JPH0650255B2 - Method for manufacturing silicon microsensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a silicon microsensor utilizing anisotropic etching of silicon, and more particularly to a method of manufacturing a support portion.

<Background of the Invention> In sensors that utilize heat balance, such as infrared sensors, flow sensors, and gas sensors, miniaturization and thinning of the heat generation part and detection part enable high sensitivity, high-speed response, and low power consumption. Become. Further, in a sensor having a movable portion such as a pressure sensor, a vibration sensor, and an acceleration sensor, high sensitivity and miniaturization can be achieved by thinning the movable portion and its supporting portion. As described above, by forming the sensor unit with a very thin support, it is possible to increase the sensitivity of the sensor, reduce the power consumption, miniaturize the sensor chip, and combine and integrate various sensors. For these reasons, the development of so-called silicon microsensors, in which the oxide film on the very surface layer of the silicon substrate and the high-concentration boron-doped layer are left and the underlying silicon is removed by etching to form the support and the sensor part, has been actively pursued. Is. The shape of the support is various, such as a bridge, a cantilever, a diaphragm. A schematic view of the support is shown in FIGS. 5 (A) (B) (C). Next, a method for forming the above-mentioned thin support will be described.

When a silicon single crystal is etched with an alkaline solution such as EPW solution (a mixed solution of ethylenediamine / pyrocatechol / water) NaOH or KOH, there is a crystal axis anisotropy in which the etching rate greatly varies depending on the crystal axis. That is, the etching rate in the <111> direction is extremely slow compared to the other <100> and <110> directions. Due to this property, for example, when a hole is formed in a (100) wafer by etching using SiO ₂ as a mask, an inverted pyramid-shaped hole surrounded by four (111) surfaces forming an angle of 54.7 ° with the wafer surface is formed. open.
In the case of a (110) wafer, a hole perpendicular to the wafer surface is opened. FIG. 5 shows an example in which a (100) wafer is used to form a thermal oxide film, which is then patterned into a mask to etch silicon. At this time, only the thermal oxide film remains as a support. In some cases, a SiO ₂ film or a Si ₃ N ₄ film formed by a CVD (Chemica Vapor Deposition) method or the like is used instead of the thermal oxide film.

As another method of forming a thin support, there is a method of utilizing the impurity concentration dependency during silicon etching. In the above-mentioned etching solution, the silicon layer in which boron is diffused at a high concentration has a low etching rate and acts as an etching stop layer. Therefore, a layer in which boron is diffused at a high concentration is formed on one side of the silicon wafer, and SiO _{2 is}
When etching is performed using Si ₃ N ₄ etc. as a mask, Fig. 5
The diaphragm of (C) is formed. However, in this case, what remains as a support is the high-concentration boron-doped layer.

<Problems to be Solved by the Invention> When a thin support is formed using an oxide film, the film thickness is 1
When the thickness is smaller than micron, the support may be curved or the mechanical strength may be weakened. On the contrary, when the thickness is increased, strain is applied due to the difference in coefficient of thermal expansion between the silicon and the oxide film, and the support is cracked or damaged. Further, a thick thermal oxide film requires a long time for production and is poor in productivity, and a film thickness obtained is at most 2 to 3 μm or less.

On the other hand, when a thin support is formed with a high-concentration boron-doped layer, the depth of boron doping can be as deep as about 10 microns, so the support can be made thicker, and since the coefficient of thermal expansion is equal to that of a silicon substrate, there is no distortion, A flat support having high mechanical strength can be obtained. However, since the high-concentration boron-doped layer has a low electric resistance, it is necessary to electrically insulate between the high-concentration boron-doped layer and the sensor material when the sensor material is to be formed on this support.

<Means for Solving Problems> In order to solve the above problems, in the manufacturing method of the present invention, a boron diffusion mask is formed on a silicon substrate, and the boron diffusion mask is provided with a bridge portion and a support for the bridge portion. A step of removing the predetermined boron diffusion mask so as to form and forming a diffusion region by exposing the silicon substrate; and a step of forming a boron diffusion layer in the diffusion region using the boron diffusion mask as a mask. A step of forming a concave portion in the silicon substrate by etching from the surface of the silicon substrate using the boron diffusion layer as an etching stop layer after removing the boron diffusion mask, and forming a bridge portion made of the boron diffusion layer, At least a step of forming an insulating film on the boron diffusion layer, and forming a sensor material and necessary electrodes on the insulating film And a process. The coefficient of thermal expansion of the insulating film such as an oxide film is different from that of silicon, but since the film thickness is thin, the coefficient of thermal expansion of the entire support is determined by the boron-doped layer, and therefore the coefficient of thermal expansion of the support is equal to that of silicon. As a result, a flat support having little thermal strain during production, high mechanical strength and high thermal strength, and no bending can be obtained.

