JPS6122777B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a potassium ion sensor, and more specifically to an insulated field effect transistor (hereinafter referred to as a field effect transistor) having a sensor gate.
The present invention relates to a method for manufacturing a potassium ion sensor in which the sensor gate surface of a FET (FET) is coated with an organic film that has selective adsorption properties for potassium ions.

Ion sensors measure the ion activity in a solution, and particularly in the medical field, there is a need for a miniaturized device that can accurately and quickly measure the ion activity in living organisms.

Conventionally, as this type of device, a measuring device using a glass electrode is known. However, those using glass electrodes have problems such as miniaturization, response time, and stability, and are severely limited in practical use. In 1972, P. Bergveld of the Netherlands removed the metal plate that made up the gate electrode of a conventional gate insulated FET, that is, a MOS FET, and used an insulating film made of silicon oxide film as an electrode, and brought the film into direct contact with an electrolyte. A report on measuring the potential of the liquid (P.
Bergveld, IEEE Trans on BME, vol, BME―
19, No. 5 pp342-351.1972). The device using this field effect transistor is smaller than the device using the glass electrode described above, and
By coating the surface of the gate portion with a membrane having ion-selective properties, specific ions can be selectively quantified, and as a result, there is particular interest in its application to the fields of medicine and physiology. In recent years, it takes
Various ion sensors using FETs are being developed, and several reports have been published on the development of ion sensors that can selectively measure the concentration of specific ions in solutions. For example, if the gate surface
It was reported in 1974 that an FET made of Si ₃ N ₄ could selectively measure hydrogen ions, and (T.
Matsuo and KD Wise, IEEE Trans.
BME, 21No6 pp485-487, 1974) Also, a potassium ion sensor was reported in 1975.
(Analytical chemistry, Vol47, No13, pp2238
(2243, November, 1975) However, in these examples, after forming the FET structure on a silicon wafer, each element was separated by scribing as in a conventional semiconductor process. After inserting it into a catheter or the like, the periphery of the cut section is coated with resin to provide insulation. Since such FET sensors are always used in an electrolytic solution, the insulation of the cut-off cross section must be perfect, but it is extremely difficult to insulate the sensor while it is inserted into a catheter, etc., so these examples are for illustrative purposes only. This was something that could be done on a laboratory scale, and not something that could be mass-produced.

The inventors of the present invention have conducted intensive studies to put the above-mentioned laboratory-scale sensor into a production process that can be mass-produced, and have discovered a manufacturing method that has a simple manufacturing process and can be mass-produced. Kosho 56-
No. 38902) is proposed as a manufacturing method for ion sensors. The sensor obtained by the above manufacturing method has an ion selective sensitive film such as a doped oxide layer coated on the surface of the SiO ₂ film or Si ₃ N ₄ of the gate insulating film, and depending on the structure of the doped oxide layer, hydrogen, sodium, etc. , potassium ions, etc. can be provided.
However, sensors coated with a doped oxide layer have highly accurate and stable ion selection characteristics for hydrogen and sodium ions, but are extremely unstable for potassium ions. Therefore, in order to obtain an ion sensor with excellent selective sensitivity to potassium ions and to put it into a production process that can be mass-produced, the present inventors conducted further studies and found that chemical substances with known selective adsorption properties for potassium ions, such as valinomycin, were It has been found that a potassium ion sensor with good selectivity can be obtained by covering the doped oxide layer with an organic film contained in the substance, for example, dissolved or immobilized. In order to put the above-mentioned sensor into a manufacturing process suitable for mass production, the inventors further conducted extensive research and found that
A novel method for manufacturing a potassium ion sensor according to the present invention has been discovered. Therefore, the object of the present invention is to have stable potassium ion selection properties,
Another object of the present invention is to provide a new method for manufacturing a potassium ion sensor suitable for mass production. That is, during or after forming a gate insulated FET structure on the silicon wafer surface, the wafer separation part is separated, an insulating film, such as an oxide film, is applied to the cross section of the separation part to insulate it, and then the gate surface This is a method for producing a potassium ion sensor, in which an FET is formed by coating the FET with an organic film containing a substance that selectively adsorbs potassium ions, and then the structure is separated into predetermined shapes from the wafer. Conventionally known chemical substances that selectively adsorb potassium ions can be used. Examples include antibiotics such as valinomycin and nonactin, and cyclic ligands such as crown ether and cryptant. As the film-forming organic substance for forming an organic film by dissolving or immobilizing the above chemical substance in an organic substance, polyvinyl chloride, celluloses, polyurethane, polystyrene, etc., and substances containing plasticizers therein can be used. . Among the above chemical substances and organic substances, from the viewpoint of measurement accuracy and stability, a combination of valinomycin or crown ether and polyvinyl chloride containing a large amount of plasticizer is preferred. It is clear that the potassium ion sensor can also be manufactured by reversing the order of the organic membrane coating step and the separation step among the manufacturing steps.

