JP2767614B2 - Manufacturing method of small oxygen electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] The present invention relates to a method for manufacturing a small oxygen electrode, which improves the adhesion between a resist and a substrate, facilitates the formation of a pattern of an electrode extending from the substrate surface to the bottom of the groove, and reduces the size with a good yield. Forming a groove in the silicon surface by anisotropically etching silicon for the purpose of enabling mass production of oxygen electrodes; and forming an insulating film from the bottom of the groove to the cathode / anode electrode to the silicon surface. A step of filling the inside of the groove with an electrolyte-containing porous material, and a gas-permeable membrane covering the silicon surface except for the exposed portion of the electrode and covering the electrolyte-containing porous material. A method for producing a small oxygen electrode, comprising the step of forming at least an electrode-sensitive portion forming region having a roughened surface as the silicon. More make up.

[Industrial applications]

The present invention relates to a method of manufacturing a small oxygen electrode, and more particularly to a method of forming a cathode and an anode of a small oxygen electrode.

The small oxygen electrode can be advantageously used in various fields for measuring the concentration of dissolved oxygen. For example, the measurement of biochemical oxygen demand (BOD) in water has been performed from the viewpoint of water quality conservation, and this small oxygen electrode can be used as a measuring device for the dissolved oxygen concentration. Further, in order to efficiently promote alcohol fermentation in the fermentation industry, it is necessary to adjust the concentration of dissolved oxygen in the fermenter, and the small oxygen electrode of the present invention can be used as a measuring instrument. Furthermore, the small oxygen electrode can be used in combination with an enzyme to form an enzyme electrode and measure the concentration of sugar, vitamins, and the like. For example, glucose is catalyzed by an enzyme called glucose oxidase and reacts with dissolved oxygen to oxidize to gluconolactone. This reduces the amount of dissolved oxygen that diffuses into the oxygen electrode cell. The glucose concentration can be measured from the consumption.

As described above, the small oxygen electrode of the present invention can be used in various fields such as environmental measurement, fermentation industry, and clinical medicine. In particular, in the clinical medicine field, the small oxygen electrode is attached to a catheter and inserted into the body. It is very useful because it is disposable and inexpensive.

[Conventional technology]

The present inventors have developed a new type of small-sized oxygen electrode using a lithography technique and an anisotropic etching technique, because a conventional glass-made oxygen electrode cannot be miniaturized and cannot be mass-produced. (JP-A-63-238548)
issue). This oxygen electrode is placed on a hole (groove) formed by anisotropic etching on a silicon substrate through an insulating film.
This is an oxygen electrode having a structure in which a book electrode is formed, an electrolyte-containing body is accommodated inside the hole, and the upper surface of the hole is finally covered with a gas-permeable membrane. This oxygen electrode is small,
Low variation in characteristics and low cost because batch mass production is possible.

[Problems to be solved by the invention]

In producing such a small oxygen electrode, an electrode sensitive portion has been formed on a mirror-polished silicon wafer surface, as in the production of a normal semiconductor device. However, in this case, the problem was the formation of the cathode and anode electrodes from the top to the bottom of the hole.

Patterning using a resist is possible without difficulty when there is only a step of about 1 μm as in a normal device. However, when a groove having a step exceeding 100 μm is formed as in this small oxygen electrode, first, it is difficult to apply the resist uniformly as a first step, and the situation shown in FIG. 5 is obtained. . That is, the resist film becomes extremely thick at the bottom of the hole, and conversely, at the edge 1e at the end of the hole, the resist is repelled and a continuous resist pattern cannot be formed. If the resist pattern is cut, unnecessary portions are etched when effective etching is performed in the fabrication of the small oxygen electrode, thereby increasing the number of disconnections and decreasing the yield. This pattern formation problem can be slightly improved by treating the surface of the substrate with HMDS (hexamethyldisilazane) or the like. Was possible. However, considering the trouble of patterning, it is preferable that the number of times of overprinting be further reduced.

