A high-adhesion platinum thin film temperature sensor without an adhesive layer and a preparation method thereof

Abstract

The present invention relates to the field of temperature sensors, and in particular to a high-adhesion platinum thin film temperature sensor without an adhesion layer and a preparation method thereof, wherein the platinum thin film temperature sensor includes an alumina ceramic substrate, a platinum thin film layer, and a silicon dioxide protective layer in order from bottom to top; the structure does not include an adhesion layer, and by improving the magnetron sputtering process and ion beam etching process parameters, the adhesion between the platinum thin film layer and the substrate is enhanced, the detection accuracy of the temperature sensor is improved, and the process preparation flow is reduced, and the preparation efficiency is improved; and in the lead packaging, it uses hot pressing welding technology and glass slurry insulation treatment, which improves the success rate of welding leads and effectively reduces noise interference. In addition, the present invention solves the problem of photoresist carbonization during ion beam etching through a multi-stage cooling etching process.

Description

Technical Field

[0001] The invention relates to the field of temperature sensors, and in particular to a high-adhesion platinum thin film temperature sensor without an adhesion layer and a preparation method thereof. Background Art

[0002] Platinum is one of the most commonly used sensitive materials for temperature sensors. It has the advantages of good linearity, high sensitivity, and high stability. The resistance of platinum resistors has a specific functional relationship with temperature, which is easy to read in the system. Common platinum thermal resistors are divided into glass package type, mica type, ceramic package type, and thin film type.

[0003] Thin-film platinum thermal resistor is a temperature sensor with platinum thin film as sensitive element. It has the characteristics of fast response speed, high precision and good linearity. It is often used to measure the temperature of high-temperature media and can meet the high-precision and fast-response detection requirements of deep-sea temperature signal detection.

[0004] In the preparation process of traditional thin-film platinum thermal resistors, since platinum cannot adhere well to substrate materials such as silicon or aluminum oxide, an adhesion layer is usually prepared between the platinum film and the substrate to enhance adhesion. Common adhesion layers include titanium, chromium, tantalum, and SiO2. In some studies, Cr2O3, MgO, and ITO are used as adhesion layers. The presence of the adhesion layer enhances the adhesion between platinum and the substrate, but during high-temperature annealing, the adhesion layer will also diffuse into the platinum layer, affecting the electrical properties of the platinum film and reducing the overall performance of the sensor device.

[0005] During the platinum film stripping process, for a platinum film with a thickness of 800nm, the photoresist will collapse, and the platinum film layer at the edge of the photoresist will also collapse, resulting in an uneven and uniform edge pattern of the prepared platinum wire, which is seriously inconsistent with the theoretical design.

[0006] At the same time, in the traditional process of using solder paste to solder silver wires on the chip surface, the excessively high welding gun temperature will cause the platinum film layer to fall off the pad, and the silver wire is unstable during the insulation process and is easy to fall off the pad. In addition, heat shrink tubing is generally used to insulate the solder joints in the traditional process, which will increase the chip packaging volume and is not suitable for miniaturized production. Summary of the invention

[0007] To solve the above problems, the present invention provides a high-adhesion platinum thin film temperature sensor without an adhesion layer and a preparation method thereof, an ion beam etching process is used to prepare a high-quality platinum thin film layer pattern, and the adhesion of the platinum thin film on the substrate is improved by improving the magnetron sputtering parameters, thereby reducing the adhesion layer between the platinum thin film and the substrate.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] A high-adhesion platinum thin film temperature sensor without an adhesion layer. The temperature sensor has no adhesion layer in its structure and only comprises a three-layer structure of an alumina ceramic substrate, a platinum thin film layer, and a silicon dioxide protective layer. The ceramic substrate is a 2-inch square Kyocera or 4-inch square Kyocera with a purity of 99.6%. The platinum thin film layer is an arc-cornered broken-line structure, including a platinum wire pattern portion and a pin portion, which is sputtered on the alumina ceramic substrate. The silicon dioxide protective layer covers the platinum wire pattern portion of the platinum thin film layer. The pin portion of the platinum thin film layer is exposed platinum. Silver wires are welded using hot pressing technology, and glass slurry is used for insulation at the welding points.

