Preparation method of piezoelectric composite substrate

Abstract

The invention relates to the technical field of semiconductor material processing, in particular to a preparation method of a piezoelectric composite substrate, which comprises the following steps: preparing two piezoelectric substrates and a support substrate; wherein one piezoelectric substrate is used as a donor substrate, and the other piezoelectric substrate is used as an auxiliary substrate; ion implantation is carried out in the donor substrate, a weakening layer is formed in the donor substrate, and the donor material layer side of the donor substrate and the auxiliary substrate are temporarily bonded through the connecting layer to form a first bonding body; stress is applied to the weakening layer, so that the weakening layer is broken, and a first composite substrate and a residual donor substrate are formed; bonding the donor material layer side of the first composite substrate with the support substrate to form a second bonding body; and corroding to remove a connecting layer of a temporary bonding interface of the donor material layer and the auxiliary substrate in the second bonding body, so that the auxiliary substrate is separated from the second bonding body, and the piezoelectric composite substrate is formed. According to the method, the piezoelectric substrate does not need to be greatly thinned, the single piezoelectric substrate can be reused, and the production cost is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of semiconductor material processing, and in particular to a method for preparing a piezoelectric composite substrate. Background Art

[0002] Lithium tantalate wafer is a commonly used piezoelectric substrate for preparing filters, usually directly using lithium tantalate bare chips; however, surface acoustic wave filters made directly from bare chips have the disadvantage of large temperature coefficient of frequency (TCF). In recent years, with the development of technology, composite substrates of piezoelectric layer on insulator (POI) have gradually begun to replace lithium tantalate bare chips for preparation; the POI structure is divided into three layers, the upper layer is lithium tantalate film, the middle is SiO2, and the bottom layer is a sandwich structure of Si; the filter prepared by POI has the characteristics of high Q value, low TCF, and low insertion loss.

[0003] There are two main technologies for producing POI composite substrates: mechanical thinning and ion implantation stripping. The following uses a 6-inch wafer to illustrate the steps of manufacturing POI using the two technologies:

[0004] 1) Mechanical thinning: Bond the polished and cleaned lithium tantalate (thickness 300-350um) to silicon oxide (oxide layer + silicon substrate), then thin the lithium tantalate to an appropriate film layer (generally 10-20um) and perform CMP polishing to obtain a POI substrate;

[0005] 2) Ion implantation stripping: prepare a single-sided polished lithium tantalate wafer and a silicon wafer with an oxide layer, and then implant ions (H+, He+) of a certain dose and depth into the polished surface of the lithium tantalate wafer; then bond the two polished surfaces of the wafers. Since the thermal expansion coefficients of the lithium tantalate wafer and the silicon wafer are relatively large, direct annealing will cause the lithium tantalate and silicon oxide to crack due to the large difference in thermal expansion deformation. Therefore, the lithium tantalate wafer needs to be thinned to a certain thickness (30-50um); finally, anneal it at a certain temperature for a period of time, and the lithium tantalate film is separated from the ion implantation layer and transferred to the silicon wafer with an oxide layer to complete the preparation of the POI substrate;

[0006] Both of the above methods require that the lithium tantalate wafer be significantly thinned. Since lithium tantalate wafers are expensive, using the above two methods to prepare POI substrates will result in very high manufacturing costs. Summary of the invention

[0007] The object of the present invention is to provide a method for preparing a piezoelectric composite substrate, which method does not require significant thinning of the piezoelectric substrate, and a single piezoelectric substrate can be reused, thereby reducing production costs.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] A method for preparing a piezoelectric composite substrate comprises: preparing two piezoelectric substrates and a supporting substrate;

[0010] The two piezoelectric substrates are made of the same material;

[0011] One of the piezoelectric substrates is used as a donor substrate, and the other piezoelectric substrate is used as an auxiliary substrate;

[0012] Performing ion implantation into the donor substrate to form a weakened layer in the donor substrate, wherein the weakened layer divides the donor substrate into a donor material layer and a residual donor substrate;

[0013] Temporarily bonding the donor material layer side of the donor substrate to the auxiliary substrate via a connecting layer to form a first bonding body;

[0014] Applying stress to the weakened layer to break the weakened layer, thereby forming a first composite substrate and a residual donor substrate formed by temporary bonding of the donor material layer and the auxiliary substrate;

[0015] bonding the donor material layer side of the first composite substrate to a supporting substrate to form a second bonded body;

[0016] The connecting layer at the temporary bonding interface between the donor material layer and the auxiliary substrate in the second bonding body is removed by etching, so that the auxiliary substrate is separated from the second bonding body to form a piezoelectric composite substrate.

