JPH09196879A - Tin oxide thin film sensor for sensing hydrogen and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the sensitivity to hydrogen by providing an insulating film existing on a semi-conductor substrate, a lower electrode existing on the insulating film, and a tin oxide thin film formed by an ion beam vapor deposition method. SOLUTION: An insulating film 102 preferably a silicon dioxide film is provided on a semi-conductor substrate 100. A lower electrode 104 preferably composed of platinum or palladium is provided on the insulating film 102. A tin oxide thin film 106 to perform a function as a sensor is spread on the electrode 104 and a portion of the insulating film 102 having no electrode 104 with thickness kept to 100-1000Å, representatively 400Å, to compose the hydrogen sensing tin oxide thin film sensor. The manufacturing method is desirably to form the insulating film 102 and the lower electrode 104 by an ion beam sputtering and the tin oxide thin film 106 by an ion beam vapor deposition method. Sputtering and vapor deposition made through ion beam are carried out under high vacuum.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a thin film sensor for sensing hydrogen and a method for manufacturing the same. More specifically, the present invention relates to a tin oxide thin film sensor for hydrogen sensing, which uses a tin oxide thin film manufactured by an ion beam deposition method without using a catalyst and has excellent sensitivity and selectivity to hydrogen, and a method for manufacturing the same.

[0002]

2. Description of the Related Art As a sensor for detecting a reducing gas such as hydrogen, an oxide such as tin oxide (SnO ₂ ) formed into a lump or a thick film is used. But,
These are not suitable for mass production because they need to be pressed into a powdery raw material and then heat-treated at a high temperature to form a sintered body. The sensitivity is also low.

A thin film sensor having a thickness of several hundred to several thousand liters is generally excellent in sensitivity, reproducibility and productivity, has low power consumption, and is advantageous in cost. However, a thin film sensor applicable to hydrogen sensing has not yet been announced.

A method of adding platinum or palladium to a tin oxide thin film to increase the sensitivity as a sensor has been studied. In such studies, it is extremely difficult to control the thickness, orientation, crystallinity, density and ultrafine pores of the thin film because the thin film is produced by physical sputtering or CVD. Is extremely complicated.

On the other hand, it has been disclosed by the present inventors that an ion beam can be used to form a high quality and high density thin film on a metal, a semiconductor and an oxide (SK Koh.
JVST-A Vol. 13, No. 4, 2123-2127 (1995)).

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thin film type hydrogen sensing sensor having high sensitivity, selectivity and reproducibility to hydrogen, low power loss, and suitable for mass production. It is to provide a manufacturing method.

[0007]

The inventors of the present invention evaporate metallic tin (Sn) by using a metal gun, and at the same time, add energy to oxygen to ionize it by a gas ion gun to cause reaction on the surface of a substrate, Tin oxide (SnO ₂ ) at room temperature
It was found to obtain vapor-deposited thin films (SK Koh et al., Environmen
t Ungyong Mulli, Vol. 7, No. 2, 246-252 (1996)), and further finding that this can be applied to the purpose of the present invention,
The present invention has been completed.

That is, the tin oxide thin film sensor for hydrogen sensing of the present invention comprises a semiconductor substrate, an insulating film existing on the substrate,
A lower electrode that is present on the insulating film at a predetermined distance, and a tin oxide thin film that is present on the lower electrode and the insulating film; or a semiconductor substrate, an insulating film that is present on the substrate, It is characterized by including a tin oxide thin film existing on the insulating film, and an upper electrode existing at a predetermined interval in the tin oxide thin film. Also, the manufacturing method is
A step of forming an insulating film on a semiconductor substrate; a step of forming a lower electrode on the insulating film at a predetermined interval; and an ion deposition on the lower electrode and the insulating film to form a tin oxide thin film. Forming steps sequentially; or
A step of forming an insulating film on a semiconductor substrate; a step of forming a tin oxide thin film on the insulating film; and a step of forming an upper electrode on the tin oxide thin film at a predetermined interval. Characterize.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the structure of the tin oxide thin film sensor for hydrogen sensing of the present invention will be described in more detail with reference to FIGS. FIG. 1 is a plan view showing a typical example of electrodes of the sensor, FIG. 2 is a sectional view showing a first embodiment of a manufactured tin oxide thin film sensor, and FIG. 3 is a manufactured tin oxide thin film sensor. It is sectional drawing which shows 2nd Embodiment.

