JPS6026455B2 - Gas/humidity sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is constructed by combining an ultrafine particle film sensitive to external agents such as gas and water vapor with a MOS field effect transistor (hereinafter referred to as MOS FET).
This invention relates to a gas/humidity sensor for detecting the concentration of molecules such as gas and water vapor with high sensitivity.

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

This takes advantage of the fact that when a specific gas comes into contact with a Pd thin film, the threshold and voltage VT of the MOS FET change depending on its concentration, and as a result, the voltage and current characteristics of the MOS FET change. be. However, when using this method for general detection targets such as gas and water vapor, there are still problems such as sensitivity that need to be resolved. The present invention
This is based on the discovery that the detection sensitivity for gas or water vapor can be dramatically increased by replacing the Pd vapor-deposited film in conventional equipment with an ultrafine particle film produced by evaporation in gas. .

Hereinafter, details of the present invention will be explained using the drawings.
FIG. 1 is a diagram for explaining the manufacturing process of an embodiment of a semiconductor sensing device having a MOS type FET structure according to the present invention.

First, this manufacturing method will be explained.

1 is, for example, a P-type silicon O substrate having an orientation of 100>, and has a resistivity of approximately IQ.

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. Thereafter, an impurity 5 for forming an n-type semiconductor, such as phosphorus, is diffused or implanted through the window 3 of the oxide film 2 by a well-known thermal diffusion method or ion implantation method to form a source region 4 and a drain region 5 ( Figure 1A). Next, after completely removing the oxide film 2, the substrate 1 is heat-treated for about 4 minutes in a steam atmosphere of 1000 Å to form a new thermal oxide film 6 of about 3000 Å. 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, the substrate 1 is converted to 202-3S04, HF-
After carefully washing in the order of NH4F, HN03, and ultrapure water, heat treatment was performed for about 20 minutes in a dry oxygen atmosphere of 900 oo, and a gate oxide film 7 with a thickness of about 100 A was formed on the window portion.
form. (Figure 1B). Thereafter, contact windows for the source region 4 and drain region 5 are selectively formed in the thermal oxide film 6.

After that, an electrode material such as AI is evaporated to form a metal thin film, and then selectively removed by a well-known photolithography method to form a predetermined source electrode 8 and drain electrode 9 (FIG. 2c). . Next, a metal ultrafine particle film such as Pd or Sn02, Zn○, Ti02, Nj
Forms an oxide ultrafine particle film such as ○.

Thereafter, this ultrafine particle film is selectively removed so that at least the ultrafine particle film 10 remains on the gate oxide film 7 (FIG. 1D). The production of an ultrafine particle film of Sn oxide will be explained using FIG. 2 as an example.

The sample holder 22 in the normal vacuum evaporation equipment
A substrate 1 having the structure shown in FIG. C is mounted so that the gate oxide film 7 side faces downward in the drawing.

Sn, Sn○, or Sn is placed on the vapor deposition boat 23.
After setting the evaporation material 24 such as 02, open the exhaust port 2.
5 by operating a vacuum pump (not shown) connected to
The inside of the vacuum evaporation layer 21 is made to have a degree of vacuum of about 5×10 −6 Torr. Then, open the cock of the 02 inlet 26, introduce the 02 gas into the vacuum evaporation equipment 21, and reduce the 02 pressure to 0.
Keep it at around 5 Tom. Next, the evaporation power source 27
The boat 23 is energized in a gas atmosphere to generate heat,
The evaporation material 24 is evaporated for 1 second to several minutes. For example, if Sn is selected as the evaporation material 24,
When a power of V was applied to the boat 23 for 1 minute, a Sn oxide ultrafine particle film with a thickness of about 1 V was formed on the surface of the substrate 1. Here, a method using resistance heating has been described as a method for evaporating the evaporation material, but it goes without saying that methods such as induction heating may also be used. The properties of the ultrafine particle film produced in this way vary considerably depending on the production conditions.

Among various production parameters, it is particularly strongly dependent on the atmosphere used in the ultrafine particle formation process, that is, the 02 gas pressure.
Taking the case of ultrafine particles of S rudder oxide as an example, at 02 gas pressure lmom, the average particle size is 100 and more, and at 02 gas pressure ITor
At r, ultrafine particles of several tens of amperes are formed. In general, 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. In ultrafine particles with a particle size of 100A, the number of surface atoms is about 20% of the total number of atoms, and the surface energy is a few percent of the binding energy.In ultrafine particles with a particle size of 20A, the former accounts for about 80% and the latter accounts for 10%. It becomes more than that. This shows that the ultrafine particle film interacts extremely sensitively with external agents such as gas and water vapor. 0 Figure 3 shows the relationship between the 02 gas pressure and the sensitivity to isobutane scum when forming an ultrafine particle film of Sn oxide.

