MEMS device functional layer preparation method and MEMS device

Abstract

The invention discloses an MEMS device functional layer preparation method and an MEMS device, and the method comprises the steps: providing a first substrate which is provided with a front surface and a back surface which are opposite to each other; etching the front surface of the first substrate, and forming a cavity in the front surface of the first substrate; providing a second substrate having opposite front and back surfaces; forming an etching stop layer on the front surface of the second substrate; bonding the front surface of the second substrate with the front surface of the first substrate to enable the etching stop layer to seal the cavity; thinning the back surface of the second substrate; carrying out deep groove etching on the back surface of the second substrate, and stopping on the etching stop layer so as to form a movable functional layer pattern above the cavity; and removing the etching stop layer between the movable functional layer pattern and the cavity. According to the invention, the integrity of the functional layer pattern on the cavity structure of the MEMS device can be improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor device manufacturing, and in particular to a method for preparing a functional layer of a MEMS device and a MEMS device. Background Art

[0002] At present, the common method for making MEMS accelerometer structure is generally as follows: making a cavity on a silicon wafer, growing a silicon oxide layer on the side of the silicon wafer with the cavity by thermal oxidation, bonding the silicon oxide layer to another clean and flat silicon wafer, and annealing at high temperature after bonding. In order to prevent the cavity from exploding during high-temperature annealing, vacuum bonding is used during bonding. After bonding, the cavity is sealed and the air pressure is less than the external atmospheric pressure. When dry etching the functional layer pattern, the moment the cavity is connected to the outside world will cause the functional layer pattern to be deformed by the external atmospheric pressure. At this time, etching is still continuing, which will cause the pattern CD at the lower surface of the functional layer to be destroyed. On the other hand, after etching penetrates the functional layer, the etching particles will splash back to the bottom of the functional layer through the bottom of the cavity, further causing damage to the bottom of the functional layer. In severe cases, it will cause the structure to break, affecting the reliability of the device. Summary of the invention

[0003] The object of the present invention is to provide a method for preparing a functional layer of a MEMS device and a MEMS device, so as to improve the integrity of the functional layer pattern on the cavity structure of the MEMS device.

[0004] In order to achieve the above object, the present invention proposes a method for preparing a functional layer of a MEMS device, comprising:

[0005] Providing a first substrate having opposite front and back surfaces;

[0006] Etching the front surface of the first substrate to form a cavity on the front surface of the first substrate;

[0007] providing a second substrate having opposite front and back surfaces;

[0008] forming an etch stop layer on the front side of the second substrate;

[0009] Bonding the front surface of the second substrate to the front surface of the first substrate so that the etch stop layer seals the cavity;

[0010] performing a thinning process on the back side of the second substrate;

[0011] Performing deep trench etching on the back side of the second substrate and stopping at the etching stop layer to form a movable functional layer pattern above the cavity;

[0012] The etching stop layer between the movable functional layer pattern and the cavity is removed.

[0013] Optionally, etching the front side of the first substrate to form a cavity on the front side of the first substrate includes:

[0014] forming a mask layer on the front surface of the first substrate;

[0015] forming a patterned photoresist layer on the mask layer;

[0016] Etching the mask layer to form an opening exposing the front side of the first substrate;

[0017] removing the photoresist layer;

[0018] Etching the first substrate to form a cavity on the front side of the first substrate;

[0019] The mask layer is removed.

[0020] Optionally, the material of the first substrate includes silicon, and the material of the mask layer includes silicon oxide;

[0021] Forming a mask layer on the front side of the first substrate includes:

[0022] A mask layer is formed on the front surface of the first substrate by using TEOS as a gas source and a chemical vapor deposition process.

[0023] Optionally, removing the mask layer includes:

[0024] The mask layer is removed by a wet etching process.

[0025] Optionally, the material of the second substrate includes silicon, and the material of the etch stop layer includes silicon oxide;

[0026] Forming an etch stop layer on the front side of the second substrate, comprising:

[0027] A thermal oxidation process is performed on the front side of the second substrate to form a silicon oxide layer as the etching stop layer on the front side of the second substrate.

[0028] Optionally, the thickness of the etch stop layer is 0.1-2 um.

