阅读说明：本技术 一种微纳结构光散射式浊度检测传感器及其制备工艺 (Micro-nano structure light scattering type turbidity detection sensor and preparation process thereof ) 是由 金庆辉 姚灵 管轶华 王欣欣 王达 于 2020-07-27 设计创作，主要内容包括：一种基于光散射式测量法检测自来水中浊度的光学微纳传感器。基于MEMS技术,该传感器以硅片为衬底,基于硅的各向异性腐蚀特性制备检测光与参考光通道；采用散射式测量法,选择850nm的红外光作为光源,选择带有黑色蔽光罩的红外接收器作为探测器,以有效地减少自然光的干扰。本发明提出的浊度传感器具有如下显著优点：1)微型化,硅基微纳结构可以有效解决检测光和参考光光路的问题,大幅减小传感器的体积；2)批量制备、低成本、易集成,将浊度传感器的制备与MEMS工艺结合,实现浊度传感器的芯片化和批量制造。该设计实现浊度检测传感器的耐用性、高性能、小型化,可以结合采集电路模块和误差修正模块使其拥有更长的寿命与检测精度。(An optical micro-nano sensor for detecting the turbidity in tap water based on a light scattering measurement method. Based on MEMS technology, the sensor takes a silicon wafer as a substrate, and a detection light channel and a reference light channel are prepared based on the anisotropic corrosion characteristic of silicon; the scattering measurement method is adopted, 850nm infrared light is selected as a light source, and an infrared receiver with a black photomask is selected as a detector, so that the interference of natural light is effectively reduced. The turbidity sensor provided by the invention has the following remarkable advantages: 1) the miniaturization is realized, the problem of the light path of the detection light and the reference light can be effectively solved by the silicon-based micro-nano structure, and the volume of the sensor is greatly reduced; 2) the method has the advantages of batch preparation, low cost and easy integration, and combines the preparation of the turbidity sensor with the MEMS process to realize the chip and batch manufacture of the turbidity sensor. The design realizes the durability, high performance and miniaturization of the turbidity detection sensor, and the turbidity detection sensor can be combined with the acquisition circuit module and the error correction module to have longer service life and detection precision.)

1. A micro-nano structure light scattering type turbidity detection sensor is characterized in that: the device comprises a substrate, wherein a semi-through channel and a semi-through hole are etched on the surface of the substrate through a KOH solution wet etching method to serve as a reference light channel and a reference light detection groove, two full-through holes are etched to serve as a signal light channel and a signal light detection groove, metal pads are sputtered on two sides of the full-through hole on the front surface of the substrate, a light source/detector with fixed size is selected, a light emitting/light sensing part of the light source/detector extends into the full-through hole, and high-temperature welding and fixing are carried out through soldering tin.

2. The micro-nano structure light scattering turbidity detection sensor according to claim 1, characterized in that: and a layer of high-transmittance glass is bonded on the back surface of the substrate.

3. A preparation process for preparing the micro-nano structure light scattering turbidity detection sensor according to claim 1, comprising the following steps:

1) selecting a four-inch silicon wafer with a (100) crystal face on the surface, polished and oxidized on one side as a substrate, wherein the thickness of an oxide layer is 1um, and the surface flatness of the silicon wafer is less than 0.1 um;

2) coating glue on the substrate, prebaking, photoetching, developing, and postbaking after developing to prepare a silicon oxide layer window on the surface of the substrate, and then etching the exposed silicon oxide layer by using a BOE solution wet method to expose a silicon substrate to prepare a light source groove, a detection light groove, a reference light groove and a corrosion window of a reference light channel;

3) repeating the steps (1) and (2) to form the light source groove and the other half of the corrosion window of the detection light groove on the back surface of the silicon wafer;

4) removing glue before metal: the operation is carried out in a liquid solution tank, the solution is prepared by adding 10-15mL of hydrogen peroxide into sulfuric acid solution, removing photoresist by using strong oxidizing property, keeping the temperature of the solution tank constant at 120 ℃, and cleaning for 10 min;

5) KOH corrosion: the solution adopts 30 percent KOH corrosive liquid, when the temperature of the solution is 50 ℃, the speed of corroding Si by 30 percent KOH is 10.3 um/h, and SiO is corroded₂The speed is 0.05-0.06 um/h, when the temperature of the solution is 40 ℃, the speed of etching Si by 30% KOH is 5 um/h, the silicon layer is etched by the anisotropic wet method under the condition of 50 ℃, and a light source groove, a detection light groove, a reference light groove and a reference light channel are prepared according to the difference of the etching speeds of the KOH to Si and SiO 2;

6) removing the residual silicon oxide layer on the back surface by adopting BOE solution;

7) preparing a metal bonding pad on the oxide layer by adopting a lift-off process;

8) glass bonding, namely bonding a layer of high-transmittance glass on the back surface of a silicon wafer, wherein the high-transmittance glass can ensure that liquid to be detected cannot permeate into a sensor during detection under the condition of not influencing a light path;

9) welding a light source/detector, namely welding the front side of the patch type light source/detector (with double-side welding spots) to the metal bonding pad in the step (7), and sputtering the metal bonding pad around the full through hole; and a certain space is left after the welding of the light source/detector on the welding pad, and the welding pad can be butted with a signal processing circuit subsequently.

