阅读说明：本技术 一种压电mems结构亲水性硅硅直接键合工艺 (Piezoelectric MEMS structure hydrophilic silicon-silicon direct bonding process ) 是由 王春慧 平鹏祥 邵金友 田洪淼 杨正杰 王小培 严超 于 2019-09-18 设计创作，主要内容包括：一种压电MEMS结构亲水性硅硅直接键合工艺,先在带有压电结构图案区的第一硅片上旋涂光刻胶作为压电材料的第一保护层,将掩膜版图案转移到第一保护层上,在第一保护层上贴上一层聚酰亚胺作为第二保护层；再将第一硅片经过氧等离子体表面活化、湿法活化处理；然后将另一块不带压电材料且经过MEMS工艺处理后具有体硅结构的第二硅片经过清洗,两块硅片通过Si-O-Si键实现预键合；本发明通过亲水性硅硅低温直接键合方法实现硅基压电MEMS结构与硅基基底的低温、气密性的高质量有效键合,并且通过压电材料的保护方法避免键合过程中化学清洗处理对任意压电材料的损伤,可实现包含压电材料的硅基压电MEMS结构与硅基基底的高可靠性键合。(A direct bonding process of hydrophilic silicon and silicon of a piezoelectric MEMS structure comprises the steps of firstly, spin-coating photoresist on a first silicon wafer with a piezoelectric structure pattern area to serve as a first protective layer of piezoelectric materials, transferring a mask pattern onto the first protective layer, and attaching a layer of polyimide on the first protective layer to serve as a second protective layer; then, the first silicon chip is subjected to oxygen plasma surface activation and wet activation treatment; then cleaning the other second silicon wafer which is not provided with the piezoelectric material and has a bulk silicon structure after being processed by the MEMS process, and pre-bonding the two silicon wafers through Si-O-Si bonds; the invention realizes the high-quality and high-airtightness effective bonding of the silicon-based piezoelectric MEMS structure and the silicon-based substrate at low temperature by the hydrophilic silicon low-temperature direct bonding method, avoids the damage of chemical cleaning treatment to any piezoelectric material in the bonding process by the protection method of the piezoelectric material, and can realize the high-reliability bonding of the silicon-based piezoelectric MEMS structure containing the piezoelectric material and the silicon-based substrate.)

1. A piezoelectric MEMS structure hydrophilic silicon direct bonding process is characterized by comprising the following steps:

firstly, spin-coating photoresist on a first silicon wafer (1) with a piezoelectric structure pattern area to serve as a first protective layer (2) of a piezoelectric material, wherein the processing method comprises the following steps: attaching a layer of adhesive tape (5) around a first silicon wafer (1) with a piezoelectric material (4), spin-coating a layer of photoresist with the thickness of 8 microns by using a spin coater, and pre-baking at 95 ℃ for 10 minutes to volatilize a solvent of the photoresist and adhere the photoresist to the first silicon wafer (1);

secondly, removing the adhesive tape (5) around the first silicon chip (1), photoetching by using a mask plate, and transferring the mask plate pattern to the first protective layer (2); the pattern on the mask is consistent with the pattern of the piezoelectric material (4), the area with the pattern on the mask is light-transmitting, and the other areas are light-proof; using a photoetching machine for front alignment, exposing for 30s, using a mixed solution of a developing solution AZ400K and deionized water in a ratio of 1:3 as a developing solution, developing for 3 minutes, and hardening for 30 minutes at 120 ℃;

thirdly, a layer of polyimide (PI adhesive tape) is attached to the first protective layer (2) to serve as a second protective layer (3), and the size of the polyimide is the same as that of the first silicon wafer (1);

fourthly, preparing a mixed solution of concentrated sulfuric acid and hydrogen peroxide according to the volume ratio of 4:1, putting the prepared first silicon wafer (1) into the prepared solution, heating the solution on a constant-temperature hot plate to 110 ℃, and keeping the constant temperature for 30 minutes; taking out the first silicon wafer (1) by using Teflon tweezers, and repeatedly cleaning the first silicon wafer in a container filled with deionized water for 10 minutes;

