CN113979623A - Wafer-level glass microstructure manufacturing method based on silicon mold - Google Patents
Wafer-level glass microstructure manufacturing method based on silicon mold Download PDFInfo
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- CN113979623A CN113979623A CN202111245615.7A CN202111245615A CN113979623A CN 113979623 A CN113979623 A CN 113979623A CN 202111245615 A CN202111245615 A CN 202111245615A CN 113979623 A CN113979623 A CN 113979623A
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B23/00—Re-forming shaped glass
- C03B23/02—Re-forming glass sheets
- C03B23/023—Re-forming glass sheets by bending
- C03B23/03—Re-forming glass sheets by bending by press-bending between shaping moulds
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
- B81C1/00—Manufacture or treatment of devices or systems in or on a substrate
- B81C1/00015—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems
- B81C1/00261—Processes for packaging MEMS devices
- B81C1/00277—Processes for packaging MEMS devices for maintaining a controlled atmosphere inside of the cavity containing the MEMS
- B81C1/00285—Processes for packaging MEMS devices for maintaining a controlled atmosphere inside of the cavity containing the MEMS using materials for controlling the level of pressure, contaminants or moisture inside of the package, e.g. getters
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B23/00—Re-forming shaped glass
- C03B23/02—Re-forming glass sheets
- C03B23/023—Re-forming glass sheets by bending
- C03B23/035—Re-forming glass sheets by bending using a gas cushion or by changing gas pressure, e.g. by applying vacuum or blowing for supporting the glass while bending
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Abstract
The invention discloses a wafer-level glass microstructure manufacturing method based on a silicon die, which comprises the steps of processing a microstructure die cavity on a first substrate wafer; processing a cavity on the second substrate wafer, and adding a certain mass of outgasing agent into the cavity; bonding the first substrate wafer, the glass wafer and the second substrate wafer; heating the three-layer bonded wafer, decomposing a gas releasing agent at high temperature to generate gas, and driving the softened glass to flow into a cavity of the microstructure die by air pressure; preserving heat, cooling and annealing; and obtaining the glass wafer with the glass microstructure by etching, thinning, grinding and polishing. The method can greatly shorten the processing time and improve the manufacturing efficiency, and is a wafer level manufacturing technology of the small-size large-depth-to-width-ratio glass microstructure.
Description
Technical Field
The invention belongs to the field of micro-electromechanical systems, and particularly relates to a method for manufacturing a wafer-level glass microstructure based on a silicon die.
Background
In the field of micro-electro-mechanical systems (MEMS) processing technology, isotropic dry etching, isotropic wet etching, anisotropic dry etching (such as deep reactive ion etching) and anisotropic wet etching techniques developed in silicon enable rapid development and application of sensors and actuators. Glass is an isotropic material, the development of the glass processing technology is far behind that of the silicon processing technology, the existing mature glass processing technology is isotropic wet etching (such as hydrofluoric acid corrosion), and the anisotropic etching of the glass is relatively slow in development. In recent years, the anisotropic dry etching technique for glass has been developed to a certain extent, and there are great limitations in processing a large aspect ratio (ratio of height to radius or side length), sidewall quality, and the like.
In 2009, the chinese invention patent "method for molding a wafer level glass device with a micro mold" (patent No. 200910028463.8) discloses a method for molding a wafer level glass device with a micro mold, which comprises the following core steps: as shown in fig. 1(a), a microelectronic processing process etches a polished silicon wafer 110 to form a mold deep cavity 120 with a specific structure; as shown in fig. 1(b), the silicon wafer 110 and the Pyrex7740 glass wafer 160 are bonded in a vacuum environment; as shown in fig. 1(c), the two bonded wafers are subjected to thermal forming at 550-900 ℃ under one atmosphere, the pressure difference between the inside and the outside of the cavity enables the softened glass to form a microstructure corresponding to the deep cavity of the mold with the specific structure, and the wafers are cooled and annealed to eliminate stress; as shown in fig. 1(d), performing chemical mechanical polishing on the glass back surface of the bonding sheet after the thermal annealing, and grinding the back surface of the glass wafer of the bonding sheet; as shown in fig. 1(e), the silicon mold layer is removed by single-sided etching to obtain the wafer-level Pyrex7740 glass micromold 170. The method is characterized in that the softened glass is made to duplicate the appearance of a silicon mold by utilizing the pressure difference of one atmosphere, and the method can realize the anisotropic corrosion effect of the glass and realize the preparation of vertical structures such as glass columns and the like. According to the existing literature, when a Pyrex7740 glass structure with the size of 1mm in aperture is processed, the time required for realizing near 100% filling degree at the temperature of more than 800 ℃ is dozens of minutes, and the aspect ratio of the processed structure is far less than 1. When a 100um Borofloat 33 glass microstructure is processed (the softening point of Pyrex7740 glass and the softening point of Borofloat 33 glass are both about 820 ℃), the time required for realizing 100% filling degree at the high temperature of more than 800 ℃ is as high as 6 h. It will be appreciated that processing microstructures of less than 100um size can take longer, and that as small as 25um sizes, a differential pressure of one atmosphere is insufficient to achieve processing. The problems of the prior art are as follows: (1) the effect of the method for molding a wafer-level glass device by using a micromold in the Chinese invention patent is that the method can prepare a glass microstructure with a large aspect ratio (which can reach more than 50: 1), but is limited by a pressure difference of one atmosphere, and actually, the method is difficult to realize a glass microstructure with a height-width ratio of 5: 1 or more high aspect ratio structures; (2) the processing time of the microstructures with the size of 100um and below is too long, and the microstructures with the size of 25um can not be processed basically; (3) the general method for processing the small-size microstructure comprises the steps of increasing the temperature, reducing the viscosity and prolonging the processing time, wherein the increase of the temperature is easy to generate bubbles in the glass, and the increase of the processing time is easy to generate cracks, defects and the like on the surface of the glass and even on the whole glass, so that the glass is devitrified and the glass property is changed; after the glass property changes, the reliability, impact resistance and the like of the whole wafer are reduced due to the influence of factors such as the thermal expansion coefficient and the like on the combination part of the glass and the silicon.