In the first embodiment of the present invention, FIG.
On a semiconductor substrate (100), preferably a silicon substrate, an insulating film (102) having a thickness of preferably 0.1 to 2 μm, typically 1 μm, preferably a silicon dioxide (SiO ₂ ) film, as shown in FIG. Exists. A lower electrode (104), preferably made of platinum or palladium, is present on the insulating film (102) with a thickness of preferably 300Å to 1 μm, typically 600Å, and the lower electrode (104) on the electrode and the insulating layer is formed. A tin oxide (SnO ₂ ) thin film (106), which functions as a sensor, is preferably formed on the portion where 100 μm is absent.
It exists at a thickness of ~ 1,000Å, typically 400Å, and constitutes a tin oxide thin film sensor for hydrogen sensing.

In a second embodiment of the invention, FIG.
As shown in, an insulating film (1
02), tin oxide thin film (106) and upper electrode (10)
4) are present in that order to form a tin oxide thin film sensor for hydrogen sensing. The material, preferable thickness, and typical thickness of each portion are the same as those in the first embodiment, and are different from the first embodiment only in that the electrodes are present on the tin oxide thin film.

In the method for manufacturing a tin oxide thin film sensor for sensing hydrogen according to the present invention, the insulating film and the upper electrode or the lower electrode are preferably formed by ion beam sputtering according to the order of the first or second embodiment described above. A tin oxide thin film is formed by the ion beam evaporation method.

These ion beam sputtering and vapor deposition are preferably carried out in a high vacuum of 10 ^-4 to 10 ^-7 Torr, more preferably 10 ^-5 to 10 ^-6 Torr.
In order to obtain a tin oxide thin film having a small slope of electric resistance with respect to temperature change and having stable sensor characteristics, the energy of oxygen ions during ion beam deposition is 0 to 100.
The range of eV is preferred and 0 eV is particularly preferred. Further, the structure of the sensor formed by such a condition is
It is preferable to use the upper electrode according to the embodiment of the present invention, and it is particularly preferable that the upper electrode is a platinum electrode.

It is generally known that, when a thin film type sensor is manufactured, an ion beam can be applied to manufacture a high quality and high density thin film of various substances including metals, semiconductors and oxides in a low temperature region. ing.

In the present invention, the manufacturing equipment used to manufacture the tin oxide thin film includes a metal gun using an existing ionized cluster beam (hereinafter referred to as ICB) as an ion source, and a cold hollow cathode type gas ion gun. And a hybrid ion beam source equipped with.

The gas ion gun has the advantage that the energy and current density of ionized gas ions can be adjusted to widely adjust various electrical and optical properties different from the crystallinity of the thin film. In this case, there is an advantage that a thin film of high quality can be manufactured with less loss of deposition material.

More specifically, first, the gas ion gun is in the form of a cold hollow cathode equipped with a grid of, for example, 5 cm, and is typically ± 20 ° at a distance of about 45 cm from the gas ion gun. It is a broad ion source with 90% uniformity of ion current density in the range of the angle. It is possible to adjust the beam profile by changing the discharge current and the accelerating voltage and accelerate the ions to 2 kV. .

On the other hand, as the ICB source, for example, the accelerating electrode has a cylindrical shape having a diameter of 3 cm, and typically 45 cm from a crucible nozzle where clusters are generated.
To have an ion current density of 50% at a distance,
It is preferable to mount a substrate.

