CN100374838C - Monolithic silicon based SOI high-temperature low-drift pressure sensor - Google Patents
Monolithic silicon based SOI high-temperature low-drift pressure sensor Download PDFInfo
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Abstract
The present invention belongs to the technical field of force-sensitive sensors, more specifically a monolithic silicon based SOI high-temperature low-drift pressure sensor, wherein four force-sensitive sensors formed into a wheatstone bridge are made of SOI materials; by adopting the techniques of the internal compensation of an SOI resistor network and the external compensation of a partial internal resistor, a zero temperature drift falls to below 1X10-6 Vs/DEG C; by adopting a beam-film-island structure, the sensibility and the linearity of the present invention are improved; by adopting a polysilicon leading wire mixed with thick boron, the surface of which is covered by an aluminum leading wire, an internal leading wire of the present invention is formed to avoid the phenomenon of rupture cause by ' step ' when the aluminum leading wire is connected with the force-sensitive sensors; by adopting a thick boron automatically ending technology, a high-sensibility high-temperature low-drift pressure sensor is made. The present invention has the advantages of simple manufacture technology, nearly 100 percent of yield and low production cost and is suitable for large-scale production.
Description
Technical Field
The invention belongs to the technical field of sensing, and particularly relates to a monolithic silicon-based SOI high-temperature low-drift pressure sensor and a manufacturing method thereof.
Background
At present, because a common monocrystalline silicon pressure sensor adopts P-N junction isolation, the finished product rate is low due to P-N junction electric leakage, the output temperature drift is large, and the temperature can not reach more than 250 ℃. The pressure sensor made of polysilicon or other SOI technology can meet the requirement of working temperature as the working temperature can reach more than 300 ℃ due to the adoption of medium isolation, but the zero drift is too large to meet the requirement of practical application.
For process reasons, micromechanical silicon pressure sensors always have a certain offset voltage. This offset voltage is typically between 50mV and 100 mV. In principle, the offset voltage can be eliminated in parallel, in series or in parallel-series. But in practice the problem is not solved. The parallel or series compensation can realize zero setting at a certain temperature, but can cause a large additional temperature drift, and the additional temperature drift caused by the compensation can generally reach 1-2 multiplied by 10 -5 VS/DEG C, which is equivalent to that the additional temperature drift caused by the change of the working temperature of 200 ℃ is more than 50% of the full-scale output, and cannot be practical. The series-parallel compensation has strict requirements on the temperature coefficient of the resistor for compensation, and cannot be practically applied.
In order to meet the urgent need of technical transformation of diesel engines for vehicles and ships, the invention develops a micromechanical SOI high-temperature low-drift pressure sensor.
Disclosure of Invention
The invention aims to provide a high-temperature low-shift pressure sensor which has low requirement on manufacturing precision, small output zero temperature drift and high yield and is suitable for large-scale production and a manufacturing method thereof.
The high-temperature low-drift pressure sensor provided by the invention is a pressure sensor of a monolithic silicon-based SOI (silicon on insulator), the structure of the pressure sensor is shown in figure 1, and a chip of the pressure sensor comprises an N - Type or P - A type silicon substrate 1; covering both sides of the silicon substrate with insulating layers 2 (e.g., a silicon dioxide layer and a silicon nitride layer); a polysilicon layer (comprising a single crystal silicon layer made of SIMOXSOI and SmartCutSOI) is deposited on the surface of the insulating layer 2, four SOI polysilicon force sensitive resistors 3 and four internally compensated SOI polysilicon network resistors 4 are generated on the surface of the insulating layer by using an oxidation photoetching technology, and an SOI doped polysilicon internal lead 5 is connected with the resistors; the surface of the polycrystalline silicon inner lead 5 is covered with an aluminum lead 6; the force sensitive resistor 3 is manufactured on the central beam area 7 and the side beam area 8; the internal compensation network resistor 4 is manufactured on the surface of the frame 9 and is free from the action of force; the back of the chip is provided with a square opening 10, and two rectangular back islands 11 are manufactured in the opening; the depth of the back island is determined by the measuring range of the sensor, the larger the measuring range is, the thickness of the island shallow silicon film is thick, and the opposite island deep silicon film is thin; a boundary beam 8 is formed between the frame and the back island, and a central beam 7 is formed between the back island and the back island; on island and beamIs a silicon film 12.