Disclosure of Invention
The invention aims to provide a wafer-level glass microstructure manufacturing method based on a silicon die, which aims to solve the problem of processing a small-size glass microstructure with a large height-width ratio, shorten the manufacturing time, improve the processing efficiency and avoid the change of glass properties.
In order to solve the technical problems, the specific technical scheme of the invention is as follows:
a wafer-level glass microstructure manufacturing method based on a silicon mold comprises the following steps:
step one, processing a microstructure mold cavity on a first substrate wafer;
step two, the diameter of the second substrate wafer is the same as that of the first substrate wafer, a cavity is processed on the second substrate wafer, and a gas release agent is added into the cavity in the second substrate wafer;
bonding the first substrate wafer, the glass wafer and the second substrate wafer with the air release agent in the cavity to realize the sealing of the cavity of the microstructure mold and the cavity;
heating the three-layer bonded wafer to any temperature point within the range from 200 ℃ lower than the softening point of the glass wafer to 200 ℃ higher than the softening point of the glass wafer; at the moment, the outgas agent is decomposed at high temperature to generate gas, and the softened glass is driven by pressure to flow into a microstructure mold cavity in the first substrate wafer; after preserving the heat for a period of time, cooling, annealing and eliminating stress;
and fifthly, removing the first substrate wafer and the second substrate wafer through corrosion, thinning, grinding and polishing to obtain the glass wafer with the glass microstructure.
Further, the first substrate wafer and the second substrate wafer are silicon wafers; the processing of the first substrate wafer and the second substrate wafer is wet etching, dry etching, a method combining dry etching and wet etching, or laser processing, a method combining laser processing and wet etching, or micro-spark processing, a method combining micro-spark processing and wet etching, or a method combining micro-ultrasonic processing, micro-ultrasonic processing and wet etching.
Further, the compound which is decomposed at high temperature to generate gas is one or more of titanium hydride, zirconium hydride and calcium carbonate.
Furthermore, the material of the glass wafer is silicate glass.
Further, in the third step, the vacuum environment is an environment less than 1000 Pa.
Further, the bonding is anodic bonding or low temperature direct bonding or fusion bonding.
Further, the cooling is to rapidly cool to room temperature and then raise the temperature to the annealing temperature for annealing or to rapidly cool to the annealing temperature for direct annealing.
Furthermore, in the third step, the first substrate wafer, the glass wafer and the second substrate wafer with the outgassing agent in the chamber are bonded by the method that the second substrate wafer with the outgassing agent in the chamber and the glass wafer are bonded to obtain two layers of bonded wafers, and then the two layers of bonded wafers are bonded with the first substrate wafer in a vacuum environment.
Furthermore, in the third step, the first substrate wafer, the glass wafer and the second substrate wafer with the outgassing agent in the chamber are bonded by bonding the first substrate wafer and the glass wafer in a vacuum environment to obtain two layers of bonded wafers, and then bonding the two layers of bonded wafers and the second substrate wafer with the outgassing agent in the chamber.
Furthermore, in the third step, the first substrate wafer, the glass wafer and the second substrate wafer with the outgassing agent in the chamber are bonded under a vacuum environment.
