CN103091013A - Miniature SU-8 optical fiber fabry-perot pressure sensor and preparation method thereof - Google Patents

Abstract

The invention discloses a miniature SU-8 optical fiber fabry-perot pressure sensor. The miniature SU-8 optical fiber fabry-perot pressure sensor is formed by a combination of traditional micro-electromechanical system (MEMS) micro machining and near-ultraviolet photoetching technology. A displacement column and a positioning groove of optical fiber are formed on a silicon sensitive film by utilizing a near-ultraviolet photoetching SU-8 photoetching adhesive layer, and an end face of the displacement column and an end face of the optical fiber form a fabry-perot cavity. Simultaneously, the invention further discloses the method of preparing the miniature SU-8 optical fiber fabry-perot pressure sensor. The main steps are that a required structure is formed through the front side of a silicon wafer and through two-time alignment photoetching, wherein the surface of the silicon wafer is processed. The back side of the silicon wafer is corroded through a wet etching method, and the required film thickness is achieved. An upper cover structure of a pressure sensor is shaped on another slice of silicon wafer through photoetching again, and bonding encapsulation is conducted through epoxy resin adhesive. The miniature SU-8 optical fiber fabry-perot pressure sensor is novel in structure, high in sensitivity, good in reliability, large in linear measurement range, low in cost and capable of being applied to micro-pressure testing in industry.

Description

Miniature SU-8 optical fiber Fabry-Perot pressure sensor and its preparation method

technical field

The invention relates to an optical fiber Fabry-Perot (FP) microstructure pressure sensor device, in particular to a pressure sensor formed by ultraviolet lithography technology and silicon wet etching technology and a preparation method thereof.

Background technique

Existing extrinsic fiber Fabry-Perot (FP) interferometer is mainly used to measure strain, which is formed by a resonant cavity formed by two cut fiber end faces placed in a quartz capillary and an air gap in the middle . Such sensors have many problems in FP cavity length control and fiber fixation.

Optical exposure is the earliest microfabrication technology used in semiconductor integrated circuits, and its important purpose is to image the pattern of the mask onto the photoresist. Although microsensors based on photolithography technology can meet the requirements of mass production, their fabrication process is complex and requires expensive semiconductor equipment and devices. With the rapid development of MEMS (Micro-Electro-Mechanical Systems, Micro-Electro-Mechanical Systems) technology, the improvement of structure, improvement of preparation methods and improvement of packaging technology have become the main demands of people for this technology.

Contents of the invention

The present invention is carried out based on the above-mentioned present situation, and the purpose is to manufacture a miniature optical fiber Fabry-Perot pressure sensor with novel structure, low cost and high precision, which is expected to be mass-produced. Meanwhile, a manufacturing method of the sensor is provided.

In order to realize the foregoing invention object, the present invention adopts following technical scheme:

Miniature SU-8 fiber optic Fabry-Perot pressure sensor, including sensing parts and upper cover, sensing parts include single-mode optical fiber, silicon sensitive membrane, optical fiber groove and SU-8 displacement column on the silicon sensitive membrane, SU The surface of the -8 displacement column is covered with a layer of antireflection film, and the single-mode optical fiber is fixed in the fiber groove, and the end face of the single-mode optical fiber is relatively separated from the SU-8 displacement column by a certain distance to form a Fabry-Perot cavity. The above-mentioned upper cover is bonded with the sensing part for packaging.

The preparation process steps of the optical fiber Fabry-Perot pressure sensor of the present invention are as follows:

a) Carry out RCA standard cleaning on the silicon wafer, respectively, use acetone, alcohol and deionized water to ultrasonically clean it for 5 minutes, and then dry it with nitrogen; pour an appropriate amount of SU-8 photoresist on the cleaned silicon wafer, Throw the glue at a certain speed to form a film of uniform thickness;

b) After pre-baking the film for a certain period of time, use a UV lithography machine to expose it, and then bake it at 65°C and 95°C for 10 minutes, soak it in a developing solution, wash off the unexposed residual glue, and perform high-temperature hardening to obtain The first layer of optical fiber groove substrate, 1/2 height of SU-8 displacement column and 1/2 height of sensing component side wall;

c) applying glue and throwing glue on the structure formed in step b);

d) Pre-baking, exposing, post-baking, developing, drying and hardening the film formed in step c) to form fiber grooves, SU-8 displacement columns and side walls of sensing components;

e) thermally evaporating and depositing a layer of AR film material on the structure formed in step d);