[0029] Optionally, performing thinning processing on the back side of the second substrate includes:

[0030] The back side of the second substrate is thinned by a mechanical grinding process to thin the second substrate to a set thickness.

[0031] Optionally, bonding the front side of the second substrate to the front side of the first substrate comprises:

[0032] The front side of the second substrate is bonded to the front side of the first substrate by using a vacuum bonding process.

[0033] Optionally, performing deep trench etching on the back side of the second substrate includes:

[0034] Performing deep groove etching on the back side of the second substrate by using a dry deep silicon etching process, and stopping the etching at the etching stop layer to form a movable functional layer pattern;

[0035] The movable functional layer pattern includes a plurality of periodically distributed deep groove structures.

[0036] Optionally, the etch stop layer under the functional layer is removed by a wet etching process.

[0037] The present invention further provides a MEMS device, wherein the MEMS device comprises a movable functional layer, and the movable functional layer is formed by using the above-mentioned method for preparing a functional layer of a MEMS device.

[0038] The beneficial effects of the present invention are:

[0039] The method of the present invention first forms a cavity structure on the front side of a first substrate, then forms an etch stop layer on the front side of a second substrate, then bonds the etch stop layer on the front side of the second substrate to the front side of the first substrate, thins the second substrate, and then performs deep groove etching on the back side of the second substrate to form a functional layer pattern, the etching stops on the etch stop layer, and then the cavity is connected to the outside by removing the etch stop layer under the functional layer. Compared with the existing method of directly etching through the functional layer to connect the cavity to the outside when etching the functional layer pattern, the method of etching the functional layer pattern by Due to the existence of the etch stop layer, when the functional layer pattern is etched, the cavity air pressure is not connected to the external air pressure, which effectively avoids the problem of deformation of the functional layer pattern caused by the moment the cavity is connected to the outside and damage to the bottom pattern of the functional layer caused by the ion beam entering the cavity and bombarding the lower surface of the functional layer; in addition, after the functional layer pattern is etched, the etch stop layer between the functional layer and the cavity is removed. Due to the protective effect of the etch stop layer, the exposed lower surface of the functional layer is not etched, which effectively improves the integrity of the bottom of the functional layer, thereby improving the reliability of the device.

[0040] Furthermore, the method of the present invention uses TEOS gas source to deposit an oxide layer on the surface of the first substrate to form a mask layer. After the cavity is etched and the mask layer is removed, the front surface of the first substrate is exposed. The front surface of the first substrate is flat and smooth, which is conducive to bonding.

[0041] Furthermore, when forming the etch stop layer, the method of the present invention forms a silicon oxide layer by thermally oxidizing the front side of the second substrate. The silicon oxide layer (etch stop layer) grown on the surface of the second substrate also replicates the flatness of the original surface of the substrate, which is beneficial to bonding. After the etch stop layer is removed by a wet process, the front side of the second substrate (functional layer) is exposed. This surface has only undergone one thermal oxidation treatment, and its flatness and smoothness are much greater than the surface prepared by the traditional direct etching method to connect the cavity. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0043] Figure 1-Figure 10 The device structure diagram corresponding to each step in a method for preparing a functional layer of a MEMS device according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0044] The following is a further detailed description of a filter chip packaging structure and a wafer-level packaging method of the present invention in combination with the accompanying drawings and specific embodiments. According to the following description and drawings, the advantages and features of the present invention will be clearer. However, it should be noted that the concept of the technical solution of the present invention can be implemented in a variety of different forms and is not limited to the specific embodiments described herein. The drawings are all in a very simplified form and are not in precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0045] The terms "first", "second", etc. in the specification and claims are used to distinguish between similar elements and are not necessarily used to describe a specific order or time sequence. It is to be understood that, where appropriate, these terms used in this way are interchangeable, for example, so that the embodiments of the invention described herein can be operated in an order other than that described or shown herein. Similarly, if the method described herein includes a series of steps, the order of these steps presented herein is not necessarily the only order in which these steps can be performed, and some of the steps described may be omitted and / or some other steps not described herein may be added to the method. If the components in a certain figure are the same as the components in other figures, although these components can be easily identified in all figures, in order to make the description of the figures clearer, this specification will not mark all the same component numbers in each figure.

