WO2024087400A1 - Bulk acoustic wave filter and manufacturing method therefor - Google Patents

Abstract

The present application relates to a bulk acoustic wave filter and a manufacturing method therefor. The manufacturing method for the bulk acoustic wave filter of the present application comprises the following steps: determining designed thicknesses of corresponding piezoelectric layers according to designed frequencies of a first resonator to an nth resonator, wherein n≥2; forming, on a wafer substrate, air cavities of the first resonator to the nth resonator, sacrificial layers, seed layers, bottom electrode layers, and piezoelectric layers having a thickness of T; trimming the thicknesses of the piezoelectric layers of the first resonator to the nth resonator to the designed thicknesses by using Ar+ ion beams, so as to form piezoelectric layers having different thicknesses of the first resonator to the nth resonator; forming top electrode layers on the trimmed piezoelectric layers of the first resonator to the nth resonator; and releasing the sacrificial layers to obtain the bulk acoustic wave filter. According to the manufacturing method for the bulk acoustic wave filter of the present application, filters having different frequencies can be manufactured on the same wafer, and the area of a chip can be greatly reduced when the filters having different frequencies are integrated.

Description

A bulk acoustic wave filter and a method for manufacturing the same

This application claims the priority of the Chinese patent application filed with the China Patent Office on October 26, 2022, with application number 202211317441.5, and invention name “A bulk acoustic wave filter and its manufacturing method”, all contents of which are incorporated by reference in this application.

Technical Field

The present application relates to the technical field of filters, and in particular to a bulk acoustic wave filter and a manufacturing method thereof.

Background technique

Acoustic resonators use the inverse piezoelectric effect to convert electrical signals into vibration (sound) signals. Due to the characteristics of the resonator itself, vibration (sound) of a specific frequency resonates and only outputs the signal. Acoustic resonators usually include surface acoustic wave (SAW) resonators, bulk acoustic wave (BAW) resonators, etc.

Bulk acoustic wave (BAW) resonators made by longitudinal resonance of piezoelectric film in the thickness direction have become indispensable RF devices in the field of high-frequency mobile communications. Bulk acoustic wave filters/duplexers provide superior filtering characteristics, such as low insertion loss, steep transition band, large power capacity, and strong anti-electrostatic discharge (ESD) capability. In addition, the processing of bulk acoustic wave (BAW) resonators is compatible with CMOS technology, which is also conducive to the final integration with circuits.

However, due to the size limitation of the interdigital electrodes, SAW resonators have difficulty breaking the frequency limit of 3 GHz, and their application in the high-frequency band of Sub-6G is restricted. The FBAR resonator common in BAW resonators has a high defect density in the polycrystalline AlN film and poor crystal quality, which affects its performance. At the same time, due to the damage to the resonator itself caused by the release of the sacrificial layer and the CMP process, the device yield is also reduced accordingly. To obtain different resonant frequencies on different resonators, the existing technology generally controls the thickness of the piezoelectric film. Since the electrode material film is generally prepared on the entire wafer by sputtering equipment, the resonators currently made on the same wafer mostly use piezoelectric films of the same thickness. In order not to increase the complexity of the process, the filter manufacturing process usually only adjusts the total thickness of the resonator area by changing the mass load layer on different resonators to obtain resonators with different resonant frequencies, and then forms a multi-stage filter through cascading.

However, the mass load formed by the electrode material increases the thickness of the electrode, which has a negative impact on the effective electromechanical coupling coefficient of the resonator itself, so the frequency adjustment range of this method is relatively low. When there is a need for duplexer and RF front-end integration, and filters with multiple frequencies are required, it is often necessary to first produce the filter discrete devices, and then integrate them after preliminary packaging, which is not conducive to reducing the area of the entire module.

Therefore, how to accurately control the resonance/filter frequency while reducing the total area of the integrated module part while improving the crystal quality, reducing device damage, and thus improving the resonator performance and yield has become an urgent problem to be solved.

Summary of the invention

Based on this, the present application provides a method for manufacturing a bulk acoustic wave filter, which can manufacture filters of different frequencies on the same wafer, and can greatly reduce the chip area when integrating filters of different frequencies; if combined with the common ground design method of the filter, the ground wire can be shared between the filters, further reducing the filter integrated chip area and increasing the chip yield on a wafer. At the same time, since the different frequency filters required by the integrated chip can be integrated together, the overall packaging of filters of different frequencies can be realized, without the need to use the form of discrete device packaging and then integrated packaging, saving packaging materials and reducing packaging costs.

