KR102160678B1 - Manufacturing method for Silicon nanowire-based piezoresistive pressure sensor - Google Patents

Abstract

The present invention provides a method for manufacturing a piezoresistive pressure sensor based on a nanowire. According to an embodiment of the present invention, the method for manufacturing a piezoresistive pressure sensor comprises the steps of: preparing a first substrate including a floated silicon nanowire and a sensor structure; preparing a second substrate with a silicon insulating film formed on one surface thereof; combining the first and second substrates so that the silicon insulating film of the second substrate is combined with the silicon nanowire floated on the first substrate and the sensor structure; and forming a first recessed area on the other surface of the second substrate. According to one embodiment of the present invention, the method for manufacturing the piezoresistive pressure sensor based on the nanowire applies a manufacturing method that a thin film deposited on one surface of the second substrate can be utilized as a diaphragm unlike a conventional manufacturing method of depositing a silicon nitride film directly on the nanowire. Accordingly, since a void phenomenon around the nanowire, which inevitably occurs during conventional diaphragm deposition, is not implemented in the present invention, the implementation of performance of a desired diaphragm becomes easier. Since the top of a second recessed area previously formed on the first substrate is implemented in a closed structure, the second depression area can be used jointly. That is, the closed structure required for operation of the piezoresistive pressure sensor.

Description

Manufacturing method for silicon nanowire-based piezoresistive pressure sensor {Manufacturing method for Silicon nanowire-based piezoresistive pressure sensor}

The present invention relates to a method of manufacturing a pressure sensor of a piezoresistance sensing method based on a silicon nanowire, and more specifically, a method of manufacturing a pressure sensor that detects a change in external pressure using the piezoresistive property of a silicon nanowire attached to a diaphragm It is about.

[Explanation of nationally supported R&D]

This study was made with the support of the Ministry of Health and Welfare, a technology development project for commercialization of micro medical robots (development of a diagnostic module for micro medical robots, task identification number: 1465029326, detailed task number: HI19C0642040019).

1 is a conceptual diagram for explaining a conventional nanowire-based pressure sensor, and the pressure sensor corresponds to a pressure sensor of a resistive type sensing method based on a MEMS (Micro-Electro-Mechanical System, MEMS) process. do. The pressure sensor of FIG. 1 includes silicon nanowires having excellent piezoresistive properties as a sensing structure. Specifically, it is a structure in which nanowires are in a diaphragm structure formed of a material such as a silicon nitride film, and a cavity is formed under the diaphragm structure. The diaphragm is suspended with a specific thickness and area for the purpose of sensing input pressure. At this time, the pressure inside the cavity must be kept constant against changes in external pressure, and in order to realize this, the diaphragm is designed in a closed structure. In the MEMS-based pressure sensor, a diaphragm is deformed by an applied external pressure and a stress is generated in the nanowires to detect a level at which resistance changes. The input pressure level can be distinguished by quantizing the amount of resistance change at this time.

In order to manufacture a pressure sensor based on a silicon nanowire as shown in FIG. 1, a silicon nitride film must be formed to include the nanowires to form a diaphragm. Conventionally, a process of forming a diaphragm by forming a silicon nitride film is performed through chemical vapor deposition or the like. However, in this conventional process, in the process of forming the silicon nitride film, void spaces (hereinafter, voids or voids) of the silicon nitride film inevitably occur at the periphery of the nanowire and the edge of the previously formed cavity, and the diaphragm performance is degraded by the void. Occurs.

In addition, in order to maintain a constant pressure level in the cavity, not only the diaphragm is implemented in a closed structure, but in the conventional manufacturing method, the lower region of the cavity must be manufactured in a closed structure through an additional wafer bonding process. There was a problem.

The present invention is to solve the problems of the prior art as mentioned above, it is possible to implement a diaphragm in which voids do not occur, and to solve the complexity of the process sequence, based on the piezoresistive effect of silicon nanowires It provides a method of manufacturing a sensitive pressure sensor.

A method of manufacturing a nanowire-based piezoresistive pressure sensor according to an embodiment of the present invention includes: preparing a first substrate including a suspended silicon nanowire and a sensor structure; Preparing a second substrate having a silicon insulating film formed on one surface thereof; Bonding the first substrate and the second substrate so that the silicon insulating layer of the second substrate is coupled to the silicon nanowires and the sensor structure floating on the first substrate; And forming a first recessed region on the other surface of the second substrate.

