Novel SAW (Surface Acoustic Wave) interdigital strip photoetching process

Abstract

The invention relates to a novel SAW (Surface Acoustic Wave) interdigital strip photoetching process, which belongs to the field of filter devices, and is realized in a splicing plate secondary exposure mode. The main technological process comprises interdigital strip exposure and bus bar exposure, and an IDT photoetching process is carried out by avoiding an interdigital strip photoetching interference region through a two-time makeup exposure mode. By means of the secondary exposure mode, the risk that the interdigital strip rubber strips fall off can be reduced, and meanwhile the line width consistency of the interdigital strips can be improved.

Description

Technical Field

[0001] The invention belongs to the field of filter devices, and in particular relates to a novel SAW interdigitated stripe photolithography process. Background Art

[0002] Surface acoustic wave (SAW) filters generally use piezoelectric crystals such as lithium niobate or lithium tantalate as substrates, and use photolithography to make two sets of cross-finger metal electrodes IDT (Interdigital Transducer) with energy conversion function on the surface of the substrate.

[0003] The traditional interdigitated stripe lithography process mainly prepares the interdigitated stripe and the bus layer at the same time through a single exposure. However, due to the large exposure area of ​​the bus bar, part of the ultraviolet light energy will be reflected to the interdigitated stripe area near the bus bar during the exposure process, resulting in the regional energy of the interdigitated stripe in this area being greater than the energy of the interdigitated stripe in the area far from the bus bar, forming an interdigitated stripe lithography interference area (such as Figure 6 As shown). Inconsistent photolithography energy between the interference area and the non-interference area will reduce the consistency of the interdigital line width, and even cause the interdigital line in the interference area to be overexposed due to excessive energy, resulting in the strip falling off. Especially when the line width of the interdigital line is close to the exposure capacity limit of the lithography machine, the line width consistency of the interdigital line is significantly reduced and the risk of the interdigital line falling off increases sharply. The photolithography interference area will exist in the bus bar area on both sides. According to the size of the interdigital and bus bar widths, the interference area width B is 0.3-5λ, where λ is the filter transmission wavelength. Summary of the invention

[0004] The present invention aims at the problems existing in the existing SAW interdigitated stripe lithography process and proposes a novel SAW interdigitated stripe lithography process. The present invention avoids the interdigitated stripe lithography interference area by double exposure to perform IDT lithography. The double exposure method can reduce the risk of interdigitated stripe glue strip falling off and improve the line width consistency of the interdigitated stripe.

[0005] In order to achieve the above object, the present invention is implemented by the following technical scheme: a novel SAW interdigitated stripe lithography process is carried out according to the following steps:

[0006] Step S1, providing a substrate and cleaning it to prepare for subsequent photolithography;

[0007] Step S2, substrate coating preparation: a layer of photoresist is evenly coated on the substrate by a coating device;

[0008] Step S3, one-time exposure process preparation: performing exposure through a first photolithography process;

[0009] Step S4, secondary exposure process preparation: performing exposure through a second photolithography process;

[0010] Step S5, development process preparation: the wafer after the secondary photolithography in step 3) and step 4) is subjected to a development process to present the entire pattern;

[0011] Step S6: metal evaporation process preparation, evaporating the required metal onto the wafer through electron beam evaporation equipment;

[0012] Step S7, stripping process preparation, removing unnecessary metal in the pattern through a wet stripping process to form a complete metal interdigitated structure.

[0013] Furthermore, the exposure pattern in step S3 is an interdigitated bar structure, and the exposure pattern in step S4 is a bus bar structure.

[0014] Furthermore, the exposure pattern in step S3 is an interdigitated stripe structure + an overlay compensation area, and the overlay compensation area is a bus bar portion close to the interdigitated stripe structure.

[0015] Furthermore, the overlay compensation area width e is greater than the photolithography limit line width a and greater than the overlay offset b; the overlay compensation area width e is less than twice the interdigital line width c and less than the busbar width d.

[0016] Furthermore, after removing the overlay compensation area from the exposure pattern in step S4, a busbar structure remains.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: different from the traditional SAW lithography process, the present application avoids the interdigital lithography interference area through the secondary lithography process to improve the line width consistency of the interdigital stripes and reduce the risk of interdigital stripes falling off. At the same time, it also proposes to set up an overlay compensation area to avoid abnormal phenomena in the interdigital stripe graphic area caused by the graphic offset of the secondary exposure.

[0018] The use of the photolithography process of the present invention can improve the consistency of the filter interdigital strips, the appearance yield of the interdigital strips and the consistency of RF performance, and can be effectively promoted to practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the first interdigitated strip exposure area in Example 1.

[0020] Figure 2 This is the second busbar exposure area in Example 2.

[0021] Figure 3 This is the morphology of the interdigitated strip structure after peeling.

[0022] Figure 4 For implementing step 2, a single exposure with a photolithography compensation area is provided.

[0023] Figure 5For the secondary exposure area in Example 2.

[0024] Figure 6 This is a schematic diagram of the primary lithography interference area. DETAILED DESCRIPTION

[0025] The following will describe the implementation methods of the present invention in detail with reference to the accompanying drawings and examples, so as to fully understand and implement the implementation process of how the present invention applies technical means to solve technical problems and achieve technical effects.

