CN112067079A - Array type automobile oil tank liquid level measurement pressure sensor and preparation method thereof - Google Patents

Abstract

The invention discloses an array type pressure sensor for measuring the liquid level of an automobile oil tank and a preparation method thereof, belonging to the technical field of pressure sensors. And photoetching and etching the back surface to obtain a silicon cup window, and corroding to obtain the strain film. The invention adopts the mode of combining femtosecond laser optical fiber doping and femtosecond laser annealing, has simple operation, high doping efficiency and selectivity to carry out laser processing on the surface of a wafer, can avoid the problems of substrate electrical parameter deterioration, injected impurity redistribution and injected pattern distortion caused by thermal annealing, and adopts an array structure as a whole so as to be convenient for detecting different heights of a liquid level.

Description

An array type automobile fuel tank liquid level measuring pressure sensor and preparation method thereof

technical field

The invention belongs to the technical field of pressure sensors, in particular to an array type pressure sensor for measuring the liquid level of an automobile fuel tank and a preparation method thereof.

Background technique

During the use of the car, it is very necessary to measure the fuel tank level. While ensuring that the driver knows the fuel level of the fuel tank in real time, it can prevent various accidents caused by the leakage of the automobile fuel tank. The early fuel tank level measurement mostly used mechanical principles. However, with the development of automotive electronics, the current measurement of fuel volume is based on changes in electrical or non-electrical physical parameters caused by changes in liquid level.

At present, the liquid level measurement methods mainly include optical fiber sensing technology, guided wave radar liquid level gauge, capacitive vacuum pressure sensor, piezoresistive pressure sensor, etc. Among them, silicon piezoresistive pressure sensors are the most widely used because of their high precision, wide measurement range, long life, simple structure, and good frequency response characteristics. When the fluid acts on the varistor, it will cause the deformation of the membrane and cause the varistor to be affected by stress, and the resistance value of the semiconductor will change. The pressure value of the fluid to be measured can be obtained through the change in resistance. However, the piezoresistive coefficient of this sensor is greatly affected by temperature. In order to facilitate temperature compensation, it is necessary to use a varistor injected with a high concentration. In the case of high-concentration injection, the piezoresistive coefficient has a relatively small correlation with temperature, and thus a small temperature coefficient can be obtained. The traditional methods of introducing impurities into silicon wafers mainly include diffusion and ion implantation. However, both methods have their own drawbacks. For example, the diffusion method is difficult to achieve selective diffusion and the diffusion concentration distribution is difficult to control, while the ion implantation method consumes It takes a long time and the equipment is expensive, and the implanted impurities are mostly in an inactive state, which needs to be activated by heat treatment. In the process of high temperature annealing, it will also lead to a series of problems such as distortion of the implantation pattern and precipitation of implanted impurities.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned problems existing in the prior art, the present invention proposes an array type pressure sensor for measuring the liquid level of an automobile fuel tank and a preparation method thereof. The Wheatstone bridge structure is formed by a varistor injected with high concentration as a whole, and the bridge arm resistance A femtosecond laser filament is used to achieve high-efficiency and fast patterning of high-concentration doping, and the implanted layer is annealed based on a femtosecond laser direct writing system.

The present invention is achieved through the following technical solutions:

A preparation method of an array type automobile fuel tank liquid level measurement pressure sensor, the specific steps are as follows:

Step 1: Coating a layer of boron dopant source on the front of the wafer surface, and magnetron sputtering a layer of silicon dioxide film with a thickness of 200nm on the surface of the coating source to prevent the dopant source from volatilizing during pulsed laser irradiation. The femtosecond laser filament realizes high-efficiency and fast patterning of high-concentration doping on the surface of the wafer, and prepares a high-concentration implanted varistor, in which the trajectory of the laser is controlled by a scanning galvanometer;

Step 2: use a femtosecond direct writing system to anneal the high-concentration implanted varistor. After the annealing treatment, the impurities are electrically activated and evenly distributed, and the annealing process is carried out under the protection of argon gas;

