CN100499877C - Chip having high sensitivity for silicon micro-capacitor microphone and preparation method thereof - Google Patents

Abstract

The invention relates to a chip used in a silicon micro capacitor microphone and a preparation method thereof. The chip includes an n-type silicon substrate, on which boron is diffused on the front to form a p+ type doped layer, silicon dioxide is deposited on the layer, etched to form an isolation layer, and a vibrating film layer is attached on it, and the vibrating film layer Metal aluminum film is deposited on the silicon substrate, and photoetched and etched into a circular aluminum film and a square aluminum electrode; there is a layer of silicon nitride protective film on the back of the silicon substrate, and a trapezoidal notch is etched from the bottom surface of the silicon substrate, the trapezoidal notch The depth reaches the p+ type doped layer, and the acoustic hole is etched vertically to the p+ type doped layer to form a perforated back plate, and there is an air gap between the perforated back plate and the vibrating film layer made of silicon nitride. The technological method that the present invention adopts, makes the air gap layer of circular structure, vibrating film and annular spacer layer, is distributed with uniform circular micro-perforation on the edge of vibrating film at the same time, has reduced the stress of vibrating film, greatly The sensitivity of the vibrating membrane is improved, and the rupture of aging is avoided.

Description

Chip with high sensitivity for silicon microcapacitor microphone and its preparation method

technical field

The invention relates to the field of silicon microcapacitor microphones, in particular to a high-sensitivity chip for silicon microcapacitor microphones and a preparation method thereof.

Background technique

The silicon microcapacitor microphone is composed of a silicon chip part and a peripheral circuit part forming a silicon microcapacitor, wherein the silicon chip part consists of a silicon substrate and a perforated (acoustic hole) backplane, air gap, isolation layer, vibrating membrane, and metal film. and metal electrodes. The usual silicon microcapacitor microphone is limited by the production method, and the air gap, isolation layer, and diaphragm are generally square, such as Micro Electro Mechanical Systems (MEMS), 1998 IEEE11th International Workshop p580-585, by P.-C. As described in "A HIGH SENSITIVITY POLYSILICON DIAPHRAGM CONDENSERMICROPHONE" by Hsu, C.H. Mastrangelo, and K.D. Wise. When making the silicon microcapacitor microphone, the bulk etching from the back of the silicon wafer can only produce a square backplate, which is then etched with hydrofluoric acid, which etches the carbon dioxide through the acoustic holes with smaller geometric dimensions on the square backplate. The silicon layer is released as a sacrificial layer of silicon dioxide. The silicon dioxide is used as a sacrificial layer and a square isolation layer at the same time. The sacrificial layer in the middle is etched to form an air gap. After the sacrificial layer is released, the remaining part of the silicon dioxide layer is used as a square isolation layer. layer. It is almost impossible to corrode the circular air gap area when hydrofluoric acid corrodes silicon dioxide slowly, and the corrosion for too long will cause the silicon nitride vibrating film to be damaged. In this way, when the sacrificial layer and the isolation layer are in a square shape, the stress on the vibrating membrane is relatively large, especially at the sharp corners, resulting in stress concentration, which in turn leads to a decrease in the sensitivity of the microphone and even aging rupture. If the above manufacturing process is adopted, even if a circular vibrating membrane is made, it will inevitably form a sharp angle of stress concentration with the irregular (non-circular) air gap area, and at the same time, a complete vibrating membrane will also keep the stress at a high level.

Contents of the invention

The purpose of the present invention is to overcome the defects that the square vibrating membrane produced by the existing manufacturing process has a large stress at the sharp corner, which leads to a decrease in the sensitivity of the microphone and even an aging crack, thereby providing a circular isolation layer and a circular diaphragm. The invention discloses a silicon microcapacitor microphone chip with high sensitivity and uniform circular microperforations on the edge of the vibrating film and a preparation method thereof.