[0017] Preferably, the ion implantation dose is 1E16 ion / cm 2 -1E18ion / cm 2 .

[0018] Preferably, the connecting layer is made of metal.

[0019] Preferably, the metal includes chromium, nickel, titanium, aluminum, copper or silver.

[0020] Preferably, the connecting layer is prepared on the donor material layer and / or the auxiliary substrate by in-situ sputtering;

[0021] The thickness of the connecting layer is 0.5-20 nm.

[0022] Preferably, the etching comprises immersing the second bonding body in a metal etching solution to separate the auxiliary substrate from the second bonding body.

[0023] Preferably, the metal corrosive liquid comprises a hydrochloric acid solution;

[0024] Preferably, the concentration of the hydrochloric acid solution is 10%-30%.

[0025] Preferably, the corrosion is corrosion under room temperature conditions;

[0026] The corrosion time is 1-20 hours.

[0027] Preferably, the method further comprises subjecting the piezoelectric composite substrate to annealing treatment;

[0028] The annealing temperature is 400-600° C., and the annealing time is 1-10 hours.

[0029] Preferably, the method of applying stress to the weakened layer comprises heating the first bonding body to 160°C-250°C and then maintaining the temperature for 0.3-10 hours. The temperature maintaining time is related to the heating temperature and the ion implantation dose. Within this condition range, the heating temperature and the temperature maintaining time can cause the weakened layer to break, thereby forming a first composite substrate and a residual donor substrate formed by temporary bonding of the donor material layer and the auxiliary substrate;

[0030] Preferably, the material of the piezoelectric substrate is lithium niobate or lithium tantalate;

[0031] The support substrate is made of a silicon substrate having a silicon oxide layer.

[0032] Beneficial effects of the present invention: When a piezoelectric composite substrate is prepared by the preparation method provided by the present invention, there is no need to significantly thin the piezoelectric substrate. Compared with the existing preparation method, in the preparation method provided by the present application, taking a 350μm piezoelectric substrate as an example, a single piezoelectric substrate can be recycled more than 50 times, and at least 50 piezoelectric composite substrates can be prepared, which greatly reduces the production cost and improves the material utilization rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic flow diagram of the preparation method of the present invention;

[0034] In the figure: 1. donor substrate; 1-1. weakened layer; 1-2. residual donor substrate; 1-3. donor material layer; 2. auxiliary substrate; 3. support substrate; 4. first bonding body; 5. first composite substrate; 6. second bonding body; 7. piezoelectric composite substrate; 8. connecting layer. DETAILED DESCRIPTION

[0035] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention.

[0036] Example 1

[0037] See also Figure 1 , prepare two piezoelectric substrates, the material of the piezoelectric substrate is lithium tantalate, the diameter is 150 mm, and the thickness is 350 μm.

[0038] And a support substrate, the support substrate is made of silicon, has a diameter of 150 mm and a thickness of 350 μm, and the surface to be bonded of the support substrate is oxidized to form an oxide layer with a thickness of 0.5 μm on the surface of the support substrate.

[0039] It should be noted that in the technical solution provided in the embodiment, the material of the piezoelectric substrate is homogeneous, and the homogeneous substrate can ensure that the thermal expansion coefficient remains consistent during the subsequent heat treatment process, thereby avoiding substrate warping caused by differences in the thermal expansion coefficient.

[0040] One of the piezoelectric substrates is used as the donor substrate 1 , and the preparation method provided in this embodiment can separate a donor material layer 1 - 3 with a thickness of less than 2 μm from the donor substrate 1 .

[0041] Another piezoelectric substrate is used as an auxiliary substrate 2. In this embodiment, the auxiliary substrate 2 is mainly used to support the donor material layers 1-3 separated from the donor substrate 1, so that the donor material layers 1-3 remain flat during the subsequent process. In a complete process flow, the thickness of the auxiliary substrate 2 will not be significantly reduced, so that the auxiliary substrate 2 can be recycled for multiple times.