[Means for solving the problem]

The present invention is a step of forming a groove on the silicon surface by anisotropically etching silicon, and a step of forming an electrode serving as a cathode / anode from the bottom of the groove to the surface of the silicon via an insulating film, A small oxygen containing a step of filling the inside of the groove with an electrolyte-containing porous material, and a step of forming a gas-permeable membrane covering the surface of the silicon except for the exposed portion of the electrode and covering the electrolyte-containing porous material. In the method of manufacturing an electrode, the silicon is formed by a method of manufacturing a small-sized oxygen electrode, characterized in that at least the electrode-sensitive portion forming region is roughened. A semiconductor substrate having a groove formed by anisotropic etching; an insulating film covering the surface of the substrate; and a cathode / anode formed from the bottom of the groove to the surface of the substrate via the insulating film. Two electrodes, an electrolyte-containing porous material filled in the groove, and a gas permeable material that covers the surface of the substrate except for the exposed portions of the two electrodes and covers the electrolyte-containing porous material. In the small oxygen electrode having a film, a small oxygen electrode is formed by using at least an electrode sensitive portion forming region having a roughened surface as the semiconductor substrate.

Although the problem at the time of applying the resist is due to the incompatibility between the substrate and the resist, as described above, it has been found that the chemical treatment cannot be expected to be very effective. Therefore, an attempt was made to form the small oxygen electrode formed on a polished mirror surface of a silicon substrate on a rough etched surface which has not been used before.
In this method, the friction between the resist and the substrate is increased by physical means during spin coating, instead of a chemical method in which it is difficult to further improve the adhesion, so that the resist is less likely to aggregate.

The surface roughness of the semiconductor substrate surface is preferably 0.5 μm or more and 2 μm or less. If the surface roughness is less than 0.5 μm, the friction is small, the effect of making the resist hard to coagulate is small and the effect of improving the yield cannot be obtained, and if the surface roughness is more than 2 μm, the substrate surface of the cathode / anode electrode is formed. Problems arise.

A gold electrode or a platinum electrode can be used as the cathode of the small oxygen electrode.

The same material as the cathode as the anode of the small oxygen electrode,
Alternatively, a silver / silver chloride electrode can be used.

Polyacrylamide gel and calcium alginate gel can be used as the electrolyte-containing porous material of the small oxygen electrode.

Potassium chloride and a polymer electrolyte can be used as the electrolyte of the small oxygen electrode.

According to the present invention, a hole (groove) is formed on a silicon substrate by anisotropic etching based on a resist pattern forming method described later, and a cathode / anode from the bottom of the hole to the surface of the substrate is interposed via an insulating film. After forming, covering the back surface of the substrate with a hydrophobic insulating film, filling the inside of the hole with the electrolyte-containing porous material, and forming a gas-permeable film on the upper portion of the porous material by dip coating. It is intended for improvement.

In carrying out the method of the present invention, a semiconductor substrate, particularly a silicon substrate, can be advantageously used as a base material of the electrode body. The insulating film can be formed from a silicon oxide film or the like. For example, when the substrate is silicon, the silicon oxide film can be easily formed by thermally oxidizing the substrate.

The cathode and the anode can be variously changed depending on whether the electrode to be manufactured is a polaro type or a galvanic type. For example, when manufacturing a polaro-type oxygen electrode, both electrodes are formed of a gold electrode or a platinum electrode, and a voltage is applied between both electrodes during measurement. In the case of the polaro type, it is preferable to use a neutral aqueous solution such as a 0.1 M potassium chloride aqueous solution which does not easily attack the underlying silicon oxide film. In addition, an electrode made of a metal, such as lead or silver, which is more susceptible to a chemical reaction than gold or platinum, is used as an anode, an electrode made of gold, platinum, or the like is used as a cathode, and a 1M aqueous solution of potassium hydroxide is used as an electrolyte. If an alkaline aqueous solution such as that described above is used, a galvanic oxygen electrode can be manufactured. Such an electrode can be advantageously formed by a film forming method such as vacuum evaporation and sputtering.