As is clear from the figure, when the 02 gas pressure becomes 0.1 Ton or more, sensitivity is exhibited, and the sensitivity becomes maximum at 0.4 to 0.8 rorr. If the pressure becomes higher than that,
The sensitivity decreases again and shows almost no sensitivity near lOTon. When the average particle size of the ultrafine particles of Sn oxide was determined from the results of the X-ray diffraction pattern, the sensitivity was found to be approximately in the range of 10 to 120 A, as shown by the wavy line in the figure.
In particular, the sensitivity is maximum in the range of 10 to 20A in average particle size. For comparison, a vapor-deposited film of Sn oxide was formed in an atmosphere of 02 gas pressure of about 10-4 tons, which is commonly practiced. According to this, almost no sensitivity was observed. The reason why the ultrafine particle film and the vapor-deposited film are essentially different in this way is considered to be due to the following properties of the ultrafine particles.

In other words, each ultrafine particle is a single crystal with an average particle diameter of several tens of amps to several hundred amps, and has properties very similar to those of the bulk, but its surface energy is much higher than that of the bulk. . An ultrafine particle film is a film in which individual ultrafine particles with these characteristics are aggregated and deposited at an appropriate density, that is, a filling rate ranging from tenths to several hundredths of the total volume, depending on the manufacturing conditions. Therefore, compared to a vapor-deposited film, the surface area in direct contact with the target gas or water vapor is much larger, and as mentioned above, the surface energy is also much higher. For this reason, the surface activity of the ultrafine particle film is extremely high, and features that cannot be predicted from the characteristics of the deposited film can be obtained. For the above reasons, the first
As shown in Figure D, a device with a MOS type FET structure in which an ultrafine particle film of a metal or oxide that is sensitive to gas or water vapor is deposited on a gate oxide film is a device with a simple vapor deposition film on the gate oxide film. It is possible to detect the concentration of gas, water vapor, etc. with extremely high sensitivity compared to a device with an attached MOS type FET structure.

FIG. 4 is a main sectional view showing another example of the present invention.

That is, electrical contact is made with the metal or oxide ultrafine particle film 10 on the gate oxide film 7, on the portion extending from the gate oxide film 7 to the field oxide film 6, or on the field oxide film 6. Like, AI or Au/C
An electrode 11 made of material r is formed so that an arbitrary voltage can be applied to the metal or oxide ultrafine particle film 10 from the outside. The gate potential can be set so that the sensitivity to gas or water vapor is maximized by applying a voltage to this electrode 11 from the outside. One of the major features of the present invention is that an ultrafine particle film is formed on a portion corresponding to the gate of a conventional MOS FET via a thin insulating film, which allows extremely high sensitivity to detect concentrations of gases and water vapor. This means that it can be detected.

Another major feature is that most of the manufacturing processes are suitable for both normal semiconductor integrated circuit manufacturing methods and thin film integrated circuit manufacturing methods, so they can be manufactured in large quantities with relative ease. Therefore, a device with high reliability and uniform characteristics can be manufactured at a relatively low cost.

[Brief explanation of the drawing]

1A, B, C, and D are process diagrams for explaining an embodiment of a semiconductor detection device according to the present invention and its manufacturing process; FIG. 2 is a diagram showing an example of an apparatus for manufacturing an ultrafine particle film; Figure 3 is a diagram showing the relationship between the 02 gas pressure, the sensitivity to isobutane gas, and the average particle diameter of the ultrafine particles during the production of an ultrafine particle film of Sn oxide, and Figure 4 explains another embodiment of the semiconductor detection device. FIG. 1...Substrate, 2...Oxide film, 3...
... window, 4 ... source region, 5 ... drain region, 6 ... oxide film, 7 ... gate oxide film, 8
. . . Source electrode, 9 . . . Drain electrode, 10 . . . Ultrafine particle film, 11 . . . Gate electrode. Figure 4 Figure 1 Figure 2 Ship

Claims (1)

[Claims] 1. A semiconductor substrate having a source region and a drain region;
A gas which is characterized by comprising a gate insulating film formed on the semiconductor substrate, and an ultrafine particle film formed of ultrafine particles having an average particle size of 10 to 120 Å on the gate insulating film. Humidity sensor. 2. The gas/humidity sensor according to claim 1, characterized in that the gate electrode is electrically contacted with the ultrafine particle film. 3. The gas/humidity sensor according to claim 1 or 2, wherein the ultrafine particle film is formed of ultrafine metal oxide particles. 4. The gas/humidity sensor according to claim 3, wherein the metal oxide is Sn oxide.