JPH06318713A - Manufacture of thin film structure and thin film structure - Google Patents

Abstract

PURPOSE:To improve the manufacturing method of the thin film structure of a diaphragm, etc., so as to increase the area of the structure against the size of a chip and, at the same time, to prevent the deterioration of temperature characteristic of the structure due to a difference in coefficient of thermal expansion. CONSTITUTION:After providing a recessed section 2 on the surface of a silicon substrate 1 and forming a dielectric layer 3 so as to fill up the section 2, the surface of the substrate 1 is polished and another silicon substrate 4 is stuck to the polished surface of the substrate 1. Then the silicon substrate 4 is polished so as to reduce the thickness of the substrate 4 on the layer 3 to a prescribed thickness and an etching hole 5 is formed to the layer 3 from the rear surface of the substrate 1. Finally, a diaphragm 6 is formed by separating the thinned silicon substrate 4 from the silicon substrate 1 by etching off the dielectric layer 3 by using an etching liquid having different etching rates against silicon and dielectric from the hole 5 so as to form a cavity section at the part which has been occupied by the layer 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a thin film structure such as a fine diaphragm or a beam, and a thin film structure formed by the method.

[0002]

2. Description of the Related Art Conventionally, there is known a technique called micromachining for applying a microfabrication technique used in a manufacturing process of a semiconductor integrated circuit to make a three-dimensional component.
According to this, it becomes possible to make an ultra-small mechanical functional component (micromechanics).

Conventionally, a thin film structure such as a fine diaphragm or a beam is formed by using an etching technique. For example, the diaphragm portion of a semiconductor pressure sensor is made by thinning a part of a silicon substrate by anisotropic or isotropic etching with respect to the silicon substrate.
That is, as shown in FIG. 12, the thin film (diaphragm) 6 is formed by etching the back surface of the silicon substrate 1 to form the recesses 8.

Further, as shown in FIG. 13, using the SOI substrate 9 in which the dielectric layer 10 is sandwiched between two silicon substrates, the dielectric layer 10 is side-etched through the etching hole 11 on the back surface to form the diaphragm 6. There is also a method.

[0005]

However, the above conventional methods have the following problems. First, when silicon etching is used, the area A of the diaphragm 6 becomes smaller than the opening area B of the recess 8 for etching as shown in FIG. The area A of the diaphragm 6 is preferably large in order to improve the sensitivity of the semiconductor pressure sensor, but on the other hand, since the opening area B is also large, there is a problem that the chip itself of the semiconductor pressure sensor becomes large.

Further, when the SOI substrate 9 is used as shown in FIG. 13, the dielectric layer 10 is laterally etched (side-etched) from the etching hole 11 to enlarge the cavity, thereby increasing the area of the diaphragm 6. But
During the etching process, the diaphragm 6 (cavity)
Is difficult to measure, it is difficult to control its size,
There is a problem in reproducibility as a manufacturing method. Furthermore, since the diaphragm 6 is supported by the dielectric layer 10,
There is also a problem that the temperature characteristics of a sensor such as a semiconductor pressure sensor are affected by the difference in the coefficient of thermal expansion from the silicon substrate.

In view of the above, the present invention increases the area of a thin film structure such as a diaphragm with respect to the size of a chip,
It is also an object of the present invention to provide a method for producing a thin film structure which is improved so as not to adversely affect the temperature characteristics, and a thin film structure produced by the method.

[0008]

In order to achieve the above object, in the method of manufacturing a thin film structure according to the present invention, a concave portion is provided on the surface of a substrate, and then a dielectric layer is formed only in this concave portion. A thin film layer is formed to a predetermined thickness on the surface of the substrate other than the dielectric layer and the concave portion, and then an etching hole reaching the dielectric layer is provided on the back surface side of the substrate,
The feature is that etching for removing the dielectric layer is performed from the etching hole.

