High-consistency single crystal film surface acoustic wave filter and preparation method thereof

Abstract

The invention belongs to the field of surface acoustic wave filter device manufacturing, and particularly relates to a high-consistency single crystal film surface acoustic wave filter and a preparation method thereof, and the preparation method comprises the following steps: spin-coating an anti-reflection film on the upper surface of a single crystal film substrate; spin-coating photoresist on the anti-reflection film and carrying out exposure treatment to obtain a first sample; dissolving the photoresist corresponding to the target metal film pattern through developing operation, and dissolving the anti-reflection film corresponding to the dissolved photoresist to obtain a second sample; and depositing a metal film on the upper surface of the second sample, and then stripping all the photoresist and the anti-reflection film to obtain the high-consistency single crystal film surface acoustic wave filter. According to the invention, the finger strip morphology of the single crystal thin film wafer and the frequency dispersibility in the filter sheet are improved through spin coating of the anti-reflection film.

Description

Technical Field

[0001] The invention belongs to the field of surface acoustic wave filter device manufacturing, and in particular relates to a high-consistency single-crystal thin-film surface acoustic wave filter and a preparation method thereof. Background Art

[0002] Surface acoustic wave (SAW) is an elastic wave generated and propagated on the surface of piezoelectric substrate material, and its amplitude decreases rapidly as the depth into the piezoelectric substrate material increases. The basic structure of SAW filter is to make two acoustic-electric transducers, namely interdigital transducers (IDT), on the polished surface of piezoelectric substrate material through semiconductor technology. When an electrical signal is applied to the interdigital transducers, mechanical vibration is generated on the surface of the piezoelectric substrate material and surface acoustic waves are generated at the same time. This surface acoustic wave propagates on the surface of the piezoelectric substrate material. The working principle of SAW filter is to convert the electrical signal into an acoustic signal through the input transducer, propagate along the surface of the crystal, and the output transducer converts the received acoustic signal into an electrical signal for output.

[0003] With the development of technology, the research on surface acoustic wave filters has become more and more in-depth. Among them, single-crystal thin-film surface acoustic wave filters have attracted widespread attention in the industry in recent years due to their excellent characteristics such as high quality factor and low frequency temperature coefficient. However, due to the rough electron capture layer and uneven thickness of piezoelectric single crystals in single-crystal thin-film wafers, single-crystal thin-film surface acoustic wave filters prepared by traditional photolithography have problems such as burrs on the interdigital transducer graphics and poor frequency dispersion within the chip. These problems have seriously deteriorated the power tolerance and yield of single-crystal thin-film surface acoustic wave filters. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a high-consistency single-crystal thin film surface acoustic wave filter and a preparation method thereof.

[0005] In a first aspect, the present invention provides a method for preparing a high-consistency single-crystal thin-film surface acoustic wave filter, comprising the following steps:

[0006] S1. Spin coating an anti-reflection film on the upper surface of the substrate;

[0007] S2. Spin-coating a photoresist on the anti-reflective film and performing an exposure process to obtain a first sample;

[0008] S3. Performing a development operation on the first sample to dissolve the photoresist corresponding to the target metal film pattern, and dissolving the anti-reflective film corresponding to the dissolved photoresist to obtain a second sample;

[0009] S3. Deposit a metal film on the upper surface of the second sample, then strip off all the photoresist and anti-reflection films, leaving the desired target metal film pattern to obtain a highly consistent single crystal thin film surface acoustic wave filter.

[0010] Furthermore, during the preparation process, the anti-reflection film has a specific absorption peak for the wavelength of the light source used for exposure, and the thickness of the anti-reflection film is greater than the thickness of the metal film.

[0011] Furthermore, the anti-reflection film has a thickness of 200-250 nm.