The thin insulating film that covers the boron-doped layer is not limited to the thermal oxide film. A SiO ₂ film formed by a CVD method, a sputtering method, or another method may be used, or a Si ₃ N ₄ film or an A ₂ O ₃ film may be used.
The film is also good. From the viewpoint of the manufacturing process, a thermal oxide film that can use the same device (diffusion device) as that of boron doping is suitable, but from the viewpoint of the coefficient of thermal expansion, a Si ₃ N ₄ film, A ₂ O ₃
Membrane is better.

<Embodiment 1> FIG. 1 shows a sectional view and a plan view of a silicon microsensor according to an embodiment of the present invention, and FIG. 2 shows a sectional view of each manufacturing step thereof.

The surface of the n-type silicon wafer 3 is thermally oxidized, and the thermal oxide film 4 is patterned by photoetching (FIG. 2 (A)). Using the patterned thermal oxide film 4 as a mask, boron is diffused to form a boron-doped layer 5 (FIG. 2 (B)). At this time, the boron concentration should be as high as possible (1 × 10 ²⁰
/ Cm ³ or more is preferable) and the junction depth is considerably deep (about 5 μm). Next, after removing the thermal oxide film 4 of the mask with a hydrofluoric acid buffer solution (Fig. 2 (C)), the mask was immersed in an EPW etching solution whose temperature was raised to near the boiling point to form a boron-doped layer 5
Etching is carried out until a bridge is formed by (Fig. 2 (D)). Further, by thermal oxidation, the oxide film 6 (about 3000 nm) which is sufficiently thin as compared with the thickness of the boron doped layer 5 is formed.
Å) is formed (Fig. 2 (E)). Finally, the thin film 7 serving as a sensor material and the electrode 8 are formed on the obtained bridge portion to complete the sensor of FIG.

<Embodiment 2> FIG. 3 shows a sectional view and a plan view of a silicon microsensor according to another embodiment of the present invention, and FIG. 4 shows a sectional view of each manufacturing step thereof.

The n-type silicon wafer 3 is thermally oxidized, and the thermal oxide film 4 is patterned by photoetching, leaving the thermal oxide film 4 only in the silicon etching portion (FIG. 4 (A)). Boron is diffused using the patterned thermal oxide film 4 as a mask to form a boron-doped layer 5. At the same time, the thermal oxide film 6 is thinly formed on the surface of the boron-doped layer 5 (FIG. 4 (B)). The boron doped layer 5 is several μm to 10 μm, and the thermal oxide film 6 is 1000 to 5 μm.
About 000Å is preferable. Next, only the oxide film 4 of the mask is removed by photoetching (FIG. 4 (C)), and then it is immersed in an EPW etching solution whose temperature is raised to near the boiling point to etch silicon. Since the boron-doped layer 5 and the oxide film are not etched, a diaphragm composed of these two layers is formed (FIG. 4 (D)). The thin film 7 serving as a sensor material and the electrode 8 are formed on the finally obtained diaphragm portion to complete the sensor shown in FIG.

<Effect of the Invention> By forming the sensor material on the support of the present invention,
A silicon microsensor with high mechanical strength and thermal strength and high reliability can be obtained.

The silicon microsensor can be applied to a sensor utilizing heat balance such as an infrared sensor, a flow sensor, and a gas sensor, and is useful for high sensitivity and low power consumption. Further, it can be applied to a sensor having a movable part such as a pressure sensor, a vibration sensor, and an acceleration sensor. Furthermore, it also contributes to miniaturization, integration, and integration of the sensor.

[Brief description of drawings]

FIG. 1 is a sectional view and a plan view of a silicon microsensor showing one embodiment of the present invention. FIG. 2 is a manufacturing process diagram of the silicon microsensor shown in FIG. FIG. 3 is a sectional view and a plan view of a silicon microsensor showing another embodiment of the present invention. FIG. 4 is a manufacturing process diagram of the silicon microsensor shown in FIG. FIG. 5 is a configuration diagram showing the shape of a support of a conventional silicon microsensor. 3 ... Silicon substrate, 4 ... Thermal oxide film, 5 ... Boron doped layer, 6 ... Thermal oxide film, 7 ... Sensor film, 8 ... Electrode.

Continuation of front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 31/0248

Claims (2)

[Claims] 1. A boron diffusion mask is formed on a silicon substrate, and the predetermined boron diffusion mask is removed to expose the silicon substrate so that the boron diffusion mask forms a bridge portion and a support for the bridge portion. Forming a diffusion-diffused region by using the boron diffusion mask as a mask in the diffusion-diffused region, and removing the boron diffusion mask by using the boron diffusion layer as an etching stop layer. Forming a recess in the silicon substrate by etching from the surface of the silicon substrate and forming a bridge portion composed of the boron diffusion layer; forming an insulating film on at least the boron diffusion layer; and forming a insulating film on the insulating film. A method for manufacturing a silicon microsensor, comprising the steps of forming a sensor material and a necessary electrode. 2. The insulating film comprises SiO ₂ , Si ₃ N ₄ , and A.
The method for manufacturing a silicon microsensor according to claim 1, wherein the method comprises at least one type of l ₂ O ₃ .