A method for manufacturing a bulk acoustic wave filter comprises the following steps:

Determine the design thickness of the corresponding piezoelectric layer according to the design frequency of the first resonator to the nth resonator, n≥2;

An air cavity, a sacrificial layer, a seed layer, a bottom electrode layer and a piezoelectric layer with a thickness of T are formed on a wafer substrate from the first resonator to the nth resonator, wherein T is greater than or equal to the designed thickness of any piezoelectric layer of the first resonator to the nth resonator;

trimming the thickness of the piezoelectric layers of the first resonator to the nth resonator to the designed thickness by using an Ar+ ion beam, thereby forming the piezoelectric layers of the first resonator to the nth resonator having different thicknesses;

forming a top electrode layer on the trimmed piezoelectric layers of the first to nth resonators;

The sacrificial layer is released to obtain a bulk acoustic wave filter.

The present application obtains resonators of various resonant frequencies by forming piezoelectric layers of different thicknesses on the same wafer, thereby reducing the electrode thickness of the bulk acoustic wave resonator, increasing the effective electromechanical coupling coefficient (kt2eff) of the resonator, and reducing the reserved slice interval between filters of different frequencies, significantly reducing the area of the filter, and greatly reducing the area of the integrated module. The use of Ar+ ion beam to trim the piezoelectric layer can accurately control the thickness and uniformity of the piezoelectric film, and the overall production time is short and efficient.

The present application also provides a bulk acoustic wave filter, which is manufactured using the above manufacturing method.

For better understanding and implementation, the present application is described in detail below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a structure after a cavity is formed on a wafer substrate according to the first embodiment.

FIG. 2 is a schematic diagram of the structure after forming a sacrificial layer provided in the first embodiment.

FIG. 3 is a schematic diagram of a structure for forming a seed layer and a bottom electrode layer and performing patterning provided in the first embodiment.

FIG. 4 is a schematic diagram of the structure after forming the piezoelectric layer provided in the first embodiment.

FIG. 5 is a schematic diagram of a structure for trimming a piezoelectric layer of a resonator using an Ar+ ion beam and a shielding plate, as provided in the first embodiment.

FIG. 6 is a schematic diagram of a structure for trimming another resonator piezoelectric layer using an Ar+ ion beam and a shielding plate provided in Example 1.

FIG. 7 is a schematic diagram of the structure of a bulk acoustic wave filter provided in the first embodiment.

Detailed ways

The present application is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

Example 1

The present embodiment provides a bulk acoustic wave filter and a manufacturing method thereof.

1-7, the bulk acoustic wave filter manufacturing method comprises the following steps:

Step 01, determining the design thickness of the corresponding piezoelectric layer according to the design frequency of the first resonator to the nth resonator, n≥2.

1 , a wafer substrate 1 is cleaned, and air cavities 2 of various resonators 101 - 1 , 101 - 2 , ... 101 - n of a filter 101 are formed on the wafer substrate 1. Specifically, the air cavities 2 may be formed by photolithography, dry etching or wet etching.

Step 02, forming a sacrificial layer on the wafer substrate 1, the sacrificial layer completely filling the air cavity 2. The sacrificial layer material is phosphorus-doped silicon oxide (PSG), and the sacrificial layer is prepared by chemical vapor deposition (CVD) process.

Step 03, referring to FIG. 2 , the surface of the substrate is ground by using a CMP process to remove the sacrificial layer protruding above the plane of the wafer substrate 1 , so that the upper surface of the sacrificial layer is flush with the upper surface of the substrate.

Step 04, referring to FIG. 3, a seed layer film is formed on the upper surface of the wafer substrate 1, and a bottom electrode layer film is formed on the upper surface of the seed layer film. The seed layer film and the bottom electrode layer film are subjected to photolithography and etching processes to form a bottom electrode pattern, to obtain a seed layer 3 and a bottom electrode layer 4, and to expose a sacrificial layer release channel 9. The seed layer material may be AlN, and the bottom electrode layer material may be one of Mo, Al and Cu.

Step 05, forming a piezoelectric layer film on the upper surface of the wafer substrate 1, the sacrificial layer 2 and the bottom electrode layer 4, and performing photolithography and etching processes on the piezoelectric layer film to remove part of the piezoelectric layer film outside the upper surface of the bottom electrode layer to obtain a piezoelectric layer 5. In the embodiment, the piezoelectric layer is an AlN film with a preferred c-axis orientation grown by magnetron sputtering.