In the method of manufacturing a nanowire-based piezoresistive pressure sensor according to an embodiment of the present invention, unlike a conventional manufacturing method in which a silicon nitride film is deposited directly on the nanowire, a thin film deposited on one surface of the second substrate is used as a diaphragm. A manufacturing method that can be utilized was applied. Accordingly, since the conventional void phenomenon around the nanowires, which inevitably occurs during diaphragm deposition, is not implemented in the present invention, it becomes easier to implement the desired diaphragm performance.

In addition, in the manufacturing method of the nanowire-based piezoresistive pressure sensor according to an embodiment of the present invention, since the upper portion of the second depression previously formed in the first substrate is implemented in a closed structure with only one wafer bonding Can be used jointly. That is, the closed structure required for the operation of the piezoresistive pressure sensor can be easily implemented without performing an additional process.

1 is a conceptual diagram illustrating a conventional nanowire-based pressure sensor.
2 is a flow chart of a method of manufacturing a nanowire-based piezoresistive pressure sensor according to an embodiment of the present invention.
3A to 3C show results of performing a silicon oxide film deposition process on the first substrate.
4A to 4C illustrate a state in which a photoresist is patterned on the first substrate.
5A to 5C illustrate a state in which an oxide layer is patterned through a silicon dioxide dry etching process and a photoresist is removed.
6A to 6C illustrate a result of forming a nanowire, a sensor structure, and a corresponding second depression region according to a silicon oxide layer pattern through a silicon dry etching process.
7A and 7B show results of forming an oxide film through a thermal oxidation process.
8A and 8B are views showing a result of etching and removing an oxide film located on a vertical surface of a second recessed region through a silicon dioxide dry etching process.
9A and 9B show results of additionally etching the second recessed area through a silicon dry etching process.
10A and 10B illustrate a state in which silicon nanowires and sensor structures are suspended through a wet etching process.
11 shows a second substrate having a silicon insulating layer formed on one surface thereof.
12A and 12B illustrate a state in which one surface of a first substrate and one surface of a second substrate are combined.
13A and 13B illustrate a result of patterning a photoresist on the other surface of the second substrate through an exposure process.
14A and 14B illustrate a state in which a diaphragm is formed by forming a first recessed region on the other surface of the second substrate.

For a detailed description of the present invention to be described later, reference is made to the accompanying drawings, which illustrate specific embodiments in which the present invention may be practiced. Detailed description embodiments are provided for the purpose of disclosing a detailed description for a person skilled in the art to practice the present invention.

Each of the embodiments of the present invention may describe a case that is different from each other, but this does not mean that the respective embodiments are mutually exclusive. For example, specific shapes, structures, and characteristics described in connection with one embodiment of the detailed description may be similarly implemented in other embodiments without departing from the spirit and scope of the present invention. In addition, it should be understood that the positions or arrangements of individual components of the embodiments disclosed herein may be variously changed without departing from the spirit and scope of the present invention. In the accompanying drawings, the size of each component may be exaggerated for description, and it is not necessary to be the same or similar to the size actually applied.

2 is a flow chart of a method of manufacturing a nanowire-based piezoresistive pressure sensor according to an embodiment of the present invention.

Referring to FIG. 2, a method of manufacturing a nanowire-based piezoresistive pressure sensor according to an embodiment of the present invention includes preparing a first substrate including a suspended silicon nanowire and a sensor structure (S100); Preparing a second substrate on which a silicon insulating film is formed on one surface (S110); Combining the first substrate and the second substrate so that the silicon insulating layer of the second substrate is coupled to the silicon nanowires and the sensor structure floating on the first substrate (S120); And forming a first recessed region on the other surface of the second substrate (S130). Here, the step of preparing the first substrate (S100) and the step of preparing the second substrate (S110) are sequentially described for ease of explanation, but there is no temporal relationship between the steps (S100, S110). . The step of preparing the first substrate (S100) and the step of preparing the second substrate (S110) may be performed simultaneously. Hereinafter, detailed steps included in each step will be described in detail with reference to FIGS. 3A to 12C.

