JPH02260333A - Manufacture of micro mechanical switch - Google Patents

Abstract

PURPOSE:To obtain a micro mechanical switch which can be formed on the same semiconductor substrate as other elements and highly integrated by locally removing an epitaxial layer under a SiO2 layer by means of electrochemical etching. CONSTITUTION:After a first Cr-Au layer 15 is formed on a SiO2 layer 3, the SiO2 layer 3 is opened in a determined pattern. A second Cr-Au layer 17 is formed, and an Au plating layer 19 is formed thereon in a determined pattern. Then, electrochemical etching is conducted by use of EPD or hydrazine aqueous solution as an etchant. Hence, an epitaxial layer 2 under the SiO2 layer 3 is locally removed, and a cantilever 3a consisting of the SiO2 layer 3 is formed. An Au electrode consisting of an Au plating layer 19 is formed on the cantilever 3a and a silicone base 1, whereby an acceleration switch can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an applied technology of silicon semiconductor micromachining technology, and is a manufacturing method of a micromechanical switch suitable for manufacturing ultra-small acceleration sensors, acceleration switches, etc. Regarding.

[Prior Art] Recently, various sensors using micromechanical switches such as acceleration switches have been developed using micromachining technology for silicon semiconductor substrates. For example, an ultra-small acceleration switch with a length of about 200 μm and a width of 20 μm is being produced (“5ilicon a
s a Mechanical Material”P
ROCEEDING OF THE IEEE VOL
, 70 No. 5 MAY 1982).

This acceleration switch has a movable part (hereinafter referred to as a cantilever) made of a swingable SiO□ film whose one end is supported by a silicon substrate, an Au electrode attached to this cantilever, and a silicon substrate. and an Au electrode formed thereon. When acceleration is applied to this acceleration switch, the cantilever beam supported at one end by the silicon substrate swings and is displaced, and the Au electrode on the cantilever beam comes into contact with the Au electrode on the substrate. ing. Thereby, acceleration can be detected as an on or off electrical signal.

Figures 3 (a) to (d) are cross-sectional views showing the conventional manufacturing method of this acceleration switch in order of process, and Figure 4 is Figure 3 (d).
FIG. 2 is a sectional view taken along line IV-IV of FIG.

First, as shown in FIG. 3(a), P type impurities such as boron are introduced at a high concentration onto a silicon substrate 11 to form a P'' layer 12.
form. After forming an epitaxial layer 13 on the entire surface, a 5-ins film 1 is formed on this epitaxial layer 13.
form 4. Next, a first Cr-Au layer 15 is formed on this 5iOz film 14, and then a first Cr-Au layer 15 is formed on this 5iOz film 14.
Predetermined regions of the layer 15 and the 5iO9 film 14 are removed by etching to provide a caO portion f5a. This first Cr
- The Au layer 15 is composed of a laminate of a lower Cr layer and an upper Au layer, and is made of Cr to improve adhesion with the n-type region.
After the Cr layer is deposited, Au is deposited on the Cr layer.

Next, as shown in FIG. 3(b), a first photoresist 16 is formed in a predetermined pattern on the first Cr--Au layer 15 so as to fill the opening 15a. Thereafter, a second Cr--Au layer 17 is formed on the entire surface by a vapor deposition method.

Next, as shown in FIG. 3(C), after a second photoresist 18 is deposited on the second Cr-Au layer 17, a predetermined pattern of openings is formed in this second photoresist 18. will be established. Then, this opening is selectively plated with Au to form an Au plating layer 19.

Next, as shown in FIG. 3(d), after removing the second photoresist 18, the second Cr--Au layer 17 is removed in the exposed region where the Au plating layer 19 is not deposited. After that, the first photoresist 16 is removed and F
Etching is performed with DP (mixture of ethylenediamine, pyrocatechol and water). In this case, the epitaxial layer 13 under the Si02M 14 in a predetermined region is locally side-etched and removed. This results in
An acceleration switch having a cantilever beam formed by the SiO3 film 14 is completed.