[0010] The present invention also provides a method for preparing the above-mentioned high-adhesion platinum thin film temperature sensor without an adhesive layer, comprising the following steps:

[0011] Step 1: sputter a platinum film layer with a thickness of 800nm ​​on the upper surface of the alumina ceramic substrate; specifically, magnetron sputtering technology is used to perform segmented sputtering on the alumina ceramic substrate at 60°C, and the pressure in the sputtering chamber is 1.8mtorr. First, high power 500W is used to sputter 100nm to improve the adhesion of the film, and then low power 300W is used to sputter 700nm to improve the density of the platinum film, thereby improving the accuracy and stability of the temperature sensor;

[0012] Step 2: Perform positive photolithography on the platinum thin film layer to obtain a photoresist pattern; specifically, use a spin coating method to drop the photoresist on the platinum thin film layer, set the speed to 3000 rpm, rotate for 30 seconds, pre-bake on a hot plate at 100°C for 1 minute, and the exposure parameter is 200mJ / cm 2 ,The development time is 1min15s. After development, the photoresist shows a platinum wire pattern. No post-baking is performed in this step to ensure that the photoresist will not be carbonized during etching;

[0013] Step 3: performing ion beam segmented cooling etching on the photoresist pattern, firstly applying a certain thickness of thermal conductive silicone grease on the back of the alumina ceramic substrate to enhance the thermal conductivity of the chip, then etching the remaining part with the photoresist pattern as a mask, and the etching angle is 90°; in the ion beam etching parameters, the ion energy and the ion beam density ensure the uniformity and consistency of the etching pattern, therefore, the present invention proposes multi-segment cooling etching, controlling the etching time to avoid carbonization of the photoresist, etching for 5 minutes each time, cooling naturally for 10 minutes, repeating 5 times, ensuring that the photoresist is cooled before carbonization, and finally obtaining a platinum wire pattern with good uniformity and steepness;

[0014] Step 4: Clean the photoresist with acetone, ethanol and deionized water, wherein the photoresist needs to be soaked in acetone for 2 hours, and finally obtain a complete platinum thin film layer platinum wire pattern; wherein the width of the platinum thin film layer platinum wire pattern is 10um or 20um; and the size of a single sensor chip is 10mm×2mm×0.4mm;

[0015] Step 5: A 1um SiO2 protective layer is prepared on the cleaned platinum thin film layer platinum wire pattern using a low pressure chemical vapor deposition process, with deposition parameters: power 400W, temperature 130°C;

[0016] Step 6: positive photolithography is performed on the SiO2 protective layer, and photoresist is dropped onto the surface of the SiO2 protective layer by spin coating to prepare a silicon dioxide protective layer pattern. The silicon dioxide protective layer pattern after development is a square, protecting the location of the platinum wire;

[0017] Step 7: Reactive ion etching is performed on the silicon dioxide protective layer at the pad of the sensor chip to expose the platinum film at the platinum wire pin to facilitate subsequent lead welding;

[0018] Step 8: Cleaning the photoresist on the surface of the sensor chip using acetone, ethanol, and deionized water. Specifically, after soaking in acetone for two hours, soaking in ethanol for 20 minutes, and then using a water gun to rinse under flowing deionized water, finally obtaining a complete silicon dioxide protective layer pattern;

[0019] Step 9: Perform welding and packaging: Use hot pressing welding technology to weld the silver wire to the pad, and apply glass paste on the solder joint for insulation. The welded silver wire on one pad is a double-wire system after being folded in half. This can eliminate lead errors and effectively improve detection accuracy.

[0020] Furthermore, the alumina ceramic substrate is a 2-inch or 4-inch Kyocera (A493) with a purity of 99.6%, and the purity of the platinum target used is 99.9999%.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The purity of the platinum target material used in the sputtering of the present invention is 99.9999%, which greatly retains the original temperature characteristics of platinum and can effectively improve the acquisition accuracy and sensitivity of the temperature sensor. The thermal expansion coefficient of the Kyocera (A493) substrate used is close to that of platinum, which can make platinum better adhere to the substrate. The platinum thin film temperature sensor does not have an adhesive layer structure, which reduces the process flow and greatly improves production efficiency.

[0023] (2) The segmented magnetron sputtering process of the present invention can make a platinum film with a thickness of 800nm ​​have high adhesion on an alumina ceramic substrate and good density. Under this condition, the grains of the sputtered film are evenly distributed, the gaps between the grain boundaries are reduced, the crystallinity of the platinum film is improved, the conductivity of the film is greatly enhanced, and the temperature coefficient of resistance of the platinum film is increased, which can ensure the long-term stability of the platinum film in practical applications.

