Thinning method of large-size piezoelectric film wafer and prepared piezoelectric film wafer

Abstract

The invention relates to preparation of a piezoelectric film wafer, and belongs to the field of MEMS. A method for thinning a large-size piezoelectric film wafer is characterized by comprising the following steps of: firstly, preparing a limiting groove of which the height is slightly greater than or equal to the target thickness of the film wafer on a substrate through a substrate patterning process, then bonding the piezoelectric wafer in the limiting groove, and finally performing chemical grinding to obtain the large-size piezoelectric film wafer. And when the piezoelectric wafer film is ground to be flush with the peripheral height of the limiting groove on the substrate, the thinning of the piezoelectric film wafer is accurately controlled. According to the method, the thickness of the piezoelectric wafer film can be accurately controlled, and the problems of cracking and damage caused by the fact that the thickness cannot be accurately controlled in an existing thinning process are solved. The invention further provides a piezoelectric film wafer based on the thinning method and a process for preparing various filters and resonators based on the method, the limitation on materials is reduced by the new process, the performance of the device is improved, and the method has a relatively high application prospect.

Description

Technical Field

[0001] The invention relates to the preparation of a piezoelectric film wafer, and in particular to a thinning method for a large-size piezoelectric film wafer and the prepared piezoelectric film wafer. Background Art

[0002] So far, with the development of MEMS technology, various devices that work with the help of acoustic wave resonance have been widely used in various fields, such as FBAR filters used in the RF front-end field and PMUT acoustic sensors used in the acoustic sensing field. These devices have one thing in common: they require piezoelectric film as a functional material and have strict requirements on the thickness of the piezoelectric film. For example, many high-frequency applications of FBAR, SMR and XBAR in the RF field require the piezoelectric film wafer to be thinned to a thickness of 2 microns or even 0.5 microns. The relatively low-frequency smart ultrasonic sensor PMUT requires a piezoelectric film with a thickness of less than 10 microns. The thin-film technology of piezoelectric materials is the basis for the application of MEMS smart acoustic sensors and acoustic filters, and is a key technology to achieve compatibility with CMOS processes, low power consumption, high resolution and high integration. At present, the thinning method of large-size piezoelectric film wafers is usually achieved by bonding and then chemical grinding or ion knife and then bonding, which has the following problems:

[0003] (1) There are two problems with the bonding and chemical grinding thinning technology. First, the piezoelectric wafer often falls off during the grinding process due to insufficient bonding strength. Second, the thickness of the film cannot be accurately controlled during the grinding process, and it is often over-thinned or under-thinned. For acoustic device films, the thickness is strongly related to the final performance.

[0004] (2) The ion knife process followed by bonding has the following problems. On the one hand, the equipment requirements are very high, and the equipment used for the ion knife process is very expensive. Secondly, the bonding process after the ion knife process requires bonding a thin film of several microns to another silicon wafer. In this process, the film is often cracked and damaged due to being too thin. Especially when used for wafer-level thinning, the film damage problem is difficult to control. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for thinning a large-size piezoelectric thin film wafer and a prepared piezoelectric thin film wafer, so as to solve the problem in the prior art that the thickness of the film cannot be accurately controlled, and the film is often over-thinned or under-thinned, or cracked and damaged due to the film being too thin.

[0006] Technical Solution

[0007] A method for thinning a large-size piezoelectric thin film wafer is characterized in that it includes the following steps: first, through a substrate patterning process, a limiting groove of the same size as the required thin film wafer is prepared on the substrate, and the height of the limiting groove is slightly greater than or equal to the target thickness of the thin film wafer after thinning, and then the piezoelectric wafer is bonded in the limiting groove, and finally chemical grinding is performed. When the piezoelectric wafer film is ground to be flush with the peripheral height of the limiting groove on the substrate, there will be a pressure feedback signal due to the grinding area and the sudden change of the material, and the grinding speed will also be reduced. By obtaining the pressure feedback signal and combining it with the grinding speed, the thinning of the piezoelectric thin film wafer can be accurately controlled.

[0008] Furthermore, in addition to preparing a limiting groove on the substrate with a height slightly greater than or equal to the required film thickness through the substrate patterning process, an observation hole is also prepared next to the side wall of the limiting groove, and the film thickness is observed through the observation hole for more precise control.

[0009] Furthermore, the piezoelectric wafer bonded in the limiting groove has a lower electrode, and the height of the limiting groove includes the height of the film and the lower electrode, or a Bragg reflection layer and a metal lower electrode need to be prepared under the piezoelectric wafer, and the height of the limiting groove includes the height of the film, the Bragg reflection layer and the metal lower electrode.