In the present invention, the circuit design of the pressure sensor is shown in fig. 7. Wherein, the resistance R 1 、R 2 、R 3 And R 4 A bridge circuit resistor, namely an SOI polysilicon force sensitive resistor 3, and 4 small resistors r connected in series in the bridge circuit 1 、r 2 、r 3 And r 4 I.e. 4 SOI polysilicon network resistors 4 for internal compensation, there are 8 resistors and 8 pins in the circuit. In the force-sensitive resistor 3, the resistor R 1 And R 4 Made in the edge beam 8 of the chip, and having a resistor R 2 And R 3 Is made in the central beam 7 of the chip. When the front surface is subjected to positive pressure, R 1 And R 4 Increase of R 2 And R 3 And the voltage is reduced, so that the bridge consisting of the four force-sensitive resistors is out of balance, and an electric signal which is in direct proportion to the pressure intensity is generated.
In the invention, the depth of the silicon film region 12 on the front surface of the chip is 5-50 μm, and the specific depth depends on the range size.
The invention adopts SOI material on single silicon substrate to form low drift pressure sensor which can work at high temperature.
The manufacturing method of the monolithic silicon-based SOI high-temperature low-drift pressure sensor comprises the following specific steps:
(1) Taking a piece of double-side polished monocrystalline silicon with the thickness of 0.3-1 mm as a substrate, and adopting a conventional oxidation photoetching process to form double-side photoetching alignment marks on two sides of the substrate. Then, continuing to oxidize and photoetching a square opening on the back surface of the substrate, and corroding the silicon surface in the square opening by using TMAH corrosive liquid, wherein the depth is 5-10 mu m.
(2) Double-sided oxidation and deposition of a silicon nitride film to form an insulating layer 2 of SiO 2 And Si 3 N 4 And (3) compounding the film, and depositing a polycrystalline silicon film on the front surface or manufacturing a monocrystalline silicon film by using SIMOXSOI and SmartCutSOI technologies.
(3) Doping boron atoms into the polycrystalline silicon (or monocrystalline silicon) film by adopting an ion beam implantation technology or a thermal diffusion technology to form a P-type conducting layer. And then, forming a polysilicon (or monocrystalline silicon) force sensitive resistor, an internally compensated polysilicon (or monocrystalline silicon) network resistor and a polysilicon (or monocrystalline silicon) internal lead doped with concentrated boron for connection on the surface by photoetching and wet (or RIE dry) etching technologies.
(4) And photoetching a rectangular back island on the back surface and photoetching a lead hole on the front surface, reversely etching an aluminum film by evaporation to form an aluminum inner lead, forming a closed-loop Wheatstone bridge between the polycrystalline silicon (or monocrystalline silicon) force sensitive resistor and the internally compensated polycrystalline silicon (or monocrystalline silicon) network resistor, and leading eight pressure welding pins out of the frames on the two sides of the primary bottom. Four of which are used to adjust the offset voltage.
(5) And carrying out wet etching on the square opening area on the back of the substrate until the depth corresponding to the required measuring range.
The advantages of the invention can be summarized as the following points:
(1) By adopting the SOI structure, the force sensitive resistor and the compensation resistor in the network are electrically completely in an insulation isolation state, and the electric leakage phenomenon can not occur even at high temperature of hundreds of degrees.
(2) The force sensitive resistor and the compensation resistor in the network made of the same material have the same temperature coefficient, precise design and ingenious internal compensation, so that the offset voltage caused by the temperature drift of the sensor is only 0.75mv and is about 1-2% of the output amplitude of full quantity within the temperature change range of 160 ℃.
(3) The stress dispersion technology is adopted, so that the overload resistance of the silicon film is greatly improved.
(4) The polycrystalline silicon inner lead doped with the concentrated boron is manufactured under the aluminum lead, so that the yield of the sensor is greatly improved, and the high reliability of long-term high-temperature work is greatly improved.
(5) The sensor chip is designed by adopting a beam-film-island structure, so that the sensor obtains excellent characteristics of high sensitivity and low nonlinearity. The design that the orientation of the force-sensitive resistor is parallel to the beam region direction is adopted, and experiments prove that the sensitivity of the force-sensitive resistor can be greatly improved.
