CN101487747B - Absolute pressure sensor chip based on surface micromachining and manufacturing method - Google Patents

Abstract

The invention relates to an absolute pressure sensor chip based on surface micromachining and a manufacturing method thereof, which is characterized in that a silicon nitride film with low stress is used as a core structure layer of the pressure sensor chip, and a polysilicon film forms a force sensitive resistor strip. The low-stress silicon nitride film is designed into a long rectangle, according to the stress distribution of the film, the longitudinal piezoresistive effect of the polysilicon resistor strips is fully utilized, the tensile stress area on the film is utilized as much as possible, one part of the pair of resistor strips is placed outside the film, and the other two resistor strips are arranged at the center of the film. And opening the bent corner part of each resistor strip into a contact hole to deposit metal so as to conduct the metal. By adopting the surface micro-machining process compatible with the IC process, the absolute pressure sensor chip with high sensitivity, good stability and high precision and the measuring range of 1KPa to 1MPa can be manufactured.

Description

An absolute pressure sensor chip based on surface micromachining and its manufacturing method

technical field

The present invention relates to providing an absolute pressure sensor chip based on surface micromachining and its manufacturing method, more precisely, providing a low-stress silicon nitride film as a structural layer, and a polysilicon film forming a force-sensitive resistor and adopting surface micromachining An absolute pressure sensor chip and a manufacturing method thereof belong to the technical field of silicon micromechanical sensors.

Background technique

The piezoresistive pressure sensor appeared in the 1960s. The subsequent development of micromechanics and technology made the sensitive components miniaturized, the sensor production was mass-produced, and the cost was reduced. It established a dominant position in the field of pressure measurement. Compared with the traditional The film combined potentiometer type, force balance type, variable inductance type, variable capacitance type, metal strain gauge type and semiconductor strain gauge type sensors are much more advanced in technology, with high sensitivity, fast response speed, good reliability and high precision. A series of advantages such as high and low power consumption, easy miniaturization and integration. In the intelligent sensor characterized by the intervention of large-scale integrated circuit and computer software technology, because it can be made into a single-chip multi-functional composite sensitive element, it constitutes the basis of the intelligent sensor.

The traditional piezoresistive pressure sensor adopts the method of diffusion or ion implantation, and is doped to obtain four silicon strain resistors, which form a stress-sensitive detection mode of Wheatstone bridge on the front side of the single crystal silicon wafer. The distance between the resistor and the substrate is generally Form a pn junction isolation. In order to meet the needs of the test range, the back is generally thinned by potassium hydroxide corrosion, which is often called bulk micromachining. In order to make an absolute pressure sensor, two silicon wafers must be pre-processed, bonded at high temperature to form a vacuum cavity, then polished and thinned to the required thickness, and then processed by bulk micromachining on the front of the bonded body to form the required pressure sensor. The graph of silicon to form a detection circuit [Kovacs GTA, Maluf NI, Petersen KE. Bulk micromachining of silicon, P IEEE, 1998, 86 (8): 1536-1551].

However, the fabrication of the absolute pressure sensor chip based on bulk micromachining has the following disadvantages: first: the pn junction is isolated between the resistance after power-on and the silicon substrate, and when the temperature of the device is above 100°C, the pn junction The leakage current is so large that the device cannot work, so it cannot meet the use of stress tests in medium and high temperature environments. Second: In order to obtain a vacuum reference cavity for absolute pressure testing, two silicon wafers must be pre-processed, bonded at high temperature in a vacuum environment, and then polished and thinned. Therefore, the initial cost is high and the process is complicated. Third: For pressure sensors processed by bulk micromachining, anisotropic wet deep etching must be performed on the back of the silicon wafer to meet the requirements of low-range testing after thinning. The area is much smaller than surface micromachining. For example: for a standard four-inch silicon wafer with a thickness of 450 μm, in order to obtain a sensitive film of a pressure sensor of 100 × 100 μm, it needs to occupy an area of 800 × 800 μm silicon wafer for bulk micromachining; Only an area of 100×100 μm is required. [Lin LW, Yun W J. Design, optimization and fabrication of surface micromachined pressure sensors, Mechatronics, 1998, 8: 505-519, 1998]. Fourth: In order to meet the needs of packaging, the pressure sensor chip processed by bulk micromachining must also be electrostatically bonded with special glass (for example, the model is Pyrex 7740) to increase the packaging strength in order to meet the actual testing needs; while the surface micromachined The chip area of the processed pressure sensor can be very small, which is more compatible with the existing microelectronic packaging technology, such as Flip chip packaging, so that both the chip production cost and the later packaging cost are far less than Bulk micromachined pressure sensor chip. The most important thing is: the process of bulk micromachined pressure sensor is not compatible with the existing integrated circuit (IC) process, so the chip cannot be integrated with signal conditioning circuits, microprocessors, etc., and the surface micromachined pressure sensor The sensor chip process is compatible with the IC process, and can integrate signal conditioning circuits, microprocessors, etc., and can integrate other test functions with the same process, such as acceleration test, temperature test, etc., making the chip multifunctional , more in line with the development requirements of the current test system integration, miniaturization and low cost.

