A method for processing a MEMS optical grade cavity lid

Abstract

The present application relates to the technical field of laser-induced etching, and particularly relates to a MEMS optical-grade cavity cover plate processing method. The method comprises the following steps: S1. selecting an optical cover plate with a required size, and cleaning the surface; S2. depositing a metal film on the surface of the optical cover plate by using a PVD process; S3. coating a negative photoresist on one side of the optical cover plate; S4. covering the cover plate containing a pattern on the surface of the photoresist to perform exposure and development, and exposing the patterned metal layer; S5. etching the metal film to manufacture a mask plate; S6. modulating a high-power infrared laser into a spatial structure light, irradiating the surface of the mask plate, and ascending and descending in the Z-axis direction; S7. etching the modified part to a required depth by using a wet etching method, and controlling the etching depth by controlling the depth of the irradiation modification area and adjusting the etching time; S8. removing the photoresist and the metal film, and obtaining an optical-grade cavity cover plate. The method has low equipment cost, fast processing speed, accurate size and shape, completely transparent cavity, and safe and environmentally-friendly process.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser-induced etching technology, in particular to a MEMS optical-grade cavity cover plate processing method. BACKGROUND

[0002] MEMS (Micro Electro Mechanical System) packaging includes chip-level assembly (or sub-zero-level packaging), chip-level packaging (or zero-level packaging), device-level packaging (or one-zero-level packaging), board-level packaging (or two-level packaging), and motherboard-level packaging (or three-level packaging). A typical MEMS microsystem package contains IC circuits, as well as working sensors, actuators, biological, fluid, chemical, optical, magnetic, and radio frequency MEMS micro devices. The package provides support and protection for internal chips and leads, as well as the necessary working environment and the necessary activity space, so that it is not disturbed and corroded by the external environment. For micro sensors and micro actuators, in addition to electrical signals, the chip also has other physical information to be connected with the outside world, such as light, sound, force, and magnetism.

[0003] Common packaging materials include metals, ceramics, glasses, and plastics. Glass packaging has good sealing, biocompatibility, and insulation, so it is more inclined to glass packaging for corrosive environments such as biomedical implant devices; glass is transparent, and wireless signals can pass through without interference, making it very suitable for scenarios that transmit optical signals and wireless signals. Glass cavity covers are generally made using a pre-formed packaging process. This method has become popular mainly because of its simplicity and ease of operation, which allows the use of standard chip bonding and wire bonding. Currently, the glass pre-forming process mainly uses femtosecond laser ablation combined with HF wet etching. The cost of a femtosecond laser device is high, and the ablation speed is slow, resulting in high pre-forming costs. The bottom of the etched cavity is difficult to achieve an ideal light transmission effect, which limits the application scenarios of optical covers. To date, this packaging has only been used for special devices such as radio frequency and medical devices, and it is necessary to develop a more general and lower-cost packaging method.

[0004] The use of femtosecond laser ablation combined with HF wet etching to manufacture optical-grade cavity covers has the following disadvantages: ① Using a subtractive 3D printing mode to ablate point by point, the efficiency is low, and the processing time is long, resulting in high costs for single covers; ② Due to the focusing characteristics of the Gaussian beam, the modified lattice is discontinuous and appears as a spatial mist, and the cavity after etching presents a frosted matte effect, which cannot be completely transparent, affecting the transmission of optical signals, and the microscopic structure is as follows: Figure 5The existing femtosecond laser modification and HF wet etching method for manufacturing the optical cavity cover plate has the following problems: 1) the femtosecond laser is expensive, and the device cost is high, which increases the product cost; 2) the etching process of the HF wet method is isotropic, and the etching direction and etching depth are not easy to control, so that the accurate feature size is not easy to obtain when the micron-level cavity structure is manufactured, and the size and shape of the etched cavity are greatly different from the ideal size and shape, and the glass itself is obviously thinned; 3) the HF solution has strong toxicity, corrosion and volatility, and the volatilized HF gas and the water vapor in the air continue to combine into hydrofluoric acid, which is highly toxic and can cause irreversible damage to the human circulatory system. SUMMARY

[0005] The application provides a MEMS optical cavity cover plate processing method, which aims to solve the problems of high device cost, slow processing speed, large size and shape deviation, non-transparent cavity, glass thinning and poor environmental protection of the etching process in the existing femtosecond laser modification and HF wet etching method for manufacturing the optical cavity cover plate.