The photoresist to be applied on the substrate after forming the electrodes except for the holes and the portions for making electrical contact is preferably a negative photoresist, for example, OMR-8 manufactured by Tokyo Ohka.
3 This type of photoresist is advantageous because it has the property of repelling an aqueous solution as a raw material when only the holes are filled with the electrolyte-containing porous material.

As described in JP-A-63-311158, for example, a substrate is immersed in an aqueous solution of acrylamide containing an electrolyte, and the substrate is slowly pulled up in a state of being immersed in such a solution. The substrate in the state is irradiated with ultraviolet rays to form a gel, or a similar method using calcium alginate gel described in Japanese Patent Application No. 63-176978.
It can be implemented advantageously.

Various electrolytes such as potassium chloride and sodium sulfate can be used as the electrolyte to be retained by the porous carrier.

Gas permeable membranes are hydrophobic and do not allow aqueous solution to pass through, but they are initially liquid and can be dip-coated or spin-coated, and can be used as an electrode material, a silicon substrate, and a silicon oxide film as an insulating film. It is also an indispensable condition that the adhesion of the electrolyte is good and the electrolyte does not leak out. Suitable gas permeable membrane materials include:
A photoresist, preferably a negative photoresist, may be used. Teflon (trade name) is oxygen permeable, but must be avoided because of poor adhesion.

[Action]

The small-sized oxygen electrode according to the present invention is used for mass-producing the small-sized oxygen electrode using the lithography technology and the thin-film forming technology used for forming the semiconductor integrated circuit. But the yield must be improved. One factor that determines yield is the formation of the cathode and anode. They are,
When formed on a flat substrate, there is no problem. However, when a large deep hole is formed on the substrate, as in the case of the small oxygen electrode which the present inventor is concerned with,
These formations are very difficult as described above. For this reason, in order to improve the yield, it is necessary to establish a method for efficiently forming them. As one of the means, the present invention does not produce an element on a mirror surface of a silicon wafer used for ordinary device fabrication, but applies an etched and roughened surface (however, a macroscopically flat surface). It was decided to use it for device fabrication. This increases the friction between the resist and the substrate during patterning, making it difficult for the resist to be repelled from the substrate during spin coating. For example, forming a resist pattern after depositing a gold thin film during cathode formation, and forming a gold electrode by etching In such a case, there is no disconnection, which is very advantageous.

〔Example〕

Next, a preferred example of a method for manufacturing a small oxygen electrode according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view showing a state of a resist applied on a substrate having a hole in which at least an electrode-sensitive portion forming region according to the present invention is roughened. The resist bath is well formed at the edge 1e of the slot by the roughened substrate surface 1r, and the resist pattern is not cut off at the corner edge 1e.

FIG. 2 is a perspective view showing a preferred example of a small oxygen electrode according to the present invention. The illustrated oxygen electrode has a rectangular parallelepiped shape. The sensitive portion is covered with the gas-permeable membrane 14, and a part of the cathode 3A and the anode 3B is exposed for connection to an attached device. Cathode 3A, anode 3
In the case of B in this example, both electrodes were constituted by gold electrodes in order to obtain a polaro type. The structure of the small oxygen electrode shown in FIG.
FIG. 3 is a sectional view taken along the line II-II. The silicon substrate 1 has holes (grooves) formed by anisotropic etching, and a silicon oxide film 2 is applied as an insulating film over the entire surface.
Further, the back surface of the substrate is covered with a hydrophobic insulating film 7 that is difficult to tear. A pair of a cathode 3A and an anode 3B are attached to the hole of the silicon substrate 1 in pairs. Cathode 3A
As shown in FIG. 2, the anode 3B and the anode 3B partially extend to the outside of the groove. The hole in the silicon substrate 1 is filled with an electrolyte-containing gel 6.
Further, a gas-permeable film layer 14 is formed above the hole so as to cover the upper part of the substrate 1.

