Novel TC-SAW process

Abstract

The invention relates to a novel TC-SAW (Temperature Compensation Surface Acoustic Wave) process, belongs to the field of temperature compensation type surface acoustic wave filters, and aims to solve the problems that an IDT metal interdigital strip is etched or corroded by plasma gas in the conventional preparation process, so that the appearance defect of the IDT metal interdigital strip is caused, and the performance of the filter is influenced. According to the method, a protective layer is deposited before a SiO2 temperature compensation layer is deposited on the surface of an interdigital electrode, the protective layer is deposited by adopting CVD or other modes, no plasma or unbiased plasma exists in the deposition process, and etching or corrosion cannot be caused to an IDT metal interdigital strip; and during subsequent deposition of the SiO2 temperature compensation layer, the IDT interdigital metal can be effectively prevented from being etched by a high-strength plasma beam, so that the IDT metal finger strip is complete in appearance, and the TC-SAW performance is improved.

Description

Technical Field

[0001] The invention belongs to the field of temperature compensation surface acoustic wave filters, and in particular relates to a novel TC-SAW process. Background Art

[0002] The temperature-compensated surface acoustic wave filter (TC-SAW for short) is a technical improvement on the conventional SAW filter by covering its IDT with a temperature compensation layer, so that the frequency temperature coefficient (TCF) of the device is reduced to 0 to -25ppm / ℃, which is a significant improvement over the temperature characteristics of conventional SAW (usually about -45 to -60ppm / ℃).

[0003] Existing TC-SAW uses PVD process to directly deposit the temperature compensation layer on the IDT metal layer, and cannot be prepared by CVD. If the SiO2 temperature compensation layer is prepared by CVD, the deposition process is that silane is thermally decomposed on the substrate surface and reacts with oxygen to form SiO2, which is then formed on the substrate surface; this method has simple equipment, fast growth rate, and easy control of film thickness, but the film uniformity is poor, the structure is loose, the corrosion rate is fast, and silane is easily oxidized to form white powder in the gas pipeline, so the deposited SiO 2 The dust pollution is serious, so CVD method cannot be used to prepare SiO 2 Temperature compensation layer.

[0004] Therefore, the SiO2 temperature compensation layer of the TC-SAW process in the present invention must be prepared by PVD. The deposition process is to make argon gas glow discharge under vacuum conditions. Under the action of the electric field force, the argon ions are accelerated to bombard the cathode target made of chain material. The atoms or molecules of the target material are separated from the target material and are accelerated to be deposited on the substrate surface to form a film under the action of the bias electric field. The accelerated plasma gas in this preparation process will cause etching or corrosion to the IDT metal layer, thereby affecting the interdigitated strip morphology of the IDT layer, making its appearance incomplete, thereby affecting the performance of the entire TC-SAW. Summary of the invention

[0005] The present invention aims to solve the problem that the IDT metal interdigital strips will be etched or corroded by plasma gas in the existing preparation process, resulting in morphological defects of the IDT metal interdigital strips and affecting the performance of the filter. The present invention first forms a protective film on the IDT surface, and then deposits SiO 2 Temperature compensation layer ensures the integrity of the IDT metal finger morphology and improves TC-SAW performance.

[0006] In order to achieve the above object, the present invention is implemented by the following technical scheme: a new TC-SAW process is carried out according to the following steps:

[0007] Step 1) Photolithography: coating, exposing and developing a photoresist on a substrate to form a finger-shaped photoresist layer;

[0008] Step 2) metal evaporation: evaporating an IDT metal layer on the substrate, the metal is deposited on the substrate) and the photoresist layer;

[0009] Step 3) photoresist stripping: using a lift-off process to strip the photoresist layer and the metal deposited on the photoresist layer to form interdigital electrodes;

[0010] Step 4) preparing a protective layer: preparing a protective layer on the interdigital electrodes and the surface of the substrate;

[0011] Step 5) Deposition: SiO is prepared on the protective layer by physical vapor deposition (PVD) 2 Temperature compensation layer;

[0012] Step 6) Subsequent process: 2 The FM metal layer is formed by evaporation on the surface of the temperature compensation layer, and then the SiO 2 The temperature compensation layer is opened, the PAD metal layer is evaporated, the passivation layer is sputtered, the passivation layer is opened and thinned, and finally the TC-SAW structure is formed.

[0013] Preferably, the protective layer is deposited by evaporation process, and SiN is deposited on the surface of the interdigital electrodes and the substrate. x or SiO 2 film.

[0014] Preferably, the protective layer is formed by a baking coating process, and a layer of protective glue is hard-baked and coated on the surface of the interdigital electrodes and the substrate.

[0015] Preferably, the thickness of the protective layer is 3 nm to 30 nm.

[0016] Preferably, the substrate material is the piezoelectric material lithium tantalate.