[0010] The substrate patterning process first prepares an oxide layer on the substrate as a mask for subsequent etching of the silicon substrate for patterning optimization, and then uses a photolithography process to prepare a patterning mask required for etching the silicon dioxide film. After the etching of the silicon dioxide mask is completed, the resist is removed, and then the limiting groove or observation hole is prepared on the substrate by wet or dry etching, and finally the oxide layer is removed.

[0011] A piezoelectric thin film wafer prepared using the above-mentioned thinning method, characterized in that: the above-mentioned thinning method can be used for wafer-level thinning of AlN, AlScN, LiNbO3, LiTaO3, NBBT, KNN, PMN-PT, PIN-PMN-PT and PZT piezoelectric materials, and the corresponding piezoelectric thin film wafers can be prepared on a silicon substrate.

[0012] A method for preparing a piezoelectric micro-electromechanical ultrasonic sensor, characterized by comprising the following steps:

[0013] Step 11, preparing a piezoelectric wafer film with a lower electrode using the above method;

[0014] Step 12, preparing a cavity, performing photolithography on the back side of the substrate as a mask for back etching, and coating the front side with photoresist to protect the front side image from being scratched during the back etching process, and then performing deep silicon etching to prepare a cavity on the back side;

[0015] Step 13, the lower electrode is led out. Photolithography is performed on the front side as a mask for subsequent ibeam etching. Then the piezoelectric wafer film is etched using the ibeam process and stopped at the lower electrode. Since the film thickness is greater than the electrode thickness, the hole connected to the lower electrode must be filled with metal before the metal electrode is prepared to lead out the lower electrode. After the lower electrode is led out, lift off to remove excess metal.

[0016] Step 14, prepare electrodes, photolithography the positions where electrodes need to be prepared on the front side; use magnetron sputtering to make the electrode metal layer; lift off the excess metal to complete the preparation of the upper and lower electrodes.

[0017] A method for preparing a thin film bulk acoustic wave resonator, characterized by comprising the following steps:

[0018] Step 21, preparing a piezoelectric wafer film with a lower electrode using the above method;

[0019] Step 22, preparing a cavity, performing photolithography on the back side of the substrate, using it as a mask for back etching, coating photoresist on the front side to protect the front side image from being scratched during the back etching process, and then performing deep silicon etching to prepare a cavity on the back side;

[0020] Step 23, frequency modulation process, using Trimmer process to perform point-to-point correction on the film thickness;

[0021] Step 24, the lower electrode is led out, and photolithography is performed on the front side as a mask for subsequent ibeam etching. Then, the piezoelectric wafer film is etched using the ibeam process and stopped at the lower electrode. Since the film thickness is greater than the electrode thickness, the hole connected to the lower electrode is first filled with metal, and then the excess metal is removed;

[0022] Step 25, prepare electrodes, photolithography the positions where electrodes need to be prepared on the front side; use magnetron sputtering to make the electrode metal layer; remove excess metal, and complete the preparation of the upper and lower electrodes.

[0023] A method for preparing a transversely excited bulk acoustic wave filter, characterized by comprising the following steps:

[0024] Step 31, preparing a piezoelectric wafer film using the above method;

[0025] Step 32, preparing a cavity, performing photolithography on the back side of the substrate, using it as a mask for back etching, coating photoresist on the front side to protect the front side image from being scratched during the back etching process, and then performing deep silicon etching to prepare a cavity on the back side;

[0026] Step 33, frequency modulation process, using Trimmer process to perform point-to-point correction on the film thickness;

[0027] Step 34, prepare electrodes, photolithography the positions where electrodes need to be prepared on the front side; use magnetron sputtering to make the electrode metal layer; remove excess metal, and complete the preparation of multiple interdigitated electrodes.

[0028] A method for preparing a solid assembly type bulk acoustic wave filter, characterized by comprising the following steps:

[0029] Step 41, prepare a piezoelectric wafer film by the method as described above, prepare a limiting groove on the substrate by substrate patterning process, photolithography the position where the Bragg reflection layer needs to be prepared, and then alternately prepare metal W by magnetron sputtering and SiO2 by PECVD to complete the preparation of the Bragg reflection layer, and remove the excess Bragg reflection layer by acetone and ultrasound;

[0030] Step 42, then bonding the piezoelectric wafer with the lower electrode into the limiting groove, and grinding the piezoelectric wafer film by chemical grinding process to be flush with the periphery height of the limiting groove on the substrate;

[0031] Step 43, frequency modulation process, using Trimmer process to perform point-to-point correction on the film thickness;

[0032] Step 44, lead out the lower electrode, perform photolithography on the front side, and use it as a mask for subsequent ibeam etching. Then, use the ibeam process to etch the piezoelectric wafer film and stop at the lower electrode. Since the film thickness is greater than the electrode thickness, first fill the hole connected to the lower electrode with metal, and then remove the excess metal.