[0046] Example 1

[0047] like Figure 1-Figure 10As shown, this embodiment provides a method for preparing a functional layer of a MEMS device, comprising:

[0048] S1: providing a first substrate 1, wherein the first substrate 1 has a front side and a back side opposite to each other;

[0049] In this embodiment, the material of the first substrate 1 is silicon, that is, the first substrate 1 is a silicon wafer.

[0050] S2: etching the front surface of the first substrate 1 to form a cavity 3 on the front surface of the first substrate 1;

[0051] This step specifically includes:

[0052] S201: Figure 1 As shown, a mask layer 2 is formed on the front surface of the first substrate 1;

[0053] In this embodiment, the material of the mask layer 2 is silicon oxide, and the thickness of the mask layer 2 is preferably 0.1-1 um. The method for forming the mask layer 2 is to use TEOS (C8H 20 O4Si, tetraethoxysilane, also known as tetraethyl silicate, ethyl orthosilicate) gas is used as a gas source, and a silicon oxide layer is formed on the front side of the first substrate 1 through a chemical vapor deposition (CVD) process as a mask layer 2.

[0054] Since photoresist is directly used as a mask for etching the first substrate 1 to make the cavity 3, there will be residual organic matter on the surface of the first substrate 1 later, which is not conducive to bonding; if the mask layer 2 is made by thermally oxidizing the surface of the first substrate 1 to form a silicon oxide layer, the Si on the surface of the silicon substrate itself will be lost due to thermal oxidation, and then the surface of the first substrate 1 cannot be guaranteed to be smooth and uniform after the mask layer 2 (silicon oxide layer) is removed later, which is not conducive to bonding. Therefore, the mask layer 2 in this method uses TEOS as a gas source, and TEOS is used as a gas source to deposit a layer of silicon oxide (0.1~1um) on the surface of the first substrate 1 as a mask layer 2. After the cavity 3 is etched and the mask layer 2 is removed, the front of the first substrate 1 is exposed, which can make the substrate surface itself flat and smooth, which is more conducive to bonding.

[0055] S202: Figure 2 As shown, a patterned photoresist layer 8 is formed on the mask layer 2;

[0056] In this step, a photoresist pattern can be produced by spin coating the photoresist, exposing, and developing.

[0057] S203: Figure 3 As shown, the mask layer 2 is etched to form an opening exposing the front side of the first substrate 1;

[0058] In this step, the mask layer 2 can be etched by a dry etching process to complete the patterning of the mask layer 2 .

[0059] S204: Continue to refer Figure 3 , removing the photoresist layer 8;

[0060] This step may adopt a wet process to wash away the residual photoresist layer 8. In other embodiments, the residual photoresist layer 8 may also be removed while the mask layer 2 is removed subsequently.

[0061] S205: Figure 4 As shown, the first substrate 1 is etched to form a cavity 3 on the front side of the first substrate 1;

[0062] In this step, the mask layer 2 is used to etch the front surface of the first substrate 1 by a dry etching process to form a cavity structure required by the device.

[0063] S206: Figure 5 As shown, the mask layer 2 is removed.

[0064] This step may adopt a wet etching process, such as using BOE (buffered oxide etchant) or VHF (gaseous hydrogen fluoride) to remove the mask layer 2 .

[0065] S3: providing a second substrate 4, wherein the second substrate 4 has a front side and a back side opposite to each other;

[0066] In this embodiment, the material of the second substrate 4 is silicon oxide.

[0067] S4: Figure 6 As shown, an etching stop layer 6 is formed on the front surface of the second substrate 4;

[0068] In this embodiment, the material of the etch stop layer 6 is silicon oxide. Since the etching rate of silicon is higher than that of silicon oxide when etching the functional pattern later, the silicon oxide layer is used as the etch stop layer 6.

[0069] In this step, a silicon oxide layer 5 is formed on the front surface of the second substrate 4 as the etching stop layer 6 by performing thermal oxidation treatment on the second substrate 4. Preferably, the thickness of the etching stop layer 6 is 0.1-2 um.