[0017] Preferably, the SiO 2 The thickness of the temperature compensation layer is 600nm~1800nm.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 2 Before forming the temperature compensation layer, a protective layer is first deposited on the IDT metal surface. The protective layer is prepared by CVD or other methods. There is no plasma or biased plasma during the deposition process, and the IDT metal fingers will not be etched or corroded. This can effectively prevent the IDT finger metal from being etched by the high-intensity plasma beam when depositing the temperature compensation layer, so that the morphology of the IDT metal fingers is complete, thereby improving the performance of TC-SAW. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the structure of a temperature compensation filter prepared by the process of the present invention.

[0020] Figure 2 Schematic diagram of photolithography.

[0021] Figure 3 Schematic diagram of IDT metal layer evaporation.

[0022] Figure 4 Schematic diagram of the interdigitated electrodes formed after photoresist stripping.

[0023] Figure 5 For the protective layer and SiO 2 Schematic diagram of the temperature compensation layer.

[0024] Figure 6 Schematic diagram of the interdigitated strip surface of the existing preparation process and the preparation process of the present invention.

[0025] Figure 7 Schematic diagram of the performance difference within the Tx passband between the preparation process of the present invention and the existing preparation process.

[0026] Figure 8 Schematic diagram of the performance difference within the Rx passband between the preparation process of the present invention and the existing preparation process.

[0027] Among them, 1 is the substrate, 2 is the interdigital electrode layer, 3 is the interdigital electrode lead-out portion, 4 is the protective layer, 5 is the SiO 2 Temperature compensation layer, 6 is the FM metal layer, 7 is the PAD metal layer, 8 is the passivation layer, 9 is the PAD contact window, and 10 is the photoresist layer. DETAILED DESCRIPTION

[0028] 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.

[0029] The structure of a temperature compensation filter prepared by a novel TC-SAW process of the present invention is as follows: Figure 1 As shown. The bottom of the temperature compensation filter is a substrate 1, which is generally made of piezoelectric material lithium tantalate. An IDT interdigital electrode 2 is formed on the substrate 1 by a photolithography process, and at the same time, an interdigital electrode lead-out portion 3 is formed as the part where the interdigital electrode 2 is connected to the outside. Then a protective layer 4 is set above the interdigital electrode 2, SiO 2 The temperature compensation layer 5 is located on the protective layer 4 for temperature compensation. The FM metal layer 6 is located on the SiO 2The PAD metal layer 7 is connected to the interdigital electrode lead-out portion 3, and the passivation layer 8 covers the FM metal layer 6 and the PAD metal layer 7. The PAD contact window 9 is formed by etching the passivation layer 8, exposing the PAD contact window 9 as a window for external connection.

[0030] The structure of the prepared temperature compensation filter (TC-SAW) is briefly introduced above, and the preparation process of the present invention is described in detail below through specific embodiments.

[0031] Example 1

[0032] A new TC-SAW process is carried out according to the following steps:

[0033] Step 1) Photolithography: Figure 2 As shown, photoresist coating, exposure and development are performed on the substrate 1, so that the photoresist shape presents a film layer morphology corresponding to the IDT pattern, forming a finger-shaped photoresist layer 10;

[0034] Step 2) Metal evaporation: Figure 3 As shown, an IDT metal layer is evaporated on a substrate 1, and the metal is deposited on the surface of the substrate 1 and the photoresist layer 10;

[0035] Step 3) Photoresist stripping: Figure 4 As shown, a lift-off process is used to strip the photoresist and the metal deposited on the photoresist;

[0036] Step 4) preparing the protective layer 4: Figure 5 As shown, a layer of SiN is deposited on the surface of the interdigital electrode 2 and the substrate 1 by using a CVD process. x Thin film, film thickness range is 3nm;

[0037] Step 5) Deposition: SiO is prepared on the protective layer 4 by physical vapor deposition (PVD). 2 Temperature compensation layer 5, using Ar ions to bombard Si target, through O 2 The ionization generates O ions, increases the bias electric field, and accelerates the movement of ions to the wafer surface, thereby forming SiO 2 Temperature compensation layer 5;

[0038] Step 6) Subsequent process: 2 The FM metal layer 6 is formed by evaporation on the surface of the temperature compensation layer, and then the SiO 2 The temperature compensation layer 5 is opened, the PAD metal layer 7 is evaporated, the passivation layer 8 is sputtered, the passivation layer 8 is opened and thinned, and then the TC-SAW structure is formed. The preparation process of the FM metal layer and the PAD contact window 9 is the same as the existing process, so it will not be repeated here.