fifthly, preparing RCA1 mixed solution of ammonium hydroxide, hydrogen peroxide and deionized water according to the ratio of 1:1:2, putting the cleaned first silicon wafer (1) in the step four into the RCA1 mixed solution, heating to 85 ℃ by using a constant temperature hot plate, and keeping the constant temperature for 15 minutes; taking out the first silicon wafer (1) by using Teflon tweezers, putting the first silicon wafer into a container filled with deionized water, repeatedly cleaning the first silicon wafer for 10 minutes, taking out the first silicon wafer and drying the first silicon wafer by using nitrogen;

sixthly, activating the surface of the oxygen plasma: putting the first silicon chip 1 with the cleaned surface into an oxygen plasma cleaning machine for surface activation treatment, wherein the activated surface is a non-piezoelectric structural surface of the first silicon chip 1;

seventhly, wet activation treatment: preparing a mixed solution of ammonium hydroxide, hydrogen peroxide and deionized water according to the ratio of 5:2:4 as a chemical activation reagent, putting a first silicon wafer (1) subjected to oxygen plasma treatment into the chemical activation reagent, heating the first silicon wafer to 80 ℃ by a hot plate, boiling the first silicon wafer for 15 minutes, taking the first silicon wafer out by a Teflon forceps, and putting the first silicon wafer into the deionized water for washing;

eighthly, cleaning the other second silicon wafer (6) which is not provided with the piezoelectric material and has a bulk silicon structure after being processed by the MEMS process by the same method from the fourth step to the seventh step;

the ninth step: placing a first silicon wafer (1) and a second silicon wafer (6) into deionized water, forming silanol bonds (Si-OH) on the surfaces of the two cleaned and surface-treated silicon wafers to enable the surfaces to form hydrophilicity, tightly attaching the two surfaces to be bonded, taking out the silicon wafers, placing the silicon wafers into a mold with the same size as the silicon wafers, aligning the silicon wafers, and forming an MEMS structure with a piezoelectric material; putting filter paper on the upper surface and the lower surface of the silicon wafer which is tightly adhered and aligned, pressing the surfaces by using a cylindrical roller die to uniformly disperse moisture between the first silicon wafer (1) and the second silicon wafer (6), and absorbing the moisture on the upper surface and the lower surface of the first silicon wafer (1) and the second silicon wafer (6) by the filter paper;

tenth, the aligned and tightly attached piezoelectric MEMS structure is placed between two glass plates (6) with flat surfaces, force is applied, and the time is kept for 15 hours; forming a Si-O-Si bond by silanol groups between the two silicon chips through molecular polymerization, and realizing pre-bonding of the two silicon chips through the Si-O-Si bond;

step ten, putting the piezoelectric MEMS structure which is bonded in advance into a muffle furnace to anneal for 10 hours at the temperature of 150 ℃ so as to enhance the molecular bond energy of Si-O-Si and further enhance the bonding strength;

and a twelfth step of removing the photoresist and the polyimide adhesive tape on the surface.

2. The piezoelectric MEMS structure hydrophilic silicon direct bonding process of claim 1, wherein: the photoresist used for the first protective layer (2) in the first step is a positive photoresist or a photosensitive polymer which is easy to remove.

3. The piezoelectric MEMS structure hydrophilic silicon direct bonding process of claim 1, wherein: the thickness of the photoresist used by the first protective layer (2) in the first step is 4 um-20 um.

4. The piezoelectric MEMS structure hydrophilic silicon direct bonding process of claim 1, wherein: and in the second step, the developing solution is NaOH solution with the concentration of 5 per mill.

5. The piezoelectric MEMS structure hydrophilic silicon direct bonding process of claim 1, wherein: the piezoelectric material in the first step is any material with positive piezoelectric effect and negative piezoelectric effect.

6. The piezoelectric MEMS structure hydrophilic silicon direct bonding process of claim 1, wherein: and the MEMS process in the eighth step comprises contact exposure photoetching, developing, ICP dry etching and silicon-based wet etching.

7. The piezoelectric MEMS structure hydrophilic silicon direct bonding process of claim 1, wherein: and in the ninth step, the filter paper is used for absorbing the water on the surface of the silicon wafer, and the silicon wafer can be dried by using a silicon wafer cleaning machine instead.

Technical Field

The invention belongs to the technical field of MEMS (micro electro mechanical system), and particularly relates to a piezoelectric MEMS structure hydrophilic silicon direct bonding process.

