Manufacturing method of small-size high-power-capacity thin-film high-frequency resistor

Abstract

The invention discloses a manufacturing method of a small-size high-power-capacity thin-film high-frequency resistor, and belongs to the technical field of resistors. The manufacturing method comprises the following steps: designing the layout of a resistor plane unit array on a diamond substrate; manufacturing a photoetching mask of each functional layer; performing laser drilling and scribing on the diamond substrate; chemically cleaning the carbonized diamond and residues; a thin film sputtering resistance layer; sputtering a surface metal electrode layer and a side metal electrode layer by a thin film; manufacturing a side electrode layer; photoetching to form a front surface electrode pattern, a back surface electrode pattern and a resistive layer pattern; carrying out substrate film heat treatment; the invention relates to resistor chip segmentation. The problems that in the prior art, diamond deposition and substrate etching are complex in technology and difficult to achieve are solved; in the prior art, laser cutting enables the surface of diamond to be carbonized, and residual carbonized layers and chips after processing are difficult to remove, so that a metalized area is seriously polluted, and the performance of a resistance layer is deteriorated. The method can be widely applied to the technical field of electronic components with diamond substrates as substrates.

Description

Technical Field

[0001] This invention belongs to the field of resistor technology, and more specifically to the field of high-frequency power resistor technology. In particular, it relates to a method for manufacturing a small-size, high-power capacity thin-film high-frequency resistor. Background Technology

[0002] Small-sized, high-power radio frequency (RF) resistors are characterized by high application frequency, good high-frequency characteristics, small size, and large power capacity. They are widely used in RF circuits in the communication field, serving functions such as impedance matching, signal isolation, pulse absorption, and level regulation. With the miniaturization and integration of electronic devices, power resistors are also becoming increasingly miniaturized and integrated, while manufacturing processes are continuously evolving towards thin-film, high-frequency, and multi-material applications. Traditional manufacturing methods for power resistors often use aluminum nitride (ANT) or beryllium oxide (BDO) substrates, but both materials have limited thermal conductivity (ANT approximately 170 W / mK to 200 W / mK, BDO approximately 230 W / mK to 260 W / mK). This results in large product size and low power density.

[0003] Diamond substrates possess a thermal conductivity of 1000 W / mK to 2000 W / mK, making them the best thermally conductive material currently available for power device fabrication. However, diamond's high hardness and brittleness make the fabrication of various small-sized components using diamond substrates extremely challenging. Currently, the primary process for fabricating power devices using diamond involves depositing a diamond film on a raw substrate using CVD, followed by grinding, polishing, dicing, and etching. A thin-film resistor is then constructed on the surface of the CVD diamond film, and its resistance is adjusted through heat treatment. Electrodes are then fabricated on the resistor surface, and finally, the substrate is removed using acid treatment. This method involves both diamond deposition and substrate etching, making the process complex and difficult to implement. Another method is to directly use a diamond substrate, and after metallizing and patterning its surface, use a laser to cut it. The problem with this method is that after the component pattern is prepared, laser cutting is required to divide the product. Laser cutting will carbonize the diamond surface, and the residual carbonized layer and debris after processing are difficult to remove. This will cause significant pollution to the metallized area and lead to deterioration of the resistive layer performance.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The technical problem to be solved by this invention is that the deposition of diamond and the etching of the substrate in the prior art are complicated and difficult to achieve; laser cutting will cause the diamond surface to carbonize, and the residual carbonized layer and debris after processing are difficult to remove, which will cause great pollution to the metallized area and lead to the deterioration of the resistive layer performance.

[0006] Therefore, the present invention provides a method for fabricating a small-size, high-power thin-film high-frequency resistor, such as... Figure 1-3 As shown. The production method is as follows: (1) Based on the design of the resistor and the planar dimensions of the diamond substrate, the planar unit array of the resistor is laid out, and the drilling positions and scribe lines on the diamond substrate are set.