The wafer-level glass microstructure manufacturing method based on the silicon die has the following advantages:
(1) the invention patent of China (the name is the manufacturing method of the wafer-level glass micro-cavity for MEMS packaging, the application number is 200910263297.X) proposes that the wafer-level spherical glass micro-cavity array is prepared by decomposing gas by using a high-temperature degasifier to drive and soften glass. The main purpose of the patent of the invention is to make the molten glass corresponding to the sealed cavity be spherical by using the positive pressure generated by decomposing gas by using the gas releasing agent, so the pressure is usually selected to be 5-10 atmospheres, and generally not more than 15 atmospheres; the spherical glass micro-cavity with overlarge pressure can be overlarge and even broken, and the size of the glass micro-cavity is generally designed according to the initial size of an etched sealed cavity; meanwhile, the heat preservation time is generally 3-5 min. In the above invention patent, the purpose of the outgas is primarily to replace the sealing air to generate the driving force. The method provided by the invention adopts the air release agent, the air release agent is decomposed at high temperature to generate gas, the air pressure is adjusted through the mass of the air release agent, so the formed pressure can be more than one atmosphere, and can reach several, tens of or even hundreds of atmospheres or more, and the air pressure is increased as far as possible under the condition that the cavity can bear the atmospheric pressure without generating rupture; in general, a large pressure of 20 atmospheres or more is selected to sufficiently increase the driving force, thereby reducing the processing time. The invention aims to utilize the air release agent to realize that the super-high pressure generates enough driving force to reduce the processing time, avoid various consequences and overcome the defects of the prior art. The introduction of the air release agent into the technical process provided by the invention brings about the following remarkable effects: 1. the large pressure brought by the air release agent can greatly shorten the processing time in a proper processing temperature range, improve the manufacturing efficiency and avoid the defects caused by processing the glass for a long time; meanwhile, the defects caused by selecting higher temperature for processing to shorten the processing time are avoided; 2. the method can realize the processing of the glass microstructure with large depth-to-width ratio (5: 1 and above); 3. the most remarkable characteristic is that the method can process glass microstructures with the magnitude of 10um or below, the processing capacity is remarkably improved, the structures such as glass micro-lens arrays and glass micro-column arrays with the magnitude of 10um or below bring remarkable characteristics and advantages, and the glass microstructures with the sizes have special application scenes. The introduction of an air release agent into the prior art route overcomes many of the disadvantages of the prior art and provides a significant advance.
(2) The method provided by the invention does not need a high-pressure heating furnace, reduces the requirements on equipment and can effectively reduce the cost; the size of the wafer processed by the high-pressure heating furnace is generally not more than 3 inches, and the processing capacity is insufficient; and the high-pressure heating furnace is difficult to rapidly cool, and the glass is easy to have property change due to overlong cooling time. The pressure of the method provided by the invention is adjusted by the mass of the gas release agent, the mass of the gas release agent can be increased to reach high pressure, the thickness of the substrate wafer can be increased, the size of the chamber can be reduced or the curvature mutation of the chamber can be avoided (for example, a hemispherical chamber, a quasi-semi-ellipsoidal chamber or a quasi-ellipsoidal chamber is adopted) in order to avoid the rupture of the chamber under high pressure, the pressure of the chamber reaches more than 10MPa, a high-pressure heating furnace is replaced by a heating furnace, and the method can be compatible with rapid cooling, has stronger operability, and reduces the total cost and the processing time. The existence of the internal large pressure does not need high-pressure external environment, and brings remarkable improvement effect.
(3) According to the three-layer bonded wafer, the middle layer is the glass wafer, the upper layer and the lower layer are the silicon wafers, and the structure can effectively reduce the warping of the wafer after cooling and annealing. After the wafer formed by bonding the glass wafer with the thickness of 4 inches and 500um and the silicon wafer with the thickness of 4 inches and 500um is subjected to high-temperature heat preservation and cooling, the warpage is as high as more than 100 um. In the scheme of the invention, the upper and lower layers of silicon wafers and the glass wafer generate stress in the cooling process, and the stress generated by the upper and lower layers of silicon wafers can effectively offset most of the stress, so that the warping of the cooled wafer can be reduced.
(4) The three-layer bonded wafer adopted by the invention has the advantages that the middle layer is the glass wafer, the upper layer and the lower layer are the silicon wafers, and the structure can effectively avoid the wafer fracture caused by uneven stress in the rapid cooling process. After the wafer formed by bonding the glass wafer with the thickness of 4 inches and 500um and the silicon wafer with the thickness of 4 inches and 500um is subjected to high-temperature heat preservation, the wafer is rapidly cooled, and the wafer cannot crack; however, after the wafer formed by bonding the glass wafer with the thickness of 6 inches and 500um and the silicon wafer with the thickness of 4 inches and 500um is subjected to high-temperature heat preservation, in the process of rapid cooling, temperature unevenness is easily generated due to the fact that the thermal conductivities of the glass contacting air and the silicon contacting air are different by two orders of magnitude, and the whole wafer is found to be cracked in a grinding manner in the experimental process, so that the preparation is failed. In the scheme of the invention, the three layers of the introduced bonded wafers have the same heat conductivity as the upper and lower layers of the silicon wafers, the bonded wafers are in contact with air, the glass wafers are clamped in the middle, the heat dissipation rates of the upper and lower layers of the silicon wafers are not greatly different in the rapid cooling process, the whole wafer is not easy to crack, and the scheme is suitable for the process of large-size wafers and has obvious improvement effect.
(5) The method provided by the invention can process glass microstructures with smaller size and larger depth-to-width ratio, and can be further expanded to other application fields such as microsensors, micro actuators and the like.