4. The preparation process of the optical micro-nano sensor according to claim 3, characterized in that: in step 2), the glue coating process selects positive glue LC100A, the glue coating speed is 1000r × 30s, and the glue coating layer is 2.4um thick.

5. The preparation process of the optical micro-nano sensor according to claim 3, characterized in that: in step 7), the lift-off process comprises at least one of a photolithography process, a magnetron sputtering process, an ultrasonic lift-off process, or any combination thereof.

Technical Field

The invention relates to a sensor for detecting turbidity in tap water and a preparation method thereof, belonging to the technical field of sensors.

Background

Turbidity is a term to express the effect of light caused by different sizes and specific gravities in water, as well as suspended and colloidal substances, microorganisms, etc. It is defined by institutions such as the foreign public health association as: samples of water are a term for the optical properties of light scattering and absorption. The contents of suspended matters, colloidal substances, plankton and other impurities in a water sample are not directly described, and the turbidity is related to the importance of food, brewing and human health. In industrial production, the turbidity of medicine, textile, printing and dyeing, electricity and water directly affects the quality of products or production processes. The turbidity measurement has wide application in the industries and departments of urban water supply, drinking water, medicine, environmental protection, health and epidemic prevention, and the like. Turbidity is one of the important criteria for ensuring water supply quality and is part of water plant evaluation of water quality.

Turbidity measurements water quality testing typically uses manual sampling, such as colorimetry to determine the specific gravity of impurities and some other methods to obtain this information, and these measurements are often random, discrete, and subject to relatively large errors. The conventional test methods have not been able to meet the requirements for automation of new water purification processes. Modern water purification techniques and production management have increased to the point where continuous measurement of water quality is possible, data can be immediately converted to electrical signals, networked in real time, and the accuracy and precision of water quality analysis tools is ensured.

Currently, the turbidity is detected by a scattered light turbidity measurement method: when a beam of light with a specific wavelength enters water, the light meets suspended particles in the water and generates scattering, and the intensity of the scattered light is in direct proportion to the turbidity of the liquid to be detected. Therefore, the turbidity of the liquid to be detected can be obtained by measuring the intensity of the scattered light, and the scattering type turbidity sensor can be divided into a forward mode, a backward mode and a vertical mode according to the position of a scattered light detector, namely different angles of the scattered light and incident light. Currently, such ninety degree scattering turbidity sensors are most widely used. It has been mentioned above that the main material affecting the scattered light is the suspended particles in the water, and the suspended particles with different sizes scatter light to different extent, but the scattered light generated by the incident light after striking the suspended particles in the ninety degree direction is least affected by the size of the suspended particles, and the generated scattered light is most stable. Therefore, most turbidity sensors on the market today use ninety-degree scattered light detection in a manner that is not difficult to understand. A schematic diagram of a ninety degree scatterometry configuration is shown in fig. 1.

The turbidity sensor is mainly used for detecting the turbidity in tap water in the intelligent water meter. The sensor is required to have high detection precision, and the turbidity parameter can be accurately detected; the volume is small, and the sensor can be arranged under the condition that the original structure of the water meter is basically unchanged; the cost is low, and the method can be used for large-scale paving and large-data analysis. The traditional turbidity detection sensor has large volume, high cost and severely limited use occasions. Meanwhile, the light source can have a self-attenuation phenomenon after long-term operation, so that the detected data are deviated.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a micro-nano structure-based scattering type turbidity sensor, which can overcome the problems and achieve the required performance index. The detection light channel and the reference light channel can be well constructed by processing the silicon substrate through silicon anisotropic wet etching. The micro-nano structure optical channel can greatly shorten the optical path when the turbidity is measured by a scattering method, so that a detector can obtain a more excellent response value, and meanwhile, the error caused by the self-attenuation of a light source can be effectively eliminated by constructing the reference optical channel and comparing signals through a single-chip microcontroller. Meanwhile, the micro-scale and batch manufacturing of the turbidity sensor can be realized through the MEMS technology, the volume is greatly reduced, and the cost is greatly reduced.