The purpose of the present invention is achieved like this:

A kind of chip that is used for silicon microcapacitor microphone with high sensitivity provided by the present invention comprises an n-type silicon substrate 1, forms p+ type doped layer 3 on the front side of silicon substrate 1 by boron diffusion, in p+ type doped layer 3. Silicon dioxide is deposited on it, photolithography and corrosion are used to form an isolation layer 4. A vibrating film layer 6 made of silicon nitride is attached to the isolating layer 4. A metal aluminum film is deposited on the vibrating film layer 6, and is subjected to photolithography and etching. Form a circular aluminum film and a square aluminum electrode 9 (as shown in Figures 4 and 5); there is a silicon nitride protective film 11 on the back side of the silicon substrate 1, and a trapezoidal notch is etched from the bottom surface of the silicon substrate 1. The depth of the trapezoidal notch reaches the p+-type doped layer 3, and the acoustic hole 7 is etched in the direction perpendicular to the p+-type doped layer 3 to form a perforated backplane. There is air between the perforated backplane and the vibrating film layer 6 made of silicon nitride. Gap 8; It is characterized in that: uniform circular micro-perforation 10 is distributed on the edge of the circular aluminum film deposited on the vibrating film layer 6 and above by photolithography and corrosion; the circular Shaped micro-perforation 10 with a diameter of 1-20 microns, the center of which is located on a concentric circle whose diameter is 70-98% of the diameter of the circular aluminum film. 1 to 10 times the central angle formed by the points.

The isolation layer 4 is annular; its thickness is 0.5-6 microns, its inner diameter is 500-3000 microns, and its radial width is 50-150 microns.

The air gap 8 is circular, with a thickness of 0.6-7 microns and a diameter of 500-3000 microns.

The vibrating membrane layer 6 is circular, with a thickness of 0.1-1 micron and a diameter of 600-3300 microns.

The etched holes on the perforated back plate are arranged in an array, and the parts other than the holes are the p+ type doped layer 3, and the boron diffusion depth is 3-20 microns.

A kind of preparation method that the invention provides has the chip that is used for silicon microcapacitance microphone with high sensitivity, and this method comprises the following steps:

[1] Take an n-type silicon substrate 1 and grow a silicon dioxide with a thickness of 0.5-2 microns through high-temperature oxidation. After photolithography, use hydrofluoric acid to etch the high-temperature silicon dioxide to make a mask 2. Carry out deep boron diffusion to form the p+ type doped layer 3 in the perforated backplane except for the hole distribution part, and the boron diffusion depth is 3-20 microns;

[2] Remove the high-temperature silicon dioxide mask 2 with hydrofluoric acid, magnetron sputter a 0.1-1 micron zinc oxide auxiliary sacrificial layer on the front side of the silicon wafer, photolithography, and phosphoric acid etch a circular auxiliary sacrificial layer; the deposited thickness is 0.5-6 micron low-temperature silicon dioxide 4; deposit silicon nitride with a thickness of 0.1-1 micron on both sides of the silicon wafer. After photolithography on the front side, the silicon nitride is etched into a circular vibrating film. The low-temperature silicon dioxide below is also etched into the same circle (the diameter of this circle is greater than the diameter of the circular zinc oxide auxiliary sacrificial layer, wherein the part corresponding to the circular zinc oxide auxiliary sacrificial layer is used as the sacrificial layer, and the remaining circles The ring part is used as an isolation layer), and the silicon nitride on the back is etched into a square silicon body etching mask after photolithography;

[3] The silicon substrate 1 is etched with potassium hydroxide from the back of the silicon wafer. When the potassium hydroxide corrodes the p+ type doped layer 3, the corrosion rate of the perforated area that has not been diffused by boron is much faster than that of the potassium hydroxide. The region of the perforated backplane that is higher than the depth of boron diffusion causes the distribution of holes on the perforated backplane to be quickly etched away to form acoustic holes 7 on the perforated backplane, and the etched perforations on the perforated backplane are arranged in an array; then, Potassium hydroxide reaches the circular zinc oxide auxiliary sacrificial layer 5 through the perforation, and the auxiliary sacrificial layer 5 composed of zinc oxide is quickly corroded to form a circular air gap with the same shape as the circular zinc oxide auxiliary sacrificial layer 5; Afterwards, the circular low-temperature silicon dioxide sacrificial layer is corroded and released with hydrofluoric acid, thereby forming a circular air gap 8;

[4] Evaporate a metal aluminum film with a thickness of 0.05 to 0.2 microns on the front of the silicon wafer, and etch a circular aluminum film and a square electrode 9 by photolithography and phosphoric acid; The circular micro-perforation 10 on the aluminum film is etched into the circular micro-perforation 10 on the silicon nitride circular vibrating film under the aluminum film.

