A method for preparing a sacrificial layer of a MEMS switch based on Damascus process

Abstract

The present invention relates to a method for preparing a sacrificial layer of a MEMS switch based on a Damascus process, comprising the steps of: S1, obtaining a wafer; S2, depositing a sacrificial layer on the surface of the wafer, wherein the material of the sacrificial layer comprises a semiconductor material; S3, etching the sacrificial layer to form a through hole on a coplanar waveguide; S4, electroplating an anchor material in the through hole to form an initial anchor; S5, polishing the sacrificial layer and the initial anchor to form a target anchor, wherein the surface of the target anchor is flush with the surface of the sacrificial layer; S6, electroplating an upper electrode on the surface of the sacrificial layer so that the upper electrode contacts the target anchor; S7, releasing the sacrificial layer to form a cantilever beam of a MEMS switch. The preparation method introduces the Damascus process into the preparation process of the sacrificial layer, effectively improves the flatness of the MEMS sacrificial layer, improves the stability of the sacrificial layer, reduces the release time of the sacrificial layer, improves the production efficiency, and is suitable for mass production of MEMS switches.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor device preparation, and in particular relates to a method for preparing a sacrificial layer of a MEMS switch based on a Damascus process. Background Art

[0002] MEMS switches are small in size, highly integrated, and have good performance. They can be integrated with shifters, filters, attenuators, etc. to form intelligent, multifunctional, and reconfigurable MEMS devices, which are used in aerospace, test instruments, communications, and other fields. The sacrificial layer is the key to the preparation of the cantilever beam of the MEMS switch. The flatness and thickness of the sacrificial layer will determine the insertion loss, isolation, and life of the MEMS switch. Therefore, the preparation of the sacrificial layer is a key technology in the MEMS switch process.

[0003] At present, sacrificial layers are generally prepared using photoresists, polyimide (PI), etc. Among them, photoresists are easily soluble in organic solvents such as acetone, which is not conducive to the cleaning process in the subsequent cantilever beam preparation process, and photoresists are less stable than sacrificial layers of other materials; the cured polyimide sacrificial layer is stable and does not react with acid or alkali, but the polyimide sacrificial layer uses a dry release process, and the release cycle is relatively long. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, the present invention provides a method for preparing a sacrificial layer of a MEMS switch based on a Damascus process. The technical problem to be solved by the present invention is achieved by the following technical solutions:

[0005] An embodiment of the present invention provides a method for preparing a sacrificial layer of a MEMS switch based on a Damascus process, comprising the steps of:

[0006] S1. Obtain a wafer, wherein a coplanar waveguide of a MEMS switch is prepared on the surface of the wafer;

[0007] S2, depositing a sacrificial layer on the surface of the wafer, wherein the material of the sacrificial layer includes a semiconductor material;

[0008] S3, etching the sacrificial layer to form a through hole on the coplanar waveguide;

[0009] S4, electroplating an anchor material in the through hole to form an initial anchor;

[0010] S5, polishing the sacrificial layer and the initial anchor point to form a target anchor point, wherein the surface of the target anchor point is flush with the surface of the sacrificial layer;

[0011] S6, electroplating an upper electrode on the surface of the sacrificial layer so that the upper electrode contacts the target anchor point;

[0012] S7, releasing the sacrificial layer to form a cantilever beam of the MEMS switch.

[0013] In one embodiment of the present invention, the semiconductor material includes one or more of silicon dioxide, amorphous silicon, and silicon nitride.

[0014] In one embodiment of the present invention, the thickness of the sacrificial layer is greater than the thickness of the target anchor point.

[0015] In one embodiment of the present invention, step S3 includes:

[0016] S31, performing through-hole patterning processing on the surface of the sacrificial layer to form a through-hole pattern area;

[0017] S32, etching the sacrificial layer in the through hole pattern area to form the through hole.

[0018] In one embodiment of the present invention, step S4 includes:

[0019] S41, preparing a first seed layer on the surface of the through hole and the sacrificial layer;

[0020] S42, performing anchor point patterning processing on the surface of the first seed layer to expose the through hole and form an anchor point pattern area;

[0021] S43, performing electrochemical deposition in the anchor point pattern area and removing the first seed layer to form the initial anchor point.

[0022] In one embodiment of the present invention, the thickness of the initial anchor point is equal to the thickness of the through hole.

