阅读说明：本技术 压阻式表压压力传感器的制造方法 (Method for manufacturing piezoresistive gauge pressure sensor ) 是由 陈志宝 于 2021-01-15 设计创作，主要内容包括：本发明公开了一种压阻式表压压力传感器的制造方法；在SOI衬底的正面利用深反应离子刻蚀法形成用于制作空腔时的腐蚀停止层的环形结构的深槽一；SOI衬底内设有中间埋氧层；埋氧层用于制作空腔时的腐蚀停止层；在深槽一内填充氧化硅,然后除去表面的氧化硅层以SOI衬底的顶层作为种子层,生长外延硅层；在外延硅层上制作压力传感器的四个压阻并形成惠斯通电桥结构；正面完成后,利用双面光刻法和深反应离子刻蚀法形成用于制作空腔的深槽二；在深槽二内填充氧化硅,并利用干法刻蚀法选择性的去除深槽二底部的氧化硅；用硅的湿法腐蚀液形成最终的腔体。本技术方案,解决了工艺偏差引起的零点漂移问题,制造出的传感器的比传统工艺制作的传感器品质更高。(The invention discloses a manufacturing method of a piezoresistive gauge pressure sensor; forming a first deep groove of an annular structure of an etching stop layer for manufacturing a cavity on the front surface of the SOI substrate by using a deep reactive ion etching method; a middle buried oxide layer is arranged in the SOI substrate; the buried oxide layer is used for manufacturing an etching stop layer when the cavity is manufactured; filling silicon oxide in the first deep groove, removing the silicon oxide layer on the surface, and growing an epitaxial silicon layer by taking the top layer of the SOI substrate as a seed layer; manufacturing four piezoresistors of the pressure sensor on the epitaxial silicon layer and forming a Wheatstone bridge structure; after the front side is finished, forming a second deep groove for manufacturing the cavity by using a double-sided photoetching method and a deep reactive ion etching method; filling silicon oxide in the second deep groove, and selectively removing the silicon oxide at the bottom of the second deep groove by using a dry etching method; and forming a final cavity by using a wet etching solution of silicon. According to the technical scheme, the problem of zero drift caused by process deviation is solved, and the manufactured sensor has higher quality than a sensor manufactured by the traditional process.)

1. A method of manufacturing a piezoresistive gage pressure sensor; the method is characterized in that: comprises that

Step 1: forming a first deep groove of an annular structure of an etching stop layer for manufacturing a cavity on the front surface of the SOI substrate by using a deep reactive ion etching method; wherein, a middle buried oxide layer is arranged in the SOI substrate; the buried oxide layer is used for manufacturing an etching stop layer when the cavity is manufactured;

step 2: filling silicon oxide in the first deep groove, and then removing the silicon oxide layer on the surface;

and step 3: taking the top layer of the SOI substrate as a seed layer, and growing an epitaxial silicon layer;

and 4, step 4: manufacturing four piezoresistors of the pressure sensor on the epitaxial silicon layer and forming a Wheatstone bridge structure;

and 5: after the front side is finished, forming a second deep groove for manufacturing the cavity by using a double-sided photoetching method and a deep reactive ion etching method; filling silicon oxide in the second deep groove, and selectively removing the silicon oxide at the bottom of the second deep groove by using a dry etching method; and forming a final cavity by using a wet etching solution of silicon.

2. The method of manufacturing a piezoresistive gage pressure sensor according to claim 1, wherein: the opening size of the first deep groove is 0.5-1.5 um.

3. The method of manufacturing a piezoresistive gage pressure sensor according to claim 2, wherein: the annular structure is a circular ring or a polygonal ring.

4. The method of manufacturing a piezoresistive gage pressure sensor according to claim 1, wherein: the top layer of the SOI substrate is monocrystalline silicon.

5. The method of manufacturing a piezoresistive gage pressure sensor according to claim 1, wherein: step 2, removing the top silicon layer and the buried oxide layer in the first deep groove by using a dry etching method, and etching the silicon substrate of the SOI substrate in the first deep groove by using a deep reactive ion etching method; the etching depth of the first deep groove is larger than 10 um.