[0012] In the second aspect, based on the preparation method of the high-consistency single-crystal thin-film surface acoustic wave filter proposed in the first aspect, the present invention provides a single-crystal thin-film surface acoustic wave filter, comprising a single-crystal thin-film wafer, an interdigital transducer, and an acoustic reflection grating; an acoustic reflection grating is respectively arranged on the left and right sides of the upper surface of the single-crystal thin-film wafer; the interdigital transducer is arranged on the upper surface of the single-crystal thin-film wafer and is located between the two acoustic reflection gratings; the single-crystal thin-film wafer comprises, from bottom to top, a substrate, an electron capture layer, an oxide layer, and a piezoelectric single crystal layer.

[0013] Furthermore, the oxide layer is made of silicon dioxide.

[0014] Furthermore, the substrate is made of silicon, sapphire, spinel or silicon carbide.

[0015] Furthermore, the electron capture layer is made of polycrystalline silicon.

[0016] Furthermore, the material of the piezoelectric single crystal layer is lithium tantalate or lithium niobate.

[0017] Beneficial effects of the present invention:

[0018] The present invention proposes a method for preparing a high-consistency single-crystal thin-film surface acoustic wave filter. Compared with the traditional preparation method, before the conventional photolithography process, an anti-reflection film is spin-coated on the surface of the single-crystal thin-film substrate, and the anti-reflection film has a specific absorption peak for the light source of the working wavelength of the exposure machine; the thickness of the anti-reflection film can make the surface reflectivity be at the trough of the reflectivity curve under the working wavelength of the exposure machine; the present invention improves the finger-shaped morphology of the single-crystal thin-film wafer and the frequency dispersion in the filter by spin-coating the anti-reflection film. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a flow chart of the method of the present invention;

[0020] Figure 2 This is a schematic diagram of the preparation process of the present invention;

[0021] Figure 3 This is a structural diagram of a high-consistency single-crystal thin-film surface acoustic wave filter of the present invention;

[0022] Figure 4 This is a comparison diagram of the morphology of the finger strips obtained by different processes of the present invention;

[0023] Figure 5 It is the frequency dispersion spectrum of different processes of the present invention. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0025] The single crystal thin film wafer is composed of a piezoelectric single crystal layer, an oxide layer, an electron capture layer and a substrate. The piezoelectric single crystal layer and the oxide layer are usually transparent materials, and the electron capture layer and the substrate are usually non-transparent materials. Because the electron capture layer usually has a rough surface, it will cause diffuse reflection during the exposure process to deteriorate the morphology of the adhesive strip. In order to reduce the influence of the diffuse reflection of the substrate and also to reduce the influence of the chromatic aberration caused by the thickness uniformity of the single crystal thin film on the exposure, the present invention adds a layer of anti-reflection film on the surface of the substrate when using the single crystal thin film wafer as the substrate to prepare the surface acoustic wave filter, so as to absorb the light entering the substrate and reflected from the substrate, thereby improving the adhesive morphology after exposure and the frequency consistency of the device.

[0026] Preferably, a method for preparing a high-consistency single-crystal thin-film surface acoustic wave filter is as follows: Figure 1 , Figure 2 , including the following steps:

[0027] S1. Spin coating an anti-reflection film on the upper surface of the substrate;

[0028] S2. Spin-coating a photoresist on the anti-reflective film and performing an exposure process to obtain a first sample;

[0029] S3. Performing a development operation on the first sample to dissolve the photoresist corresponding to the target metal film pattern, and dissolving the anti-reflective film corresponding to the dissolved photoresist to obtain a second sample;

[0030] S3. Deposit a metal film on the upper surface of the second sample, then strip off all the photoresist and anti-reflection films, leaving the desired target metal film pattern to obtain a highly consistent single crystal thin film surface acoustic wave filter.

[0031] Specifically, the anti-reflection film is a non-photosensitive glue having a specific absorption peak to the light source of the working wavelength of the exposure machine; during the preparation process, the thickness of the anti-reflection film is greater than the thickness of the metal film.