Drawings
FIG. 1 is a schematic view of the structure of the present invention.
FIG. 2 is a schematic process flow diagram.
Fig. 3 shows an output zero offset compensation circuit (parallel compensation).
Fig. 4 shows an output offset compensation circuit (series compensation).
Fig. 5 is an output zero offset compensation circuit (series-parallel compensation).
Fig. 6 shows an output zero offset compensation circuit (with a bridge resistor and a small zero setting resistor).
Fig. 7 is a pressure sensor circuit.
Fig. 8 is a graphical representation of the interface etch of the silicon film with the rim or back island.
Fig. 9 is a graphical representation of etching at the interface of the silicon film and the rim or back island (low radius of curvature change at the interface).
Reference numbers in fig. 1: (1) Is N - Type or P - A type silicon substrate, and (2) an insulating layer (SiO) 2 And Si 3 N 4 Composite film), (3) polysilicon (or monocrystalline silicon) force sensitive resistor, (4) inner compensated polysilicon (or monocrystalline silicon) network resistor, (5) inner lead of polysilicon (or monocrystalline silicon) doped with boron, (6) aluminum lead, (7) central beam region, (8) edge beam region, (9) chip frame, (10) square opening, (11) rectangular back island, and (12) silicon film region.
Detailed Description
The present invention uses SOI material to form a Wheatstone bridge circuit operating at high temperature.
Four bridge resistors of a Wheatstone bridge in a general diffused silicon piezoresistive pressure sensor form a P-type resistor area on an N-type (100) silicon single crystal by adopting a thermal diffusion or ion beam doping method, and the resistors are insulated in electrical property by back-to-back P-N junctions. Since the reverse current of the P-N junction is a function of temperature, when the pressure sensor operates at high temperature (> 100 ℃), the reverse current can seriously affect the normal operation of the sensor. Therefore, such sensors cannot be used at high temperatures. The adoption of silicon insulation medium to isolate bridge circuit resistance is the research hotspot of the international high temperature sensor at present. In recent years, a variety of SOI materials have been successfully developed, including polysilicon SOI, SIMOXSOI, smartCutSOI, and the like. The present invention uses these SOI materials to make practical high temperature pressure sensors and allows for certain mass production. Wherein the polysilicon SOI and SmartCutSOI materials are the current mature SOI materials. The polysilicon SOI material is prepared by depositing a 600nm polysilicon layer on a thermally grown oxide layer and a silicon nitride composite film by vapor deposition. The SmartCutSOI material is prepared by adopting an intelligent stripping method, the thickness of silicon at the top layer is 600nm, and the thickness of a buried oxide layer is 600nm.
The invention uses bridge resistors with high precision and high symmetry.
At present, most of the domestic and foreign diffused silicon pressure sensors adopt a wheatstone bridge structure form consisting of four bridge resistors with completely equal resistance values. Wherein, a power supply is added at two ends, and voltage signals with variable pressure resistance are output at two ends. When pressure is applied to the pressure-receiving surface, the resistance values of two of the bridges are increased, and the resistance values of the other two bridges are decreased, so that the bridge is unbalanced, and an electric signal which is in a linear relation with the pressure is generated at the output end. When no stress is applied to the pressure surface, the electrical signal at the output end is strictly zero. However, due to the limitation of the actual process, any domestic and foreign pressure sensor has a certain unregulated voltage. Can be eliminated by a method of connecting external resistors in series and parallel. However, since the resistance material of the external circuit is different from the semiconductor material constituting the bridge resistor, their temperature coefficients cannot be made uniform. Thus, when the zero adjustment is realized at a certain temperature, when the use temperature changes in a large range, the offset voltage which has been subjected to zero adjustment can cause a large additional temperature drift along with the change of the use temperature, which causes the measurement error of the system. The magnitude of the error is determined by the magnitude of the change in ambient temperature. The problem is therefore even more serious for sensors operating at high temperatures. In order to overcome the defect, a computer-assisted laser correction method is adopted abroad to directly correct the internal compensation zero-setting resistor on the crystal of the chip, but the method has expensive equipment investment and low production efficiency, so that the price of the device is high. The invention designs an internal compensation scheme of the SOI resistance network through theoretical analysis to replace an expensive compensation method, so that the additional temperature drift caused by zero point compensation is reduced by dozens of times.
