Temperature drift self-compensating SOI pressure sensor
The invention is a divisional application of patent application with the application number of 201110375349.X and the name of the invention of 'temperature drift self-compensation SOI pressure sensor' which is provided on 23.11.2011.
Technical Field
The invention relates to a pressure sensor, in particular to a temperature drift self-compensation SOI pressure sensor, belonging to the technical field of MEMS sensors.
Background
The pressure sensor manufactured by using the piezoresistive effect of silicon is characterized in that a group of diffusion resistors with almost equal resistance values are formed on the surface of a silicon wafer by adopting the ion implantation and diffusion processes in the integrated circuit process, and the resistors are interconnected by metal to form a Wheatstone bridge. When the elastic sensitive diaphragm is deformed under the action of external pressure to generate stress, the bridge circuit resistance on the elastic sensitive diaphragm correspondingly changes, and the sensor outputs an electric signal proportional to the external pressure, so that the pressure is measured.
The piezoresistive micro pressure sensor is the earliest researched and industrialized MEMS (micro electro mechanical system) technical product, most piezoresistive pressure sensors adopt a PN junction isolation mode, and the structure has the defect of overlarge temperature drift; in addition, when the working temperature is higher than 125 ℃, the leakage of the PN junction is rapidly increased, so that the sensor fails. The high temperature pressure sensor is a pressure sensor which can normally work in an environment higher than 125 ℃, has been highly regarded in the pressure sensor by virtue of excellent high temperature working capacity, is one of important fields of sensor research, and is one of high-tech technologies which are mastered by governments in various countries. The high-temperature pressure sensor plays an important role in petroleum, chemical industry, metallurgy, industrial process control, weapon industry and even food industry, the high-temperature pressure sensor can not be used for detection under a plurality of environmental conditions, and particularly the high-temperature pressure sensor in a weapon system is indispensable to a power system.
In addition, since the resistor is a temperature sensitive device, the zero point and the sensitivity of the pressure sensor before compensation change with the change of temperature, which greatly affects the accuracy of the sensor, and the temperature drift compensation is usually performed on the pressure sensor. The conventional pressure sensor compensation is divided into hardware compensation and software compensation, wherein the hardware compensation needs a large amount of manpower, the temperature drift test before compensation is carried out on each chip within the use temperature range, then different devices such as diodes, thermistors and the like are selected for compensation, the consistency is poor, and the workload is large; software compensation cost is high, most of domestic ASIC chips are imported for compensation at present, price is high, and development of domestic sensor industry is limited.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and provides the temperature drift self-compensation SOI pressure sensor which has the advantages of compact structure, realization of temperature drift self-compensation, cost reduction, high stability, wide application range, safety and reliability, is suitable for batch production and greatly improves the working temperature range and has good consistency.
According to the technical scheme provided by the invention, the temperature drift self-compensation SOI pressure sensor comprises an SOI substrate, wherein a bridge resistor which is used for configuring a Wheatstone bridge is arranged on the SOI substrate, a compensation resistor which is used for carrying out temperature compensation on the Wheatstone bridge is arranged on the surface of the SOI substrate, which is correspondingly provided with the bridge resistor, and interconnected leads which are electrically connected are arranged on the compensation resistor and the bridge resistor; the bridge resistor and the compensation resistor are isolated by an insulating isolation layer and a passivation layer, the insulating isolation layer covers the SOI substrate, and the passivation layer covers the insulating isolation layer; and etching the SOI substrate corresponding to the other side where the bridge resistor is arranged to form a pressure chamber and a pressure sensitive film, which are located right below the bridge resistor.
The SOI substrate comprises a substrate, wherein an insulating medium layer is deposited on the substrate, and a conductive material is deposited on the insulating medium layer to form the SOI substrate.
And a glass sheet is bonded on one side of the SOI substrate corresponding to the side for forming the pressure cavity, the glass sheet is correspondingly matched with the SOI substrate and the pressure cavity, and the glass sheet seals the pressure cavity on the SOI substrate.