[0024] (3) The multi-stage cooling etching process of the present invention is different from the traditional stripping process, which requires a long processing time and may have the risk of damaging the workpiece. It realizes the preparation of platinum thin film platinum wire pattern by ion beam etching process, and can process more materials in the same time, thereby improving the process preparation efficiency. At the same time, the multi-stage cooling etching process can effectively solve the carbonization problem caused by the sensitivity of photoresist to ion beam temperature, thereby preparing higher quality platinum wire patterns.

[0025] (4) The present invention uses hot pressing welding technology to weld the silver wire to the pad, which solves the problem that the platinum film layer is easily detached from the substrate, improves the success rate of welding leads, and uses glass paste to insulate and package the solder joints. Only a very thin layer of glass paste is needed to fix the silver wire, which does not increase the chip volume and reduces noise interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic structural diagram of a high-adhesion platinum thin film temperature sensor unit without an adhesive layer according to an embodiment of the present invention;

[0027] Figure 2 This is a process flow chart of preparing a high-adhesion platinum thin film temperature sensor without an adhesion layer according to an embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram of packaging a high-adhesion platinum thin film temperature sensor without an adhesive layer according to an embodiment of the present invention;

[0029] In the figure: 1-alumina ceramic substrate; 2-platinum thin film layer; 3-silicon dioxide protective layer; 4-photoresist; 5-silver wire; 6-glass slurry.

[0030] Figure 4 This is the platinum film adhesion test result;

[0031] In the figure: (a) the film fell off before the improved process, (b) the film did not fall off after the improved process. DETAILED DESCRIPTION

[0032] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0033] like Figure 1As shown, a high-adhesion platinum thin film temperature sensor without an adhesion layer of the present invention has a single size of 10mm×2mm×0.4mm, and includes an alumina ceramic substrate 1, a high-purity platinum thin film layer 2 and a silicon dioxide protective layer 3 from bottom to top. The alumina ceramic substrate 1 uses Kyocera: A493, which has a similar thermal expansion coefficient to platinum, and platinum can be better attached to the substrate; a high-purity platinum thin film layer 2 with a thickness of 800nm ​​is prepared by a magnetron sputtering process, and the purity of the sputtered platinum target material is 99.9999%, ensuring good temperature characteristics of platinum; by setting different sizes of power segmented sputtering platinum thin film layers, the adhesion and density of the platinum thin film layer are improved, and at the same time, the uniformity of the film thickness is accurately controlled by controlling the sputtering time, and the high repeatability of the preparation process is achieved; in summary, the selection of the substrate and the optimization of the magnetron sputtering process parameters can reduce the existence of the adhesion layer, and effectively solve the problem of the adhesion layer diffusing to the platinum thin film layer to cause platinum layer contamination.

[0034] Further, a high-adhesion platinum thin film temperature sensor without an adhesion layer of the present invention adopts an ion beam etching process to prepare a platinum thin film layer platinum wire pattern. The ion beam etching process is a pure physical process for etching platinum wire, which can improve the resolution of nano patterns, change the ion beam etching angle to control the graphic contour, and the etched pattern has good directionality and high steepness. However, the photoresist is greatly affected by temperature during the ion beam etching process, which easily causes the problem of photoresist carbonization. The carbonized photoresist is still difficult to remove even after heating and soaking in organic cleaning and degumming liquid. If ultrasonic cleaning, cotton swab erasing and other methods are used, the adhesion, surface roughness and uniformity of the platinum film will be greatly damaged. Therefore, the segmented ion etching process applies thermal conductive silicone grease to the ceramic sheet to enhance thermal conductivity, and adjusts the etching and cooling time at the same time, which solves the problem of photoresist carbonization and pollution of the platinum film during ion beam etching.

[0035] Furthermore, the platinum thin film layer of the high-adhesion platinum thin film temperature sensor without an adhesive layer of the present invention is a zigzag structure with a circular arc corner, including a platinum wire pattern portion and a pin portion, the pin portion is exposed platinum, and the silver wire is welded by hot pressing welding technology, and the welding point is insulated by glass slurry 6, which improves the success rate of welding the lead and effectively reduces noise interference.