6. The method of manufacturing a piezoresistive gage pressure sensor according to claim 1, wherein: the step 1 is as follows: filling an oxidation protection layer on the side wall and the bottom of the first deep groove through an oxidation process; and after the filling is finished, removing the oxide layer on the surface of the SOI substrate.

7. The method of manufacturing a piezoresistive gage pressure sensor according to claim 1, wherein: the depth of the epitaxial layer in step 3 is determined by the measuring range of the pressure sensor.

8. The method of manufacturing a piezoresistive gage pressure sensor according to claim 1, wherein: step 5 is as follows:

s51, deeply etching the bottom surface of the SOI substrate by using a dry method to form a second deep groove for manufacturing the cavity;

s52, depositing a barrier layer on the side wall and the bottom of the second deep groove;

s53, removing the barrier layer at the bottom of the second deep groove by utilizing an anisotropic etching method, and reserving the side wall of the second deep groove to form a side wall protective layer;

and S54, taking the side wall protection layer of the second deep groove as a mask, and continuously utilizing anisotropic wet etching to finally form a cavity.

9. The method of manufacturing a piezoresistive gage pressure sensor according to claim 8, wherein: the deep groove II is designed in a hole shape, and the size of the deep groove II is smaller than that of the inner ring of the deep groove I.

10. The method of manufacturing a piezoresistive gage pressure sensor according to claim 9, wherein: during wet etching, the middle buried oxide layer of the SOI substrate, the oxide layer on the side wall of the deep groove and the oxide layer on the side wall of the deep groove are all self-stopping barrier layers of the wet etching.

Technical Field

The invention relates to a preparation method of a pressure sensor, in particular to a manufacturing method of a piezoresistive gauge pressure sensor.

Background

At present, the mainstream electrical response type pressure sensor responds to the pressure in real time by converting the deformation of a device generated under the action of pressure into the change of electrical performance parameters of the sensor. The piezoresistive pressure sensor is simple in preparation process, high in response stability, strong in anti-interference capability, high in sensitivity, good in linearity, and simple and easy in subsequent processing circuit, is widely applied, and becomes a research hotspot in the field of the current flexible pressure sensor.

Piezoresistive pressure sensors comprise three main components: piezoresistors, stress films and silicon islands. The four piezoresistors form a Wheatstone bridge, the pressure acting on the sensor is converted into the change of the resistance value of the piezoresistor through the stress change of the film, the changed resistance value is detected by a corresponding measuring circuit, and finally, the magnitude of the measured pressure acting on the film is measured.

Due to the large temperature coefficient of the piezoresistive effect and the large mismatch of the resistance manufactured by the traditional method, the piezoresistive pressure sensor often has large sensitivity drift, zero output and zero drift. These disadvantages have limited the use of piezoresistive pressure sensors in high-end, accurate pressure measurement applications. Since the 20 actual 80 s, the technicians in the field have conducted extensive research on zero output and its drift, and found that the main factors affecting the zero drift include layout errors, offset errors in the processing process, and irregularities of diffusion resistance.

How to solve the problem of zero drift caused by process variation well and to manufacture a high-quality piezoresistive pressure sensor is a problem that applicants have addressed and intend to overcome.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention provides a manufacturing method of a piezoresistive gage pressure sensor.

In order to achieve the purpose, the invention adopts the technical scheme that: a method of manufacturing a piezoresistive gage pressure sensor; the method is characterized in that: comprises that

Step 1: forming a first deep groove of an annular structure of an etching stop layer for manufacturing a cavity on the front surface of the SOI substrate by using a deep reactive ion etching method; wherein, a middle buried oxide layer is arranged in the SOI substrate; the buried oxide layer is used for manufacturing an etching stop layer when the cavity is manufactured;

step 2: filling silicon oxide in the first deep groove, and then removing the silicon oxide layer on the surface;

and step 3: taking the top layer of the SOI substrate as a seed layer, and growing an epitaxial silicon layer;

and 4, step 4: manufacturing four piezoresistors of the pressure sensor on the epitaxial silicon layer and forming a Wheatstone bridge structure;

and 5: after the front side is finished, forming a second deep groove for manufacturing the cavity by using a double-sided photoetching method and a deep reactive ion etching method; filling silicon oxide in the second deep groove, and selectively removing the silicon oxide at the bottom of the second deep groove by using a dry etching method; and forming a final cavity by using a wet etching solution of silicon.