The glass sheet is provided with a glass hole penetrating through the glass sheet, and the glass hole is communicated with the pressure cavity. The compensation resistor comprises a constant voltage power supply compensation resistor or a constant current power supply compensation resistor.
The insulating medium layer is made of silicon dioxide, silicon nitride or the composition of the silicon dioxide and the silicon nitride. The insulating isolation layer includes a silicon nitride layer.
The passivation layer includes a silicon nitride layer. The material of the interconnection lead comprises aluminum or gold. The conductive material is polysilicon or nano-silicon, and is deposited on the insulating medium layer through LPCVD or PECVD.
The invention has the advantages that: the substrate of the pressure sensor adopts an SOI substrate, so that the stability and the working temperature range of the sensor are greatly improved, and the pressure sensor can be applied to various industrial control fields, particularly high-temperature environments; for the pressure sensor, the temperature drift is a problem which is not easy to solve, and the temperature self-compensation of the pressure sensor is realized by arranging a constant voltage power supply compensation resistor and a constant current power supply compensation resistor on an SOI substrate, and selecting the constant voltage power supply compensation resistor or the constant current power supply compensation resistor to be connected with a Wheatstone bridge configured by bridge resistors according to the requirement; after self-compensation, the zero temperature drift and the sensitivity temperature drift can be effectively controlled, and the requirements of consumer electronics and industrial control can be met; the cost is extremely low due to the integration process; the semiconductor process is adopted, the method is suitable for batch production, the product consistency is good, the sensitivity is high, and the method can be applied to various environments such as micro-pressure, low-pressure, medium-pressure and high-pressure environments.
Drawings
FIG. 1 is a schematic structural diagram of the present invention.
Fig. 2 to 7 are sectional views of the process steps of the present invention, wherein:
fig. 2 is a cross-sectional view of forming an SOI substrate.
FIG. 3 is a cross-sectional view of the bridge resistor and the compensation resistor after they are formed.
Fig. 4 is a cross-sectional view after depositing an insulating spacer and etching a wire hole.
Fig. 5 is a cross-sectional view after forming interconnect leads.
Fig. 6 is a cross-sectional view after forming a passivation layer.
Fig. 7 is a sectional view after forming a pressure sensitive membrane.
Fig. 8 is a cross-sectional view of a bonded glass sheet after forming an absolute pressure sensor.
Fig. 9 is a cross-sectional view of the gauge pressure sensor after formation.
Fig. 10 is a top view of the invention after encapsulation.
Description of reference numerals: 1-substrate, 2-insulating medium layer, 3-bridge circuit resistor, 4-constant voltage power supply compensation resistor, 5-constant current power supply compensation resistor, 6-insulating isolation layer, 7-interconnection lead, 8-passivation layer, 9-pressure cavity, 10-pressure sensitive film, 11-glass sheet and 12-glass hole.
Detailed Description
The invention is further illustrated by the following specific figures and examples.
As shown in fig. 1: in order to improve the measurement accuracy and the temperature adaptive range of the pressure sensor, the pressure sensor comprises an SOI substrate, conductive materials are deposited on the SOI substrate, a bridge resistor 3 which is used for being configured into a Wheatstone bridge is obtained, in order to reduce the temperature drift influence, a compensation resistor is arranged on the SOI substrate and comprises a constant voltage power supply compensation resistor 4 or a constant current power supply compensation resistor 5, the constant voltage power supply compensation resistor 4 and the constant current power supply compensation resistor 5 are arranged on the SOI substrate, the constant voltage power supply compensation resistor 4 or the constant current power supply compensation resistor 5 is selected according to needs, and the influence of temperature on output detection signals of the Wheatstone bridge can be reduced. Four bridge resistors 3 are provided on the SOI substrate, and the four bridge resistors 3 form respective arms of a wheatstone bridge.