Step 3: deposit a layer of Si ₃ N ₄ on both the front and the back of the wafer, which has a better passivation effect than the oxide layer, and obtains contact holes through photolithography and ICP etching;

Step 4: forming a mask for the metal electrode layer by photolithography, then magnetron sputtering a layer of Al film, removing the photoresist to complete the stripping of the metal layer, forming wires and pads, and completing the ohmic contact between the aluminum and the varistor;

Step 5: Protect the front side, perform photolithography etching on the Si ₃ N ₄ layer deposited on the back side, and then obtain a silicon cup window, and obtain a strained film with a thickness of 25-50 μm through chemical etching;

Step 6: bonding the prepared device with borosilicate glass, forming a vacuum sealed cavity in the middle, and preparing a silicon cup-type pressure sensor.

Preferably, the femtosecond laser filament described in step 1 is formed by focusing a laser beam in the air through a quartz lens with a focal length of 100 cm, the length of the formed filament is about 3 cm, and the diameter of the filament is about 100 μm, The center wavelength of the laser used is 800 nm, the repetition frequency is 500 Hz, the pulse width is 35 fs, the single pulse energy is 0-3.5 mJ, and argon is used as the protective gas.

Preferably, the thickness of the wafer in step 1 is 300 μm, the boron doping source is a mixture of boron trioxide and anhydrous ethanol according to a mass-to-volume ratio of 10g:100ml, and the thickness of the silicon dioxide film is is 200 nm, and the concentration of the high-concentration doping is 10 ²⁰ /cm ² or more.

Preferably, the femtosecond laser direct writing system described in step 2 uses a laser with a center wavelength of 800 nm, a pulse width of 100 fs, a repetition frequency of 2.5 kHz, and argon as the protective gas.

Preferably, the thickness of the Al thin film described in step 4 is 100nm-120nm.

Compared with the prior art, the advantages of the present invention are as follows:

1. The present invention adopts femtosecond laser filament to achieve high-concentration doping of wafers, with simple operation and high doping efficiency, and can selectively perform laser treatment on the wafer surface.

2. The present invention adopts the femtosecond direct writing system to anneal the implanted layer, the equipment is simple, the operation is easy, and various defects on the wafer surface can be effectively absorbed, and the deterioration of the electrical parameters of the substrate caused by thermal annealing and implantation can be avoided. Impurity redistribution and implant pattern distortion.

3. The fuel tank liquid level measurement pressure sensor proposed by the present invention adopts an array structure, which is convenient for the detection of different heights of the liquid level.

Description of drawings

In order to illustrate the specific embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that are required to be used in the description of the specific embodiments or the prior art. Similar elements or parts are generally identified by similar reference numerals throughout the drawings. In the drawings, each element or section is not necessarily drawn to actual scale.

Fig. 1 is the structural representation of the array type automobile fuel tank liquid level measuring pressure sensor of the present invention;

FIG. 2 is a flow chart of the preparation process of the array type automobile fuel tank liquid level measurement pressure sensor of the present invention.

Detailed ways

The embodiments of the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to illustrate the technical solutions of the present invention more clearly, so they are only used as examples, and cannot be used to limit the protection scope of the present invention.

It should be noted that, unless otherwise specified, the technical or scientific terms used in this application should have the usual meanings understood by those skilled in the art to which the present invention belongs.

Example 1

The invention discloses a preparation method of an array type automobile fuel tank liquid level measurement pressure sensor. Based on a circuit with a Wheatstone bridge structure, firstly, a femtosecond laser filament is used to realize high-efficiency, rapid patterning and high-concentration doping on the surface of a coating source wafer, and a circuit is prepared. The high-concentration implanted varistor, and the femtosecond direct writing system is used to anneal the implanted layer, and then the passivation layer is deposited and the contact hole is obtained by photolithography and etching, and the metal aluminum wire is obtained by photolithography and magnetron sputtering. and pads. Then, a silicon cup window is obtained by photolithography and etching on the back side, and a strained film of a specific thickness is obtained by etching. Finally, the prepared device is bonded with borosilicate glass to prepare an array silicon cup pressure sensor.