In a further improvement, the opening size of the first deep groove is 0.5 to 1.5 um.

In a further improvement, the annular structure is a circular ring or a polygonal ring.

In a further improvement, the top layer of the SOI substrate is monocrystalline silicon.

The further improvement, step 2 also includes utilizing the dry etching method to remove top silicon layer and buried oxide layer in the deep groove I, and then utilizing the deep reactive ion etching method to etch the silicon substrate of SOI substrate in the deep groove I; the etching depth of the first deep groove is larger than 10 um.

In a further improvement, the step 2 is as follows: filling an oxidation protection layer on the side wall and the bottom of the first deep groove through an oxidation process; and after the filling is finished, removing the oxide layer on the surface of the SOI substrate.

In a further improvement, the epitaxial layer depth of step 3 is determined by the range of the pressure sensor.

In a further improvement, the step 5 is as follows: s51, deeply etching the bottom surface of the SOI substrate by using a dry method to form a second deep groove for manufacturing the cavity; s52, depositing a barrier layer on the side wall and the bottom of the second deep groove; s53, removing the barrier layer at the bottom of the second deep groove by utilizing an anisotropic etching method, and reserving the side wall of the second deep groove to form a side wall protective layer; and S54, taking the side wall protection layer of the second deep groove as a mask, and continuously utilizing anisotropic wet etching to finally form a cavity.

The further improvement is that the deep groove II adopts a hole-shaped design, and the size of the hole-shaped design is smaller than that of the inner ring of the deep groove I.

In the further improvement, during wet etching, the middle buried oxide layer of the SOI substrate, the oxide layer on the side wall of the deep groove and the oxide layer on the side wall of the deep groove are all self-stop barrier layers for wet etching.

After the technical scheme of the application is adopted, the deviation between the edge position of the cavity (namely the cavity boundary formed by the inner diameter of the first deep groove) and the position of the piezoresistance is controlled by the front photoetching alignment capability. The back cavity of the traditional piezoresistive gauge pressure sensor is positioned by aligning the front photoetching mark with the back photoetching process, so that in the traditional process, the error between the edge position of the cavity and the piezoresistive position comprises the sum of the registration error between the back photoetching process and the front photoetching process and the process error after the back cavity is corroded by a wet method.

In a common semiconductor processing procedure, front-side photoetching adopts a rear layer to register a front layer between devices of the same model, and the registration accuracy of the front layer and the rear layer is very high and is generally controlled below 0.5 um. The precision of front-back photoetching alignment is generally controlled below 5um due to the influence of different photoetching machine models and capabilities, and the distance between 4 piezoresistive resistors and the boundary of a sensing film can be influenced by a larger photoetching alignment error, which is an important reason for causing zero drift of the pressure sensor.

By adopting the manufacturing method of the invention, the problem of zero drift caused by process deviation is greatly reduced by utilizing the high consistency of the same type and the same process capability of front-side photoetching. Compared with the piezoresistive gauge pressure sensor manufactured by the traditional manufacturing process, the manufactured piezoresistive gauge pressure sensor has good uniformity of devices in a chip and repeatability of devices among chips, and is more suitable for mass production.

Drawings

Fig. 1 is a schematic plan view of a piezoresistive pressure sensor structure.

FIG. 2 is a cross-sectional view of a first embodiment of a process for manufacturing a piezoresistive gage pressure sensor.

FIG. 3 is a second cross-sectional view of a manufacturing process of a piezoresistive gage pressure sensor.

Fig. 4 is a cross-sectional structural schematic diagram three of a manufacturing process of the piezoresistive gage pressure sensor.

Fig. 5 is a cross-sectional view of a fourth embodiment of a manufacturing process of the piezoresistive gage pressure sensor.

Fig. 6 is a cross-sectional schematic illustration of a fifth manufacturing process for a piezoresistive gage pressure sensor.

Fig. 7 is a cross-sectional view of a sixth embodiment of a manufacturing process for a piezoresistive gage pressure sensor.

