KR100217882B1 - Manufacturing method of isfet type dissolved carbon dioxide sensor - Google Patents

Abstract

The present invention relates to a field effect transistor pH sensor manufactured through a semiconductor device manufacturing process, and more particularly to a method for manufacturing a field effect transistor type dissolved carbon dioxide partial pressure sensor for measuring the dissolved carbon dioxide partial pressure in an aqueous solution or blood using a pH sensor. It is about. Features of the present invention include a silicon substrate 1, a source region 2, a drain region 3, a silicon oxide layer 4, a silicon nitride pH sensing layer 5, an aluminum metal electrode 6, a reference electrode 7 ), The FET type carbon dioxide sensor composed of the hydrogel film 8 and the gas permeable membrane 9 forms a hydrogel film and a gas permeable membrane by using a photopolymerizable photosensitive polymer. It is to prevent the polymerization by the action so that they have a double-membrane structure, the hydrogel film is formed by using a hydrophilic acrylamide and hydroxyethyl methacrylate (HEMA) excellent in patterning properties at the same time. The carbon dioxide partial pressure sensor manufactured by the present invention can solve the problem of pinhole generation and irregular surface generation and irregular surface generation in the sensing film due to the use of the conventional mylar film, and also has the advantage of easy adjustment of the thickness of the sensing film. Will be.

Description

Method for manufacturing field effect transistor type dissolved carbon dioxide sensor

The present invention relates to a field effect transistor pH sensor manufactured through a semiconductor device manufacturing process, and in particular to manufacturing a high quality field effect transistor type dissolved carbon dioxide partial pressure sensor for measuring dissolved carbon dioxide partial pressure in aqueous solution or blood using a pH sensor. It is about a method.

In general, the measurement of the dissolved carbon dioxide partial pressure (pCO ₂ ) in aqueous solution or blood is applied to medical diagnosis, chemical analysis or environmental measurement. In particular, the measurement of the dissolved carbon dioxide partial pressure in the blood using the pCO ₂ sensor is a very important part in the medical field because it can determine the lung ventilation, alveolar gas exchange capacity or the amount of blood gas transported into body tissues.

The blood gas analyzers that have been used up to now are not only expensive, but also require a large amount of blood samples for blood gas analysis, and have a problem of pretreating the blood samples for a long time.

In order to solve this problem, studies are being actively conducted to miniaturize and integrate pCO ₂ sensors using semiconductor technology or microfabrication technology such as FET type sensors. Tsukada and W. Schelter formed Ag / AgCl electrodes on silicon nitride (Si3N4) gates of FET-type sensors, and used polyimide to create micro-pools. After forming, a technique of manufacturing a micro carbon dioxide partial pressure sensor has been proposed by forming a gel electrolyte and a gas permeable membrane. In addition, Ph. Arpuint and A. Van den Berg have reported the formation of hydrogels and gas permeation membranes using photolithography in the fabrication of such micro carbon dioxide partial pressure sensors. [K. Tsukada, Y. Miyahara, Y. Shibta and H. Miyagi, Anintegated chemical sensor with multiple ion and gas sensors, Sensors and Actuators B, 291-295 (1990). W. Schelter, W. Gumbrecht and B. Montag, Combination of amperometic and potentiometric sensor principles for on-line blood monitering, Sensors and Actuators B, 6, 91-95 (1992). Ph. Arquint, A. van den Berg, BH van der Schoot and NF de Rooij, Sensors and Actuators B, 340-344 (1993).

1 shows a cross-sectional structure of a pCO ₂ sensor using a ion ion field effect transistor pH sensor. The pCO ₂ sensor includes a silicon substrate 1, a source region 2, a drain region 3, and silicon oxide (SiO 2). It consists of pH sensing layer (5), aluminum metal electrode (6), reference electrode (NiCr / Ag / AgCl) (7), hydration gel film (8), gas permeation film (9) and pH sensing gate (10). Is showing.

Here, the hydrogel film for the pCO ₂ sensor can form a photocrosslinked or copolymerized photosensitive polymer material through photolithography. First, a hydrogel film of the dissolved carbon dioxide sensor by a photolithography process using a photocrosslinked photosensitive polymer solution. The formation process is as follows.

1.5 g of poly (vinyl pyrrolidone-co-vinyl acetate) and 0.1 g of the crosslinking agent 4,4'-diazidostilbene-2,2'-disulfonic acid disodium salt were dissolved in 3.5 g of a solvent of water. To this solution, 0.042 g of NaHCO _{3 and} 0.029 g of NaCl were added as an internal electrolyte to prepare a photoresist for forming a hydrogel film. The hydrated gel film is formed through the process of rotating the photoresist prepared as described above on the pH sensor having the Ag / AgCl electrode shown in FIG. 1 and exposing and developing the UV light source.