[0006] The application provides a MEMS optical cavity cover plate processing method, which comprises the following steps:

[0007] S1. selecting an optical cover plate with a required size and cleaning the surface;

[0008] S2. depositing a metal film on the surface of the optical cover plate by using a PVD process;

[0009] S3. coating a negative photoresist on one side of the optical cover plate;

[0010] S4. covering the cover plate containing a pattern on the surface of the photoresist for exposure and development to expose the patterned metal layer,

[0011] S5. etching the metal film to manufacture a mask plate;

[0012] S6. modulating a high-power infrared laser into a spatial structure light, irradiating the surface of the mask plate, and lifting in the Z-axis direction to cause the irradiated optical cover plate to be continuously and regionally modified in the Z-axis direction;

[0013] S7. etching the modified part to a required depth by using a wet etching method, and controlling the etching depth by controlling the irradiation modification zone depth and adjusting the etching time;

[0014] S8. removing the photoresist by using a degreasing agent, and removing the metal film by using a wet etching method, to obtain the optical cavity cover plate.

[0015] As a further improvement of the application, in the step S1, the optical cover plate processing process with a required size comprises the following cases:

[0016] After the whole piece of glass is cut into single optical cover plates to be processed, the processes of steps S2 to S8 are performed; or the cavity array is first made on the whole piece of glass, and then the single shaped optical cover plates are cut after the processes of steps S2 to S8 are completed.

[0017] As a further improvement of the present application, the exposure process in step S4 includes the following cases: LDI laser direct writing process is used for single piece small batch processing, or mask exposure process is used for whole piece large batch processing.

[0018] As a further improvement of the present application, in step S4, the specific process of development is: the photoresist is developed with a developer, fixed with a fixer, and rinsed clean with deionized water.

[0019] As a further improvement of the present application, the etching process of step S5 includes but is not limited to wet etching and dry etching.

[0020] As a further improvement of the present application, in step S6, a high-power infrared structured light is used, and the modulation method and process thereof include but are not limited to:

[0021] The high-power laser emits an internal flat-top light laser beam, which is reflected by a mirror to change the processing direction, and then modulated into a spatial structured light by a compound eye lens.

[0022] As a further improvement of the present application, in step S6, the spatial structured light is formed by the diffraction effect of the flat-top light laser beam passing through the compound eye lens, and the spatial structured light converges to form a focusing plane at the working distance position. When the focusing plane moves downward from the surface of the optical cover plate along the Z-axis direction to irradiate the surface of the mask plate, the modified region is gradually deepened to the required depth.

[0023] As a further improvement of the present application, in step S7, the etching liquid for etching the modified part includes but is not limited to a strong alkali solution.

[0024] As a further improvement of the present application, the material of the optical cover plate includes but is not limited to transparent brittle materials such as glass, quartz and sapphire.

[0025] The present application has the advantages that a method for making a glass cavity cover plate based on structured light area selective irradiation modification and environmentally friendly alkali wet etching is provided, which has low equipment cost, fast processing speed, accurate size and shape, completely transparent cavity, and safe and environmentally friendly process. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a process flow chart of the MEMS optical grade cavity cover plate processing method of the present application;

[0027] Figure 2is a schematic diagram of the mechanism for constructing spatial structured light in the present application;

[0028] Figure 3 is a schematic diagram of the mechanism for constructing spatial structured light in the present application;

[0029] Figure 4 is a comparison diagram of Gaussian light beam and flat-top light beam in the present application;

[0030] Figure 5 is a microstructure diagram of the prior art of the present application for fabricating optical-grade cavity cover plate by femtosecond laser and HF wet etching. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application will be further described in detail below in combination with the drawings and examples.

[0032] The present application discloses a MEMS optical-grade cavity cover plate processing method, which applies spatial structured light 45 to irradiate glass cover plate 1 to modify the region, and then uses the significant difference in etching efficiency between the modified region and the non-modified region to obtain a high-transmittance optical-grade cavity cover plate by wet etching. Figure 1 As shown in the figure, the implementation steps are as follows.

[0033] S1. Select a glass cover plate 1 of the required size, clean the surface, as shown in part ① in the figure. Figure 1 The glass cover plate 1 can be cut into a single corresponding size to be processed from a whole piece of glass, or a cavity array can be made on the whole piece of glass first, and then cut into a single formed glass cover plate 1 after all processes are completed.