Background

The piezoelectric material has a piezoelectric effect or an inverse piezoelectric effect, can realize mutual conversion between electric energy and mechanical energy, can realize the functions of driving, sensing, energy collection and the like by being applied to a piezoelectric MEMS structure developed in the MEMS field through a single chip, and is a hotspot technology with great application potential. The effective bonding of the silicon-based piezoelectric MEMS structure containing the piezoelectric material and the silicon-based substrate is a key and even decisive factor for developing a plurality of piezoelectric MEMS devices such as a piezoelectric microdroplet jet printing head, a piezoelectric micro-fluid pump, a piezoelectric micro-sensor and the like, and the bonding technology with high reliability is very important for the development of the piezoelectric MEMS technology.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a hydrophilic silicon direct bonding process for a piezoelectric MEMS structure, which realizes effective bonding of a silicon-based piezoelectric MEMS structure containing piezoelectric materials and a silicon-based substrate.

In order to achieve the purpose, the invention adopts the technical scheme that:

a piezoelectric MEMS structure hydrophilic silicon direct bonding process comprises the following steps:

firstly, spin-coating photoresist on a first silicon wafer 1 with a piezoelectric structure pattern area to serve as a first protective layer 2 of a piezoelectric material, wherein the processing method comprises the following steps: attaching a layer of adhesive tape 5 around a first silicon wafer 1 with a piezoelectric material 4, spin-coating a layer of photoresist with the thickness of 8 microns by using a spin coater, and baking for 10 minutes at 95 ℃ to volatilize a solvent of the photoresist and adhere the photoresist to the first silicon wafer 1;

secondly, removing the adhesive tape 5 around the first silicon chip 1, carrying out photoetching by using a mask plate, and transferring the mask plate pattern to the first protective layer 2; the pattern on the mask is consistent with the pattern of the piezoelectric material 4, the area with the pattern on the mask is light-transmitting, and the other areas are light-proof; using a photoetching machine for front alignment, exposing for 30s, using a mixed solution of a developing solution AZ400K and deionized water in a ratio of 1:3 as a developing solution, developing for 3 minutes, and hardening for 30 minutes at 120 ℃;

thirdly, a layer of polyimide (PI adhesive tape) is attached to the first protective layer 2 to serve as a second protective layer 3, and the size of the polyimide is the same as that of the first silicon chip 1;

fourthly, preparing a mixed solution of concentrated sulfuric acid and hydrogen peroxide according to the volume ratio of 4:1, putting the prepared first silicon chip 1 into the prepared solution, heating the first silicon chip on a constant-temperature hot plate to 110 ℃, and keeping the constant temperature for 30 minutes; taking out the silicon wafer by using Teflon tweezers, and repeatedly cleaning the silicon wafer in a container filled with deionized water for 10 minutes;

fifthly, preparing an RCA1 mixed solution of ammonium hydroxide, hydrogen peroxide and deionized water according to the ratio of 1:1:2, putting the cleaned first silicon wafer 1 in the RCA1 mixed solution, heating to 85 ℃ by using a constant temperature hot plate, and keeping the constant temperature for 15 minutes; taking out the first silicon wafer 1 by using Teflon tweezers, putting the first silicon wafer into a container filled with deionized water, repeatedly cleaning the first silicon wafer for 10 minutes, taking out the first silicon wafer and drying the first silicon wafer by using nitrogen;

sixthly, activating the surface of the oxygen plasma: putting the first silicon chip 1 with the cleaned surface into an oxygen plasma cleaning machine for surface activation treatment, wherein the activated surface is a non-piezoelectric structural surface of the first silicon chip 1;

seventhly, wet activation treatment: preparing a mixed solution of ammonium hydroxide, hydrogen peroxide and deionized water according to the ratio of 5:2:4 as a chemical activation reagent, putting the first silicon wafer 1 subjected to oxygen plasma treatment into the chemical activation reagent, heating the first silicon wafer to 80 ℃ by a hot plate, boiling the first silicon wafer for 15 minutes, taking the first silicon wafer out by a Teflon forceps, and putting the first silicon wafer into the deionized water for washing;

eighthly, cleaning the other second silicon wafer 6 which is not provided with the piezoelectric material and has a bulk silicon structure after being processed by the MEMS process by the same method from the fourth step to the seventh step;