Example 2

To facilitate the understanding of this embodiment, first of all, the preparation method of an array type automobile fuel tank liquid level measurement pressure sensor proposed in the embodiment of the present invention will be introduced in detail. ), the bridge arm resistance adopts femtosecond laser filament to achieve high-efficiency and fast patterning and high-concentration doping, and the injection layer is annealed based on the femtosecond laser direct writing system.

A preparation method of an array type automobile fuel tank liquid level measurement pressure sensor, the specific steps are as follows:

Step 1: Coat a layer of boron doping source (diboron trioxide: anhydrous ethanol = 10g:100ml) on the surface (front side) of the wafer with a thickness of 300 μm, and magnetron sputter a layer of 200nm thick on the surface of the coating source. A silicon dioxide film to prevent the doping source from volatilizing when irradiated by a pulsed laser, a femtosecond laser filament was used to achieve patterned high-concentration doping on the wafer surface (Fig. 2a), by changing the laser scanning speed (corresponding to the same sample The number of laser pulses at the position) to control the doping depth of the wafer. In the doping process, argon is used as the protective gas to prepare a high-concentration implanted varistor whose surface concentration can reach more than 10 ²⁰ /cm ² , where The trajectory of the laser is controlled by a scanning galvanometer. Here, the wafer can be efficiently and rapidly doped based on the advantage of the large diameter of the femtosecond laser filament.

Step 2: Use a femtosecond direct writing system to anneal the high-concentration implanted varistor (Figure 2b), use a titanium-doped sapphire femtosecond laser amplifier produced by Spectra-Physics, and the spot diameter on the wafer surface after focusing is 260 μm , the impurities are electrically activated and evenly distributed after the annealing treatment. The annealing process is carried out under the protection of argon gas. Compared with the traditional thermal annealing treatment, femtosecond laser annealing can effectively absorb various defects on the wafer surface, and can avoid Thermal annealing leads to the deterioration of the electrical parameters of the substrate, the redistribution of implanted impurities and the distortion of the implanted pattern.

Step 3: A layer of Si ₃ N ₄ is deposited on both the front and back of the wafer, which has a better passivation effect than the oxide layer. Contact holes are obtained by photolithography and ICP etching (Fig. 2c). This is Vias for ohmic contact between aluminum and varistor.

Step 4: Form a mask for the metal electrode layer by photolithography, then magnetron sputter an Al thin film with a thickness of 100nm-120nm, remove the photoresist and complete the metal layer stripping to form wires and pads (Figure 2d), complete The aluminum is in ohmic contact with the varistor.

Step 5: Protect the front side, perform photolithography etching on the Si ₃ N ₄ layer deposited on the back side, and then obtain the silicon cup window. After chemical etching, a strained film with a thickness of 25-50 μm is obtained (Figure 2e). This step needs to ensure that The varistors are just on the strained membrane and are symmetrical to each other.

Step 6: Bond the prepared device with borosilicate glass under high vacuum (Fig. 2f), adopt anodic bonding technology, form a vacuum sealed cavity in the middle, prepare a silicon cup-type pressure sensor, and select glass as the substrate of the material Errors caused by thermal mismatch between the chip and the substrate can be reduced.

In this embodiment, the femtosecond laser filament is formed by focusing a laser beam in the air through a quartz lens with a focal length of 100 cm. The length of the formed filament is about 3 cm, and the diameter of the filament is about 100 μm. The center wavelength of the laser used is 800 nm, the repetition frequency is 500 Hz, the pulse width is 35 fs, the single pulse energy is 0-3.5 mJ, and argon is used as the protective gas.

In this example, the femtosecond laser direct writing system uses a laser with a center wavelength of 800 nm, a pulse width of 100 fs, a repetition frequency of 2.5 kHz, and argon as a protective gas.