[0023] In one embodiment of the present invention, step S5 includes:

[0024] The sacrificial layer is polished by using a polishing machine and silicon polishing liquid.

[0025] In one embodiment of the present invention, the precision of the polishing process is less than 100 nm, and the thickness of the sacrificial layer after the polishing process is equal to the thickness of the target anchor point.

[0026] In one embodiment of the present invention, step S6 includes:

[0027] S61, preparing a second seed layer on the surface of the sacrificial layer;

[0028] S62, performing upper electrode patterning processing on the surface of the second seed layer to form an upper electrode pattern area, wherein the upper electrode pattern area exposes the anchor point;

[0029] S63, performing electrochemical deposition on the upper electrode pattern region and removing the second seed layer to form the upper electrode.

[0030] In one embodiment of the present invention, step S7 includes:

[0031] The sacrificial layer is released by hydrofluoric acid gas using a hydrogen fluoride etcher to form the cantilever beam.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The preparation method of the present invention introduces the Damascus process into the preparation process of the sacrificial layer, adopts semiconductor material as the sacrificial layer material, effectively improves the flatness of the MEMS sacrificial layer, improves the stability of the sacrificial layer, reduces the release time of the sacrificial layer, and improves the production efficiency. The prepared sacrificial layer has simple process, high flatness, easy release, and high reliability, and is suitable for mass production of MEMS switches. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic flow chart of a method for preparing a sacrificial layer of a MEMS switch based on a Damascus process provided in an embodiment of the present invention;

[0035] Figure 2a-2g A schematic diagram of a process of preparing a sacrificial layer of a MEMS switch based on a Damascus process provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0037] Embodiment 1

[0038] See also Figure 1 and Figure 2a-2g , Figure 1 A schematic diagram of a process for preparing a sacrificial layer of a MEMS switch based on a Damascus process provided by an embodiment of the present invention, Figure 2a-2g A schematic diagram of a method for preparing a sacrificial layer of a MEMS switch based on a Damascus process provided in an embodiment of the present invention. The preparation method comprises the following steps:

[0039] S1. Obtain a wafer 10, wherein the wafer 10 includes a substrate 11 and a coplanar waveguide 12 located on the substrate 11, see Figure 2a .

[0040] Specifically, the wafer 10 may include a substrate 11 and a coplanar waveguide 12 located on the substrate.

[0041] Furthermore, the wafer 10 includes a substrate 11 and structures such as MEMS switch contacts 13, drive electrodes 14, isolation layers 15, and coplanar waveguides 12 (CPW) prepared on the surface of the substrate 11, wherein the relative positions of the MEMS switch contacts 13, drive electrodes 14, isolation layers 15, and coplanar waveguides 12 (CPW) refer to the structure of the MEMS switch in the prior art. Specifically, the material of the substrate 11 includes but is not limited to Si, the material of the MEMS switch contacts 13 includes but is not limited to SiN, the material of the drive electrodes 14 includes but is not limited to Au, Pt, etc., and the material of the isolation layer 15 includes but is not limited to SiN x The materials of CPW12 include but are not limited to Au, Pt, etc.

[0042] S2. Depositing a sacrificial layer 20 on the surface of the wafer 10. The material of the sacrificial layer 20 includes a semiconductor material. Figure 2b .

[0043] Specifically, the sacrificial layer 20 can be deposited by pulsed laser deposition (PLD), molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD) or plasma enhanced chemical vapor deposition (PECVD). The material of the sacrificial layer 20 includes semiconductor materials; wherein the semiconductor material includes one or more of silicon dioxide, amorphous silicon, and silicon nitride. The thickness of the deposited sacrificial layer 20 needs to be greater than the thickness of the target anchor point in the final MEMS switch.

[0044] In a specific embodiment, SiO2 is deposited on the surface of the wafer using a PECVD process, and the thickness of the target anchor point in the MEMS switch is 3 μm, so the thickness of the deposited SiO2 is greater than 3 μm.

[0045] S3, etching the sacrificial layer 20, forming a through hole 30 on the coplanar waveguide, see Figure 2c . Specifically including the steps:

[0046] S31 , performing through-hole patterning processing on the surface of the sacrificial layer 20 to form a through-hole pattern area.