[0032] Specifically, the anti-reflection film has a thickness of 200-250 nm.

[0033] Preferably, a high consistency single crystal thin film surface acoustic wave filter, such as Figure 3 As shown, it includes a single crystal thin film wafer, an interdigital transducer, and an acoustic reflection grating; an acoustic reflection grating is respectively arranged on the left and right sides of the upper surface of the single crystal thin film wafer; the interdigital transducer is arranged on the upper surface of the single crystal thin film wafer and is located between the two acoustic reflection gratings; the single crystal thin film wafer includes a substrate, an electron capture layer, an oxide layer, and a piezoelectric single crystal layer from bottom to top.

[0034] Specifically, the oxide layer is made of silicon dioxide.

[0035] Specifically, the substrate is made of silicon, sapphire, spinel or silicon carbide.

[0036] Specifically, the electron capture layer is made of polycrystalline silicon.

[0037] Specifically, the piezoelectric single crystal layer material is lithium tantalate or lithium niobate.

[0038] like Figure 4 As shown, the left picture shows an article prepared by the present invention, and the right picture shows an article prepared by a conventional process. By comparing the photolithography process with adding an anti-reflective coating and the conventional photolithography process, the finger stripe morphology is significantly improved.

[0039] like Figure 5 As shown, by comparing the lithography process with adding an anti-reflective coating and the conventional lithography process, the on-chip consistency of the filter is improved from 48.81% to 53.57% (the proportion of filter devices within the 2M range).

[0040] In the present invention, unless otherwise clearly stipulated and limited, the terms such as "installation", "setting", "connection", "fixation" and "rotation" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. Unless otherwise clearly defined, ordinary technicians in this field can understand the specific meanings of the above terms in the present invention according to the specific circumstances.

[0041] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-consistency single-crystal thin-film surface acoustic wave filter, characterized in that: The following steps are involved: S1. Spin coating an anti-reflection film on the surface of a single crystal thin film substrate; S2. Spin-coating a photoresist on the anti-reflective film and performing an exposure process to obtain a first sample; S3. Performing a development operation on the first sample to dissolve the photoresist corresponding to the target metal film pattern, and dissolving the anti-reflective film corresponding to the dissolved photoresist to obtain a second sample; S4. Deposit a metal film on the upper surface of the second sample, and then strip off all the photoresist and anti-reflection films to obtain a high-consistency single-crystal thin-film surface acoustic wave filter.

2. The method for preparing a high-consistency single-crystal thin-film surface acoustic wave filter according to claim 1, characterized in that: During the preparation process, the thickness of the anti-reflection film is greater than the thickness of the metal film.

3. A high-consistency single-crystal thin-film surface acoustic wave filter, prepared by the method for preparing a high-consistency single-crystal thin-film surface acoustic wave filter according to any one of claims 1 to 2, characterized in that: It includes a single crystal thin film wafer, an interdigital transducer, and an acoustic reflection grating; an acoustic reflection grating is respectively arranged on the left and right sides of the upper surface of the single crystal thin film wafer; the interdigital transducer is arranged on the upper surface of the single crystal thin film wafer and is located between the two acoustic reflection gratings; the single crystal thin film wafer includes a substrate, an electron capture layer, an oxide layer, and a piezoelectric single crystal layer from bottom to top.

4. A high consistency single crystal thin film surface acoustic wave filter according to claim 3, characterized in that: The oxide layer is made of silicon dioxide.

5. The high consistency single crystal thin film surface acoustic wave filter according to claim 3, characterized in that: The substrate is made of silicon, sapphire, spinel or silicon carbide.

6. The high consistency single crystal thin film surface acoustic wave filter according to claim 3, characterized in that: The electron capture layer is made of polycrystalline silicon.

7. The high consistency single crystal thin film surface acoustic wave filter according to claim 3, characterized in that: The material of the piezoelectric single crystal layer is lithium tantalate or lithium niobate.

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