CN101266176A - Silicon-on-insulator silicon-bonded high-temperature pressure sensor chip and manufacturing method - Google Patents

Abstract

The invention relates to a high-temperature press sensor of silicon-silicon-bonded-based silicon on an insulator (SOI) and a producing method, belonging to the field of sensor chip, characterized in that a shallow slot and a gas vent on a support silicon substrate are all formed through anisotropic etch; suitable depth of the shallow slot can be obtained by controlling etching time so as to accomplish over-voltage protection for the device; the support silicon substrate is bonded with an inverted SOI chip; a piezoresistor is produced on the top layer of silicon after reducing and polishing the back of the SOI chip. The device can operate normally at high temperature using SOI buried oxide layer for isolation of sensitive component and elastic component.

Description

Silicon-on-insulator silicon-bonded high-temperature pressure sensor chip and manufacturing method

technical field

The invention relates to a silicon-on-insulator silicon-on-insulator (SOI) high-temperature pressure sensor chip and a manufacturing method thereof, which belong to the field of sensor chips.

Background technique

As the most commercially successful MEMS device, silicon-based pressure sensors have been widely used and technologically advanced in the fields of petroleum, aerospace, medical equipment, and automotive electronics in the past few decades. However, because the traditional bulk silicon pressure sensor uses a pn junction as an electrical isolation method, it will eventually fail due to the increase of the reverse leakage current in an environment above 125°C (Diem et al. published on page 8 of Sensors and Actuators A 46-47 (1995) SOI 'SIMOX' from bulk to surface micromachining, a new age for silicon sensors and actuators. One article). The use of SOI materials can play a significant role in improving the high temperature performance of pressure sensors. Compared with traditional bulk silicon pressure sensors, SOI pressure sensors use insulating buried oxide layer isolation instead of pn junction isolation, which greatly enhances the ability of the device to withstand high temperatures. In addition, compared with the polysilicon pressure sensor, because the top layer of SOI is a single crystal silicon material, the mechanical properties are much better than the polysilicon pressure sensor, and the sensitivity is greatly improved.

Ordinary SOI high-temperature pressure sensors (such as Fabrication and temperature coefficient compensation technology of low cost high temperature pressure sensor published by Q.Wang et al. on page 468 of Sensors and Actuators A120 (2005)) adopt long-term anisotropic etching to form silicon cups The structure is used as a process for making stress films, so it is difficult to ensure the uniformity of different positions of the film and stress films prepared in different batches, resulting in low process stability. However, the present invention intends to bond the silicon wafer with the shallow groove in advance and the SOI wafer that is turned upside down, and adopt the original top layer silicon of the SOI wafer as the stress film, which not only enhances the process reliability, but also because the thickness of the film is determined by the thickness of the SOI raw material. decision, so process stability and device consistency can be guaranteed. Combined with mature grinding and chemical mechanical polishing technology, the force sensitive resistor isolated from the stress film is fabricated on the thin layer of single crystal silicon remaining after SOI back grinding and polishing, so it is expected to solve the application at high temperature higher than 125°C and Non-linear problems can also bring process stability and device miniaturization convenience at the same time, and overvoltage protection can also be realized by properly setting the depth of the corroded shallow groove, which further improves the practicability of the device, thereby leading to the invention Purpose.

Contents of the invention

The invention proposes a silicon-on-insulator (SOI) high-temperature pressure sensor chip bonded with silicon and a manufacturing method thereof. The provided pressure sensor chip is shown in Figure 1, and the device includes an anisotropically etched supporting silicon substrate and a sensitive element formed by SOI micromachining. The supporting silicon substrate is n-type or p-type, shallow grooves 2 are formed by anisotropic etching on the front side of the silicon substrate, and air guide holes 4 are also formed by anisotropic deep etching on the back side; the SOI sheet used is p-type. Grinding and polishing are carried out after bonding the supporting silicon substrate with shallow grooves and air guide holes to the inverted SOI wafer. A stress film 1 is prepared on the SOI structure above the shallow groove, and a force-sensitive resistor 5 is insulated and isolated through a silicon dioxide buried layer 6 , and the electrical connection between the force-sensitive resistors is realized through metal leads and lead-out electrodes 7 .

The silicon-on-insulator silicon-on-insulator high-temperature pressure sensor chip of the silicon-silicon bonding described in the present invention, under the condition that the lateral dimension of the film is determined, the measuring range is determined by the thickness, the measuring range is usually 0.1MPa-100MPa, and the film thickness is 20μm-200μm , the depth of the shallow groove on the substrate silicon is 1 μm to 20 μm.

