JPH0892730A - Production of chromium-oxygen alloy thin film - Google Patents

Abstract

PURPOSE: To prepare a chromium-oxygen alloy thin film having low oxygen content and low temp. coefficient of resistance hardly affected by temp. change without unnecessarily lowering the characteristic of chromium that chromium has high sensitivity to strain, and capable of effectively being used as a thin film for a strain gauge. CONSTITUTION: This chromium-oxygen alloy thin film 0.1-3at.% in oxygen content is produced by using chromium as a target and applying high-frequency sputtering method in an argon-oxygen gaseous mixture atmosphere of 10<-4> -10<-2> Pa order in gaseous oxygen partial pressure. As a result the temp. dependency of the resistance of the thin film is controlled.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a chromium-oxygen alloy thin film. More specifically, it relates to a method for producing a chromium-oxygen alloy thin film that is effectively used as a strain gauge thin film.

[0002]

2. Description of the Related Art In various mechanical sensors such as a pressure sensor and an acceleration sensor, a strain gauge thin film for utilizing a change in electric resistance due to strain is used. It is well known that such strain gauge thin films are made of an alloy material such as a chromium-based material or a semiconductor material, and the latter has a drawback that it is easily affected by temperature changes.

On the other hand, among the chromium alloy materials, the Ni--Cr alloy thin film has a small gauge factor showing strain sensitivity (K =
There is a problem of about 1.6 ~ 2.1), and in the case of Cr-O-Si alloy thin film, the oxygen content is 2 to 30 atom%, preferably
It is set to 15 to 20 atomic% (Japanese Patent Laid-Open No. 2-76201), and the inclusion of such a relatively high content of oxygen inherently has a high gauge factor, and thus high sensitivity to strain. The characteristics of the chromium having Cr will be reduced more than necessary.

[0004]

The object of the present invention is not to reduce the characteristic of chromium, which originally has a high gauge factor, that is, high sensitivity to strain, unnecessarily, in other words, a low oxygen content and a low temperature. It is an object of the present invention to provide a method for producing a chromium-oxygen alloy thin film that has a low temperature coefficient of resistance that is not easily affected by changes and therefore can be effectively used as a strain gauge thin film.

[0005]

SUMMARY OF THE INVENTION The object of the present invention is as follows.
A chromium-oxygen alloy with an oxygen content of about 0.1 to 3 atomic% is applied by applying a thin film formation method in an argon-oxygen mixed gas atmosphere with a partial pressure of oxygen gas on the order of 10 ^-4 to 10 ^-2 Pa, targeting chromium. This is accomplished by producing a thin film.

Any physical or chemical vapor deposition method can be used as a thin film forming means in a mixed gas atmosphere of argon and oxygen with chromium as a target, for example, vacuum vapor deposition method, ion plating method, plasma CVD method. Although a method or the like can be used, a high frequency sputtering method is preferably used. The high frequency sputtering method is performed using a film forming apparatus as shown in FIG. 1, for example.

A chromium target (purity 99.9%) 2 and a substrate 3 facing the chromium target 2 are attached inside the film forming chamber 1 of this film forming apparatus, and an insulating material such as glass, alumina, polyimide resin or the like is used. The back surface of the substrate made of a conductor such as steel, aluminum, titanium, or silicon or a semiconductor having an insulating thin film formed on the surface thereof is heated to a temperature of about 80 to 200 ° C. by the infrared lamp 4 or the like, and at that time, a film is formed. The substrate is preferably rotated during the film forming operation in order to achieve uniform thickness and temperature.

Argon gas and oxygen gas for forming the high frequency sputtering atmosphere are supplied into the film forming chamber 1 after the flow rates thereof are adjusted by the mass flow controllers 7 and 8 from the cylinders 5 and 6, respectively. By adjusting this flow rate ratio, the partial pressure of oxygen gas in the argon-oxygen mixed gas is in the order of 10 ^-4 to 10 ^-2 Pa, preferably 10 ^-3.
Set to Pa order.

Prior to the supply of the mixed gas, the film forming chamber 1 is evacuated to a pressure of about 10 ⁻³ Pa or less by a vacuum pump 10. Immediately before starting the film formation, sputter etching of the target surface and the substrate surface is also performed to prevent the entry of impurities.

The film formation is performed under the conditions of pressure of about 1 × 10 ^{-1 to} 6 × 10 ^-1 Pa, with the effective power of about 200 to 1500 W, preferably about 500 to 1500 W generated from the high frequency power source 9, and the chromium target. Two
By high frequency sputtering. The film formation rate at this time depends on the active power, for example, about 10 nm / min when the active power is 500 W, and a thin film is formed on the substrate with a film thickness of about 50 to 1000 nm, preferably about 200 to 400 nm. To be done. The formed alloy thin film is preferably heat-treated at about 200 to 500 ° C. for about 1 to 5 hours to homogenize it.

On the substrate on which the chromium-oxygen alloy thin film is formed in this manner, electrodes connected to this thin film are attached by any known method to form a strain gauge.