f) Photolithographically form a protective layer on the back of the silicon wafer by plate alignment, perform wet etching, control the etching depth by controlling the time, obtain the required film thickness, and form a silicon sensitive film;

g) Cut out a flat end face of a section of single-mode fiber with a fiber cutter, and grind and polish the end face of the single-mode fiber with an optical fiber grinder; insert the precisely cut and end-face treated optical fiber into the fiber groove, and fix it by dispensing glue;

h) Re-clean a piece of silicon wafer, and spin glue on its surface to form a film with uniform thickness;

i) Perform pre-baking and photolithography on the film formed in step h) to form a corresponding upper cover structure;

j) Glue the side wall of the sensing part and the corresponding upper cover structure and package it in a vacuum environment to protect the sensing part and ensure the internal vacuum.

Through the structure obtained by the above sensor processing steps, the front end of the displacement column and the end face of the optical fiber form an FP cavity, and the light directly enters the FP cavity through the optical fiber, avoiding the influence of other media on the optical path; the main material required in the sensor manufacturing process is SU-8 optical fiber Resist, SMF, silicon wafer, materials are easy to collect and cheap. The cavity length of the FP cavity is controlled according to the position where the fiber is embedded. The whole manufacturing process adopts the methods of cutting, etching, and photolithography, the sensor has high mechanical performance, and the manufacturing steps are simple. Therefore, the optical fiber pressure sensor with simple manufacture, high sensitivity, large dynamic measurement range and good reliability can be realized by means of the present invention.

Description of drawings

Fig. 1 is a schematic diagram of the sensing principle of the miniature SU-8 optical fiber Fabry-Perot pressure sensor of the present invention. (a) is a schematic diagram of the sensor, (b) is the formed Fabry-Perot cavity, and (c) is a schematic diagram when it is under pressure.

Figure 2 is a schematic diagram of the sensor structure, (a) top view, (b) side sectional view. Among them, 2-1: The optical fiber groove formed by SU-8 through two photolithography; 2-2: The side wall of the sensing part obtained by SU-8 photolithography; 2-3: SU-8 obtained by one photolithography Fiber trench substrate; 2-4: silicon substrate.

Fig. 3 is a flow chart of the main process of manufacturing the sensor of the present invention.

Figure 4 is the demodulation system used in sensor applications, 4-1: sensor analyzer; 4-2: 2×2 coupler; 4-3: sensor head.

Figure 5 shows the experimental results of a sensor with a film thickness of 200 microns and a cavity length of 180.418 microns.

Detailed ways

The sensing component of the present invention mainly includes a single-mode optical fiber, a silicon sensitive film and a SU-8 displacement column. The optical fiber is a bare optical fiber (that is, a core plus cladding structure), and the silicon sensitive film is obtained by wet etching to obtain the required film thickness. Using overlay technology to form displacement columns and fiber fixing grooves on one side of the silicon sensitive film, fix the single-mode fiber, and then bond and package with the upper cover.

Figure 1 is a schematic diagram of the principle of pressure sensing, in which, 1-1: linkage structure: cuboid displacement column obtained by SU-8 lithography; 1-2: anti-reflection film; Optical fiber; 1-4: Silicon sensitive film. The end face of SU-8 displacement column 1-1 and the end face of optical fiber 1-3 have a certain distance to form a Fabry-Perot cavity. When the silicon sensitive membrane 1-4 is under pressure, it will deform. SU-8 displacement column 1- 1 and the distance D between the end face of optical fiber 1-3 changes accordingly, becomes D'.

Present embodiment prepares the step of miniature SU-8 optical fiber Fabry-Perot pressure sensor as follows:

a) Carry out RCA standard cleaning on silicon wafer 3-1, use acetone (purity 99.7%), alcohol (purity 99.7%), deionized water (resistivity 18.2MΩ) to ultrasonically clean for 5 minutes, and then use nitrogen gas (concentration 99.7%) Blow dry; pour an appropriate amount of SU-8 photoresist on the cleaned silicon wafer, pre-uniform at an initial speed of 250rpm for 20 seconds, and accelerate at a speed of 600rpm for 2 minutes to form a film with a uniform thickness of 200μm 3-2 ;

b) After pre-baking at 70°C for 6 hours to evaporate the solvent, use a UV lithography machine to expose, the exposure intensity is 15mW/cm ² , and the exposure time is 30 seconds. After baking at 95°C for 5 minutes, soak in developing solution, wash off the unexposed residual glue, place the sample on a hot plate at 170°C for 30 minutes at high temperature, and obtain the first layer of optical fiber groove bottom liner 2- 3. 1/2 height SU-8 displacement column 3-3 and 1/2 height side wall 3-4;