[0033] Step 45, prepare electrodes, photolithography the positions where electrodes need to be prepared on the front side; use magnetron sputtering to make the electrode metal layer; remove excess metal, and complete the preparation of the upper and lower electrodes.

[0034] A method for preparing an electro-optical modulator, characterized by comprising the following steps:

[0035] Step 51, preparing a piezoelectric wafer film using the above method;

[0036] Step 52, waveguide process, depositing a Ti metal layer for Ti diffusion on the front side of the substrate by magnetron sputtering, leaving the area where Ti diffusion is required by photolithography plus ibeam etching process, and after debonding, using a high temperature diffusion process to diffuse Ti into the piezoelectric crystal film, thereby changing the refractive index to form a waveguide;

[0037] Step 53, photolithography is performed on the front surface to mark the position where the electrode needs to be prepared, and then the electrode metal layer is formed by magnetron sputtering, and finally the excess metal is removed to complete the preparation of the electrode.

[0038] Beneficial Effects

[0039] The method for thinning a large-size piezoelectric thin film wafer of the present invention first prepares a limiting groove on a substrate through a graphic substrate process, wherein the height of the limiting groove is the thickness of the piezoelectric wafer film with a lower electrode or the thickness of the piezoelectric wafer film plus the Bragg reflection layer and metal electrode that need to be prepared below the piezoelectric wafer, and then the piezoelectric wafer is bonded in the limiting groove, and then the surface of the piezoelectric wafer film is ground to the same plane as the substrate through a chemical grinding process. In this way, the thickness of the piezoelectric wafer film can be accurately controlled, solving the problem of being unable to accurately control the thickness in the current thinning process, resulting in cracking and breakage. Within the thickness range of 0.5 microns to 200 microns, the thickness of the piezoelectric thin film wafer can be accurately controlled to any desired target thickness.

[0040] The present invention also proposes a process for preparing various filters and resonators based on the thinning method, which reduces the restrictions of existing processes on materials, improves various performances of devices, and has high application prospects and great promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic flow chart of the thinning method of the present invention;

[0042] Figure 2 This is a schematic diagram of the process of application example 1 of the present invention;

[0043] Figure 3 This is a schematic diagram of the process of application example 2 of the present invention;

[0044] Figure 4 This is a schematic diagram of the process of application example 3 of the present invention;

[0045] Figure 5 This is a schematic diagram of the process of Application Example 4 of the present invention;

[0046] Figure 6 This is a schematic diagram of the process of Application Example 5 of the present invention. DETAILED DESCRIPTION

[0047] The present invention is further described below in conjunction with specific embodiments and drawings.

[0048] As attached Figure 1As shown, in order to solve the problems of the existing thinning process, the present invention proposes a thinning method for a large-size piezoelectric thin film wafer, comprising the following steps: first, through a substrate patterning process, a limiting groove with a height slightly greater than or equal to the target thickness of the thin film wafer, also called a thickness limiting groove, is prepared on the substrate, and then the piezoelectric wafer is bonded in the limiting groove, and finally chemical grinding is performed. When the piezoelectric wafer film is ground to be flush with the peripheral height of the limiting groove on the substrate, there will be a pressure feedback signal due to the sudden change of the grinding area and the material, and the grinding speed will also be reduced. By obtaining the pressure feedback signal and combining it with the grinding speed, the thinning of the piezoelectric thin film wafer can be accurately controlled.

[0049] During the grinding process, the lateral shear force is the main cause of bond failure, and the groove design will provide a lateral protection to improve the bond strength, especially the bond strength in the shear force direction can be strengthened through the side wall of the groove, so that it can withstand greater lateral shear force during the grinding process.

[0050] Through the substrate patterning process, in addition to preparing a limiting groove on the substrate with a height slightly greater than or equal to the required film thickness, an observation hole is also prepared next to the side wall of the limiting groove to observe the film thickness through the observation hole for more precise control.