[0007] (2) Design photolithography masks for resistive layer, electrode layer and bottom layer on diamond substrate.

[0008] (3) Use a laser to drill holes and scribing lines on a diamond substrate to create a planar array of resistor units.

[0009] (4) By selecting a chemical cleaning process, the carbonized diamond and residue after laser processing are cleaned.

[0010] (5) A resistor layer is sputtered on the substrate surface with scribing grooves and through holes by thin film sputtering process.

[0011] (6) The surface and side metal electrode layers are completed in one step by thin film sputtering process.

[0012] (7) Photolithography forms the front surface electrode pattern.

[0013] (8) Photolithography forms the resistive layer pattern.

[0014] (9) Heat treatment is performed on the substrate after photolithography.

[0015] (10) The resistor is divided by mechanically dividing along the grooves without contacting the functional film layer of the resistor and without generating any extra material.

[0016] Technical effects of the invention: Resistors prepared using this method have good adhesion, good appearance quality, and high yield because laser processing is performed first, followed by the fabrication of the resistive and metal layers.

[0017] Breaking through the limitations of traditional substrate thermal conductivity, diamond substrates are used as resistor substrates to achieve small size and high power density. Thin film fabrication is used, and gold wire bonding is used for mounting, which meets the requirements of micro-assembly processes and facilitates integration into small-sized RF systems.

[0018] The preparation process of this invention is simple, with high production efficiency and yield. It solves the problems of diamond's high hardness, difficult processing, carbonization during laser processing, impurity residue, poor adhesion of the metal layer, poor electrical stability, and low splitting precision.

[0019] It can be widely used in the field of electronic components technology with diamond substrates. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the preparation process of the present invention.

[0021] Figure 2 This is a schematic diagram of the resistor structure according to an embodiment of the present invention.

[0022] Figure 3 This is a schematic diagram of the substrate layout and perforation of the present invention.

[0023] In the figure: 1 is the diamond substrate, 2 is the resistive layer, 3 is the electrode underlayer, 4 is the electrode blocking layer, 5 is the front surface electrode, 6 is the side surface electrode, 7 is the back electrode, 8 is a single resistor planar unit, 9 is the grounding through hole, 10 is the alignment through hole, and 11 is the back scribing groove. Detailed Implementation

[0024] like Figure 1-3 As shown, the method for fabricating a small-size, high-power thin-film high-frequency resistor, taking an RF power resistor with dimensions of 1.0mm × 1.0mm × 0.38mm, a power of 30W, and an operating frequency of 30GHz as an example, is implemented as follows: The resistive layer is made of tantalum nitride (TaN).

[0025] The material for the metal underlayer is titanium tungsten (TiW).

[0026] The material of the metal barrier layer is nickel (Ni).

[0027] The material of the surface electrode layer is gold (Au).

[0028] (1) Substrate selection and layout design Select a diamond disc with a diameter of 65mm, a thickness of 0.38mm, and single-sided polishing. The surface roughness is less than 100nm and the back roughness is less than 2µm. Based on the size of a single resistor and the structure of the grounding terminal, design a layout diagram for laser drilling and scribing, and add alignment holes.

[0029] (2) Laser drilling and scribing A high-power picosecond laser cutting machine is used to perform laser processing on diamond according to the layout design. First, lines are scribing on the roughened back surface with a depth of 0.15mm to 0.2mm and a groove width of 50µm. Then, metallized grounding through holes and alignment holes are prepared on the polished surface. The grounding through holes are 0.2mm to 0.3mm wide and 10.4mm long, and the alignment holes are circular through holes with a diameter of 0.3mm to 0.4mm.

[0030] (3) Cleaning Cleaning of laser-processed diamond substrates in four steps: 1) Use ultrasonic cleaning to sonicate the substrate with water (40kHz, 20 minutes).

[0031] 2) Chemical cleaning is used. Mixed acid solution (concentrated sulfuric acid / nitric acid = 3 / 1), and the substrate is placed in the prepared acid solution. The substrate is cleaned by heating in a water bath at 80℃±10℃ for 30min±10min to remove surface residues and surface carbon compounds.