Step 06, determining the design thickness of the corresponding piezoelectric layer according to the design frequency of the first resonator to the nth resonator; using Ar ⁺ ion beam to trim the thickness of the piezoelectric layer of the first resonator to the nth resonator to the design thickness:

N is taken from 1 to n, and the following process is repeated respectively:

Take the Nth shielding plate, make an alignment mark or an alignment mark area at the fixed position of the shielding plate and the wafer substrate, and the shielding plate can completely cover the wafer substrate;

A hole is opened in the orthographic projection area corresponding to the Nth resonator voltage layer on the Nth shielding plate;

The actual thickness of the piezoelectric layer is measured to calculate the trimmed thickness, wherein the trimmed thickness = the actual thickness - the designed thickness;

Align and fix the Nth shielding plate to the wafer substrate (the shielding plate is fixed on the wafer substrate or fixed on the device), bombard with Ar+ ion beam 7, trim the piezoelectric layer of the Nth resonator, and reduce the trimming thickness. During the trimming, the environmental vacuum degree is not less than ^10-7 Torr;

The shielding plate is made of any one of Pt, ceramic material, SiC and _SiO2 that is resistant to Ar+ ion beam etching.

5 , the piezoelectric layer of the resonator 101 - 2 is trimmed using a shielding plate 6 - 2 and an Ar + ion beam 7 .

6 , the piezoelectric layer of the resonator 101 - n is trimmed using a shielding plate 6 - n and an Ar + ion beam 7 .

In other embodiments, only one shielding plate may be used to trim the piezoelectric layers of the first resonator to the nth resonator. Specifically:

Take a shielding plate, make an alignment mark or an alignment mark area at the fixed position of the shielding plate and the wafer substrate, and the shielding plate completely covers the wafer substrate;

Open holes in the orthographic projection areas corresponding to the voltage layers of the first resonator to the nth resonator on the shielding plate;

The shielding plate is aligned and fixed to the wafer substrate, and the voltage layers of the first resonator to the nth resonator are bombarded one by one with an Ar+ ion beam, and the piezoelectric layers of the first resonator to the nth resonator are trimmed to reduce the trimming thickness.

Step 07, see Figure 7, sputter the top electrode layer 8 on the piezoelectric layer 5, form the required pattern through photolithography and etching processes, form a "sandwich" structure, and then release the sacrificial layer through the sacrificial layer release channel 9 to form a cavity, so as to realize the production of filters of different frequencies on the same wafer.

The present application also provides a bulk acoustic wave filter, which is manufactured using the above-mentioned manufacturing method.

The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present application, and the present application is also intended to include these modifications and modifications.

Claims (20)

