Optimization method of bulk acoustic wave resonator filter release hole structure

Abstract

The invention discloses an optimization method for a release hole structure of a bulk acoustic wave resonator filter. The optimization method comprises the following steps: step 1, adding an auxiliary release structure on the upper surface and / or the lower surface of a release hole position; wherein the lattice mismatch rate of the auxiliary release structure material and the piezoelectric layer material is lower than 5%, the auxiliary release structure is annular, the inner diameter of the auxiliary release structure is not smaller than the center value of the designed diameter of the release hole, and the auxiliary release structure is not in contact with the top electrode or the bottom electrode. Step 2, preparing a release hole: taking silicon oxide as a hard mask, and performing release hole patterning at the position of the release hole to form a vertical release hole; and 3, preparing a cavity: releasing the sacrificial layer material through the release hole, and forming the cavity communicated with the release hole below the bottom electrode. By adding the auxiliary release structure on the surface of the release hole, the overall structural strength of the release hole can be enhanced, the shape and size are easy to control, microdefects around the release hole are avoided, and the yield of the device can be effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor process, in particular to a method for optimizing a release hole structure of a bulk acoustic wave resonator filter. Background Art

[0002] With the development of communication system equipment, the requirements for integration, high power and large bandwidth are getting higher and higher, and conventional filters can no longer meet their development needs. Film Bulk Acoustic Resonator (FBAR) has the characteristics of miniaturized packaging, broadband and high power tolerance, which makes it have broader application prospects and development space in 5G communication systems.

[0003] The core structure of FBAR is a "sandwich" structure consisting of bottom electrode-piezoelectric layer-top electrode. Its working principle is to use the piezoelectric effect to realize the conversion between electrical energy and mechanical energy. When the device is subjected to an external bias electric field, the electric field is applied to the piezoelectric film through the top and bottom electrodes. The piezoelectric film is subjected to the field strength and produces periodic deformation under the action of the inverse piezoelectric effect, thereby causing vibration between the electrodes to generate body acoustic waves. In order to confine the acoustic waves in the device, a common structure is that the bottom electrode and the top electrode are in contact with the air to form a contact interface, so a cavity is usually required under the bottom electrode. For process preparation needs, before the bottom electrode is prepared, the cavity is filled with sacrificial material; when the piezoelectric layer and the top electrode are prepared, the solution or gas that reacts with the sacrificial layer material is allowed to contact and react with the sacrificial layer material through the release hole, so as to remove the sacrificial layer material and form a cavity.

[0004] The release holes are located in the piezoelectric layer. Currently, holes are opened in the piezoelectric layer mainly through photolithography patterning and wet etching to leak out the sacrificial layer material underneath.

[0005] At present, the sacrificial layer material is usually PSG, and the piezoelectric layer material is usually AlN / AlScN. However, due to the high lattice mismatch rate between AlN / AlScN and PSG, which is usually more than 10%, the lattice orientation of the piezoelectric layer grown above it is poor, which makes the film quality of the piezoelectric layer directly above the sacrificial layer material worse than that of other areas.

[0006] Furthermore, in the process of preparing the release holes, silicon oxide is usually used as a hard mask for patterning the release holes. The lattice mismatch rate between silicon oxide and the piezoelectric layer material AlN / AlScN is relatively high, usually exceeding 10%, which not only leads to poor film quality of silicon oxide, but also causes many defects at the interface between the two, such as Figure 5 The discontinuous sawtooth shown, etc.

[0007] In the subsequent process of preparing the release hole by wet etching, the wet etching process is isotropic, such as Figure 4 As shown in the figure, the etching solution will not only corrode the unprotected area in the silicon oxide hard mask to form release holes, but also penetrate through the defects and voids in the interface between the two, and corrode the piezoelectric layer material protected by the silicon oxide hard mask. The size of the release hole finally formed will become larger. When the over-corrosion is serious, the piezoelectric layer in the effective area will be corroded, which will affect the performance of the device. In addition, the edge of the release hole will be discontinuous and jagged. In the subsequent use of the device, there are cases such as Figure 6 Risk of cracks shown. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide an optimization method for the release hole structure of a bulk acoustic wave resonator filter in view of the deficiencies of the above-mentioned prior art. The optimization method for the release hole structure of a bulk acoustic wave resonator filter can effectively ensure the size of the release hole, the complete morphology of the release hole, the continuous and defect-free edge of the release hole, and the structural strength of the release hole by adding an auxiliary release structure on the surface of the release hole, thereby ensuring the stability of the release hole during the subsequent use of the device, thereby improving the yield of the device and ensuring the service life of the device.

