JPH0636980A - Manufacture of thin film - Google Patents

Abstract

PURPOSE:To eliminate inconvenience that the side surface of a recessed part for forming a thin film turns to a slant, facilitate miniaturization of a semiconductor device of high sensitivity, and improve manufacturing yield. CONSTITUTION:The surface of a silicon substrate 11 is oxidized. An oxide film 12 formed by the oxidation is selectively eliminated and a recessed part 13 is formed. A silicon wafer 14 is stacked on an oxide film 12, and annealed at a high temperature, thereby bonding the silicon wafer 14 to the silicon substrate 11 via the oxide film 12. A second substrate formed by bonding is polished and thinned, thereby making a thin film part 15 positioned on the recessed part 13 function as a diaphragm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvements in a method for producing a thin film.

[0002]

2. Description of the Related Art When manufacturing a semiconductor device, it is sometimes necessary to manufacture a diaphragm or a thin film having a cantilever structure. That is, for example, in a pressure sensor or an absolute pressure sensor, a thin film that functions as a diaphragm is formed, and gauge resistors and electrodes are formed on the thin film to form an element. In the acceleration sensor, a thin film having a cantilever structure is formed, and gauge resistors and electrodes are formed on the thin film to form an element.

Conventionally, such a thin film has been manufactured by etching a substrate. This will be described with respect to the absolute pressure sensor. The absolute pressure sensor has a structure as shown in FIG. In FIG. 3, the glass pedestal 21
A silicon chip 22 is bonded to the top of the above, and a recess 23 is formed on the lower surface of the silicon chip 22. By forming such recesses 23, the thin film portion 24 is produced in the silicon chip 22, and the thin film portion 24 functions as a diaphragm. The recess 23 is sealed by bonding the silicon chip 22 to the glass pedestal 21. At that time, the recess 23 is brought into a vacuum state and the recess 23 serves as a vacuum reference chamber. Silicon chip 22
Gauge resistance is formed on the thin film portion 24 by diffusion of impurities, and electrodes and the like are provided to form an element.

Here, the diaphragm 24 is manufactured as shown in FIG. First, as shown in FIG. 4A, a mask 25 is formed on the lower surface of the silicon chip 22, and then the mask 25 is processed to provide a window 26 for etching. Then, etching is performed through the window 26, and at that time, an anisotropic etching liquid such as KOH is usually used as the etching liquid. Thus, as shown in FIG. 4B, the recess 23 is formed in the window 26.

[0005]

However, the conventional method of forming a thin film by anisotropically etching a silicon chip causes a problem in miniaturizing a semiconductor device such as a pressure sensor.

That is, as shown in FIG. 4, when the thin film portion 24 is formed by anisotropically etching the silicon chip 22, the side surface of the concave portion 23 to be formed becomes an inclined surface,
Therefore, the effective size a of the thin film portion (diaphragm) 24 is always smaller than the size b of the window 26 of the mask 25. This size difference is the same as long as the silicon chips 22 have the same thickness. That is, the recess 23
Since the area occupied by the sloping side surface does not change, if the window 26 is reduced in order to reduce the size of the semiconductor device (the size in the horizontal direction in the drawing), the effective size a as a diaphragm is relatively large with respect to the size b of the window 26. It becomes smaller and smaller.

Therefore, in order to obtain higher sensitivity as the semiconductor device is designed to be smaller, the thickness of the thin film portion 24 must be reduced (because the effective size is small), and the manufacturing and management difficulties increase. However, there arises a problem that the manufacturing yield is deteriorated.

In view of the above, the present invention solves the inconvenience caused by the inclined side surface of the recess for forming the thin film, and improves the manufacturing yield when miniaturizing a highly sensitive semiconductor device. It is an object of the present invention to provide a method for producing a thin film that can be used.

[0009]

In order to achieve the above object, in the method of manufacturing a thin film according to the present invention, the surface of the first silicon substrate to be a support is oxidized, and the oxide film formed by this is oxidized. After partially removing the recesses to form the recesses, the second silicon substrate is overlaid on the oxide film and annealed at a high temperature to bond the first and second substrates through the oxide film. Next, the feature is that the bonded second substrate is polished to form a thin film.

[0010]

When the first and second silicon substrates are annealed at a high temperature with the oxide film interposed, the first and second silicon substrates are firmly bonded to each other. Since a recess is formed in the oxide film between the first and second silicon substrates, when the second silicon substrate is polished to be a thin film, the thin film portion located above the recess is moved to the diaphragm. Can function as Since the effective size of the thin film portion located above this recess is almost the same as the size of the recess, the individual chip size can be made slightly larger than the size of the recess and the thin film portion above it. . for that reason,
It is easy to reduce the size of the chip while increasing the sensitivity by increasing the size of the thin film portion on the recess.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a sectional view showing each step of a method of manufacturing a thin film according to an embodiment of the present invention. In this embodiment, SIO (Silicon-on-Insulator)
Technology is being used. First, as shown in FIG. 1A, the silicon substrate 11 is oxidized to form a silicon oxide (silicon dioxide) film 12 on the surface thereof. The thickness of the oxide film 12 is about 1 to 2 μm.