Drawings
FIG. 1(a) is a schematic cross-sectional view of a prior art silicon wafer with a deep cavity of a mold having a specific structure;
FIG. 1(b) is a schematic cross-sectional view of a bonded silicon wafer and Pyrex7740 glass wafer with a deep cavity of a mold of a specific structure in the prior art;
fig. 1(c) is a schematic cross-sectional view of a prior art thermoformed bonding sheet;
FIG. 1(d) is a schematic cross-sectional view of a prior art bond pad after being thermoformed and after being lapped flat;
FIG. 1(e) is a schematic cross-sectional view of a prior art bonded wafer after planarization and polishing to remove a silicon mold layer;
FIG. 2(a) is a schematic cross-sectional view of a first substrate wafer of the present invention;
FIG. 2(b) is a schematic cross-sectional view of a first substrate wafer processed with a microstructured mold cavity of the present invention;
FIG. 3(a) is a schematic cross-sectional view of a second substrate wafer of the present invention;
FIG. 3(b) is a schematic cross-sectional view of a second substrate wafer having a chamber formed therein according to the present invention;
FIG. 3(c) is a schematic cross-sectional view of a second substrate wafer chamber having an outgassing agent therein in accordance with the present invention;
FIG. 4 is a schematic cross-sectional view of a first substrate wafer, a glass wafer, and a second substrate wafer bonded to form a three-layer bonded wafer according to the present invention;
FIG. 5 is a schematic cross-sectional view of a three-layer bonded wafer after high temperature processing in accordance with the present invention;
FIG. 6 is a schematic cross-sectional view of a glass wafer with glass microstructures of the present invention with the first substrate wafer and the second substrate wafer removed;
FIG. 7 is a schematic cross-sectional view of a glass wafer with a polished glass microstructure according to the present invention;
FIG. 8(a) is a schematic cross-sectional view of a second substrate wafer with a chamber having a rectangular cross-section in accordance with the present invention;
FIG. 8(b) is a schematic cross-sectional view of a second substrate wafer with a chamber having a trapezoidal cross-section in accordance with the present invention;
FIG. 8(c) is a schematic cross-sectional view of a second substrate wafer with a chamber having an arc or arc-like cross-section in accordance with the present invention;
FIG. 9 is a top view of a chamber processed on a second substrate wafer of the present invention;
the notation in the figure is: 10. a first substrate wafer; 20. a microstructured mold cavity; 30. a second substrate wafer; 40. a chamber; 50. a gas releasing agent; 60. a glass wafer; 70. a glass microstructure; 110. a silicon wafer; 120. a special structure mold deep cavity; 160. pyrex7740 glass wafer; 170. pyrex7740 glass microstructure.
Detailed Description
For better understanding of the purpose, structure and function of the present invention, the following describes a method for manufacturing a wafer level glass microstructure based on a silicon mold in further detail with reference to the accompanying drawings.
The invention comprises the following steps:
step one, processing a microstructure mold cavity 20 on a first substrate wafer 10;
step two, the diameter of the second substrate wafer 30 is the same as that of the first substrate wafer 10, a cavity 40 is processed on the second substrate wafer 30, and an air release agent 50 is added into the cavity 40 in the second substrate wafer 30;
bonding the first substrate wafer 10, the glass wafer 60 and the second substrate wafer 30 with the outgassing agent 50 in the cavity 40 to realize the sealing of the microstructure mold cavity 20 and the cavity 40;
the method for bonding the first substrate wafer, the glass wafer and the second substrate wafer with the outgassing agent in the cavity comprises the steps of firstly bonding the second substrate wafer with the outgassing agent in the cavity and the glass wafer to obtain two layers of bonded wafers, then bonding the two layers of bonded wafers and the first substrate wafer in a vacuum environment or bonding the first substrate wafer and the glass wafer in the vacuum environment to obtain two layers of bonded wafers, and then bonding the two layers of bonded wafers and the second substrate wafer with the outgassing agent in the cavity or bonding the first substrate wafer, the glass wafer and the second substrate wafer with the outgassing agent in the cavity in the vacuum environment.
Step four, heating the three-layer bonded wafer to any temperature point within the range from 200 ℃ lower than the softening point of the glass wafer 60 to 200 ℃ higher than the softening point of the glass wafer 60; at this point, the outgas 50 decomposes at high temperature to generate gas, and the softened glass is driven by pressure to flow into the microstructure mold cavity 20 in the first substrate wafer 10; after preserving the heat for a period of time, cooling, annealing and eliminating stress;
and step five, removing the first substrate wafer 10 and the second substrate wafer 30 through corrosion, thinning, grinding and polishing to obtain the glass wafer 60 with the glass microstructure.
The first embodiment:
as shown in fig. 2 to 9, a method for manufacturing a wafer level glass microstructure based on a silicon mold specifically includes:
step one, as shown in fig. 2(a) and 2(b), a microstructure mold cavity 20 is machined on a first substrate wafer 10. Microstructure mold cavities 20 include trapezoidal, pyramidal, hemispherical, and cylindrical cavities. The trapezoid cavity or the pyramid cavity can be etched and processed by a 40% potassium hydroxide strong base solution (KOH) or a 25% tetramethylammonium hydroxide solution (TMAH) wet method, the hemispherical cavity can be etched and processed by an HNA solution (mixed liquid of hydrofluoric acid, nitric acid and deionized water in a certain proportion or mixed liquid of hydrofluoric acid, nitric acid and acetic acid in a certain proportion) wet method, and the cylindrical cavity can be etched and processed by a Deep Reactive Ion Etching (DRIE) or anisotropic wet method. The processing of the microstructure mold cavity 20 can also be realized by one of a method combining laser processing and wet etching, a method combining dry etching and wet etching, a method combining micro-electric spark processing and wet etching, and a method combining micro-ultrasonic processing and wet etching. The first substrate wafer 10 is a silicon wafer. The silicon wafer thickness may be 300um, 500um, 800um, 1mm, 2mm or more, the silicon wafer diameter may be 2 inches, 4 inches, 6 inches, 8 inches, 12 inches, with a 6 inch 1mm thick silicon wafer being selected as an example. The open aperture or edge length of the microstructure mold cavities 20 may be 5um, 10um, 50um, 100um, 500um, 1mm, 2mm or more, illustratively an array of microstructure mold cavities 20 with 100um, 500um, 1mm open aperture are machined on a 6 inch, 1mm thick silicon wafer; the depth of the microstructure mold cavities 20 can be 10um, 50um, 100um, 200um, 300um, 400um, 500um or more, as an example to machine microstructure mold cavities 20 having a depth of about 500 um. The depth of the microstructure mold cavity 20 needs to be less than the thickness of the silicon wafer, for example, the thickness of the silicon wafer is 500um, and the depth of the cylindrical ring cavity is 300 um.