The diameter of the zinc oxide circular auxiliary sacrificial layer is 500-3000 microns, and the thickness is 0.1-1 micron, and the diameter of the silicon nitride circular vibrating film (equal to the diameter of the circular low-temperature silicon dioxide layer) is 600 ~3300 microns, the diameter of which is 100-300 microns larger than the diameter of the circular auxiliary sacrificial layer; the thickness of the annular low-temperature silicon dioxide layer is 0.5-6 microns;

The more easily corroded zinc oxide is used as the auxiliary sacrificial layer, and the sacrificial layer is composed of the more difficult to corrode low-temperature silicon dioxide; therefore, the actual air gap is the air gap formed after the circular zinc oxide auxiliary sacrificial layer is corroded by potassium hydroxide It is composed of air gaps formed after the circular low-temperature silicon dioxide layer on the zinc oxide is etched by hydrofluoric acid.

After bulk etching, potassium hydroxide quickly removes the circular zinc oxide film through perforation, thereby forming a circular air gap area; afterward, when hydrofluoric acid etches the circular low-temperature silicon dioxide sacrificial layer, the hydrofluoric acid etching solution can Erosion is carried out vertically upwards with the plane of the entire circular area. Since the geometric scale in the vertical direction of the sacrificial layer (about 1 to 6 microns) is much smaller than the geometric scale in the horizontal direction (half of the interval between adjacent perforations, about 20 to 40 microns), the low temperature silicon dioxide sacrificial layer can be reduced by about ten times. While maintaining the exact same shape as the zinc oxide assisted sacrificial layer, hydrofluoric acid releases the silicon dioxide sacrificial layer to maintain a circular shape.

The advantages of the present invention are:

The high-sensitivity chip used for silicon microcapacitor microphones provided by the present invention adopts a new process method to make a circular structure of air gap layer, isolation layer and vibrating membrane, which reduces the stress of the vibrating membrane. The sensitivity of the vibrating film is greatly improved, and aging cracking is avoided; at the same time, since the corrosion direction of silicon dioxide sacrificial layer silicon dioxide is not the horizontal direction with a large scale in the past, but the vertical direction with a small scale, the corrosion speed is relatively fast. Fast, reducing the strong corrosion of the silicon nitride vibrating film while releasing the sacrificial layer with hydrofluoric acid in the past.

In the chip provided by the present invention, uniform circular micro-perforations are distributed on the vibrating film layer 6 and the metal aluminum film deposited on it through photolithography and corrosion to form circular micro-perforations. The stress of the silicon nitride circular vibrating membrane is released to a certain extent, and the diameter of the perforation is small enough to maintain a large sound resistance, which greatly improves the sensitivity of the vibrating membrane and avoids cracking due to aging.

Illustration

Fig. 1 is the cross-sectional schematic diagram formed after the deep boron diffusion is carried out on the front side of the silicon wafer by the preparation method of the present invention

Fig. 2 is deposition, lithography, etch circular auxiliary sacrificial layer in the preparation method of the present invention, low-temperature silicon dioxide, deposits, lithography, etch circular vibrating membrane, etch circular vibrating membrane The cross-sectional schematic diagram of the lower circular isolation layer and circular sacrificial layer, photolithography and etching out the mask of the square silicon body etching on the back

Fig. 3 is a schematic cross-sectional view formed after bulk etching silicon wafers, etching auxiliary sacrificial layers and releasing sacrificial layers to form a circular air gap layer in the preparation method of the present invention

Fig. 4 is a schematic cross-sectional view of the chip in the silicon microcapacitance microphone of the present invention by depositing and photoetching a circular metal aluminum film, photoetching and etching a circular micro-perforation

Fig. 5 is the plan view of the chip that the present invention is used in silicon microcapacitance microphone

Fig. 6 is the bottom view of the chip that the present invention is used in silicon micro capacitor microphone

Fig. 7 is the flowchart of the preparation method of the microphone chip of the present invention