[0032] 3) Use an ultrasonic cleaner for a second cleaning. Place the substrate in a high-efficiency degreasing cleaner, acetone, and clean water for ultrasonic cleaning for half an hour each.

[0033] 4) Plasma activation is used, employing a mixture of argon and hydrogen gas (ratio 4:1) for plasma treatment (350W power, 5 minutes) to improve the adhesion to the substrate surface.

[0034] (4) Splashing A tantalum nitride (TaN) resistive layer was sputtered onto a polished diamond substrate using reactive magnetron sputtering. The material used was tantalum nitride (TaN), and the sputtering target was a 99.99% pure tantalum target. The sputtering parameters were set as follows: vacuum degree 8 × 10⁻⁶. -7 Pa, sputtering power 500W, argon and nitrogen mixed gas (argon flow rate 41.7 sccm, nitrogen flow rate 1 sccm), control the TCR of the resistive layer after sputtering ≤100ppm.

[0035] A titanium-tungsten-gold (TiW / Ni / Au) electrode layer is sputtered on both the front and back sides of the substrate using reactive magnetron sputtering. A surface electrode layer is then sputtered on the surface after the tantalum nitride layer has been sputtered. First, a titanium-tungsten metal transition layer is sputtered, followed by a gold layer for the front surface electrode layer, with a gold layer thickness of not less than 2.0 µm. Next, the substrate is flipped so that the back side faces upward, and a back metal underlayer titanium-tungsten layer, a barrier nickel layer, and a back surface electrode layer gold layer are sputtered, with a gold layer thickness of 1 µm. Finally, the substrate is flipped back to the front side, and a thin gold layer with a thickness of 0.5 µm is sputtered on top of the gold layer for the front surface electrode layer.

[0036] Sputtering parameters for titanium-tungsten: power 1000W, argon flow rate 100sccm; sputtering parameters for gold: power 1000W, argon flow rate 70sccm.

[0037] (5) Photolithography to fabricate resistor patterns 1) First, use a glue sprayer to spray a 7µm thick photoresist onto the back of the metallized diamond. After spraying the glue, place the substrate (with the glue side facing up) flat on a hot plate for baking. The baking temperature is (100±5)℃ and the time is (90±2)s. After baking, apply a layer of high-temperature tape to the back of the substrate that has been sprayed with glue. Then flip it to the front side, spray the glue on the front side, and bake it.

[0038] 2) Select the corresponding photomask and align it; expose the product using an exposure machine.

[0039] 3) Develop the exposed substrate using the appropriate photoresist developer.

[0040] 4) Select a suitable etching solution for step-by-step etching. First etch gold, then etch titanium and tungsten. Use gold etching solution for etching gold, with an etching time of 90 seconds ± 10 seconds. Use a mixture of ammonia and hydrogen peroxide (volume ratio 2:1) for etching titanium and tungsten, with an etching time of 90 seconds ± 10 seconds.

[0041] 5) Remove residual adhesive from the product surface using analytical grade acetone solution.

[0042] 6) Following steps 1) to 5), spray adhesive, dry, expose, develop, and etch to complete the preparation of the tantalum nitride layer pattern. Tantalum etchant is used to etch the tantalum nitride for 10 seconds.

[0043] (6) Heat treatment The photolithographically etched substrate is placed in a constant temperature oven at 400℃±20℃ for 30 minutes to eliminate stress between film layers and produce a tantalum oxide thin film on the surface of the tantalum nitride film to protect the resistive film layer, while further reducing TCR to within ±20ppm.

[0044] (7) Fragment With the scribed groove side of the substrate facing down, apply a UV film to the upper surface and a protective film to the lower surface. Use a mechanical segmentation dicing machine (table spacing 0.6mm~0.7mm, dicing plate indentation 0.15mm~0.2mm) to mechanically press and cut the diamond substrate along the scribed groove to complete the segmentation of a single product.