Contents of the invention

Based on the above-mentioned shortcomings in the fabrication of absolute pressure sensor chips based on bulk micromachining, the purpose of the present invention is to provide a pressure sensor chip based on surface micromachining and a fabrication method.

Specifically, the present invention adopts the low-stress silicon nitride (LS SiN) film as the core structure layer of the pressure sensor chip, and the polysilicon film is deposited on the LS SiN film, and is produced by dry etching by optimizing the structure and position. A force sensitive resistor strip is formed.

In order to improve the output sensitivity, the film region of the LS SiN film is designed as a long rectangle, as shown in Figure 1. According to the stress distribution diagram of the film area, as shown in Figure 2, make full use of the longitudinal piezoresistive effect of the polysilicon resistance strips, and try to use the part of the tensile stress on the LS SiN film, and place a part of a pair of resistance strips outside the LS SiN film , so that it not only ensures that four equivalent resistance strips constitute the Wheatstone test circuit, but also makes the two resistance strips distributed on the long side of the LS SiN film area, all of which are in the tensile stress area, and the tensile stress makes the resistance strips is stretched, the resistance becomes larger. The other two resistance strips are arranged in the center of the LS SiN membrane area, all of which are in the compressive stress area of the membrane area. The resistance strips are compressed and compressed, the length becomes shorter and the resistance becomes smaller. When it is deformed, the resistance of one pair of resistance strips becomes larger, and the resistance of the other pair of resistance strips becomes smaller. Under the excitation of voltage, there is a voltage difference at the output end, and the external pressure can be detected by detecting the output voltage. At the same time, because the stress at the bent corner of each resistance strip is opposite to the stress on the resistance strip, the signal output is reduced; in order to improve the output sensitivity, during manufacturing and processing, metal is deposited by opening a contact hole to guide it. Pass, such a smart design greatly improves the output sensitivity, as shown in Figures 3 and 4.

The pressure sensor chip for Tingge of the present invention is manufactured by surface micromachining compatible with the IC process. Specifically, ① first construct a sacrificial layer, and then use low-pressure chemical vapor deposition successively on the silicon wafer after high-temperature oxidation and nitriding Low-temperature silicon oxide (LTO) and phosphorus-doped low-temperature silicon oxide (PSG) are deposited by LPCVD method, and a sacrificial layer is formed after etching, in which PSG is used as an etching channel; Stressed silicon nitride (LS SiN) film is used as the core structure layer of the pressure sensor chip, on which a polysilicon film is deposited by LPCVD, polysilicon is doped by boron diffusion or boron ion implantation, and after high-temperature annealing activates the dopant, Corrosion forms four protruding polysilicon force-sensitive resistors, which are precisely arranged at the pressure-sensitive position of the LS SiN structure layer; the high-temperature activation condition of the dopant is 950-1200°C under the protection of nitrogen, annealing for 40-60 minutes; ③ forming an absolute The vacuum reference chamber for the pressure test, as shown in Figure 5(c), uses reactive ion etching (RIE) on the LS SiN structure layer to etch out the corrosion holes that release the sacrificial layer, and soaks the silicon wafer in concentrated hydrogen fluorine In the acid solution, the time is precisely controlled, and the sacrificial layer of LTO and PSG is completely etched away, so that its position becomes a cavity; then LPCVD is used to deposit tetraethoxysilane (Si(OC ₂ H ₅ ) 4) into silicon The silicon oxide (TEOS) generated by the decomposition of the source seals the corrosion hole. Since the air pressure in the furnace tube is very low (53.2Pa at 720°C) when LPCVD grows TEOS, the air pressure in the closed cavity is less than 15Pa at room temperature such as 25°C. Vacuum reference cavity close to the absolute pressure sensor; ④ Aluminum wiring, deposit thin LS SiN in LPCVD as an insulating layer on the polysilicon resistor, open the contact hole, sputter the metal layer, and complete the metal lead by alloying after corrosion; ⑤ Final dicing, placement and testing, packaging.