[0009]

When the concave portion is formed on the surface of the substrate, the dielectric layer is formed only on this concave portion, and then the thin film layer is formed on the entire surface thereof, the thin film layer is formed on the dielectric layer and on the substrate surface other than the concave portion. As a result, the dielectric layer formed in the recess is surrounded by the thin film layer and embedded in the substrate.
Therefore, if the dielectric layer is removed by etching from the etching hole provided on the back surface side, that portion becomes a cavity, and the thin film layer thereabove is separated from the substrate to become a diaphragm. The area of the diaphragm is equal to the area of the cavity,
Since this is equal to the area of the recess formed at the beginning, the controllability of the size of the diaphragm is very good. Since the dielectric layer is entirely removed and the diaphragm is supported by the remaining portion when the recess is formed, the problem due to the difference in the thermal expansion coefficient between the substrate and the dielectric layer can be avoided.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to the drawings. First, as shown in FIG. 1, a recess 2 is provided on the surface of a silicon substrate 1. That is, a predetermined etching mask is formed by using the photolithography technique, and only a predetermined portion is isotropically or anisotropically etched to form the recess 2 having a predetermined size. When the diaphragm is formed later, the depth of the recess 2 is not less than the distance from the substrate 1 of the diaphragm, that is, the distance required for the movable range of the diaphragm (for example, about 5 μm).
And

Next, as shown in FIG. 2, a dielectric layer 3 is formed on the entire surface of the substrate 1 so as to fill the recesses 2. The dielectric layer 3 is made of silicon dioxide, for example, and is deposited by a flame hydrolysis deposition method or the like. The thickness of the dielectric layer 3 is preferably thicker than the depth of the recess 2. Then, the surface of the silicon substrate 1 is polished until the silicon substrate 1 is exposed as shown in FIG. It is desirable that this polished surface has a mirror finish.

Then, as shown in FIG. 4, another silicon substrate 4 is attached to the surface of the silicon substrate 1 which has undergone the above steps without any inclusions. For example, the two silicon substrates 1 and 4 are bonded by performing a heat treatment at 1000 ° C. in a nitrogen atmosphere.

In this way, a structure in which the thin dielectric layer 3 is completely embedded in the silicon substrates 1 and 4 is completed.
As shown in FIG. 5, one of these substrates 4 is polished to a predetermined thickness. Although the front surface side substrate 4 is polished here, the back surface side substrate 1 may be polished. The upper portion of the dielectric layer 3 of the silicon substrate 4 thinned by this polishing will later become a diaphragm. That is, the thickness of the polished silicon substrate 4 determines the thickness of the diaphragm.

Thereafter, a predetermined portion on the back surface side of the silicon substrate 1 is isotropically or anisotropically etched to form an etching hole 5 reaching the dielectric layer 3 as shown in FIG.

Then, the dielectric layer 3 is etched through the etching hole 5 and removed. In this case, a hydrofluoric acid-based etching liquid having a large difference in etching rate between silicon and the dielectric is selected as the etching liquid. As a result, the etching automatically stops only in the dielectric layer 3,
As shown in FIG. 7, a structure in which the dielectric layer 3 is a cavity is completed. The thinned portion of the silicon substrate 4 on the cavity serves as the diaphragm 6.

According to such a manufacturing method, the area of the diaphragm 6 is the area of the cavity, that is, the dielectric layer 3
Area, that is, the area of the recess 2 formed first.
Therefore, the controllability of the size of the diaphragm 6 is very good, and the manufacture is easy. In addition, the size of the diaphragm 6 can be expanded to the size of the chip,
It is possible to reduce the size of the chip. Moreover, since the supporting portion of the diaphragm 6 is the edge portion left when the recess 2 is first etched, it is made of silicon, and there is no inconvenience caused by the partial difference in the coefficient of thermal expansion.

In the above manufacturing method, as shown in FIG.
As shown in FIG. 5, the thick silicon substrate 4 is replaced by the silicon substrate 1
Although a thin film which will later become a diaphragm is formed by polishing the silicon substrate 4 after bonding to the substrate, it is also possible to make it by depositing silicon using an epitaxial growth method or a plasma CVD method.