The application temperature range of the MEMS pressure sensor is extended to more than 200°C through the buried oxide layer of SOI, as shown in Figure 4, the MEMS high-temperature pressure sensor chip based on the SOI wafer and silicon-silicon bonding technology described in the present invention operates at room temperature and 200°C The test curve below. The thickness of the stress film can be more accurately defined through the thickness of the top silicon of the initial SOI, ensuring the consistency of the same batch of devices and the stability of the process. The use of silicon-silicon thermocompression bonding technology can easily realize the miniaturization of devices and avoid process instability caused by long-term anisotropic corrosion. Since the depth of the shallow groove is generally set according to the displacement of the stress film under the full-scale pressure, in order to achieve overpressure protection, generally only a short-term corrosion is required, and relatively speaking, the short-term corrosion process is more controllable. These advantages make the SOI-based MEMS high-temperature pressure sensor with a new structure proposed by the present invention more practical.

The SOI high-temperature pressure sensor chip proposed by the present invention adopts the layout of the traditional bulk silicon pressure sensor in the layout of the force-sensitive resistors, as shown in Figure 2 (a) and (b), which consists of two pairs that increase or decrease with the change of stress respectively. The reduced resistance forms a Wheatstone bridge, and the top layer silicon is etched by ion implantation and diffusion and reactive ion beam etching or deep reactive ion beam etching to make the resistance of the bridge equal and doped to reduce the size of the device. of non-linearity. Comparing the two layouts, the resistor layout in Figure 2(a) can obtain a larger output signal, but the resistor strips are scattered, and it is difficult to guarantee the doping uniformity. The resistance distribution of the pressure sensor chip proposed by the present invention is shown in the equivalent circuit diagram 2 (c). If R represents the size of the resistance, ΔR represents the change value of the resistance when the applied pressure changes. At this time, _R1 and _R3 become (R+ΔR), while the other pair of resistors R ₂ and R ₄ becomes (R-ΔR), in the case of input Vs, the output signal is (VsΔR/R).

The SOI high-temperature pressure sensor chip with a new structure based on the bonding technology provided by the present invention has an overall structure obtained by silicon wafers and SOI wafers by silicon-silicon bonding technology. As shown in FIG. 1, the device includes an anisotropically etched silicon substrate 3 and stress-sensitive elements formed by SOI micromachining. The silicon substrate is p-type or n-type, shallow grooves 2 are formed by anisotropic etching on the front side, and gas guide holes 4 are also formed by anisotropic deep etching on the back side, and the SOI sheet used is P-type. The part prepared on the SOI sheet above the shallow trench includes a stress film 1 , a force sensitive resistor isolated by a silicon dioxide buried layer 6 , and a metal lead wire and an extraction electrode 7 for electrical connection on the force sensitive resistor.

It is characterized in that the resistance values of the force-sensitive resistors constituting the Wheatstone bridge are equal and the doping concentration of the resistance region is the same; the doping type of the resistance region is p-type, and the doping concentration after diffusion is 10 ¹⁷ ~ 10 ²⁰ /cm ² ; The area where the ohmic contact connection lead is required is also p-type doped, and the doping concentration after diffusion is greater than 10 ²⁰ /cm ² .

It is characterized in that the force sensitive resistor is arranged at the edge of the film or the area with the highest stress in the middle, as shown in Figure 2(a) and (b). The stress in the membrane changes linearly with the pressure difference between the upper and lower surfaces of the membrane. Due to the difference in position and direction of the two pairs of resistors forming the bridge, the sign of the stress change is opposite, resulting in the opposite change of the resistance value. The output voltage signal obtained at this time will be the same as that received by the membrane. proportional to the pressure difference.

The manufacturing method of the MEMS high-temperature pressure sensor chip based on SOI and bonding technology proposed by the present invention includes the following steps: find out the best piezoresistive position on the film through stress analysis, complete the design and prepare the photolithography plate; use p-type or n Type silicon wafer, use the oxide layer as a mask to etch the shallow groove and the air guide hole below in KOH or TMAH solution after front and back alignment photolithography, as shown in Figure 3 (1); The undercut is bonded to the shallow groove surface of the etched silicon wafer, as shown in Figure 3(2); the SOI upper layer is thinned to 1-5 μm by grinding and chemical mechanical polishing, as shown in Figure 3(3); through ion implantation and diffusion Form piezoresistive area and ohmic contact area, use RIE or DRIE etching to form force sensitive resistor, as shown in Figure 3 (4); photolithography lead hole, sputtering metal, alloy to complete the electrical connection of the chip; dicing, testing, packaging, The preparation of the sensor chip is completed, as shown in Fig. 3(5).

