CN118117986A - Method for forming surface acoustic wave resonator - Google Patents

Abstract

A method of forming a surface acoustic wave resonator device, comprising: forming a piezoelectric layer; forming a first metal material layer on the piezoelectric layer; etching the first metal material layer to a target thickness by adopting a first dry etching process, wherein the etching thickness of the first dry etching process is a preset thickness, and the first metal material layer is etched by the first dry etching process at a first etching rate; and etching the first metal material layer with the residual target thickness by adopting a second dry etching process until the surface of the piezoelectric layer is exposed to form an electrode structure, wherein the second dry etching process etches the first metal material layer with a second etching rate which is smaller than the first etching rate. The residual first metal material layer is etched through the second dry etching process with smaller etching rate, so that the etching controllability of the first metal material layer can be effectively improved, the over etching of the piezoelectric layer is further reduced, the influence of the piezoelectric layer on the working frequency of the filter is reduced, and the performance and the process yield of the device structure are improved.

Description

Method for forming surface acoustic wave resonator

Technical Field

The invention relates to the technical field of semiconductors, in particular to a method for forming a surface acoustic wave resonance device.

Background

A Radio Frequency (RF) front-end chip of a wireless communication device includes a power amplifier, an antenna switch, a Radio Frequency filter, a multiplexer, a low noise amplifier, and the like. Among them, radio frequency filters include piezoelectric surface acoustic wave (SurfaceAcoustic Wave, SAW) filters, piezoelectric bulk acoustic wave (Bulk Acoustic Wave, BAW) filters, microelectromechanical system (Micro-Electro-MECHANICAL SYSTEM, MEMS) filters, integrated passive device (INTEGRATED PASSIVEDEVICES, IPD) filters, and the like.

The SAW resonator has a high quality factor (Q value), and is manufactured into an RF filter with low insertion loss (insertion loss) and high out-band rejection (out-band rejection), that is, a SAW filter, which is a mainstream RF filter currently used in wireless communication devices such as mobile phones and base stations. SAW resonators have a negative temperature coefficient of frequency (Temperature Coefficient of Frequency, TCF), i.e. the resonant frequency (resonant frequency) of the resonator decreases when the temperature increases, and increases when the temperature decreases, reducing the reliability and stability of the SAW filter. In order to improve the characteristic that the resonance frequency of the SAW resonator drifts along with the working temperature, a temperature compensation layer is added on the piezoelectric layer, the temperature compensation layer has opposite frequency temperature coefficients of the piezoelectric layer, and the temperature compensation layer and the piezoelectric layer are combined to enable the frequency temperature coefficient of the whole resonator to trend to be zero, so that the reliability and the stability of the filter are improved. Such SAW resonators including a temperature compensation layer are called temperature compensation SAW (Temperature Compensated SAW, TC-SAW) resonators, and filters composed of TC-SAW resonators are called TC-SAW filters.

However, the surface acoustic wave resonator device still has many problems.

Disclosure of Invention

The invention solves the problem of providing a method for forming a surface acoustic wave resonance device so as to improve the performance and the process yield of a device structure.

In order to solve the above problems, the present invention provides a method for forming a surface acoustic wave resonator device, including: forming a piezoelectric layer; forming a first metal material layer on the piezoelectric layer; forming a mask layer on the first metal material layer, wherein the mask layer covers part of the top surface of the first metal material layer; taking the mask layer as a mask, etching the first metal material layer to a target thickness by adopting a first dry etching process, wherein the etching thickness of the first dry etching process is a preset thickness, and the first dry etching process etches the first metal material layer with a first etching rate; and etching the first metal material layer with the target thickness by using the mask layer as a mask through a second dry etching process until the surface of the piezoelectric layer is exposed, so as to form an electrode structure, wherein the first metal material layer is etched through the second dry etching process at a second etching rate which is smaller than the first etching rate.

Optionally, the preset thickness is greater than the target thickness.

Optionally, the preset thickness is 70% -90% of the thickness of the first metal material layer.

Optionally, before the first dry etching process is performed, the method further includes: acquiring the value of the preset thickness; acquiring a numerical value of the first etching rate; obtaining the etching time of the first dry etching process according to the ratio of the value of the preset thickness to the value of the first etching rate; and stopping the first dry etching process according to the etching time.