The tin oxide thin film sensor formed as described above can be effectively used without doping, but in order to further improve its electrical and chemical properties and sensitivity to hydrogen, doping May be given. Doping can be performed by implanting at least one metal selected from palladium, platinum, silver and aluminum as a dopant on the basis of the tin oxide thin film.

In order to improve the thermal stability of the tin oxide thin film sensor formed according to the first or second embodiment, the thin film sensor is placed in air, preferably at 600 ° C. or lower,
More preferably 300 to 600 ° C., typically 500
At a temperature of ℃, preferably 10 minutes to 2 hours, typically 1
Heat treatment may be performed for a time. When the heat treatment temperature exceeds 600 ° C., the thin film becomes SnO ₂ completely, crystal defects disappear, and the crystal grain size increases, so that the reactivity with respect to the target gas decreases and the sensitivity decreases.

[0021]

The tin oxide thin film sensor for hydrogen sensing provided by the present invention comprises an excellent tin oxide thin film and a platinum electrode or a palladium electrode, and is used as a pure tin oxide thin film without doping or catalysis. However, it has excellent sensor characteristics such as high electrical sensitivity to hydrogen, excellent selectivity and reproducibility. Furthermore, the method for producing a tin oxide thin film sensor for hydrogen sensing of the present invention is suitable for mass production and can provide the above tin oxide thin film sensor with excellent productivity.

[0022]

The present invention will be described in more detail with reference to the following examples. The present invention is not limited by these examples.

The sensitivities of the produced hydrogen sensing sensors to the respective target gases to be measured were calculated by the formula (I) by measuring the electric resistivity in air and in the target gas having a predetermined concentration.

[Equation 1] Where R _{a is} the electrical resistivity of the sensor in air R _{g is} the electrical resistivity of the sensor in air containing the gas to be measured

The selectivity of the sensor was evaluated by comparing the sensitivity of the sensor to various gases.

Example 1 On a Si substrate of 10 mm × 5 mm, with a high vacuum of 10 ⁻⁶ Torr,
SiO _{2 in} a mixed gas with a volume ratio of argon and oxygen of 3: ₂
Was carried out by ion beam sputtering to form a SiO ₂ insulating layer having a thickness of 1 μm. Next, a screen was formed on the insulating layer so as to form electrodes having a pattern shown in FIG.
The thickness of platinum is 60 by r-ion beam sputtering.
It was vapor-deposited on 0Å to make a lower electrode.

Then, by a gas ion gun, oxygen is ionized to set the ion beam energy (Vi) to 0, 300, 500 or 1,000 eV, respectively, and ICB
A tin oxide thin film having a thickness of 400 Å is deposited on the lower electrode and on the portion of the SiO ₂ insulating layer where the lower electrode is not formed by irradiating and vaporizing Sn having a purity of 99.995% or more contained in the crucible. It was vapor-deposited. Take out this stack,
A heat treatment was performed in air at 500 ° C. for 1 hour to produce a hydrogen sensing sensor whose cross section is shown in FIG.

The electrical resistance was measured for the four hydrogen sensing sensors thus obtained, which were prepared by using platinum as the lower electrode and changing the ion beam energy when the tin oxide thin film was formed. .

FIG. 4 shows changes in electric resistance with temperature. From Fig. 4, the oxygen ion energy is 0 eV.
At this time, the slope of the electric resistance with respect to the change in temperature is particularly small, which shows stable characteristics, and it is clear that the activation energy is extremely low.

Example 2 The conditions for forming each component were the same as in Example 1 except that the ion beam energy for forming the tin oxide thin film was 300 eV, and the electrode formation position and the electrode material were as follows. Instead, the changes in the electrical resistances of the three obtained sensors with temperature were compared. (1) Platinum lower electrode (first embodiment) (2) Platinum upper electrode (second embodiment) (3) Palladium upper electrode (second embodiment)

FIG. 5 shows the result. As is clear from FIG. 5, when the energy of oxygen ions is 300 eV, the structure of the sensor is preferably in the form of the upper electrode shown in FIG. 3, and platinum is most preferably used as the electrode material in the structure.