A method for manufacturing a bulk acoustic wave filter comprises the following steps: Determine the design thickness of the corresponding piezoelectric layer according to the design frequency of the first resonator to the nth resonator, n≥2; An air cavity, a sacrificial layer, a seed layer, a bottom electrode layer and a piezoelectric layer with a thickness of T are formed on a wafer substrate from the first resonator to the nth resonator, wherein T is greater than or equal to the designed thickness of any piezoelectric layer of the first resonator to the nth resonator; Determine the corresponding piezoelectric layer thickness according to the design frequency of the first resonator to the nth resonator; trimming the thickness of the piezoelectric layers of the first resonator to the nth resonator to the designed thickness using an Ar ⁺ ion beam, thereby forming the piezoelectric layers of the first resonator to the nth resonator having different thicknesses; forming a top electrode layer on the trimmed piezoelectric layers of the first to nth resonators; The sacrificial layer is released to obtain a bulk acoustic wave filter. The method for manufacturing a bulk acoustic wave filter according to claim 1, wherein: trimming the thickness of the piezoelectric layer using an Ar ⁺ ion beam comprises the following steps: N is taken from 1 to n, and the following process is repeated respectively: Take the Nth shielding plate, make an alignment mark or an alignment mark area at the fixed position of the shielding plate and the wafer substrate, and the shielding plate can completely cover the wafer substrate; A hole is opened in the orthographic projection area corresponding to the Nth resonator voltage layer on the Nth shielding plate; The Nth shielding plate is aligned and fixed to the wafer substrate, and the piezoelectric layer of the Nth resonator is trimmed to a designed thickness by bombarding with an Ar ⁺ ion beam; The shielding plate is made of a material resistant to Ar+ ion beam etching. The method for manufacturing a bulk acoustic wave filter according to claim 1, wherein: trimming the thickness of the piezoelectric layer using an Ar ⁺ ion beam comprises the following steps: Take a shielding plate, make an alignment mark or an alignment mark area at the fixed position of the shielding plate and the wafer substrate, and the shielding plate can completely cover the wafer substrate; Open holes in the orthographic projection areas corresponding to the voltage layers of the first resonator to the nth resonator on the shielding plate; The shielding plate is aligned and fixed to the wafer substrate, and the voltage layers of the first resonator to the nth resonator are bombarded one by one with an Ar ⁺ ion beam, so that the piezoelectric layers of the first resonator to the nth resonator are trimmed to a designed thickness; The shielding plate is made of a material resistant to Ar+ ion beam etching. According to the method for manufacturing a bulk acoustic wave filter according to claim 2, before the Ar ⁺ ion beam bombardment, the method further comprises: measuring the actual thickness of the piezoelectric layer, calculating the trimmed thickness, wherein the trimmed thickness = the actual thickness - the designed thickness, controlling the Ar ⁺ ion beam intensity and the bombardment time, so that the piezoelectric layer is thinned by the trimmed thickness to obtain a piezoelectric layer of the corresponding designed thickness. According to the method for manufacturing a bulk acoustic wave filter according to claim 3, before the Ar ⁺ ion beam bombardment, the method further comprises: measuring the actual thickness of the piezoelectric layer, calculating the trimmed thickness, wherein the trimmed thickness = actual thickness - designed thickness, controlling the Ar ⁺ ion beam intensity and bombardment time, so that the piezoelectric layer is thinned by the trimmed thickness to obtain a piezoelectric layer of the corresponding designed thickness. The method for manufacturing a bulk acoustic wave filter according to claim 2, wherein: the material of the shielding plate is a composite of one or more of Pt, ceramic material, SiC and _SiO2 . The method for manufacturing a bulk acoustic wave filter according to claim 3, wherein: the material of the shielding plate is a composite of one or more of Pt, ceramic material, SiC and _SiO2 . The method for manufacturing a bulk acoustic wave filter according to claim 1, wherein when the piezoelectric layer is trimmed by using an Ar ⁺ ion beam, the degree of vacuum of the environment is not less than 10 ^-7 Torr. The method for manufacturing a bulk acoustic wave filter according to claim 1, wherein: the specific method of forming the air cavity, sacrificial layer, seed layer, bottom electrode layer and piezoelectric layer of the first resonator to the nth resonator is: cleaning the wafer substrate and forming an air cavity on the wafer substrate; Forming a sacrificial layer on the wafer substrate, and using a CMP process to make the upper surface of the sacrificial layer flush with the upper surface of the substrate; A seed layer film and a bottom electrode layer film are sequentially formed on the wafer substrate and the upper surface of the sacrificial layer, and the seed layer film and the bottom electrode layer film are subjected to photolithography and etching processes to form a bottom electrode pattern, and expose a sacrificial layer release channel; A piezoelectric layer film is formed on the upper surfaces of the wafer substrate, the sacrificial layer and the bottom electrode layer, and the piezoelectric layer film is subjected to photolithography and etching processes to remove the piezoelectric layer film outside the upper surface of the bottom electrode layer to obtain a piezoelectric layer. The method for manufacturing a bulk acoustic wave filter according to claim 5, wherein: The air cavity is formed by photolithography, dry etching or wet etching process; The sacrificial layer is formed by sputtering, chemical vapor deposition, physical vapor deposition, or spin coating; The seed layer and the bottom electrode layer are formed by a sputtering process. According to the method for manufacturing a bulk acoustic wave filter according to claim 5, wherein: the sacrificial layer material includes phosphorus-doped silicon oxide, metal or polymer; the seed layer material is AlN; the bottom electrode layer material is one of Mo, Al and Cu; and the piezoelectric layer is an AlN film with c-axis preferential orientation. A bulk acoustic wave filter is manufactured by the manufacturing method according to claim 1. A bulk acoustic wave filter is manufactured by the manufacturing method according to claim 2. A bulk acoustic wave filter is manufactured by the manufacturing method according to claim 3. A bulk acoustic wave filter is manufactured by the manufacturing method according to claim 4. A bulk acoustic wave filter is manufactured by the manufacturing method according to claim 5. A bulk acoustic wave filter is manufactured by the manufacturing method according to claim 6. A bulk acoustic wave filter is manufactured by the manufacturing method according to claim 7. A bulk acoustic wave filter is manufactured by the manufacturing method according to claim 8. A bulk acoustic wave filter is manufactured by the manufacturing method according to claim 9.

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