The bonding of the micro-machined silicon substrate sheet and the SOI sheet adopts silicon-silicon thermocompression bonding technology. The bonding process includes: RCA standard cleaning, microwave plasma activation, megasonic cleaning, hot pressing pre-bonding (bonding temperature 200 ° C to 500 ° C, pressure 1 ~ 50 bar, time 5 ~ 100 minutes) and high temperature annealing reinforcement ( Temperature 900°C-1200°C, 1-4 hours).

The present invention adopts the bonding of silicon wafers with shallow grooves and air holes and SOI wafers, and silicon silicon bonding replaces the anode bonding of silicon and glass in the preparation of traditional silicon pressure sensors, which not only brings greater flexibility to subsequent processes , The consistency of the thermal expansion coefficient between the same materials makes the residual stress of the device smaller. By controlling the depth of the shallow groove, overvoltage protection can be conveniently realized on the basis of miniaturization of the overall size of the device. Processing piezoresistive devices on SOI materials not only enables the devices to be used reliably at high temperatures, but also ensures the long-term stability of the devices at room temperature. The embossed resistance structure is also easy to obtain a more consistent resistance to form a bridge. The use of ion implantation and diffusion to achieve heavy doping and adjust the doping concentration in the relief piezoresistor can enable the device to effectively achieve self-compensation under the condition of temperature changes and increase the use value of the device. The related technologies adopted in the present invention are all mature micro-machining processes, the prepared pressure sensor has good process repeatability and stability, the product yield can be guaranteed, and is suitable for mass production.

Description of drawings

Fig. 1 is the schematic structural diagram of the pressure sensor chip in the present invention, wherein 1 is the monocrystalline silicon stress film, 2 is the shallow groove, 3 is the supporting silicon substrate, 4 is the air guide hole, 5 is the force sensitive element, and 6 is silicon dioxide The buried layer, 7 is a metal lead and an extraction electrode;

Fig. 2 is the top view schematic diagram and equivalent circuit of force sensitive resistor layout in the present invention, (a) and (b) are the situation that two pairs of resistors are all arranged on the edge of the film and one of them is arranged in the middle of the film, (c) is Arrangement circuit of two resistors.

Fig. 3 is a partial process flow chart of the pressure sensor of the present invention, wherein (1) is the bulk silicon structure after the shallow groove and vent hole are etched out; (2) realizes silicon-silicon bonding for the SOI sheet and the bulk silicon structure; (3) After grinding and chemical mechanical polishing; (4) the force sensitive element obtained by etching; (5) sputtering metal, lithography lead corrosion, and completing alloying.

Fig. 4 is a test curve of a pressure sensor chip with a range of 1 MPa at 200°C in the present invention.

Detailed ways

The following examples will help to understand the present invention, but do not limit the content of the present invention. The manufacturing method of silicon-on-insulator high-temperature pressure sensor chip suitable for silicon-silicon bonding in the range of 1MPa:

Using 4-inch 450μm N-type (100) double-polished single-crystal silicon wafers, the resistivity is 1-10ohm.cm, and 4-inch P-type double-polished SOI wafers, the thickness of the top silicon layer and the buried layer are 60 microns and 1 micron respectively , the top silicon resistivity 1-10ohm.cm.

1. Clean the silicon wafer and then oxidize it, use positive and negative photolithography alignment, use the oxide layer as a mask to etch shallow grooves and air guide holes in KOH solution, corresponding to Figure 3 (1);

2. SOI wafers and silicon wafers are bonded on the shallow groove surface. Use 400°C vacuum in the bonding machine, pressurize 2bar for 20 minutes, and then dry oxygen in a 1200°C high-temperature furnace for 4 hours for bonding reinforcement, corresponding to the figure 3(2);

3. Perform mechanical grinding and chemical mechanical polishing on the back of the SOI sheet, and the thickness of the remaining top layer silicon on the buried oxide layer is about 2 μm, corresponding to Figure 3 (3);

4. Use boron ion implantation and diffusion to form a light boron region on the top silicon surface as the next region to form a force-sensitive resistor. The implantation energy and dose are 100KeV, 4E15cm ^-2 , and the diffusion conditions are nitrogen at 1000°C for 2 hours. After diffusion The concentration of doping ions is about 10 ¹⁸ /cm ² ; re-implant the concentrated boron region as the ohmic contact region for electrical connection, the energy is 80KeV, the dose is 4E16cm ^-2 , and the diffusion condition is 1100℃ dry oxygen atmosphere and annealing for 1 hour; after diffusion The doping concentration is about 2×10 ²⁰ /cm ² ;