Optionally, determining the etching end point of the second dry etching process according to the intensity change of the end point detection curve spectrum.

Optionally, the process parameters of the first dry etching process include: the etching gas includes: SF ₆、Cl₂、O₂ and Ar; wherein the volumetric flow rate of SF ₆ is 10sccm to 50sccm; the volume flow rate of Cl ₂ is 15sccm to 70sccm; the volume flow rate of O ₂ is 2sccm to 50sccm; ar has a volume flow of 2sccm to 50sccm; the source power is 400w to 1200w; bias power is 80w to 280w; the etching chamber pressure is 5mt to 25mt.

Optionally, the process parameters of the second dry etching process include: the etching gas includes: SF ₆、Cl₂、O₂ and Ar; wherein the volumetric flow rate of SF ₆ sccm to 30sccm; the volume flow rate of Cl ₂ is 5sccm to 40sccm; the volume flow rate of O ₂ is 2sccm to 60sccm; ar has a volume flow of 2sccm to 40sccm; the source power is 400w to 1200w; bias power is 60w to 180w; the etching chamber pressure is 5mt to 15mt.

Optionally, the material of the first metal material layer includes: tungsten or molybdenum.

Optionally, the electrode structure includes: and the first metal layer is formed after the etching treatment of the first metal material layer.

Optionally, before etching the first metal material layer, the method further includes: forming a second metal material layer on the first metal material layer, wherein the material density of the second metal material layer is smaller than that of the first metal material layer; and etching the second metal material layer until the top surface of the first metal material layer is exposed.

Optionally, the electrode structure further includes: a second metal layer formed by etching the second metal material layer; the second metal layer is formed on the first metal layer.

Optionally, the material of the second metal material layer includes: aluminum, aluminum copper or aluminum magnesium copper.

Optionally, the electrode structure includes: a first bus and a second bus arranged in parallel along a first direction, the first direction being parallel to the piezoelectric layer surface; the first bus is connected with the first electrode strips, the second direction is parallel to the surface of the piezoelectric layer, and the first direction is perpendicular to the second direction; the second bus is connected with the second electrode strips, the first electrode strips and the second electrode strips are placed in a staggered mode, and the first electrode strips and the second electrode strips are partially overlapped along the second direction.

Optionally, after forming the electrode structure, the method further includes: forming a temperature compensation layer on the piezoelectric layer, wherein the temperature compensation layer covers the electrode structure; and forming a protective layer on the temperature compensation layer.

Compared with the prior art, the technical scheme of the invention has the following advantages:

In the method for forming the surface acoustic wave resonator, the first metal material layer is etched to the target thickness through the first dry etching process with the higher etching rate, the remaining first metal material layer is etched through the second dry etching process with the lower etching rate, the first dry etching process is higher in etching rate, high in etching selection ratio and good in uniformity, the second dry etching process is lower in etching rate, the bombardment energy of plasma is small, the etching controllability of the first metal material layer can be effectively improved, ideal electrode structure morphology is formed, over etching of the piezoelectric layer is reduced, damage to the piezoelectric layer is avoided, the influence on the working frequency of the filter is reduced, and the performance, the stability and the process yield of the device structure are improved.

Further, the preset thickness is greater than the target thickness. Because the etching rate of the first dry etching process on the first metal material layer is higher, the whole etching time of the first metal material layer is reduced by distributing larger preset thickness, and the processing efficiency is improved.

Drawings

Fig. 1 is a schematic structural view of a surface acoustic wave resonator device;

fig. 2 to 8 are schematic structural views of steps of a method for forming a surface acoustic wave resonator device according to an embodiment of the present invention;

fig. 9 to 12 are schematic structural views of steps of a method for forming a surface acoustic wave resonator device according to another embodiment of the present invention.

Detailed Description

As described in the background, there are still problems with the surface acoustic wave resonator device. The following will specifically explain.

Fig. 1 is a schematic structural view of a surface acoustic wave resonator device.

Referring to fig. 1, the temperature-compensated surface acoustic wave resonator device (i.e., TC-SAW resonator) mainly comprises a piezoelectric layer 100, an electrode structure 101, a temperature compensation layer 102 and a protection layer 103, wherein the electrode structure 101 is generally composed of a single layer metal or multiple layers of metals, and tungsten is often used as the lowest metal layer of the electrode structure 101 because of its high density and stable chemical properties.