At this time, it was observed that the hydrated film was formed only below 3 μm, and it was difficult to obtain a hydrated gel film having a thickness greater than that. This is because the crosslinking reaction occurs first in the upper part of the hydrogel film during exposure, and it is determined that UV light is difficult to penetrate to the lower part containing the solvent. Accordingly, the photocrosslinkable photosensitive polymer solution is a hydrogel for photolithography. It was found that the film was not suitable as a material for forming a film.

Next, a process of forming the hydrogel gel film 8 for the carbon dioxide partial pressure sensor by photolithography using a photopolymerizable photosensitive polymer will be described. First, a hydrophilic monomer such as 2-hydroxyethyl methacylyate (hereinafter referred to as HEMA) or acrylamide is dissolved in a solvent such as water and ethylene glycol, and a photoinitiator is added thereto to prepare a photosensitive polymer solution. do. The photoresist at this time was 2.875 g of HEMA, 0.1 g of 2,2-dimethoxy-2-phenyl-acetophone (DMPA) as a photoinitiator, 0.05 g of N, N'-methylene bisacrylamide (MBAA) as a crosslinking agent, and polyvinyl as a thickener. It is prepared with 3.0 g, 1.9 g, 0.1 M NaHCO ₃ and NaCl salts of pilolidone (PVP), solvent water and ethylene glycol (EG), respectively.

Thereafter, the photosensitive polymer solution is spun onto a photosensitive field effect transistor pH sensor (pH-ISFET) forming an Ag / AgCl reference electrode to form a thin film and to prevent contact with oxygen in the air. The film is covered with a Mylar film), and a mask is placed thereon and exposed to an ultraviolet light source. Specifically, the photolithography process forms a thin film by dropping about 50 mg of the upper photoresist at a rotational coating speed of 1500 rpm (25 seconds), and then exposes the mylar film to block exposure to oxygen in the air. 120 seconds) and develop (40 seconds) using ethanol as a solvent to prepare a hydrogel gel film.

In the photolithography process of the hydrogel film using the photopolymerized photosensitive liquid, oxygen in the air causes the polymerization inhibitory action, and thus the pattern of the hydrogel film was formed only when the mylar film was used as the oxygen barrier film. This is shown in FIG. And even when the pattern was obtained, the interface was not clear as shown in the sensing film pattern diagram of FIG.

In addition, in the photolithography process, the mylar film must be peeled off for the post-exposure development. In this process, the surface state of the hydrogel film becomes very irregular and the thickness control problem occurs. After forming the hydrogel film and inspecting it through an optical microscope, as shown in FIG. 3, a large number of fine pinholes exist on the surface of the sensing film, which is invisible even after covering the mylar film. It was found that the polymerization did not proceed in the presence of the rinsed off during development.

Therefore, the pH sensor using such a sensing membrane may cause hydrogen ion sensitivity in the solution under measurement when the measured aqueous solution passes through the gas permeation membrane and reaches the internal hydrogel film during the measurement of the dissolved carbon dioxide partial pressure.

On the other hand, in the gas permeation film forming process of the pCO ₂ sensor by photolithography method, in order to prevent contact with oxygen in the air, the mylar film is covered on the photosensitive liquid polymer thin film, which is rotated, and then put on a mask and exposed to a UV light source. have. The reason why the mylar film is used during the photolithography process is that photopolymerization or photocrosslinking is caused by oxygen polymerization inhibition when oxygen in the air comes into contact with the photosensitive polymer layer of the rotary coated thin film to form a hydrogel or gas permeable membrane. This is because the hydrogel film or gas permeable film to be formed due to the reaction is not obtained with a fine pattern.

However, in the manufacture of the pCO ₂ sensor by the conventional photolithography method as described above, the following two problems occur when the hydrogel film or the like uses the mylar film to avoid contact with oxygen in the air.

One is to cover the mylar film on the photosensitive liquid coated with a thin film to form a hydrogel film or a gas permeable membrane, and to remove the mylar film for development after exposure to a UV light source through a mask. Due to the adhesion between the mylar films, a hydrogel film or gas permeable membrane with a high degree of surface curvature is obtained, and in addition, pinholes are generated in severe cases, so that the carbon dioxide partial pressure sensor element is manufactured poorly or the lifetime of the sensor element is shortened. to be.