Drawing logo:

1. n-(100) silicon wafer 2. High temperature silicon dioxide 3. p+ type doped layer

4. Low temperature silicon dioxide layer 5. Auxiliary sacrificial layer (zinc oxide) 6. Vibration film layer (silicon nitride)

7. Acoustic hole 8. Air gap (formed after releasing the sacrificial layer)

9. Aluminum film and electrodes 10. Round micro-perforation 11. Protective film

1n ^- (100) Si 2 high temperature SiO ₂ 3p ⁺ doped Si 4 low temperature SiO ₂ 5 zinc oxide 6, 11 silicon nitride 9 aluminum film and electrode

Detailed ways

Referring to the accompanying drawings in conjunction with the preparation method of the present invention, the specific structure of the microphone chip of the present invention will be described in detail

Example 1

A kind of chip that the present invention is used in silicon microcapacitance microphone provided by the present embodiment, referring to accompanying drawing 4-6; This chip comprises an n-type silicon substrate 1, forms p+ type by boron diffusion on the front side of silicon substrate 1 The doped layer 3 has a thickness of 3 or 20 microns; silicon dioxide is deposited on the p+ type doped layer 3 and photoetched and etched into an annular isolation layer 4, the inner diameter of the annular isolation layer 4 is 500 or 3000 microns, The radial width is 50 or 150 microns; a circular vibrating film layer 6 made of silicon nitride is attached to the isolation layer 4, and the vibrating film layer 6 is deposited, photoetched, and etched into a circular metal aluminum film and a square electrode 9. Uniform circular micro-perforations 10 are arranged on the edge of the vibrating film and the circular aluminum film; the diameter of the circular micro-perforations 10 is 1-20 microns; the center of the circle is located at 70-98% of the diameter of the circular aluminum film On the concentric circles, the central angle formed by the centers of two adjacent micro-perforations is 1 to 10 times the central angle formed by the intersection points of the micro-perforations and the concentric circles. There is a layer of silicon nitride protective film 11 on the reverse side of the silicon substrate 1, and a trapezoidal gap is etched out from the bottom surface of the silicon substrate 1. Acoustic holes 7 form a perforated back plate, and an air gap 8 is formed between the perforated back plate and the vibrating membrane layer 6 made of silicon nitride; the air gap 8 is circular, with a thickness of 0.6 or 7 microns and a diameter of 500 or 3000 microns. The holes etched on the perforated backplane are arranged in an array, and the acoustic holes 7 have a side length of 30 microns and an interval of 30 microns. The thickness of the diaphragm layer 6 is 0.1 or 1 micron.

Example 2

The preparation method of the present invention is described in detail in conjunction with accompanying drawing 7 and specific examples:

[1] Take an n-type silicon substrate 1 and grow a silicon dioxide with a thickness of 1.5 microns through high-temperature oxidation. After photolithography, use hydrofluoric acid to etch the high-temperature silicon dioxide to make a mask 2, and place it Carry out deep boron diffusion to form the p+ type doped layer 3 in the perforated backplane except for the hole distribution part, and the boron diffusion depth is 10 microns;

[2] After removing the high-temperature silicon dioxide mask with hydrofluoric acid, a 0.5-micron-thick zinc oxide auxiliary sacrificial layer is magnetron sputtered on the front of the silicon wafer, and a circular auxiliary sacrificial layer 5 is formed by photolithography and phosphoric acid etching. The diameter of the auxiliary sacrificial layer is 1000 microns, and the thickness is 0.5 microns; on the front side of the silicon wafer 1, a low-temperature silicon dioxide 4 with a thickness of 3 microns is deposited by plasma-enhanced chemical vapor deposition (PECVD); Silicon nitride with a thickness of 0.5 microns is deposited on both sides by low-pressure chemical vapor deposition equipment (LPCVD). The low-temperature silicon dioxide under the silicon nitride is also etched into the same circle by ICP (the diameter of this circle is larger than the circular zinc oxide auxiliary sacrificial layer, and the part corresponding to the circular zinc oxide auxiliary sacrificial layer is used as the sacrificial layer, The rest of the annular part is used as the isolation layer 4, the thickness of which is 0.5-6 microns, the inner diameter is 500-3000 microns, and the radial width is 50-150 microns), and the silicon nitride is etched into a square silicon by ICP after photolithography on the back. A mask for body etching; the diameter of the silicon nitride circular diaphragm 6 (equal to the diameter of the circular low-temperature silicon dioxide layer) is 1500 microns, which is 500 microns larger than the diameter of the circular auxiliary sacrificial layer; wherein The diameter of the zinc oxide circular auxiliary sacrificial layer is 500-3000 microns, and the thickness is 0.1-1 micron; the diameter (equal to the diameter of the circular low-temperature silicon dioxide layer) of the silicon nitride circular diaphragm is 600-3000 microns. 3300 microns, the diameter of which is 100-300 microns larger than the diameter of the circular auxiliary sacrificial layer; the thickness of the annular low-temperature silicon dioxide layer is 0.5-6 microns;