[0070] Preferably, in this step, by simultaneously performing thermal oxidation treatment on the front and back sides of the second substrate 4, a silicon oxide layer 5 with a thickness of 0.1 to 2 um is grown on both sides of the second substrate 4, so that stress balance can be achieved on both sides of the second substrate 4, and the second substrate 4 can still remain flat after thermal oxidation growth without warping and deformation, and the silicon oxide layer 5 grown on the surface of the second substrate 4 also replicates the flatness of the original surface of the second substrate 4, which is conducive to bonding. At the same time, the process of forming the silicon oxide layer by thermal oxidation treatment is also simpler.

[0071] In other optional embodiments, silicon nitride may also be used as the etch stop layer 6. For example, a silicon nitride layer may be directly deposited on the front surface of the second substrate 4 as the etch stop layer 6, and then removed by wet etching, which can also achieve a similar effect.

[0072] S5: Figure 7 As shown, the front side of the second substrate 4 is bonded to the front side of the first substrate 1, so that the etch stop layer 6 closes the cavity 3;

[0073] In this step, the front side of the second substrate 4 is bonded to the front side of the first substrate 1 by a vacuum bonding process.

[0074] Specifically, the etching stop layer 6 on the front side of the second substrate 4 is bonded to the front side of the first substrate 1 (the supporting area outside the cavity 3) in a vacuum environment, and then high-temperature annealing is performed. After bonding, the cavity 3 is sealed and the gas pressure is less than the external atmospheric pressure.

[0075] S6: Figure 8 As shown, the back side of the second substrate 4 is thinned;

[0076] In this step, the back side of the second substrate 4 can be thinned by mechanical grinding process, and the silicon oxide layer on the back side of the second substrate 4 and part of the second substrate 4 can be removed to thin the second substrate 4 to a set thickness. The set thickness is preferably 10 to 50 um, corresponding to the thickness of the thinned second substrate 4, that is, the thickness of the functional layer.

[0077] S7: Fig. 9 As shown, deep trench etching is performed on the back side of the second substrate 4 and the etching stops at the etching stop layer 6 to form a movable functional layer pattern 7 above the cavity 3;

[0078] In this step, a dry deep silicon etching process is used to perform deep groove etching on the back side of the second substrate 4, and the etching stops at the etching stop layer 6 to form a movable functional layer pattern 7;

[0079] In this embodiment, the dry deep silicon etching process preferably uses the Bosch process to perform deep groove etching on the second substrate 4 to form a functional layer pattern. First, a patterned mask (not shown) is formed on the back side of the second substrate 4, and then the back side of the second substrate 4 is etched. The etching process is mainly as follows: the etching gas is SF6, and the passivation gas is C4F8. Etching is performed along the depth direction through a cycle of "etching-passivation-etching", and the etching stops at the silicon oxide layer 5 (i.e., the etching stop layer 6) at the bonding interface. After the etching is completed, the residual mask is removed.

[0080] In this embodiment, the movable functional layer pattern 7 formed by etching includes a plurality of periodically distributed deep groove structures. If the MEMS device is an acceleration sensor, the movable functional layer formed by etching includes a movable comb-shaped structure.

[0081] During the etching process of this step, due to the presence of the etching stop layer 6, the functional layer will not be directly etched through, the cavity 3 is still closed by the etching stop layer 6, and the air pressure in the cavity 3 is not connected to the external air pressure, thereby effectively avoiding deformation of the functional layer caused by the moment when the cavity 3 is connected to the outside world and damage to the functional layer caused by the ion beam entering the cavity 3 and bombarding the lower surface of the functional layer.

[0082] S8: Fig.10 As shown, the etching stop layer 6 between the movable functional layer pattern 7 and the cavity 3 is removed, and the etching stop layer 6 in the bonding connection area between the front surface of the first substrate 1 and the front surface of the second substrate 4 is retained.

[0083] In this step, the etch stop layer 6 below the functional layer is removed by a wet etching process. In the specific implementation process, HF removal is required according to the thickness of the etch stop layer 6 and the specific conditions of CD, such as BOE solution or VHF, and the etching time is controlled to completely remove the etch stop layer 6 (SiO2) at the corresponding position of the movable functional layer, and the etch stop layer 6 (SiO2) at the bonding support connection position can be retained.