In summary, the present invention provides an absolute pressure sensor chip based on surface micromachining and its manufacturing method, which can provide high-sensitivity, good stability, and high-precision absolute pressure sensor chip. Appropriately modifying the size, an absolute pressure sensor chip with a range from 1KPa to 1MPa can be obtained. The manufacturing method is compatible with the IC process, and can be integrated with signal conditioning circuits, microprocessors, and other test functions, and can be produced in large quantities at low cost. , which is characterized in that low-stress silicon nitride films deposited by LPCVD are used as structural films, and polysilicon resistors deposited by LPCVD are used as force sensitive resistors to form a Wheatstone detection circuit, which avoids the pressure sensor chip resistors and substrates processed by bulk micromachining. The leakage current phenomenon caused by the bottom pn junction isolation makes the sensor performance more stable, higher precision, lower cost and easier integration.

Description of drawings

Figure 1 shows a schematic diagram of the structure of a long rectangular film (a) a top view, (b) a part of the structure of a long rectangular film

Figure 2 shows the stress distribution diagram of a long rectangular film

Figure 3 is the layout of the designed pressure sensor chip resistance

Figure 4 is the stress change of the designed pressure sensor chip resistance

Figure 5 shows the flow chart of the absolute pressure sensor chip fabrication process based on surface micromachining

Photo of the pressure sensor chip produced in Figure 6

In the figure, 1 represents the metal lead; 2 represents the bent part of the polysilicon resistor; 3 represents the long rectangular low-stress silicon nitride film; 4 represents the polysilicon resistance strip; 5 represents the original silicon chip; 6 represents the high temperature silicon oxide; 7 represents the first 8 represents phosphorus-doped low-temperature silicon oxide; 9 represents low-temperature silicon oxide; 10 represents the second layer of low-stress silicon nitride; 11 represents polysilicon resistance strips; 12 represents the vacuum chamber; Stressed silicon nitride; 14 represents the metal connection; 15 represents the silicon oxide (TEOS) formed by the decomposition of tetraethoxysilane (Si(OC ₂ H ₅ ) 4 ) as the silicon source; 16 represents the corrosion caused by the sacrificial layer at the displacement The hole is blocked by TEOS; 17 represents the bent corner of the resistor, which is connected with metal; 18 represents the polysilicon resistor; 19 represents the low-stress silicon nitride film.

Detailed ways

The substantive features and remarkable progress of the present invention will be further described below through specific implementation, but the present invention is by no means limited to the described embodiments.

Absolute pressure sensor chip based on surface micromachining with a range of 450KPa and its manufacturing method: the thickness h of the designed LS SiN structure layer is 1.2 μm, the long side 2b of the long rectangular membrane area is 360 μm, and the short side 2a is 48 μm, as shown in Figure 1 (a) shown. The thickness of the polysilicon resistor is 0.4 μm, the resistance value is 5000 ohms, and the thickness of the sacrificial layer is 2 μm.

The specific implementation steps are:

1. Build a sacrificial layer,

As shown in Figure 5(a), since the surface microcomputer machining is only processed on one side, the initial silicon wafer can be a double-polished or single-polished silicon wafer, and there is no requirement for thickness and crystal orientation. After standard cleaning, rinse with deionized water for 10-20 minutes, dehydrate in a spin dryer, and dry.

Thermally oxidize (Oxide) 0.1-1 μm in an oxidation furnace; then enter a low-pressure vapor-phase chemical deposition (LPCVD) furnace to deposit low-stress silicon nitride (LS SiN) 0.1-1 μm, and then deposit low-temperature silicon oxide ( LTO) 1.0 ~ 2.0 μm. The first photoetching of LTO, and then corroding LTO with buffered hydrofluoric acid (BOE, the volume ratio of ammonia water and hydrofluoric acid is 7:1) at 38°C, and then degumming in concentrated sulfuric acid at 120°C, and rinsing with deionized water Afterwards, perform standard cleaning, rinse with deionized water for 10 to 20 minutes, and then enter the LPCVD furnace to grow phosphorous-doped low-temperature silicon oxide (PSG) of 0.1 to 1 μm after drying. Define the shape of PSG by photolithography for the second time, corrode PSG in BOE solution at 38°C, remove the glue in concentrated sulfuric acid at 120°C, rinse with deionized water, and then standard clean, rinse with deionized water for 10 to 20 minutes ,.