[0034] S2. Deposit a metal film 2 on the surface of the glass cover plate 1 by PVD process, and the thickness of the metal film 2 is 0.5-1.5um, as shown in part ② in the figure. Figure 1 The metal film 2 can be Au or Gr.

[0035] S3. Coating a negative photoresist 3 on one side of the glass cover plate 1; the coating thickness is 2-40um, as shown in part ③ in the figure. Figure 1 The negative photoresist 3 can be selected from photoresist 3 suitable for 365nm or 405nm ultraviolet waveband.

[0036] S4. Cover the cover plate containing the pattern on the surface of the photoresist 3 for exposure and development, to expose the patterned metal layer, as shown in part ④ in the figure. Figure 1 Batch production can use mask exposure process, or single-piece production can also use LDI (Laser Direct Imaging) process, and the 2.38% THAM ultraviolet photoresist 3 is developed with developer, then fixed with fixing solution, and then the glass cover plate 1 is rinsed clean with deionized water.

[0037] For the 2 patterning exposure process in step S4, LDI laser direct writing technology can be used for single-chip small batch processing, or mask exposure technology can be used for positive large batch processing, and the exposure pattern width ranges from 5 to 500 um.

[0038] S5. Etching the metal film to make a mask, such as Figure 1 Part V in the specification. Wet etching, dry etching such as RIE, ICP, DRIE can be used. However, it is not limited to wet etching and dry etching, and other methods that can etch the metal layer are also applicable to the method.

[0039] Wherein, the mask refers to a mask plate used for exposure process patterning.

[0040] RIE (Reactive Ion Etching), a kind of microelectronic dry etching process.

[0041] ICP (Inductively Coupled Plasma), that is, inductively coupled plasma etching is an important part of microfabrication technology. It has been widely used in the fields of integrated optics, optoelectronics, micro-mechanical systems (MEMS), photonic crystals, etc.

[0042] DRIE (Deep Reactive Ion Etching), a kind of deep reactive ion etching, is a kind of dry etching process mainly used for micro-electro-mechanical systems.

[0043] S6. Modulate the 3000-5000 watt high-power infrared laser into a spatial structure light 45, irradiate the surface of the mask, and at the same time, lift up and down in the Z-axis direction at a speed of 3-50 um / s to a depth slightly deeper than the required cavity depth, such as Figure 1 Part VI in the specification, the irradiated glass cover plate 1 has undergone continuous regional modification in the Z-axis direction, such as Figure 1 Part VII in the specification, Figure 1 The shadow in part VII is to clearly express the range of the modified region 5, and in practice, the apparent form, color, and transparency of the modified region do not change at all. The structure light spot is modulated to 3x3mm or 5x5mm or other sizes according to the selected laser power and processing material, and the power density can reach 50KW / cm 2 . Different materials, different thicknesses of glass, and different laser irradiation times.

[0044] S7. Wet etching is used to etch the modified part to the required depth, and the etching depth is determined by controlling the irradiation modification depth and adjusting the etching time. The longer the etching time, the deeper the etching depth, such as Figure 1 Part VIII in the specification.

[0045] S8. Using a degreasing agent to remove the glue, using wet etching to remove the metal plating layer, an optical grade cavity cover plate is obtained, see Figure 1 Part (9) of the description.

[0046] The optical cover plate processed by the method is not limited to glass cover plate 1, and the materials applied can also include but are not limited to transparent brittle materials such as quartz and sapphire.

[0047] Unlike the glass modification mechanism realized by femtosecond laser, the step S6 of the application adopts to construct a spatial structure light 45 outside the laser, and to realize selective area modification of the glass cover plate 1 by moving the focusing plane 46 formed by the spatial structure light up and down. The flat-top spatial structure light 45 constructed by the fly's eye lens 44 is fully diffracted, the power density in the focusing plane 46 is large, and the energy is uniformly distributed, so the processing speed is fast and can be improved by several tens of times. The irradiation modification is a spatial continuous structure, which will not produce a conical pit shape like single-point irradiation of Gaussian light, and the modified area has no obvious difference with the glass material in appearance, so the cavity after etching is completely transparent. The mechanism of constructing the spatial structure light 45 is as follows.

[0048] As shown in Figure 2 , the high-power laser 41 emits an internal flat-top light laser beam 42, which is reflected by the mirror 43 to change the direction suitable for processing. The square internal flat-top light is modulated into a spatial structure light 45 by the fly's eye lens 44 (or DOE element), and the spatial structure light 45 irradiates the cavity cover plate. Under the shielding of the mask, only the patterned part will pass through the spatial structure light 45, and the glass cover plate 1 will be regionally modified along the laser conduction direction.

