WO2003102974A1

WO2003102974A1 - Platinum thin film and thermal sensor

Info

Publication number: WO2003102974A1
Application number: PCT/JP2002/005426
Authority: WO
Inventors: Kazuhiko Tsutsumi; Hiroshi Ohji; Akira Yamashita
Original assignee: Mitsubishi Denki Kabushiki Kaisha
Priority date: 2002-06-03
Filing date: 2002-06-03
Publication date: 2003-12-11
Also published as: JPWO2003102974A1

Abstract

A platinum thin film having a silicon substrate (1) in a flat plate form and, formed thereon in the following order, an insulating film (3) and a platinum thin film (6), wherein the insulating film (3) comprises an oxide or nitride whose intermetallic compound with platinum has no eutectic point between platinum at a temperature of 850˚C or lower and thus has a TCR of 3500 ppm/˚C or more. A thermal sensor, wherein a heat-sensitive resistor (6) and a temperature detecting portion are formed by using the above platinum thin film as a heat-sensitive resisting film, and the silicon substrate (1) in a flat plate form is partly removed under the region in which the heat-sensitive resistor is formed, to thereby form a diaphram portion (12). The thermal sensor exhibits improved sensitivity.

Description

Specification

Platinum thin film and thermal sensors

The present invention relates to a heating element itself for measuring a flow rate or a flow rate of a fluid based on a heat transfer phenomenon from a heating element or a portion heated by the heating element to a fluid, and to a thermal sensor such as a flow rate sensor. Background art

Utilizing a substantially unique functional relationship established between the flow rate or flow rate of the fluid and the heat transfer amount from the heating element disposed in the fluid to the fluid, the flow rate or the flow rate of the fluid is determined based on the heat transfer rate. 2. Description of the Related Art A heat-sensitive flow element configured to detect a flow rate or a flow sensor using the flow rate detection element has been widely used for detecting an intake air amount of an internal combustion engine.

FIG. 11 is a partial cross-sectional view of a conventional heat-sensitive flow rate detecting element disclosed in, for example, Japanese Patent Application Laid-Open No. 4-29667, and FIG. 12 is a plan view of a state in which a protective film is removed. It is. In the figure, 102 is an opening (hollow portion) formed from the back side of a flat substrate 101 made of silicon, 103 is a base film provided on the surface of the flat substrate 101, Reference numeral 105 denotes a back surface protective film provided on the back surface of the flat substrate 1, and reference numerals 106 and 107 each denote a thin-film thermal resistor made of platinum disposed on the base film 103. The heat-sensitive antibodies 106, 107 and the base film 103 are covered with an insulating protective film 104. Here, the base film 103, the protective film 104, and the back surface protective film 105 are made of an insulating film made of Si ₃ N ₄ or SiO ₂ . It should be noted that the heat-sensitive resistors 106 and 107 are formed on the flat base material 101 below the film-forming portion. The opening 102 is formed by removing a part of the flat substrate 1 made of silicon using an etching solution that does not damage Si ₃ N ₄ or SiO ₂ .

In the conventional flow rate detection element as described above, the heating current flowing through the heat-sensitive resistors 106 and 107 is such that the temperature difference between the heat-sensitive resistor 107 and the temperature compensation resistor 108 is constant. In addition, it is kept constant by a control circuit (not shown). Arrow 110 indicates the direction of air flow.

For example, when the airflow increases and the temperature of the thermal resistor 107 decreases, the current flowing through the thermal resistor 106 increases by that much, and the thermal resistor 107 and the temperature compensation resistor 108 increase. The current source of the heat-sensitive resistor 106 is controlled so that the temperature difference between them becomes constant. Therefore, the voltage applied to the heat-sensitive resistor 106 to flow a current through the heat-sensitive resistor 106 is such that the more heat transferred from the heat-sensitive resistor 107 to the airflow, In other words, it increases as the airflow velocity increases.

As described above, the voltage applied to the thermal resistor 106 is a function of the flow velocity of the gas to be measured, so that the flow velocity of the gas or the flow rate of the gas passing through a predetermined passage can be measured. .