[0045] The test data and comparative analysis of the resistors of this invention are shown in Tables 1-3.

[0046] Table 1. Test values ​​of resistance TCR of the present invention Sample number 1 2 3 4 5 6 R0(25℃) 49.626 49.745 49.917 49.87 49.556 49.822 R1(-55℃) 49.633 49.765 49.93 49.877 49.559 49.839 TCR- -1.763 -5.026 -3.255 -1.755 -0.757 -4.265 R0(25℃) 49.617 49.721 49.916 49.873 49.588 49.822 R2(+125℃) 49.632 49.715 49.907 49.909 49.566 49.813 TCR+ 3.023 -1.207 -1.803 7.218 -4.437 -1.806 Table 2. Record of resistance value changes during a 1000-hour cycle life test with 30W DC power applied to the resistor of the present invention. Sample number 1 2 3 4 5 6 R0 (initial value) 50.070 50.960 50.130 50.150 50.660 50.860 R1 (1000 hours) 50.150 51.130 50.270 50.150 50.860 51.040 rate of change 0.160 0.334 0.279 0.000 0.395 0.354 Table 3. Comparison of power temperature between the resistor of the present invention and an aluminum nitride-based resistor of the same size and structure under the same mounting method and heat dissipation conditions.

[0047] In summary, this invention proposes using diamond substrates as the base material for small-sized power devices. However, most of the substrates sold by diamond processors are large circular pieces, and since diamond is currently the hardest material, it is impossible to complete the product segmentation and shaping using ordinary mechanical cutting methods. This invention proposes a method of scribing and drilling diamond substrates using picosecond lasers.

[0048] Combined with mechanical segmentation, products of a certain size are segmented, and the yield of the diced products is ≥85%.

[0049] High-power high-frequency resistors require grounding at one or both ends. For components made from diamond substrates, the traditional process of first preparing the surface, then cutting and metallizing the end faces is quite difficult. This invention simplifies the process by pre-drilling grounding holes on the diamond surface and completing the surface and side metallization in one step during the metallization process using thin-film sputtering. This greatly reduces the difficulty of preparing the diamond substrate metal edge-wrapping process.

[0050] Diamond substrates are expensive. Poor design and layout of the scribe lines and grounding vias can lead to material waste and substrate breakage during functional layer fabrication. Current designs typically use a single white border for each product. This invention employs a high-utilization layout design that allows multiple products to share a single via for side metallization while maintaining sufficient connection strength. This method maximizes the use of the diamond substrate and minimizes breakage during production.

[0051] After laser processing, a large amount of residue and degraded carbon substances will adhere to the surface of the diamond and the sides of the through holes. If the cleaning is not thorough, it will greatly affect the adhesion of the metal layer in the subsequent process. This invention uses a strong acid water bath with a certain ratio to effectively clean the carbonized diamond and surface residue after laser processing, greatly improving the adhesion of the metal layer on the diamond surface and the sidewalls of the through holes.

[0052] For high-power, high-frequency resistor applications, the resistance layer's total resistance coefficient (TCR) and the resistor's stability under long-term high-temperature operation are crucial for ensuring the resistor's functionality and long-term stable operation. This invention, through control of sputtering parameters combined with heat treatment processes, achieves a resistance TCR within ±20ppm, and the resistance change does not exceed 1% after a 1000-hour power cycle life test.

[0053] During photolithography, if the trenches or through-holes are not protected, the metal on the sidewalls and within the trenches will be etched away by the etching solution, severely affecting the product's appearance and reliability. Currently, the main production method involves applying adhesive tape to the back for protection, but this method is ineffective for substrates with trenches on the back. This invention employs a two-pronged approach: first, spraying adhesive to protect the back, and then applying adhesive tape. This combined method effectively protects the metal layers on the back, the inner walls of the through-holes, and within the trenches from etching.