Preparing the first substrate (S100) may include shaping the silicon nanowire pattern and the sensor structure pattern on a silicon oxide film formed on one surface of the first substrate; Etching a region of the first substrate that does not overlap with the silicon oxide layer through a silicon dry etching process to form a second recessed region and determining the thickness of the silicon nanowire and the sensor structure; Determining widths of the silicon nanowires and the sensor structure by performing a thermal oxidation process on the first substrate; Removing the oxide film formed on the bottom surface of the second recessed region by the thermal oxidation process; Further performing a silicon dry etching process to expand a vertical region of the second recessed region; And floating the silicon nanowires and the sensor structure through a wet etching process. Hereinafter, the step of preparing the first substrate (S100) will be described in order with reference to FIGS. 3A to 10B.

3A to 3C show results of performing a silicon oxide film deposition process on the first substrate. 3A is a perspective view showing the overall structure of the first substrate, FIG. 3B is a plan view of the first substrate, and FIG. 3C is a cross-sectional view of the first substrate taken along lines A-A', B-B', and C-C'. It is a cross-sectional view respectively shown.

3A to 3C, a silicon oxide film 102 may be formed on one surface of the first substrate 100. The first substrate 100 may be a silicon on insulator (SOI) substrate. The first substrate 100 may have a structure in which silicon 101, a silicon oxide film 102, and silicon 101 are sequentially stacked. A silicon oxide film 102 may be further formed on the upper silicon 101. The silicon oxide layer 102 may be formed by various methods, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), and thermal oxidation.

4A to 4C illustrate a state in which the photoresist 103 is patterned on the first substrate 100. 5A to 5C illustrate a state in which an oxide layer is patterned through a silicon dioxide dry etching process and a photoresist is removed.

The step of shaping the silicon nanowire pattern and the sensor structure pattern on a silicon oxide layer formed on one surface of the first substrate may include patterning a photoresist 103 on the silicon oxide layer through a photolithography process, and the patterning. It may include shaping the silicon nanowire pattern and the sensor structure pattern through a silicon dioxide dry etching process according to the photosensitive agent.

Patterning the photoresist 103 on the silicon oxide layer 102 may be performed through a photolithography, and the photoresist pattern 103 is used to distinguish the nanowire pattern 103A from the sensor structure pattern 103B. Can be created. The nanowire pattern 103A is a pattern for forming a silicon nanowire, and may be patterned to have a smaller width than the sensor structure pattern 103B. Referring to FIGS. 4A to 4C, it can be seen that the nanowire pattern 103A is patterned to have a smaller width than the sensor structure pattern 103B. Here, the sensor structure may include an electrode and other components necessary to detect a level at which resistance is changed due to the occurrence of stress in the nanowire.

The silicon oxide layer 102 may be patterned through a silicon dioxide dry etching process so as to correspond to the pattern 103 formed on the silicon oxide layer 102. 5A to 5C, it can be seen that the nanowire pattern 102A and the sensor structure pattern 102B are generated through the above process of selectively etching the silicon oxide layer 102. The above pattern may be used to implement a silicon nanowire and a sensor structure on the first substrate 100 in the next step.

6A to 6C illustrate results of forming a silicon nanowire, a sensor structure, and a second recessed region 104 through a silicon dry etching process. 6A to 6C, an etching process for silicon 101 in which the silicon oxide layer 102 is not disposed may be performed through a silicon dry etching process. Since the silicon oxide layer 102 is not disposed thereon, an area etched through a silicon dry etching process may be defined as the second recessed area 104. Here, the nanowire pattern 102A and the sensor structure pattern 102B are a kind of mask, and may prevent etching of the silicon 101 disposed below. As shown in FIG. 6C, a silicon nanowire 101A and a sensor structure 101B may be formed in correspondence with the nanowire pattern 102A and the sensor structure pattern 102B included in the silicon oxide layer 102, respectively. . The height H of the etched silicon 101 may be defined as the thickness of the silicon nanowire 101A. By controlling the silicon dry etching process conditions, the desired thickness of the silicon nanowire can be realized.

7A and 7B show results of forming an oxide film through a thermal oxidation process. The silicon 101 of the first substrate 101 may be oxidized through a thermal oxidation process to form an oxide film 102 ′.