the ninth step: placing a first silicon wafer 1 and a second silicon wafer 6 into deionized water, forming silanol bonds (Si-OH) on the surfaces of the two cleaned and surface-treated silicon wafers to enable the surfaces to form hydrophilicity, tightly attaching the two surfaces to be bonded, taking out the two surfaces to be placed into a die with the same size as the silicon wafers to align, and forming an MEMS structure with a piezoelectric material; placing filter paper on the upper surface and the lower surface of the silicon wafer which is tightly adhered and aligned, pressing the surfaces by using a cylindrical roller die so as to uniformly disperse the moisture between the first silicon wafer 1 and the second silicon wafer 6, and absorbing the moisture on the upper surface and the lower surface of the first silicon wafer 1 and the second silicon wafer 6 by the filter paper;

the tenth step, putting the aligned and tightly adhered piezoelectric MEMS structure between two glass plates 7 with flat surfaces, applying force and keeping for 15 hours; forming a Si-O-Si bond by silanol groups between the two silicon chips through molecular polymerization, and realizing pre-bonding of the two silicon chips through the Si-O-Si bond;

step ten, putting the piezoelectric MEMS structure which is bonded in advance into a muffle furnace to anneal for 10 hours at the temperature of 150 ℃ so as to enhance the molecular bond energy of Si-O-Si and further enhance the bonding strength;

and a twelfth step of removing the photoresist and the polyimide adhesive tape on the surface.

The photoresist used for the first protective layer 2 in the first step is a positive photoresist or a photosensitive polymer that is easily removed.

The photoresist thickness that first protective layer 2 used in the first step be 4um ~ 20 um.

And in the second step, the developing solution is NaOH solution with the concentration of 5 per mill.

The piezoelectric material in the first step is any material with positive piezoelectric effect and negative piezoelectric effect.

And the MEMS process in the eighth step comprises contact exposure photoetching, developing, ICP dry etching and silicon-based wet etching.

And in the ninth step, the filter paper is used for absorbing the water on the surface of the silicon wafer, and the silicon wafer can be dried by using a silicon wafer cleaning machine instead.

The invention realizes the high-quality and high-airtightness effective bonding of the silicon-based piezoelectric MEMS structure and the silicon-based substrate at low temperature by the hydrophilic silicon low-temperature direct bonding method, avoids the damage of chemical cleaning treatment to any piezoelectric material in the bonding process by the protection method of the piezoelectric material, and can realize the high-reliability bonding of the silicon-based piezoelectric MEMS structure containing the piezoelectric material and the silicon-based substrate.

Drawings

FIG. 1 is a schematic view of a silicon wafer 1 according to the present invention.

Fig. 2 is a top view of a first passivation layer 2 formed on a silicon wafer 1 according to the present invention.

Fig. 3 is a schematic diagram of the patterned first passivation layer 2 according to the present invention.

Fig. 4 is a schematic diagram of fabricating a second passivation layer 3 on the first passivation layer 2 according to the present invention.

Fig. 5 is a top view of the second protective layer 3 of the present invention.

FIG. 6 is a schematic diagram of the pre-bonding process pressurization of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

A piezoelectric MEMS structure hydrophilic silicon direct bonding process comprises the following steps:

firstly, spin-coating photoresist on a first silicon wafer 1 with a piezoelectric structure pattern area to serve as a first protective layer 2 of a piezoelectric material, wherein the photoresist thickness of the first protective layer 2 is 4-20 um, and the processing method comprises the following steps: attaching a layer of adhesive tape 5 around a first silicon wafer 1 with piezoelectric material 4, spin-coating a layer of photoresist with a thickness of 8 microns by using a spin coater, and prebaking at 95 ℃ for 10 minutes to volatilize a solvent of the photoresist and adhere the photoresist to the first silicon wafer 1, as shown in fig. 1 and 2;

secondly, removing the adhesive tape 5 around the first silicon chip 1, carrying out photoetching by using a mask plate, and transferring the mask plate pattern to the first protective layer 2; the pattern on the mask is consistent with the pattern of the piezoelectric material 4, the area with the pattern on the mask is light-transmitting, and the other areas are light-proof; using a photoetching machine for front alignment, exposing for 30s, using a mixed solution of a developing solution AZ400K and deionized water in a ratio of 1:3 as a developing solution, developing for 3 minutes, and hardening for 30 minutes at 120 ℃, wherein the obtained pattern is shown in FIG. 3;

thirdly, a layer of polyimide (PI tape) is attached to the first protective layer 2 to serve as a second protective layer 3, wherein the size of the polyimide is the same as that of the first silicon wafer 1, as shown in fig. 4 and 5;