Next, an example of a method for manufacturing a potassium ion sensor according to the present invention will be explained in detail in the order of each step with reference to the drawings.

(1) Gate insulated FET structure formation process Humid oxidation process P ^- -Clean the silicon wafer and make it to the specified thickness by chemical etching. Next, scribe the wafer to an appropriate size and
Humidified oxidation is performed at ℃ for 1 hour to form a SiO ₂ film of about 6000 Å on the wafer surface.

Photoetching process A double-sided mask alignment device forms source and drain diffusion patterns on the front surface of the wafer, and a mask alignment pattern on the back surface.

N-type source and drain diffusion process Phosphorus _atoms are
Perform predeposition, 1200℃, dry air for 13 days.
Perform time diffusion. In this way, the depth is about 10μ.
m, and an n-type semiconductor with a surface concentration of Ns10 ¹⁸ /cm ³ is formed.

P ⁺ type channel stopper layer diffusion process After creating a channel stopper layer diffusion pattern by photo-etching, boron is diffused using BBr ₃ to form a P ⁺ type channel stopper layer.

Contact layer diffusion process After creating a pattern for contact diffusion by photoetching, using POC ₃
Perform predeposition of phosphorus atoms at 1050℃,
Drive in 1200℃ wet air for 30 minutes.

Photoetching Using the pattern shown in FIG. 1, the SiO ₂ of the gate portion 1, contact portion 2, substrate terminal portion 3, and at least the cut-off portion 4 around the gate portion is etched.

Full surface oxidation process: The entire surface is thermally oxidized at 1150°C in dry air for 30 minutes to form a SiO ₂ film of approximately 1000 Å.

Si ₃ N ₄ and SiO ₂ layer formation process by CVD method Si ₃ N ₄ of about 1000 Å each is deposited on the entire surface by CVD (Chemical Vapor Deposition) method.
film and then a SiO ₂ film.

Double-sided photo-etching process A pattern for the cut-off part and contact part is formed on the front side, and a pattern for the cut-off part on the back side is formed by photo-etching.

(2) Separation process: Etch the Si ₃ N ₄ in the separation area, source and drain contact areas with hot phosphoric acid. Next, only the contact portions are masked with picane, and the SiO ₂ layers at the cut-off portions on both sides are etched with HF. The exposed Si cut-off part is etched with a water-amine solution, and the FET tip cut-off part is etched.
Separate from the Si substrate.

(3) Separation cross-section insulation process The Si surface exposed by Si etching is heated to 1200°C.
Heat treatment is performed in wet air for 30 minutes to form an SiO ₂ insulating film. Some of the SiO ₂ layer formed on the Si ₃ N ₄ is removed by etching with an HF-based solution.

(4) Contact area aluminum evaporation process Contact area SiO ₂ etching process As shown in Figure 2, the FET tip (the comb-shaped part) that is away from the Si substrate is covered with picane 5, and the root Etch the SiO ₂ in the contact area to create a contact hole 6.

Aluminum evaporation process: Cover everything except the contact hole with an aluminum evaporation mask, and evaporate aluminum onto the source contact portion, drain contact portion, and substrate terminal portion. After vapor deposition, heat treatment is performed at 500℃ to strengthen the adhesion of A.

(5) Organic membrane coating process A solution of an organic polymer compound in which a ligand that is selective for potassium ions is dissolved alone or together with a plasticizer, or a ligand that is selective for potassium ions is bonded to a covalent bond. Therefore, a solution of an organic polymer compound immobilized within the molecule is uniformly and thinly applied to the gate surface, and the solvent is evaporated to form a potassium ion selective adsorption film.