7A and 7B, the oxide film 102 ′ may be formed as the silicon 101 is thermally oxidized from the surface to the inside. Accordingly, an oxide film 102' is formed from one surface of the silicon 101 located in the second recessed region 104 to the inside. That is, the oxide film 102 ′ may be formed not only on the silicon 101 but also on the silicon nanowire 101A and the sensor structure 101B. As the oxide layer 102' is formed, the width of the silicon nanowire 101A may be reduced. That is, the time of the oxide film forming process can be adjusted so that the desired width W of the silicon nanowire 101A is reached. The width W of the silicon nanowire 101A may be determined according to the formation of the oxide layer 102'. That is, by individually performing the above-described silicon dry etching process conditions and the oxide layer process, the desired thickness and width of the silicon nanowires may be determined. In addition, through such a process, the silicon nanowire 101A and the sensor structure 101B are surrounded by an oxide layer 102 on the upper side and an oxide layer 102 ′ generated through a thermal oxidation process.

8A and 8B are views showing the result of etching and removing the oxide film located on the vertical surface of the second recessed area through a silicon dioxide dry etching process, and FIGS. 9A and 9B are additional etching of the second recessed area through a silicon dry etching process. Shows the result.

Referring to FIGS. 8A and 8B, it can be seen that the oxide layer 102' corresponding to the second recessed region 104 is etched through a silicon dioxide dry etching process. That is, the oxide layer 102 ′ formed on the bottom surface of the second recessed region 104 may be removed through a silicon dioxide dry etching process.

In addition, referring to FIGS. 9A and 9B, silicon 101 corresponding to the second recessed region 104 may be etched through a silicon dry etching process. The oxide layer 102 positioned on the silicon nanowire 101A and the sensor structure 101B functions as a mask, and the remaining portion of the silicon 101 that does not overlap in a vertical direction on the oxide layer 102 may be vertically etched. . That is, the vertical region of the second recessed region 104 may be expanded by further performing a silicon dry etching process. Here, since the first substrate 101 is an SOI substrate, after the silicon dry etching process, the buried oxide 102 may be exposed to the outside. The depth that is further etched through the silicon dry etching process determines the height of the cavity required for the operation of the pressure sensor.

Through the silicon dioxide dry etching process and an additional silicon dry etching process, a silicon nanowire 101A to be suspended and a lower silicon structure of the sensor structure 101B may be formed. Here, the lower silicon structure corresponds to a structure removed in a wet etching process described later.

10A and 10B illustrate a state in which a silicon nanowire and a sensor structure are suspended through a wet etching process.

10A and 10B, the silicon nanowire 101A and the sensor structure 101B may be floated through a wet etching process. That is, a lower structure generated through a silicon dioxide dry etching process and an additional silicon dry etching process may be removed. The lower silicon structure exposed through the silicon dry etching process may be removed through a wet etching process. Here, in the lower silicon structure, the oxide layers 102 and 103 are not present on the sidewalls and are exposed, and may be removed by a wet etching process. As an alkaline aqueous solution having anisotropic etching properties in such a wet etching process, potassium hydroxide (KOH), tetramethyl-ammonium-hydroxide (TMAH), or ethylene diamine pyrocatechol, EDP) can be utilized. Through this, the silicon nanowire 101A and the lower silicon region of the sensor structure 101B are etched, and the silicon nanowire 101A and the sensor structure 101B may be suspended.

Through this process, a first substrate including the suspended silicon nanowires and the sensor structure may be prepared.

As shown in FIG. 11, a silicon insulating layer 201 may be formed on one surface of the second substrate 200 (S110 ).

11 shows a second substrate having a silicon insulating layer formed on one surface thereof. Referring to FIG. 11, the second substrate 200 may be a silicon substrate, and the silicon insulating layer 201 formed on one surface may be a silicon oxide layer or a silicon nitride layer. The silicon insulating layer 201 may be formed to have a thin thickness. The silicon insulating layer 201 is combined with the silicon nanowire 101 to be used as a diaphragm structure. The silicon insulating layer 201 may be formed through a chemical vapor deposition (CVD) method, but is not limited thereto.

After the first substrate 100 and the second substrate 200 are prepared, the first substrate 100 and the second substrate 200 are combined (S120).