[0012]

[Action] and

The oxygen content rate of the thin film to be formed can be controlled by adjusting the partial pressure of oxygen gas in the argon-oxygen mixed gas.
In particular, the temperature dependence of the thin film resistance can be adjusted. More specifically, the lower the oxygen content in the formed thin film, the higher the gauge factor, while the temperature coefficient of resistance (TCR), which shows the temperature dependence of the thin film resistance, is the most in the 10 ^-3 Pa order. Get lower.

As described above, the chromium-oxygen alloy thin film of the present invention obtained by thinning in an argon-oxygen mixed gas atmosphere having a specific oxygen gas partial pressure has an oxygen content of about 0.1 to 3 atoms.
%, Preferably about 0.5 to 2.5 atom%, more preferably 1.0 to
It has a low oxygen content of 1.9 atomic%, and therefore has a high gauge ratio that chromium originally has, in other words, does not lower the high sensitivity to strain more than necessary, and has a low resistance temperature coefficient that is not easily affected by temperature changes. Therefore, it can be said that it has desirable characteristics as a thin film material for strain gauges.

[0014]

EXAMPLE A sputtering thin film was manufactured by the method as described above using the film forming apparatus shown in FIG. For the substrate, a borosilicate glass plate (thickness 1 mm) washed with an organic solvent and an alkaline detergent was used by heating it to 130 ° C, and the inside of the film formation chamber was set to 8 × 10 ^-4 Pa before introducing the mixed gas. It was evacuated under reduced pressure. Various flow rate ratios (oxygen gas partial pressure)
Pressure of 2.5 × 10 while supplying argon-oxygen mixed gas of
^-1 Pa, 500W active power for about 40 minutes, film thickness
A 400 nm chromium-oxygen alloy thin film was formed on the substrate.

A gauge pattern is formed on the chromium-oxygen alloy thin film formed on the substrate by applying a photolithography method and an etching method using a resist,
After that, high frequency sputtering of gold is performed to attach electrodes,
Test pieces were prepared. In the test piece 11 shown in FIG. 2,
Reference numeral 12 is a substrate, 13 is a gauge portion, and 14 and 14 'are electrodes. The test piece was heat-treated for 4 hours in the air at 300 ° C. after being manufactured.

Using this test piece, the gauge factor and the temperature coefficient of resistance (TCR) were measured. Gauge rate measurement is
The gauge factor was obtained from the relationship between the strain and the amount of resistance change using the method of four-point bending as shown in FIG. Here, 11 is a test piece, 15 and 16 are 4-point bending tables, 17 is a displacement detector, 18
Is an ohmmeter.

The temperature coefficient of resistance was calculated from the amount of resistance change by measuring the resistance at temperatures of -40, 0, 25, 75 and 130 ° C. Further, the composition of the thin film was measured by photoelectron spectroscopy. Before the measurement, the oxide on the film surface was removed by an ion gun, and the composition inside the film was measured.

The measurement results of the above items are shown in the following table. No. oxygen gas partial pressure (Pa) gauge factor TCR (ppm / K) resistivity (Omega · m) oxygen content ^{(atomic%) 1 2.0 × 10 -4 13.5} 860 3.3 × 10 -7 0.6 2 2.0 × 10 - ^{3 12.0 720 4.5 × 10 -7 0.8} 3 3.8 × 10 -3 11.5 400 7.1 × 10 -7 1.2 4 5.9 × 10 -3 8.5 70 1.3 × 10 -6 1.1 5 6.1 × 10 -3 8.2 -30 1.7 × 10 - ⁶ 1.9 6 1.1 × 10 ^-2 6.3 -300 4.2 × 10 ^-6 1.7 7 1.5 × 10 ^-2 5.7 -540 7.8 × 10 ^-6 2.5 From the above results, argon with a partial pressure of oxygen gas of the order of 10 ^-3 Pa- Oxygen mixed gas is used, especially the oxygen content is 1.1 to 1.9.
It can be seen that the thin film with atomic% has excellent characteristics such as high gauge ratio (8.2 to 8.5) and low temperature coefficient of resistance (within ± 100 ppm / K).

[Brief description of drawings]

FIG. 1 is a schematic diagram of a film forming apparatus used in a method of the present invention.

FIG. 2 is a schematic diagram of a test piece used for measuring a gauge factor and a temperature coefficient of resistance.

FIG. 3 is a schematic diagram of a gauge factor measuring method.

[Explanation of symbols]

 1 Film Forming Chamber 2 Chromium Target 3 Substrate 5 Argon Gas Cylinder 6 Oxygen Gas Cylinder 9 High Frequency Power Supply

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Claims (2)

[Claims] 1. A target of chromium, 10 ^-4 to 10 ^-2 Pa
A method for producing a chromium-oxygen alloy thin film having an oxygen content of about 0.1 to 3 atomic%, characterized by applying a thinning means in an argon-oxygen mixed gas atmosphere having an oxygen gas partial pressure of the order. 2. A strain gauge thin film comprising a chromium-oxygen alloy thin film having an oxygen content of about 0.1 to 3 atomic% obtained by the method of claim 1.