On the other hand, in the manufacturing process of the FET type dissolved carbon dioxide partial pressure sensor by photolithography, a process is performed after removing the mylar film after covering the mylar film after exposing the photoresist to form a hydrogel film or a gas permeable film and exposing it. This is accompanied by the fact that such a process is not applicable to the general semiconductor device mass production process, and therefore is not suitable for mass production of a carbon dioxide partial pressure sensor.

An object of the present invention is to solve the problems in the prior art as described above through the semiconductor manufacturing technology by the photolithography method to enable the mass production of FET-type carbon dioxide partial pressure sensor and to improve the yield and reliability of sensor products electric field The present invention provides a method for manufacturing an effect transistor-type dissolved carbon dioxide sensor.

A feature of the present invention is that when the FET-type dissolved carbon dioxide sensor is coated with a thin film of a photopolymerizable photosensitive polymer solution to form a hydrogel and a gas permeable membrane on an Ag / AgCl reference electrode, the polymerization is sufficient even if they come into contact with oxygen in the air. By adding an oxygen reducing agent to the photosensitive polymer solution so as to obtain an inhibitory effect, the field effect transistor-type dissolved carbon dioxide having a double layer structure of a hydrogel film and a gas permeable film using photolithography without using a mylar film It is to provide a method of manufacturing a sensor.

1 is a cross-sectional structure diagram of a field effect transistor type dissolved carbon dioxide partial pressure sensor.

2 is a surface view of a sensing film when formed using a polyester film in the manufacture of a FET-type dissolved carbon dioxide partial pressure sensor according to a conventional method.

3 is a graph illustrating a surface state measurement of a sensing film of a FET-type dissolved carbon dioxide partial pressure sensor manufactured according to a conventional method.

4 is a surface view of a hydrogel film formed by the present invention.

5 is a graph of I _D -V _D characteristics of the carbon dioxide partial pressure sensor manufactured according to the present invention.

Figure 6 is a graph of the detection characteristics when the CO ₂ concentration is different when manufacturing the carbon dioxide partial pressure sensor according to the present invention.

7 is a response time characteristic graph according to the hydrogen ion concentration change in the measurement solution of the carbon dioxide partial pressure sensor prepared according to the present invention.

* Explanation of symbols for main parts of the drawings

1 silicon substrate 2 source region

3: drain region 4: silicon oxide (SiO ₂ ) layer

5: silicon nitride (Ph sensing) layer 6: aluminum metal electrode

7: reference electrode (NiCr / Ag / AgCl) 8: hydrogel film

9: gas permeable membrane

Hereinafter, the present invention will be described.

The dissolved carbon dioxide partial pressure sensor using the ion-sensing field effect transistor pH sensor is a silicon substrate (1), a source region (2), a drain region (3), a silicon oxide (SiO2) layer (4), as shown in FIG. And a silicon nitride (Si 3 N 4) pH sensing layer 5, an aluminum metal electrode 6, a reference electrode 7, a hydrogel film 8 and a gas permeable film 9.

In order to prevent the polymerization of oxygen during the formation of the hydrogel film 8 of the partial pressure sensor, N, N, N ', N'-tetramethyl ethylenediamine (TED) is used as an oxygen reducing agent (O ₂ quencher). Was used.

To prepare the photoresist, HEMA 2.875g, DMPA 0.1g as photoinitiator, MBAA 0.05g as crosslinker, PVP 0.1g as thickener and 3.0g / 1.9g as solvent / water / EG respectively, 0.1M sodium bicarbonate, sodium salt salt After mixing to prepare a photoresist, 0.6 g of TED, which is an oxygen reducing agent, was added thereto, followed by sufficiently stirring to prepare a final photoresist.

4 shows the hydrogel film when the photolithography process was performed using the photoresist thus prepared under conditions of a rotational application speed of 1500 rpm (25 seconds), exposure 240 seconds, and developing ethanol (10 seconds). Drawing.

Under these conditions, the hydrogel film was formed by photolithography, and then the rotational coating speed was 1000 rpm (25 seconds) using a gas permeable membrane-forming photosensitive solution consisting of 2.95 g of UV-oligomer, 2.5 g of THF, 0.15 g of DMPA, and 0.3 g of TED. A gas permeable film was formed under a photoetch process condition of 210 seconds of exposure and 10 seconds of developing toluene.

5 shows the I _D -V _D characteristics of the carbon dioxide partial pressure sensor manufactured according to the above-described photolithography process, and shows that the hydrogel acts as an internal electrolyte. However, the sensitivity of the FET type CO2 partial pressure sensor manufactured in this way was relatively low at 32mV / decade. This was attributed to the lack of water content of the hydrogel film.