In this way, conventionally, high concentration (1020 atoms/cIil)
Taking advantage of the property that the P+ layer into which impurities have been introduced is not etched by FDP, the epitaxial layer 13 below a predetermined region of the SiO2 film 14 is etched away, thereby removing the cantilevered beam formed by the 5io2 film 14. A micromechanical switch is formed.

[Problems to be Solved by the Invention] However, since the P+ layer 12 contains impurities at an extremely high concentration, it is difficult to form an epitaxial layer 13 made of single crystal silicon without crystal defects on the P+ layer 12. It is extremely difficult.

Furthermore, even if it were possible to form the epitaxial layer 13 without crystal defects, S
When thermally oxidizing (approximately 1100 degrees Celsius) the P'' layer 12, the impurity (boron) in the P'' layer 12 diffuses into the epitaxial layer 13 above the P+ layer 12 and the silicon substrate 11 below. The impurity concentration and thickness will change.

For this reason, conventionally, when elements such as resistors, diodes, or transistors are formed together with micromechanical switches on a semiconductor substrate, there is a problem in that the electrical characteristics of these elements change.

The present invention has been made in view of such problems, and includes:
A method for manufacturing a micromechanical switch that can be formed on the same semiconductor substrate as other elements without changing the electrical characteristics of other elements, and that can be highly integrated. The purpose is to provide

[Means for Solving the Problems] A method for manufacturing a micromechanical switch according to the present invention includes a step of forming an epitaxial layer of a second conductivity type on a silicon semiconductor substrate of a first conductivity type, and a step of forming an SiO2 film on the epitaxial layer. forming a predetermined area of the 5 inch
and a step of locally removing the epitaxial layer below the 5iO9 film through the opening by electrochemical etching. do.

[Operations] In the present invention, the epitaxial layer below the SiO3 film is locally removed by electrochemical etching. In this case, for example, if the first conductivity type semiconductor substrate is N type, by connecting this substrate to the anode of the power source and applying the etchant to the cathode side, the N type semiconductor substrate will not be dissolved in the etchant. Not etched. Then, by adding the above polarity and voltage, SiO2
Only the P-type epitaxial layer below the film is etched away. As a result, a space is formed below the Sio2 film, and one end of the SiO□ film becomes a free end and the other end becomes a fixed end and is supported by the epitaxial layer, forming a cantilever of the N5io2 film.

According to the method of the present invention, it is not necessary to form a high concentration impurity layer in the manufacturing process of a micromechanical switch. Therefore, even if a micromechanical switch and other elements are formed together on the same semiconductor substrate, the micromechanical switch will not affect the electrical characteristics of the other elements.

[Embodiments] Next, embodiments of the present invention will be described with reference to the accompanying drawings.

FIGS. 1(a) to 1(d) are cross-sectional views illustrating an example method of the present invention in the order of steps.

First, as shown in FIG. 1(a), an N-type silicon substrate 1 is
A P-type epitaxial layer 2 is formed thereon to a thickness of 2 μm or more, preferably 3 to 4 μm, and the surface of this epitaxial layer 2 and the bottom surface of the silicon substrate 1 are thermally oxidized to form 5in2 films 3 and 4. do. Note that the SiO□ films 3 and 4 can also be formed by CVD (chemical vapor deposition).

Next, as shown in FIG. 1(b), a predetermined region of the SiO2 film 3 is opened, and an N-type impurity is diffused through this opening at a concentration of 1020 atoms/d to connect it to the silicon substrate 1. An N''' region 5 is formed. Note that this N+ region 5 can also be formed on the lower surface side of the silicon substrate 1. In this case, the SiO2 film 4 formed on the lower surface of the substrate 1 is opened,
N type impurities are diffused into the silicon substrate 1 through this opening to form an N+ region. This N+ region 5 is formed to serve as an electrode and make electrical contact with the N-type silicon substrate 1 during electrochemical etching, which will be described later. Considering the current conduction efficiency in electrochemical etching, the N" region 5 is preferably formed on the upper surface of the silicon substrate 1 on the same side as the P-type epitaxial layer 2 to be etched.