Furthermore, organic polymer compounds in which a ligand position having selectivity for potassium ions is fixed within the molecule by covalent bonds are classified in the Department of Macromolecular Science...Chemistry (J.MACROMOL.SCI. -CHEM.) Volume A7(5), No.
Pages 1015-1033 (1973), Journal of the Chemical Society...Chemical
Communications (JCSCHEM.COMM.)
It is described on pages 394 to 396 (1976).

(6) Semiconductor separation process Individual FETs are separated from the wafer substrate using a scriber. 3 and 4 show a plan view and a cross-sectional view of a potassium ion sensor obtained by the manufacturing method of the present invention. In the same figure, 1
Reference numeral 7 indicates a gate portion, 7 indicates a drain terminal, 8 indicates a source terminal, 9 indicates a drain diffusion layer, 10 indicates a source diffusion layer, and 11 indicates a channel stopper.

FET created by the above process
Attach the lead wire to the aluminum evaporated part of the board, and use an insulating material to support it with an appropriate support.
For example, the FET can be reinforced by attaching it with epoxy resin or the like, making it easier to handle.

[Example 1] Valinomycin on the gate covered with Si ₃ N ₄
A solution prepared by dissolving 10 mg of dioctyl adipate, 800 mg of dioctyl adipate, and 350 mg of polyvinyl chloride in 13 ml of THF was uniformly applied, and the THF was evaporated to form a film. This was repeated 10 times to form a film without pinholes. The potassium FET fabricated in this way has a gate-to-source voltage (V _{GS ) and potassium ions as shown in Figure 5a at a drain current (D) of 30 μA and a drain-to-source voltage (V DS )} of 2 V. The relationship with concentration (ogak ⁺ ) is given. At a potassium ion concentration of 5 or less, the Nernst relationship holds, and the slope of the straight line at 20° is -59 mV/pK. Note that FET with gate covered with Si ₃ N ₄
is almost insensitive to potassium ions. In addition, when a film is formed using a solution of 800 mg of dioctyl adipate and 350 mg of polyvinyl chloride dissolved in 13 ml of THF, the result is as shown in Figure 5b.
FET was completely insensitive to potassium ions.

[Example ₂ ] _Dibenzo-
18-Crown-6 10mg, dibentil phthalect
500mg, polyvinyl chloride 500mg in cyclohexane
A solution dissolved in 10 ml was applied uniformly and the solvent was evaporated to form an organic film of polyvinyl chloride containing crown ether. The gate-source voltage (V _GS ) of the potassium ion sensor formed in this way
The relationship between and potassium ion concentration (og ak ⁺ ) is shown in the figure.
It is shown in 5C. Measurement is D=30, μA,
This was done with V _DS =2V. At a potassium ion concentration of 4 or less, the Nernst relationship was almost satisfied.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the oxide film etching pattern of the gate part, contact part, and separation part.
The figure is a sectional view for explaining the etching of the contact part, FIGS. 3 and 4 are a plan view and a sectional view of a potassium ion sensor manufactured by the method of the present invention, and FIG. It is a graph showing the potassium concentration dependence of a potassium ion sensor coated with a membrane.

Claims (1)

[Scope of Claims] 1. During or after forming a gate insulated field effect transistor structure on the surface of a silicon wafer, a step of separating a separated portion at the periphery of the gate portion of the wafer, and applying an insulating film to the separated cross section. A method for producing a potassium ion sensor, which comprises the steps of: insulating the wafer with an organic film; coating the gate surface with an organic film containing a substance that selectively adsorbs potassium ions; and cutting and separating transistors from the wafer into predetermined shapes. 2. Potassium ions according to claim 1, wherein the organic membrane containing a substance that selectively adsorbs potassium ions is a membrane made of a mixture of a substance that selectively adsorbs potassium ions and an organic polymer substance. How the sensor is manufactured. 3. The method according to claim 1, wherein the organic membrane containing a substance that selectively adsorbs potassium ions is an organic polymer membrane in which a substance that selectively adsorbs potassium ions is immobilized by covalent bonds. Method for manufacturing a potassium ion sensor.