[0036] like Figure 2 As shown, a method for preparing a high-adhesion platinum thin film temperature sensor without an adhesive layer comprises the following steps:

[0037] Step 1: sputtering a platinum film layer 2 with a thickness of 800nm ​​on the upper surface of the alumina ceramic substrate 1, specifically: using magnetron sputtering technology, using different powers of high and low to sputter in stages on the alumina ceramic substrate 1 at 60°C, during sputtering, the air pressure in the sputtering chamber is 1.8mtorr, first using high power 500W to sputter 100nm to improve the adhesion of the film, and then using low power 300W to sputter 700nm to improve the density of the platinum film, thereby improving the accuracy and stability of the temperature sensor;

[0038] Step 2: Perform positive photolithography on the platinum thin film layer 2 generated in step 1; specifically: use the spin coating method to drop the photoresist 4 on the platinum thin film layer 2, set the speed to 3000 rpm, rotate for 30 seconds, pre-bake on a hot plate at 100°C for 1 minute, and the exposure parameter is 200mJ / cm 2 ,The development time is 1min15s. After development, the photoresist shows a platinum wire pattern. No post-baking is performed in this step to ensure that the photoresist will not be carbonized during etching;

[0039] Step 3: The photoresist pattern 4 generated in step 2 is subjected to ion beam segmented cooling etching. During etching, a certain thickness of thermal conductive silicone grease is first applied to the back of the alumina ceramic substrate 1 to enhance the thermal conductivity of the chip. Then, the photoresist pattern 4 is used as a mask to etch the remaining portion. The etching angle is 90°. Each etching is 5 minutes, and cooling is 10 minutes. This is repeated 5 times to ensure that the photoresist is cooled before carbonization. Finally, a platinum wire pattern with good uniformity and steepness is obtained.

[0040] Step 4: using acetone, ethanol, and deionized water to clean the photoresist pattern 4, wherein the photoresist pattern 4 needs to be immersed in acetone for 2 hours, and finally obtaining a complete platinum thin film layer platinum wire pattern with a width of 10um or 20um;

[0041] Step 5: On the platinum thin film layer platinum wire pattern generated in step 4, a 1um SiO2 protective layer 3 is prepared by low pressure chemical vapor deposition process, and the deposition parameters are: power 400W, temperature 130°C;

[0042] Step 6: positive photolithography is used on the SiO2 protective layer 3 generated in step 5 to prepare a silicon dioxide protective layer pattern. The photoresist 4 is also dropped onto the surface of the SiO2 protective layer 3 by spin coating. The photoresist pattern after development, i.e., the silicon dioxide protective layer pattern, is a square to protect the location of the platinum wire.

[0043] Step 7: Reactive ion etching is performed on the silicon dioxide protective layer at the pad of the sensor chip to expose the platinum film at the platinum wire pin to facilitate subsequent lead welding;

[0044] Step 8: Use acetone, ethanol, and deionized water to clean the photoresist on the surface of the sensor chip prepared in step 7. Soak it in acetone for 2 hours to finally obtain a complete silicon dioxide protective layer pattern.

[0045] Step 9: Welding package: Figure 3 As shown, the silver wire 5 is welded to the pad by hot pressing welding technology, and glass paste is applied at the welding point for insulation. The welding silver wire on one pad is a double-wire system after folding in half, which can eliminate the lead error and effectively improve the detection accuracy. Specifically, the width of the welding silver wire is 0.1mm and the length is 7cm. The silver wire used is folded and welded, which can effectively eliminate the lead error and improve the measurement accuracy. The two folded silver wires are of the same length. The silver wire used is a varnished silver wire, which effectively avoids signal interference and improves the detection accuracy. The welding technology adopts hot pressing welding, which is suitable for the packaging and welding of micro-nano sensor devices, effectively improves the welding success rate, and reduces the fall of the platinum film from the substrate.

[0046] Adhesion test

[0047] The substrate used in this experiment is Kyocera (A493) with a purity of 99.6%, and the platinum target has a purity of 99.9999%.

[0048] Control group: After thoroughly cleaning the ceramic sheet with acetone-ethanol-deionized water, a 800nm ​​platinum film was sputtered on the surface of the ceramic substrate by DC magnetron sputtering. The experiment found that the film layer sputtered with a single power was very easy to fall off, and it would bulge from the substrate during the subsequent annealing process, causing the platinum wire to break.

[0049] Experimental group: After the ceramic wafer was thoroughly cleaned with acetone-ethanol-deionized water, it was first sputtered with a high power of 500W for 100nm to improve the adhesion of the film, and then with a low power of 300W for 700nm.