The compensation method for the output zero point offset basically comprises a parallel compensation method and a series compensation method, which are respectively shown in fig. 3 and fig. 4. Taking the parallel compensation method shown in FIG. 3 as an example, R is the resistance of four bridge circuits 1 ＝R 3 ＝R 4 ＝R B And the resistor R at the lower left corner 2 Slightly larger, can be expressed as R 2 ＝R B (1 + β), where β is an order of magnitude of 10 -2 A small amount of (a). Then, as long as at R 2 Is connected in parallel with a resistor R with proper size P The bridge can be brought back into balance with zero output mismatch. Parallel resistor R P The conditions of (A) are as follows:
it can be shown that, to a first approximation,
for example, R B =5k Ω, β =0.02, then R is present P =250k Ω. The same is true for the series compensation shown in FIG. 2, but the series compensation resistor is a small resistor, R S ＝βR B . At β =0.02, R S ＝100Ω。
The above compensation method is always at a certain temperature t o The following procedures were carried out. Deviation t upon temperature change o Due to the temperature coefficient of resistance α of the bridge resistor b (generally about + 0.2%) and the temperature coefficient alpha of the external compensation resistor d The (near zero) difference, in turn, unbalances the bridge circuit and causes the offset voltage. Having a temperature coefficient of offset voltage of
The offset voltage at temperature t is:
for example at alpha b ＝+0.2％，α d ＝0，β＝0.04，V S TCO = -100 μ V/° C when the voltage is 5V. Offset voltage change V caused by 100 ℃ temperature change OS = 10mV, which is very large for practical applications.
In order to reduce the offset voltage temperature coefficient caused by compensation, a series-parallel compensation method can also be adopted. As shown in fig. 5. The method is theoretically feasible, requires more measurement or calculation in practical application, is inconvenient to use and has few practical applications.
The invention designs a convenient and practical method. In the compensation method, in addition to four bridge resistors, four small resistors for internal initial zero adjustment are connected in series in a loop during circuit design. When the zero-crossing is carried out, the initial adjustment is realized by utilizing four internal small resistors, so that the offset voltage is greatly reduced, namely the beta value is reduced by more than one order of magnitude, namely 10 -3 Of the order of (d). In this case, some of the legs of the wheatstone bridge are no longer a single resistor, but rather are often composed of a bridge resistor and one or more small compensation resistors connected in series. Then, a proper small resistor can be selected, and an external resistor is connected in parallel to the small resistor for fine zero adjustment, as shown in fig. 6. Therefore, the method can be a parallel zeroing method of partial resistance. The lower left arm in fig. 6 is formed of two resistors, one of which is a bridge resistor R B (1-. Alpha.), and the other is a small resistance R for adjustment B (α + β), where α and β are both on the order of a few thousandths. In practice, the other arms may be formed by bridge resistors and compensation resistors, but for simplicity the figures are drawn as a single resistor.
According to the parallel zero-setting method, an external resistor R is connected in parallel with a small resistor P And realizing zero setting. After zeroing, the temperature coefficient of the offset zero caused by further temperature change is as follows:
for a specific (α + β) value k, the maximum value of the zero-point offset temperature coefficient occurs under the condition of α = β, where the zero-point offset temperature coefficient is:
at α b -α d ＝2×10 -3 /° c, k = α + β =0.005 and V s When =5V, we have TCO max =3.1 μm. This value is only one-thirtieth of the value obtained with a simple parallel compensation method compared to 100 μm.