[0051] The piezoelectric wafer bonded in the limiting groove has a lower electrode, and the height of the limiting groove includes the height of the film and the lower electrode, or a Bragg reflection layer and a lower electrode need to be prepared under the piezoelectric wafer, and the height of the limiting groove includes the height of the film, the Bragg reflection layer and the lower electrode.

[0052] The substrate patterning process first prepares an oxide layer on the substrate as a mask for subsequent etching of the silicon substrate for patterning optimization, and then uses a photolithography process to prepare a patterning mask required for etching the silicon dioxide film. After the etching of the silicon dioxide mask is completed, the resist is removed, and then the limiting groove or observation hole is prepared on the substrate by wet or dry etching, and finally the oxide layer is removed.

[0053] Substrate patterning process step 1: Use furnace tube thermal oxidation process, PECVD, LPCVD or ALD process to prepare an oxide layer as a mask for subsequent etching of the silicon substrate for patterning optimization. Thermal oxidation process parameters: temperature 1100°C, oxygen flow rate 5SLPM / min;

[0054] Substrate patterning process step 2: Use photolithography to prepare the mask required for etching the silicon dioxide film. Photolithography process parameters: 700nm-2.1um thick, exposure 3s-10s, development time 50s;

[0055] Substrate patterning process step 3: Use RIE or BOE to etch the silicon dioxide mask and remove the glue. BOE process parameters: BOE at room temperature for 3 minutes;

[0056] Substrate patterning process step 4: Prepare limiting grooves and observation holes for observing thickness through wet KOH etching or dry RIE etching, and then use BOE to grind and remove the oxide layer. KOH process parameters: 50℃ 40% KOH for 20 minutes.

[0057] Bonding process: Bond the piezoelectric wafer in the limiting groove, which can be achieved by BCB bonding, gold-gold bonding or gold-silicon bonding. The gold-gold bonding process parameters are: temperature 380°C, pressure 5000N, and duration 60min.

[0058] Chemical grinding process: Use chemical grinding process to grind the single crystal material to the same position as the limit groove. After the protruding single crystal is ground, the pressure will decrease due to the larger contact area, and the grinding speed will slow down, which makes it easier to control the thickness of the single crystal film to prevent over-grinding. There will also be a signal feedback of pressure mutation on the equipment, which can accurately control the thickness of the film. Finally, the depth of grinding down after the piezoelectric wafer and the silicon substrate are flush can be determined through the observation hole, so as to accurately control the process. CMP process parameters: down pressure 2psi-3psi, back pressure 20psi-30psi, polishing pad speed 70rpm, rotor speed 10rpm, polishing liquid 60ml / min.

[0059] The above-mentioned thinning method can be used for wafer-level thinning of piezoelectric materials including but not limited to AlN, AlScN, LiNbO3, LiTaO3, NBBT ((1-x)Na0.5Bi0.5TiO3-xBaTiO3), PMN-PT ((1-x)Pb(Mg1 / 3Nb2 / 3)O3xPbTiO3), PIN-PMN-PT, KNN and PZT (PbZrO3-PbTiO3), and the corresponding piezoelectric thin film wafers can be prepared on a silicon substrate.

[0060] The areas of piezoelectric film wafers currently processed are generally two inches, four inches, six inches, eight inches and twelve inches. As for the thickness, the thinner the film, the more difficult it is to prepare. The method of the present invention can be used to process films with a thickness of less than 30 microns, with a minimum of 0.5 microns, which solves the problem of preparing films with a thickness of less than 30 microns required in the latest devices in the MEMs field. Even if the film needs to be processed to be very thin to meet the application scenario, it can also be achieved using the method of the present invention.

[0061] The piezoelectric film wafer prepared by the thinning method can be applied to a variety of filters and resonators. Some preparation and application examples are given below.

[0062] Application Example 1

[0063] Preparation method for piezoelectric micro-electromechanical ultrasonic sensor, as shown in the attached Figure 2 To illustrate, the following steps can be taken:

[0064] Step 11, using the above method to prepare a piezoelectric wafer film with a lower electrode, the thickness of the piezoelectric wafer film after thinning is less than 10 microns;

[0065] Step 12, prepare the cavity, perform photolithography on the back side of the substrate as a mask for back etching, photolithography process parameters: glue thickness of more than 10um, exposure 30s-50s, development 90s; apply photoresist on the front side to protect the front image from being scratched during the back etching process, glue coating process parameters: glue thickness of about 2um, oven 120℃ for 15min hardening; then use deep silicon etching to prepare the cavity on the back side, deep silicon etching process parameters: platen power 16W, coil power 600W, C4F8 95sccm, SF6 45sccm, Etec time 3s, passivation time 4s;