fourthly, preparing a mixed solution of concentrated sulfuric acid and hydrogen peroxide according to the volume ratio of 4:1, and paying attention to the fact that the preparation process is a heat release process, pouring the hydrogen peroxide solution into the concentrated sulfuric acid solution slowly, and stirring the solution slowly by using a glass rod to release heat; putting the prepared first silicon chip 1 into the prepared solution, heating the solution on a constant-temperature hot plate to 110 ℃, and keeping the constant temperature for 30 minutes; taking out the silicon wafer by using Teflon tweezers, and repeatedly cleaning the silicon wafer in a container filled with deionized water for 10 minutes;

fifthly, preparing an RCA1 mixed solution of ammonium hydroxide, hydrogen peroxide and deionized water according to the ratio of 1:1:2, putting the cleaned first silicon wafer 1 in the RCA1 mixed solution, heating to 85 ℃ by using a constant temperature hot plate, and keeping the constant temperature for 15 minutes; taking out the first silicon wafer 1 by using Teflon tweezers, putting the first silicon wafer into a container filled with deionized water, repeatedly cleaning the first silicon wafer for 10 minutes, taking out the first silicon wafer and drying the first silicon wafer by using nitrogen;

sixthly, activating the surface of the oxygen plasma: putting the first silicon chip 1 with the cleaned surface into an oxygen plasma cleaning machine for surface activation treatment, wherein the activated surface is a non-piezoelectric structural surface of the first silicon chip 1;

seventhly, wet activation treatment: preparing a mixed solution of ammonium hydroxide, hydrogen peroxide and deionized water according to the ratio of 5:2:4 as a chemical activation reagent, putting the first silicon wafer 1 subjected to oxygen plasma treatment into the chemical activation reagent, heating the first silicon wafer to 80 ℃ by a hot plate, boiling the first silicon wafer for 15 minutes, taking the first silicon wafer out by a Teflon forceps, and putting the first silicon wafer into the deionized water for washing;

eighthly, cleaning the other second silicon wafer 6 which is not provided with the piezoelectric material and has a bulk silicon structure after being processed by the MEMS process by the same method from the fourth step to the seventh step;

the ninth step: placing a first silicon wafer 1 and a second silicon wafer 6 into deionized water, forming a large number of silanol bonds (Si-OH) on the surfaces of the two cleaned and surface-treated silicon wafers to enable the surfaces to form hydrophilicity, tightly attaching the two surfaces to be bonded, taking out the two surfaces to be bonded, placing the two surfaces into a mold with the same size as the silicon wafers, aligning the two surfaces to form an MEMS structure with a piezoelectric material; placing filter paper on the upper surface and the lower surface of the silicon wafer which is tightly adhered and aligned, pressing the surfaces by using a cylindrical roller die with proper force so as to uniformly disperse the moisture between the first silicon wafer 1 and the second silicon wafer 6, and absorbing the moisture on the upper surface and the lower surface of the first silicon wafer 1 and the second silicon wafer 6 by the filter paper;

tenth, the aligned and tightly adhered piezoelectric MEMS structure is placed between two glass plates 7 with flat surfaces and no particles, a force of about 1500N is applied, and the pressure is kept for 15 hours; silanol groups between the two silicon wafers form Si-O-Si bonds through molecular polymerization, and the two silicon wafers realize pre-bonding through the Si-O-Si bonds, as shown in FIG. 6;

step ten, putting the piezoelectric MEMS structure which is bonded in advance into a muffle furnace to anneal for 10 hours at the temperature of 150 ℃ so as to enhance the molecular bond energy of Si-O-Si and further enhance the bonding strength;

and twelfth, tearing off the polyimide adhesive tape on the surface of the bonded piezoelectric MEMS structure device, soaking the bonded piezoelectric MEMS structure device in acetone and absolute ethyl alcohol for 10 minutes respectively, taking out the photoresist on the surface, and putting the piezoelectric MEMS structure device into an oxygen plasma dry-method photoresist remover to remove the photoresist invisible to naked eyes so as to ensure the photoresist is removed cleanly.

The foregoing is directed to embodiments of the present application and it is noted that numerous modifications and adaptations may be made by those skilled in the art without departing from the principles of the present application and are intended to be within the scope of the present application.