Fig. 8 is a seventh cross-sectional view of a manufacturing process of the piezoresistive gage pressure sensor.

Fig. 9 is a cross-sectional view of an eighth embodiment of a manufacturing process for a piezoresistive gage pressure sensor.

Fig. 10 is a cross-sectional schematic illustration nine of a manufacturing process of a piezoresistive gage pressure sensor.

Fig. 11 is a cross-sectional schematic diagram ten of a manufacturing process of a piezoresistive gage pressure sensor.

Fig. 12 is a cross-sectional view showing an eleventh example of a manufacturing process of the piezoresistive gage pressure sensor.

Fig. 13 is a cross-sectional view twelve illustrating a manufacturing process of the piezoresistive gage pressure sensor.

Fig. 14 is a thirteen schematic sectional view of a manufacturing process of the piezoresistive gage pressure sensor.

Fig. 15 is a fourteenth cross-sectional view of a manufacturing process of the piezoresistive gage pressure sensor.

Fig. 16 is a schematic fifteen cross-sectional view of a manufacturing process of the piezoresistive gage pressure sensor.

Fig. 17 is a cross-sectional schematic view sixteen of a manufacturing process of a piezoresistive gage pressure sensor.

Fig. 18 is a schematic seventeenth cross-sectional view of a process of manufacturing the piezoresistive gage pressure sensor.

Fig. 19 is a cross-sectional structural schematic eighteen of a manufacturing process of a piezoresistive gage pressure sensor.

Fig. 20 is a nineteenth schematic cross-sectional view of a process for manufacturing a piezoresistive gage pressure sensor.

Detailed Description

The preferred embodiments of the present invention will be further explained with reference to the accompanying drawings so that the technical solutions of the present invention can be better understood.

A method of manufacturing a piezoresistive gage pressure sensor, comprising the steps of 1: forming a first deep groove of an annular structure of an etching stop layer for manufacturing a cavity on the front surface of the SOI substrate with the middle buried oxide layer arranged inside by utilizing a deep reactive ion etching method; the intermediate buried oxide layer plays a role of an etching stop layer when the cavity is manufactured. The first deep groove is designed to be a closed annular structure, and the first deep groove defines the transverse dimension of the cavity of the pressure sensor. Then removing the top silicon layer and the middle buried oxide layer in the first deep groove by using a dry etching method, and etching the silicon substrate of the SOI substrate in the first deep groove by using a deep reactive ion etching method; the etching depth of the first deep groove is larger than 10 um.

With respect to SOI substrates, the most mature SOI substrates currently on the market using the most processes are prepared by SIMOX or smart cut techniques, with a top silicon thickness typically in the range of 0.1um to 0.2um, and an intermediate buried oxide thickness in the range of 0.1um to 2um, with a typical value of 0.5 um. The thickness of the SOI substrate that can be used in the present invention is obviously not limited thereto, and those skilled in the art can adjust the thickness according to actual needs.

FIG. 1 shows the most critical layers and structures in the fabrication process of a piezoresistive gage pressure sensor, including front side deep trench one and back side deep trench two forming a cavity and a bridge resistor on an SOI substrate. As can be seen from fig. 1, the projection of the first deep groove is a quadrilateral ring, and the projection of the first deep groove may be a circular ring or another shape of opposite side ring structure. In addition, the shape and/or depth of the first deep groove can be adjusted according to actual needs (adjustable). It is noted that the structure of the first deep groove is annular, and the annular dimension of the first deep groove is designed according to the size of the pressure chip; typical values of the opening size of the first deep trench are 0.5 to 1.5um (the opening size is not too large, so that the first deep trench can be conveniently filled in the subsequent process). To better illustrate the formation of the first deep trench, please refer to fig. 2-5, wherein fig. 2 shows an SOI substrate with an intermediate buried oxide layer, and fig. 3-5 show the three states of the first deep trench, the trench passing through the intermediate buried oxide layer, and the trench terminating.

Step 2: and filling silicon oxide in the first deep groove, and then removing the silicon oxide layer on the surface.