c) Pre-homogenize the structural silicon wafer formed in step b) at an initial speed of 250rpm for 20 seconds, and accelerate to spin at a speed of 600rpm for 2 minutes to apply glue;

d) Pre-bake the film formed in step c) at 70°C for 6 hours, with an exposure intensity of 15mW/cm ² , expose for 30 seconds, and then bake for 3 minutes at 65°C as the initial temperature, then raise the temperature to 95°C Perform post-baking for 5 minutes, develop, blow dry with nitrogen, and complete the second step of photolithography after 170°C high temperature hardening for 30 minutes to form the side walls 3-5 of the fiber groove, the displacement column structure 1-1 and the side wall structure of SU-8 2-2;

e) On the structure formed in step d), thermal evaporation deposits a layer of anti-reflection film material: 50nm thick silver film 3-6;

f) Form a protective layer on the back of the silicon wafer by photolithography in the way of plate alignment, use KOH solution with a concentration of 20% to heat to 70°C, and perform wet etching, and control the etching depth by controlling the time, and it can be obtained after about 2 hours Required film thickness to form a silicon sensitive film 1-4;

g) Cut out a flat end face of a section of single-mode fiber 1-3 with a fiber cutter, and grind and polish the end face of the single-mode fiber with an optical fiber grinder; insert the precisely cut and end-face treated optical fiber, and fix it by dispensing glue;

h) Re-clean a piece of silicon wafer 3-7, and spin glue on its surface to form a film with uniform thickness;

i) Perform pre-baking and photolithography on the film formed in step h) to form the upper cover structure 3-8;

j) Apply glue to the side wall 2-2 of the sensing part and the corresponding upper cover structure 3-8, and bond and package it with epoxy resin glue in a vacuum environment to protect the sensing part and ensure the internal vacuum.

Claims (2)

1. Miniature SU-8 optical fiber Fabry-Perot pressure sensor, including sensing parts and upper cover, is characterized in that the sensing parts include single-mode optical fiber, silicon sensitive film and optical fiber groove and SU located on the silicon sensitive film -8 displacement column, the surface of the SU-8 displacement column is covered with a layer of antireflection film, the single-mode fiber is fixed in the fiber groove, and the end face of the single-mode fiber is separated from the SU-8 displacement column by a certain distance to form a Fabry - a Perot cavity, the upper cover is bonded with the sensing part for encapsulation. 2. the preparation method of miniature SU-8 optical fiber Fabry-Perot pressure sensor as claimed in claim 1, its processing technology step is as follows: a) Carry out RCA standard cleaning on the silicon wafer, respectively, use acetone, alcohol and deionized water to ultrasonically clean it for 5 minutes, and then dry it with nitrogen; pour an appropriate amount of SU-8 photoresist on the cleaned silicon wafer, Throw the glue at a certain speed to form a film of uniform thickness; b) After pre-baking the film for a certain period of time, use a UV lithography machine to expose it, and then bake it at 65°C and 95°C for 10 minutes, soak it in a developing solution, wash off the unexposed residual glue, and perform high-temperature hardening to obtain The first layer of optical fiber groove substrate, 1/2 height of SU-8 displacement column and 1/2 height of sensing component side wall; c) applying glue and throwing glue on the structure formed in step b); d) Pre-baking, exposing, post-baking, developing, drying and hardening the film formed in step c) to form fiber grooves, SU-8 displacement columns and side walls of sensing components; e) thermally evaporating and depositing a layer of AR film material on the structure formed in step d); f) Photolithographically form a protective layer on the back of the silicon wafer by plate alignment, perform wet etching, control the etching depth by controlling the time, obtain the required film thickness, and form a silicon sensitive film; g) Cut out a flat end face of a section of single-mode fiber with a fiber cutter, and grind and polish the end face of the single-mode fiber with an optical fiber grinder; insert the precisely cut and end-face treated optical fiber into the fiber groove, and fix it by dispensing glue; h) Re-clean a piece of silicon wafer, and spin glue on its surface to form a film with uniform thickness; i) Perform pre-baking and photolithography on the film formed in step h) to form a corresponding upper cover structure; j) Glue the side wall of the sensing part and the corresponding upper cover structure and package it in a vacuum environment to protect the sensing part and ensure the internal vacuum.

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