12A and 12B illustrate a state in which one surface of a first substrate and one surface of a second substrate are combined. 12A and 12B, the first substrate (101A) and the sensor structure 101B floating on the first substrate 100 are combined with the silicon insulating layer 201 of the second substrate 200. 100) and the second substrate 200 may be combined. That is, the first substrate 100 and the second substrate 200 may be combined so that one surface of the first substrate 100 and one surface of the second substrate 200 contact each other. The first substrate 100 and the second substrate 200 may be combined so that the silicon insulating layer 201 of the second substrate 200 contacts the oxide layer 102 of the first substrate 100. The oxide film 102 of the first substrate 100 is a structure formed on the silicon nanowire 101A and the sensor structure 101B, and is in a mutually coupled state, and the silicon insulating film 201 and the oxide film 102 are in contact with each other. By bonding, the silicon nanowire 101A in a suspended state is also bonded to the silicon insulating film 201.

This bonding step may utilize thermal compression bonding among wafer bonding methods. However, the present invention is not limited thereto, and fusion bonding, eutectic bonding, or depending on the material type of the bonding surface of the first substrate 100 and the second substrate 200 or according to the bonding material. The step S110 may be performed through various wafer bonding methods such as anodic bonding.

In addition, as the first substrate 100 and the second substrate 200 are combined, the first substrate 100 is closed by the second substrate 200 and the first substrate 100 has a closed structure. The second recessed region 104 previously formed therein functions as a cavity and maintains a constant pressure level.

Next, a first recessed area is formed on the other surface of the second substrate 200 (S130).

In this step (S120), a photoresist is applied to the other surface of the second substrate 200, followed by patterning the other surface of the second substrate 200 and a first depression corresponding to the cavity of the first substrate through a silicon dry etching process. Forming a region and removing the photosensitizer. That is, the first depression region may be formed on the second substrate so that the shape or size (diameter) of the cavity corresponds.

13A and 13B illustrate a result of patterning a photoresist on the other surface of the second substrate through an exposure process. The circular pattern 202 shown in FIGS. 13A and 13B is exemplary, and may have various shapes according to the shape of the diaphragm structure included in the pressure sensor. In addition, the diameter of the depression structure according to the silicon dry etching in the next step is determined according to the size of the exposure pattern performed in this step, and through this, the diameter size of the desired diaphragm can be implemented.

14A and 14B illustrate a state in which a diaphragm is formed by forming a first recessed region on the other surface of the second substrate. The first depression region 203 may be formed in the inner direction with respect to the other surface of the second substrate 200 according to the exposure pattern, and the photoresist 202 is removed. After proceeding to the photosensitive agent removal step, one surface of the second substrate 200 is patterned with a photosensitive agent to implement a first depression region 203 through silicon dry etching for the distinguished etching region The silicon insulating film 201 deposited on the surface can operate as a floating diaphragm. The first depression area 203 may be formed by etching the second substrate 200 so that the silicon insulating layer 201 is exposed to the outside. The floating silicon insulating film 201 can function as a diaphragm, which is a thin plate that is deformed according to external pressure, and the nanowire 101A bonded to the silicon insulating film 201 generates stress according to the deformation of the diaphragm, resulting in resistance. Can change. The sensor structure 101B connected to the nanowire 101A transmits the resistance change signal of the nanowire 101A to the electrode. That is, a pressure sensor based on nanowires may be provided.

In the method of manufacturing a nanowire-based piezoresistive pressure sensor according to an embodiment of the present invention, unlike a conventional manufacturing method in which a silicon nitride film is deposited directly on the nanowire, a thin film deposited on one surface of the second substrate is used as a diaphragm. A manufacturing method that can be utilized was applied. Accordingly, since the conventional void phenomenon around the nanowires, which inevitably occurs during diaphragm deposition, is not implemented in the present invention, it becomes easier to implement the desired diaphragm performance.

In addition, in the manufacturing method of the nanowire-based piezoresistive pressure sensor according to an embodiment of the present invention, since the upper portion of the second depression previously formed in the first substrate is implemented in a closed structure with only one wafer bonding Can be used jointly. That is, the closed structure required for the operation of the piezoresistive pressure sensor can be easily implemented without performing an additional process.