The electrode structure 101 is generally prepared by an evaporation process or a sputtering process, the film formed by the evaporation process is generally subjected to pattern transfer by using a lift off process, but the film formed by the evaporation process is poorer in metal compactness than the film formed by the sputtering process, and the metal profile angle of the electrode structure 101 formed by the lift off process is generally affected by the photoresist morphology by 70-80 °. The film metal formed by the sputtering process has higher compactness, but the pattern transfer cannot be performed by using a stripping process, and the pattern transfer is generally performed by using a dry etching process. However, the damage of the piezoelectric layer 100 (as shown in part a of fig. 1) is easily caused by the dry etching, and the damage of the piezoelectric layer 100 affects the working frequency of the filter, resulting in excessive performance and design differences, and lower yield of the manufacturing process.

On the basis, the invention provides a method for forming the surface acoustic wave resonance device, which etches a first metal material layer to a target thickness through a first dry etching process with a higher etching rate, etches the rest first metal material layer through a second dry etching process with a smaller etching rate, the first dry etching process has a higher etching rate, a high etching selectivity ratio and good uniformity, the second dry etching process has a slow etching rate, the bombardment energy of plasma is small, the etching controllability of the first metal material layer can be effectively improved, an ideal electrode structure morphology is formed, the over etching of the piezoelectric layer is reduced, the damage of the piezoelectric layer is avoided, the influence on the working frequency of a filter is reduced, and the performance, the stability and the process yield of the device structure are improved.

In order that the above objects, features and advantages of the invention will be readily understood, a more particular description of the invention will be rendered by reference to the appended drawings.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than as described herein, and therefore the present invention is not limited to the specific embodiments disclosed below.

Fig. 2 to 8 are schematic structural views of steps of a method for forming a surface acoustic wave resonator device according to an embodiment of the present invention.

Referring to fig. 2, a piezoelectric layer 200 is formed.

The materials of the piezoelectric layer 200 include: lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate, aluminum nitride alloy, gallium nitride, or zinc oxide.

In this embodiment, the piezoelectric layer 200 is made of 127 ° to 129 ° Y-X cut lithium niobate.

Referring to fig. 3, a first metal material layer 201 is formed on the piezoelectric layer 200.

In this embodiment, the material of the first metal material layer 201 is tungsten, and the tungsten is used as the bottom metal layer of the electrode structure formed later because of its high material density and stable chemical property.

In other embodiments, molybdenum may also be used as the material of the first metal material layer.

Referring to fig. 4, a mask layer 202 is formed on the first metal material layer 201, and the mask layer 202 covers a portion of the top surface of the first metal material layer 201.

The method for forming the mask layer 202 includes: forming a mask material layer (not shown) on the first metal material layer 201; forming a photoresist layer (not shown) on the mask material layer, the photoresist layer exposing a portion of a top surface of the mask material layer; etching the mask material layer by taking the photoresist layer as a mask until the surface of the first metal material layer 201 is exposed, so as to form the mask layer 202; after forming the mask layer 202, the photoresist layer is removed.

Referring to fig. 5, the mask layer 202 is used as a mask, a first dry etching process is used to etch the first metal material layer 201 to a target thickness d1, the etching thickness of the first dry etching process is a preset thickness d2, and the first dry etching process etches the first metal material layer 201 to have a first etching rate.

Before the first dry etching process is performed, the method further comprises: acquiring the value of the preset thickness d 2; acquiring a numerical value of the first etching rate; obtaining etching time t of the first dry etching process according to the ratio of the value of the preset thickness d2 to the value of the first etching rate; and stopping the first dry etching process according to the etching time t.

The preset thickness d2 may be set according to an empirical rule, for example, the preset thickness d2 may be 70% to 90% of the thickness of the first metal material layer 201.

The first etching rate may be obtained by testing the first dry etching process with a step meter to etch a sample, where the material of the sample is the same as the material of the first metal material layer 201.

In one embodiment, the first metal material layer 201 has a thickness ofThe preset thickness d2 is distributed to be 80% of the thickness of the first metal material layer 201, and the first etching rate is/>The etching time of the corresponding first dry etching process is 3000/4800×0.8×60=30s.