[0047] First, a photoresist is spin-coated on the surface of the sacrificial layer 20; then the device is dried to remove moisture in the photoresist and improve the adhesion of the photoresist; the photoresist is then exposed and developed; finally, the device is dried again to remove water stains, improve the adhesion of the photoresist, and form a through-hole pattern area, which exposes the surface of the sacrificial layer 20.

[0048] S32 , etching the sacrificial layer 20 in the through hole pattern area to form a through hole 30 .

[0049] Specifically, a magnetic neutral loop discharge (NLD) plasma etching process can be used to etch the sacrificial layer 20 in the through hole pattern area, and then the photoresist outside the through hole pattern area is removed to form a through hole 30 in the sacrificial layer, and the through hole 30 is connected to the coplanar waveguide 12.

[0050] S4, electroplating anchor material in the through hole 30 to form an initial anchor 40, see Figure 2d . Specifically include the steps:

[0051] S41 , preparing a first seed layer in the through hole 30 and on the surface of the sacrificial layer 20 .

[0052] Specifically, a layer of metal is grown on the surface of the device, i.e., in the through hole 30 and on the surface of the sacrificial layer 20, to form a first seed layer located on the surface of the coplanar waveguide 12 and the surface of the sacrificial layer 20 in the through hole 30; the thickness of the first seed layer is relatively thin and fills the bottom of the through hole 30; the material of the first seed layer includes but is not limited to Ti\Au, Cr\Au, etc.

[0053] S42, performing anchor point patterning processing on the surface of the first seed layer to expose the through hole 30 and form an anchor point pattern area.

[0054] First, spin-coat photoresist on the surface of the first seed layer; then dry the device to remove moisture from the photoresist and improve the adhesion of the photoresist; then expose and develop the photoresist; finally, dry the device again to remove water stains, improve the adhesion of the photoresist, and form an anchor graphic area, which exposes the through hole again.

[0055] S43 , performing electrochemical deposition in the anchor point pattern region and removing the first seed layer to form an initial anchor point 40 .

[0056] First, an anchor material is electrochemically deposited on the surface of the device to fill the through hole 30; then, the photoresist on the surface of the first seed layer outside the through hole 30 is removed, so that the anchor material on the photoresist is also removed; finally, the first seed layer outside the through hole is removed to form an initial anchor 40. The anchor material includes but is not limited to gold.

[0057] Specifically, the initial anchor 40 is formed by the first seed layer and the anchor material on the first seed layer, and the thickness thereof is equal to the thickness of the through hole 30 .

[0058] In a specific embodiment, the thickness of the sacrificial layer SiO2 is greater than 3 μm. Therefore, the depth of the formed through hole 30 is greater than 3 μm, and the thickness of the initial anchor point 40 is also greater than 3 μm.

[0059] S5, polishing the sacrificial layer 20 and the initial anchor point 40 to form a target anchor point 50, the surface of the target anchor point 50 is flush with the surface of the sacrificial layer 20, see Figure 2e .

[0060] Specifically, the sacrificial layer 20 is polished by using a polishing machine and silicon polishing liquid to form the sacrificial layer 20 with high surface flatness and the target anchor point 50, wherein the target anchor point 50 is formed by the first seed layer and the anchor point material.

[0061] Specifically, the precision of the polishing process is less than 100 nm, and the thickness of the sacrificial layer 20 after the polishing process is equal to the thickness of the target anchor point 50 in the MEMS switch.

[0062] In a specific embodiment, the thickness of the sacrificial layer SiO2 is 5μm, the thickness of the initial anchor point 40 is 5μm (for example, it can be formed by a 1μm first seed layer and a 4μm anchor material). After polishing, the thickness of the sacrificial layer SiO2 is 3μm, and the target anchor point 50 is formed by a 1μm first seed layer and a 2μm anchor material, and its thickness is 3μm.

[0063] S6. Electroplating the upper electrode 60 on the surface of the sacrificial layer 20 makes the upper electrode 60 contact the target anchor point 50. Figure 2f . Specifically including the steps:

[0064] S61 , preparing a second seed layer on the surface of the sacrificial layer 20 .

[0065] Specifically, a layer of metal is grown on the surface of the device, that is, the surface of the target anchor point 50 and the sacrificial layer 20 to form a second seed layer; the material of the second seed layer includes but is not limited to Ti\Au, Cr\Au, etc.

