JP2701845B2 - Manufacturing method of silicon thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a method for manufacturing a silicon thin film for integrally forming a thin film such as a diaphragm or a cantilever on a silicon substrate. (Prior Art) For example, in a semiconductor vibration sensor, it is necessary to integrally form a cantilever-like thin film on a silicon substrate. For this purpose, conventionally, a silicon nitride film is formed in advance on the surface of a silicon substrate, and the nitride film is etched into a required shape.
Thereafter, the silicon in contact with the lower side of the nitride film is removed by etching so as to form a cantilever. (Problems to be Solved by the Invention) However, in the above-described manufacturing method, since a strain gauge or the like cannot be formed by diffusion in a silicon nitride thin film formed integrally with a silicon substrate, a polysilicon film is formed on the thin film. It must be formed into a strain gauge, and there is a problem that characteristics such as the response of the strain gauge cannot be sufficiently enhanced. Therefore, an object of the present invention is to provide a method of manufacturing a silicon thin film that can form a strain gauge having excellent characteristics on a thin film. [Structure of the Invention] (Means for Solving the Problems) In a method for manufacturing a silicon thin film according to the present invention, a p ⁺ region is selectively formed on a surface of a silicon substrate by diffusion and the p ⁺ region is covered. an epitaxial layer serving as a thin film is grown, then, after forming an oxide layer on the front surface of the epitaxial layer to form an opening in the oxide layer, connected to the p ⁺ region in the epitaxial layer through the opening p ⁺
Regions are formed by diffusion, then the p ⁺ regions are made porous by anodizing and then oxidized to form silicon dioxide regions, and the silicon dioxide regions are etched through the openings to remove thin films. It has a characteristic in what it forms. Further, a silicon dioxide region is formed by selectively ion-implanting oxygen ions into a portion below a portion to be formed into a thin film in a silicon substrate, an opening reaching the silicon dioxide region is formed, and the dioxide is formed through the opening. The silicon region may be removed by etching to form a thin film. (Operation) The silicon dioxide region in the silicon substrate can be formed by, for example, thermal oxidation after p-type silicon anodic treatment or ion implantation. The silicon dioxide region can be selectively etched and removed by utilizing the difference in etching rate between silicon dioxide and silicon, thereby forming a thin film integrated with the silicon substrate. Since this thin film is made of silicon, it is possible to easily form a strain gauge or the like having excellent characteristics by diffusion of impurities. (Embodiment) A first embodiment in which the present invention is applied to the manufacture of a semiconductor vibration sensor will be described below with reference to FIGS. First, as shown in FIG. 1 (A), an acceptor impurity is diffused at a high concentration in a predetermined region of a p-type silicon wafer 1 to form a p ⁺ region 2 as a high concentration region. 2), an n-type epitaxial layer 3 is grown. Thereby, a silicon substrate 4 in which the epitaxial layer 3 is overlaid on the silicon wafer 1 is formed,
p ⁺ region 2 is buried under epitaxial layer 3. Thereafter, an oxide film 5 is formed on the entire surface, and p ⁺
As shown in FIG. 2, a U-shaped opening 5a is formed in a region corresponding to the region 2 by etching (FIG. 2C). Next, by using the oxide film 5 as a mask, acceptor impurities are diffused from the surface to form a vertical p ⁺ region 6 reaching the p ⁺ region 2 in the epitaxial layer 3. Thereafter, the p ⁺ regions 2, 6 are made porous by anodizing. This is because, as described in detail in, for example, JP-A-48-102988, the silicon wafer 1 is immersed in hydrofluoric acid together with the electrodes, and the electrodes are placed between the p ⁺ regions 2, 6 and the electrodes. This is done by applying a DC low voltage as negative, which results in the p ⁺ region
A part of the silicon in 2,6 is converted to H ₂ SiF ₆ and eluted,
^{The +} regions 2 and 6 are made porous. In this case, since such electrolytic etching proceeds due to the presence of holes in the silicon crystal, only the p ⁺ regions 2, 6 selectively become porous silicon. Thereafter, for example, if an oxidation treatment step of heating in an oxygen atmosphere is performed, the porous silicon is easily oxidized. Therefore, as shown in FIG. In contact therewith, a porous silicon dioxide region 7 is formed. When the silicon wafer 1 is etched with hydrofluoric acid or buffered hydrofluoric acid, the silicon dioxide region 7 is selectively removed because the etching rate of silicon dioxide by hydrofluoric acid is much higher than that of silicon. , This is the third
As shown in the figure, the cantilever 8 is integrated with the silicon substrate 4.