In this example, the array type pressure sensor for measuring the liquid level of the automobile fuel tank adopts an array type structure (Fig. 1), which is convenient for the detection of different heights of the liquid level.

The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above-mentioned embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, These simple modifications all belong to the protection scope of the present invention.

In addition, it should be noted that the specific technical features described in the above-mentioned specific embodiments can be combined in any suitable manner unless they are inconsistent. In order to avoid unnecessary repetition, the present invention provides The combination method will not be specified otherwise.

In addition, the various embodiments of the present invention can also be combined arbitrarily, as long as they do not violate the spirit of the present invention, they should also be regarded as the contents disclosed in the present invention.

Claims (6)

1. a preparation method of array type automobile fuel tank liquid level measurement pressure sensor, is characterized in that, concrete steps are as follows: Step 1: Coating a layer of boron dopant source on the front of the wafer surface, and magnetron sputtering a layer of silicon dioxide film with a thickness of 200nm on the surface of the coating source to prevent the dopant source from volatilizing during pulsed laser irradiation. The femtosecond laser filament realizes high-efficiency and fast patterning of high-concentration doping on the surface of the wafer, and prepares a high-concentration implanted varistor, in which the trajectory of the laser is controlled by a scanning galvanometer; Step 2: use a femtosecond direct writing system to anneal the high-concentration implanted varistor. After the annealing treatment, the impurities are electrically activated and evenly distributed, and the annealing process is carried out under the protection of argon gas; Step 3: deposit a layer of Si ₃ N ₄ on both the front and the back of the wafer, which has a better passivation effect than the oxide layer, and obtains contact holes through photolithography and ICP etching; Step 4: forming a mask for the metal electrode layer by photolithography, then magnetron sputtering a layer of Al film, removing the photoresist to complete the stripping of the metal layer, forming wires and pads, and completing the ohmic contact between the aluminum and the varistor; Step 5: Protect the front side, perform photolithography etching on the Si ₃ N ₄ layer deposited on the back side, and then obtain a silicon cup window, and obtain a strained film with a thickness of 25-50 μm through chemical etching; Step 6: bonding the prepared device with borosilicate glass, forming a vacuum sealed cavity in the middle, and preparing a silicon cup-type pressure sensor. 2. the preparation method of a kind of array type automobile fuel tank liquid level measuring pressure sensor as claimed in claim 1, it is characterized in that, the femtosecond laser filament described in the step 1 is the quartz lens that the laser beam passes through the focal length and is 100cm at 100cm. The length of the filament formed by focusing in the air is about 3cm, the diameter of the filament is about 100μm, the laser center wavelength is 800nm, the repetition frequency is 500Hz, the pulse width is 35fs, and the single pulse energy is 0-3.5 mJ, using argon as shielding gas. 3. The preparation method of an array type automobile fuel tank liquid level measurement pressure sensor as claimed in claim 1, wherein the wafer thickness described in the step 1 is 300 μm, and the boron doping source is dioxide trioxide The boron and anhydrous ethanol are mixed according to a mass-volume ratio of 10g:100ml, the thickness of the silicon dioxide film is 200nm, and the concentration of the high-concentration doping is more than 10 ²⁰ /cm ² . 4. the preparation method of a kind of array type automobile fuel tank liquid level measurement pressure sensor as claimed in claim 1, is characterized in that, the femtosecond laser direct writing system described in step 2 adopts laser center wavelength to be 800nm, and pulse width is 100fs , the repetition frequency is 2.5kHz, and argon is used as the protective gas. 5 . The preparation method of an array type automobile fuel tank liquid level measurement pressure sensor according to claim 1 , wherein the thickness of the Al thin film described in step 4 is 100 nm-120 nm. 6 . 6 . An array type pressure sensor for measuring the liquid level of an automobile fuel tank, characterized in that it is prepared by the method according to any one of claims 1 to 5 .

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