The present invention described above has been described with reference to the embodiments shown in the drawings, but these are only exemplary and those of ordinary skill in the art will appreciate that various modifications and variations of the embodiments are possible therefrom. . However, such modifications should be considered to be within the technical protection scope of the present invention. Therefore, the true technical protection scope of the present invention should be determined by the technical spirit of the appended claims.

100: first substrate 101: silicon
102: silicon oxide film 102': oxide film
103: photoresist 104: second depression region
200: second substrate 201: silicon insulating film
202: photosensitive agent 203: first recessed region

Claims (12)

Preparing a first substrate including the suspended silicon nanowires and the sensor structure;
Preparing a second substrate having a silicon insulating film formed on one surface thereof;
Bonding the first substrate and the second substrate so that the silicon insulating layer of the second substrate is coupled with the silicon nanowires and the sensor structure floating on the first substrate; And
A method of manufacturing a nanowire-based piezoresistive pressure sensor comprising forming a first recessed region on the other surface of the second substrate. The method of claim 1,
Preparing the first substrate,
A step of shaping the silicon nanowire pattern and the sensor structure pattern on a silicon oxide film formed on one surface of the first substrate;
A b step of etching a region of the first substrate that does not overlap with the silicon oxide layer through a silicon dry etching process to form a second recessed region and determining a thickness of the silicon nanowire and the sensor structure;
A step c of determining widths of the silicon nanowires and the sensor structure by performing a thermal oxidation process on the first substrate;
A d step of removing the oxide film formed on the bottom surface of the second recessed region by the thermal oxidation process;
An e step of further performing a silicon dry etching process to expand a vertical area of the second recessed area; And
A method of manufacturing a pressure sensor of a piezoresistive method based on a nanowire, comprising the step f of floating the silicon nanowire and the sensor structure through a wet etching process. The method of claim 2,
The step a includes patterning a photoresist on the silicon oxide layer through a photolithography process, and shaping the silicon nanowire pattern and the sensor structure pattern through a silicon dioxide dry etching process according to the patterned photoresist. Nanowire-based piezoresistive pressure sensor manufacturing method comprising. The method of claim 2,
The method of manufacturing a nanowire-based piezoresistive pressure sensor, characterized in that the thickness and width of a desired silicon nanowire are determined by individually performing the b and c step. The method of claim 2,
Manufacturing of a nanowire-based piezoresistive pressure sensor, characterized in that the silicon nanowire to be suspended in the f-th step and the lower silicon structure of the sensor structure are formed through the d step and the e step Way. The method of claim 2,
In the wet etching process of step f, potassium hydroxide (KOH), tetramethyl-ammonium-hydroxide (TMAH), or ethylenedimine pyrocatechol as an alkaline aqueous solution having anisotropic etching properties. (ethylene diamine pyrocatechol, EDP) is a nanowire-based piezoresistive method of manufacturing a pressure sensor, characterized in that it is utilized. The method of claim 1,
The method of manufacturing a nanowire-based piezoresistive pressure sensor, wherein the silicon insulating layer is a silicon oxide layer or a silicon nitride layer. The method of claim 7,
The silicon insulating layer is formed on the second substrate through chemical vapor deposition (CVD). A method of manufacturing a pressure sensor based on a nanowire piezoresistive method. The method of claim 2,
The step of combining the first substrate and the second substrate,
Characterized in that one surface of the first substrate and one surface of the second substrate are coupled,
A method of manufacturing a nanowire-based piezoresistive pressure sensor in which the second recessed region functions jointly by combining the first substrate and the second substrate. The method of claim 9,
The step of combining the first substrate and the second substrate,
A method of manufacturing a nanowire-based piezoresistive pressure sensor bonded through thermal compression bonding, fusion bonding, eutectic bonding, or anodic bonding. The method of claim 9,
The method of manufacturing a nanowire-based piezoresistive pressure sensor, wherein the first depression region is formed on the other surface of the second substrate so as to correspond to the cavity. The method of claim 11,
The first recessed region is a method of manufacturing a nanowire-based piezoresistive pressure sensor, characterized in that the silicon insulating layer formed on one surface of the second substrate is formed by dry silicon etching so that the floating diaphragm can operate.

Images