The small oxygen electrode shown in FIGS. 2 and 3 can be advantageously manufactured, for example, by a manufacturing process shown in FIG. 4 in order. The main body after the electrodes are formed as shown in FIG. 4A can be manufactured through the following steps. In the following description, in order to facilitate understanding, a case where only one oxygen electrode is formed on one wafer is described. However, in practice, a large number of small oxygen electrodes are simultaneously formed. I want to be understood. Here, the case where calcium alginate gel is used as the electrolyte-containing gel will be described based on Japanese Patent Application No. 63-176978. In the following embodiments, “substrate surface” or “wafer surface” refers to a surface whose surface has been roughened by etching, and “substrate back surface” or “wafer back surface” refers to a surface opposite thereto (this substrate back surface). May be either a mirror surface or an etched surface). The surface roughness of the substrate surface is preferably 0.5 μm or more and 2 μm or less.

1.Wafer cleaning 350μm thick substrate surface roughened to 1μm
A (100) plane 2-inch silicon wafer was prepared and washed with a mixed solution of hydrogen peroxide and ammonia and concentrated nitric acid.

_2. Formation of SiO ₂ film A silicon wafer was subjected to wet thermal oxidation to form a 0.8 μm thick SiO ₂ film on the entire surface.

(The substrate surface roughness is maintained even after the SiO ₂ film is formed.) 3. Formation of etching pattern Negative photoresist (OMR-83, Tokyo Ohka, viscosity 60c)
After applying P) on a silicon wafer surface having a rough substrate surface, exposure, development and rinsing were performed to form an etching resist pattern on the wafer.

4. Application of resist The same negative photoresist as that used in the above process was applied to the back surface of the substrate, and baked at 150 ° C for 30 minutes.

5. Etching of SiO ₂ film The wafer was immersed in a 50% hydrofluoric acid: 40% ammonium fluoride = 1: 6 aqueous solution, and the exposed portions of the SiO ₂ that were not coated with the photoresist were removed by etching. Subsequently, the resist was removed with a sulfuric acid / aqueous hydrogen peroxide (2: 1) solution.

6. Anisotropic etching of silicon Anisotropic etching of silicon was performed in a 35% aqueous solution of potassium hydroxide at 80 ° C. Etching depth 300μm. After the completion of the etching, the wafer was washed with pure water.

After the completion of the anisotropic etching, the SiO ₂ film used at the time of etching was removed. This was performed in a 50% hydrofluoric acid: 40% ammonium fluoride = 1: 6 aqueous solution as in the case of 5.

To grow an SiO ₂ film is formed a silicon wafer the entire surface of 7.SiO ₂ film, and subsequently again 1. washing steps were wet thermal oxidation of the wafers. A film having a thickness of 0.8 μm was formed.

8. Formation of chromium and gold thin films On the substrate surface, a chromium thin film (400 mm, for adhesion between gold and the substrate) and a gold thin film (4000 mm) were formed by vacuum evaporation.

9.Formation of resist pattern for electrode formation Negative photoresist (OMR-83 manufactured by Tokyo Ohka, viscosity 60c)
Using P), a resist pattern for electrode formation was formed on the gold thin film on the wafer. If a continuous pattern could not be formed at once, it was post-baked at 150 ° C and then overprinted again using a 300 cP resist.

10. Etching of Gold and Chromium The substrate on which the resist pattern was formed was immersed in the following etching solution for gold and chromium in this order, and the exposed gold and chromium portions were removed by etching.
After washing with pure water, sulfuric acid / hydrogen peroxide (2: 1)
The resist was removed by the solution.

Gold etching solution: 4 g KI and 1 g I ₂ dissolved in 40 ml of water Chromium etching solution: 0.5 g NaOH and 1 g K ₃ Fe (CN)
₆ dissolved in 4 ml of water FIG. 4 (A) shows a state in which a gold electrode is formed.