[0042] Specifically, the donor substrate 1 and the auxiliary substrate 2 have surfaces to be bonded. Before bonding the donor substrate 1 and the auxiliary substrate 2, the following operations need to be performed, including: semiconductor-grade cleaning of the donor substrate 1 and the auxiliary substrate 2; ion implantation from the side of the surface to be bonded of the donor substrate 1, the type of ions being hydrogen ions, and the implantation concentration being 1E17 ion / cm 2 , the implantation depth is 1 μm; aluminum is selected as the target material, and a 2.5 nm thick aluminum film is sputtered on the bonding surfaces of the donor substrate 1 and the auxiliary substrate 2 by in-situ sputtering.

[0043] When performing metal sputtering, the donor substrate 1 and the auxiliary substrate 2 do not need to be additionally heated and can be kept at room temperature. During sputtering, the distance between the target and the substrate is maintained at 50-200 mm, argon is used as the protective gas, and sputtering is performed at a sputtering power of 1000 W and a sputtering pressure of 10 Pa.

[0044] After the sputtering is completed, the sputtering surfaces of the donor substrate 1 and the auxiliary substrate 2 are placed opposite each other, and a pressure of 50 KN is applied to bond the donor substrate 1 and the auxiliary substrate 2 together to form a first bonding body 4. The first bonding body 4 includes the auxiliary substrate 2, the connecting layer 8 of aluminum material, the donor material layer 1-3, the weakened layer 1-1, and the residual donor substrate 1-2 stacked in sequence.

[0045] In this embodiment, the weakened layer 1-1 in the first bonding body 4 is broken by applying stress, so that the residual donor substrate 1-2 is separated from the first bonding body 4. In this embodiment, the stress is applied by applying thermal stress. Specifically, the first bonding body 4 is placed in an environment of 200° C. for 3 hours to break the weakened layer 1-1.

[0046] In some other feasible implementations, laser may be used to irradiate the weakened layer 1 - 1 , and the weakened layer 1 - 1 may also be broken.

[0047] It should be noted that when the first bonding body 4 is heat-treated, since the donor substrate 1 and the auxiliary substrate 2 are both made of lithium tantalate, their thermal expansion coefficients are relatively large, and irregular stress will be generated inside each other after being heated. In this embodiment, the donor substrate 1 and the auxiliary substrate 2 are connected by a connecting layer 8 made of a metal material. Since the metal material has good ductility, the connecting layer 8 can balance the stress generated by the donor substrate 1 and the auxiliary substrate 2, so that the first bonding body 4 will not produce significant warping during heat treatment. When the weakening layer 1-1 breaks, there will be significant stress changes in the donor substrate 1, but the stress will act on the connecting layer 8 and be weakened as the metal stretches, so that the thinner donor material layer 1-3 can still remain flat and will not break.

[0048] When the residual donor substrate 1-2 is separated from the first bonding body 4, a first composite substrate 5 is formed. The first composite substrate 5 includes an auxiliary substrate 2, an aluminum connection layer 8, and a donor material layer 1-3 stacked in sequence. The surface to be bonded of the first composite substrate 5, that is, the surface on the donor material layer 1-3 side, is surface treated to meet the bonding conditions. The supporting substrate 3 is taken, and the oxidized surface of the supporting substrate 3 is surface treated to meet the bonding conditions. The oxidized surface of the supporting substrate 3 is permanently bonded to the surface to be bonded of the first composite substrate 5 to form a second bonding body 6.

[0049] The second bonding body 6 includes an auxiliary substrate 2, an aluminum connection layer 8, donor material layers 1-3, and a support substrate 3 stacked in sequence. In this embodiment, the connection layer 8 is removed by etching to separate the auxiliary substrate 2 from the second bonding body 6 to form a piezoelectric composite substrate 7.

[0050] Specifically, the second bonding body 6 is corroded by immersing it in a metal corrosive solution. The metal corrosive solution used in this embodiment is a 30% hydrochloric acid solution. After immersion at room temperature for 8 hours, the connection layer 8 will be corroded and lose its connectivity.

[0051] In some feasible implementations, the metal etching solution also includes other solutions besides the hydrochloric acid solution. The metal etching solution only needs to be able to corrode the connecting layer without corroding silicon, silicon oxide, lithium niobate, and lithium tantalate. The present invention does not impose too many restrictions.