[0054] Finally, it should be noted that the above embodiments are merely examples for clear illustration. This invention includes, but is not limited to, the above embodiments, and it is neither necessary nor possible to exhaustively describe all possible implementations. Those skilled in the art can make other variations or modifications based on the above description. All implementation schemes that meet the requirements of this invention are within the protection scope of this invention.

Claims

1. A method for fabricating a small-size, high-power, high-capacity thin-film high-frequency resistor, characterized in that, The production method is as follows: (1) Based on the design of the resistor and the planar dimensions of the diamond substrate, the planar unit array of the resistor is laid out, and the drilling positions and scribing lines on the diamond substrate are set. (2) Design photolithography masks for resistive layer, electrode layer, and underlay on diamond substrate; (3) Use a laser to first drill holes and scribing lines on a diamond substrate to create a planar array of resistor units; (4) The carbonized diamond and residue after laser processing are cleaned by selective chemical cleaning process; (5) A resistor layer is sputtered on the surface of a substrate with scribing grooves and through holes using a thin film sputtering process; (6) The surface and side metal electrode layers are completed in one step by thin film sputtering process; (7) Photolithography is used to form the front electrode pattern; (8) Photolithography is used to form the resistive layer pattern; (9) Heat-treat the photolithographically etched substrate; (10) The resistor is divided by mechanically dividing along the grooves without contacting the functional film layer of the resistor and without generating any extra material.

2. The method for fabricating a small-size, high-power thin-film high-frequency resistor as described in claim 1, characterized in that: The resistive layer is made of tantalum nitride (TaN). The material of the metal underlayer is titanium tungsten (TiW); The material of the metal barrier layer is nickel (Ni); The material of the surface electrode layer is gold (Au).

3. The method for fabricating a small-size, high-power thin-film high-frequency resistor as described in claim 2, characterized in that: The substrate selection and layout design uses a diamond disc with a diameter of 65mm, a thickness of 0.38mm, and single-sided polishing. The surface roughness is less than 100nm and the back roughness is less than 2µm. Based on the size of a single resistor and the structure of the grounding terminal, a layout diagram for laser drilling and scribing is designed, and alignment holes are added.

4. The method for fabricating a small-size, high-power thin-film high-frequency resistor as described in claim 2, characterized in that: The laser drilling and scribing are performed on the diamond using a high-power picosecond laser cutting machine according to the layout design. First, scribing is done on the roughened back surface with a scribing depth of 0.15mm to 0.2mm and a groove width of 50µm. Then, the side metallized grounding through holes and alignment holes are prepared on the polished surface. The grounding through holes have a width of 0.2mm to 0.3mm and a length of 10.4mm, and the alignment holes are circular through holes with a diameter of 0.3mm to 0.4mm.

5. The method for fabricating a small-size, high-power thin-film high-frequency resistor as described in claim 2, characterized in that: Cleaning of laser-processed diamond substrates in four steps: 1) The substrate was ultrasonically cleaned with water for 20 minutes at a speed of 40 kHz. 2) Chemical cleaning is used. The cleaning solution is a mixed acid solution of concentrated sulfuric acid / nitric acid = 3 / 1. The substrate is placed in the prepared acid solution and cleaned for 30min ± 10min by heating in a water bath at 80℃±10℃ to remove surface residues and surface carbon compounds. 3) Use an ultrasonic cleaner for a second cleaning. Place the substrate in a high-efficiency degreasing cleaner, acetone, and clean water for ultrasonic cleaning for half an hour each time. 4) Plasma activation is adopted, using a mixed gas of argon and hydrogen in a ratio of 4:1 for plasma treatment, with process parameters of 350W power and 5 minutes, to improve the adhesion of the substrate surface.