2. Definition of polysilicon force sensitive resistor

As shown in Figure 5(b), the silicon wafer after cleaning and drying is put into the LPCVD furnace to grow LS SiN1.2μm, and then the polysilicon film (Poly) is deposited in the LPCVD furnace with a thickness of 0.4μm, which is diffused by boron or Boron ion implantation makes the polysilicon film doped, in order to activate impurities and eliminate the defects caused by diffusion or implantation, and make the impurities evenly distributed, the silicon wafer is annealed at a high temperature of 950°C to 1200°C under the protection of nitrogen for 40 minutes to 60 minutes. The third photolithography of the shape of the poly silicon force sensitive resistor strip, using dry inductively coupled plasma etching ICP to leave the poly silicon force sensitive resistor strip at the required position on the LS SiN, and then in concentrated sulfuric acid at 120 °C After removing glue, rinse with deionized water, and then rinse with deionized water for 10 to 20 minutes after standard cleaning.

3. Form a vacuum reference chamber for absolute pressure testing

As shown in Fig. 5(c), the silicon wafer after drying was lithographically defined for the fourth time, and the LS SiN was etched by active ion etching RIE, and then the sacrificial layer was etched in 40% HF for 5 minutes to 30 minutes. Rinse with deionized water for 10 to 20 minutes, soak in deionized water for 10 to 20 hours, and then rinse with deionized water for 10 to 20 minutes after standard cleaning. After drying, enter the LPCVD furnace to grow TEOS decomposed from tetraethoxysilane (Si(OC ₂ H ₅ ) 4 ) as the silicon source to seal the corrosion holes. The fifth photolithography defines the TEOS plug. The TEOS is etched by BOE at 38°C, and then rinsed with deionized water for 10 to 20 minutes. After standard cleaning, rinse with deionized water for 10 to 20 minutes. drying.

4. Aluminum wiring

As shown in Figure 5(d), put the dried sheet into the LPCVD furnace to grow LS SiN 0.1μm~0.2μm insulating layer. The sixth photolithography defines the contact hole, the LS SiN is etched by RIE, and the aluminum Al film is sputtered after 0.6 μm to 1.2 μm. The seventh photolithography of Al,

Al is etched in the Al etching solution, and then rinsed with deionized water for 10 to 20 minutes. drying. Alloying in an alloy furnace at a high temperature of 450°C under nitrogen protection;

5. Dicing, patching and testing. The photo of the chip after dicing is shown in Figure 6.

Claims (4)