[0049] The power range of the high-power laser 41 is 3000-5000W, the waveband is 1064±10nm, and the beam mode is internal flat-top light. The so-called flat-top light (TH) is a concept corresponding to Gaussian light, which is a beam with flat and uniform intensity and energy density distribution, sharp edges, and energy rapidly dropping to zero. The shape of the flat-top light beam can be square, rectangular, straight, circular or any other shape, as shown in Figure 4 The left side of the figure is a Gaussian beam, and the right side is a flat-top beam.

[0050] The mirror 43 is coated with a 45-degree full reflection film, and the reflectivity of 1064nm laser is 99.99%. The lens material is SiC, and an internal water cooling structure is designed.

[0051] The fly's eye lens 44 is a rectangular fly's eye matrix, and the material is quartz or liquid crystal DOE element. The fly's eye unit size is a square array of 100x100nm-5x5um±5%, which can also be made into a rectangle if there is a special requirement. The working distance WD of the fly's eye lens 44 is 20-30mm, the focal depth is 3-50um, the thickness is ≧100um, and the upper and lower surfaces are coated with infrared antireflection film.

[0052] The compound eye unit is equivalent to a set of combined lens array, the unit size is processed into λ / 4-λ, wherein λ is the laser wavelength, since the physical size of the compound eye unit is less than or equal to the laser wavelength, the square internal flat top light will have a diffraction effect after passing through the compound eye lens 44, and part of the flat top light will also be diffracted when passing through the adjacent gap of the compound eye unit, and then be modulated into a spatial structure light 45. The spatial structure light 45 converges at the working distance WD position to form a focusing plane 46 with a focal depth of 3-5 um, and the laser energy density in this range is as high as 50 KW / cm 2 When irradiating the glass, a regional modification can be generated, and the focusing plane 46 moves downward from the glass surface, and the modified region gradually deepens to the required depth, as shown in Figure 3 .

[0053] In step S7, the etching liquid for etching the modified part is a strong alkali solution. According to the article “Laser-assisted etching of borosilicate glass in potassium hydroxide” published by OST Eastern Switzerland University of Applied Sciences, Buchs, Switzerland, it is shown that using a KOH solution to etch the glass after selective regional irradiation by laser, the irradiated region has a faster etching efficiency than the non-irradiated region, and the etching has a significant anisotropy. Using this method to complete the etching of the modified region not only has high efficiency, but also has little damage to the glass body. The strong alkali is an embodiment of the etching liquid, but is not limited to the strong alkali solution etching method. Other solutions that can etch glass are also suitable for the etching liquid of the present application.

[0054] The main chemical composition of the glass is: SiO2 70-73%, Na2O 13-15%, GaO, AL2O3, MgO, a total of 14-20%, and additionally containing trace amounts of Fe2O3 about 0.1%, the above proportions are molar content percentages. Taking KOH as an example of the etching liquid, the chemical reaction equation for etching is: SiO2+2KOH==K2SiO3+H2O, wherein K2SiO3 is a water-soluble substance. Compared with HF wet etching, the chemical reagents and chemical reaction intermediates used have the characteristics of non-toxicity, small pollution, safety and environmental protection.

[0055] The concentration of the KOH solution used in the etching process is preferably 8.5±0.5 mol / l, and the temperature range for etching control is 80±3℃. Based on the research report, the present application further increases the ultrasonic assisted etching, the frequency range of the ultrasonic assisted etching is 20KHz-100KHz, and the etching efficiency is 30-50um / H, which further improves the etching efficiency.

[0056] The structure light selective irradiation wet etching method for manufacturing the MEMS optical-grade cavity cover plate has the following advantages compared with the prior art:

[0057] 1) The used equipment has low cost, simple structure and is easy to adjust.

[0058] 2) The mask is manufactured by using the exposure patterning process, the minimum feature size can be less than 5 um, the mask can be made into a cavity structure with accurate shape and size, and it can play a good shielding effect on the structure light irradiation, so the shape of the modified area is accurate. The structure light modification has a strong guiding effect on the etching direction, and the etching efficiency of the modified area is significantly higher than that of the glass itself. Compared with HF solution etching, the shape accuracy is greatly improved after etching, the cavity sidewall can be made almost completely vertical, the laser modified interface is smooth, the cavity after etching is completely transparent, which is more conducive to the transmission of optical signals, and finally the etching has less thinning on the body, so that a high-quality optical-grade cavity cover plate can be obtained.