5. Using reactive ion beam etching to form a force sensitive resistor on the top layer of silicon, corresponding to Figure 3 (4);

6. Sputter aluminum, photolithography, metal aluminum corrosion, corresponding to Figure 3 (5), and finally complete alloying;

7. Dicing, wiring, testing, and complete the preparation of the pressure sensor chip.

Claims (10)

1, the chip of high-temp pressure sensor of a kind of SOI of Si-Si bonding is characterized in that described pressure sensor chip is to adopt Si-Si bonding to form by supporting silicon substrate and SOI sheet; Comprise by anisotropic etch support stress film is arranged, realize the force sensing resistance that insulation is isolated by the silicon dioxide buried regions and relies on metal wire on the positive shallow slot that forms of silicon substrate, gas port that the back side forms, the p type soi structure on the shallow slot and extraction electrode realization force sensing resistance between the electricity connection.

2, press the chip of high-temp pressure sensor of the SOI of the described Si-Si bonding of claim 1; it is characterized in that displacement that the positive shallow slot degree of depth that forms of described support silicon substrate produces under full scale pressure according to stress film is set; thereby realization overvoltage protection, the shallow slot degree of depth are 1 μ m-20 μ m.

3, press the chip of high-temp pressure sensor of the SOI of the described Si-Si bonding of claim 1, the thickness that it is characterized in that described stress film is 20 μ m-100 μ m.

4, press the chip of high-temp pressure sensor of the SOI of claim 1 or 3 described Si-Si bondings, it is characterized in that described pressure sensor chip range is under the condition that the lateral dimension of stress film is determined, be that described range is 0.1MPa-100MPa by the decision of the thickness of stress film.

5, press the chip of high-temp pressure sensor of the SOI of the described Si-Si bonding of claim 1, it is characterized in that force sensing resistance is distributed in the edge or the middle maximum stress zone of stress film; The stress film internal stress is linear change with stress film upper and lower surface pressure differential.

6, by the chip of high-temp pressure sensor of the SOI of the described Si-Si bonding of claim 1, the force sensing resistance resistance equal and opposite in direction and the resistance region doping content that it is characterized in that constituting resistance bridge are identical; The resistance region doping type is the p type; The zone of making Ohmic contact connection lead-in wire on the resistance also is that the p type mixes.

7, press the chip of high-temp pressure sensor of the SOI of the described Si-Si bonding of claim 1, it is characterized in that described support silicon substrate is n type or p type.

8, making is characterized in that as the method for the chip of high-temp pressure sensor of the SOI of each described Si-Si bonding in the claim 1,2,3,5,6 or 7 step of making is:

(a) find out pressure drag position best on the film by stress analysis, finish designing and producing reticle;

(b) adopt p type or n type silicon chip, after the positive and negative aligning photoetching, adopt oxide layer do mask in potassium hydroxide or tetramethyl ammonium hydroxide solution, erode away shallow slot and below gas port;

(c) adopt silicon silicon thermocompression bonding technology with the shallow slot face bonding of SOI sheet back-off with corrosion silicon chip well;

(d) adopt grinding or wet etching the SOI substrate layer to be thinned to 1-5um in conjunction with chemically mechanical polishing;

(e) inject and spread piezoresistive regions and the ohmic contact regions dopant ion concentration that acquisition needs by ion, adopt reactive ion beam etching (RIBE) or deep reactive ion bundle etching to form force sensing resistance;

(f) electricity that lithography fair lead, splash-proofing sputtering metal, photoetching corrosion, alloy are finished chip connects;

(g) making of pressure sensor chip is finished in scribing, lead-in wire, test.

9, by the method for making of the chip of high-temp pressure sensor of the SOI of the described Si-Si bonding of claim 8, the technology that it is characterized in that the thermocompression bonding of step c silicon silicon comprises: a) RCA standard cleaning, b) microwave plasma activation c) is cleaned d) the pre-bonding of hot pressing million, 200 ℃ to 500 ℃ of bonding temperatures, pressure 1～50bar, 5～100 minutes bonding duration, e) and high annealing reinforce, temperature is 900 ℃～1200 ℃, and the annealing duration is 1～4 hour.

10, by the method for making of the chip of high-temp pressure sensor of the SOI of the described Si-Si bonding of claim 8, it is characterized in that spreading back dopant ion concentration is 10 ¹⁷～10 ²⁰/ cm ²Diffusion back dopant ion concentration is greater than 10 ²⁰/ cm ²

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