[0066] S62 , performing upper electrode patterning processing on the surface of the seed layer to form an upper electrode pattern area, wherein the upper electrode pattern area exposes the target anchor point 50 .

[0067] First, photoresist is spin-coated on the surface of the second seed layer; then the device is dried to remove moisture in the photoresist and improve the adhesion of the photoresist; the photoresist is then exposed and developed; finally, the device is dried again to remove water stains, improve the adhesion of the photoresist, and form an upper electrode pattern area.

[0068] S63 , performing electrochemical deposition on the upper electrode pattern region and removing the second seed layer to form an upper electrode 60 .

[0069] First, an anchor material is electrochemically deposited on the device surface; then, the photoresist outside the upper electrode pattern area is removed, thereby removing the upper electrode material on the photoresist; finally, the second seed layer outside the upper electrode pattern area is removed to form an upper electrode 60.

[0070] Specifically, the material of the upper electrode 60 includes but is not limited to gold, and its thickness is 2 μm.

[0071] S7, release the sacrificial layer 20, and form the cantilever beam 70 of the MEMS switch, see Figure 2g .

[0072] Specifically, a hydrogen fluoride etcher is used to release the sacrificial layer through hydrofluoric acid gas to form a cantilever beam 70 . The cantilever beam 70 is formed by connecting the target anchor point 50 and the upper electrode 60 .

[0073] The preparation method of this embodiment introduces the Damascus process into the preparation process of the sacrificial layer, and uses semiconductor materials as the sacrificial layer material, which effectively improves the flatness of the MEMS sacrificial layer, improves the stability of the sacrificial layer, reduces the release time of the sacrificial layer, and improves production efficiency. The prepared sacrificial layer has simple process, high flatness, easy release, and high reliability, and is suitable for mass production of MEMS switches.

[0074] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A method for preparing a sacrificial layer of a MEMS switch based on a Damascus process, characterized in that: Includes steps: S1. Obtain a wafer, wherein a coplanar waveguide of a MEMS switch is prepared on the surface of the wafer; S2, depositing a sacrificial layer on the surface of the wafer, wherein the material of the sacrificial layer comprises a semiconductor material, and the semiconductor material comprises one or more of silicon dioxide, amorphous silicon, and silicon nitride; S3, etching the sacrificial layer to form a through hole on the coplanar waveguide comprises: S31, performing through-hole patterning processing on the surface of the sacrificial layer to form a through-hole pattern area; S32, etching the sacrificial layer in the through hole pattern area to form the through hole; S4, electroplating an anchor material in the through hole to form an initial anchor, including: S41, preparing a first seed layer on the surface of the through hole and the sacrificial layer; S42, performing anchor point patterning processing on the surface of the first seed layer to expose the through hole and form an anchor point pattern area; S43, performing electrochemical deposition in the anchor point pattern area and removing the first seed layer to form the initial anchor point; S5, polishing the sacrificial layer and the initial anchor point using a polishing machine and silicon polishing liquid to form a target anchor point, wherein the surface of the target anchor point is flush with the surface of the sacrificial layer; S6, electroplating an upper electrode on the surface of the sacrificial layer so that the upper electrode contacts the target anchor point, including: S61, preparing a second seed layer on the surface of the sacrificial layer; S62, performing upper electrode patterning processing on the surface of the second seed layer to form an upper electrode pattern area, wherein the upper electrode pattern area exposes the anchor point; S63, performing electrochemical deposition on the upper electrode pattern region and removing the second seed layer to form the upper electrode; S7. Using a hydrogen fluoride etcher, the sacrificial layer is released by hydrofluoric acid gas to form a cantilever beam of the MEMS switch.

2. The method for preparing a MEMS switch sacrificial layer based on the Damascus process according to claim 1, characterized in that: The thickness of the sacrificial layer is greater than the thickness of the target anchor point.

3. The method for preparing a MEMS switch sacrificial layer based on Damascus process according to claim 1, characterized in that: The thickness of the initial anchor point is equal to the thickness of the through hole.

4. The method for preparing a MEMS switch sacrificial layer based on Damascus process according to claim 1, characterized in that: The precision of the polishing process is less than 100 nm, and the thickness of the sacrificial layer after the polishing process is equal to the thickness of the target anchor point.

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