CN119263202A - A method for protecting anodic bonding surface in deep silicon etching - Google Patents

Abstract

The invention provides a method for protecting an anode bonding surface in deep silicon etching, which comprises the steps of providing a wafer, sequentially forming a protective layer and a blocking layer on the surface of the wafer, patterning the blocking layer and the protective layer by utilizing photoetching and etching processes, preparing a required structure by taking the patterned blocking layer as an etching mask through the deep silicon etching process, removing the blocking layer by utilizing a dry etching process, and removing the protective layer by utilizing a dry photoresist removing process. By adding a protective layer which is easy to remove between the bonding surface and the etching barrier layer in deep silicon etching, the problem that the roughness of the bonding surface is high due to ion bombardment can be prevented by the existence of the protective layer on the bonding surface when the barrier layer is removed in subsequent dry etching.

Description

Method for protecting anode bonding surface in deep silicon etching

Technical Field

The application relates to the technical field of semiconductors, in particular to a method for protecting an anode bonding surface in deep silicon etching.

Background

Wafer bonding is very widely used in MEMS (Micro-Electro-MECHANICAL SYSTEM, microelectromechanical system) processes, and the roughness of the bonding surface of a wafer has a direct effect on the bonding strength. Some semiconductor devices, particularly some mems devices, such as piezoelectric sensors, inertial sensors, gas sensors, etc., require large cavity structures to be fabricated based On SOI (Silicon-On-Insulator) wafers and finally to perform their corresponding functions by wafer bonding. The manufacturing of the large cavity structure needs deep silicon etching to form a large cavity on the silicon layer, the manufacturing method of the large cavity has a certain difficulty in technology, and besides the photoresist is used for defining the shape to be etched, a thin film blocking layer with higher selectivity to the silicon material is deposited under the photoresist, so that the etching depth required by the deep silicon etching is supported, and the silicon dioxide material is usually selected.

In the final wafer bonding process, the roughness requirements on the bonding surface are very high, typically less than 3 nanometers, to ensure a final good bonding effect. In the case of the need for anodic bonding, the thin film barrier layer needs to be removed first, so that the BOX layer (buried oxide layer) of the SOI wafer is exposed due to the formation of the cavity structure, cannot be removed by wet etching, and can only be removed by dry etching. In the removal process, the wafer surface (i.e., the final bonding surface) is also roughened by the bombardment of the etching gas, and the roughness of the final bonding surface is typically in the order of hundred nanometers, which cannot guarantee the final bonding effect.

Therefore, it is desirable to provide a method of protecting the anodic bonding surface during deep silicon etching to protect the wafer bonding surface to improve its roughness and increase subsequent bonding strength.

It should be noted that the foregoing description of the background art is only for the purpose of providing a clear and complete description of the technical solution of the present application and is presented for the convenience of understanding by those skilled in the art. The above-described solutions are not considered to be known to the person skilled in the art simply because they are set forth in the background of the application section.

Disclosure of Invention

The invention aims to provide a method for protecting an anode bonding surface in deep silicon etching so as to obtain a semiconductor device with low bonding surface roughness and good bonding effect.

In order to solve the above problems, the following provides a method for protecting an anode bonding surface in deep silicon etching, comprising:

S1, providing a wafer, and sequentially forming a protective layer and a barrier layer on the surface of the wafer;

S2, patterning the barrier layer and the protective layer by utilizing photoetching and etching processes;

s3, preparing a required structure by using the patterned barrier layer as an etching mask through a deep silicon etching process;

S4, removing the blocking layer by using a dry etching process, and removing the protective layer by using a dry photoresist removing process.

By adding a protective layer which is easy to remove between the bonding surface and the etching barrier layer in deep silicon etching, the problem that the roughness of the bonding surface is high due to ion bombardment can be prevented by the existence of the protective layer on the bonding surface when the barrier layer is removed in subsequent dry etching.

In step S1, the formation of the protective layer includes spin-coating polyimide on the wafer surface and performing a curing process at a temperature between 350 ℃ and 400 ℃. The polyimide material has better high temperature resistance, mechanical property and chemical stability, and is easy to remove in a dry etching mode.

In step S1, the barrier layer is formed by a low temperature deposition process having a deposition temperature lower than that of the curing process. The low-temperature deposition can reduce the outgassing phenomenon of the polyimide layer, and better ensures the stability of the process.

In step S1, the barrier layer is a silicon dioxide layer. The silicon dioxide layer is a common barrier layer in the deep silicon etching process, and the etching selectivity ratio of silicon is very high, so that the process is more mature.

In step S2, it includes:

S201, spin coating photoresist on the surface of the barrier layer, exposing and developing to obtain a photoresist pattern;

S202, using a photoresist pattern as an etching mask, and patterning the barrier layer and the protective layer through a dry etching process;

S203, removing the residual photoresist on the surface of the barrier layer by utilizing a wet photoresist removing process.

Transferring the pattern to the protective layer and the barrier layer, and then obtaining a final structure through deep silicon etching by taking the patterned barrier layer as an etching mask.

