Method for manufacturing a MEMS device and MEMS device

Abstract

This invention provides a method for manufacturing MEMS devices by forming wafer-level packages using APCVD. [Solution] A method for manufacturing a MEMS device includes the steps of: fabricating a MEMS structure on the surface of a substrate; forming a first trench and a narrower second trench on the surface of the substrate; etching the substrate through the first and second trenches to form a recess and holding the MEMS structure on the recess; depositing a sacrificial layer on the surface of the substrate; etching the sacrificial layer to expose the surface of the substrate and form a sealing region surrounding the MEMS structure; depositing a silicon layer that covers the sacrificial layer and connects to the substrate in the sealing region; forming an opening in the silicon layer to expose the sacrificial layer above the second trench; removing the sacrificial layer through the second trench to form a cavity; and closing the second trench by performing heat treatment in a hydrogen-containing atmosphere.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a MEMS device and a MEMS device, and particularly to a method for manufacturing a MEMS device with wafer-level packaging of a MEMS device and a MEMS device.

Background Art

[0002] Some types of MEMS devices, such as IR bolometers and electrostatic resonators, require a vacuum environment for operation. In recent years, as a wafer-level packaging method for MEMS devices, an epi-seal process has been proposed in which a polysilicon layer is epitaxially grown in a high vacuum to vacuum-seal a MEMS structure.

[0003] In the epi-seal process, a thick polysilicon layer is formed on a substrate on which a MEMS structure is formed in a high vacuum to vacuum-seal the MEMS structure on the substrate. For forming the polysilicon layer, a reduced-pressure CVD process using an RPCVD (Reduced Pressure Chemical Vapor Deposition) apparatus is used.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] [Summary] In the epi-seal process, there is a problem that the productivity is low because the film formation rate in the reduced-pressure CVD process is slow. In addition, there is also a problem that the reduced-pressure CVD process requires an expensive RPCVD apparatus that can withstand high-temperature processes.

[0006] Therefore, this disclosure aims to provide a method for manufacturing MEMS devices using wafer-level packaging that utilizes APCVD (Atmospheric Pressure CVD) equipment instead of RPCVD equipment, and to provide MEMS devices.

[0007] One form of this disclosure is, A method for manufacturing a MEMS device, A step of preparing a substrate having a front surface and a back surface, The process of fabricating a MEMS structure on the surface of the substrate, A step of forming a first trench and a second trench having a smaller cross-sectional area of ​​opening than the first trench on the surface of the substrate, A recess formation step involves etching the substrate through a first trench and a second trench to form recesses within the substrate and holding the MEMS structure on top of the recesses, A process of depositing a sacrificial layer on the surface of the substrate, A process of etching the sacrificial layer to expose the substrate surface and create a sealing region surrounding the MEMS structure, A silicon layer deposition process in which a silicon layer is deposited to cover the sacrificial layer and connect to the surface of the substrate in the sealing region, A step of forming an opening in the silicon layer to expose the sacrificial layer above the second trench, The process involves supplying etchant through a second trench, removing the sacrificial layer, and forming a cavity. A method for manufacturing a MEMS device, comprising a sealing step of closing a second trench by performing heat treatment in a hydrogen-containing atmosphere to form a wafer-level packaging structure in which the MEMS structure is sealed in a cavity formed from the recess and the cavity.

[0008] Other forms of this disclosure include: A substrate having a front surface and a back surface, A MEMS structure supported in a hollow manner on a recess provided on the surface of the substrate, The MEMS structure includes a silicon layer deposited on the surface of the substrate such that the top of the MEMS structure forms a cavity, A MEMS device in which a MEMS structure is wafer-level packaged in a cavity formed from recesses and cavities, This MEMS device has a substrate thickness below the opening in the silicon layer that is thinner than the total thickness from the front to the back of the substrate. [Brief explanation of the drawing]

[0009] [Figure 1] This is a plan view of the MEMS device according to the present invention. [Figure 2] This is a cross-sectional view showing the steps of the manufacturing method for a MEMS device according to the present invention. [Figure 3] This is a cross-sectional view showing the steps of the manufacturing method for a MEMS device according to the present invention. [Figure 4] This is a cross-sectional view showing the steps of the manufacturing method for a MEMS device according to the present invention. [Figure 5] This is a cross-sectional view showing the steps of the manufacturing method for a MEMS device according to the present invention. [Figure 6] This is a cross-sectional view showing the steps of the manufacturing method for a MEMS device according to the present invention.