[3] The silicon substrate 1 is etched with potassium hydroxide from the back of the silicon wafer. When the potassium hydroxide corrodes the p+ type doped layer 3, due to the corrosion rate of the perforated area without boron diffusion by potassium hydroxide The region of the perforated backplane that is much higher than the depth of boron diffusion causes the hole distribution of the perforated backplane to be quickly etched away, forming acoustic holes 7 perpendicular to the perforated backplane, and the etched acoustic holes 7 on the perforated backplane are in an array The acoustic hole (7) has a side length of 30-80 microns and an interval of 30-80 microns; then, potassium hydroxide reaches the circular zinc oxide auxiliary sacrificial layer 5 through perforation, and the auxiliary sacrificial layer 5 made of zinc oxide After etching, an air gap 8 identical in shape to the circular zinc oxide auxiliary sacrificial layer 5 is formed; afterwards, the circular low-temperature silicon dioxide sacrificial layer (that is, the silicon dioxide layer located in the circular zinc oxide auxiliary sacrificial layer) is formed with hydrofluoric acid. The part above the sacrificial layer) is corroded and released to form an air gap, thereby forming a circular air gap 8 together with the aforementioned air gap with the same shape as the circular zinc oxide auxiliary sacrificial layer 5; wherein the air gap 8 is circular, and its thickness It is the sum of the thickness of the ring-shaped isolation layer (4) and the corroded zinc oxide layer, which is 0.6-7 microns, and the diameter is 500-3000 microns;

[4] Evaporate a metal aluminum film with a thickness of 0.1 micron on the front surface of the silicon wafer 1, and perform photolithography and phosphoric acid etching to form a circular metal aluminum film and square electrodes 9 . After the photoresist is removed, the circular micro-perforation on the circular aluminum film is etched by photolithography and phosphoric acid, and then the circular micro-perforation is etched on the silicon nitride circular vibrating film under the aluminum film. Circular micro-perforation 10 diameters 2 microns, the center of which is located on a concentric circle whose diameter is 95% of the diameter of the circular aluminum film, and the center angle formed by the centers of two adjacent micro-perforations is formed by the intersection of micro-perforations and concentric circles 3 times the central angle.

Claims (2)