11. Hydrophobic insulating film formed on the back of the substrate Hydrophobic insulating film (ES-100 made by Shin-Etsu Silicone)
1) Uniformly coated and baked at 150 ° C 12. Resist coating (Fig. 4 (B)) On the surface of the main body, except for the hole 5 and the pad part for making electrical contact, a negative photo Resist (Tokyo Ohka)
OMR-83, viscosity 60 cP) 4. This was performed by applying a photoresist on the surface of the wafer, and performing exposure and development after pre-baking.

13. Cutting of substrate A large number of oxygen electrodes formed on the substrate were cut into chips. (The scribe line may be removed in advance in the above-mentioned resist exposure and development process.) 14. Make the inside of the hole hydrophilic. Dip the tip of the chip into a 1M aqueous solution of sodium hydroxide. As a result, portions not covered with the resist became hydrophilic.

15. Filling of calcium alginate gel (FIG. 4 (C)) The following two types of solutions were prepared for forming an electrolyte-containing gel.

Solution A: A solution in which sodium alginate is dissolved in a 0.1 M aqueous solution of potassium chloride.

Sodium alginate concentration 0.2%.

Solution B: Calcium chloride dissolved in 0.1 M aqueous potassium chloride solution.

Calcium chloride concentration 5%.

When the chip of FIG. 4 (B) is immersed in the solution A and slowly pulled up, the solution A is repelled from the resist film and remains only in the hole 5 because the negative type photoresist film 4 is hydrophobic. Was. Next, when this chip was immersed in the solution B, the solution A instantly gelled.

16. Coating of gas permeable membrane (FIG. 4 (D)) A gas permeable membrane 14 was coated on the electrolyte-containing gel 6 so as to cover the gel. In this example, the gas permeable membrane
The same negative photoresist as used in Step 3 and the like was used. That is, a negative photoresist (Tokyo Oka)
OMR-83 (trade name), viscosity 60 cP) was applied by dip coating. This resist is exposed and developed immediately without pre-baking, and then the small oxygen electrode body is left in pure water or saturated steam for 24 hours to remove the thinner in the resist and complete the gas permeable film and the insulating film for the side wall. I let it. This resist film is also formed on the back surface, which advantageously acts to further improve the insulating properties.

〔The invention's effect〕

According to the method of the present invention, since the adhesion between the resist and the substrate is improved, it is particularly easy to form an electrode pattern extending from the substrate surface to the bottom of the hole, and the electrode can be formed with a small amount of labor. .

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a state of a resist applied on a perforated substrate having a roughened electrode sensitive portion forming region according to the present invention, and FIG. 2 is a preferred example of a small oxygen electrode according to the present invention. FIG. 3 is a sectional view taken along line II-II of the electrode of FIG. 2, and FIGS. 4A to 4D are small oxygen electrodes shown in FIGS. 2 and 3. FIG. 5 is a cross-sectional view showing the latter half of the manufacturing process in order, and FIG. 5 is a cross-sectional view showing a state of a resist applied on a substrate having holes (grooves) on a mirror-polished silicon wafer surface by a conventional method. It is. 1 is a substrate, 1r is a roughened substrate surface, 1s is a mirror-polished substrate surface, 1e is an edge portion of a hole (groove) forming portion, 2 is an insulating film, 3A and 3B are electrodes, and 4 is a photoresist film. 5 is a hole, 6 is an electrolyte-containing gel, 7 is a hydrophobic insulating film, 14 is a gas permeable film,

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Naomi Kojima 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited (56) References JP-A-63-238548 (JP, A) JP-A-60-66821 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) G01N 27/404

Claims (1)

(57) [Claims] 1. A step of forming a groove in the silicon surface by anisotropically etching silicon, and a step of forming an electrode serving as a cathode / anode from the bottom of the groove to the surface of the silicon via an insulating film. And filling the inside of the groove with an electrolyte-containing porous material, and forming a gas-permeable membrane that covers the surface of the silicon except for the exposed portion of the electrode and covers the electrolyte-containing porous material. A method for manufacturing a small-sized oxygen electrode, comprising using, as the silicon, at least an electrode-sensitive portion forming region having a roughened surface.