The measurement principle described above is the case of constant temperature difference control in which the resistance value of the thermal resistor 107 is kept at a predetermined value regardless of the flow velocity.However, the heating current to the thermal resistor 106 is kept constant. In addition, the flow velocity can be detected from the change in the resistance value of the thermal resistor 107 according to the flow velocity.

A conventional thermal flow sensor is configured as described above. The higher the temperature coefficient of resistance (Temperature Coefficient of Resistance) of a platinum thin film, the higher the measurement sensitivity. Therefore, a platinum thin film with a large TCR is expected. I have been waiting. However, the TCR of bulk platinum is 3920 ppm / ° C. Despite this, platinum thin films stay at around 3000 ppm / ° C.

FIG. 13 shows the TCR of a platinum thin film formed by forming a SiNx insulating base film on a flat silicon substrate and forming a film thereon by sputtering. For example, when the platinum film thickness is 0.2 zm, the temperature coefficient of resistance becomes the maximum at the heat treatment temperature of 700 ° C and is 3100 ppmZ ° C, but the TCR decreases at the heat treatment temperature higher than that. Fig. 14 shows the results of electron microscopic observation of the surface state of the platinum thin film after heat treatment. In the figure, (a) shows the surface condition after heat treatment at 800 ° C, and (b) shows the surface condition after heat treatment at 1000 ° C. Precipitated particles are observed at 800 ° C as shown in (a) in the figure, and do not exist as a thin film at 100 o ° c as shown in (b) in the figure, and all of the platinum thin film turns into particles. This is thought to be due to the fact that the heat treatment caused the platinum and SiNx in the underlayer to react, and the melting point of the formed silicon-platinum intermetallic compound to be below 850 ° C. In other words, at a heat treatment temperature of 800 ° C, a part of the silicon-platinum intermetallic compound partially melts and starts to precipitate, and at a heat treatment temperature of 1000 ° C, the silicon-platinum intermetallic compound is completely melted and becomes particulate. That's why.

A similar report was also made in Sensors and Actuators A 3076 (2001) 1-7 (A3076 (2001) 1-7), in which a platinum thin film resistor formed by magnetron sputtering ( even 1 ¹ Rei_1 ^ heat treatment temperature 600 ° C at 3 100 p pm / ° C to become but the heat treatment temperature 60 0 ° C or more film thickness 0.3 111) by increasing the heat treatment temperature, TCR decreases. These are due to the low melting point of the intermetallic compound of platinum formed by diffusion between the platinum thin film and the underlayer.

On the other hand, in-vehicle thermal sensors are Reducing the number of revolutions during grayed, there is needed Nozomu want to reduce C 0 ₂ emissions by subtracting the consumption gasoline, there is a need for a flow sensor air flow of 1 g / s can be measured. When a platinum thin film is applied to an in-vehicle flow sensor, the sensitivity for measuring the flow rate of lg / s was insufficient when the temperature coefficient of resistance was 310 Opp mZ ° C.

In the actual use, in order to prevent a short circuit caused by water droplets, it is necessary to form a protective film on the platinum film, protected by spin coating Bae one strike consisting mainly of S i 0 ₂ film When a protective film is formed and subjected to a heat treatment for stabilizing the protective film, if the platinum film thickness is more than 0.6 m, the protective film is cracked and cannot be used. Therefore, the platinum thin film is preferably thin.

The present invention has been made in order to solve the above-mentioned conventional problems, and provides a platinum thin film having a larger temperature coefficient of resistance than a conventional one on a flat silicon substrate. An object of the present invention is to provide a highly sensitive thermal sensor by configuring a sensor. Disclosure of the invention

The first platinum thin film of the present invention is a platinum thin film formed on an insulating film on a flat silicon substrate, and the temperature coefficient of resistance of the platinum thin film is 350 ppm / ° C or more. However, if a thermal sensor is formed using this platinum thin film, the sensitivity of the sensor is improved.