[0010] [Detailed explanation] Figure 1 is a plan view of an embodiment of the MEMS device according to the present invention, where the entire device is represented as 100. The silicon layer that vacuum-seals the MEMS structure is not shown so that the MEMS structure is visible.

[0011] The MEMS device 100 has a substrate 10 made of, for example, silicon. A recess 40 is provided on the surface of the substrate 10, and a MEMS structure consisting of a movable electrode 50 and a fixed electrode 60 is arranged opposite each other on the recess 40 via a groove 55. The movable electrode 50 and the fixed electrode 60 are connected to the substrate 10 in an insulated state by an isolation joint (IJ) 15.

[0012] On the surface of the substrate 10, a first trench 20 and a second trench 30 for forming the recess 40 are provided (the second trench 30 is finally closed). The second trench 30 has a smaller cross-sectional area in the XY plane of the opening than the first trench 20.

[0013] An insulating layer 17 made of, for example, silicon oxide is provided at the peripheral and central portions of the substrate 10. Further, the insulating layer 17 has regions along the periphery and the central region removed so that the surface of the substrate 10 is exposed, and a silicon layer for vacuum-sealing the MEMS structure is connected to this portion.

[0014] A wiring layer 19 is provided across IJ15 on the movable electrode 50 and the fixed electrode 60 and is electrically connected to, for example, a pad electrode (not shown).

[0015] In the MEMS device 100, a silicon layer (80 in FIG. 4) is formed so as to be connected around the substrate 10, and the MEMS structure including the movable electrode 50 and the fixed electrode 60 inside is vacuum-sealed.

[0016] Next, a method for manufacturing the MEMS device 100 according to an embodiment of the present invention will be described. FIGS. 2 to 6 are cross-sectional views of steps showing the manufacturing method of the MEMS device 100. FIGS. 2 to 6 are cross-sectional views when FIG. 1 is viewed in the II-II direction, but there are also portions that do not correspond to FIG. 1.

[0017] The manufacturing method of the MEMS device 100 according to an embodiment of the present invention includes the following steps 1 to 7.

[0018] Step 1: As shown in FIG. 2, a substrate 10 made of, for example, silicon and having a front surface and a back surface is prepared. Next, a trench is formed at a predetermined position on the surface of the substrate 10, and an isolation joint (IJ) 15 made of, for example, silicon oxide is formed by oxidizing the inside. Further, an insulating layer 17 made of, for example, silicon oxide is formed so as to cover the peripheral and central portions of the surface of the substrate 10, and a wiring layer 19 made of, for example, copper is formed thereon.

[0019] Next, a resist mask (not shown) is formed on the surface of the substrate 10, and anisotropic etching is performed using RIE with a mixed gas of SF6 and C4F8, for example, to form a first trench 20 and a second trench 30. The first trench 20 has a relatively wide opening, while the second trench 30 has an opening with a smaller cross-sectional area in the XY plane than the first trench 20. In Figure 2, the width of the opening of the first trench 20 is 1 to 3 μm, and the width of the opening of the second trench 30 is 0.5 to 0.7 μm. In particular, the second trench 30 consists of multiple square trenches, each with a side length of 0.5 to 0.7 μm in the XY plane. Furthermore, the second trench 30 is shallower than the first trench 20, with the depth of the first trench being 10 to 30 μm and the depth of the second trench 30 being 5 to 15 μm.

