Preparation method for reducing standing wave effect during exposure of wafer

Abstract

A preparation method for reducing a standing wave effect during exposure of a wafer. The method comprises the following steps: S1, coating a back surface of a wafer with an antireflection film, wherein the wafer is a wafer made of a piezoelectric material, and the antireflection film is a semiconductor thin film; S2, spin-coating, with a photoresist, the surface of the wafer that has been coated with the antireflection film, and performing exposure and development processing, so as to form a photolithographic pattern; S3, stripping the photoresist off the wafer on which the photolithographic pattern has been formed; and S4, removing the antireflection film from the wafer off which the photoresist has been stripped. By means of the preparation method, a standing wave effect caused by interference between reflected light from a front surface of a wafer and reflected light from a back surface of the wafer can be reduced, such that an interdigitated appearance is improved to form a perfect sidewall structure, and the flexibility of design of a wafer can also be improved.

Description

Preparation method for reducing standing wave effect of wafer exposure

Technical field

[0001] The present invention relates to the technical field of wafer preparation, and in particular to a preparation method for reducing a standing wave effect of wafer exposure. [Background Technology]

[0002] With the development of fifth-generation wireless communication technology solutions, smartphones need to increase filters to support the increasing number of frequency bands. However, the dense frequency bands have led to a significant increase in interference between uplink signals in the system. To ensure high-quality data communication across the spectrum, a typical high-end smartphone requires at least 50 RF front-end filters. With the continuous upgrading of communication technology (such as 5G mobile phones) and the deployment of new technologies such as carrier aggregation (CA) and multiple-input multiple-output (MIMO), the number of communication frequency bands continues to increase, and this number will continue to grow rapidly.

[0003] A surface acoustic wave (SAW) resonator is a transducer-type passive bandpass filter fabricated by exploiting the piezoelectric effect and the physical properties of surface acoustic wave propagation. SAW resonators are gaining increasing attention in communication circuit design due to their compact size, strong radiation resistance, high speed, low power consumption, and high reliability. The resonant frequency of a SAW resonator can be precisely tuned over a wide range using photolithography techniques. Its small form factor, low connection loss, and low cost make it ideal for monolithic integration of filters with varying frequencies.

[0004] The most important process in the front-end preparation of surface acoustic wave filters is exposure, which determines the width of the interdigital fingers and the metallization rate, thereby affecting the center frequency and bandwidth of the filter. However, the lithium tantalate or lithium niobate wafers used in related technologies are transparent in the ultraviolet band and are prone to the standing wave effect (as shown in Figure 1) caused by the interference of reflected light from their upper and lower surfaces (front and back), resulting in wavy interdigital sidewalls (as shown in Figure 2), thereby affecting the performance of the filter. Of course, the standing wave effect can be optimized by calculating the relationship between the wafer's refractive index and wafer thickness to optimize the choice of wafer film thickness, but this will limit the choice of wafer thickness and reduce the degree of freedom in design to a certain extent.

[0005] [Summary of the invention]

[0006] The object of the present invention is to provide a preparation method for reducing the standing wave effect of wafer exposure, so as to solve the problem in the related art that the wafer is very likely to cause the standing wave effect or its design freedom is limited.

[0007] In order to solve the above technical problems, the present invention provides a preparation method for reducing the standing wave effect of wafer exposure, which comprises the following steps:

[0008] S1. Coating an anti-reflection film on the back side of a wafer; wherein the wafer is a piezoelectric material wafer, and the anti-reflection film is a semiconductor thin film;

[0009] S2, spin-coating a photoresist on the surface of the wafer coated with the anti-reflection film and performing exposure and development processes to form a photolithography pattern;

[0010] S3, stripping the photoresist on the wafer with the photolithography pattern formed thereon;

[0011] S4, removing the anti-reflection film on the wafer after stripping the photoresist.

[0012] Preferably, step S2 specifically includes the following sub-steps:

[0013] S21, spin coating optical resist on the surface of the wafer coated with the anti-reflection film;

[0014] S22, exposing the wafer after spin-coating the photoresist;

[0015] S23, removing the unexposed area of ​​the wafer after exposure;

[0016] S24 , coating the wafer with a metal film after removing the unexposed area to form a photolithography pattern.

[0017] Preferably, the wafer is made of any one of lithium tantalate, lithium niobate and quartz.

[0018] Preferably, the semiconductor film is made of at least one of silicon and germanium, and has a thickness of 10 nm to 2 μm.

[0019] Preferably, in step S1, the anti-reflection film is deposited by electron beam evaporation.

[0020] Preferably, in step S2, the photoresist is spin-coated using a high-speed spin machine.

[0021] Preferably, in step S3, the exposure is performed using a DUV light source through a mask.

[0022] Preferably, in step S23 , before removing the unexposed area of ​​the wafer after exposure, the exposed wafer is first spin-coated with a developer.