1. a kind of chip that is used for silicon microcapacitor microphone with high sensitivity; Comprise an n-type silicon substrate (1), form p+ type doped layer (3) at the frontal diffusion boron of silicon substrate (1), in The p+ type doped layer (3) is formed into an isolation layer (4) by depositing silicon dioxide, photolithography, and etching, and a vibrating film layer (6) made of silicon nitride is attached thereon, and the vibrating film layer (6) Deposit and lithography, etch into a circular metal aluminum film (9) and a square metal aluminum electrode (9); there is a layer of silicon nitride protective film (11) on the back side of the silicon substrate (1), from the silicon substrate A trapezoidal notch is etched on the bottom surface of the sheet (1), the depth of the trapezoidal notch reaches the p+ type doped layer (3), and an acoustic hole (7) is etched perpendicular to the p+ type doped layer (3) to form a perforated back plate, an air gap (8) is formed between the perforated back plate and the vibrating film layer (6); it is characterized in that: the metal aluminum film deposited on the vibrating film layer (6) and above is photoetched and corroded into a circle On the edge of the shaped aluminum film, uniform circular micro-perforations (10) are arranged; the diameter of the circular micro-perforations (10) is 1-20 microns, and its center is located at a concentric circle whose diameter is 70-98% of the diameter of the circular aluminum film. Above, the central angle formed by the centers of two adjacent micro-perforations is 1 to 10 times the central angle formed by the two points where the micro-perforations intersect with the concentric circle; The isolation layer (4) is annular; its thickness is 0.5-6 microns, its inner diameter is 500-3000 microns, and its radial width is 50-150 microns; The air gap (8) is circular, and its thickness is the sum of the thickness of the annular isolation layer (4) and the corroded zinc oxide layer, which is 0.6-7 microns, and its diameter is 500-3000 microns. The vibrating membrane layer (6) is circular, with a thickness of 0.1-1 micron and a diameter of 600-3300 microns; The acoustic holes (7) etched on the perforated back plate are arranged in an array, and the parts other than the holes are p+-type doped layers (3), and the boron diffusion depth is 3 to 20 microns; The acoustic hole (7) has a side length of 30-80 microns and an interval of 30-80 microns. 2. a method for preparing the chip with high sensitivity for silicon microcapacitor microphone as claimed in claim 1, the method may further comprise the steps: [1] Take an n-type silicon substrate (1) and grow a silicon dioxide with a thickness of 0.5-2 microns through conventional high-temperature oxidation. After photolithography, use hydrofluoric acid to etch the high-temperature silicon dioxide to make a mask (2) , and perform deep boron diffusion on the front side of the silicon wafer to form a p+ type doped layer (3) in the perforated backplane except for the hole distribution part, and the boron diffusion depth is 3 to 20 microns; [2] Use hydrofluoric acid to remove the high-temperature silicon dioxide mask (2) prepared in step [1], and then magnetron sputtering a zinc oxide auxiliary sacrificial layer with a thickness of 0.5 microns on the front of the silicon wafer. Etching a circular auxiliary sacrificial layer; depositing low-temperature silicon dioxide (4) with a thickness of 0.5-6 microns on the front side of the silicon wafer; depositing silicon nitride with a thickness of 0.1-1 microns on both sides of the silicon wafer, and After photolithography, the silicon nitride is etched into a circular diaphragm (6) by a plasma etching machine, and the low-temperature silicon dioxide under the silicon nitride is also etched into the same circular shape by a plasma etching machine. The diameter of the circle is larger than that of the circular zinc oxide auxiliary sacrificial layer (5), wherein the part corresponding to the circular zinc oxide auxiliary sacrificial layer is used as the sacrificial layer, and the rest of the annular part is used as the isolation layer (4). SiC is etched by a plasma etching machine into a mask (10) for etching a square silicon body; The diameter of the zinc oxide circular auxiliary sacrificial layer is 500-3000 microns; The silicon nitride circular diaphragm has a diameter of 600-3300 microns and a thickness of 0.5-6 microns; 【3】Etch the silicon substrate (1) with potassium hydroxide from the back of the silicon wafer. The corrosion rate of the perforated backplane is much higher than that of the perforated backplane area with deep boron diffusion, so that the hole distribution of the perforated backplane is quickly corroded, and acoustic holes (7) are formed perpendicular to the perforated backplane. The acoustic holes (7) are arranged in an array; then, potassium hydroxide reaches the circular zinc oxide auxiliary sacrificial layer (5) through perforation, and the auxiliary sacrificial layer (5) composed of zinc oxide is etched completely to form a circular zinc oxide sacrificial layer (5). The auxiliary sacrificial layer (5) has exactly the same shape; after that, the circular low-temperature silicon dioxide sacrificial layer is corroded and released with hydrofluoric acid, thereby forming a circular air gap (8); [4] Evaporate a metal aluminum film with a thickness of 0.05 to 0.2 microns on the front side of the silicon wafer (1), and photoetch and phosphoric acid etch out a circular metal aluminum film and a square electrode (9). After removing the photoresist, the photo engraving and phosphoric acid etching out circular micro-perforations (10) on the circular aluminum film, and then etching circular micro-perforations (10) on the silicon nitride circular vibrating film under the aluminum film.

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