Referring to fig. 6, in fig. 6, an oxidation protection layer is filled on the sidewall and bottom of the first deep trench (the protection layer determines that the first deep trench can be used as a barrier layer in a subsequent wet etching process for the backside), after the filling, the oxide layer on the surface of the SOI substrate is removed, and the oxide layer on the surface can be removed by a wet etching process (BOE or HF), a dry etching process or a chemical mechanical polishing process (shown in fig. 7).

And step 3: and taking the monocrystalline silicon on the top layer of the SOI substrate as a seed layer to grow an epitaxial silicon layer. As shown in fig. 8, an epitaxial layer is grown with the top silicon layer of the SOI as a seed layer, and the formed epitaxial layer is a pressure sensing film layer of the pressure sensor. The larger the pressure range is, the thicker the sensing film layer of the pressure sensor needs to be, and the thinner sensing film layer can not bear the action of higher pressure, so that the strain layer is damaged, and the device fails. Those skilled in the art will appreciate that the thickness of the epitaxial layer grown is determined based on the span of the pressure sensor.

And 4, step 4: four piezoresistors of the pressure sensor are fabricated on the epitaxial silicon layer and form a Wheatstone bridge configuration. As shown in fig. 9 to 14, fig. 9 to 14 are schematic reference diagrams of the stages of fabricating the device layer of the piezoresistive pressure sensor on the epitaxial layer, and the fabrication process mainly includes the steps of forming the piezoresistors by high-concentration implantation, forming the silicon oxide isolation layer and the contact holes, forming the metal wiring layer, and forming the passivation PAD protection layer. Those skilled in the art will recognize that since the structure of the device layer of the piezoresistive pressure sensor is well-established and the features of this patent are not in the structure of the device layer, the detailed process of the device layer will not be described herein and reference may be made to the conventional design and process parameters in the art.

And 5: after the front side is finished, forming a second deep groove for manufacturing the cavity by using a double-sided photoetching method and a deep reactive ion etching method; filling silicon oxide in the second deep groove, and selectively removing the silicon oxide at the bottom of the second deep groove by using a dry etching method; and forming a final cavity by using a wet etching solution of silicon.

Fig. 15 to 20 are schematic reference views at various stages of preparing a second deep trench and a cavity, where the second deep trench is only a channel for subsequent wet etching, and the photolithographic alignment accuracy with the front level does not affect the positional deviation of the piezoresistive position from the cavity edge. The specific manufacturing process comprises the following steps: s51, deeply etching the bottom surface of the SOI substrate by using a dry method to form a second deep groove for manufacturing the cavity; a second deep groove adopts a hole-shaped design, the size of the second deep groove is generally smaller than that of the inner ring of the first deep groove, and S52, a barrier layer is deposited on the side wall and the bottom of the second deep groove; and S53, removing the barrier layer at the bottom of the second deep trench by utilizing an anisotropic etching method, and reserving the side wall of the second deep trench to form a side wall protective layer (the protective layer determines that the first deep trench can be used as a barrier layer in subsequent wet etching). And S54, taking the side wall protection layer of the second deep groove as a mask, and continuously utilizing anisotropic wet etching to finally form a cavity.

From the above description, those skilled in the art can clearly understand the technical solutions of the present application, and in order to better explain the technical solutions of the present application, the principles of the present application will be further explained.

The depth of the front deep groove I and the back deep groove II determines the longitudinal dimension of the pressure sensor cavity. The first deep groove determines the transverse dimension of the pressure cavity, and the accuracy of the transverse dimension of the pressure cavity directly influences the zero drift of the device. During wet etching, the middle buried oxide layer of the SOI substrate, the oxidation protection layer on the side wall of the first deep groove and the oxidation protection layer on the side wall of the second deep groove are all barrier layers for wet etching, so that the final size of the cavity can be accurately controlled.

It is also understood that the arrangement and adjustment of the positions of the units in the sensor structure can be freely performed according to the needs, and the invention is within the protection scope of the present application. In the present invention, the shape and depth of the first and second deep grooves and the position and size of the piezoresistive means may be arbitrarily adjusted as required.

The above embodiments are merely illustrative of the technical concept and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the content of the present invention and implement the present invention, and not to limit the protection scope of the present invention, and all equivalent changes or modifications made according to the spirit of the present invention should be covered by the protection scope of the present invention.