[0039] Example 2

[0040] A new TC-SAW process is carried out according to the following steps:

[0041] Step 1) Photolithography: Figure 2 As shown, photoresist coating, exposure and development are performed on the substrate 1, so that the photoresist shape presents a film layer morphology corresponding to the IDT pattern, forming a finger-shaped photoresist layer 10;

[0042] Step 2) Metal evaporation: Figure 3 As shown, an IDT metal layer is evaporated on a substrate 1, and the metal is deposited on the surface of the substrate 1 and the photoresist layer 10;

[0043] Step 3) Photoresist stripping: Figure 4 As shown, a lift-off process is used to strip the photoresist and the metal deposited on the photoresist;

[0044] Step 4) Preparation of protective layer 4: Using CVD process to deposit a layer of SiN on the surface of the interdigital electrode 2 and the substrate 1 x Thin film, film thickness range is 8nm;

[0045] Step 5) Deposition: SiO is prepared on the protective layer 4 by physical vapor deposition (PVD). 2 Temperature compensation layer, using Ar ions to bombard Si target, passing O 2 The ionization generates O ions, increases the bias electric field, and accelerates the movement of ions to the wafer surface, thereby forming SiO 2 Temperature compensation layer 5;

[0046] Step 6) Subsequent process: 2 The FM metal layer 6 is formed by evaporation on the surface of the temperature compensation layer, and then the SiO 2 The temperature compensation layer 5 is opened, the PAD metal layer 7 is evaporated, the passivation layer 8 is sputtered, the passivation layer 8 is opened and thinned, and then the TC-SAW structure is formed.

[0047] Example 3

[0048] A new TC-SAW process is carried out according to the following steps:

[0049] Step 1) Photolithography: Figure 2 As shown, photoresist coating, exposure and development are performed on the substrate 1, so that the photoresist shape presents a film layer morphology corresponding to the IDT pattern, forming a finger-shaped photoresist layer 10;

[0050] Step 2) Metal evaporation: Figure 3 As shown, an IDT metal layer is evaporated on a substrate 1, and the metal is deposited on the surface of the substrate 1 and the photoresist layer 10;

[0051] Step 3) Photoresist stripping: Figure 4 As shown, a lift-off process is used to strip the photoresist and the metal deposited on the photoresist;

[0052] Step 4) Preparation of protective layer 4: Using CVD process to deposit a layer of SiN on the surface of the interdigital electrode 2 and the substrate 1 x Thin film, film thickness range is 15nm;

[0053] Step 5) Deposition: SiO is prepared on the protective layer 4 by physical vapor deposition (PVD). 2 Temperature compensation layer, using Ar ions to bombard Si target, passing O 2 The ionization generates O ions, increases the bias electric field, and accelerates the movement of ions to the wafer surface, thereby forming SiO 2 Temperature compensation layer 5;

[0054] Step 6) Subsequent process: 2 The FM metal layer 6 is formed by evaporation on the surface of the temperature compensation layer, and then the SiO 2 The temperature compensation layer 5 is opened, the PAD metal layer 7 is evaporated, the passivation layer 8 is sputtered, the passivation layer 8 is opened and thinned, and then the TC-SAW structure is formed.

[0055] Example 4

[0056] A new TC-SAW process is carried out according to the following steps:

[0057] Step 1) Photolithography: Figure 2 As shown, photoresist coating, exposure and development are performed on the substrate 1, so that the photoresist shape presents a film layer morphology corresponding to the IDT pattern, forming a finger-shaped photoresist layer 10;

[0058] Step 2) Metal evaporation: Figure 3 As shown, an IDT metal layer is evaporated on a substrate 1, and the metal is deposited on the surface of the substrate 1 and the photoresist layer 10;

[0059] Step 3) Photoresist stripping: Figure 4 As shown, a lift-off process is used to strip the photoresist and the metal deposited on the photoresist;

[0060] Step 4) Preparation of protective layer 4: Using CVD process to deposit a layer of SiO on the surface of the interdigital electrode 2 and the substrate 1 2 Thin film, film thickness range is 25nm;

[0061] Step 5) Deposition: SiO is prepared on the protective layer 4 by physical vapor deposition (PVD). 2Temperature compensation layer, using Ar ions to bombard Si target, passing O 2 The ionization generates O ions, increases the bias electric field, and accelerates the movement of ions to the wafer surface, thereby forming SiO 2 Temperature compensation layer 5;

[0062] Step 6) Subsequent process: 2 The FM metal layer 6 is formed by evaporation on the surface of the temperature compensation layer, and then the SiO 2 The temperature compensation layer 5 is opened, the PAD metal layer 7 is evaporated, the passivation layer 8 is sputtered, the passivation layer 8 is opened and thinned, and then the TC-SAW structure is formed.

[0063] In the above four embodiments, a layer of SiNx or SiO2 with a thickness of 3-30 nm is first deposited before depositing the SiO2 temperature compensation layer on the IDT metal surface. 2 The protective film is used as a protective film. The protective film is deposited by CVD or other methods. There is no plasma or bias plasma during the deposition process, which will not cause etching or corrosion to the IDT metal fingers; and when the SiO2 temperature compensation layer is subsequently deposited, it can effectively prevent the IDT finger metal from being etched by the high-intensity plasma beam.