The technological parameters of the first dry etching process comprise: the etching gas includes: SF ₆、Cl₂、O₂ and Ar; wherein the volumetric flow rate of SF ₆ is 10sccm (standard cubic centimeter per minute) to 50sccm; the volume flow rate of Cl ₂ is 15sccm to 70sccm; the volume flow rate of O ₂ is 2sccm to 50sccm; ar has a volume flow of 2sccm to 50sccm; the source power is 400w (watts) to 1200w; bias power is 80w to 280w; the etch chamber pressure is 5mt (millitorr) to 25mt.

Referring to fig. 6 and 7, fig. 7 is a schematic cross-sectional view taken along line A-A in fig. 6, and the first metal material layer 201 with the target thickness d1 is etched by using a second dry etching process with a second etching rate smaller than the first etching rate until the surface of the piezoelectric layer 200 is exposed, so as to form an electrode structure 203.

The first metal material layer is etched to the target thickness d1 through a first dry etching process with a higher etching rate, the remaining first metal material layer 201 is etched through a second dry etching process with a lower etching rate, the first dry etching process is higher in etching rate, high in etching selectivity ratio and good in uniformity, the second dry etching process is lower in etching rate, the bombardment energy of plasma is small, the etching controllability of the first metal material layer 201 can be effectively improved, the ideal electrode structure 203 morphology is formed, the over etching of the piezoelectric layer 200 is reduced, the damage to the piezoelectric layer 200 is avoided, the influence on the working frequency of a filter is reduced, and the performance, the stability and the process yield of the device structure are improved.

And determining the etching end point of the second dry etching process according to the intensity change of an end point detection (EDP) curve spectrum.

In this embodiment, the endpoint detection uses an optical emission spectroscopy (OpticalEmissionSpectroscopy, OES), which specifically includes: and collecting and detecting an end point detection curve of an element signal of etching gas in the process of etching the first metal material layer 201 by the second dry etching process, gradually changing the element signal of the etching gas along with the progress of etching, and delaying for a preset time to consider that the first metal material layer 201 is completely etched after capturing a characteristic peak of the element signal of the etching gas, wherein the second dry etching process is immediately stopped at the moment to reduce etching damage to the piezoelectric layer 200.

In other embodiments, an interferometric endpoint method (Interferometry End Point, IEP) may also be used to monitor the thickness of the first metal material layer to determine if the first metal material layer has reached an etch endpoint.

The preset thickness d2 is greater than the target thickness d1. Since the etching rate of the first dry etching process on the first metal material layer 201 is faster, the overall etching time of the first metal material layer 201 is reduced by allocating a larger preset thickness d2, and the process efficiency is improved.

The process parameters of the second dry etching process comprise: the etching gas includes: SF ₆、Cl₂、O₂ and Ar; wherein the volumetric flow rate of SF ₆ sccm to 30sccm; the volume flow rate of Cl ₂ is 5sccm to 40sccm; the volume flow rate of O ₂ is 2sccm to 60sccm; ar has a volume flow of 2sccm to 40sccm; the source power is 400w to 1200w; bias power is 60w to 180w; the etching chamber pressure is 5mt to 15mt.

And adjusting at least one parameter of the flows of etching gases SF ₆、Cl₂、O₂ and Ar and the bias power in the process parameters of the second dry etching process so that the second etching rate is smaller than the first etching rate.

In this embodiment, the bias power of the second dry etching process is smaller than that of the first dry etching process, so that the ion bombardment energy in the second dry etching process can be reduced while the second etching rate is smaller than the first etching rate, thereby forming a more ideal electrode structure 203 morphology and reducing over etching of the piezoelectric layer 200.

In other embodiments, the flow ratio of SF ₆ in the second dry etch process may also be reduced or the flow ratio of Cl ₂、O₂ may be increased compared to the first dry etch process, such that the second etch rate is less than the first etch rate.

