control devices for receiving systems.

[0003] The traditional quartz oscillator wafer processing technology adopts mechanical processing, which is mainly processed according to the process flow of quartz crystal rod → crystal orientation scribing → crystal rod cutting → wafer grinding → wafer size processing → wafer shape processing → wafer etching.

[0004] At present, the requirements for the size and product precision of quartz oscillator chips are getting higher and higher, which is becoming increasingly difficult for traditional mechanical processing technology. QMEMS lithography technology similar to semiconductor technology has come into being. A passivation layer is physically deposited on the surface of the polished quartz substrate by magnetron sputtering. Then, a photolithography layer is made on the passivation layer using semiconductor photolithography technology. Through high-precision photolithography exposure, the designed predetermined pattern is formed on the quartz wafer. The passivation layer etching solution is used in turn to remove the deposited material not covered by the photolithography layer. Then, through the wet etching step, the exposed quartz material is etched in the depth direction. By controlling the etching solution ratio and the etching temperature, the quartz material MEMS structure processing can be formed. After processing, the quartz oscillator product has good size consistency.

[0005] Although the QMEMS processing technology can achieve high-quality production of quartz oscillator chips, the main components of the passivation layer materials in its processing are metal chromium and metal gold. Although the use of metal material gold can be recycled through chemical methods to reduce product production costs. However, the production cost of QMEMS quartz oscillators is still high. According to relevant data analysis, the production cost of quartz oscillators processed by QMEMS technology is 3 to 5 times that of quartz oscillators processed by traditional processes. The high production cost is also one of the factors limiting the mass production of this process. Summary of the invention

[0006] The present invention aims to obtain finer processing accuracy in the quartz wafer processing technology, while minimizing the use of precious metal Au, and only performing Au barrier layer coating once, thereby avoiding the disadvantage that the Au barrier layer needs to be coated multiple times in the QMEMS process, reducing the production cost of the enterprise, and meeting the processing accuracy requirements of the quartz oscillator wafer at a lower cost.

[0007] The technical solution adopted by the present invention to achieve its purpose is as follows:

[0008] The present invention adopts the following procedures: cleaning quartz substrate, coating barrier film, double-sided etching, wet etching, convex lithography, convex etching, frequency fine tuning, wherein the quartz substrate (large) can be separated into quartz wafer (small, i.e. the desired finished product) after processing. The specific operation steps are as follows:

[0009] S1. Cleaning the quartz substrate: placing the quartz substrate in a cleaning solution and heating it to remove organic matter and other impurities attached to the surface of the quartz substrate; then sequentially ultrasonically cleaning with pure water, ultrasonically cleaning with ethanol, and finally dehydrating and drying it in an oven and removing it for use;

[0010] S2. Barrier film coating: The cleaned quartz substrate is placed in the magnetron sputtering coating machine through the rack, and the vacuum chamber is evacuated to 1×10 -5 Pa or less, the surface of the quartz substrate is first pretreated with plasma, and then magnetron sputtering is used to coat a 10nm thick Cr film and a 300nm thick Au film, and the coating requires double-sided coating processing;

[0011] S3. Double-sided etching: The double-sided coated quartz substrate is coated with a negative photoresist with uniform thickness on both sides, and the double-sided etching machine is used to perform overlay alignment exposure on both sides of the quartz substrate to produce the pattern required for wet etching; after the double-sided etching pattern is inspected, the Au metal is etched with a mixed solution of iodine and potassium iodide, and the etching time is controlled within 3 minutes (i.e., the Au etching solution is used to etch the area not protected by the photoresist, thereby removing the excess Au film); then, the Cr metal is etched with a mixed solution of ammonium cerium nitrate and glacial acetic acid, and the etching time is controlled within 2 minutes (i.e., the Cr etching solution is used to etch the area not protected by the photoresist, thereby removing the excess Au film); The area protected by the photoresist and the Au film is etched to remove the redundant Cr film); after etching, an optical microscope is inspected to require that the metal barrier film is completely etched and the edges are neat and straight; the present invention uses a mixed solution of iodine and potassium iodide to etch Au metal, which has a good dissolution effect, is convenient for industrial operation, and controls the etching depth; the present invention uses a non-oxidizing acid to provide an acidic environment for ammonium cerium nitrate, avoids the problem of reduced oxidizability of ammonium cerium nitrate due to hydrolysis, and improves the problem of large surface roughness of the substrate after etching and poor etching effect; at the same time, the etching depth can be controlled to achieve ideal etching accuracy and effect;