Next, as shown in FIG. 1(C), after forming a first Cr--Au layer 15 on the SiO□ film 3,
are opened in a predetermined pattern. Figure 2 shows this SiO2
3 is a plan view showing a pattern of openings 6 formed in a membrane 3. FIG. As shown in FIG. 2, the opening 6 has a U-shape. Thereafter, a photoresist (not shown) is patterned in the same manner as the first photoresist 16 (see FIG. 3), a second Cr-Au layer 17 is formed, and a second Cr-Au layer 17 is formed using photolithography technology. An Au plating layer 19 is formed on the Cr-Au layer 17 in a predetermined pattern. Then, the photoresist below the Au plating layer 19 is removed.

Next, as shown in FIG. 1(d), a 50% by volume aqueous solution of FDP or hydrazine is used as an etchant,
Perform electrochemical etching. As a result, S
The epitaxial layer 2 below the iO2 film 3 is locally removed. At this time, the N+ region 5 is connected to the anode of the power source as an electrode, and the etchant is placed on the cathode side. In this electrochemical etching, an N-type silicon substrate 1
Since it is connected to the anode side via the N+ region 5, it is not etched and is protected by voltage. On the other hand, 5
The P-type epitaxial layer 2 below the TOA film 3 has an opening 6
The portions that come into contact with the etchant through the etching process are etched, and after a predetermined period of time, the epitaxial layer 2 in a predetermined region below the SiO2 film 3 is etched away.

As a result, cantilever beams 3a made of the 5iOa film 3 are formed.

As described above, according to this embodiment, an acceleration switch is obtained in which an Au electrode made of the Au plating layer 19 is formed on the cantilever beam 3a and the silicon substrate 1, and this acceleration switch basically has the structure shown in FIG. It has the same structure as the conventional acceleration switch shown in FIG. 4(d) and FIG.

In this embodiment, unlike the conventional method, the P+ layer is not formed in the manufacturing process of the acceleration switch, so that various other elements can be formed on the same silicon substrate. Therefore, high integration is possible.

[Effects of the Invention] As explained above, according to the present invention, the movable part of the micromechanical switch is formed by removing the epitaxial layer below the SiO2 film by electrochemical etching. Even if it is formed on the same semiconductor substrate as other elements, the electrical characteristics of the other elements will not change.

This makes it possible to highly integrate semiconductor devices having micromechanical switches, making the present invention extremely useful. In addition, if the thickness of the epitaxial layer is set appropriately, the thickness will not change, so a gap of a predetermined size can be formed below the movable part of the micromechanical switch. It is possible to appropriately regulate the swing range.

This can prevent the movable part from breaking when the micromechanical switch is used.

[Brief explanation of drawings]

1(a) to (d) are cross-sectional views showing the method according to the present invention in the order of steps, FIG. 2 is a plan view of a silicon substrate in the process of manufacturing the same, and FIG. 3(a) to (d) are FIG. 4 is a cross-sectional view showing a conventional method for manufacturing an acceleration switch in the order of steps, and FIG. 4 is a cross-sectional view taken along the line IV--IV in FIG. 3(d).

Claims (1)

[Claims] (1) A step of forming a second conductivity type epitaxial layer on a first conductivity type silicon semiconductor substrate, a step of forming a SiO_2 film on this epitaxial layer, and a step of locally removing the SiO_2 film in a predetermined region. A method for manufacturing a micromechanical switch, comprising the steps of forming an opening, and locally removing the epitaxial layer below the SiO_2 film through the opening by electrochemical etching.