[0023] Preferably, in step S3, the photoresist is stripped using a chemical solvent or a plasma oxidation system.

[0024] Preferably, in step S4, the anti-reflection film is removed by wet etching or dry etching: the anti-reflection film is removed by wet etching: the wet etching is carried out using a mixed solution of hydrofluoric acid, nitric acid and water, or a mixed solution of hydrofluoric acid, nitric acid and acetic acid, or a tetramethylammonium hydroxide solution, or a potassium hydroxide solution.

[0025] Compared with the related art, the preparation method of reducing the standing wave effect of wafer exposure in the present invention is to coat the back side of the wafer with an anti-reflection film of semiconductor material, so that the anti-reflection film can absorb the ultraviolet light incident on the back side of the wafer, thereby greatly reducing the probability of reflected light. Based on the narrow band gap of the semiconductor material, the valence electrons in the valence band easily enter the conduction band, so the short-wave absorption limit will shift to the long wave. Therefore, the transparent region of the material is generally in the near-infrared and infrared bands, and it has good absorption of light in the ultraviolet and visible bands. After all the processes of the acoustic layer are completed, the anti-reflection film on the back side is removed to carry out the process preparation of other layers. That is, by coating the anti-reflection film of semiconductor material on the back side of the wafer, the standing wave effect caused by interference between the reflected light from the front and back sides of the wafer is greatly reduced, thereby improving its interdigital morphology to form a perfect sidewall structure, thereby improving the electrical performance and power tolerance of the filter. In addition, due to the absorption of reflected light, it is no longer necessary to consider the relationship between the refractive index and film thickness of the wafer, that is, the film thickness of the wafer is no longer restricted, greatly increasing its design freedom.

Brief Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive efforts. Among them:

[0027] FIG1 is a schematic diagram of the interference effect between the light emitted from the upper and lower surfaces of a wafer in the related art;

[0028] FIG2 is a schematic diagram of a structure of a wafer with wavy interdigitated sidewalls in the related art;

[0029] FIG3 is a schematic flow chart of the steps of a preparation method for reducing the standing wave effect of wafer exposure provided by an embodiment of the present invention;

[0030] FIG4 is a schematic flow chart of sub-steps of step S2 in a method for reducing standing wave effects in wafer exposure according to an embodiment of the present invention;

[0031] FIG5 is a schematic diagram of the interdigitated surface morphology of a wafer prepared by a preparation method for reducing the standing wave effect of wafer exposure according to an embodiment of the present invention. [Specific implementation method]

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0033] An embodiment of the present invention provides a preparation method for reducing the standing wave effect of wafer exposure, as shown in FIG3 , comprising the following steps:

[0034] S1. Apply an anti-reflection film to the back of the wafer.

[0035] Wherein, the wafer is a piezoelectric material wafer, and is made of any one of lithium tantalate, lithium niobate and quartz.

[0036] The anti-reflection film is a semiconductor film, that is, the anti-reflection film is a film made of semiconductor material; the semiconductor film contains silicon or germanium, that is, the semiconductor film can be made of silicon or germanium, or the semiconductor film is doped with silicon or germanium. Of course, the semiconductor film can also be made of other semiconductor materials.

[0037] The thickness of the semiconductor film is 10 nm to 2 μm.

[0038] The anti-reflection film is deposited by electron beam evaporation.

[0039] S2. Spin-coating photoresist on the surface of the wafer coated with the anti-reflection film and performing exposure and development processes to form a photolithography pattern.

[0040] Specifically, as shown in FIG4 , step S2 specifically includes the following sub-steps:

[0041] S21, spin coating optical resist on the surface of the wafer coated with the anti-reflection film;

[0042] S22, exposing the wafer after spin-coating the photoresist;

[0043] S23, removing the unexposed area of ​​the wafer after exposure;

[0044] S24 , coating the wafer with a metal film after removing the unexposed area to form a photolithography pattern.

[0045] The photoresist is spin-coated using a high-speed rotating machine; the exposure is performed using a DUV light source through a mask; and before removing the unexposed area of ​​the wafer after exposure, the exposed wafer is spin-coated with a developer.

[0046] S3, stripping the photoresist on the wafer with the photolithography pattern formed thereon.

[0047] Wherein, the stripping of the photoresist is performed by a chemical solvent or a plasma oxidation system.

[0048] S4, removing the anti-reflection film on the wafer after stripping the photoresist.

[0049] The anti-reflection film is removed by wet etching or dry etching. The wet etching is performed using a mixed solution of hydrofluoric acid (HF), nitric acid (HNO3) and water, or a mixed solution of hydrofluoric acid, nitric acid and acetic acid (CH3COOH), or a tetramethylammonium hydroxide (TMAH) solution, or a potassium hydroxide (KOH) solution; the ratio of hydrofluoric acid, nitric acid and water is 1:3:8, and the ratio of hydrofluoric acid, nitric acid and acetic acid is also 1:3:8. Of course, according to actual needs, the wet etching can also be performed using other similar solutions.