Next, a second embodiment will be described.
This embodiment applies the present invention to manufacture of a semiconductor pressure sensor. First, through the steps of FIGS. 1 to 5 described above, a silicon substrate 1 having a dielectric layer 3 embedded therein as shown in FIG. 8 is obtained. Then, as shown in FIG. 9, a circuit 7 of a pressure sensor such as a diffusion region or an electrode serving as a strain gauge is formed on the surface side so as to be at an appropriate position with respect to the position of the dielectric layer 3.

Thereafter, a predetermined portion of the back surface side of the silicon substrate 1 is isotropically or anisotropically etched to reach the dielectric layer 3 as shown in FIG.
To form. Then, the dielectric layer 3 is etched through the etching hole 5 and removed. Also in this case, as in the case of the above-described first embodiment, by selecting a hydrofluoric acid-based etching solution having a large difference in etching rate between silicon and the dielectric as the etching solution, the etching is automatically performed only by the dielectric layer 3. Try to stay in place.

Then, as shown in FIG. 11, the dielectric layer 3
The portion where there was is a hollow portion, and the portion above it is the diaphragm 6, and the pressure sensor circuit 7 such as a strain gauge is formed on this diaphragm 6.

When the semiconductor pressure sensor is manufactured in this way,
The position of the circuit 7 such as a strain gauge can be accurately determined with respect to the size and position of the diaphragm. Further, since there is no part of the dielectric having a thermal expansion coefficient different from that of silicon, a semiconductor pressure sensor having good temperature characteristics can be obtained.

Although the diaphragm is formed in each of the above embodiments, it is needless to say that a thin film structure such as a cantilever structure can be manufactured in addition to the diaphragm. Further, although a semiconductor pressure sensor is taken as an example of the sensor, it goes without saying that it can be applied to the manufacture of other sensors using a thin film structure such as a diaphragm or a beam structure.

[0023]

As described above with reference to the embodiments,
According to the method of manufacturing a thin film structure of the present invention, when manufacturing a structure in which a thin film such as a diaphragm or a cantilever structure is separated from a substrate, it is possible to reduce the chip area with respect to the area of the diaphragm or the like. is there. In addition, the controllability of the area of the diaphragm and the like is good and the manufacture is easy. Moreover, it is possible to prevent the temperature characteristics from being deteriorated due to the partial difference in the thermal expansion coefficient. Therefore, various sensors having a thin film structure manufactured by this method can be manufactured at low cost, can be miniaturized, and have excellent temperature characteristics.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a first process of a manufacturing method according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a second process of the same example.

FIG. 3 is a cross-sectional view showing a third process of the same example.

FIG. 4 is a cross-sectional view showing a fourth process of the same example.

FIG. 5 is a sectional view showing a fifth process of the example.

FIG. 6 is a sectional view showing a sixth process of the example.

FIG. 7 is a sectional view showing a seventh process of the example.

FIG. 8 is a cross-sectional view showing the first process of the manufacturing method according to the second embodiment.

FIG. 9 is a sectional view showing a second process of the same example.

FIG. 10 is a cross-sectional view showing the third process of the same example.

FIG. 11 is a sectional view showing a fourth process of the example.

FIG. 12 is a sectional view showing a conventional example.

FIG. 13 is a sectional view showing another conventional example.

[Explanation of symbols]

 1, 4 Silicon substrate 2, 8 Recessed portion 3, 10 Dielectric layer 5, 11 Etching hole 6 Diaphragm 7 Pressure sensor circuit 9 SOI substrate

Claims (2)

[Claims] 1. A step of forming a concave portion on a surface of a substrate, a step of forming a dielectric layer only on the concave portion, and then a thin film layer having a predetermined thickness on the dielectric layer and on the surface of the substrate other than the concave portion. And a step of forming an etching hole reaching the dielectric layer on the back surface side of the substrate, and a step of performing etching to remove the dielectric layer from the etching hole. And a method for manufacturing a thin film structure. 2. A structure having a thin film, which is manufactured by the method of manufacturing a thin film structure according to claim 1, and is separated from a substrate at least in part.