A method for manufacturing a MEMS sensor

Abstract

This invention provides a method for fabricating a MEMS sensor, comprising: depositing an isolation layer on a silicon wafer; fabricating protrusions and etching leads on the isolation layer using polysilicon as a sacrificial layer; depositing a low-stress silicon nitride layer on the silicon wafer with the sacrificial layer as a structural layer and a sensitive film; etching out etching release holes; allowing XeF2 gas to pass through the etching release holes to etch the sacrificial layer, stopping the etching when the color of all protrusions changes; cleaning and drying the silicon wafer; and depositing a silicon nitride-silicon dioxide-silicon nitride multilayer material at the etching release holes to obtain a sealing layer to seal the etching release holes. The method of this invention uses polysilicon as a sacrificial layer and XeF2 to etch the sacrificial layer, resulting in a faster and easier-to-control etching rate, and avoids device damage due to etching of the sensor structural layer or other parts, thus improving the device yield.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device technology, and in particular to a method for fabricating a MEMS sensor. Background Technology

[0002] MEMS (Micro Electro Mechanical Systems) are miniature integrated systems that utilize integrated circuit manufacturing and microfabrication technologies to fabricate microstructures, microsensors, microactuators, control processing circuits, and even interfaces, communication, and power supplies onto one or more chips. MEMS fabrication processes include bulk silicon microfabrication, surface silicon microfabrication, and special microfabrication techniques. Sensors fabricated using MEMS technology are widely used in various fields. When fabricating piezoresistive pressure sensors and piezoresistive accelerometers using surface silicon microfabrication, cavities need to be formed beneath the structural layers. The traditional method uses silicon dioxide or doped silicon dioxide as a sacrificial layer, followed by etching out etched holes, etching with a specific concentration of hydrofluoric acid, and finally sealing the etched holes with doped silicon dioxide. This etching process is lengthy and corrodes the structural layers and other exposed parts of the device. If the etching time is too long, there is a possibility of completely damaging the device, leading to process failure. Furthermore, using only one material to seal the etched holes results in poor hermeticity. This reduces the device yield and is detrimental to reducing production costs and improving manufacturing efficiency.

[0003] Therefore, it is necessary to propose a new manufacturing method to solve the problems existing in the current technology. Summary of the Invention

[0004] The purpose of this invention is to provide a method for fabricating MEMS sensors to improve yield and maintain the stability of device performance for a longer period of time.

[0005] To achieve the above objectives, the present invention provides a method for fabricating a MEMS sensor, comprising:

[0006] S1: Deposit an isolation layer on the silicon wafer;

[0007] S2: Using polysilicon, a boss and an etched lead adjacent to the boss are formed on the isolation layer as a sacrificial layer, thereby obtaining a silicon wafer with a sacrificial layer;

[0008] S3: Deposit a low-stress silicon nitride layer on a silicon wafer with a sacrificial layer as a structural layer and a sensitive film;

[0009] S4: Perform photolithography and etching on the structural layer above the corrosion lead to obtain corrosion release holes;

[0010] S5: Place the silicon wafer in an XeF2 gas atmosphere, allowing the XeF2 gas to etch the sacrificial layer through the etching release holes. At the same time, observe whether the color of the protrusions under the structural layer changes. Stop etching when all the protrusions have changed color. Clean the silicon wafer and dry it.

[0011] S6: Deposit a multilayer material of silicon nitride-silicon dioxide-silicon nitride at the corrosion release hole to obtain a sealing layer to seal the corrosion release hole.

[0012] Step S2 specifically includes:

[0013] S21: Deposit a layer of polysilicon on the isolation layer, and perform photolithography and etching to pattern it and form protrusions;

[0014] S22: Deposit another layer of polysilicon on the isolation layer, and perform photolithography and etching to pattern it and form etched leads.

[0015] Following step S3, step S3' is also included: fabricating a sensitive device on the sensitive membrane that changes based on the deformation of the sensitive membrane.

[0016] The MEMS sensor is a piezoresistive pressure sensor or a piezoresistive accelerometer, and the sensitive device is a piezoresistive resistor; or the MEMS sensor is a resistance temperature detector (RTD) gas sensor or a resistance temperature detector (RTD) humidity sensor, and the sensitive device is a thermistor.

[0017] The sensitive device is a varistor, and step S3' specifically includes:

[0018] S31': Deposit a layer of low-stress polycrystalline silicon on the sensitive film, and perform boron ion implantation annealing, photolithography and etching to pattern it into a varistor;

[0019] S32': Deposit a layer of low-stress silicon nitride as a protective layer for the varistor, and photolithographically and etch the protective layer of the varistor to form the lead hole of the varistor;

[0020] S33': Fabricate the electrode leads of the varistor at the lead hole of the varistor.