[0050] In addition, the step 2 and its sub-steps S21-S24 are all for forming a photolithography pattern, and can be adaptively modified, added or deleted without affecting the technical effect achieved by the preparation method for reducing the standing wave effect of wafer exposure.

[0051] Compared with the related art, the preparation method for reducing the standing wave effect of wafer exposure in this embodiment is to coat an anti-reflection film of semiconductor material on the back of the wafer, so that the ultraviolet light incident on the back of the wafer can be absorbed by the anti-reflection film, thereby greatly reducing the probability of reflected light. Based on the narrow band gap of the semiconductor material, the valence electrons in the valence band can easily enter the conduction band, so the short-wave absorption limit will shift to the long wave, so the transparent area of ​​the material is generally in the near-infrared and infrared bands, and has good absorption of light in the ultraviolet and visible bands. After all the processes of the acoustic layer are completed, the anti-reflection film on the back is removed to carry out the process preparation of other layers. That is, by coating the anti-reflection film of semiconductor material on the back of the wafer, the standing wave effect caused by the interference between the reflected light on the front and back of the wafer is greatly reduced, thereby improving its interdigital morphology (as shown in Figure 5) to form a perfect sidewall structure, thereby improving the electrical performance and power tolerance of the filter. In addition, due to the absorption of reflected light, there is no need to consider the relationship between the refractive index of the wafer and the film thickness, that is, the film thickness of the wafer is no longer restricted, which greatly improves its design freedom.

[0052] In addition, the present invention further provides an embodiment of a filter, wherein the wafer of the filter is prepared by incorporating the preparation method for reducing the standing wave effect of wafer exposure in the above embodiment. Because the wafer of the filter in this embodiment is prepared by incorporating the preparation method for reducing the standing wave effect of wafer exposure in the above embodiment, it can also achieve the technical effect achieved by the preparation method for reducing the standing wave effect of wafer exposure in the above embodiment, and will not be further described here.

[0053] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A preparation method for reducing the standing wave effect of wafer exposure, characterized in that: The preparation method for reducing the standing wave effect of wafer exposure comprises the following steps: S1. coating the back side of a wafer with an anti-reflection film; wherein the wafer is a piezoelectric material wafer, and the anti-reflection film is a semiconductor film; S2, spin-coating a photoresist on the surface of the wafer coated with the anti-reflection film and performing exposure and development treatment to form a photolithography pattern; S3, stripping the photoresist on the wafer with the photolithography pattern formed; S4, removing the anti-reflection film on the wafer after stripping the photoresist.

2. The method for reducing the standing wave effect of wafer exposure according to claim 1, characterized in that: The step S2 specifically includes the following sub-steps: S21, spin coating optical resist on the surface of the wafer coated with the anti-reflection film; S22, exposing the wafer after spin coating the photoresist; S23, removing the unexposed area of ​​the wafer after exposure; S24, coating the wafer with a metal film after removing the unexposed area to form a photolithography pattern.

3. The method for reducing the standing wave effect of wafer exposure according to claim 1, characterized in that: The wafer is made of any one of lithium tantalate, lithium niobate and quartz.

4. The method for reducing the standing wave effect of wafer exposure according to claim 1, characterized in that: The semiconductor film is made of at least one of silicon and germanium, and has a thickness of 10 nm to 2 μm.

5. The method for reducing the standing wave effect of wafer exposure according to claim 1, characterized in that: In the step S1, the anti-reflection film is deposited by electron beam evaporation.

6. The method for reducing the standing wave effect of wafer exposure according to claim 1, characterized in that: In the step S2, the photoresist is spin-coated by a high-speed spin machine.

7. The method for reducing standing wave effect of wafer exposure according to claim 1, characterized in that: In the step S3, the exposure is performed using a DUV light source through a mask.

8. The method for reducing standing wave effect of wafer exposure according to claim 2, characterized in that: In the step S23, before removing the unexposed area of ​​the wafer after exposure, the exposed wafer is first spin-coated with a developer.

9. The method for reducing standing wave effect of wafer exposure according to claim 1, characterized in that: In the step S3, the photoresist is stripped by a chemical solvent or a plasma oxidation system.

10. The method for reducing standing wave effect of wafer exposure according to claim 1, characterized in that: In step S4, the anti-reflection film is removed by wet etching or dry etching: the wet etching is performed using a mixed solution of hydrofluoric acid, nitric acid and water, or a mixed solution of hydrofluoric acid, nitric acid and acetic acid, or a tetramethylammonium hydroxide solution, or a potassium hydroxide solution.

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