[0012] S4. Wet etching: Place the quartz substrate and the spacer separately into a special etching fixture, and etch the quartz material in the etching solution; different etching solution concentrations and temperatures have a great influence on the edge of the final quartz oscillator wafer; after wet etching, the quartz oscillator wafer size processing is completed, and the negative photoresist is removed using a photoresist stripping solution;

[0013] S5. Boss photolithography: After wet etching, the quartz wafer size processing is completed, the negative photoresist on the quartz wafer is removed by using a photoresist stripping solution, and then the photoresist layer is double-sidedly coated again. The quartz substrate is exposed on both sides by using a photolithography machine to produce boss photolithography patterns and wafer crack groove patterns. The metal barrier film not protected by the photoresist is removed by using an Au metal etching solution and a Cr metal etching solution in turn to expose the area to be etched;

[0014] S6. Boss etching: Put the quartz substrate and the separate spacer into the special etching fixture again, put the whole into the etching solution for the second quartz double-sided etching, the temperature of the etching solution is lower than the wet etching temperature in step S4, and the boss height is controlled by etching; after the quartz etching is completed, use the photoresist stripping solution to remove the surface photoresist layer, use the Au metal etching solution and the Cr metal etching solution to remove the barrier metal layer, and use the splitter to separate the quartz wafer from the quartz substrate;

[0015] S7. Frequency fine-tuning: Put the quartz wafers into the quartz wafer sorting machine, and test the quartz wafer frequency in different bins. Use NH 4 F etching liquid is used for fine-tuning etching, and after etching, the frequency dispersion of batch quartz wafers is narrowed.

[0016] The key technologies that need to be mentioned in particular are:

[0017] In step S1, the cleaning liquid is [C 3 H 4 O 2 ] n (Acrylic polymer): C 6 H 8 O 7 (Citric acid): CHN 2 O 8 (Edetic acid): H 2 O (deionized water) = 25:22:53:1500, temperature condition is 51.2°C;

[0018] In step S4, the etching solution is a etching mother solution diluted with deionized water, and the weight proportion of the etching mother solution in the etching solution is 55%. In terms of molar ratio, the etching mother solution is HF:HNO 3 :H 2 SO 4 :H 2 O2 =16:1:35:6, temperature condition is 58.3℃;

[0019] In step S6, the etching solution is the etching mother solution diluted with deionized water, and the weight proportion of the etching mother solution in the etching solution is 55%. In terms of molar ratio, the etching mother solution is HF:HNO 3 :H 2 SO 4 :H 2 O 2 =16:1:35:6, and the temperature condition is 55.1℃.

[0020] The beneficial effects of the present invention are:

[0021] The processing technology of the present invention reduces the usage of precious metal Au to the greatest extent. By means of one coating and two photolithography processes, the disadvantage that the Au barrier layer needs to be coated multiple times in the QMEMS process is avoided, thereby reducing the development cost of the enterprise.

[0022] Experiments have proved that by adopting the piezoelectric crystal photolithography etching process described in the present invention, the frequency-temperature characteristic of the quartz crystal oscillator is within the test range of -40 to 95°C, the test frequency jumps within the range of ±8ppm, and the maximum value of the resonant resistance is 28.1Ω, meeting the requirements of the product setting indicators (test frequency drift is not more than ±12ppm, and resonant resistance is not more than 40Ω). The product quality rate is 96.45%, which significantly reduces product costs and enhances the market competitiveness of production enterprises. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a process flow chart.

[0024] Figure 2 It is the relationship between the concentration of the corrosive solution and the corrosion rate under the condition of 58.3℃.

[0025] Figure 3 It is the relationship between corrosion temperature and corrosion rate under the condition of 55.0wt% concentration of corrosion solution. DETAILED DESCRIPTION

[0026] The present invention is described in detail below in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should belong to the scope of protection of the present invention.

[0027] Example 1

[0028] The present invention adopts the following procedures: cleaning the quartz substrate, plating a barrier film, double-sided etching, wet etching, boss photolithography, boss etching, and frequency fine tuning. The specific operation steps are as follows:

[0029] S1. Cleaning the quartz substrate: The quartz substrate is placed in a cleaning solution and heated for cleaning to remove organic matter and other impurities attached to the surface of the quartz substrate. The cleaning solution is calculated by molar ratio as [C 3 H 4 O 2 ] n (Acrylic polymer): C 6 H 8 O 7 (Citric acid): CHN 2 O 8 (Edetic acid): H 2 O (deionized water) = 25:22:53:1500, the cleaning temperature is 51.2°C; then pure water ultrasonic cleaning (40kHz, 10 minutes), ethanol ultrasonic cleaning (900kHz, 8 minutes), finally dehydration and drying in an oven and taking out for standby;