[0066] Step 13, the lower electrode is led out, and photolithography is performed on the front side as a mask for subsequent ibeam etching. The photolithography process parameters are: glue thickness of about 1um, exposure of about 3s, and development time of 45s; then the piezoelectric wafer film is etched using the ibeam process and stopped at the lower electrode. The ibeam process parameters are: ion beam voltage 500V, Ar 20sccm; since the film thickness is greater than the electrode thickness, the hole connected to the lower electrode is first filled with metal to lead out the lower electrode, and the filling process is completed by magnetron sputtering. The magnetron sputtering process parameters are: Al metal power 150W, working pressure 3mTorr; the excess metal is removed by lift off, and the process parameters are: acetone plus ultrasonic removal;

[0067] Step 14, prepare the electrode, photolithography the position where the electrode needs to be prepared on the front side, the photolithography process parameters are: glue thickness of about 1um, exposure of about 3s, and development time of 45s; use magnetron sputtering to make the electrode metal layer, magnetron sputtering process parameters; Al metal power 150W, pressure 3mTorr; use lift off acetone plus ultrasonic removal to remove excess metal, and complete the preparation of the upper and lower electrodes.

[0068] The existing process of PMUT uses high vacuum magnetron sputtering to complete electrodes and polycrystalline AlN or polycrystalline AlScN piezoelectric films, or uses high vacuum magnetron sputtering to prepare PZT piezoelectric films and electrodes.

[0069] In the application of PUMT intelligent ultrasonic sensors, the operating frequency is not as high as the RF frequency. The medical ultrasound field is at the MHz level, and the ultrasonic ToF is at the KHz level. However, the piezoelectric performance requirements are higher. This process technology can be used to process piezoelectric materials with higher piezoelectric coefficients such as PMN-PT, PIN-PMN-PT and NBBT into piezoelectric films. Compared with AlN, whose piezoelectric coefficient d33 is only about 5pC / N, PMN-PT can reach 1500pc / N, and NBBT can reach 416pC / N. This process technology can greatly improve the performance of PMUT devices.

[0070] Application Example 2

[0071] Method for preparing thin film bulk acoustic wave resonator, such as the attached Figure 3 As shown, the following steps are taken:

[0072] Step 21, using the above method to prepare a piezoelectric wafer film with a lower electrode, the target thickness of the piezoelectric wafer film is less than 2 microns;

[0073] Step 22, preparing a cavity, performing photolithography on the back side of the substrate, using it as a mask for back etching, coating photoresist on the front side to protect the front side image from being scratched during the back etching process, and then performing deep silicon etching to prepare a cavity on the back side;

[0074] Step 23, frequency modulation process, using Trimmer process to perform point-to-point correction on the film thickness; Trimmer process parameters: RF Power 96W, Ar 3sccm, vacuum degree 2e-5mbar, ion beam voltage 1000V, ion beam current 15mA, acceleration voltage 100V;

[0075] Step 24, the lower electrode is led out, and photolithography is performed on the front side as a mask for subsequent ibeam etching. Then, the piezoelectric wafer film is etched using the ibeam process and stopped at the lower electrode. Since the film thickness is greater than the electrode thickness, the hole connected to the lower electrode is first filled with metal, and then the excess metal is removed;

[0076] Step 25, prepare electrodes, photolithography the positions where electrodes need to be prepared on the front side; use magnetron sputtering to make the electrode metal layer; remove excess metal, and complete the preparation of the upper and lower electrodes.

[0077] The existing process of FBAR uses a high vacuum magnetron sputtering process to complete the preparation of electrodes and polycrystalline AlN or polycrystalline AlScN piezoelectric films. However, the process of the present invention uses a substrate patterning optimization method to prepare a groove slightly greater than or equal to the target film thickness and an observation hole for measuring the thickness on the silicon substrate, prepare a bottom electrode for the piezoelectric single crystal wafer and bond the bottom electrode end to the groove of the substrate, and then thin the wafer to the target thickness through CMP, and finally prepare the upper electrode. The advantage is that it can overcome the limitations of materials. The reason why FBAR currently uses polycrystalline AlN and polycrystalline AlScN with insufficient piezoelectric performance is mainly because only AlN and AlScN are mature in magnetron sputtering, and polycrystalline PZT is not suitable for filter applications due to excessive loss, and single crystal piezoelectric materials including single crystal AlN themselves have better performance than current polycrystalline materials. The method of the present invention can reliably prepare various single crystal piezoelectric films, thereby breaking through the limitations of materials to achieve FBAR devices with better performance.