The second platinum thin film of the present invention is a platinum thin film formed on an insulating film on a flat silicon substrate, and a material constituting the insulating film in contact with the platinum thin film among the insulating films is the following material: The material is characterized in that the eutectic point of the intermetallic compound with platinum and platinum is not less than 850 ° C. By selecting such a material, an insulating film is formed on a flat silicon substrate. Formed and white on it When a gold thin film is formed and heat-treated at 850 ° C or more, the temperature coefficient of resistance (TCR) of the platinum thin film can be set to 3500 ppm / ° C or more.If a thermal sensor is constructed using this platinum thin film, The sensitivity is improved. Further, since the thickness of the platinum thin film is 0.5 zm or less, a protective film can be easily formed by a method such as spin coating.

Further, in the platinum thin film according to the first or second aspect of the present invention, the material constituting the insulating film in contact with the platinum thin film in the insulating film is an oxide or nitride of aluminum or zirconium. Even if heat treatment is performed at a high temperature (850 ° C or higher) after the thin film is formed, platinum and aluminum platinum intermetallic compound or part of zirconium platinum intermetallic compound do not melt during the heat treatment, that is, platinum and aluminum platinum Since the eutectic point between the intermetallic compound and the eutectic point between platinum and the zirconium platinum intermetallic compound is not below 850 ° C, stable heat treatment is possible, and the resistance temperature coefficient TCR of the platinum thin film is reduced. 3 It can be controlled to 500 ppm / ° C or more.

In the platinum thin film according to the above invention, since the second insulating film made of an oxide or nitride of aluminum or zirconium is further formed on the platinum thin film, even if a heat treatment is performed after the formation of the second insulating film, the resistance of the platinum thin film is reduced. Temperature coefficient TCR can be controlled to 3500 ppmZ ° C or more.

A thermal sensor according to the present invention includes: an insulating support film disposed on a first surface of a flat silicon substrate; a heat-sensitive resistor made of a heat-sensitive resistance film; and a temperature detecting unit formed on the support film. In a thermal sensor in which the base material is partially removed below the region where the thermal resistor is formed and the diaphragm is formed, at least the platinum thin film is used as the thermal resistor, so that the resistance temperature is low. The temperature coefficient TCR can be controlled to 3500 ppm / ° C or more, improving the sensitivity of the thermal sensor. • Brief description of the drawing

FIG. 1 is a schematic diagram for explaining a thermal sensor equipped with a platinum thin film according to a first embodiment of the present invention, in which (a) is a partial plan view of a thermal resistor, and (b) is a thermal sensor. FIG. 2 is a view for explaining the manufacturing process of the sensor element of the type sensor, and FIG. 2 is a view for explaining the manufacturing process. In the figure, (1) to (8) show the order of steps. FIG. 3 is a diagram for explaining the relationship between the resistance temperature coefficient of the platinum thin film on the aluminum oxide base film and the heat treatment temperature in comparison with the conventional one. The horizontal axis is the heat treatment temperature, and the vertical axis is the resistance temperature coefficient ( TCR).

FIG. 4 is a sensor element cross-sectional view for explaining a thermal sensor according to a second embodiment of the present invention.

FIG. 5 is a sectional view of a sensor element for explaining a thermal sensor according to a third embodiment of the present invention.

FIG. 6 is a sectional view of a sensor element for explaining a thermal sensor according to a fourth embodiment of the present invention.

FIG. 5 is a sectional view of a sensor element for explaining a thermal sensor according to a fifth embodiment of the present invention.

FIGS. 8 and 9 are views for explaining a flow sensor as a thermal sensor according to a sixth embodiment of the present invention.

FIG. 10 is a diagram for explaining the relationship between TCR and the flow rate drift. The horizontal axis represents the temperature coefficient of resistance (TCR), and the vertical axis represents the flow rate drift.