In order to achieve the purpose, the invention provides the following technical scheme:

a micro-nano structure light scattering turbidity detection sensor comprises a substrate, wherein a semi-through channel and a semi-through hole are etched on the surface of the substrate through a KOH solution wet method to serve as a reference light channel and a reference light detection groove, and two full-through holes are etched to serve as a signal light channel and a signal light detection groove.

As an improvement of the invention, a layer of high-transmittance glass is bonded on the back surface of the substrate.

A preparation process for preparing the micro-nano structure light scattering turbidity detection sensor comprises the following steps:

1) selecting a four-inch silicon wafer with a (100) crystal face on the surface and a polished and oxidized single surface as a substrate, wherein the thickness of an oxide layer is 1um, and the surface flatness of the silicon wafer is less than 0.1 um;

2) coating glue on the substrate, prebaking, photoetching, developing, and postbaking after developing to prepare a silicon oxide layer window on the surface of the substrate, and then etching the exposed silicon oxide layer by using a BOE solution wet method to expose a silicon substrate to prepare a light source groove, a detection light groove, a reference light groove and a corrosion window of a reference light channel;

3) repeating the steps (1) and (2) to form a light source groove and the other half of the corrosion window of the detection light groove on the back surface of the silicon wafer;

4) removing photoresist before metal: the operation is carried out in a liquid solution tank, the solution is prepared by adding 10-15mL of hydrogen peroxide into sulfuric acid solution, removing photoresist by using strong oxidizing property, keeping the temperature of the solution tank constant at 120 ℃, and cleaning for 10 min;

5) KOH corrosion: the solution adopts 30 percent KOH corrosive liquid, when the temperature of the solution is 50 ℃, the speed of corroding Si by 30 percent KOH is 10.3 um/h, and SiO is corroded₂The speed is 0.05-0.06 um/h, when the temperature of the solution is 40 ℃, the speed of etching Si by 30% KOH is 5 um/h, the silicon layer is etched by the anisotropic wet method under the condition of 50 ℃, and a light source groove, a detection light groove, a reference light groove and a reference light channel are prepared according to the difference of the etching speeds of the KOH to Si and SiO 2;

6) removing the residual silicon oxide layer on the back surface by adopting BOE solution;

7) preparing a metal bonding pad on the oxide layer by adopting a lift-off process;

8) the glass bonding is realized, a layer of high-transmittance glass is bonded on the back surface of the silicon wafer, and the high-transmittance glass can ensure that liquid to be detected cannot permeate into a sensor during detection under the condition of not influencing a light path;

9) welding a light source/detector, namely welding the front side of the patch type light source/detector (with double-side welding spots) to the metal bonding pad in the step (7), and sputtering the metal bonding pad around the full through hole; and a certain space is left after the welding of the light source/detector on the welding pad, and the welding pad can be butted with a signal processing circuit subsequently.

In the step 2), the positive glue LC100A is selected in the gluing process, the gluing speed is 1000r × 30s, and the gluing layer thickness is 2.4 um.

As an improvement of the above preparation process, in step 7), the lift-off process includes at least one or any combination of a photolithography process, a magnetron sputtering process, and an ultrasonic lift-off process.

Compared with the prior art, the invention has the advantages that: a method for preparing turbidity sensor based on micro-processing technology is developed and used, which integrates the detection of reference light and the detection of signal light on a microchip, thus greatly widening the application occasions of the sensor. And because no harmful substance is generated in the detection after the preparation, the method can be used in the occasions with high safety level requirements such as tap water pipelines. The novel underwater turbidity detection sensor microchip designed and produced has the remarkable advantages of high safety, high reliability, small size, long service life and capability of being prepared in batches and reducing cost, and provides support for large-scale application of turbidity sensors in the field of tap water monitoring.

Drawings

FIG. 1 is a schematic diagram of a ninety-degree scattering light measurement method according to the prior art;

FIG. 2 is a top view of a micro-nano silicon structure substrate in an embodiment of the invention;

FIG. 3 is a flow chart of a turbidity sensor processing process.

Detailed Description

Embodiments of the micro-nano structure light scattering type turbidity detection sensor and the preparation process thereof according to the present invention are further described with reference to the accompanying drawings.

As shown in the attached drawing, the embodiment is a micro-nano structure light scattering turbidity detection sensor, which comprises a substrate 1, wherein a semi-through channel and a semi-through hole are etched on the surface of the substrate as a reference light channel 2 and a reference light detection groove 3 by using a KOH solution wet etching method, and two full-through holes are etched as a signal light channel 4 and a signal light detection groove 5. Furthermore, the substrate is covered with metal pads 6 for subsequent sensor mounting.