[0078] Application Example 3

[0079] A method for preparing a transversely excited bulk acoustic wave filter, as shown in the attached Figure 4 Instructions: Use the following steps:

[0080] Step 31, preparing a piezoelectric wafer film using the above method, wherein the target thickness of the piezoelectric wafer film is less than 2 microns;

[0081] Step 32, preparing a cavity, performing photolithography on the back side of the substrate, using it as a mask for back etching, coating photoresist on the front side to protect the front side image from being scratched during the back etching process, and then performing deep silicon etching to prepare a cavity on the back side;

[0082] Step 33, frequency modulation process, using Trimmer process to perform point-to-point correction on the film thickness;

[0083] Step 34, prepare electrodes, photolithography the positions where electrodes need to be prepared on the front side; use magnetron sputtering to make the electrode metal layer; remove excess metal, and complete the preparation of multiple interdigitated electrodes.

[0084] Currently, XBAR must use single crystal piezoelectric materials with better performance, so the piezoelectric materials can adopt epitaxial methods such as PLD or MOCVD, or the bonding and thinning method, or the ion knife and bonding method.

[0085] The method of the present application has a wider range of material selection compared to the epitaxial method. For example, the PMN-PT, PIN-PMN-PT, and NBBT mentioned above can all be thin-filmed using the method of the present application. Epitaxy is currently mainly limited to two materials: single-crystal AlN and AlScN thin films. Because it is an epitaxial technology, the crystal orientation is related to the substrate. For example, substrates such as sapphire are not directly compatible with CMOS processes, and the materials and their crystal orientations are limited. Compared with the bonding and thinning method, the method provided by the present application can effectively and accurately control the thickness of the film, and can greatly improve the bonding strength to prevent falling off during the thinning process.

[0086] Application Example 4

[0087] A method for preparing a solid assembly type bulk acoustic wave filter, as shown in the attached Figure 5 Instructions: Use the following steps:

[0088] Step 41, prepare a piezoelectric wafer film with a thickness of less than 2 microns by the above method, after preparing a limiting groove on the substrate through a substrate patterning process, photolithography is performed to determine the position where the Bragg reflection layer needs to be prepared, and the photolithography process parameters are: a glue thickness of about 1 um, an exposure of about 3 seconds, and a development time of 45 seconds; then, metal W is prepared by magnetron sputtering and SiO2 is prepared by PECVD alternately to complete the preparation of the Bragg reflection layer, and the magnetron sputtering process parameters are: power 250W, pressure 3mTorr, and PECVD process parameters are: SiH 45sccm, N2O 1000sccm, N2 500sccm, pressure 900mTorr, Power 30W, and temperature 300°C; and the excess Bragg reflection layer is removed by acetone and ultrasound;

[0089] Step 42, then bonding the piezoelectric wafer with the lower electrode into the limiting groove, and grinding the piezoelectric wafer film by chemical grinding process to be flush with the periphery height of the limiting groove on the substrate;

[0090] Step 43, frequency modulation process, using Trimmer process to perform point-to-point correction on the film thickness;

[0091] Step 44, lead out the lower electrode, perform photolithography on the front side, and use it as a mask for subsequent ibeam etching. Then, use the ibeam process to etch the piezoelectric wafer film and stop at the lower electrode. Since the film thickness is greater than the electrode thickness, first fill the hole connected to the lower electrode with metal, and then remove the excess metal.

[0092] Step 45, prepare electrodes, photolithography the positions where electrodes need to be prepared on the front side; use magnetron sputtering to make the electrode metal layer; remove excess metal, and complete the preparation of the upper and lower electrodes.

[0093] The SMR process is currently almost the same as FBAR, using high vacuum magnetron sputtering to complete the preparation of electrodes and polycrystalline AlN or polycrystalline AlScN piezoelectric films.

[0094] Compared with the existing SMR process, the method of the present application can select single crystal piezoelectric materials with better performance and choose a better crystal orientation.