[0030] S2. Barrier film coating: The cleaned quartz substrate is placed in the magnetron sputtering coating machine through the rack, and the vacuum chamber is evacuated to 1×10 -5 Pa or less, the surface of the quartz substrate is first pretreated with plasma, and then magnetron sputtering is used to coat a 10nm thick Cr film and a 300nm thick Au film, and the coating requires double-sided coating processing;

[0031] S3. Double-sided etching: after double-sided coating, the quartz substrate is coated with a negative photoresist with uniform thickness on both sides, and the double-sided etching machine is used to perform overlay alignment exposure on both sides of the quartz substrate to produce the pattern required for wet etching; after the double-sided etching pattern is inspected, the Au metal is etched with a mixed solution of iodine and potassium iodide (in terms of mass ratio, iodine: potassium iodide: deionized water = 1:3:30), and the etching time is controlled within 3 minutes; then, the Cr metal is etched with a mixed solution of ammonium cerium nitrate and glacial acetic acid (in terms of mass ratio, ammonium cerium nitrate: glacial acetic acid: deionized water = 10:1:30), and the etching time is controlled within 2 minutes; after etching, an optical microscope inspection is performed, requiring that the metal barrier film is completely etched and the edges are neat and straight;

[0032] S4. Wet etching: Place the quartz substrate and the spacer into a special etching fixture, and perform double-sided etching of the quartz material in the etching solution. The etching solution in the wet etching is the etching mother solution diluted with deionized water. The etching mother solution is HF:HNO 3 :H 2 SO 4 :H 2 O 2=16:1:35:6, the weight proportion of the etching mother liquid in the etching solution is 55%, and the temperature condition is 58.3°C; different etching solution concentrations and temperatures have a great influence on the edge of the final quartz wafer; after wet etching, the quartz wafer size processing is completed, and the negative photoresist is removed using a photoresist stripping solution;

[0033] S5. Boss photolithography: After wet etching, the quartz wafer size processing is completed, the negative photoresist on the quartz wafer is removed by using a photoresist stripping solution, and then the photoresist layer is double-sidedly coated again. The quartz substrate is exposed on both sides by using a photolithography machine to produce boss photolithography patterns and wafer crack groove patterns. The metal barrier film not protected by the photoresist is removed by using an Au metal etching solution and a Cr metal etching solution in turn to expose the area to be etched;

[0034] S6. Boss etching: Put the quartz substrate and the spacer into the special etching fixture again, and put the whole into the etching solution for the second quartz double-sided etching. The temperature of the etching solution is lower than the wet etching temperature in step S4. The boss height is controlled by slow etching. The etching solution is the etching mother solution diluted with deionized water. The etching mother solution is HF:HNO 3 :H 2 SO 4 :H 2 O 2 =16:1:35:6, the weight proportion of the etching mother liquid in the etching liquid is 55%, and the temperature condition is 55.1°C; after the quartz etching is completed, the surface photoresist layer is removed by using a photoresist stripping liquid, the barrier metal layer is removed by using an Au metal etching liquid and a Cr metal etching liquid, and the quartz oscillator wafer is separated from the quartz substrate by using a splitter;

[0035] S7. Frequency fine-tuning: Put the quartz oscillator chip into the quartz chip sorting machine, and test the quartz chip frequency in different bins. Use NH 4 F etching liquid is used for fine-tuning etching, and after etching, the frequency dispersion of batch quartz wafers is narrowed.

[0036] The quartz wafer obtained after processing the quartz substrate was measured with a quartz wafer size measuring instrument, and the quartz wafer size test data shown in Table 1 was measured. The standard deviation of the wafer length σ was 1.10μm, and the standard deviation of the wafer width σ was 1.52μm, which met the process target requirements. The dimensional accuracy of the product after processing σ<2μm.

[0037] Table 1 Quartz wafer size measurement data

[0038] Serial number Wafer length Wafer width unit 1 1.8014 1.2767 mm 2 1.7978 1.2733 mm 3 1.7981 1.2725 mm 4 1.7993 1.2722 mm 5 1.8004 1.2767 mm 6 1.8001 1.2729 mm 7 1.7991 1.2748 mm 8 1.8007 1.2749 mm 9 1.7995 1.2746 mm 10 1.8002 1.2739 mm 11 1.8007 1.2733 mm AVG 1.799755 1.274164 mm Range R 3.6 4.5 μm Standard deviation 1.10 1.52 μm

[0039] It can be seen that the advantages of the present invention are:

[0040] 1) Compared with the existing QMEMS process, the present invention adopts a specific corrosion mixture formula and temperature conditions, and achieves higher processing accuracy by controlling the corrosion process. The quartz crystal oscillator size processing accuracy can reach <2μm, which is <10μm compared with the existing quartz crystal oscillator processing technology, and the dimensional accuracy is significantly improved.