[0009] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0010] A method for optimizing a release hole structure of a bulk acoustic wave resonator filter comprises the following steps.

[0011] Step 1, adding an auxiliary release structure: adding an auxiliary release structure on the upper surface and / or lower surface of the release hole position; wherein the lattice mismatch rate between the auxiliary release structure material and the piezoelectric layer material is less than 5%, the auxiliary release structure is annular, and the inner diameter of the auxiliary release structure does not exceed the maximum value of the design diameter of the release hole; the auxiliary release structure does not contact the top electrode or the bottom electrode.

[0012] Step 2, preparing release holes: using silicon oxide as a hard mask, patterning the release holes at the release hole positions to form vertical release holes.

[0013] Step 3, preparing a cavity: releasing the sacrificial layer material through the release hole, and forming a cavity below the bottom electrode that is connected to the release hole.

[0014] In step 1, the radial width of the auxiliary release structure is greater than the minimum deviation dimension of the lithography.

[0015] In step 1, the auxiliary release structure is an oriented metal made of the same material as the top electrode or the bottom electrode.

[0016] When the auxiliary release structure is disposed on the upper surface of the release hole, the thickness of the auxiliary release structure is not less than the thickness of the top electrode.

[0017] When the auxiliary release structure is disposed on the lower surface of the release hole, the thickness of the auxiliary release structure does not exceed the thickness of the bottom electrode.

[0018] In step 1, when the auxiliary release structure is disposed on the upper surface of the release hole, the thickness of the auxiliary release structure is equal to the thickness of the top electrode.

[0019] When the auxiliary release structure is disposed on the lower surface of the release hole, the thickness of the auxiliary release structure is equal to the thickness of the bottom electrode.

[0020] Auxiliary release structures are added to the upper and lower surfaces of the release hole position; the thickness of the auxiliary release structure located on the upper surface of the release hole position is not less than the thickness of the top electrode; the thickness of the auxiliary release structure located on the lower surface of the release hole position does not exceed the thickness of the bottom electrode.

[0021] The materials of the top electrode and the bottom electrode are a composite or alloy of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium and chromium.

[0022] The material of the auxiliary release structure is Mo.

[0023] In step 1, the longitudinal cross-section of the auxiliary release structure is a rectangle or an isosceles trapezoid.

[0024] The present invention has the following beneficial effects:

[0025] 1. The present invention can effectively ensure the size of the release hole, the complete morphology of the release hole, the continuous and defect-free edge of the release hole, and the structural strength of the release hole by adding an auxiliary release structure on the surface of the release hole, thereby ensuring the stability of the release hole during the subsequent use of the device, thereby improving the yield of the device and ensuring the service life of the device.

[0026] 2. The present invention does not need to add new process modules in the process of forming the structure. The process steps and process methods are easy to implement and have universal applicability. In some embodiments, the release hole structure can be added to the bottom electrode and / or top electrode layout. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic top view of a bulk acoustic wave resonator filter according to an embodiment of the present invention is shown.

[0028] Figure 2 The embodiment 1 of the present invention shows Figure 1 The production flow chart of the cross-sectional schematic diagram of AA' in the figure; wherein, (a) is a schematic diagram after the top electrode is completed; (b) is a schematic diagram of the etching of the top electrode and the auxiliary release structure; (c) is a schematic diagram after the release hole and the cavity are completed.

[0029] Figure 3 The embodiment 2 of the present invention shows Figure 1Schematic diagram of the cross-section of AA' in the figure; wherein, (a) is a schematic diagram of the etching of the bottom electrode and the auxiliary release structure; (b) is a schematic diagram after the piezoelectric layer and the top electrode are completed; (c) is a schematic diagram after the release hole and the cavity are completed.

