JPS6388438A - Mosfet chemical electrode - Google Patents

Abstract

PURPOSE:To enable stable operation as electrode, by covering the electrode with a resin film except for a exposed surface thereof through which gate metal senses chemical species. CONSTITUTION:A P-type silicon wafer undergoes a patterning so that a channel are 4 set by a drain region 2 and a source region 3 is formed at a part on a substrate. Then, the entire surface of the silicon wafer is subjected to thermal oxidation except for a drain terminal setting section 21 and a source terminal setting section 31 thereof to form an oxide film. Moreover, a silicon nitride film is laminated on the film to obtain a MOSFET element 1. A gold or platinum film 7 is formed tight on a gate insulation film of the element 1 through a metal layer 6 made of chromium or titanium to form a gate material. Then, the work is covered with an insulating and water-resistant resin film at least except for a gate metal exposed at a part of a portion thereof corresponding to the area 4 so that chemical species in a solution to be measured only contact with the exposed part of gate metal, and none of other parts. This minimizes the amount of chemical species which permeates the film 7 to reach the metal layer 6.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a MOSFET chemical electrode. More specifically, the present invention relates to a MOSFET chemical electrode using platinum/gold as a gate metal, which is used for measuring various ions and chemical substances that undergo ion changes.

(b) Conventional technology Recently, silicon nitride (Sis
N4) Form a gate metal made of gold, platinum, etc. in close contact with each other through a film? = A MOSFET chemical electrode has been proposed,
It is expected to be used as a variety of ion sensors due to its miniaturization, quantization, and improved S/N ratio, and can also be used as a detection sensor for various substrates by immobilizing and combining biological solvents such as enzymes. It is expected.

Such a FET chemical electrode may be formed by directly forming a gate metal such as platinum or the like on a gate insulating film, but
Since this gate metal tends to peel off when used in an aqueous solution, devices in which a gate metal such as gold or platinum is closely formed through a metal film such as chromium or titanium are known.

(c) Problems to be Solved by the Invention However, in the above MOS FET chemical electrode, the metal film such as gold or platinum constituting the gate metal is thin film-like from the viewpoint of its responsiveness and the above-mentioned adhesion. However, these ions leak through the thin film of gold or platinum from the underlying chromium or titanium metal film, which is formed to increase the adhesion of the metal film to the gate insulating film.・There is a problem that it is difficult to obtain stable operation as an electrode.

The present invention has been made in view of the above circumstances, and is particularly intended to provide a MOSFET chemical electrode using gold or platinum as a gate metal, which operates stably as an electrode.

(d) Means for Solving the Problems Thus, according to the present invention, an insulating film is coated on a semiconductor element having a channel region between a drain region and a source region, and an insulating film is provided to cover at least the channel region. It consists of a MOSFET element in which a gold or platinum film is closely formed on a film part through a chromium or titanium film, and the gold or platinum film part, excluding at least the gold or platinum film part located on the channel region or a part thereof, is A MOSFET chemical electrode is provided in which the membrane is protected by being coated with a protective film having insulation and water resistance.

In the chemical electrode of the present invention, the gate metal on the gate insulating film is coated and protected with an insulating and water-resistant protective film so that at least a portion of the metal is exposed, thereby preventing elution of gate metal components. It is characterized by being configured as follows.

The MOSFET element used for the above chemical electrode usually has a drain region, a source region, and a channel region defined by a gate insulating film in one part of the semiconductor substrate, and terminals for these drain and source regions are set in another part. A structure in which a gate metal is set on a gate insulating film is suitable. The gate metal formed on the gate insulating film is composed of a chromium or titanium metal film and a gold or platinum film.
It is preferable that the gate insulating film is formed of a layer, and that a chromium or titanium metal film is formed between the gate insulating film and the gold or platinum film and covered with the gold or platinum film. The gate metal is formed in close contact with at least a portion of the gate insulating film corresponding to the channel region. The above-mentioned chromium or titanium metal film is used as an adhesive base layer to enhance the adhesion of the gold or platinum film to the gate insulating film, and therefore its formed film thickness is the minimum thickness that can function as the base layer. It is preferable to adjust the thickness, and the number of layers is usually about 100. The gold or platinum film formed on this film constitutes the gate metal and is the part that is sensitive to chemical species in the measurement atmosphere, so the thickness of the formed film is sufficient to cover the underlying chromium or titanium metal film. In addition, from the viewpoint of responsiveness, it is usually set to several thousand to Iμm. Note that the base layer may be a mixed layer of chromium and titanium, or may be composed of two layers of chromium and titanium. The gate metal may be a mixed layer of gold and platinum, or may be composed of two layers of gold and platinum.

A protective film is formed on the gate metal. The protective film is formed for the purpose of preventing chemical species in the measurement atmosphere from penetrating into the gate metal and eluting the underlayer. The material for the protective film is selected from a material that has insulating properties and water resistance in the solution to be measured, and rubber-based resins are suitable, for example silicone resins are preferred, but the material is not limited to the above-mentioned rubber-based resins. Any material having the properties may be used, and epoxy resin or the like may be used.

The protective film is formed so as to expose at least a portion of the gate metal corresponding to the channel region and cover the gate metal. The above-mentioned exposed at least part refers to the minimum area that can come into contact with chemical species in the measurement atmosphere and provide sufficient responsiveness as a FET chemical electrode. The protective film is formed to have a thickness of 0.5 mm or more from the viewpoint of durability in the measurement atmosphere.