[0041] 2) Compared with the existing QMEMS process that requires more than two Au metal and Cr metal barrier layers, the present quartz crystal oscillator production process only requires one Au and Cr metal barrier layer coating, thus reducing production costs.

Claims

1. A piezoelectric crystal photolithography etching process, characterized in that: The following steps are involved: S1. Cleaning the quartz substrate: The quartz substrate is cleaned, dehydrated and dried for standby use; S2. Barrier film coating: After step S1, the cleaned quartz substrate is magnetron sputtered on both sides to coat Cr / Au thin film; S3. Double-sided etching: The double-sided coated quartz substrate is coated with negative photoresist on both sides, and the double-sided etcher is used to perform overlay and alignment exposure on both sides of the quartz substrate to produce the pattern required for wet etching. After the double-sided etching pattern is inspected, the Au metal is etched using a mixed solution of iodine and potassium iodide, and the etching time is controlled within 3 minutes. Then, the Cr metal is etched using a mixed solution of ammonium cerium nitrate and glacial acetic acid, and the etching time is controlled within 2 minutes. S4 wet etching: the quartz substrate after step S3 is loaded into a separate spacer into a special etching fixture, and double-sided etching of the quartz material is performed in the etching solution; S5. Boss photolithography: After wet etching, the quartz wafer size processing is completed, the negative photoresist on the quartz wafer is removed, and then the double-sided coating is re-made to form a photoresist layer, and the quartz substrate is exposed on both sides by a photolithography machine to make boss photolithography patterns and wafer crack groove patterns, and the metal barrier film not protected by the photoresist is removed by Au metal etching solution and Cr metal etching solution in turn to expose the area to be etched; S6. Boss etching: Put the quartz substrate and the spacer into the special etching fixture again, put the whole into the etching solution for the second quartz double-sided etching, the temperature of the etching solution is lower than the wet etching temperature in step S4, and the boss height is controlled by etching. After the quartz etching is completed, the surface photoresist layer is removed, and the barrier metal layer is removed using Au metal etching solution and Cr metal etching solution, and the quartz wafer is separated from the quartz substrate using a splitter; S7. Frequency fine-tuning: Put the quartz wafers into the quartz wafer sorting machine, test the quartz wafer frequency in different bins, and use NH4F etching liquid to fine-tune the quartz wafers with different bin frequencies. After etching, the frequency dispersion of the batch of quartz wafers is narrowed.

2. A piezoelectric crystal photolithography etching process according to claim 1, characterized in that: In step S1, the quartz substrate is placed in a cleaning solution for heating and cleaning, and then sequentially cleaned with pure water ultrasonic cleaning and ethanol ultrasonic cleaning, and finally dehydrated and dried in an oven and taken out for standby use.

3. A piezoelectric crystal photolithography etching process according to claim 2, characterized in that: In step S1, the cleaning solution is acrylic acid polymer: citric acid: edetic acid: deionized water = 25:22:53:1500 in molar ratio, and the temperature is 51.2°C.

4. The piezoelectric crystal photolithography etching process according to claim 1, characterized in that: In step S2, the cleaned quartz substrate is placed in a magnetron sputtering coating machine, and the vacuum chamber is evacuated to 1×10 -5 Pa, the surface of the quartz substrate is first pretreated with plasma, and then a 10nm thick Cr film and a 300nm thick Au film are magnetron sputtered. The coating requires double-sided coating processing.

5. The piezoelectric crystal photolithography etching process according to claim 1, characterized in that: In step S4 wet etching, the etching liquid is a etching mother liquid diluted with deionized water, and the weight proportion of the etching mother liquid in the etching liquid is 55%. In terms of molar ratio, the etching mother liquid is HF:HNO3:H2SO4:H2O2=16:1:35:6, and the temperature condition is 58.3°C.

6. The piezoelectric crystal photolithography etching process according to claim 1, characterized in that: In step S6, the boss corrosion, the corrosion liquid is the corrosion mother liquid diluted with deionized water, the weight proportion of the corrosion mother liquid in the corrosion liquid is 55%, and the molar ratio of the corrosion mother liquid is HF:HNO3:H2SO4:H2O2=16:1:35:6, and the temperature condition is 55.1°C.

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