With continued reference to fig. 6, the electrode structure 203 includes: a first bus 2031 and a second bus 2032 arranged in parallel along a first direction X, the first direction X being parallel to the surface of the piezoelectric layer 200; a plurality of first electrode strips 2033 arranged in parallel along a second direction Y, wherein the first bus 2031 is connected to the plurality of first electrode strips 2033, the second direction Y is parallel to the surface of the piezoelectric layer 200, and the first direction X is perpendicular to the second direction Y; the second bus 2032 is connected with the plurality of second electrode bars 2034, the first electrode bars 2033 and the second electrode bars 2034 are staggered, and the first electrode bars 2033 and the second electrode bars 2034 are partially overlapped along the second direction Y.

The electrode structure 203 includes: and a first metal layer 203a formed by etching the first metal material layer 201.

Referring to fig. 8, the view directions of fig. 8 and fig. 7 are identical, and after the electrode structure 203 is formed, a temperature compensation layer 204 is formed on the piezoelectric layer 200, and the temperature compensation layer 204 covers the electrode structure 203; a protective layer 205 is formed on the temperature compensation layer 204.

In this embodiment, the temperature compensation layer 204 and the piezoelectric layer 200 have opposite temperature frequency shift characteristics, and the frequency temperature coefficient (TemperatureCoefficient of Frequency, TCF) can be adjusted to be 0ppm/°c, so that the characteristic that the operating frequency of the surface acoustic wave resonator drifts with the operating temperature is improved, and the frequency-temperature stability is higher. A surface acoustic wave resonator device including a temperature compensation layer is called a temperature compensated surface acoustic wave resonator device (i.e., TC-SAW resonator).

In this embodiment, the materials of the temperature compensation layer 204 include: silicon dioxide, silicon oxyfluoride or silicon oxycarbide.

In this embodiment, the materials of the protective layer 205 include: one or more of silicon nitride, aluminum nitride, silicon oxynitride, aluminum oxide, and silicon carbide.

It should be noted that, before forming the temperature compensation layer, the mask layer 202 needs to be removed.

Fig. 9 to 12 are schematic structural views of steps of a method for forming a surface acoustic wave resonator device according to another embodiment of the present invention.

In this embodiment, a method for forming a surface acoustic wave resonator device is described based on the above embodiment (fig. 3), and the difference from the above embodiment is that: the electrode structure 203 further comprises a second metal layer. The following will explain the embodiments with reference to the drawings.

Referring to fig. 9, a second metal material layer 301 is formed on the first metal material layer 201, and the material density of the second metal material layer 301 is smaller than that of the first metal material layer 201.

The materials of the second metal material layer 301 include: aluminum, aluminum copper or aluminum magnesium copper.

In this embodiment, the material of the second metal material layer 301 is aluminum.

In other embodiments, a third metal material layer may also continue to be formed on the second metal material layer.

Referring to fig. 10, the second metal material layer 301 is etched until the top surface of the first metal material layer 201 is exposed.

The electrode structure 203 further includes: and a second metal layer 301a formed by etching the second metal material layer 301.

In other embodiments, when a third metal material layer is continuously formed on the second metal material layer, the corresponding electrode structure further includes: and the third metal layer is formed after the etching treatment of the third metal material layer.

Referring to fig. 11, after the second metal material layer 301 is etched, a dry etching process is used to etch the first metal material layer 201 to form the electrode structure 203.

In this embodiment, the etching process, the technical effect, the specific structure of the electrode structure 203, and the like of the first metal material layer 201 are specifically described with reference to fig. 5 to 7 and related descriptions, and will not be described herein again.

In this embodiment, the second metal layer 301a is formed on the first metal layer 203 a.

Referring to fig. 12, after the electrode structure 203 is formed, a temperature compensation layer 204 is formed on the piezoelectric layer 200, and the temperature compensation layer 204 covers the electrode structure 203; a protective layer 205 is formed on the temperature compensation layer 204.

In this embodiment, the technical effects of the temperature compensation layer 204 and the materials of the temperature compensation layer 204 and the protection layer 205 are specifically described with reference to fig. 7 and the related description, and will not be described herein again.

It should be understood that the examples and embodiments herein are illustrative only and that various modifications and changes can be made by one skilled in the art without departing from the spirit and scope of the application as defined by the appended claims.