In step S202, the dry etching is performed by a dielectric film etching machine. The dielectric film etching machine is adopted to etch the dielectric film, which belongs to industry standard, and the process is more mature and has good compatibility.

After step S4, a second wafer is provided, and the wafer and the second wafer are subjected to anodic bonding.

And before the anodic bonding, cleaning the wafer. Impurities possibly introduced in the dry photoresist stripping process are removed through cleaning treatment, so that the performance of the device is improved.

Compared with the prior art, the invention mainly solves the problem that the bonding effect is affected due to overlarge bonding surface roughness in the traditional anode bonding process after deep silicon etching. Compared with the traditional process, the invention is characterized in that a protective layer is additionally introduced for protecting the bonding surface during dry etching of the barrier layer, thereby solving the problem of overlarge bonding surface roughness in the traditional process.

Drawings

In order to more clearly illustrate the technical solutions of specific embodiments of the present invention, the drawings that are needed in the description of the embodiments will be briefly described below, and it is obvious that the drawings described below are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort to a person of ordinary skill in the art.

Fig. 1 is a schematic structural diagram of a deep silicon etched structure in the prior art provided by the invention.

Fig. 2 is a flowchart of a method for protecting an anodic bonding surface in deep silicon etching according to the present invention.

Detailed Description

The foregoing and other features, aspects, and advantages of the present invention will become more apparent from the following detailed description of a preferred embodiment, which proceeds with reference to the accompanying drawings. The directional terms mentioned in the following embodiments, such as up, down, left, right, front or rear, etc., are only referring to the directions of the attached drawings. Thus, the directional terminology is used for purposes of illustration and is not intended to be limiting of the invention.

Embodiments of the present application will be described in detail below with reference to the attached drawings. However, it will be understood by those of ordinary skill in the art that in various embodiments of the present application, numerous specific details are set forth in order to provide a thorough understanding of the present application. The claimed application may be practiced without these specific details and with various changes and modifications based on the following embodiments.

Some semiconductor devices, particularly some mems devices, such as piezoelectric sensors, inertial sensors, gas sensors, etc., require large cavity structures to be fabricated based On SOI (Silicon-On-Insulator) wafers and finally to perform their corresponding functions by wafer bonding. Fig. 1 is a schematic structural diagram of a deep silicon etched large cavity structure in the prior art. Referring to fig. 1, an SOI wafer includes a bottom silicon layer 1, a buried oxide layer 2, and a top silicon layer 3. The fabrication of large cavity structures is performed by deep silicon etching, and a thin film barrier layer, i.e. barrier layer 4, with a high selectivity to silicon material is typically formed on the surface of the top silicon layer 3 prior to etching in order to be able to support the etch depth required for deep silicon etching. When the anodic bonding is to be performed subsequently, the barrier layer 4 needs to be removed, and the buried oxide layer 2 of the SOI wafer is exposed, so that the barrier layer 4 cannot be removed by wet etching, but can be removed by dry etching. In the process of removing the barrier layer 4 by dry etching, the surface (i.e., the final bonding surface) of the top silicon layer 3 is roughened by being bombarded by etching gas, and the final bonding effect cannot be ensured.

The steps in the following embodiments do not correspond to the summary of the invention.

Embodiment one:

fig. 2 is a flowchart of a method for protecting an anodic bonding surface in deep silicon etching according to the present invention.

Referring to fig. 2, the present invention provides a method of protecting an anodic bonding surface in deep silicon etching, the method comprising the steps of:

Step 1, providing a wafer.

Referring to a in fig. 2, the wafer provided in this embodiment is an SOI wafer, comprising, from bottom to top, a bottom silicon layer 1, a buried oxide layer 2, and a top silicon layer 3.

SOI wafers have wide application in MEMS device fabrication, and thus SOI wafers are exemplified. The application is not limited to the specific materials and forms of wafers, but may be, for example, monocrystalline silicon wafers or other semiconductor wafers.

And 2, forming a protective layer 5 on the surface of the wafer.

Referring to b of fig. 2, in the present embodiment, the protective layer 5 is formed by spin-coating a polyimide material on the wafer surface and performing a curing process.

In this embodiment, the material of the protective layer 5 is polyimide, because the material can withstand high temperatures and is easily removed by dry etching. In other embodiments, other materials having similar properties may be used. In this embodiment, the curing treatment temperature for the polyimide is 350 ℃, and in other embodiments, the curing treatment temperature may be between 350 ℃ and 400 ℃.

And 3, forming a barrier layer 4 on the surface of the protective layer 5.

Referring to b of fig. 2, in the present embodiment, the barrier layer 4 is formed on the surface of the protective layer 5 by a low temperature deposition process at a temperature lower than the curing temperature of the polyimide material used. If the deposition temperature is higher, the polyimide may generate outgassing (outgassing) phenomenon, which has influence on the process and equipment.