[0064] Example 5

[0065] A new TC-SAW process is carried out according to the following steps:

[0066] Step 1) Photolithography: Figure 2 As shown, photoresist coating, exposure and development are performed on the substrate 1, so that the photoresist shape presents a film layer morphology corresponding to the IDT pattern, forming a finger-shaped photoresist layer 10;

[0067] Step 2) Metal evaporation: Figure 3 As shown, an IDT metal layer is evaporated on a substrate 1, and the metal is deposited on the surface of the substrate 1 and the photoresist layer 10;

[0068] Step 3) Photoresist stripping: Figure 4 As shown, a lift-off process is used to strip the photoresist and the metal deposited on the photoresist;

[0069] Step 4) preparing the protective layer 4: using a baking coating process, hard baking and coating a layer of protective glue on the IDT metal layer and the surface of the substrate 1;

[0070] Step 5) Deposition: SiO is prepared on the protective layer 4 by physical vapor deposition (PVD). 2 Temperature compensation layer, using Ar ions to bombard Si target, passing O 2 The ionization generates O ions, increases the bias electric field, and accelerates the movement of ions to the wafer surface, thereby forming SiO 2Temperature compensation layer 5;

[0071] Step 6) Subsequent process: 2 The FM metal layer 6 is formed by evaporation on the surface of the temperature compensation layer, and then the SiO 2 The temperature compensation layer 5 is opened, the PAD metal layer 7 is evaporated, the passivation layer 8 is sputtered, the passivation layer 8 is opened and thinned, and then the TC-SAW structure is formed.

[0072] The present invention uses hard baking to coat a layer of SiN on the IDT metal surface. x or SiO 2 A special glue (containing silica sol) with similar thin film properties is used as a protective film. The special glue is hard-baked to remove residual solvents in the glue and increase the strength of the glue, so that the IDT finger metal can be effectively prevented from being etched by the high-intensity plasma beam when the temperature compensation layer is deposited, thereby ensuring the integrity of the IDT metal finger morphology.

[0073] like Figure 6 As shown in the figure, (a) is that no protective film is prepared on the IDT surface, the surface of the interdigital strips is corroded, and the edges are blurred. (b) is that a protective layer 4 is deposited on the IDT surface, the interdigital strips are not corroded, and the edges are clear and complete. Compared with the existing manufacturing process, the present invention sets a protective layer 4 on the IDT metal surface, so that the morphology of the IDT metal fingers is complete, which also has a certain effect on improving the TC-SAW performance. Figure 7-Figure 8 As shown, the jitter within the passband improves by 0.2dB-0.5dB.

[0074] 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 new TC-SAW process, characterized by: Follow these steps: Step 1) photolithography: coating, exposing and developing a photoresist on a substrate (1) to form a finger-shaped photoresist layer (10); Step 2) metal evaporation: evaporating an IDT metal layer on the substrate (1), wherein the metal is deposited on the substrate (1) and the photoresist layer (10); Step 3) photoresist stripping: using a lift-off process to strip the photoresist layer (10) and the metal deposited on the photoresist layer (10) to form interdigital electrodes (2); Step 4) preparing a protective layer (4): preparing a protective layer (4) on the surfaces of the interdigitated electrodes (2) and the substrate (4); Step 5) Deposition: Preparing a SiO2 temperature compensation layer (5) on the protective layer (4) by physical vapor deposition (PVD); Step 6) Subsequent process: forming an FM metal layer (6) by evaporating on the surface of the SiO2 temperature compensation layer (5), then opening holes in the SiO2 temperature compensation layer (5), evaporating a PAD metal layer (7), sputtering a passivation layer (8), opening windows in the passivation layer (8) and performing a thinning operation, and finally forming a TC-SAW structure.

2. A novel TC-SAW process according to claim 1, characterized in that: The protective layer (4) is deposited by evaporation process to deposit SiN on the surface of the interdigital electrode (2) and the substrate (1). x Or SiO2 film.

3. A novel TC-SAW process according to claim 1, characterized in that: The protective layer (4) is formed by a baking coating process, and a layer of protective glue is hard-baked and coated on the surface of the interdigital electrodes (2) and the substrate (1).

4. A novel TC-SAW process according to claim 2 or 3, characterized in that: The thickness of the protective layer (4) is 3 nm to 30 nm.

5. A novel TC-SAW process according to claim 4, characterized in that: The substrate 1 is made of piezoelectric material lithium tantalate.

6. A novel TC-SAW process according to claim 4, characterized in that: The thickness of the SiO2 temperature compensation layer is 600nm-1800nm.

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