JPH0752172B2 - Ion sensor manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing an ion sensor, and more particularly to ion selection in which a polymer thin film type ion sensitive film is formed on a gate insulating film of a field effect transistor. The present invention relates to a method for manufacturing a strong field effect ion sensor.

(Prior Art) Ion selection for detecting a predetermined ion activity in an electrolytic solution or an aqueous solution by forming a chemoselective film containing an ion-sensitive substance according to a detection target on the gate portion of a field effect transistor Field Effect Transistor (Ion Selective Fiel)
Various types are conventionally known as d Effect Transitor (hereinafter abbreviated as ISFET).

(Problems of Prior Art) In the meantime, for example, as shown in FIG. 1, a silicon dioxide insulating film (4) is formed on the surface of a semiconductor substrate (1) having a source diffusion region (2) and a drain diffusion region (3). ) Is an inorganic insulating film such as Si ₃ N ₄ , Al ₂ O ₃ , Ta ₂ O ₂ or the like, which is deposited on the insulating film (5). The polymer liquid film type ion-sensitive film (6) is a polymer film.
However, conventionally used polymer films such as polyvinyl chloride and polyurethane do not generally have sufficient adhesion to the gate film, which is an inorganic insulating film, and peel off when immersed in the liquid to be detected. There is a drawback that it cannot be used. Therefore, as a means for solving this problem, for example, a method of fixing a polymer liquid film type ion-sensitive film on a gate insulating film using a silane coupling agent has been proposed.

However, the method as described above has a drawback that the manufacturing cost becomes high because the process is complicated and the manufacturing is troublesome.

In addition, the polymer liquid membrane type ion-sensitive membrane produced by the conventional method causes various defects on the surface of the sensitive membrane when it is immersed in the eluate to be detected for a long time for measurement. For example, the surface of the film becomes uneven, and sometimes the film itself peels off from the device, leaving problems in stability and durability.

Therefore, it is difficult to easily and inexpensively manufacture a polymer liquid film type ISFET excellent in performance, stability and durability by the conventional method.

Therefore, as one of the solutions to the above problems, in order to form a polymer liquid film type ion-sensitive film, in a solution containing a plasticizer, an additive and an ion-sensitive substance according to the detection purpose,
In addition to having excellent adhesion and adhesion, a solution prepared by mixing "Urushi" that can form a firm film is used as the film material. After applying this solution on the gate insulating film surface of ISFET, the temperature is set to 25 A method of curing "Urushi" in a constant temperature and constant humidity atmosphere in which the temperature is controlled to -30 ° C and the humidity is controlled to 80 to 90% has been proposed.

This method contributes to solving problems such as performance, stability, and durability that result from the above-mentioned surface defects, and at the same time requires the use of a troublesome manufacturing method for improving the adhesion and the adhesion. Since it disappears, it also greatly contributes to the reduction of manufacturing cost.

However, on the other hand, in curing the solution for forming the sensitive film containing "Urushi", the method using a constant temperature and constant humidity atmosphere as described above not only makes the apparatus itself large and expensive, but also requires time for curing. On the contrary, if the apparatus is made small and inexpensive, the control accuracy of constant temperature and constant humidity is lowered, and the apparatus is easily affected by the outside air temperature and the outside air humidity, and the time required for curing varies. For this reason, it is difficult to obtain a stable quality, and there is a problem in surface uniformity.

(Object of the invention) The object of the present invention is to reduce the ISFET having a polymer liquid film type ion-sensitive film, which can be used stably for a long period of time with less deterioration in sensitivity, and is simple and inexpensive. It is to provide a means that can be manufactured in a short time.

(Means of the Present Invention for Solving Problems) The feature of the present invention resides in that "Urushi" plasticizer, which is a film material and is applied on the gate insulating film (5) of FIG.
This is to irradiate the solution (6) composed of the additive and the ion-sensitive substance with far-infrared rays, thereby hardening the "urushi" to form a sensitive film.

(Operation) Urushiol, which is the main component of "Urushi" which is a film material, has an infrared absorption spectrum region of 3 µm and 6 to 10 µm. Therefore, by radiating a wavelength centered on the infrared absorption region of urushiol, which is the main component, the vibration energy of urushiol is increased, and the polymerization reaction in urushiol is activated and curing is further promoted. As a result, the adhesion between the ion sensitive film and the gate film is improved.

In addition to this, the radiated far infrared energy is hardly absorbed by the air in the middle and directly acts on the film material, so that the effect is efficiently performed. In the conventional method using a constant temperature and constant humidity atmosphere, curing is mainly performed from the surface of the film using water, whereas in the case of the present invention using far infrared rays, the radiant energy is not limited to the surface of the film. Instead, it acts on the interior as well, so that the energy penetrates deeply and is absorbed, thus promoting hardening from the surface and from the inside. Therefore, the time required for curing can be significantly shortened as compared with the conventional method using a constant temperature and constant humidity atmosphere. Moreover, since it is less affected by the outside air temperature and the like, the time required for curing does not vary, so that the quality can be kept constant.