[0059] 3) The efficiency of the laser processing part is more than ten times higher than that of the existing point-by-point scanning process, especially for larger cavities, the processing efficiency is significantly improved, and batch and large-scale production can be easily realized, thereby reducing the manufacturing cost.

[0060] 4) Since there is still a large gap between the dot matrix of the point-by-point scanning method, the modified area appears to be misty and discontinuous, while the structure light irradiation realizes the continuity of the modified area, so the etching efficiency is also significantly improved, the etching surface is smoother, and the cavity is almost completely transparent.

[0061] 5) The etching liquid and the intermediate products of the chemical reaction have no toxic side effects and are safe and environmentally friendly.

[0062] The above is a further detailed description of the present application in combination with specific preferred embodiments, and the specific implementation of the present application should not be limited to these descriptions. For ordinary skilled persons in the technical field to which the present application belongs, some simple deductions or substitutions can be made without departing from the concept of the present application, and all of them should be considered as falling within the protection scope of the present application.

Claims

1. A method for fabricating a MEMS optical-grade cavity cover plate, characterized in that, The method comprises the following steps: S1. Selecting an optical cover plate with a desired size and cleaning the surface; S2. Depositing a metal film on the surface of the optical cover plate by PVD process; S3. Coating a negative photoresist on one side of the optical cover plate; S4. Covering the cover plate with a pattern on the surface of the photoresist for exposure and development to expose the patterned metal layer; S5. Etching the metal film to make a mask plate; S6. Modulating a high-power infrared laser into spatial structure light, irradiating the surface of the mask plate, and moving up and down in the Z-axis direction to cause continuous regional modification of the irradiated optical cover plate in the Z-axis direction; S7. Etching the modified part to the desired depth by wet etching, and controlling the etching depth by controlling the irradiation modification zone depth and adjusting the etching time; S8. Removing the photoresist using a degreasing agent and removing the metal film using wet etching to obtain an optical-grade cavity cover plate; In step S6, a high-power infrared structure light is used, and its modulation method and process include but are not limited to: The high-power laser emits an internal flat-top light laser beam, which is reflected by a mirror to change the processing direction, and then passes through a compound eye lens to be modulated into spatial structure light; In step S6, the spatial structure light is formed by the diffraction effect of the flat-top light laser beam passing through the compound eye lens, and the spatial structure light converges to form a focusing plane at the working distance position. When the focusing plane moves downward from the surface of the optical cover plate along the Z-axis direction, the modified region gradually deepens to the desired depth; A 3000-5000W high-power infrared laser is modulated into spatial structure light (45), which irradiates the surface of the mask plate while moving up and down in the Z-axis direction at a speed of 3-50um / s to a depth slightly deeper than the desired cavity depth. The high-power laser has a power range of 3000-5000W and a wavelength of 1064±10nm. The working distance WD of the compound eye lens is 20-30mm, the focal depth is 3-50um, the thickness is ≧100um, and the upper and lower surfaces are coated with infrared antireflection film.

2. The method of claim 1, wherein the MEMS optical grade cavity lid is processed by, In step S1, the processing process of the optical cover plate with a desired size includes the following cases: After cutting a whole transparent optical plate into a single optical cover plate to be processed, steps S2 to S8 are performed; or first make a cavity array on the whole transparent optical plate, and then cut it into a single formed optical cover plate after completing steps S2 to S8.

3. The method of claim 1, wherein the MEMS optical grade cavity lid is processed by, The exposure process in step S4 includes the following cases: LDI laser direct writing process for single small batch processing, or mask exposure process for whole large batch processing.

4. The method of claim 1 or 3, wherein the MEMS optical grade cavity lid is processed by a method comprising: In step S4, the specific process of development is to develop with a photoresist developer, fix with a fixing solution, and then rinse the optical cover plate with deionized water.

5. The method of claim 1, wherein the MEMS optical grade cavity lid is processed by, The etching process in step S5 includes but is not limited to wet etching and dry etching.

6. The method of claim 1, wherein the MEMS optical grade cavity lid is processed by, In step S7, the etching solution for etching the modified part includes but is not limited to strong alkali solution.

7. The method of claim 1, wherein the MEMS optical grade cavity lid is processed by a method comprising: The material of the optical cover plate includes but is not limited to transparent and brittle materials such as glass, quartz and sapphire.

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