A preparation method for preparing the residual chlorine detection sensor comprises the following steps:

1) selecting a four-inch silicon wafer with a (100) crystal face on the surface and a polished and oxidized single side as a substrate, wherein the thickness of an oxide layer is 1um, and the surface flatness of the silicon wafer is less than 0.1um as shown in figures 3-1 and 3-2;

2) the above substrate was coated (positive resist LC100A, 1000r x 30s, 2.4um thick as in fig. 3-3), pre-baked (hotplate temperature 110 ℃, time 90 s), photo-etched (exposure time 15 s), developed (FHD-320 developer, development time 40 s), post-developed (135 ℃, 30min, acting as a firm resist film). Preparing a silicon oxide layer window shown in the figures 3-4, etching the exposed silicon oxide layer by using a BOE solution wet method to expose a silicon substrate, and preparing corrosion windows of a light source groove, a detection light groove, a reference light groove and a reference light channel, as shown in figures 3-5;

3) repeating the steps (1) and (2) to form the other half of the etching windows of the light source groove and the detection light groove on the back surface of the silicon wafer, as shown in fig. 3-6, 3-7, 3-8, and 3-9 (since the reference light groove and the reference light channel do not need to pass through the object to be detected, a through hole is not formed by double-sided etching);

4) metal pre-strip (this operation is performed in a liquid bath); the components are sulfuric acid solution and hydrogen peroxide solution of 10-15mL, the principle is to remove photoresist by using strong oxidizing property, the temperature of a solution tank is kept constant at 120 ℃, the cleaning time is 10min, and the result is shown in figures 3-10;

5) KOH corrosion: the solution adopts 30 percent KOH corrosive liquid, when the temperature of the solution is 50 ℃, the speed of corroding Si by the 30 percent KOH is 10.3 um/h, and the speed of corroding SiO2 is 0.05-0.06 um/h. When the temperature of the solution is 40 ℃, the speed of etching Si by 30% KOH is 5 um/h, the silicon layer is etched by the anisotropic wet method under the condition of 50 ℃, and a light source groove, a detection light groove, a reference light groove and a reference light channel are prepared according to the difference of the etching speeds of the KOH to Si and SiO2, as shown in figures 3-11;

6) removing the residual silicon oxide layer on the back surface by using BOE solution, as shown in FIGS. 3-12;

7) the lift-off process is adopted (the process comprises: photolithography process, magnetron sputtering process, ultrasonic lift-off process) to prepare a metal pad on the oxide layer, as shown in fig. 3-13;

8) bonding glass, namely bonding a layer of high-transmittance glass on the back surface of a silicon wafer, and ensuring that liquid to be detected does not permeate into a sensor during detection under the condition that a light path is not influenced as much as possible, as shown in figures 3-14;

9) and (3) light source/detector welding, namely welding (7) the front surface of the patch type light source/detector (with double-sided welding spots) to a metal bonding pad sputtered around the through hole (when the light source/detector is placed for welding, the light emitting/light sensing part of the light source/detector can extend into the through hole), wherein a certain space is still left after the light source/detector is welded on the bonding pad, and then the bonding pad can be butted with a signal processing circuit.

The technical key point to be solved by the invention is the detection of the turbidity in tap water, the design core is a light-splitting micro-nano structure constructed based on the MEMS technology, and a micro light source and a detector are selected, so that the preparation method of the turbidity sensor with miniaturization, high performance and low price is provided, and the market vacancy is made up. The key points are as follows: preparing reference light, detection light and signal light channels on a silicon substrate based on (100) silicon wafer potassium hydroxide wet etching;

a potassium hydroxide wet etching process is adopted, a double-sided polished silicon oxide wafer with a (100) crystal face on the surface is selected as a substrate, a half-through channel and a half-through hole are etched by the wet etching to serve as a reference light channel and a reference light detection groove, and two full-through holes are etched to serve as a signal light channel and a signal light detection groove. The micro-nano process can realize the detection of signal light and the detection of reference light at the same time in an extremely small size.

The prepared device is subjected to scribing, routing and packaging to complete the preparation of the whole sensor, and can be used for actual experimental test and application.

The invention has the following beneficial effects: a method for preparing turbidity sensor based on micro-processing technology is developed and used, which integrates the detection of reference light and the detection of signal light on a microchip, thus greatly widening the application occasions of the sensor. And because no harmful substance is generated in the detection after the preparation, the method can be used in the occasions with high safety level requirements such as tap water pipelines. The novel underwater turbidity detection sensor microchip designed and produced has the remarkable advantages of high safety, high reliability, small size, long service life and capability of being prepared in batches and reducing cost, and provides support for large-scale application of turbidity sensors in the field of tap water monitoring.

The above description of the preferred embodiments of the present invention is provided to enable those skilled in the art to make various changes and modifications without departing from the spirit of the present invention, and these changes and modifications should be construed as being included in the scope of the present invention.