[0021] In step S4, there are multiple corrosion release holes, and the multiple corrosion release holes are arranged around the boss.

[0022] In step S6, the sealing layer is obtained, specifically by: depositing silicon nitride, silicon dioxide, and silicon nitride by PECVD to obtain a silicon nitride-silicon dioxide-silicon nitride multilayer material, and performing photolithography and etching to pattern the multilayer material, thereby fabricating the sealing layer. The total thickness of the sealing layer is greater than the depth of the etched release hole.

[0023] The thicknesses of silicon nitride, silicon dioxide, and silicon nitride in the silicon nitride-silicon dioxide-silicon nitride multilayer material are respectively...

[0024] In step S5, before XeF2 gas etches the sacrificial layer through the etching release holes, the area except for the etching release holes is covered with photoresist.

[0025] The silicon wafer is N+ <100> The single-layer silicon wafer has an isolation layer made of low-stress silicon nitride.

[0026] The thickness of the isolation layer is The thickness of the boss is The thickness of the etched lead is And the thickness of the structural layer is

[0027] The MEMS sensor fabrication method of this invention uses polycrystalline silicon as a sacrificial layer before forming the cavity, and then etches the sacrificial layer with a XeF2 gas atmosphere. This etching process does not damage other parts of the structure, and the etching rate is not excessively slow, but rather faster and easier to control. Compared to the traditional method of using silicon dioxide as a sacrificial layer and HF etching, this avoids damaging the device structure, thereby improving the yield. Furthermore, the MEMS sensor fabrication method of this invention employs a multi-layer material filling and etched hole sealing method. The molecular structures of the multi-layer materials are staggered, which improves density and thus enhances hermeticity, allowing the device performance to remain stable for a longer period.

[0028] In summary, the MEMS sensor fabrication method of the present invention not only significantly improves the yield rate, but also allows the device performance to remain stable for a longer period due to better hermeticity. Attached Figure Description

[0029] Figure 1 This is an overall flowchart of a method for fabricating a MEMS sensor according to an embodiment of the present invention.

[0030] Figures 2A-2J Is it like this? Figure 1 The diagram shows a cross-sectional view of the silicon wafer at each step of the MEMS sensor fabrication process. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0032] like Figure 1The diagram shows a flowchart of a method for fabricating a MEMS sensor according to an embodiment of the present invention. The specific application scope of the fabrication method is mainly focused on the field of MEMS sensors that require the use of silicon surface micromachining technology to form cavities.

[0033] In this embodiment, the MEMS sensor is an absolute pressure and piezoresistive pressure sensor, fabricated using MEMS surface silicon micromachining technology. The working principle of the pressure sensor is as follows: when an external load is applied to the sensitive diaphragm, the diaphragm deforms, causing the piezoresistor on the diaphragm to also deform, thus changing its resistance value. A Wheatstone bridge composed of four piezoresistors outputs the change in voltage, thereby measuring the corresponding pressure value. The sensitivity of the pressure sensor's sensitive diaphragm, the airtightness of the cavity, and the placement of the piezoresistors are key to improving its performance.

[0034] In other embodiments, the MEMS sensor may be a piezoresistive pressure sensor, a piezoresistive accelerometer, a resistance temperature detector (RTD) gas sensor, a resistance temperature detector (RTD) humidity sensor, etc. Accordingly, the sensing device corresponding to the piezoresistive pressure sensor and the piezoresistive accelerometer is a piezoresistor based on the piezoresistive effect, and the sensing device corresponding to the resistance temperature detector (RTD) gas sensor and the resistance temperature detector (RTD) humidity sensor is a thermistor based on the temperature effect of resistance.

[0035] like Figure 1 As shown, the method for fabricating a MEMS sensor proposed in this invention includes the following steps:

[0036] Step S1: As Figure 2A As shown, an isolation layer 200 is deposited on silicon wafer 100;

[0037] The isolation layer is used to achieve electrical isolation from the silicon wafer substrate.

[0038] In this embodiment, the deposition is performed using an LPCVD process. The silicon wafer is N+. <100> Single-layer polished silicon wafer. In this embodiment, the insulating layer is low-stress silicon nitride, and its thickness is [missing information]. In other embodiments, the material of the insulating layer may be optional and the thickness may be within [specific range]. It is adjustable within a certain range.

[0039] Step S2: Using polysilicon, a boss 301 and an etched lead 302 adjacent to the boss are fabricated on the isolation layer 200 as a sacrificial layer, thereby obtaining a silicon wafer with a sacrificial layer.