The circuit design of an actual pressure sensor is shown in fig. 7. Considering that the header has only 8 leads, the actual resistor design is divided into four bridge resistors (R) 1 、R 2 、R 3 And R 4 ) Four polysilicon small resistors (r) for internal compensation are additionally designed 1 、 r 2 、r 3 And r 4 ). Thus, there are a total of eight resistors and eight leadouts. Wherein, the four bridge circuit resistors are 40 square, the two power supply end adjusting resistors above are 0.9 square, and the power supply end for adjustment is V -1 ，V o And V +1 . The two adjusting resistors at the lower ground end are 0.3 square, and the ground end selected for adjustment is G -1 ，G o And G and +1 . Under the ideal process condition, the circuit is completely symmetrical, and the power supply end V is selected o And ground terminal G o The bridge output is zero. But the circuits cannot be completely paired for process reasonsWeighing, i.e. at optional power supply terminal V o And ground terminal G o The output of the bridge is not zero, typically in the range of 0 to 100 mV. Under the condition, if different power supply ends and different ground ends are selected according to the direction of the offset voltage to carry out initial adjustment on the offset voltage, the offset voltage can be greatly reduced. The offset voltage after initial adjustment of the circuit shown in fig. 7 can be reduced to below 5 mV. After the initial adjustment, a small resistor is properly selected for external parallel compensation.
Assuming that a small resistance of 0.3 square is chosen,
and is provided with (alpha) b -α d )＝2×10 -3 /℃，
Obtained according to formula (1)
I.e. TCO max ≈10 -6 V S 。
At V S TCO at 5V max = 4.7 μ V/° c. Namely, the offset voltage caused by offset compensation is delta V when the temperature changes 160 DEG C o ＝7.5×10 -5 V S ＝0.75mV。
Through the reasonable design of the SOI resistance network, as few leads as possible are added, and the combination of the resistance networks is used for high-precision internal compensation of zero points, so that 75mV of original offset can be covered with about 5mV of precision. And the resistance used for parallel compensation only accounts for about five dry parts of the bridge circuit resistance.
The layout design optimization scheme of the invention is as follows:
pressure sensors are fabricated on (100) silicon single crystals, and well-established techniques are available. The beam-film structure, the flat-film double-island structure, the beam-film-island structure and the like are successfully designed, but no mature design experience can be circulated when the pressure sensor is manufactured by using the SOI material. As the bridge resistor is a resistor strip made of polysilicon material in the beam region, the orientation of the resistor strip is different from that of a single crystal, and the theoretical analysis result shows that if the same layout design is adopted, the sensitivity of the resistor strip is only about one third of that of a silicon single crystal. Through repeated demonstration of theoretical analysis and process experiments, the orientation of the polysilicon bridge resistor should be parallel to the beam region, resulting in the structural design scheme shown in fig. 1. The result shows that the structural design scheme shown in figure 1 can be adopted to obtain the high-temperature pressure sensor made of the polysilicon SOI material with high sensitivity and low nonlinearity. Meanwhile, the high-temperature low-drift pressure sensor with excellent performance can be manufactured by the cooperation of the SOI resistance network which is reasonably designed with high precision and is used for zero point internal compensation.
The stress homogenizing technology of the high-overload pressure-resistant structure-chip of the invention is as follows:
pressure sensors used in diesel cars and diesel boats must have a high overload pressure resistant structure to prevent damage to surge pressure in the cylinders. The edge of the film area of the pressure sensor is designed and processed into a slowly-changing structure, stress concentration is realized in the force-sensitive resistance area, stress dispersion is realized in the non-force-sensitive resistance area, and the overload capacity of the sensor chip can be further improved.
In the beam-film-island structure, although there is a dual-island stopper structure, under high overload conditions, the silicon film will break first from the rim edge. This is because the conventional island film structure forms a silicon film and a back island from the back side of the silicon wafer by using a conventional masked anisotropic wet etching. The silicon film is a (100) crystal plane, and the side surfaces of the frame and the back big island are both (111) crystal planes, and the included angle is an acute angle of 54.74 degrees. According to the mechanical principle, there is a stress concentration effect in the corner region, and after the silicon film is pressed on the front surface or the back surface, the corner region has an extreme value of stress concentration, so that the fracture occurs from the corner region firstly. After the stress uniform structure is introduced, the corner area becomes a fillet area with certain circular curvature, so that the stress extreme value of the area is reduced.