[0020] Next, the sidewalls of the first trench 20 and the second trench 30 are covered with a silicon oxide layer (not shown), and then the substrate 10 is etched by plasma isotropic etching using SF6 gas or XeF2 gas through the first trench 20 and the second trench 30. As a result, the substrate 10 is etched below the first trench 20 and the second trench 30, forming recesses 40, and a MEMS structure is formed that is raised from the substrate 10. In Figures 1 and 2, the left side is the movable electrode 50 and the right side is the fixed electrode 60, with a groove 55 formed between them. In Figure 2, the Z-direction position of the recesses 40 is different below the first trench 20 and below the second trench 30, but they form a continuous recess 40.

[0021] Step 2: As shown in Figure 3, a sacrificial layer 70 made of, for example, TEOS (tetra ethoxy silane) is formed on the surface of the substrate 10 by CVD. The sacrificial layer 70 is also deposited inside the first trench 20 and the second trench 30. Subsequently, the sacrificial layer 70 is etched using a resist mask (not shown) to form openings 75 and expose the surface of the substrate 10 (see also Figure 1). The openings 75 are formed along the periphery of the substrate 10 so as to surround the MEMS structure consisting of the movable electrode 50 and the fixed electrode 60. In the areas where the insulating layer 17 and the wiring layer 19 are formed, the surface of the substrate 10 is not exposed.

[0022] Step 3: As shown in Figure 4, a silicon layer 80 made of, for example, polycrystalline silicon is deposited over the entire surface using APCVD (Atmospheric Pressure CVD). Subsequently, the silicon layer 80 is etched using a resist mask (not shown) to form an opening 85 so that the sacrificial layer 70 above the second trench 30 is exposed.

[0023] Step 4: As shown in Figure 5, the sacrificial layer 70 is selectively removed using gaseous hydrogen fluoride as an etchant through the opening 85. Since the first trench 20 and the second trench 30 are connected via the recess 40, the sacrificial layer 70 is completely removed inside the opening 75 that is formed to surround the MEMS structure. As a result, a cavity 25 is also formed on the substrate 10, connected to the recess 40 by the first trench 20.

[0024] Step 5: For example, 10-10 -2 The substrate 10 is annealed in a Torr hydrogen atmosphere at 1000-1200°C, preferably 1100°C, for 20-30 minutes. This annealing causes the silicon constituting the substrate 10 to migrate, sealing the second trench 30 as shown in Figure 6. As a result, the recess 40 and the cavity 25 form a cavity, which is sealed between the substrate 10 and the silicon layer 80 in the hydrogen atmosphere.

[0025] Through the above process, the MEMS structure formed on the surface of the substrate 10 is sealed within the recess 40 and cavity 25 formed between the substrate 10 and the silicon layer 80, thereby enabling the fabrication of a wafer-level packaged MEMS device 100. The recess 40 and cavity 25 are in a hydrogen atmosphere.

[0026] If necessary, for example, a pad electrode (not shown) may be formed on the silicon layer 80 and electrically connected to the wiring layer 19. For the connection between the pad electrode and the wiring layer 19, for example, a portion of the silicon layer 80 that has been insulated by surrounding it with a trench may be used.

[0027] Furthermore, by annealing the substrate 10, a vacuum can be created inside the cavity formed by the recesses 40 and the void 25. For example, by heating the substrate 10 to several hundred to 1000°C in air, the hydrogen sealed in the recesses 40 and the void 25 moves to the outside through the silicon layer 80 and the substrate 10, creating a vacuum inside.

[0028] In the MEMS device 100 fabricated by the above process, the thickness of the substrate 10 (distance in the Z-axis direction from the front to the back surface) is thinner below the opening 85 than the thickness of the substrate prepared in step 1. More specifically, it is thinner than the thickness below the insulating layer 17, for example. This is because in the migration process of step 5, the substrate material moves and fills the second trench 30.

[0029] Alternatively, for example, the opening 85 may be filled with a silicon layer 90 using the APCVD method.