In order to lead out the bridge resistor 3, the constant voltage power supply compensation resistor 4 and the constant current power supply compensation resistor 5, the bridge resistor 3, the constant voltage power supply compensation resistor 4 and the constant current power supply compensation resistor 5 are provided with interconnection leads 7 which are electrically connected. Meanwhile, the bridge resistor 3, the constant voltage power supply compensation resistor 4 and the constant current power supply compensation resistor 5 are isolated by an insulating isolation layer 6 and a passivation layer 8, and the insulating isolation layer 6 covers the SOI substrate and covers the bridge resistor 3, the constant voltage power supply compensation resistor 4 and the constant current power supply compensation resistor 5 correspondingly; a passivation layer 8 is deposited overlying the insulating spacer layer 6. The SOI substrate is provided with a pressure cavity 9 corresponding to the other side provided with the bridge resistor 3, in order to form the pressure cavity 9, the process of wet etching or combination of dry etching and wet etching is carried out on the SOI substrate, the pressure cavity 9 extends inwards from the surface of the SOI substrate, the distance of the inward extension of the pressure cavity 9 is less than the thickness of the SOI substrate, so as to form a pressure sensitive film 10, and the thickness of the pressure sensitive film 10 is determined by parameters such as the sensitivity of a pressure sensor. The pressure chamber 9 and the pressure-sensitive membrane 10 are located directly below the bridge resistor 3.
As shown in fig. 8 and 9: according to different requirements, a glass sheet 11 is bonded on one side of the SOI substrate, which correspondingly forms the pressure cavity 9, and the glass sheet 11 is correspondingly matched with the SOI substrate and the pressure cavity 9; thereby enabling the formation of gauge pressure sensors and absolute pressure sensors. When used as a gauge pressure sensor, the glass sheet 11 is perforated with glass holes 12, and the glass holes 12 communicate with the pressure chamber 9. When acting as an absolute pressure sensor, the glass plate 11 closes the pressure chamber 9.
As shown in fig. 2 to 7: in order to obtain the pressure sensor with the structure, the following process steps can be carried out: (1) determining the thickness, doping type and resistivity of a substrate material, the sizes of a chip and a sensitive film and the like according to the parameter requirements of the sensor, determining a linear stress region on the pressure sensitive film 10 through theoretical calculation, and arranging bridge circuit resistance, compensation resistance and metal interconnection; because different power supply modes and temperature drift compensation modes are different, a compensation network for constant voltage power supply and a compensation network for constant current power supply can be integrated on the same chip during design to form a universal chip, and a user can connect the chip according to the needs of the user; finally, completing the design and manufacturing the photoetching plate;
(2) as shown in fig. 2: an insulating medium layer 2 is deposited on the upper surface of the substrate 1, and the insulating medium layer 2 can be silicon dioxide, silicon nitride or a compound of silicon dioxide and silicon nitride and is used as an insulating isolation medium layer of an SOI structure;
(3) depositing polysilicon or growing nano-silicon on the insulating dielectric layer 2 by an LPCVD (low pressure Chemical Vapor deposition) or pecvd (plasma Enhanced Chemical Vapor deposition) deposition technique to form an SOI substrate; because the characteristics of the polycrystalline silicon and the nano silicon are different, the performances of the produced sensors are different;
(4) because the bridge resistor 3 and the compensation resistor have different parameters, the polysilicon or the nano-silicon at the top layer needs to be doped and annealed by adopting different ion implantation concentrations, and the polysilicon or the nano-silicon is etched to form the bridge resistor 3, the constant voltage power supply compensation resistor 4 and the constant current power supply compensation resistor 5 respectively, wherein the parameters of the bridge resistor 3, the constant voltage power supply compensation resistor 4 and the constant current power supply compensation resistor 5 are determined by the theoretical design of the first step and are influenced by the processes of implantation concentration, etching precision and the like, and finally the performances of zero point output, temperature drift and the like of the sensor are influenced; as shown in fig. 3:
