JPS6026456B2 - Gas/humidity sensor and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a MOS type field effect transistor (hereinafter referred to as MOS) and a MOS type field effect transistor (hereinafter referred to as MOS The present invention relates to a gas/humidity sensor for detecting the concentration of molecules such as gas and water vapor, which is configured by combining a type FET (FET), and a method for manufacturing the same.

Conventionally, a device of this type has been proposed in which a thin Pd film of approximately 100 Å thick is formed by vacuum evaporation on a portion corresponding to the gate of a MOS FET.

This is based on the fact that when gas comes into contact with the Pd thin film, the threshold voltage VT of the MOS FET changes depending on its concentration, and as a result, the voltage-current characteristics of the MOS FET change. be. However, there are still issues with this method, such as sensitivity, that need to be resolved before it can be used for general detection targets such as gas and water vapor. The present invention reduces the sensitivity to gas or water vapor by firmly adhering at least the gate oxide film with a resin in which ultrafine particles produced by evaporation in gas are dispersed, instead of the Pd deposited film in conventional equipment. It has been made possible to easily obtain products with dramatically improved and uniform characteristics.

The details of the present invention will be explained below using the drawings. FIG. 1 is for explaining the manufacturing process of an embodiment of a gas/humidity sensor having a MOS type FET structure according to the present invention.

In the figure, 1 is, for example, p with an orientation of 100>
It is a shaped silicon substrate and has a resistivity comparable to that of IQ-skin. After forming an oxide film 2 of about 3000 Å on the surface of the substrate 1, the oxide film in a predetermined area is removed by a well-known photolithography method to form a window 3. An impurity for forming an n-type semiconductor, such as phosphorus, is diffused or implanted through this window 3 by a well-known thermal axis diffusion method or ion implantation method to form a source region 4 and a drain region 5 (FIG. 1A). Next, after completely removing the oxide film 2, the substrate 1 is
After heat treatment for about 40 minutes in a steam atmosphere at ℃, a new 30
A thermal oxide film 6 of about 00A is formed. A portion of this thermal oxide film 6 is selectively removed by conventional photolithography to open a window for forming a gate oxide film. Then, after carefully cleaning the substrate 1 in the order of 02-5S04, HF-NH4F, HN03, and ultrapure water, it was heat-treated in a dry oxygen atmosphere at 900°C for about 20 minutes.
Form a gate thermal oxide film 7 with a thickness of oA (FIG. 1B)
. Thereafter, contact windows for source region 4 and drain region 5 are selectively formed in oxide film 6.

Next, a metal thin film such as N is formed on the entire surface of the substrate 1 by vapor deposition or the like, and then selectively removed by a well-known photolithography method.
Forming the source electrode 8 and drain electrode 9 (FIG. 1C)
. Then, a commercially available photosensitive resin, such as AZ1400 (trade name: Shipley Co., Ltd.), was diluted to four times the amount with thinner, and spun onto the substrate 1 at a spinner rotation speed of 500 pm to a thickness of several hundred amps. Apply.

After prebaking at 90 qo for about 2 minutes, the other photosensitive resin is removed by a well-known photolithography method, leaving only the photosensitive resin film 10 on the gate oxide film 7 (see Fig. 1). D).

In this photolithography process, in order to minimize curing of the photosensitive resin film, it is desirable to carry out the heat treatment at as low a temperature as possible in a short time. After that, board 1
metal such as Pd or SN02, Ti02,
An ultrafine particle film 11 of oxide such as Zn◯ or Ni◯ is formed.

Thereafter, the substrate 1 is heated in air at a temperature of about 150 qo for about 3 minutes. By this heat treatment, the ultrafine particles are adhered and held on the gate oxide film 7 very firmly. Thereafter, ultrafine particles other than those held by the photosensitive resin film 1 are blown off by blowing air or N2 gas onto the substrate 1 using an air brush or the like (FIG. 1F). As a result, an ultrafine particle film 12 is formed along the surface of the photosensitive resin film 10. Although a photosensitive resin is used as an example here, it is a matter of course that a thermoplastic resin sensitive to electron beams, X-rays, etc. may also be used, without departing from the gist of the present invention. Here, S
Taking the production of an ultrafine particle film of n oxide as an example, the method for forming ultrafine particles will be explained in detail using FIG. 2.

The first sample holder 22 in the normal vacuum evaporation layer
The substrate 1 shown in Figure D is attached and fixed so that the resin pus 10 faces downward in the drawing. In the vapor deposition boat 23, Sn, Sn
After setting the evaporation material 24 such as O or Sn02, a vacuum pump (not shown) connected to the exhaust port 25 is operated to bring the inside of the device 1 to a degree of vacuum of approximately 5×10-6 Tom. After that, the cock of the 02 gas inlet 26 is opened, the 02 gas is introduced into the device 1, and the pressure is set to 0.5, for example.
Keep it at about ton.

Next, the boat 23 is energized by the evaporation power source 27 to generate heat, and the evaporation material 24 is heated under the 02 gas atmosphere.
evaporate for a few seconds to several minutes. For example, evaporation material 24
When Sn is used as
When a power of 4 V was applied for 1 minute, an ultrafine Sn oxide particle film with a thickness of about 1 French was formed on the substrate 1. Although the resistance heating method has been described here as an example of a method for evaporating the evaporation material, it goes without saying that other methods such as induction heating and infrared heating may also be used.