Thus, when forming a hydrogel film using a HEMA-based photoresist, a second photoresist containing hydrophilic acrylamide was prepared to compensate for the lack of water content in the hydrogel film. Was investigated.

The second photoresist was prepared by acrylamide 2.0g, riboflavin-5-phosphate 0.05g photoinitiator, MBAA 0.25g crosslinking agent, PVP 0.15g thickener, 0.5g TED oxygen scavenger, and water / glycerine 1.5g / It consisted of 1.5 and 0.1 M NaHCO ₃ NaCl salt.

Next, the experiment was performed while changing the photolithography process conditions such as coating, exposure (UV), and development (water) by a spin coater, and the surface loss was severe during shrinkage and development of the film after exposure. Therefore, it was judged that the photo etching of the hydrogel film using the photosensitive liquid containing acrylamide as a main component was difficult.

In the case of forming a hydrogel film using a photosensitive liquid containing acrylamide or HEMA as a main component as the photopolymerizable monomer, HEMA and acrylamide are used to compensate for the problem of lack of moisture in the photogel process or the inside of the hydrogel film of the manufactured sensor. Photolithography using a third photosensitive solution containing at the same time was investigated.

The third photoresist was prepared by HEMA 2.875g, acrylamide 0.5g, photoinitiator DMPA 0.1g, crosslinking agent MBAA 0.5g, thickener PVP 0.1g, oxygen damper TED 0.6g and solvent water / ethylene glycol 3.0g / 1.9 g and 0.1 M NaHCO ₃ NaCl salt.

The photolithography process was performed under conditions of a rotational coating speed of 1000 rpm (25 seconds), exposure (210 seconds), developing ethanol, and water (10 seconds). It was found that a very precise hydrogel film pattern was obtained here. Therefore, pCO ₂ sensor can be manufactured by making a hydrogel film under these conditions and forming a gas permeable membrane thereon.

Figure 6 shows the detection curve according to the change of carbon dioxide concentration of the dissolved carbon dioxide partial pressure sensor of the present invention showed a linear phase in the range of carbon dioxide concentration 10 ^-3 mol / 1 ~ 10 ⁰ mol / l and the sensitivity is 53mV / decade dissolved carbon dioxide It is supposed to work as a sensor.

7 shows a response time curve different from the concentration change of (H ⁺ ) in the measurement solution by the sensor of the present invention.

As described above, the present invention is limited to the film thickness control in addition to the problem of pinhole generation on the surface of the film, which is a problem that occurs during the adsorption and desorption by using a mylar film when the sensing film is formed in the field effect transistor type sensor previously reported. This problem has been solved by preparing and using a photosensitive liquid containing an oxygen reducing agent, and it is possible to eliminate the use of the mylar film that has been used in the conventional sensor manufacturing. Since the partial pressure sensor can be manufactured, the unique effect of mass production of high-quality sensor products is exhibited.

Claims (3)

Silicon substrate 1, source region 2, drain region 3, silicon oxide pH sensing layer 5, aluminum metal electrode 6, reference electrode 7, hydration gel film 8 and gas permeable film ( 9) A method of manufacturing a FET type carbon dioxide partial pressure sensor composed of 9), in order to avoid the polymerization inhibitory effect by oxygen when forming a hydrogel film and a gas permeable membrane for a carbon dioxide sensor by photolithography using a photopolymerizable polymer. A method of manufacturing a field effect transistor-type dissolved carbon dioxide sensor, comprising forming a double-layered sensing film using, N ', N'-tetramethyl ethylenediamine (TED) as an oxygen scavenger. The method of claim 1, wherein the hydrogel film is prepared with a photopolymerized photosensitive solution having a composition of HEMA and acrylamide monomer, DMPA as a photoinitiator, MBAA as a crosslinking agent, PVP as a thickener and water / ethylene glycol as a solvent, and NaHCO ₃ , NaC 1 salt. Thereafter, a photoresist prepared by putting TED for preventing an oxygen polymerization inhibiting action is formed in a photolithography process to form a field effect transistor-type dissolved carbon dioxide sensor. The method of claim 1, wherein the gas permeable membrane is formed using a photoresist prepared by preparing a UV-oligomer, a photoinitiator DMPA, a photopolymerizable photosensitive solution having a THF composition of solvent, and adding TED therein to prevent oxygen polymerization inhibition. Method for producing a field effect transistor type dissolved carbon dioxide sensor, characterized in that.

Images