[0030] Thus, the manufacturing method for MEMS devices according to the embodiment of the present invention enables wafer-level packaging using the general-purpose APCVD (atmospheric pressure CVD), which has a high film deposition rate, without using RPCVD (reduced pressure CVD) as in the conventional episeal process. Therefore, compared to the manufacturing method of MEMS devices using the conventional episeal process, higher productivity and cost reduction are possible.

[0031] In particular, since it eliminates the need to use expensive RPCVD, it becomes possible to fabricate MEMS devices 100 using standard ASIC wafer manufacturing processes.

[0032] In the embodiment of the present invention, a silicon substrate was used as the substrate 10, but an SOI (Silicon On Insulator) substrate may also be used. When the oxide layer of the SOI substrate is used as an etching stopper in the process of forming the recess 40 by etching, the distance in the Z-axis direction from the surface of the substrate to the bottom surface of the recess 40 is equal at the bottom of the first trench 20 and the bottom of the second trench.

[0033] <Note> This disclosure is, A method for manufacturing a MEMS device, A step of preparing a substrate having a front surface and a back surface, The process of fabricating a MEMS structure on the surface of the substrate, A step of forming a first trench and a second trench having a smaller cross-sectional area of ​​opening than the first trench on the surface of the substrate, A recess formation step involves etching the substrate through a first trench and a second trench to form recesses within the substrate and holding the MEMS structure on top of the recesses, A process of depositing a sacrificial layer on the surface of the substrate, A process of etching the sacrificial layer to expose the substrate surface and create a sealing region surrounding the MEMS structure, A silicon layer deposition process in which a silicon layer is deposited to cover the sacrificial layer and connect to the surface of the substrate in the sealing region, A step of forming an opening in the silicon layer to expose the sacrificial layer above the second trench, The process involves supplying etchant through a second trench, removing the sacrificial layer, and forming a cavity. A method for manufacturing a MEMS device, comprising a sealing step of closing a second trench by performing heat treatment in a hydrogen-containing atmosphere to form a wafer-level packaging structure in which the MEMS structure is sealed in a cavity formed from the recess and the cavity. This manufacturing method allows for wafer-level packaging using the fast-deposition, general-purpose APCVD (atmospheric pressure CVD) without the need for RPCVD (reduced pressure CVD) as in conventional episeal processes, resulting in high productivity and cost reduction. In particular, since it eliminates the need for expensive RPCVD, it becomes possible to fabricate MEMS devices using standard ASIC wafer manufacturing processes.

[0034] This disclosure may include a dehydrogenation step by heating after the sealing step. This step allows the MEMS structure to be vacuum sealed.

[0035] In this disclosure, the recess formation step may include a step of covering the side walls of the first trench and the second trench with an oxide film, and a step of isotropically etching the substrate below the first trench and the second trench using an etchant.

[0036] In this disclosure, the second trench preferably has a square opening on the surface of the substrate with sides of 0.5 to 0.7 μm. This is to ensure that the second trench is properly closed by migration.

[0037] In this disclosure, the silicon layer deposition process is a process of depositing a silicon layer using the APCVD method. This eliminates the need to use expensive RPCVD, thereby reducing manufacturing costs and enabling the application of general-purpose manufacturing processes.

[0038] In this disclosure, the etchant is preferably gaseous hydrofluoric acid, because it can effectively remove the sacrificial layer through the second trench.

[0039] In this disclosure, the sealing process is a process of migrating the substrate material by annealing. By using migration, a vacuum or hydrogen sealing structure can be easily fabricated.

[0040] This disclosure may further include a step of depositing an additional silicon layer on top of the silicon layer by APCVD to fill the openings, in order to improve the durability of the MEMS device.

[0041] This disclosure is, A substrate having a front surface and a back surface, A MEMS structure supported in a hollow manner on a recess provided on the surface of the substrate, The MEMS structure includes a silicon layer deposited on the surface of the substrate such that the top of the MEMS structure forms a cavity, A MEMS device in which a MEMS structure is wafer-level packaged in a cavity formed from recesses and cavities, This MEMS device has a substrate thickness below the opening in the silicon layer that is thinner than the total thickness of the substrate from the front to the back surface. The substrate thickness below the opening in the silicon layer is reduced because the second trench is sealed by migration.