Claims (14)

1. A method of forming a surface acoustic wave resonator device, comprising:

Forming a piezoelectric layer;

Forming a first metal material layer on the piezoelectric layer;

Forming a mask layer on the first metal material layer, wherein the mask layer covers part of the top surface of the first metal material layer;

Taking the mask layer as a mask, etching the first metal material layer to a target thickness by adopting a first dry etching process, wherein the etching thickness of the first dry etching process is a preset thickness, and the first dry etching process etches the first metal material layer with a first etching rate;

And etching the first metal material layer with the target thickness by using the mask layer as a mask through a second dry etching process until the surface of the piezoelectric layer is exposed, so as to form an electrode structure, wherein the first metal material layer is etched through the second dry etching process at a second etching rate which is smaller than the first etching rate.

2. The method of forming a surface acoustic wave resonator device of claim 1 wherein the predetermined thickness is greater than the target thickness.

3. The method of forming a surface acoustic wave resonator device according to claim 2, wherein the predetermined thickness is 70% to 90% of the thickness of the first metal material layer.

4. The method of forming a surface acoustic wave resonator device of claim 1, further comprising, prior to performing the first dry etching process: acquiring the value of the preset thickness; acquiring a numerical value of the first etching rate; obtaining the etching time of the first dry etching process according to the ratio of the value of the preset thickness to the value of the first etching rate; and stopping the first dry etching process according to the etching time.

5. The method of forming a surface acoustic wave resonator device according to claim 1, wherein an etching endpoint of the second dry etching process is determined based on an intensity variation of an endpoint detection curve spectrum.

6. The method of forming a surface acoustic wave resonator device of claim 1, wherein the process parameters of the first dry etching process include: the etching gas includes: SF ₆、Cl₂、O₂ and Ar; wherein the volumetric flow rate of SF ₆ is 10sccm to 50sccm; the volume flow rate of Cl ₂ is 15sccm to 70sccm; the volume flow rate of O ₂ is 2sccm to 50sccm; ar has a volume flow of 2sccm to 50sccm; the source power is 400w to 1200w; bias power is 80w to 280w; the etching chamber pressure is 5mt to 25mt.

7. The method of forming a surface acoustic wave resonator device of claim 1, wherein the process parameters of the second dry etching process include: the etching gas includes: SF ₆、Cl₂、O₂ and Ar; wherein the volumetric flow rate of SF ₆ sccm to 30sccm; the volume flow rate of Cl ₂ is 5sccm to 40sccm;

the volume flow rate of O ₂ is 2sccm to 60sccm; ar has a volume flow of 2sccm to 40sccm; the source power is 400w to 1200w; bias power is 60w to 180w; the etching chamber pressure is 5mt to 15mt.

8. The method of forming a surface acoustic wave resonator device of claim 1, wherein the material of the first metal material layer comprises: tungsten or molybdenum.

9. The method of forming a surface acoustic wave resonator device of claim 1, wherein the electrode structure comprises: and the first metal layer is formed after the etching treatment of the first metal material layer.

10. The method of forming a surface acoustic wave resonator device of claim 9, further comprising, prior to etching the first metal material layer: forming a second metal material layer on the first metal material layer, wherein the material density of the second metal material layer is smaller than that of the first metal material layer; and etching the second metal material layer until the top surface of the first metal material layer is exposed.

11. The method of forming a surface acoustic wave resonator device of claim 10, wherein the electrode structure further comprises: a second metal layer formed by etching the second metal material layer;

the second metal layer is formed on the first metal layer.

12. The method of forming a surface acoustic wave resonator device of claim 10 wherein the material of the second metal material layer comprises: aluminum, aluminum copper or aluminum magnesium copper.

13. The method of forming a surface acoustic wave resonator device of claim 1, wherein the electrode structure comprises: a first bus and a second bus arranged in parallel along a first direction, the first direction being parallel to the piezoelectric layer surface; the first bus is connected with the first electrode strips, the second direction is parallel to the surface of the piezoelectric layer, and the first direction is perpendicular to the second direction; the second bus is connected with the second electrode strips, the first electrode strips and the second electrode strips are placed in a staggered mode, and the first electrode strips and the second electrode strips are partially overlapped along the second direction.

14. The method of forming a surface acoustic wave resonator device of claim 1, further comprising, after forming the electrode structure: forming a temperature compensation layer on the piezoelectric layer, wherein the temperature compensation layer covers the electrode structure; and forming a protective layer on the temperature compensation layer.