[0050] The film adhesion is qualitatively measured by the peeling method. The specific method is to attach a tape to the surface of the film, then apply tension to the tape, and after pulling off the attached tape, the adhesion is judged based on the area of ​​the film that is peeled off. The test results are as follows: Figure 4 As shown: (a) is a platinum film layer sputtered at a single power. After the tape is peeled off, the film detachment area is 100%. Figure (b) is the surface of the film sputtered in segments, leaving only slight traces of the tape, and no platinum has fallen off. It can be seen that segmented sputtering effectively improves the adhesion of the film.

[0051] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a high-adhesion platinum thin film temperature sensor without an adhesive layer, characterized in that: The following steps are involved: Step 1: sputtering a platinum film layer with a thickness of 800 nm on the upper surface of the alumina ceramic substrate; Step 2: performing positive photolithography on the platinum thin film layer to obtain a photoresist pattern; Step 3: performing ion beam segmented cooling etching on the photoresist pattern, using the photoresist pattern as a mask and etching the remaining part, with an etching angle of 90°, etching for 5 minutes each time, cooling naturally for 10 minutes, and repeating for 5 times; Step 4: Use acetone, ethanol, and deionized water to clean the photoresist to obtain a complete platinum thin film layer platinum wire pattern; Step 5: A 1um SiO2 protective layer is prepared on the cleaned platinum thin film layer platinum wire pattern using a low pressure chemical vapor deposition process, with deposition parameters: power 400W, temperature 130°C; Step 6: Using positive photolithography on the SiO2 protective layer to prepare a silicon dioxide protective layer pattern, the silicon dioxide protective layer pattern after development is square, protecting the location of the platinum wire; Step 7: Reactive ion etching is performed on the silicon dioxide protective layer at the pad of the sensor chip to expose the platinum film at the platinum wire pin; Step 8: Cleaning the photoresist on the surface of the sensor chip using acetone, ethanol, and deionized water, wherein the sensor chip needs to be immersed in acetone for 2 hours to obtain a complete silicon dioxide protective layer pattern; Step 9: Welding and packaging: Use hot pressing technology to weld the silver wire to the pad, and apply glass paste at the solder joint for insulation. The welded silver wire on one pad is a double-wire system after being folded in half; The step one comprises the following steps: using magnetron sputtering technology, segmented sputtering on an alumina ceramic substrate at 60°C, the air pressure in the sputtering chamber is 1.8 mtorr, first using high power 500W to sputter 100nm, and then using low power 300W to sputter 700nm, the alumina ceramic substrate is a 2-inch or 4-inch Kyocera with a purity of 99.6%, and the platinum target material used has a purity of 99.9999%.

2. The method for preparing a high-adhesion platinum thin film temperature sensor without an adhesive layer as claimed in claim 1, characterized in that: The step 2 comprises the following steps: Use spin coating to drop photoresist on the platinum film layer, set the speed to 3000 rpm, spin for 30 seconds, pre-bake on a hot plate at 100°C for 1 minute, and the exposure parameter is 200 mJ / cm 2 ,The development time is 1min15s. After development, the photoresist shows a platinum wire pattern. No post-baking is performed in this step.

3. The method for preparing a high-adhesion platinum thin film temperature sensor without an adhesive layer as claimed in claim 1, characterized in that: In the step three, a certain thickness of thermal conductive silicone grease needs to be applied on the back of the alumina ceramic substrate to enhance the thermal conductivity of the chip.

4. The method for preparing a high-adhesion platinum thin film temperature sensor without an adhesive layer as claimed in claim 1, characterized in that: In the step 4, the width of the platinum wire pattern of the platinum thin film layer is 10 um or 20 um.

5. The method for preparing a high-adhesion platinum thin film temperature sensor without an adhesive layer as claimed in claim 1, characterized in that: The size of a single sensor chip is 10mm×2mm×0.4mm.

6. A high-adhesion platinum thin film temperature sensor without an adhesive layer, prepared by the preparation method according to any one of claims 1 to 5, characterized in that: The temperature sensor has no adhesive layer in its structure, and only includes a three-layer structure of an alumina ceramic substrate, a platinum thin film layer, and a silicon dioxide protective layer; the platinum thin film layer is an arc-cornered zigzag structure, including a platinum wire pattern portion and a pin portion, which is sputtered on the alumina ceramic substrate, and the silicon dioxide protective layer covers the platinum wire pattern portion of the platinum thin film layer. The pin portion of the platinum thin film layer is exposed platinum, and the silver wire is welded by hot pressing technology, and the welding point is insulated by glass slurry.

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