[0030] Figure 4 A schematic diagram of wet etching is shown.

[0031] Figure 5 A discontinuous jagged pattern of the release hole edge is shown.

[0032] Figure 6 A picture of the microcracks of the release hole is shown.

[0033] Figure 7 Shows the FIB cutting image of the release hole after adding an auxiliary release structure.

[0034] Among them are:

[0035] 201 - substrate; 202 - sacrificial layer material; 203 - bottom electrode; 204 - piezoelectric layer; 205 - top electrode; 206 - auxiliary release structure; 207 - release hole; 208 - cavity. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific preferred embodiments.

[0037] In the description of the present invention, it should be understood that the terms "left side", "right side", "upper part", "lower part" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. "First", "second" and the like do not indicate the importance of the components, and therefore cannot be understood as limiting the present invention. The specific dimensions used in this embodiment are only for illustrating the technical solution, and do not limit the scope of protection of the present invention.

[0038] like Figure 1 As shown, a method for optimizing the release hole structure of a bulk acoustic wave resonator filter includes the following steps.

[0039] Step 1, adding an auxiliary release structure: adding an auxiliary release structure on the upper surface and / or lower surface of the release hole position.

[0040] The lattice mismatch rate between the auxiliary release structure material and the piezoelectric layer material is less than 5%, and the auxiliary release structure material is preferably an oriented metal that is the same as the material of the top electrode or the bottom electrode.

[0041] In the present invention, the materials of the top electrode and the bottom electrode are preferably a composite or alloy of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium and chromium, etc. Further, the top electrode, the bottom electrode and the auxiliary release structure are preferably Mo with an orientation of 110.

[0042] Furthermore, the auxiliary release structure is annular, and its longitudinal cross-section is rectangular or isosceles trapezoidal.

[0043] The inner diameter of the auxiliary release structure does not exceed the maximum value of the design diameter of the release hole; the radial width of the auxiliary release structure is greater than the minimum deviation size of the lithography, and the outer side of the auxiliary release structure does not contact the top electrode or the bottom electrode.

[0044] Step 2, preparing release holes: using silicon oxide as a hard mask, patterning the release holes at the release hole positions to form vertical release holes.

[0045] Step 3, preparing a cavity: releasing the sacrificial layer material through the release hole, and forming a cavity below the bottom electrode that is connected to the release hole.

[0046] In the present application, the release hole structure of the BAW resonator filter has the following three preferred embodiments.

[0047] Embodiment 1 The auxiliary release structure is arranged on the upper surface of the release hole position

[0048] A method for optimizing a release hole structure of a bulk acoustic wave resonator filter comprises the following steps.

[0049] Step 1: Add auxiliary release structure

[0050] Step 1-1, sequentially growing a bottom electrode 203 on a substrate 201 filled with a sacrificial layer material 202, and performing a patterning process to form a pattern of the bottom electrode 203; wherein the sacrificial layer material is PSG.

[0051] Step 1-2: sequentially deposit the piezoelectric layer 204 and the top electrode 205 to form Figure 2 Figure (a) in .

[0052] Next, a photoresist is coated on the surface of the top electrode, and a fluorine-based mixed gas (SF6:O2) is used to etch the top electrode using an RIE device to form a Figure 2 (b) shows the top electrode 205 and the auxiliary release structure 206. In the embodiment, the auxiliary release structure is located on the upper surface of the release hole, and the thickness of the auxiliary release structure is not less than the thickness of the top electrode. In this embodiment, the top electrode is directly etched, so the thickness of the auxiliary release structure is consistent with the thickness of the top electrode, and the material is Mo.

[0053] In this embodiment, the piezoelectric layer material is preferably AlN. The lattice mismatch rate between AlN and Mo is very low, which can reach -1.2%, and the difference in thermal expansion coefficient is +8.9%.