Step two, as shown in fig. 3(a), fig. 3(b) and fig. 3(c), a cavity 40 is processed on the second substrate wafer 30; a mass of outgassing agent 50 is added to the chamber 40 in the second substrate wafer 30. The diameter of the second substrate wafer 30 is the same as the diameter of the first substrate wafer 10. Preferably, the thickness of the second substrate wafer 30 is equal to the thickness of the first substrate wafer 10, so as to perform a partial stress cancellation function. As an example, the second substrate wafer 30 has a thickness of 1 mm. What is needed isThe chamber 40 may be a trapezoidal chamber, a cylindrical chamber, a rectangular parallelepiped chamber, or the like. The cylinder chamber and the cuboid chamber can be realized by a method combining Deep Reactive Ion Etching (DRIE), anisotropic wet etching processing, laser processing and wet etching, a method combining dry etching and wet etching, a method combining micro-spark processing and wet etching, a method combining micro-ultrasonic processing and wet etching and the like, as shown in FIG. 8 (a); the trapezoid chamber can be processed by wet etching with 40% potassium hydroxide (KOH) or 25% tetramethylammonium hydroxide (TMAH), as shown in fig. 8 (b); the semi-ellipsoid or ellipsoid-like cavity can be etched by HNA solution (mixed liquid of hydrofluoric acid, nitric acid and deionized water at a certain ratio, or mixed liquid of hydrofluoric acid, nitric acid and acetic acid at a certain ratio) by wet method, or by XeF2And (c) dry etching processing, as shown in fig. 8 (c). Various top views of chamber 40 are shown in fig. 9. The opening aperture of the cavity 40 is larger than the opening aperture of the microstructure mold cavity 20, the depth of the cavity 40 can be 50um, 100um, 500um or more, and the volume of the cavity 40 is larger than the volume of the required gas release agent 50 with certain mass. The outgas 50 is a compound that decomposes at high temperature to generate gas, and may be one or more of titanium hydride, zirconium hydride, and calcium carbonate, and titanium hydride is used as an example. The mass of titanium hydride chosen can provide a pressure of 20 atmospheres after pyrolysis.
And step three, bonding the first substrate wafer 10 and the glass wafer 60 in a vacuum environment to obtain two layers of bonded wafers, so as to seal the microstructure mold cavity 20. The diameter of the glass wafer 60 is the same as the diameter of the silicon wafer, and the thickness of the glass wafer 60 is greater than the depth of the microstructure mold cavity 20. The glass wafer 60 is a silicate glass wafer, and a borosilicate glass with a Pyrex7740 model is used as an example. The vacuum environment is less than 1000Pa, including 100Pa, 10Pa, 1Pa, 0.001Pa, 10Pa-7Pa. The bonding is one of anodic bonding, low-temperature direct bonding and fusion bonding, and the anodic bonding is selected here as an example, and the vacuum environment is about 10 Pa.
Step four, as shown in fig. 4, bonding the two layers of bonded wafers and the second substrate wafer 30 with the outgassing agent 50 in the chamber 40 to obtain a three-layer bonded wafer, thereby sealing the chamber 40. The bonding is one of anodic bonding, low-temperature direct bonding and fusion bonding, and here, anodic bonding is selected as an example, and vacuum environment of about 10Pa is selected for bonding. The bonding condition can be bonding under the environment of one atmosphere, or bonding under the vacuum condition, or bonding under the environment of more than one atmosphere (the maximum bonding environment of the existing conventional commercial bonding machine is 2 atmospheres); preferably, bonding under vacuum is generally used.
Step five, as shown in fig. 5, heating the three-layer bonded wafer to any temperature point within the range from 200 ℃ lower than the softening point of the glass wafer 60 to 200 ℃ higher than the softening point of the glass wafer 60; at the moment, the outgas agent is decomposed at high temperature to generate gas, and the softened glass is driven by pressure difference to flow into the microstructure mould in the first substrate wafer; and (5) after preserving the heat for a period of time, cooling, and annealing to eliminate the stress. The cooling may be rapid cooling to room temperature and then raising the temperature to the annealing temperature for annealing, or rapid cooling to the annealing temperature for direct annealing. In the example, the borosilicate glass with Pyrex7740 is selected, the softening point is 821 ℃, the heat preservation temperature can be 750 ℃, 780 ℃, 800 ℃, 820 ℃, 850 ℃ and 880 ℃, and the proper heat preservation time is selected according to the size of the micro-structure mold cavity 20 and the quality of the added outgas 20, so that a certain filling degree is ensured, and in some cases, 95% of the filling degree is required.