[0040] The sacrificial layer serves as a filler to form the boss and the etched leads so that they can be released later; the boss becomes a vacuum cavity after release, allowing the sensitive diaphragm to deform when an external load is applied; and the etched leads act as a "trigger" when the boss is released.

[0041] In this embodiment, the etched leads are arranged around the boss.

[0042] Step S2 specifically includes:

[0043] Step S21: As Figure 2B As shown, a layer of polysilicon is deposited on the isolation layer 200, and photolithography and etching are performed on it (i.e. the deposited polysilicon) to pattern it and form a boss 301.

[0044] In this embodiment, the deposition is performed using an LPCVD process. In this embodiment, the boss has a thickness of... In other embodiments, its thickness is It is adjustable within a certain range.

[0045] Step S22: As Figure 2C As shown, a layer of polysilicon is deposited again on the isolation layer 200, and photolithography and etching are performed on it to pattern it and form etched leads 302.

[0046] In this embodiment, the deposition is performed using an LPCVD process. The thickness of the etched lead is... Furthermore, in other embodiments, its thickness is... It is adjustable within a certain range.

[0047] Step S3: As Figure 2D As shown, a low-stress silicon nitride layer is deposited on the entire silicon wafer with a sacrificial layer as a structural layer and a sensitive film 400.

[0048] Low-stress silicon nitride serves as both a structural layer for devices and a sensitive film.

[0049] In this embodiment, the deposition is performed using an LPCVD process. The thickness of the sensitive film 400 is... Furthermore, in other embodiments, its thickness is... It is adjustable within a certain range.

[0050] In addition, after step S3, step S3' is also included: fabricating a sensitive device 500 on the sensitive membrane 400 that changes based on the deformation of the sensitive membrane.

[0051] In this embodiment, the sensitive device is a varistor, and step S3' specifically includes:

[0052] Step S31': As Figure 2E As shown, a layer of low-stress polysilicon is deposited on the sensitive film 400, boron ion implantation annealing is performed on it, and then photolithography and etching are performed on the polysilicon to pattern it into a varistor 500.

[0053] The deposition was performed using an LPCVD process. The thickness of the varistor is... In other embodiments, its thickness is adjustable.

[0054] Step S32': As Figure 2F As shown, a low-stress silicon nitride layer is deposited as a protective layer 501 for the varistor; the protective layer of the varistor is photolithographically and etched to form the lead hole of the varistor.

[0055] In this embodiment, the thickness of the protective layer of the varistor is In other embodiments, its thickness is adjustable. The protective layer of the varistor is deposited over the entire silicon wafer.

[0056] Step S33': As Figure 2G As shown, electrode leads 502 of the varistor are fabricated at the lead hole of the varistor.

[0057] The electrode leads are formed using a lift-off process and by sputtering Au. The thickness of the electrode leads of the varistor is [missing information]. Furthermore, in other embodiments, its thickness is adjustable.

[0058] Step S4: As Figure 2H As shown, the sensitive film 400 above the corrosion lead is photolithographically etched and etched to obtain a corrosion release hole 401 penetrating the sensitive film 400;

[0059] In this embodiment, there are multiple corrosion release holes, and these multiple corrosion release holes are arranged around the boss.

[0060] Step S5: As Figure 2I As shown, the silicon wafer is placed in an XeF2 gas atmosphere, allowing the XeF2 gas to etch the sacrificial layer through the etching release holes (Note: the area except for the etching release holes is covered with photoresist). At the same time, the color of the protrusions under the sensitive film 400 is observed to change multiple times. When the color of all the protrusions has changed, the etching is stopped, the silicon wafer is cleaned and dried.

[0061] The sensitive membrane 400 is not transparent; observation is achieved through the penetrating power of a microscope.

[0062] At this point, the cavity structure is formed.

[0063] The protrusions beneath the structural layer were originally grayish-brown, but the color changed to orange. When the color completely changed, it indicated that all the polycrystalline silicon had been completely etched away.

[0064] Step S6: As Figure 2J As shown, a multilayer material of silicon nitride-silicon dioxide-silicon nitride is deposited at the corrosion release holes to obtain a sealing layer 402, which is used to seal all corrosion release holes.

[0065] The sealing layer is obtained by: depositing silicon nitride, silicon dioxide, and silicon nitride using PECVD to obtain a silicon nitride-silicon dioxide-silicon nitride multilayer material, and performing photolithography and etching to pattern the multilayer material, thereby fabricating the sealing layer.