[0095] Application Example 5

[0096] Method for preparing an electro-optical modulator, as shown in the attached Figure 6 As shown, the following steps are taken:

[0097] Step 51, preparing a piezoelectric wafer film using the above method, wherein the target thickness of the piezoelectric wafer film is less than 6 microns;

[0098] Step 52, waveguide process, depositing a Ti metal layer for Ti diffusion on the front side of the substrate by magnetron sputtering, magnetron sputtering process parameters: Ti metal 250W, working pressure 3mTorr; using photolithography process plus ibeam etching process to leave the area where Ti diffusion is required, ibeam process parameters: ion beam voltage 500V, Ar 20sccm; after debonding, using high temperature diffusion process to diffuse Ti into the piezoelectric crystal film, thereby changing the refractive index to form a waveguide, diffusion process parameters: about 1000°C, annealing for about 7h;

[0099] Step 53, photolithography is performed on the front side to mark the position where the electrode needs to be prepared, and then the electrode metal layer is prepared by magnetron sputtering. The magnetron sputtering process parameters are: Au power 150W, pressure 3mTorr; finally, the excess metal is removed to complete the preparation of the electrode.

[0100] In the existing process of photoelectric modulator, the electrodes are mostly realized by magnetron sputtering or thermal evaporation process in PVD. In terms of piezoelectric crystals, lithium niobate and lithium tantalate are mainly used, and the process used is ion knife plus bonding or bonding plus thinning process.

[0101] Compared with the bonding and thinning method, the method of the present application can effectively and accurately control the thickness of the film, and can greatly improve the bonding strength to prevent falling off during the thinning process.

[0102] Compared with ion knife plus bonding, ion knife technology has requirements for the crystal orientation of the material, which greatly limits the material. Currently, lithium niobate and lithium tantalate thinned by ion knife are not the crystal orientations with the best performance. However, the method of this patent has no restrictions on the crystal orientation, and the optimal crystal orientation can be selected to improve device performance. Secondly, the subsequent stripping and bonding of the ion knife often leads to problems such as film rupture.

Claims

1. A method for thinning a large-size piezoelectric film wafer. Features The method comprises the following steps: first, through a substrate patterning process, a limiting groove of the same size as the required thin film wafer is prepared on the substrate, and the height of the limiting groove is slightly greater than or equal to the target thickness of the thin film wafer after thinning. Then, the piezoelectric wafer is bonded in the limiting groove, and finally chemical grinding is performed. When the piezoelectric wafer film is ground to be flush with the peripheral height of the limiting groove on the substrate, the thinning of the piezoelectric thin film wafer is precisely controlled.

2. The method for thinning a large-size piezoelectric thin film wafer as claimed in claim 1, Features: In addition to preparing a limiting groove with a height slightly greater than or equal to the required film thickness on the substrate through the substrate patterning process, an observation hole is also prepared next to the side wall of the limiting groove. The film thickness is observed through the observation hole for more precise control.

3. The method for thinning a large-size piezoelectric thin film wafer as claimed in claim 1, Features: The piezoelectric wafer bonded in the limiting groove has a lower electrode, and the height of the limiting groove includes the height of the film and the lower electrode, or a Bragg reflection layer needs to be prepared under the piezoelectric wafer, and the height of the limiting groove includes the height of the film, the Bragg reflection layer and the lower electrode; when the piezoelectric wafer film is ground to be flush with the peripheral height of the limiting groove on the substrate, there will be a pressure feedback signal and the grinding speed will also be reduced due to the sudden change of the grinding area and the material, and the thinning of the piezoelectric film wafer can be accurately controlled by obtaining the pressure feedback signal and combining the grinding speed.

4. The method for thinning a large-size piezoelectric thin film wafer as claimed in claim 1, 2 or 3, Features: The substrate patterning process first prepares an oxide layer on the substrate as a mask for subsequent etching of the silicon substrate for patterning optimization, and then uses a photolithography process to prepare a patterning mask required for etching the silicon dioxide film. After the etching of the silicon dioxide mask is completed, the resist is removed, and then the limiting groove or observation hole is prepared on the substrate by wet or dry etching, and finally the oxide layer is removed.

5. A piezoelectric thin film wafer prepared by the thinning method according to claim 1, Features: The thinning method as described in claim 1 can be used for wafer-level thinning of AlN, AlScN, LiNbO3, LiTaO3, NBBT, PMN-PT, PIN-PMN-PT, KNN and PZT piezoelectric materials, and corresponding piezoelectric thin film wafers can be prepared on a silicon substrate.