[0054] The auxiliary release structure is in the shape of a ring with a rectangular cross section, the shape of the inner ring is consistent with the shape of the release hole, and the outer ring is a closed pattern with a width of preferably 4 microns. The auxiliary release structure corresponds to the position of the release hole, is located on the upper surface of the release hole, and is preferably formed by wet etching or dry etching.

[0055] Step 2: preparing the release hole, which specifically includes the following steps.

[0056] Step 2-1, growing silicon oxide on the surface of the piezoelectric layer 204, coating photoresist, photolithography to form a release hole pattern, using BOE (HF: NH4F) solution to etch the silicon oxide, using acetone and isopropyl alcohol to remove the resist, to form a release hole pattern.

[0057] Step 2-2: Use 1%-80°C KOH solution to etch the piezoelectric layer 204 to complete the etching of the release hole 207. Figure 2 (c) as shown.

[0058] Step 3, preparing a cavity: using HF gas and dry etching equipment to release the sacrificial layer material 202 to form a cavity 208 .

[0059] Embodiment 2 The auxiliary release structure is arranged on the lower surface of the release hole position

[0060] Step 1: Adding an auxiliary release structure, specifically including the following steps.

[0061] Step 1-1, growing a bottom electrode 203 on a substrate filled with a sacrificial layer material 202; wherein the sacrificial layer material is PSG.

[0062] Step 1-2, coating the surface of the bottom electrode 203 with photoresist, using fluorine-based mixed gas (SF6:O2), using RIE equipment for etching, to form the bottom electrode 203 pattern and the auxiliary release structure 206. In this embodiment, the auxiliary release structure is located on the bottom electrode, that is, located on the lower surface of the release hole, the thickness of the auxiliary release structure is consistent with the thickness of the top electrode, the material is Mo, the auxiliary release structure is annular, the cross-section is preferably an isosceles trapezoid, the width is 4 microns, such as Figure 3 (a) shown.

[0063] Step 2: preparing the release hole, which specifically includes the following steps.

[0064] Step 2-1, sequentially growing a piezoelectric layer 204 and a top electrode 205 on the surface of the bottom electrode 203, such as Figure 3 (b) as shown.

[0065] Step 2-2: Coat photoresist on the surface of the top electrode, use a fluorine-based mixed gas (SF6:O2), and use RIE equipment to etch to form a top electrode pattern.

[0066] Step 2-3, growing silicon oxide on the surface of the piezoelectric layer, coating photoresist, photolithography to form a release hole pattern, using BOE (HF: NH4F) solution to etch the silicon oxide, using acetone and isopropyl alcohol to remove the resist, and forming a release hole pattern.

[0067] Step 2-4: Use 1%-80°C KOH solution to etch the piezoelectric layer to complete the etching of the release hole.

[0068] Step 3, preparing a cavity: using HF gas and dry etching equipment to release the sacrificial layer material 202 to form a cavity 208 .

[0069] In Example 3, auxiliary release structures are added to both the upper and lower surfaces of the release hole position. For details, please refer to Examples 1 and 2, which will not be repeated here. At this time, the thickness of the auxiliary release structure located on the upper surface of the release hole position is preferably equal to the thickness of the top electrode; the thickness of the auxiliary release structure located on the lower surface of the release hole position is preferably equal to the thickness of the bottom electrode.