Sixthly, as shown in fig. 6, removing the first substrate wafer 10 and the second substrate wafer 30 by wet etching; as shown in fig. 7, a glass wafer 60 with glass microstructures 70 is then obtained by thinning, grinding and polishing.
Second embodiment:
as shown in fig. 2 to 9, a wafer level glass microstructure manufacturing technique based on a silicon mold specifically includes:
step one, as shown in fig. 2(a) and 2(b), a microstructure mold cavity 20 is machined on a first substrate wafer 10. Microstructure mold cavities 20 include trapezoidal, pyramidal, hemispherical, and cylindrical cavities. The trapezoid cavity or the pyramid cavity can be etched and processed by a 40% potassium hydroxide strong base solution (KOH) or a 25% tetramethylammonium hydroxide solution (TMAH) wet method, the hemispherical cavity can be etched and processed by an HNA solution (mixed liquid of hydrofluoric acid, nitric acid and deionized water in a certain proportion or mixed liquid of hydrofluoric acid, nitric acid and acetic acid in a certain proportion) wet method, and the cylindrical cavity can be etched and processed by a Deep Reactive Ion Etching (DRIE) or anisotropic wet method. The processing of the microstructure mold cavity 20 can also be realized by one of a method combining laser processing and wet etching, a method combining dry etching and wet etching, a method combining micro-electric spark processing and wet etching, and a method combining micro-ultrasonic processing and wet etching. The first substrate wafer 10 is a silicon wafer. An exemplary 8 inch 2mm thick silicon wafer is processed with 10um, 50um, 100um arrays of microstructure mold cavities 20. The depth of the microstructure mold cavity 20 is about 250 um.
Step two, as shown in fig. 3(a), fig. 3(b) and fig. 3(c), a cavity 40 is processed on the second substrate wafer 30; a mass of outgassing agent 50 is added to the chamber 40 in the second substrate wafer 30. The diameter of the second substrate wafer 30 is the same as the diameter of the first substrate wafer 10. Preferably, the thickness of the second substrate wafer 30 is equal to the thickness of the first substrate wafer 10, so as to perform a partial stress cancellation function. As an example, the second substrate wafer 30 has a thickness of 2 mm. The chamber 40 may be a trapezoidal chamber, a cylindrical chamber, a rectangular parallelepiped chamber, or the like. The cylinder chamber and the cuboid chamber can be realized by a method combining Deep Reactive Ion Etching (DRIE), anisotropic wet etching processing, laser processing and wet etching, a method combining dry etching and wet etching, a method combining micro-spark processing and wet etching, a method combining micro-ultrasonic processing and wet etching and the like, as shown in FIG. 8 (a); the trapezoidal body chamber can be filled with 40% potassium hydroxide (KOH) strong base solution or 25% tetramethylammonium hydroxide (T)MAH) wet etching process, as shown in fig. 8 (b); the semi-ellipsoid or ellipsoid-like cavity can be etched by HNA solution (mixed liquid of hydrofluoric acid, nitric acid and deionized water at a certain ratio, or mixed liquid of hydrofluoric acid, nitric acid and acetic acid at a certain ratio) by wet method, or by XeF2And (c) dry etching processing, as shown in fig. 8 (c). Various top views of chamber 40 are shown in fig. 9. The aperture of the opening of the chamber 40 is 300um, and the depth of the chamber 40 is 200 um. The outgas 50 is a compound that decomposes at high temperature to generate gas, and may be one or more of titanium hydride, zirconium hydride, and calcium carbonate, which is exemplified by calcium carbonate. The selected calcium carbonate can provide 50 atmospheres of pressure after pyrolysis.
And step three, bonding the first substrate wafer 10 and the glass wafer 60 in a vacuum environment to obtain two layers of bonded wafers, so as to seal the microstructure mold cavity 20. The diameter of the glass wafer 60 is the same as the diameter of the silicon wafer, and the thickness of the glass wafer 60 is greater than the depth of the microstructure mold cavity 20, for example, 500um is selected. The glass wafer 60 is a silicate glass wafer, here for example borosilicate glass of the type Borofloat 33. The vacuum environment is less than 1000Pa, including 100Pa, 10Pa, 1Pa, 0.001Pa, 10Pa-7Pa. The bonding is one of anodic bonding, low-temperature direct bonding and fusion bonding, and low-temperature direct bonding is selected here as an example, and the vacuum environment is about 0.1 Pa.
Step four, as shown in fig. 4, bonding the two layers of bonded wafers and the second substrate wafer 30 with the outgassing agent 50 in the chamber 40 to obtain a three-layer bonded wafer, thereby sealing the chamber 40. The bonding is one of anodic bonding, low-temperature direct bonding and fusion bonding, and low-temperature direct bonding is selected here as an example, and vacuum environment of about 10Pa is selected for bonding.