6. A method for preparing a piezoelectric micro-electromechanical ultrasonic sensor, Features The steps include: Step 11, preparing a piezoelectric wafer film with a lower electrode by the method as claimed in claim 1; Step 12, preparing a cavity, performing photolithography on the back side of the substrate as a mask for back etching, and coating the front side with photoresist to protect the front side image from being scratched during the back etching process, and then performing deep silicon etching to prepare a cavity on the back side; Step 13, the lower electrode is led out. Photolithography is performed on the front side as a mask for subsequent ibeam etching. Then the piezoelectric wafer film is etched using the ibeam process and stopped at the lower electrode. Since the film thickness is greater than the electrode thickness, the hole connected to the lower electrode must be filled with metal to lead out the lower electrode. After the lower electrode is led out, lift off to remove excess metal. Step 14, prepare electrodes, photolithography the positions where electrodes need to be prepared on the front side; use magnetron sputtering to make the electrode metal layer; lift off the excess metal to complete the preparation of the upper and lower electrodes.

7. A method for preparing a thin film bulk acoustic resonator, Features The steps include: Step 21, preparing a piezoelectric wafer film with a lower electrode by the method as claimed in claim 1; Step 22, preparing a cavity, performing photolithography on the back side of the substrate, using it as a mask for back etching, coating photoresist on the front side to protect the front side image from being scratched during the back etching process, and then performing deep silicon etching to prepare a cavity on the back side; Step 23, frequency modulation process, using Trimmer process to perform point-to-point correction on the film thickness; Step 24, the lower electrode is led out, and photolithography is performed on the front side as a mask for subsequent ibeam etching. Then, the piezoelectric wafer film is etched using the ibeam process and stopped at the lower electrode. Since the film thickness is greater than the electrode thickness, the hole connected to the lower electrode is first filled with metal, and then the excess metal is removed; Step 25, prepare electrodes, photolithography the positions where electrodes need to be prepared on the front side; use magnetron sputtering to make the electrode metal layer; remove excess metal, and complete the preparation of the upper and lower electrodes.

8. A method for preparing a transversely excited bulk acoustic wave filter, Features The steps include: Step 31, preparing a piezoelectric wafer film by the method as claimed in claim 1; Step 32, preparing a cavity, performing photolithography on the back side of the substrate, using it as a mask for back etching, coating photoresist on the front side to protect the front side image from being scratched during the back etching process, and then performing deep silicon etching to prepare a cavity on the back side; Step 33, frequency modulation process, using Trimmer process to perform point-to-point correction on the film thickness; Step 34, prepare electrodes, photolithography the positions where electrodes need to be prepared on the front side; use magnetron sputtering to make the electrode metal layer; remove excess metal, and complete the preparation of multiple interdigitated electrodes.

9. A method for preparing a solid-state bulk acoustic wave filter, Features The steps include: Step 41, preparing a piezoelectric wafer film by the method as claimed in claim 1, after preparing a limiting groove on the substrate through a substrate patterning process, photolithography is performed to form a position where a Bragg reflection layer is required, and then metal W is prepared by magnetron sputtering and SiO2 is prepared by PECVD alternately to complete the preparation of the Bragg reflection layer, and the excess Bragg reflection layer is removed by acetone and ultrasound; Step 42, then bonding the piezoelectric wafer with the lower electrode into the limiting groove, and grinding the piezoelectric wafer film by chemical grinding process to be flush with the periphery height of the limiting groove on the substrate; Step 43, frequency modulation process, using Trimmer process to perform point-to-point correction on the film thickness; Step 44, lead out the lower electrode, perform photolithography on the front side, and use it as a mask for subsequent ibeam etching. Then, use the ibeam process to etch the piezoelectric wafer film and stop at the lower electrode. Since the film thickness is greater than the electrode thickness, first fill the hole connected to the lower electrode with metal, and then remove the excess metal. Step 45, prepare electrodes, photolithography the positions where electrodes need to be prepared on the front side; use magnetron sputtering to make the electrode metal layer; remove excess metal, and complete the preparation of the upper and lower electrodes.

10. A method for preparing an electro-optical modulator, Features The steps include: Step 51, preparing a piezoelectric wafer film by the method as claimed in claim 1; Step 52, waveguide process, depositing a Ti metal layer for Ti diffusion on the front side of the substrate by magnetron sputtering, leaving the area where Ti diffusion is required by photolithography plus ibeam etching process, and after debonding, using a high temperature diffusion process to diffuse Ti into the piezoelectric crystal film, thereby changing the refractive index to form a waveguide; Step 53, photolithography is performed on the front surface to mark the position where the electrode needs to be prepared, and then the electrode metal layer is formed by magnetron sputtering, and finally the excess metal is removed to complete the preparation of the electrode.

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