The gradual change structure with a certain curvature and a half warp is formed at the boundary of the silicon film and the frame or the back island, which cannot be realized by adopting the common anisotropic wet etching because the etching results in a sharp corner region. The invention adopts the disclosed invention patent<Mask-maskless etching technique for multi-layer micromechanical structures>(patent No.: ZL97106555.1, international patent Main Classification No. C23F1/32, certificate No.: no. 62426). As shown in fig. 8, a pattern with a mask is first etched on the back surface of the chip near the frame or the back island, the mask is etched in KOH etchant, and after etching to a certain depth, siO is removed 2 Retention of Si 3 N 4 Then, maskless etching is performed. The side surface formed during the masked etching is the (111) crystal surface, and after the unmasked etching, the (111) surface is gradually replaced by the fast-etched (311) surface. After the (311) surface completely replaces the (111) surface, the junction between the (311) surface and the underlying (100) surface is etched, as shown in point a in fig. 9, and the angle between the two surfaces is no longer the same, but a circular arc surface with a low curvature radius appears. This is because some of the slow-etching surfaces are gradually exposed at the interface between the (311) and (100) surfaces, preventing further advancement of the fast-etching surface (311).
Assuming that there is a mask etch depth of h O The maskless etching depth is d, the ratio of the etching rates of the (311) surface and the (111) surfaceIs gamma 3 . For 40% KOH etching solution, due to γ 3 =1.71, the relationship between the advancing distance S and the maskless lithography depth d is:
in which theta is the angle between (311) plane and (111) plane, and is equal to 22.5 °
In principle, the value of the advancing distance S to the frame when the etch depth of the back island is d (311) can be precisely controlled by the above relation. According to the thickness a of the silicon film, the etching depth b of the front beam area and the etching depth h with a mask O And the back island limiting gap C is formed, when the total thickness of the silicon wafer is T, the distance S from the surface (311) to the frame is as follows:
S＝1.89[T-(a+b+c+h O )]
however, the results of the experiments suggest that the advance rate is changed because the slow-corrosion surface adjacent to the (311) surface is gradually exposed after the (311) surface completely replaces the (111) surface. Empirical data is that the designed distance of the masked etched trench edges from the rim or island is about 0.8 times the theoretical calculated (311) face advance.
In the invention, the SOI polycrystalline silicon inner lead doped with boron is manufactured under the aluminum lead, so that the reliability of the high-temperature pressure sensor can be greatly improved. Reliability in low drift refractory pressure sensors is a very prominent parameter. Generally, the inner leads are independent aluminum leads or tungsten-titanium-copper-aluminum multilayer composite wiring. Because the SOI polysilicon force sensitive resistor has a certain thickness, when the aluminum lead is led to the press-welding foot of the frame from the lead hole of the force sensitive resistor, a step is passed. When the polysilicon film is thicker and the aluminum layer is thinner, the aluminum lead is broken at the edge of the step, which results in failure of the device. Particularly, after the sensor works at high temperature and high pressure for a long time, the aluminum lead at the step position is easy to break, the sensor is ineffective, and the reliability is greatly reduced. The characteristic of the invention is that the force sensitive resistor and the compensation resistor in the network are made, and at the same time, the polysilicon inner lead doped with boron is made, so that they are connected into one body. And boron is fully doped from the lead holes of the force-sensitive resistor and the compensation resistor in the network to the pressure welding pins of the frame, so that the polysilicon lead becomes a low-resistance polysilicon lead, no step is added in the process, but the problem of fracture of the aluminum lead is ingeniously solved. When the aluminum wire is led out on its surface, there is no "step" of any unevenness. The high reliability of the high-temperature high-pressure sensor in the long-term working process is ensured.
The following are the specific fabrication steps of the pressure sensor of the present invention,
1. double-sided thermal growth of SiO 2 。
2. And carrying out double-sided photoetching to form front and back photoetching alignment marks, which is shown in a figure 2 (1).
3. Double-sided thermal growth of SiO 2 。
4. And photoetching a back large film and protecting the front side with glue.
5. The back large film was etched, see fig. 2 (2).
6. Double-sided thermal growth of SiO 2 。
7. Polysilicon is deposited, see fig. 2 (3).
8. The polysilicon layer is doped with boron impurities to form a certain sheet resistance.
9. And photoetching a resistance area on the front side, and photoetching a back island and a wafer dividing groove on the back side.
10. The polysilicon regions exposed on the front and back sides are etched, see fig. 2 (4).
11. And photoetching the lead hole area.
12. And doping high-concentration boron impurities into the lead hole region.
13. And (5) evaporating and plating an aluminum layer.
14. The aluminum wire was etched back, see fig. 2 (5).
15. And alloying the aluminum with the concentrated boron region in the lead hole to form ohmic contact.
16. And (5) carrying out wet etching on the back island and the slicing groove by using a special fixture until the required depth is reached. See fig. 2 (6).