[0026] Example 1

[0027] A novel SAW interdigitated stripe lithography process is carried out in the following steps:

[0028] Step S1, providing an LN substrate and cleaning it to prepare for subsequent photolithography;

[0029] Step S2, substrate coating preparation: a layer of photoresist is evenly coated on the substrate by a coating device;

[0030] Step S3: Figure 1 The single exposure process shown is prepared: exposure is performed through the first photolithography process, and the exposure pattern is an interdigitated stripe structure;

[0031] Step S4: Figure 2 As shown, the secondary exposure process is used for preparation: exposure is performed through the second photolithography process, and the exposure pattern is a busbar structure;

[0032] Step S5, development process preparation: the wafer after the secondary photolithography in step 3) and step 4) is subjected to a development process to present the entire pattern;

[0033] Step S6: metal evaporation process preparation, evaporating the required metal onto the wafer through electron beam evaporation equipment;

[0034] Step S7: Figure 3 As shown, the stripping process is used to remove the unnecessary metal in the pattern through a wet stripping process to form a complete metal interdigitated structure.

[0035] This embodiment adopts the double exposure of the plate to perform the interdigitated stripe lithography process, which can avoid the influence of the interdigitated stripe interference area on the line width consistency and appearance of the interdigitated stripe.

[0036] Example 2

[0037] A novel SAW interdigitated stripe lithography process is carried out in the following steps:

[0038] Step S1, providing an LN substrate and cleaning it to prepare for subsequent photolithography;

[0039] Step S2, substrate coating preparation: a layer of photoresist is evenly coated on the substrate by a coating device;

[0040] Step S3: Figure 4 As shown, one-time exposure process preparation: exposure is performed through the first photolithography process, and the exposure pattern is an interdigitated stripe structure + an overlay compensation area, and the overlay compensation area is a bus bar portion close to the interdigitated stripe structure;

[0041] In addition, the overlay compensation area width e is greater than the photolithography limit line width a, and greater than the overlay offset b; the overlay compensation area width e is less than twice the interdigital line width c, and less than the busbar width d;

[0042] Step S4: Figure 5 As shown, the secondary exposure process is prepared: exposure is performed through the second photolithography process, and after the exposure pattern is removed from the overlay compensation area, the remaining busbar structure;

[0043] Step S5, development process preparation: the wafer after the secondary photolithography in step 3) and step 4) is subjected to a development process to present the entire pattern;

[0044] Step S6: metal evaporation process preparation, evaporating the required metal onto the wafer through electron beam evaporation equipment;

[0045] Step S7, stripping process preparation, removing unnecessary metal in the pattern through a wet stripping process to form a complete metal interdigitated structure.

[0046] On the basis of the double exposure process in the above embodiment, in order to prevent the overlap of the first exposure and the second exposure from causing the exposure of the busbar to enter the interdigital stripe area, this embodiment sets an overlay compensation area in the first exposure area. The single exposure with the overlay compensation area will not cause the pattern overlap due to the overlay offset problem during the double exposure, thereby making the interdigital stripe pattern abnormal. The process in this embodiment can further improve the appearance yield of the filter interdigital stripe.

[0047] The substrate in the present invention is not limited to LN substrate, and can also be applicable to quartz substrate, LT substrate, POI substrate, etc. Moreover, the splicing double exposure process of the present invention is applicable to the field of SAW filters, including Normal SAW, TC-SAW, TF-SAW, etc. The present invention can improve the consistency of the filter interdigital strips, the appearance yield of the interdigital strips, and the consistency of RF performance, and can be effectively promoted to practical applications.

[0048] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A novel SAW interdigitated stripe lithography process, characterized in that: Follow these steps: Step S1, providing a substrate and cleaning it to prepare for subsequent photolithography; Step S2, substrate coating preparation: a layer of photoresist is evenly coated on the substrate by a coating device; Step S3, one-time exposure process preparation: performing exposure through a first photolithography process; Step S4, secondary exposure process preparation: performing exposure through a second photolithography process; Step S5, development process preparation: the wafer after the secondary photolithography in step 3) and step 4) is subjected to a development process to present the entire pattern; Step S6: metal evaporation process preparation, evaporating the required metal onto the wafer through electron beam evaporation equipment; Step S7, stripping process preparation, removing unnecessary metal in the pattern through a wet stripping process to form a complete metal interdigitated structure.

2. A novel SAW interdigitated stripe lithography process according to claim 1, characterized in that: The exposure pattern in step S3 is an interdigitated bar structure, and the exposure pattern in step S4 is a bus bar structure.

3. A novel SAW interdigitated stripe lithography process according to claim 1, characterized in that: The exposure pattern in step S3 is an interdigitated stripe structure + an overlay compensation area, and the overlay compensation area is a bus bar portion close to the interdigitated stripe structure.

4. A novel SAW interdigitated stripe lithography process according to claim 3, characterized in that: The overlay compensation zone width e is greater than the photolithography limit line width a and greater than the overlay offset b; the overlay compensation zone width e is less than twice the interdigital line width c and less than the busbar width d.

5. A novel SAW interdigitated stripe lithography process according to claim 4, characterized in that: After removing the overlay compensation area from the exposure pattern in step S4, the busbar structure remains.

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