FIG. 11 is a cross-sectional view of a sensor element showing the appearance of a conventional thermal sensor, and FIG. 12 is a plan view for explaining the layout of resistors in the thermal sensor of FIG. Fig. 13 is a diagram showing the relationship between the temperature coefficient of resistance and the heat treatment temperature of platinum thin films of different thicknesses formed on a silicon nitride underlayer, with the horizontal axis representing the heat treatment. The vertical axis is the temperature coefficient of resistance (TCR). Fig. 14 shows the results of electron microscopic observation of the surface state of the platinum thin film on the silicon nitride underlayer. In the figure, (a) shows the precipitated particles on the surface of the platinum thin film after heat treatment at 800 ° C. FIG. 2 (b) is a view showing precipitated particles on the surface of the platinum thin film after heat treatment at 100 ° C. BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is based on the finding that a conventional platinum thin film has a temperature of 310 ppm / ° C., which is smaller than the TCR of bulk platinum. In other words, the heat treatment can be performed at a temperature exceeding 800 ° C, which is a heat treatment temperature at which the TCR has been reduced, which stably heats at a high temperature. Specifically, when a platinum and an intermetallic compound are formed directly under the platinum thin film so that the platinum thin film can be stably heat-treated at a high temperature, the eutectic point of the intermetallic compound and platinum is set at 850 ° C By providing an oxide or nitride containing a metal material not shown below as an insulating film, and by providing the insulating film directly above the platinum thin film, it is possible to suppress the formation of particles of the platinum thin film during high-temperature heat treatment. As a result, a platinum thin film with a TCR of more than 350 ppm Z ° C and a TCR closer to bulk was realized, and the sensitivity of the thermal sensor was improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Example 1.

FIG. 1 is a view for explaining a platinum thin film and a thermal sensor on which the platinum thin film is mounted according to one embodiment of the present invention. FIG. 1 (a) is a partial plan view of the thermal sensor, and FIG. () Is a partial sectional view.

In the figure, 1 is a flat substrate made of silicon, and 3 is a base film made of aluminum oxide 3a provided on the surface of the flat substrate 1. It is an insulating film. Reference numeral 6 denotes a thin-film heat-sensitive resistor made of platinum disposed on the insulating film 3. The heat-sensitive resistor 6 or the insulating film 3 is an insulating protective film 4 made of a silicon oxide film 4a. Covered with. Further, the flat substrate 1 below the portion where the thermal resistor 6 is formed is removed to form the cavity 2. Here, the insulating (base) film 3 functions as a support film.

Next, the manufacturing process of this embodiment will be briefly described with reference to the drawings. FIG. 2 is a diagram showing a manufacturing process flow. (1) to (8) in the figure indicate the order of the steps, which will be described in the order of the steps.

(1) Prepare a silicon wafer 1 (thickness: 380 zm) with a (100) plane orientation, with a thermal oxide film 9 having a thickness of 0.5 m.

(2) An aluminum oxide film 3 a having a thickness of about 2 μm is formed as a base film 3 on the thermal oxide film 9 by, for example, a sputtering method.

(3) For example, a platinum film 6a having a thickness of 0.2 / m is formed on the aluminum oxide film 3a by a sputtering method.

(4) Heat treatment in air at 900 ° C for 1 hour using a heat treatment furnace.

(5) Using a photolithography method, the platinum film 6a is patterned as shown in the plan view of (a) in FIG. 1 to form the thermal resistor 6 and the wiring part (wiring is shown in the drawing). Not).

(6) As the protective film 4, a silicon oxide film 4a is formed to a thickness of about 0.5 μm by a spin coating method, and then a heat treatment for stabilizing the protective film is performed.

(7) Open the pad portion 11 for wire bonding by dry etching.

(8) Open the oxide film on the back surface and remove the silicon base material by jet etching to form the diaphragm 12 and the silicon oxide under the diaphragm. The oxide film is removed, and the cavity 2 is formed and completed.

In the above process, the heat treatment temperature in the fourth step (4) was set to 900 ° C. Figure 3 shows the relationship between this heat treatment temperature and the temperature coefficient of resistance of the platinum thin film (thickness: 0.2 zm). The result of the examination is shown in comparison with the conventional one. At a heat treatment temperature of 900 ° C or higher (at least 850 ° C or higher), a TCR of 3500 ppm / ° C or higher was obtained.