1. A kind of absolute pressure sensor chip based on surface micromachining, it is characterized in that adopting by the silicon nitride film of low stress as the structural layer of pressure sensor chip, polysilicon film is deposited on the silicon nitride film of low stress; Polysilicon Thin films form force-sensitive resistance strips; four equivalent resistance strips form a Wheatstone detection circuit, and two of the four equal resistance strips are distributed on the long side of the long rectangular film area and are in the tensile stress area. The two resistance strips are arranged in the center of the film area, in the compressive stress area of the film area; the film area of the low-stress silicon nitride film is designed as a long rectangle, and the longitudinal piezoresistive effect of the polysilicon resistance strips is used to connect a pair of resistance strips. A part of it is placed on the outside of the film. 2. make the method for the absolute pressure sensor chip based on surface micromachining as claimed in claim 1, it is characterized in that being compatible with IC process, adopt the low stress silicon nitride film of LPCVD deposition as the structure layer of chip, on top Deposit polysilicon film by LPCVD, boron diffusion or ion implantation, activate impurities after high-temperature annealing, form force-sensitive resistance strips at sensitive positions of low-stress silicon nitride after dry etching, and then form Wheatstone detection circuit by metal leads; specifically Include the following steps: ① Constructing a sacrificial layer On the silicon wafer after high temperature oxidation and nitriding, LTO and PSG are successively deposited by LPCVD method, and the sacrificial layer is formed after etching, in which PSG is used as the etching channel; ②Then define the polysilicon force sensitive resistance bar, use LPCVD to deposit LS SiN film as the structural layer of the pressure sensor chip, use LPCVD to deposit polysilicon film on the LS SiN film, make the polysilicon doped by boron diffusion or boron ion implantation, high temperature annealing After the dopant is activated, four protruding polysilicon force-sensitive resistance strips are formed by etching, which are arranged at the pressure-sensitive position of the LS SiN structure layer; ③ Form a vacuum reference chamber for absolute pressure testing, use reactive ion etching on the LS SiN structure layer to etch out the corrosion holes that release the sacrificial layer, soak the silicon wafer in concentrated hydrofluoric acid solution, control the time, and completely corrode Remove the sacrificial layer of LTO and PSG to make its position into a cavity; then use LPCVD to deposit silicon oxide decomposed from tetraethoxysilane as the silicon source to seal the etching hole. At 25°C, the air pressure in the sealed cavity is close to Vacuum reference chamber for absolute pressure sensors; ④ Aluminum wiring, use LPCVD to deposit thin LS SiN as an insulating layer on the force sensitive resistor strip of polysilicon, after opening the contact hole, sputter the metal layer, and complete the metal lead by alloying after corrosion; ⑤ Final dicing, placement and testing, packaging; The LPCVD is low-pressure chemical vapor deposition, LTO is low-temperature silicon oxide, PGS is phosphorus-doped low-temperature silicon oxide, and LS SiN is low-stress silicon nitride. 3. according to the manufacture method of the absolute pressure sensor chip based on surface micromachining according to claim 2, it is characterized in that 1. Build a sacrificial layer a) Clean the initial double-polished or single-polished silicon wafers, rinse them with deionized water for 10 to 20 minutes, dehydrate and dry them with a spin dryer; b) Place the silicon wafer treated in step a into an oxidation furnace for thermal oxidation; then enter the LPCVD furnace to deposit LS SiN, and then deposit LTO in the LPCVD furnace; c) The first photoetching of LTO, and then corroding the LTO in a buffered BOE solution at 38°C, and then degumming in concentrated sulfuric acid at 120°C, rinsed with deionized water, and rinsed with deionized water for 10~ 20 minutes, after drying, enter the LPCVD furnace to grow PSG; d) Define the shape of PSG by photolithography for the second time, corrode PSG in buffered BOE solution at 38°C, remove the glue in concentrated sulfuric acid at 120°C, rinse with deionized water, then standard clean and rinse with deionized water 10-20 minutes; 2. Define polysilicon force sensitive resistor strip a) Put the silicon wafer cleaned and dried in step 1 into an LPCVD furnace to grow LS SiN, then deposit a polysilicon film in an LPCVD furnace, and dope and activate the polysilicon film by boron diffusion or boron ion implantation; b) The shape of the polysilicon resistance strip is formed by the third photolithography, which is to leave a polysilicon force sensitive resistance strip at the required position on the LS SiN by using a dry inductively coupled plasma etching process, and then remove it in concentrated sulfuric acid at 120°C. Glue, rinse with deionized water, after cleaning, rinse with deionized water for 10 to 20 minutes; 3. Form a vacuum reference chamber for absolute pressure testing a) Define the etching hole by photolithography for the fourth time on the silicon wafer dried in step 2, etch LS SiN by reactive ion etching method, and then etch the sacrificial layer in 40% HF by volume concentration for 5 minutes to 30 minutes , rinse with deionized water for 10 to 20 minutes; and soak in deionized water for 10 to 20 hours, after cleaning, rinse with deionized water for 10 to 20 minutes; b) After drying, enter the LPCVD furnace to grow silicon oxide decomposed by tetraethoxysilane as the silicon source to seal the corrosion hole; c) The fifth photolithography defines the silicon oxide plug decomposed by the silicon source, etch the silicon oxide decomposed by the silicon source in a buffered BOE solution at 38°C, and finally rinse it with deionized water for 10 to 20 minutes. Rinse with water for 10-20 minutes, dry; form a vacuum reference cavity close to the absolute pressure sensor; 4. Aluminum wiring a) Put the slice dried in step 3 into the LPCVD furnace to grow the LS SiN insulating layer; b) The sixth photolithography defines the contact hole, the LS SiN is etched by reactive ion etching, and then the aluminum Al film is sputtered. Rinse with water for 10-20 minutes, dry; then alloy in an alloy furnace at 450°C under nitrogen protection; The buffered BOE solution is a solution of ammonia water and hydrofluoric acid with a volume ratio of 7:1. 4. by the manufacture method of the absolute pressure sensor chip based on surface micromachining according to claim 2 or 3, it is characterized in that the air pressure of the vacuum reference chamber close to absolute pressure in the vacuum reference chamber that forms absolute pressure test in step 3 is less than 15 Pa.

Images