In the present invention, the gate metal is formed by a method appropriately selected from methods known in the art, such as vapor deposition and sputtering. An example of a method for coating an underlayer consisting of a chromium or titanium metal film with a gold or platinum film is to first form the underlayer by vapor deposition using a mask that exposes a region sufficiently containing the channel region corresponding portion; Next, a gold or platinum film may be formed by sputtering using a mask that exposes a region sufficiently containing the deposited base layer.

For forming the protective film that covers and protects the gate metal, a method of applying a corresponding resin solution is preferable since the intended exposed portion can be easily formed as described above.

(E) Function According to the present invention, a gold or platinum film is formed in close contact with the gate insulating film through a metal layer made of chromium or titanium to constitute the gate metal, and furthermore, this gate metal is formed at least in a portion corresponding to the channel region. The exposed part of the gate metal is covered with an insulating and water-resistant resin film, and the chemical species in the solution to be measured come into contact only with the exposed part of the gate metal and not with other parts. The amount of chemical species that penetrate the platinum film and reach the chromium or titanium metal layer is minimized.

The present invention will be described in detail below with reference to Examples, but the present invention is not limited thereby.

(f) Example P-type silicon wafer substrate (5X 3 X 0.3n+*
), photolithography, doping, masking, etc. are applied to the drain region (2
), the channel area (4) set in the source area (3)
) was patterned on a part of the substrate.

Next, the drain terminal setting part (21) and the source terminal setting part (31) of the patterned silicon wafer are
Thermal oxidation was carried out on the entire surface of the silicon wafer except for
SiOz) was formed, and then CVD method [silane 15
d/min, ammonia 212/min, and hydrogen 2.5Q/min] to form a MOSFET element (1) by laminating a silicon nitride film (S isN 4) with a thickness of 1000 nm.
I got it.

5ift/5 of the above obtained 1 MOSFET element (1)
A gate portion (5) is set on the isNa insulating film so as to sufficiently cover the channel region (4),
Metal chromium (6) is evaporated to a thickness of 200 mm through a metal mask having a 2φ hole with the gate N(5) in the center, and then a metal mask having a 2.5φ hole in the same manner is formed. 3 by sputtering platinum (7) through a mask.
The chromium metal film was formed to a thickness of 1,000 mm to completely cover the chromium metal film to form a gate metal (FIG. 2 shows a partial plan view of this state).

Silicone resin (
KE45. (manufactured by Shin-Etsu Chemical Co., Ltd.) (8), first apply the entire area around the gate metal formation area, especially on the boundary with the gate insulating film, then gradually apply toward the center, and finally The coating was applied so that the gate metal was exposed only in the portion corresponding to the channel region. After that, it is dried at 30° C. for 24 hours to form a silicone resin film with a thickness of about 0.5 mm. A partial plan view of this state is shown in FIG. 3. The side surfaces of the silicon wafer were insulated with the silicone resin described above, and the back surface was insulated with an alumina thin plate.

The static properties of the chemical electrode thus obtained were investigated as follows. That is, using the electrode and a silver-silver chloride electrode, the gate metal part of the chemical electrode and the silver-silver chloride electrode are immersed in a phosphate buffer solution with a pH of 6.118, and a 0.0. 5V and 4V voltage (vD
Voltage of silver-silver chloride electrode (V cS) when applying s)
As a result of measuring the variation in the drain current (Vl) of the chemical electrode due to the variation, the properties shown in FIG. 4 were obtained. This result shows that the chemical electrode of the present invention operates stably in an aqueous solution. Further, after being continuously immersed in the above aqueous solution for 100 days, static characteristics were measured in the same manner as above, and stable operation was confirmed, and no peeling of the gate metal was observed.

(G) Effects of the Invention According to this invention, the gate metal is coated with an insulating and water-resistant resin film except for the exposed surface that is sensitive to chemical species, so that the curdling species that permeate the gate metal are suppressed as much as possible. Therefore, it is possible to obtain a MOSFET chemical electrode that is resistant to elution of the chromium or titanium metal layer and operates stably over a long period of time in response to chemical species such as Ot and Hto. It is also possible to fabricate a stable enzyme electrode by immobilizing an enzyme on the exposed gate metal surface of this chemical electrode.

[Brief explanation of the drawing]

Figure 1 shows a MOSFE used in a chemical electrode as an example of this invention.
FIG. 2 is a partial plan view of the gate metal forming part of the MOSFET element; FIG. 3 is a diagram corresponding to FIG. 2 of a MOSFET coated with silicone resin; and FIG. 4 is a chemical electrode of the present invention. FIG. 2 is a graph showing the static characteristics of the sample in a buffer solution. (1) ---・-・MOS FET element, (2)
...Drain region, (3) ...Source region, 4) ...Channel region, (5) ...
...Gate part, (6) ...Chromium metal film,
(7)...Platinum film, (8)...Silicon tree 111291゜III Figure 2

Claims (1)

[Claims] 1. An insulating film is coated on a semiconductor element having a channel region between a drain region and a source region, and a chromium or titanium film is interposed on at least a portion of the insulating film that covers the channel region. A MOSFET device consisting of a MOSFET element in which a gold or platinum film is closely formed on the channel region, and the gold or platinum film has insulating properties and water resistance except for at least the part of the gold or platinum film located on the channel region or a part thereof. A MOSFET chemical electrode protected by a membrane. 2. The MOSFET chemical electrode according to claim 1, wherein the protective film having insulation and water resistance is made of silicone resin.