[0042] In this disclosure, the recess may include at least two portions with different depths from the surface of the substrate. The difference in the openings of the first trench and the second trench results in different depths of the recesses formed beneath them.

[0043] In this disclosure, the MEMS structure may include movable and fixed electrodes connected to a substrate via IJ and held hollow within a cavity.

[0044] In this disclosure, the cavity may be in a hydrogen atmosphere or a vacuum, in order to maintain an inert atmosphere for the MEMS structure. [Industrial applicability]

[0045] The manufacturing method for MEMS devices according to the present invention can be applied to wafer-level packaging of resonators, filters, temperature sensors, pressure sensors, mass sensors, and the like. [Explanation of symbols]

[0046] 10 circuit boards 15. Isolation Joint (IJ) 17. Insulating layer 19 Wiring layer 20 The first trench 30 The second trench 40 recess 50 movable electrodes 55 Groove 60 Fixed electrode 70 layers of victims 75 Opening 80 silicon layer 85 Opening 90 Silicon Layers 100 MEMS devices

Claims

1. A method for manufacturing a MEMS device, A step of preparing a substrate having a front surface and a back surface, A step of creating a MEMS structure on the surface of the substrate, The process involves forming a first trench and a second trench having a smaller cross-sectional area of ​​opening than the first trench on the surface of the substrate. A recess formation step is performed by etching the substrate through the first trench and the second trench to form a recess in the substrate and holding the MEMS structure on the recess, A step of depositing a sacrificial layer on the surface of the substrate, A step of etching the sacrificial layer to expose the surface of the substrate and forming a sealing region surrounding the MEMS structure, A silicon layer deposition step in which a silicon layer is deposited to cover the sacrificial layer and to connect to the surface of the substrate in the sealing region, A step of forming an opening in the silicon layer to expose the sacrificial layer above the second trench, The process involves supplying etchant through the second trench and removing the sacrificial layer to form a cavity, A method for manufacturing a MEMS device, comprising a sealing step of closing the second trench by performing heat treatment in a hydrogen-containing atmosphere to form a wafer-level packaging structure in which the MEMS structure is sealed in a cavity formed from the recess and the cavity.

2. The manufacturing method according to claim 1, further comprising a dehydrogenation step by heating after the sealing step.

3. The recess formation step is, A step of covering the side walls of the first trench and the second trench with an oxide film, The method according to claim 1, comprising the step of isotropically etching the substrate below the first trench and the second trench using an etchant.

4. The method according to claim 1, wherein the second trench has a square opening on the surface of the substrate with sides of 0.5 to 0.7 μm.

5. The method according to claim 1, wherein the silicon layer deposition step is a step of depositing a silicon layer by the APCVD method.

6. The method according to claim 1, wherein the etchant is gaseous hydrofluoric acid.

7. The method according to claim 1, wherein the sealing step is a step of migrating the material of the substrate by annealing.

8. The method according to claim 1, further comprising the step of depositing a silicon layer on the silicon layer by APCVD so as to fill the opening.

9. A substrate having a front surface and a back surface, A MEMS structure supported in a hollow manner on a recess provided on the surface of the substrate, The above MEMS structure includes a silicon layer deposited on the surface of the substrate such that the above portion forms a cavity, A MEMS device in which the MEMS structure is wafer-level packaged in a cavity formed from the recess and the cavity, A MEMS device in which the thickness of the substrate below the opening provided in the silicon layer is thinner than the thickness of the substrate from the front surface to the back surface.

10. The MEMS device according to claim 9, wherein the recess comprises at least two portions with different depths from the surface of the substrate.

11. The MEMS device according to claim 9, wherein the MEMS structure includes a movable electrode and a fixed electrode connected to the substrate via an isolation joint and held hollow within the cavity.

12. The MEMS device according to claim 9, wherein the cavity is in a hydrogen atmosphere or a vacuum.

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