The TCR of this platinum thin film is obtained as follows. Temperature measurement accuracy A platinum thin film resistor, which is the object to be measured, is energized in a Florinart temperature-controlled by a platinum resistance thermometer at 0.02 ° C, and the resistance value of the platinum thin film is measured by the four-terminal method. Measure. At this time, the resistance of the temperature-stable platinum thin-film resistor at which the temperature change of the measurement temperature (measurement sample temperature) of the Florinato becomes ± 0.02 ° C or less is determined by the amount of current (0. 1mA) is passed through the platinum thin film resistor and measured. In the temperature range of 20 ° C to 80 ° C, measure 5 times at each temperature every 5 ° C, calculate the average resistance value and the average temperature of 5 times, and calculate the temperature range of 20 ° C to 80 ° by the least square method. Calculate the slope of the linear approximation line of the platinum thin film resistance value at ° C and the resistance value at o ° c, and divide this slope by the resistance value at o ° c.

In the above embodiment, the aluminum oxide film was used as the base film 3, but the portion in contact with the thermal resistor 6 was an insulator, and platinum was diffused at the interface between the base film and the platinum thin film during heat treatment. If platinum and a part of the intermetallic compound are not melted during the heat treatment, heat treatment for obtaining a high TCR becomes possible, and therefore, other materials may be used. That is, if the eutectic point between platinum and the intermetallic compound is not below 850 ° C, a platinum thin film having at least TCR 3500 ppm / ° C can be obtained. For example, the material of the base film 3 is, for example, aluminum nitride, zirconium oxide or Zirconium nitride may be used. Example 2.

FIG. 4 is a view for explaining a thermal sensor equipped with a platinum thin film according to one embodiment of the present invention, and is a partial cross-sectional view of the thermal sensor.

In the figure, 1 is a flat substrate made of silicon, on which a thermal oxide film 9 is formed, and 3 is an insulating base film provided on the surface of the flat substrate 1, which is made of aluminum oxide 3a and nitrided. It consists of two layers of silicon 3b. Reference numeral 6 denotes a thin-film heat-sensitive resistor made of platinum disposed on the base film 3. The heat-sensitive resistor 6 or the base film 3 is covered with an insulating protective film 4 made of a silicon oxide film. ing. Further, the flat substrate 1 below the portion where the thermal resistor 6 is formed is removed to form the cavity 2. Here, the insulating (base) film 3 functions as a support film.

Next, the manufacturing process of this embodiment will be briefly described.

(1) Prepare a silicon wafer 1 (thickness: 380 Π 1) having a plane orientation (100) with a thermal oxide film 9 having a thickness of 0.5 zm.

(2) For example, after forming silicon nitride by 1.8 / Π1 by a sputtering method, an aluminum oxide film is formed on the thermal oxide film 9 to a thickness of 0.

(3) For example, a platinum film having a thickness of 0.3 zm is formed on the aluminum oxide film 3a by a sputtering method.

(4) Heat treatment in air at 1000 ° C for 1 hour using a heat treatment furnace.

(5) Using a photolithography method, pattern the platinum film 6a as shown in the plan view of (a) in FIG. 1 to form the thermal resistor 6 and the wiring part (wiring not shown) . (6) As the protective film 4, an oxide silicon film 4a of about 0.5 m is formed by a spin coating method, and then a heat treatment for stabilizing the protective film is performed.

(7) Open the pad portion 11 for wire bonding by dry etching.

(8) The oxide film on the back surface is opened, the silicon substrate is removed by wet etching to form a diaphragm 12, and the silicon oxide film below the diaphragm is removed, and the cavity 2 is formed and completed.

The platinum thin-film resistor thus produced has the same effects as those described in the first embodiment, so that the platinum thin film can have a TCR of 350 ppm / ⁰ C or more.

In addition, since the underlying film is made of two layers and the lower layer is made of silicon nitride for which stress control is easier, stress control of the diaphragm can be more easily performed. Although an example in which aluminum oxide is used for the base film 3a immediately below the platinum film is shown here, it goes without saying that the same effect can be obtained by using aluminum nitride or zirconium oxide / zirconium nitride as the aluminum oxide. No. Example 3.