[0070] The present invention optimizes the formation process of the release hole by pre-reserving an auxiliary release structure at the position corresponding to the release hole. The auxiliary material of the release hole is a material with a (110) orientation. In the embodiment, Mo with a (110) orientation, which is the same as the electrode material, is selected as the material of the auxiliary release structure. In Example 1, the auxiliary release structure is located above the release hole. During the patterning process of the upper electrode, the auxiliary release structure is formed therewith and is located at the position of the release hole. Then, the patterning of the release hole is performed, and silicon oxide is still used as a hard mask for the overall structure, which ensures that the piezoelectric layer material in the non-release hole area is not corroded during the patterning process of the release hole. At the position of the release hole, since there is Mo above the release hole, the lattice mismatch rate between it and the piezoelectric layer material AlN / AlScN is low, which can ensure that the interface between the two is more compact, and prevent the corrosive solution from penetrating into the interface through voids and defects during the process of wet etching to form the release hole, and corroding the protected piezoelectric layer material. Figure 7As shown, the edge of the release hole finally formed is continuous and complete, and the corrosion stops at the inner edge of the auxiliary release structure, which well guarantees the size of the release hole and the stability of the device structure. In Example 2, the auxiliary release structure is located below the release hole, and is formed together during the patterning process of the lower electrode. In the subsequent patterning process of the release hole, silicon oxide is still used as a hard mask for the overall structure, which ensures that the piezoelectric layer material in the non-release hole area is not corroded during the patterning process of the release hole. At the position of the release hole, since there is an auxiliary release structure below the release hole, its material is Mo, and the presence of Mo is beneficial to the crystallinity of the piezoelectric layer above it, improves the film quality, ensures that the piezoelectric layer material at this location is more dense, and the film quality of the silicon oxide above it is also improved, reducing the defects and voids between the interfaces of the two, and ensuring that the corrosion solution will not penetrate into the release hole during the formation process, and corrode the piezoelectric layer in the protected area. Ensure the integrity of the size and structure of the release hole, and further ensure the mechanical strength of the device.

[0071] The preferred embodiments of the present invention are described in detail above; however, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all belong to the protection scope of the present invention.

Claims

1. A method for optimizing the release hole structure of a bulk acoustic wave resonator filter, characterized in that: The steps include: Step 1, adding an auxiliary release structure: adding an auxiliary release structure on the upper surface and / or lower surface of the release hole position; wherein the lattice mismatch rate between the auxiliary release structure material and the piezoelectric layer material is less than 5%, the auxiliary release structure is annular, and the inner diameter of the auxiliary release structure does not exceed the maximum value of the design diameter of the release hole; the auxiliary release structure does not contact the top electrode or the bottom electrode. Step 2, preparing release holes: using silicon oxide as a hard mask, patterning the release holes at the release hole positions to form vertical release holes. Step 3, preparing a cavity: releasing the sacrificial layer material through the release hole, and forming a cavity below the bottom electrode that is connected to the release hole.

2. The method for optimizing the release hole structure of a BAW resonator filter according to claim 1, characterized in that: In step 1, the radial width of the auxiliary release structure is greater than the minimum deviation dimension of the lithography.

3. The method for optimizing the release hole structure of a BAW resonator filter according to claim 1, characterized in that: In step 1, the auxiliary release structure is an oriented metal made of the same material as the top electrode or the bottom electrode.

4. The method for optimizing the release hole structure of a BAW resonator filter according to claim 3, characterized in that: When the auxiliary release structure is disposed on the upper surface of the release hole, the thickness of the auxiliary release structure is not less than the thickness of the top electrode. When the auxiliary release structure is disposed on the lower surface of the release hole, the thickness of the auxiliary release structure does not exceed the thickness of the bottom electrode.

5. The method for optimizing the release hole structure of a BAW resonator filter according to claim 4, characterized in that: In step 1, when the auxiliary release structure is disposed on the upper surface of the release hole position, the thickness of the auxiliary release structure is equal to the thickness of the top electrode. When the auxiliary release structure is disposed on the lower surface of the release hole position, the thickness of the auxiliary release structure is equal to the thickness of the bottom electrode.

6. The method for optimizing the release hole structure of a BAW resonator filter according to claim 3, characterized in that: Auxiliary release structures are added to the upper and lower surfaces of the release hole position; the thickness of the auxiliary release structure located on the upper surface of the release hole position is not less than the thickness of the top electrode; the thickness of the auxiliary release structure located on the lower surface of the release hole position does not exceed the thickness of the bottom electrode.

7. The method for optimizing the release hole structure of a BAW resonator filter according to claim 3, characterized in that: The materials of the top electrode and the bottom electrode are a composite or alloy of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium and chromium.

8. The method for optimizing the release hole structure of a BAW resonator filter according to claim 7, characterized in that: The material of the auxiliary release structure is Mo.

9. The method for optimizing the release hole structure of a BAW resonator filter according to claim 1, characterized in that: In step 1, the longitudinal cross-section of the auxiliary release structure is a rectangle or an isosceles trapezoid.

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