Example 3 In addition to the method of forming the platinum upper electrode according to the second embodiment by setting the ion beam energy at the time of forming the tin oxide thin film to 0 eV, the conditions for forming each component are described in Example 1. A sensor having a tin oxide thin film was prepared in the same manner as in. A sensing test was conducted using this sensor.

The sensitivity of each reducing gas was measured at a measuring temperature of 100 to 500 ° C. using air containing 3,000 ppm of hydrogen, propane or methane, respectively.

The results are shown in FIG. As is clear from FIG. 6, propane has a low sensitivity up to 250 ° C. and methane has a low sensitivity up to 450 ° C., and the sensitivity sharply rises above these temperatures, and at 500 ° C., propane is 47.33.
%, Methane showed a sensitivity of 21.23%. In comparison, hydrogen uses pure tin oxide as a thin film for sensors,
Although no doping was performed, the sensitivity was 99.3% or more in the entire temperature range.

Next, at a measuring temperature of 150 ° C. or 250 ° C., the hydrogen concentration in the air was changed between 100 and 5,000 ppm, and the sensitivity was measured. FIG. 7 shows the result. At any temperature, the higher the concentration, the higher the sensitivity. At the measurement temperature of 250 ° C., particularly suitable characteristics were exhibited, and measurement at a fine concentration was also possible.

At the measurement temperature of 250 ° C., the hydrogen concentration is set to 1
Gradual increase in the range of 00 to 5,000 ppm
Fig. 8 shows the change in output voltage when returning from 0ppm to air. FIG. 8 shows the response time (unit:
Seconds) and recovery time (unit: seconds) when returned to air. The response characteristics reliably distinguished by the concentration were excellent within 11 seconds, and the recovery characteristics showed a fast recovery time of 4 seconds.

FIG. 9 shows the results of investigation of response / recovery characteristics at a hydrogen concentration of 500 ppm while changing the measurement temperature.
And shown in Table 1. Higher temperatures showed faster response / recovery times, with a response time of 12 seconds and a recovery time of 2 seconds at 250 ° C., which was shorter than the industrially usable limit of 20 seconds.

[0037]

[Table 1]

[Brief description of drawings]

FIG. 1 is a representative plan view of electrodes of a tin oxide thin film sensor for sensing hydrogen according to the present invention.

FIG. 2 is a cross-sectional view showing a structure of a tin oxide thin film sensor for sensing hydrogen according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional view showing the structure of a tin oxide thin film sensor for hydrogen sensing according to a second embodiment of the present invention.

FIG. 4 is a temperature of a sensor having a platinum lower electrode of the present invention-
It is a graph which shows an electric resistance characteristic.

FIG. 5 is a graph comparing the temperature-electrical resistance characteristics of sensors with different electrode positions and electrode materials.

FIG. 6 is a graph showing temperature-sensitivity characteristics of a sensor having a platinum upper electrode on which a tin oxide thin film is formed with oxygen ion energy of 0 eV, to hydrogen, propane, and methane.

FIG. 7 is a graph showing hydrogen concentration-sensitivity characteristics of a sensor having a platinum upper electrode on which a tin oxide thin film is formed with oxygen ion energy of 0 eV.

FIG. 8 is a graph showing hydrogen concentration-output voltage characteristics of a sensor having a platinum upper electrode on which a tin oxide thin film is formed with oxygen ion energy of 0 eV.

FIG. 9 is a graph showing the response / recovery characteristics at various temperatures of a sensor having a platinum upper electrode on which a tin oxide thin film was formed with oxygen ion energy of 0 eV.