(5) depositing an insulating isolation layer 6, as shown in fig. 4, as a metalized isolation layer, wherein the insulating isolation layer 6 may be silicon nitride; photoetching a lead hole and injecting ions at the corresponding end parts of the bridge resistor 3, the constant voltage power supply compensation resistor 4 and the constant current power supply compensation resistor 5 to form an ohmic contact concentrated boron region; by depositing metal interconnect wires 7 within the wire holes, as shown in fig. 5; the metal of the interconnection lead 7 can be aluminum or gold (including multilayer metal), and for a high-temperature pressure sensor chip, gold is used as the lead, the usable temperature range is wider, the maximum usable temperature range can be 350 ℃, and aluminum can be usually used only in the temperature range within 180 ℃;
(6) back-etching the lead and the pressure welding block, and carrying out alloying treatment, as shown in figure 5;
(7) as shown in fig. 6, depositing a passivation layer 8, wherein the passivation layer 8 may be made of silicon nitride and used as a passivation layer of the sensor, and depositing a conductive material to be used as a shielding layer, and etching the passivation layer and the shielding layer to expose a bonding area, i.e., an area corresponding to the interconnection lead 7;
(8) as shown in fig. 7, the back surface of the SOI substrate is etched back, and a pressure chamber 9 with a certain depth is etched by adopting a wet etching process or a dry-wet etching process, wherein a substrate material with a certain thickness is reserved on the pressure chamber 9 to form a pressure sensitive membrane 10 of the sensor, and the thickness of the pressure sensitive membrane 10 is determined by parameters such as the sensitivity of the sensor;
(9) determining whether the glass sheet 11 needs to be bonded according to different applications, wherein the glass sheet 11 is divided into a perforated glass sheet and a non-perforated glass sheet, and a gauge pressure sensor and an absolute pressure sensor can be manufactured respectively; as shown in fig. 8 and 9, absolute pressure product and gauge pressure product, 11 is a glass sheet used in the silicon-glass bonding process, and 12 is a glass hole of glass perforated in the gauge pressure product;
(10) scribing, packaging and testing to finish the preparation of the pressure sensor.
As shown in fig. 1 and 10: when in use, the bridge resistors 3 are respectively connected with corresponding external terminals through corresponding electrodes 7; under zero pressure, theoretically, the resistance values of 4 bridge arm resistors should be the same, the bridge is in a balanced state, and the output of the pressure sensor is 0; when pressure acts on the pressure sensitive film 10, the pressure can cause deformation of the pressure sensitive film 10, after the pressure sensitive film 10 is correspondingly deformed, the impedance value of the bridge circuit resistor 3 can be correspondingly changed, the bridge circuit is not balanced any more, the sensitivity of the pressure sensor can be obtained by detecting an output signal corresponding to an external terminal of the pressure sensor, and detection of an external pressure signal can be realized. The constant-voltage power supply compensation resistor 4 or the constant-current power supply compensation resistor 5 is selected according to requirements and connected with a Wheatstone bridge configured by the bridge resistors 3 through an interconnection lead 7, the constant-current power supply compensation resistor 5 is connected in parallel for compensation, and the constant-voltage power supply compensation resistor 4 is connected in series for compensation. When the temperature changes, the temperature compensation is realized through the voltage division of the constant voltage power supply compensation resistor 4 or the shunt of the constant current power supply compensation resistor 5, and the output precision of the pressure sensor is improved.
The substrate of the pressure sensor adopts the SOI substrate, so that the stability and the working temperature range of the sensor are greatly improved, and the pressure sensor can be applied to various industrial control fields, particularly high-temperature environments; for the pressure sensor, the temperature drift is a problem which is not easy to solve, and the temperature self-compensation of the pressure sensor is realized by arranging a constant voltage power supply compensation resistor 4 and a constant current power supply compensation resistor 5 on an SOI substrate, and selecting the constant voltage power supply compensation resistor 4 or the constant current power supply compensation resistor 5 to be connected with a Wheatstone bridge configured by bridge resistors 3 according to the requirement; after self-compensation, the zero temperature drift and the sensitivity temperature drift can be effectively controlled, and the requirements of consumer electronics and industrial control can be met; the cost is extremely low due to the integration process; the semiconductor process is adopted, the method is suitable for batch production, the product consistency is good, the sensitivity is high, and the method can be applied to various environments such as micro-pressure, low-pressure, medium-pressure and high-pressure environments.