Next, as shown in FIG. 1B, the oxide film 12 is processed to partially and selectively remove the oxide film 12. Thus, the concave portion 13 is formed. This step is performed by selective etching using an HF-based etchant and a suitable mask.

Thereafter, as shown in FIG. 1C, a silicon wafer 14 is overlaid on this oxide film 12. 2 like this
These two silicon substrates 11 and 14 are annealed at a high temperature in a state where they are overlapped with each other with the oxide film 12 interposed therebetween. This is performed, for example, in a nitrogen atmosphere at 1100 ° C.
By this step, the two silicon substrates 11 and 14 are firmly bonded via the oxide film 12.

Next, as shown in FIG. 1D, the surface of the silicon wafer 14 is polished to form a thin film. As a result, the silicon wafer 14 is thinned to about 2 to 10 μm.

This silicon wafer 14 is a substrate for forming an element, and after the polishing step as described above is completed, the step proceeds to the element forming step. Here, if an absolute pressure sensor is to be manufactured, a region that becomes a gauge resistance is formed by impurity diffusion, then the entire surface is covered with an insulating layer, then a contact hole is formed, and the gauge resistance region is formed through the contact hole. An electrode is formed so as to contact with. After that, if testing is performed and the chip is divided, each element of the absolute pressure sensor is completed.

In this case, the recess 13 formed in the oxide film 12
Is the stage where the silicon wafers 14 are bonded (C in FIG. 1)
Then, it is close to a vacuum. This is because, as described above, the joining process is performed at a high temperature of 1100 ° C., and sealing is performed at that temperature. Therefore, the recess 13 functions as a vacuum reference chamber of the absolute pressure sensor. Then, the thin film portion 15 located on the concave portion 13 functions as a diaphragm that is deformed according to the external pressure.

Recessed portion 1 for forming this diaphragm
Since 3 is formed by etching the silicon oxide film 12 and etching is performed to a depth of about 1 to 2 μm, the effective size of the diaphragm is almost the same as the size of the recess 13. Therefore, individual chips can be obtained by cutting into a size slightly larger than the size of the recess 13 and the thin film part 15 thereon. In other words, it is easy to increase the effective size of the diaphragm even if the chip of each element is downsized.

The fact that the size of the diaphragm can be increased in this way means that the sensitivity can be increased without making the diaphragm so thin. Moreover, since the entire chip is formed of the same silicon material, stress is not generated due to a difference in thermal expansion coefficient and the characteristics can be stabilized. For these reasons, it becomes possible to easily manufacture an absolute pressure sensor having a small size, high sensitivity, and stable characteristics, and it is possible to improve the manufacturing yield.

In the above embodiment, as shown in FIG. 1B, only the oxide film 12 was selectively removed to form the concave portion 13. However, the concave portion 13 was formed as shown in FIG. It could be something like digging up to.
This is an anisotropic etchant such as KOH or RIE.
It can be performed by silicon etching such as plasma etching or plasma etching. By doing so, the depth of the recess 13 becomes deeper, that is, the thickness of the vacuum reference chamber becomes thicker, so that the deformed diaphragm will not come into contact with the bottom of the recess 13. As a result, the thin film portion 15 on the concave portion 13 can be made extremely thin to have high sensitivity.

In the above, the embodiment to which the present invention is applied when manufacturing the absolute pressure sensor having the diaphragm has been described. However, the present invention is not limited to any one as long as it manufactures a semiconductor device having a thin film. Anything can be applied. For example, it can be applied when manufacturing an acceleration sensor having a thin film having a cantilever structure instead of a diaphragm, and is very effective.

[0021]

As described above with reference to the embodiments,
According to the method of manufacturing a thin film of the present invention, it becomes possible to easily manufacture a small and highly sensitive semiconductor device having a thin film,
The manufacturing yield can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing each step of a thin film manufacturing method according to an embodiment of the present invention.

FIG. 2 is a sectional view of another embodiment.

FIG. 3 is a sectional view of an absolute pressure sensor according to a conventional example.

FIG. 4 is a cross-sectional view showing each step of a method of manufacturing a thin film according to a conventional example.

[Explanation of symbols]

 11 Silicon Substrate 12 Silicon Oxide Film 13, 23 Recess 14 Silicon Wafer 15, 24 Thin Film Part 21 Glass Pedestal 22 Silicon Chip 25 Mask 26 Etching Window

Claims (1)

[Claims] 1. A step of oxidizing the surface of a first silicon substrate to be a support, a step of selectively removing an oxide film formed in the oxidation step to form a recess, and then a second step. A step of bonding the first and second substrates through the oxide film by stacking the silicon substrate on the oxide film and annealing at a high temperature; and polishing the second substrate after the bonding. And a step of forming a thin film.