[Explanation of symbols]

 100 Semiconductor Substrate 102 Insulating Film 104 Electrode 106 Tin Oxide Thin Film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Choi Yuan-guk, New Town Apartment, 903 No. 5 Dong-gu, Yangcheon-gu, Seoul, Republic of Korea 303-1202 (72) Inventor, Yin Xu, Bei-dong 6, Gwacheon, Gyeonggi-do, Republic of Korea No. Sumiko Apartment 501-507 (72) Inventor Zhao Shun Ue 100-4-18, Juan An, South-gu, Incheon-gu, Incheon, Republic of Korea 7/4 (72) Inventor Choi Dong-soo 2 Takagatsu, Ansan City, Gyeonggi-do, Republic of Korea 670, Dong-dong Sungkook Apartment 706-402 (72) Inventor All Jin-suk 440-19, Tsukiji-dong, Ansan-si, Gyeonggi-do, Republic of Korea

Claims (18)

[Claims] 1. A semiconductor substrate, an insulating film existing on the substrate, a lower electrode existing on the insulating film at a predetermined distance, and a tin oxide thin film existing on the lower electrode and the insulating film. A tin oxide thin film sensor for sensing hydrogen, which is characterized in that 2. The tin oxide thin film sensor for sensing hydrogen according to claim 1, wherein the lower electrode is platinum or palladium. 3. The lower electrode has a thickness of 300Å to 1 μm.
The tin oxide thin film sensor for sensing hydrogen according to claim 1, which is m 2. 4. A semiconductor substrate, an insulating film existing on the substrate, a tin oxide thin film existing on the insulating film, and an upper electrode existing on the tin oxide thin film at a predetermined interval. And a tin oxide thin film sensor for hydrogen sensing. 5. The tin oxide thin film sensor for sensing hydrogen according to claim 4, wherein the upper electrode is platinum or palladium. 6. The upper electrode is platinum, as recited in claim 5.
A tin oxide thin film sensor for hydrogen sensing as described. 7. The upper electrode has a thickness of 300Å to 1 μm.
The tin oxide thin film sensor according to claim 4, wherein the tin oxide thin film sensor has m 2. 8. The tin oxide thin film sensor for sensing hydrogen according to claim 1, wherein the insulating film has a thickness of 0.1 to 2 μm. 9. The tin oxide thin film has a thickness of 100 to 100 nm.
The tin oxide thin film sensor for hydrogen sensing according to claim 1 or 4, which has a thickness of 1,000 Å. 10. A step of forming an insulating film on a semiconductor substrate; a step of forming a lower electrode on the insulating film at a predetermined interval; and ion deposition on the lower electrode and the insulating film. A method for manufacturing a tin oxide thin film sensor for hydrogen sensing, which comprises sequentially performing a step of forming a tin oxide thin film by means of the following method. 11. The manufacturing method according to claim 10, wherein the lower electrode is formed by using an ion beam sputtering method. 12. A step of forming an insulating film on a semiconductor substrate; a step of forming a tin oxide thin film on the insulating film; and a step of forming an upper electrode on the tin oxide thin film at a predetermined interval. A method for manufacturing a tin oxide thin film sensor for hydrogen sensing, which comprises sequentially performing the steps. 13. The manufacturing method according to claim 12, wherein the upper electrode is formed by using an ion beam sputtering method. 14. The tin oxide thin film is deposited under high vacuum while tin is deposited by an ion crust beam source,
11. The surface of a sample is irradiated with oxygen after ionizing oxygen using a cold hollow cathode type ion gun, and formed.
Or the manufacturing method according to 12. 15. The method according to claim 14, wherein the tin oxide thin film is formed in a state where the energy of the oxygen ions is 0 to 100 eV. 16. The manufacturing method according to claim 10, further comprising a step of performing heat treatment in air at a temperature of 600 ° C. or lower after forming the tin oxide thin film. 17. The manufacturing method according to claim 10, wherein after the tin oxide thin film is formed, a step of injecting a dopant into the thin film is further performed. 18. The method according to claim 10, wherein the dopant is selected from platinum, palladium, silver and aluminum.