6. The method for fabricating a small-size, high-power thin-film high-frequency resistor as described in claim 2, characterized in that: The resistive layer was sputtered using tantalum nitride (TaN) resistive layer. Reactive magnetron sputtering was employed to sputter a resistive layer with a sheet resistance of 35Ω onto the polished surface of a diamond substrate. The material was tantalum nitride (TaN), and the sputtering target was a 99.99% pure tantalum target. The sputtering parameters were set as follows: vacuum degree 8 × 10⁻⁶. -7 Pa, sputtering power 500W, argon and nitrogen mixed gas (argon flow rate 41.7 sccm, nitrogen flow rate 1 sccm), control the TCR of the resistive layer after sputtering within ±100ppm.

7. The method for fabricating a small-size, high-power thin-film high-frequency resistor as described in claim 2, characterized in that: The sputtering of the metal layer involves sputtering a titanium-tungsten-gold (TiW / / Ni / Au) electrode layer. The titanium-tungsten-gold (TiW / Ni / Au) electrode layer is sputtered on the front and back sides of the substrate using reactive magnetron sputtering. A surface electrode layer is sputtered on the surface after the tantalum nitride layer is sputtered. First, a titanium-tungsten metal transition layer is sputtered, and then a gold layer is sputtered on the front surface electrode layer. The thickness of the gold layer is not less than 2.0µm. Then flip the substrate so that the back side is facing up, and sputter the back metal base layer (titanium-tungsten), the barrier layer (nickel), and the back surface electrode layer (gold). The gold layer thickness is 1µm. Finally, flip it to the front side and sputter a thin gold layer on the front surface electrode layer (gold). The thickness is 0.5µm. Sputtering titanium-tungsten process parameters: power 1000W, argon flow rate 100sccm; Nickel sputtering process parameters: power 1000W, argon flow rate 70sccm; Sputtering gold process parameters: power 1000W, argon flow rate 70sccm.

8. The method for fabricating a small-size, high-power thin-film high-frequency resistor as described in claim 2, characterized in that, The photolithography fabrication process for each layer of the resistor pattern is as follows: 1) First, use a glue sprayer to spray a 7µm thick photoresist onto the back of the metallized diamond. After spraying the glue, place the substrate with the glue side facing up on a hot plate for baking. The baking temperature is (100±5)℃ and the time is (90±2)s. After baking, apply a layer of high-temperature tape to the back of the substrate that has been sprayed with glue. Then flip it to the front side, spray the glue on the front side, and bake it. 2) Select the corresponding photomask and align it; Expose the product using an exposure machine; 3) Develop the exposed substrate using the appropriate photoresist developer; 4) Select a suitable etching solution for step-by-step etching. First etch gold, then etch titanium and tungsten. Use gold etching solution for etching gold, with an etching time of 90 seconds ± 10 seconds. Use a mixed solution of ammonia and hydrogen peroxide with a volume ratio of 2:1 for etching titanium and tungsten, with an etching time of 90 seconds ± 10 seconds. 5) Remove residual adhesive from the product surface using analytical grade acetone solution; 6) Following steps 1) to 5), spray adhesive, dry, expose, develop, and etch to complete the preparation of the tantalum nitride layer pattern. Tantalum etchant is used to etch the tantalum nitride for 10 seconds.

9. The method for fabricating a small-size, high-power thin-film high-frequency resistor as described in claim 2, characterized in that: The resistive layer and electrode layer patterns are fabricated using photolithography. The heat treatment process for the photolithographic substrate is as follows: the photolithographic substrate is placed in a constant temperature oven at 400℃±20℃ for 30 minutes to eliminate the stress between the film layers, and a tantalum oxide thin film is produced on the surface of the tantalum nitride film layer to protect the resistive film layer, while further reducing the TCR to within ±20ppm.

10. The method for fabricating a small-size, high-power thin-film high-frequency resistor as described in claim 2, characterized in that: The resistor is divided by placing the scribed grooved surface of the substrate downwards, attaching a µV film to the upper surface and a protective film to the lower surface, using a mechanical segmentation dicing machine with a table spacing of 0.6mm to 0.7mm and a dicing plate indentation of 0.15mm to 0.2mm, and mechanically pressing the diamond substrate along the scribed groove to divide it into individual products.

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