In this embodiment, the barrier layer 4 is made of silicon dioxide. The silicon dioxide film is adopted because in the deep silicon etching process, the etching selectivity ratio of silicon dioxide and silicon is very high, and the silicon dioxide film is common in the industry. The role of the barrier layer 4 is to define the structure as an etch mask in a subsequent deep silicon etch.

In other embodiments, other materials may be selected to form the barrier layer 4, as long as the deposition temperature of the thin film process is low and the etch selectivity to the silicon material is high. In terms of application, thin film processes with deposition temperatures below 350 ℃ are possible, such as low temperature silicon nitride films.

And 4, preparing a required structure on the wafer by utilizing photoetching and etching processes.

Referring to fig. 2c, specifically, a photoresist layer is formed on the surface of the barrier layer 4, then a pattern is transferred to the photoresist layer through steps such as exposure, development and the like to obtain a photoresist pattern, pattern definition is realized, then the barrier layer 4 and the protective layer 5 are etched according to the photoresist pattern, the pattern is transferred to the barrier layer 4 and the protective layer 5 to be patterned, then the residual photoresist material on the surface of the barrier layer 4 is removed through a wet photoresist removing process, and finally a deep silicon etching process is performed by taking the barrier layer 4 as an etching mask until a final required structure is prepared, as shown in fig. 2 c.

In this embodiment, the barrier layer 4 and the protective layer 5 are etched by a dielectric film etcher, because the dielectric film etcher for etching a dielectric film is an industry standard. In other embodiments, other dry etches may be used directly.

And 5, removing the residual barrier layer 4 by using a dry etching process.

The surface barrier layer 4 is removed here because the anodic bonding is to be performed subsequently. Since the buried oxide layer 2 of the SOI wafer is exposed at this time, the barrier layer 4 cannot be removed by wet etching, but can be removed by dry etching.

In the process of adopting the dry etching barrier layer 4, since a layer of polyimide material exists below the barrier layer 4, the bonding surface (namely the surface of the top silicon layer 3) of the wafer cannot be damaged in the process of etching gas bombardment, and the bonding surface can be well protected, so that the bonding surface meeting the requirement of final bonding roughness is obtained.

And 6, removing the residual protective layer 5 by using a dry photoresist removing process.

The dry photoresist removing process for polyimide material is usually a plasma dry etching process using oxygen as the main etching gas, and this step is the prior art and is not described in detail herein. Thus, the structure preparation work on the wafer is completed, and the anode bonding can be performed subsequently.

And 7, providing a second wafer and performing anodic bonding.

And (3) cleaning the product obtained in the step (6) to remove impurities possibly introduced in the dry photoresist removing process, and then performing an anodic bonding process with the provided second wafer.

The use of certain conventional english terms or letters for the sake of clarity of description of the invention is intended to be exemplary only and not limiting of the interpretation or particular use, and should not be taken to limit the scope of the invention in terms of its possible chinese translations or specific letters.

It should also be noted that in this document, relational terms such as "first" and "second" and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions.

Claims (8)

1. A method for protecting an anodic bonding surface during deep silicon etching, comprising: S1. providing a wafer, and sequentially forming a protective layer and a barrier layer on the surface of the wafer; S2, patterning the barrier layer and the protective layer by photolithography and etching processes; S3, using the patterned barrier layer as an etching mask, preparing the desired structure through a deep silicon etching process; S4. Remove the barrier layer by using a dry etching process, and remove the protective layer by using a dry stripping process. 2. A method for protecting an anodic bonding surface during deep silicon etching according to claim 1, characterized in that in step S1, the formation of the protective layer includes spin coating polyimide on the surface of the wafer and performing a curing treatment, and the temperature of the curing treatment is between 350°C and 400°C. 3. A method for protecting an anodic bonding surface in deep silicon etching according to claim 2, characterized in that in step S1, the barrier layer is formed by a low-temperature deposition process, and the deposition temperature of the low-temperature deposition process is lower than the temperature of the curing treatment. 4 . The method for protecting an anodic bonding surface in deep silicon etching according to claim 1 , wherein in step S1 , the barrier layer is a silicon dioxide layer. 5. The method for protecting an anodic bonding surface during deep silicon etching according to claim 1, characterized in that in step S2, it comprises: S201, spin coating a photoresist on the surface of the barrier layer and performing exposure and development treatment to obtain a photoresist pattern; S202, using the photoresist pattern as an etching mask, patterning the barrier layer and the protective layer through a dry etching process; S203, removing the remaining photoresist on the surface of the blocking layer by using a wet stripping process. 6 . The method for protecting an anodic bonding surface in deep silicon etching according to claim 5 , characterized in that, in step S202 , the dry etching is performed by a dielectric film etcher. 7 . The method for protecting an anodic bonding surface during deep silicon etching according to claim 1 , wherein after step S4 , a second wafer is provided, and the first wafer is anodically bonded to the second wafer. 8 . The method for protecting the anodic bonding surface in deep silicon etching according to claim 7 , wherein the wafer is cleaned before the anodic bonding.