[0084] In this step, after removing the etching stop layer 6 by HF, the front surface of the second substrate 4 is exposed. This surface has only been thermally oxidized once, and its flatness and smoothness are much greater than the surface prepared by directly etching the connecting cavity 3, further improving the integrity of the functional layer pattern.

[0085] Example 2

[0086] This embodiment provides a MEMS device, which includes a movable functional layer. The movable functional layer is formed by the method for preparing a MEMS device functional layer described in Embodiment 1.

[0087] In the MEMS device of this embodiment, since its movable functional layer is formed by the method for preparing the functional layer of the MEMS device described in Embodiment 1, the pattern integrity of the movable functional layer is higher and the performance of the device is more reliable.

[0088] It should be noted that the various embodiments in this specification are described in a related manner, and the same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the structural embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0089] The above description is only a description of the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention. Any changes or modifications made by a person skilled in the art in the field of the present invention based on the above disclosure shall fall within the scope of protection of the claims.

Claims

1. A method for preparing a functional layer of a MEMS device, characterized in that: include: Providing a first substrate having opposite front and back surfaces; Etching the front surface of the first substrate to form a cavity on the front surface of the first substrate; providing a second substrate having opposite front and back surfaces; forming an etch stop layer on the front side of the second substrate; Bonding the front surface of the second substrate to the front surface of the first substrate so that the etch stop layer seals the cavity; performing a thinning process on the back side of the second substrate; Performing deep trench etching on the back side of the second substrate and stopping at the etching stop layer to form a movable functional layer pattern above the cavity; The etching stop layer between the movable functional layer pattern and the cavity is removed.

2. The method for preparing a functional layer of a MEMS device according to claim 1, characterized in that: Etching the front side of the first substrate to form a cavity on the front side of the first substrate, comprising: forming a mask layer on the front surface of the first substrate; forming a patterned photoresist layer on the mask layer; Etching the mask layer to form an opening exposing the front side of the first substrate; removing the photoresist layer; Etching the first substrate to form a cavity on the front side of the first substrate; The mask layer is removed.

3. The method for preparing a functional layer of a MEMS device according to claim 2, characterized in that: The material of the first substrate includes silicon, and the material of the mask layer includes silicon oxide; Forming a mask layer on the front side of the first substrate includes: A mask layer is formed on the front surface of the first substrate by using TEOS as a gas source and a chemical vapor deposition process.

4. The method for preparing a functional layer of a MEMS device according to claim 3, characterized in that: The removing the mask layer comprises: The mask layer is removed by a wet etching process.

5. The method for preparing a functional layer of a MEMS device according to claim 1, characterized in that: The material of the second substrate includes silicon, and the material of the etch stop layer includes silicon oxide; Forming an etch stop layer on the front side of the second substrate, comprising: A thermal oxidation process is performed on the front side of the second substrate to form a silicon oxide layer as the etching stop layer on the front side of the second substrate.

6. The method for preparing a functional layer of a MEMS device according to claim 5, characterized in that: The thickness of the etching stop layer is 0.1-2 um.

7. The method for preparing a functional layer of a MEMS device according to claim 5, characterized in that: The thinning process of the back side of the second substrate comprises: The back side of the second substrate is thinned by a mechanical grinding process to thin the second substrate to a set thickness.

8. The method for preparing a functional layer of a MEMS device according to claim 1, characterized in that: Bonding the front side of the second substrate to the front side of the first substrate, comprising: The front side of the second substrate is bonded to the front side of the first substrate by using a vacuum bonding process.

9. The method for preparing a functional layer of a MEMS device according to claim 5, characterized in that: Performing deep trench etching on the back side of the second substrate includes: Performing deep groove etching on the back side of the second substrate by using a dry deep silicon etching process, and stopping the etching at the etching stop layer to form a movable functional layer pattern; The movable functional layer pattern includes a plurality of periodically distributed deep groove structures.

10. The method for preparing a functional layer of a MEMS device according to claim 1, characterized in that: The etching stop layer under the functional layer is removed by a wet etching process.

11. A MEMS device, characterized in that: The MEMS device comprises a movable functional layer, and the movable functional layer is formed by using the method for preparing a MEMS device functional layer according to any one of claims 1 to 10.

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