Claims (4)
1. A monolithic silicon-based SOI high-temperature low-drift pressure sensor is characterized in that a chip comprises an N - Type or P - A silicon substrate (1) covered with insulating layers (2) on both sides; depositing a polycrystalline silicon layer on the surface of the insulating layer (2) or manufacturing a monocrystalline silicon layer, generating four SOI polycrystalline silicon force sensitive resistors (3) and four SOI polycrystalline silicon network resistors (4) for internal compensation on the surface of the insulating layer (2) by using an oxidation photoetching technology, and forming a polycrystalline silicon inner lead (5) doped with concentrated boron to be connected with the resistors; covering an aluminum lead (6) on the surface of the polycrystalline silicon inner lead (5); the SOI polysilicon force-sensitive resistor (3) is manufactured in the central beam (7) and the edge beam (8); the internal compensation polysilicon network resistor (4) is manufactured on the surface of the frame (9) and is free from the action of force; the back surface of the chip is provided with a square opening (10), two rectangular back islands (11) are manufactured in the opening, and the depth of each back island is determined by the measuring range of the sensor; a boundary beam (8) is arranged between the frame and the back island, and a central beam (7) is arranged between the back island and the back island; around the back island and the beam is a silicon film (12).
2. Pressure sensor according to claim 1, characterized in that the resistance R of the force sensitive resistor (3) 1 And R 4 Made in the edge beam (8) and having a resistance R 2 And R 3 Is manufactured in the central beam (7); when the front surface is subjected to positive pressure, R 1 And R 4 Increase of R 2 And R 3 And the voltage is reduced, so that the bridge consisting of the four force-sensitive resistors is out of balance, and an electric signal which is in direct proportion to the pressure intensity is generated.
3. Pressure sensor according to claim 1, characterized in that the silicon membrane region (12) of the front side of the chip has a depth of 5 μm to 50 μm.
4. A method for preparing a pressure sensor according to claim 1, characterized by comprising the steps of:
(1) Taking a piece of double-sided polished monocrystalline silicon with the thickness of 0.3-1 mm as a substrate (1), adopting a conventional oxidation photoetching process, firstly forming double-sided photoetching alignment marks on two sides of the substrate, then continuously oxidizing and photoetching a square opening (10) on the back side of the substrate, and corroding the silicon surface in the square opening by using TMAH corrosive liquid, wherein the depth is 5-10 mu m;
(2) Oxidizing the two sides and depositing a silicon nitride film to obtain an insulating layer (2), and then depositing a polycrystalline silicon film on the front side or manufacturing a monocrystalline silicon film by using SIMOX SOI and SmartCut SOI technologies;
(3) Doping boron atoms into the polycrystalline silicon or monocrystalline silicon film by adopting an ion beam injection technology or a thermal diffusion technology to form a P-type conducting layer, and forming a polycrystalline silicon or monocrystalline silicon force sensitive resistor (3), an internally compensated polycrystalline silicon or monocrystalline silicon network resistor (4) and a polycrystalline silicon or monocrystalline silicon internal lead (5) doped with concentrated boron for connection on the surface by adopting photoetching and wet method or RIE dry etching technology;
(4) Photoetching a rectangular back island (11) on the back surface, photoetching a lead hole on the front surface, and reversely etching an aluminum film by evaporation to form an aluminum inner lead (6), so that a closed-loop Wheatstone bridge is formed between a polycrystalline silicon or monocrystalline silicon force sensitive resistor (3) and an internally compensated polycrystalline silicon or monocrystalline silicon network resistor (4), and eight press welding pins are led out from frames (9) on two sides of a substrate, wherein four of the press welding pins are used for adjusting offset voltage;
(5) And carrying out wet etching on the square opening area on the back of the substrate until the depth corresponding to the required measuring range.
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| CN116429300B (en) * | 2023-06-12 | 2023-09-22 | 之江实验室 | Ultrahigh temperature pressure sensing chip and system based on monocrystalline silicon and micro-channel cooling |
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