[0052] In this embodiment, the hydrochloric acid solution has no significant effect on other materials after a short period of immersion except for the corrosive effect on the connection layer 8 in the second bonding body 6 .

[0053] After the above-mentioned etching treatment, the auxiliary substrate 2 is separated from the second bonding body 6, and a piezoelectric composite substrate 7 formed by stacking the support substrate 3 and the donor material layers 1-3 can be obtained.

[0054] The obtained piezoelectric composite substrate 7 is subjected to annealing treatment to repair the lattice defects caused by ion implantation, thereby obtaining a piezoelectric composite substrate product.

[0055] The preparation method provided in this embodiment does not require thinning of the donor substrate 1. The residual donor substrate 1-2 is polished and cleaned and then recycled as a new donor substrate 1 until it is consumed and cannot meet the process requirements. Taking the donor substrate with an initial thickness of 350 μm provided in this embodiment as an example, which is also the thickness of the substrate conventionally sold on the market, since there is no need to thin the donor substrate, a single donor substrate can be recycled at least 50 times, and 50 piezoelectric composite substrates 7 can be prepared. Similarly, the auxiliary substrate 2 can also be reused until it cannot meet the process requirements. Since the damage to the auxiliary substrate 2 is small during the entire process, the auxiliary substrate 2 can be recycled more times.

[0056] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, various obvious changes, readjustments and substitutions can be made without departing from the protection scope of the present invention. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a piezoelectric composite substrate, characterized in that: Prepare two piezoelectric substrates and a supporting substrate; One of the piezoelectric substrates is used as a donor substrate, and the other piezoelectric substrate is used as an auxiliary substrate; Performing ion implantation into the donor substrate to form a weakened layer in the donor substrate, wherein the weakened layer divides the donor substrate into a donor material layer and a residual donor substrate; Temporarily bonding the donor material layer side of the donor substrate to the auxiliary substrate via a connecting layer to form a first bonding body; Applying stress to the weakened layer to break the weakened layer, thereby forming a first composite substrate and a residual donor substrate formed by temporary bonding of the donor material layer and the auxiliary substrate; bonding the donor material layer side of the first composite substrate to a supporting substrate to form a second bonded body; The connecting layer at the temporary bonding interface between the donor material layer and the auxiliary substrate in the second bonding body is removed by etching, so that the auxiliary substrate is separated from the second bonding body to form a piezoelectric composite substrate.

2. The method for preparing a piezoelectric composite substrate according to claim 1, characterized in that: The connecting layer is made of metal.

3. The method for preparing a piezoelectric composite substrate according to claim 2, characterized in that: The metal includes chromium, nickel, titanium, aluminum, copper or silver.

4. The method for preparing a piezoelectric composite substrate according to claim 3, characterized in that: The connecting layer is prepared on the donor material layer and / or the auxiliary substrate by in-situ sputtering; The thickness of the connecting layer is 0.5-20 nm.

5. The method for preparing a piezoelectric composite substrate according to any one of claims 1 to 4, characterized in that: The etching includes immersing the second bonding body in a metal etching solution to separate the auxiliary substrate from the second bonding body.

6. The method for preparing a piezoelectric composite substrate according to claim 5, characterized in that: The metal corrosive liquid comprises a hydrochloric acid solution; Preferably, the concentration of the hydrochloric acid solution is 10%-30%.

7. The method for preparing a piezoelectric composite substrate according to claim 5, characterized in that: The corrosion is corrosion under room temperature conditions; The corrosion time is 1-20 hours.

8. The method for preparing a piezoelectric composite substrate according to claim 1, characterized in that: The piezoelectric composite substrate is further annealed; The annealing temperature is 400-600° C., and the annealing time is 1-10 hours.

9. The method for preparing a piezoelectric composite substrate according to claim 1, characterized in that: The method of applying stress to the weakened layer comprises heating the first bonding body to 160° C.-250° C. and then maintaining the temperature for 0.3-10 hours.

10. The method for preparing a piezoelectric composite substrate according to claim 1, characterized in that: The material of the piezoelectric substrate is lithium niobate or lithium tantalate; The support substrate is made of a silicon substrate having a silicon oxide layer.

Images