Also, the absorption of far infrared energy generates heat,
Viscosity of the surface of the "Urushi" is reduced, the uniformity of the surface can be greatly improved, the film surface can be flattened more than in the conventional technique, and a uniform film can be formed.

As described above, since the "Urushi" film having good adhesiveness and adhesiveness is formed, the problems of the conventional organic film such as peeling and surface rupture are improved, and the durability can be expected to be improved.

Next, examples of the present invention and comparative examples with products by the conventional method will be described.

(Examples) "Urushi" 733 mg as a material for an ion-sensitive membrane Tetrakis [3,5-bis (trifluoromethyl) phenyl borate potassium salt (K ⁺ -TEPB) as a plasticizer containing 1 wt% of phthalic acid di- A solution in which 590 mg of 2-ethylhexyne and 10 mg of valinomycin as a K ⁺ ion sensitizer were sufficiently dissolved was applied onto a silicon nitride (Si ₃ N ₄ ) film which is a gate insulating film of ISFET. Then, as shown in the side view of FIG. 2, this ISFET (8) is coated with "Urushi" and is placed in the far-infrared radiation device so that the gate portion is located directly below the far-infrared heater (7). A far infrared ray having a wavelength of 3 to 10 μm as a central wavelength was irradiated for one week to produce a K ⁺ -ISFET. In FIG. 2, (9) is a support base.

(Comparative Example) On the other hand, for comparison with the conventional one, the same ion-sensitive film forming solution as in the example was applied on the gate insulating film of the same ISFET, and the temperature was 25 to 30 ° C and the humidity was 80 to 90%. It was placed in a constant temperature and constant humidity oven and cured to produce K ⁺ -ISFET.

Then, this was compared with the example in terms of curing time, change in sensitivity, and the like.

As a result, it took about 2 weeks to obtain a film equivalent to that of the example according to the conventional method (comparative example). In contrast, that of the embodiment is about 1 / week because it is one week as described above.
A cure time of 2. Therefore, according to the present invention, curing can be performed using a small apparatus which is easy to handle and is small in size.

Also by driving the source follower circuit to give a K ^+-ISFET according to a conventional method, the results shown in Figure 3 were compared with time change of the sensitivity of the K ^+-ISFET according to the invention. In the figure, the ∘ mark corresponds to the present invention, and the ● mark corresponds to the conventional method. As is clear from this, immediately after fabrication, both were 50 mV / d.
Although it has the sensitivity of ecade, it was observed that the conventional method drastically decreased the sensitivity below 40 mV / decade after the 10th day. On the other hand, according to the present invention, the sensitivity is
It will be less than 40mV / decade after the 20th day. Therefore, the one according to the present invention has a much more gentle decrease in sensitivity than the one by the conventional method, and the one having a longer life than that by the conventional method can be obtained.

(Effects of the Invention) As described above, according to the present invention, as compared with the conventional method,
It is possible to provide an ion selective field effect transistor (ISFET) that is inexpensive, can be manufactured in a short time, and has good performance that can be used stably for a long time.

[Brief description of drawings]

FIG. 1 is a sectional view of an ISFET provided with an ion sensitive film, FIG. 2 is an explanatory view of a far infrared ray irradiation procedure, and FIG. 3 is an experimental result diagram showing sensitivity and elapsed days of the ISFET according to the conventional method and the present invention. . (1) ... P-type silicon substrate, (2) ... source diffusion region, (3) ... drain diffusion region, (4) ... first gate insulating film, (5) ... second gate insulating film, (6) …… Polymer liquid membrane type ion sensitive membrane, (7) …… Far infrared radiation device, (8) …… ISFET, (9) …… Supporting base, (10) ……
Urushi sensitive membrane.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Saori Takasuka 4-12-16 Kanda, Ikeda-shi, Osaka Prefecture Carpenter's dormitory (72) Kazuo Tsutsumi 23-26 Yamate-cho, Hanno City, Saitama Prefecture (72) Inventor Kashiwakura Minoru 10-10 Minamimachi, Hanno-shi, Saitama Examiner Tomoyasu Nomi (56) References JP-A-63-36139 (JP, A) JP-A-53-123996 (JP, A)

Claims (1)

[Claims] 1. A method for producing a field effect type ion sensor for forming a polymer liquid film type ion sensitive film from a solution containing a plasticizer, an additive and an ion sensitive substance according to an ion to be detected. A method for producing an ion sensor, characterized in that the drying and curing of the lacquer which is the film material in the solution is carried out by far infrared rays having a wavelength of 3 to 10 μm.