Step five, as shown in fig. 5, heating the three-layer bonded wafer to any temperature point within the range from 200 ℃ lower than the softening point of the glass wafer 60 to 200 ℃ higher than the softening point of the glass wafer 60; at this time, the outgas 50 decomposes at high temperature to generate gas, and the softened glass is driven by the pressure difference to flow into the microstructure mold in the first substrate wafer 10; and (5) after preserving the heat for a period of time, cooling, and annealing to eliminate the stress. The cooling may be rapid cooling to room temperature and then raising the temperature to the annealing temperature for annealing, or rapid cooling to the annealing temperature for direct annealing. By way of example, Borofloat 33 glass having a softening point of 820 ℃ is selected, and the incubation temperature may be selected to be 820 ℃, 850 ℃, 880 ℃ for an appropriate incubation time to ensure a certain degree of filling, depending on the size of the microstructured mold cavity 20 and the quality of the added outgas 20.
Sixthly, as shown in fig. 7, removing a part of the second substrate wafer 30 and the glass wafer 60 by thinning, grinding and polishing, and then removing the first substrate wafer 10 by wet etching to obtain the glass wafer 60 with the glass microstructure 70.
The invention has the following advantages:
(1) the prior Chinese patent invention (the name is the manufacturing method of the wafer-level glass micro-cavity for MEMS packaging, and the application number is 200910263297.X) proposes that the wafer-level spherical glass micro-cavity array is prepared by decomposing gas by using a high-temperature gas release agent and driving and softening the glass. The main purpose of the patent of the invention is to make the molten glass corresponding to the sealed cavity be spherical by using the positive pressure generated by decomposing gas by using the gas releasing agent, so the pressure is usually selected to be 5-10 atmospheres, and generally not more than 15 atmospheres; the spherical glass micro-cavity with overlarge pressure can be overlarge and even broken, and the size of the glass micro-cavity is generally designed according to the initial size of an etched sealed cavity; meanwhile, the heat preservation time is generally 3-5 min. In the above invention patent, the purpose of the outgas is primarily to replace the sealing air to generate the driving force. The method provided by the invention adopts the air release agent, the air release agent is decomposed at high temperature to generate gas, the air pressure is adjusted through the mass of the air release agent, so the formed pressure can be more than one atmosphere, and can reach several, tens of or even hundreds of atmospheres or more, and the air pressure is increased as far as possible under the condition that the cavity can bear the atmospheric pressure without generating rupture; in general, a large pressure of 20 atmospheres or more is selected to sufficiently increase the driving force, thereby reducing the processing time. The invention aims to utilize the air release agent to realize that the super-high pressure generates enough driving force to reduce the processing time, avoid various consequences and overcome the defects of the prior art. The introduction of the air release agent into the technical process provided by the invention brings about the following remarkable effects: 1. the large pressure brought by the air release agent can greatly shorten the processing time in a proper processing temperature range, improve the manufacturing efficiency and avoid the defects caused by processing the glass for a long time; meanwhile, the defects caused by selecting higher temperature for processing to shorten the processing time are avoided; 2. the method can realize the processing of the glass microstructure with large depth-to-width ratio (5: 1 and above); 3. the most remarkable characteristic is that the method can process glass microstructures with the magnitude of 10um or below, the processing capacity is remarkably improved, the structures such as glass micro-lens arrays and glass micro-column arrays with the magnitude of 10um or below bring remarkable characteristics and advantages, and the glass microstructures with the sizes have special application scenes. The introduction of an air release agent into the prior art route overcomes many of the disadvantages of the prior art and provides a significant advance.
(2) The method provided by the invention does not need a high-pressure heating furnace, reduces the requirements on equipment and can effectively reduce the cost; the size of the wafer processed by the high-pressure heating furnace is generally not more than 3 inches, and the processing capacity is insufficient; and the high-pressure heating furnace is difficult to rapidly cool, and the glass is easy to have property change due to overlong cooling time. The pressure of the method provided by the invention is adjusted by the mass of the gas release agent, the mass of the gas release agent can be increased to reach high pressure, the thickness of the substrate wafer can be increased, the size of the chamber can be reduced or the curvature mutation of the chamber can be avoided (for example, a hemispherical chamber, a quasi-semi-ellipsoidal chamber or a quasi-ellipsoidal chamber is adopted) in order to avoid the rupture of the chamber under high pressure, the pressure of the chamber reaches more than 10MPa, a high-pressure heating furnace is replaced by a heating furnace, and the method can be compatible with rapid cooling, has stronger operability, and reduces the total cost and the processing time. The existence of the internal large pressure does not need high-pressure external environment, and brings remarkable improvement effect.
(3) According to the three-layer bonded wafer, the middle layer is the glass wafer, and the upper layer and the lower layer are the silicon wafers, so that the wafer warpage after cooling and annealing can be effectively reduced. After the wafer formed by bonding the glass wafer with the thickness of 4 inches and 500um and the silicon wafer with the thickness of 4 inches and 500um is subjected to high-temperature heat preservation and cooling, the warpage is as high as more than 100 um. In the scheme of the invention, the upper and lower layers of silicon wafers and the glass wafer generate stress in the cooling process, and the stress generated by the upper and lower layers of silicon wafers can effectively offset most of the stress, so that the warping of the cooled wafer can be reduced.