Is formed. According to this embodiment, since the cantilever 8 is constituted by the epitaxial layer 3 of silicon, a diffusion resistor formed by diffusing impurities in advance by a general planar technique is formed, and the strain gauge is thereby formed. Is very easy to construct. Therefore, in this type of vibration sensor in which the cantilever 8 vibrates due to the vibration and is detected by the strain gauge, the strain gauge can be constituted by a diffusion resistor having particularly excellent responsiveness.
High performance as a vibration sensor can be achieved. In addition, the thickness dimension of the cantilever 8 is the same as that of the epitaxial layer 3.
Therefore, the degree of freedom in setting the thickness dimension can be made extremely high. FIG. 4 shows a second embodiment of the present invention, which is different from the first embodiment in that a thin film is formed into a diaphragm and a silicon dioxide region is formed by ion implantation. To outline the manufacturing method, first, silicon wafer
Oxygen ions are implanted into the silicon wafer 10 by ion implantation to form a silicon dioxide region 11 in the silicon wafer 10 (FIG. 1A). In this case, the depth position of the silicon dioxide region 11 (and thus the thickness of the diaphragm) can be arbitrarily set by the accelerating voltage of the ion implantation apparatus. Thereafter, impurities are diffused on the surface of the silicon wafer 10 to form diffusion resistances 12 at, for example, four places, and these are wired in a bridge shape to form a strain gauge and a bonding pad 13.
Is formed (FIG. 2B). Then, an opening 14 reaching the silicon dioxide region 11 is formed in the silicon wafer 10 by a dry etching method of silicon (FIG. 3C), and the silicon wafer 10 is further etched with, for example, buffered hydrofluoric acid. Then, since the etching rate of silicon dioxide by hydrofluoric acid is much higher than that of silicon, the silicon dioxide region 11 is selectively removed by etching, and a diaphragm-like thin film 15 is formed. Thereafter, for example, in a vacuum, a passivation film 16 of silicon nitride is formed on the entire silicon wafer 10 by a plasma CVD method, and the opening 14 is closed, so that the lower central portion 17 of the thin film 15 remains in a vacuum state. It will be sealed. According to this embodiment, since the hollow portion 17 is in a vacuum state, the thin film 15 bends and deforms according to the absolute value of the external pressure, and a signal is obtained from the strain gauge accordingly. In this case, the thin film 15 is made of silicon and has a diffusion resistance.
Because the strain gauge can be configured by 13
As in the previous embodiment, it is possible to improve the performance as compared with the related art in which the strain gauge is constituted by polysilicon. In the present invention, the thin film integrally formed on the silicon substrate is not limited to the above-mentioned cantilever or diaphragm shape, but may be any shape as required. [Effects of the Invention] As described above, the present invention forms a thin film by selective etching of a silicon dioxide region formed in a silicon substrate. This has an excellent effect that a high-performance strain gauge can be formed.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 3 show a first embodiment of the present invention. FIG. 1 is a cross-sectional view of a silicon wafer for sequentially showing manufacturing steps, and FIG. 2 is a portion of the silicon wafer. FIG. 3 is a plan view, FIG. 3 is a perspective view showing a completed form, and FIG. 4 is a diagram corresponding to FIG. 1 showing a second embodiment of the present invention. In the drawing, 4 is a silicon substrate, 8 is a cantilever (thin film), 10 is a silicon wafer (silicon substrate), and 15 is a thin film.

Claims (1)

(57) [Claims] A thin film for forming a strain gauge composed of a diffusion resistor is formed integrally with a silicon substrate, and a p ⁺ region is selectively formed on the surface of the silicon substrate by diffusion, and a thin film is formed so as to cover the p ⁺ region. An epitaxial layer is grown, and thereafter, an oxide layer is formed on the front surface of the epitaxial layer, an opening is formed in the oxide layer, and the p ⁺ region connected to the p ⁺ region is diffused in the epitaxial layer through the opening. After formation, these p ⁺ regions are made porous by anodizing and then oxidized to form a silicon dioxide region, and the silicon dioxide region is removed by etching through the opening to form a thin film. A method for producing a silicon thin film, comprising: 2. Forming a thin film for forming a strain gauge composed of a diffusion resistor integrally with a silicon substrate, wherein oxygen ions are selectively implanted into a portion of the silicon substrate below a portion to be formed into a thin film, thereby forming a silicon dioxide region. Forming an opening reaching this silicon dioxide region,
A method of manufacturing a silicon thin film, wherein the silicon dioxide region is removed by etching through the opening to form a thin film.