[0066] The thicknesses of silicon nitride, silicon dioxide, and silicon nitride in the silicon nitride-silicon dioxide-silicon nitride multilayer material are respectively... In other embodiments, its thickness is adjustable, as long as the sealing layer can completely seal the release hole, that is, the deposition thickness of the sealing layer should be greater than the depth of the corrosion release hole.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. Various variations can be made to the above embodiments of the present invention. All simple and equivalent changes and modifications made in accordance with the claims and description of this application fall within the protection scope of the claims of this patent. All aspects not described in detail in this invention are conventional technical content.

Claims

1. A method for fabricating a MEMS sensor, characterized in that, include: Step S1: Deposit a low-stress silicon nitride isolation layer with a thickness of 2000-5000 Å on the silicon wafer; Step S2: Using polycrystalline silicon, a boss with a thickness of 8000-20000 Å and an etched lead with a thickness of 2000-4000 Å surrounding and adjacent to the boss are sequentially fabricated on the isolation layer as a sacrificial layer, thereby obtaining a silicon wafer with a sacrificial layer. Step S3: Deposit a layer of low-stress silicon nitride with a thickness of 8000-12000 Å on the silicon wafer with the sacrificial layer, which serves as both a structural layer and a sensitive film. Step S4: Perform photolithography and etching on the structural layer above the corrosion lead to obtain multiple corrosion release holes arranged around the protrusions that penetrate the sensitive film; Step S5: Place the silicon wafer with etching release holes in an XeF2 gas atmosphere, so that the XeF2 gas can etch the sacrificial layer through the etching release holes. At this time, the etching lead acts as a fuse. At the same time, observe whether the color of the protrusions under the structural layer changes. Stop etching when all the protrusions have changed color. Clean the silicon wafer and dry it to form a cavity structure. Step S6: Deposit a silicon nitride-silicon dioxide-silicon nitride multilayer material at the corrosion release hole to obtain a sealing layer to seal the corrosion release hole. The total thickness of the sealing layer is greater than the depth of the corrosion release hole.

2. The method for fabricating a MEMS sensor according to claim 1, characterized in that, Step S2 specifically includes: Step S21: Deposit a layer of polysilicon on the isolation layer, and perform photolithography and etching to pattern it and form protrusions; Step S22: Deposit another layer of polysilicon on the isolation layer, and perform photolithography and etching to pattern it and form etched leads.

3. The method for fabricating a MEMS sensor according to claim 1, characterized in that, Following step S3, step S3' is also included: fabricating a sensitive device on the sensitive membrane that changes based on the deformation of the sensitive membrane.

4. The method for fabricating a MEMS sensor according to claim 3, characterized in that, The MEMS sensor is a piezoresistive pressure sensor or a piezoresistive accelerometer, and the sensitive device is a piezoresistive resistor; or the MEMS sensor is a resistance temperature detector (RTD) gas sensor or a resistance temperature detector (RTD) humidity sensor, and the sensitive device is a thermistor.

5. The method for fabricating a MEMS sensor according to claim 3, characterized in that, The sensitive device is a varistor, and step S3' specifically includes: Step S31': Deposit a layer of low-stress polycrystalline silicon on the sensitive film, and perform boron ion implantation annealing, photolithography and etching to pattern it into a varistor; Step S32': Deposit a layer of low-stress silicon nitride as a protective layer for the varistor, and photolithographically and etch the protective layer of the varistor to form the lead hole of the varistor; Step S33': Fabricate the electrode leads of the varistor at the lead hole of the varistor.

6. The method for fabricating a MEMS sensor according to claim 1, characterized in that, In step S4, there are multiple corrosion release holes, and the multiple corrosion release holes are arranged around the boss.

7. The method for fabricating a MEMS sensor according to claim 1, characterized in that, In step S6, the sealing layer is obtained, specifically by: depositing silicon nitride, silicon dioxide, and silicon nitride by PECVD to obtain a silicon nitride-silicon dioxide-silicon nitride multilayer material, and performing photolithography and etching to pattern the multilayer material, thereby fabricating the sealing layer.

8. The method for fabricating a MEMS sensor according to claim 1, characterized in that, The thicknesses of silicon nitride, silicon dioxide, and silicon nitride in the silicon nitride-silicon dioxide-silicon nitride multilayer material are 6000 Å, 4000 Å, and 6000 Å, respectively.

9. The method for fabricating a MEMS sensor according to claim 1, characterized in that, In step S5, before XeF2 gas etches the sacrificial layer through the etching release holes, the area except for the etching release holes is covered with photoresist.

10. The method for fabricating a MEMS sensor according to claim 1, characterized in that, The silicon wafer is N+ <100> The single-layer silicon wafer has an isolation layer made of low-stress silicon nitride.

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