The properties of the ultrafine particle film thus obtained vary considerably depending on the manufacturing conditions.

Among various production parameters, it is particularly strongly dependent on the atmosphere used in the ultrafine particle formation process, that is, the pressure of the 02 gas. Taking the case of ultrafine particles of Sn oxide as an example, at 02 gas pressure 1 plate orr, the average particle size is 100-odd A, and at 02 gas pressure IT
om, ultrafine particles of several tens of amperes are formed. Generally, as the particle size of ultrafine particles becomes smaller, the proportion of the surface in the particles increases, and the proportion of surface energy in the total energy of the particles increases. That is, surface activity increases. Therefore, it is extremely sensitive to external agents such as gas and water vapor. FIG. 3 shows the dependence of the Sn oxide ultrafine particle film on 02 gas pressure on isobutane gas.

As is clear from the solid line in the figure, the sensitivity increases when the 02 gas pressure in the manufacturing atmosphere is 0.1 Ton or more, and 0.4 to 0.
．． Sensitivity is maximum when town is on. When the 02 gas pressure becomes higher than that, the sensitivity decreases and reaches a sensitivity of about lmom. The average particle diameter of the Sn oxide ultrafine particles determined from the X-ray diffraction pattern is as shown by the broken line in the figure. From this, it can be seen that sensitivity is observed when the average particle size is 10 to 120A. For comparison, a Sn oxide vapor deposited film of 10
When fabricated in an atmosphere of -4 Tom and examined for sensitivity, only extremely low sensitivity was obtained. The reason why the ultrafine particle film exhibits superior properties as a sensor compared to the vapor-deposited film is considered to be due to the following reasons.

That is, each ultrafine particle has an average particle size of 10A to 1
It is a single crystal with a diameter of about 20A and exhibits properties similar to those of the bulk, but its surface energy is much higher than that of the bulk. Ultrafine particle films are made by aggregating individual ultrafine particles with such characteristics at an appropriate density, that is, at a filling rate of one-tenth to several hundredths of the total thinness, depending on the manufacturing conditions. Because it is a deposited film, it has a much larger surface area that comes into direct contact with the target gas and water vapor than a vapor-deposited film.
Moreover, as mentioned above, the surface energy is also much higher. In other words, the surface activity of the ultrafine particle film is much higher than that of the vapor-deposited film. For this reason, by attaching a resin film that holds ultrafine particles of a metal or oxide that is sensitive to gas or water vapor on the gate oxide film of a MOS type FET, it is possible to replace the conventional deposited film on the gate oxide film. MOS attached to
It responds to the concentration of gases, water vapor, etc. with extremely high sensitivity compared to type FETs.

One of the major features of the present invention is that an ultrafine particle film of metal or oxide held by resin is formed on the gate-corresponding part of the MOS FET through a thin insulating material. Ultrafine metal or oxide particles are firmly held on the gate oxide film, making it possible to stably detect the concentration of gas, water vapor, etc. with extremely high sensitivity.

Other major features are that ultrafine particles of metal or oxide can be formed only in predetermined areas with great ease and precision, and most of the manufacturing process of the device is similar to the manufacturing process of normal semiconductor integrated circuits and thin film integrated circuits. Because it is suitable for both
The advantage is that the device of the present invention can be manufactured relatively easily and in large quantities, and therefore a device with high reliability and uniform characteristics can be manufactured at a relatively low cost.
Furthermore, in the present invention, the adhesion of the ultrafine particle film of metal or oxide to the gate oxide film is very strong, and there are almost no restrictions on the use of the gas or atmosphere to be measured, allowing the device to be used in a wide range of environments. It also has the advantage of being able to

In addition, since the shape of the metal or oxide ultrafine particle film can be determined as it is by conventional photo-etching techniques, it is possible to easily form a pattern of about two mountains and rivers with great precision.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the manufacturing process of an embodiment of a semiconductor detection device according to the present invention, FIG. 2 is a diagram showing an example of the configuration of an apparatus for manufacturing an ultrafine particle film, and FIG. 3 is a diagram showing an example of the configuration of an ultrafine particle film of Sn oxide. FIG. 2 is a diagram showing the relationship between the 02 gas pressure, its sensitivity, and the average particle size of ultrafine particles during production. 1...Substrate, 4...Source region, 5...
...Drain region, 7...Gate oxide film, 1
0... Resin film, 12... Ultrafine particle film. Figure 1 Figure 1 Figure 2 Ship

Claims (1)

[Claims] 1. A semiconductor substrate having a source region and a drain region;
A gate insulating film formed on the semiconductor substrate, and an ultrafine particle film formed of ultrafine particles with an average particle diameter of 10 to 120 Å held on the gate insulating film by a resin film. A gas/humidity sensor featuring: 2. After forming a resin film on at least the gate insulating film of a semiconductor substrate having at least a source region, a drain region, and a gate oxide film, and further adhering ultrafine particles with an average particle size of 10 to 120 Å, the resin film is Gas/humidity characterized by softening, adhering the ultrafine particles, hardening the resin film, and further removing particles other than the ultrafine particles held in the resin film to form an ultrafine particle film. How to manufacture the sensor. 3. A method for manufacturing a gas/humidity sensor, characterized by evaporating Sn or its oxide in an O_2 gas atmosphere at a pressure of 0.1 to 10 Torr, and depositing ultrafine particles of Sn oxide on at least a resin film. .