(4) The three-layer bonded wafer adopted by the invention has the advantages that the middle layer is the glass wafer, the upper layer and the lower layer are the silicon wafers, and the structure can effectively avoid the wafer fracture caused by uneven stress in the rapid cooling process. After the wafer formed by bonding the glass wafer with the thickness of 4 inches and 500um and the silicon wafer with the thickness of 4 inches and 500um is subjected to high-temperature heat preservation, the wafer is rapidly cooled, and the wafer cannot crack; however, after the wafer formed by bonding the glass wafer with the thickness of 6 inches and 500um and the silicon wafer with the thickness of 4 inches and 500um is subjected to high-temperature heat preservation, in the process of rapid cooling, temperature unevenness is easily generated due to the fact that the thermal conductivities of the glass contacting air and the silicon contacting air are different by two orders of magnitude, and the whole wafer is found to be cracked in a grinding manner in the experimental process, so that the preparation is failed. In the scheme of the invention, the three layers of the introduced bonded wafers have the same heat conductivity as the upper and lower layers of the silicon wafers, the bonded wafers are in contact with air, the glass wafers are clamped in the middle, the heat dissipation rates of the upper and lower layers of the silicon wafers are not greatly different in the rapid cooling process, the whole wafer is not easy to crack, and the scheme is suitable for the process of large-size wafers and has obvious improvement effect.
(5) The method provided by the invention can process glass microstructures with smaller size and larger depth-to-width ratio, and can be further expanded to other application fields such as microsensors, micro actuators and the like.
It is to be understood that the present invention has been described with reference to certain embodiments, and that various changes in the features and embodiments, or equivalent substitutions may be made therein by those skilled in the art without departing from the spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
Claims (10)
1. A wafer-level glass microstructure manufacturing method based on a silicon mold is characterized by comprising the following steps:
step one, processing a microstructure mold cavity on a first substrate wafer;
step two, the diameter of the second substrate wafer is the same as that of the first substrate wafer, a cavity is processed on the second substrate wafer, and a gas release agent is added into the cavity in the second substrate wafer;
bonding the first substrate wafer, the glass wafer and the second substrate wafer with the air release agent in the cavity to realize the sealing of the cavity of the microstructure mold and the cavity;
heating the three-layer bonded wafer to any temperature point within the range from 200 ℃ lower than the softening point of the glass wafer to 200 ℃ higher than the softening point of the glass wafer; at the moment, the outgas agent is decomposed at high temperature to generate gas, and the softened glass is driven by pressure to flow into a microstructure mold cavity in the first substrate wafer; after preserving the heat for a period of time, cooling, annealing and eliminating stress;
and fifthly, removing the first substrate wafer and the second substrate wafer through corrosion, thinning, grinding and polishing to obtain the glass wafer with the glass microstructure.
2. The silicon mold based wafer level glass microstructure fabrication method of claim 1, wherein the first and second substrate wafers are silicon wafers; the processing of the first substrate wafer and the second substrate wafer is wet etching or dry etching or a method combining dry etching and wet etching, or a method combining laser processing or laser processing and wet etching, or a method combining micro-electric spark processing or micro-electric spark processing and wet etching, or a method combining micro-ultrasonic processing or micro-ultrasonic processing and wet etching.
3. The method of claim 1, wherein the outgas agent is a compound that decomposes at high temperature to generate gas and is one or more of titanium hydride, zirconium hydride, and calcium carbonate.
4. The method of claim 1, wherein the glass wafer is made of silicate glass.
5. The silicon mold based wafer level glass microstructure fabrication method of claim 1, wherein the bonding is anodic bonding or low temperature direct bonding or fusion bonding.
6. The method of claim 1, wherein in step four, the cooling is performed by rapidly cooling to room temperature and then raising the temperature to the annealing temperature for annealing or by rapidly cooling to the annealing temperature for direct annealing.
7. The method for manufacturing a wafer level glass microstructure based on a silicon die as claimed in claim 1, wherein the bonding of the first substrate wafer, the glass wafer, and the second substrate wafer with the outgassing agent in the chamber in the third step is achieved by first achieving bonding of the second substrate wafer with the outgassing agent in the chamber and the glass wafer to obtain a two-layer bonded wafer, and then achieving bonding of the two-layer bonded wafer and the first substrate wafer in a vacuum environment.
8. The method for manufacturing a wafer level glass microstructure based on a silicon mold as claimed in claim 1, wherein the step three is to bond the first substrate wafer, the glass wafer and the second substrate wafer with the outgassing agent in the chamber by bonding the first substrate wafer and the glass wafer under vacuum environment to obtain two layers of bonded wafers, and then bond the two layers of bonded wafers and the second substrate wafer with the outgassing agent in the chamber.
9. The method of claim 1, wherein the step three comprises bonding the first substrate wafer, the glass wafer, and the second substrate wafer with the outgassing agent in the chamber simultaneously in a vacuum environment.
10. The method of claim 1, wherein in step three, the vacuum environment is an environment less than 1000 Pa.
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