FIG. 5 is a view for explaining a thermal sensor equipped with a platinum thin film according to one embodiment of the present invention, and is a partial cross-sectional view of the thermal sensor. This is an example in which the protective film 4 of Example 1 is formed of the aluminum oxide film 4b.

In the figure, 1 is a flat substrate made of silicon, on which a thermal oxide film 9 is formed, and 3 is an insulating base film provided on the surface of the flat substrate 1 and made of aluminum oxide. Reference numeral 6 denotes a thin-film heat-sensitive resistor made of white gold disposed on the base film 3. The ground film 3 is covered with an insulating protective film 4 made of an aluminum oxide film 4b. Further, the flat substrate 1 below the portion where the thermal resistor 6 is formed is removed to form the cavity 2. Here, the insulating (base) film 3 functions as a support film.

Next, the manufacturing process of this embodiment will be briefly described.

(1) Prepare a silicon wafer 1 (thickness: 380 m) having a plane orientation (100) with a thermal oxide film 9 having a thickness of 0.5 / m.

(2) For example, an aluminum oxide film 3a is formed on the thermal oxide film 9 to a thickness of 2.0 j by a sputtering method.

(3) For example, a platinum film is formed on the aluminum oxide film to a thickness of 0.5 zm by a sputtering method.

(4) Using a photolithography method, pattern the platinum film 6a as shown in the plan view of (a) in FIG. 1 to form the thermal resistor 6 and the wiring part.

(Wiring not shown).

(5) As the protective film 4, an aluminum oxide film 4b is formed about 1 m by, for example, a sputtering method.

(6) Using a heat treatment furnace, perform heat treatment at 110 ° C for 1 hour in air.

(7) Open the pad portion 11 for wire bonding by dry etching.

(8) Open the back oxide film, remove the silicon substrate by gate etching to form the diaphragm 12, and remove the silicon oxide film under the diaphragm to form the cavity 2 and complete .

The platinum thin film resistor thus produced has the same effect as described in the first embodiment, so that the TCR of the platinum thin film is set to 350 ppmZ ° C More than that.

In addition, when the thermal resistor 6 made of a platinum thin film is used by generating heat, a heat treatment for stabilizing the protective film is required for the reliability of the protective film. Therefore, the heat treatment for stabilizing the protective film can be omitted because the TCR can be increased and the protective film can be stabilized. Here, an example in which aluminum oxide is used immediately below and immediately above the platinum thin film has been described. However, it is needless to say that the same effect can be obtained by using aluminum nitride or zirconium oxide / zirconium nitride as the aluminum oxide. Absent. Example 4.

FIG. 6 is a view for explaining a thermal sensor equipped with a platinum thin film according to one embodiment of the present invention, and is a partial cross-sectional view of the thermal sensor.

In the figure, 1 is a flat substrate made of silicon, on which a thermal oxide film 9 is formed, and 3 is an insulating base film provided on the surface of the flat substrate 1 and made of aluminum oxide 3a . Reference numeral 6 denotes a thin-film heat-sensitive resistor made of platinum disposed on the base film 3, and these heat-sensitive resistors 6 or the base film 3 is an insulating protective film 4 made of a silicon nitride film 4c. It is covered with. Further, the flat substrate 1 below the portion where the thermal resistor 6 is formed is removed to form the cavity 2. Here, the insulating (base) film 3 functions as a support film.

Although the structure is similar to that shown in FIG. 1 of Embodiment 1, in this embodiment, the protective film 4 is once formed of aluminum oxide 4b, and after heat treatment, it is patterned together with the thermal resistor. Another film was formed as a final protective film. Next, the manufacturing process of this embodiment will be briefly described.

(1) Prepare a silicon wafer 1 (thickness: 380〃m) having a plane orientation (100) with a thermal oxide film 9 having a thickness of 0.5 m.

(2) For example, an aluminum oxide film 3a is formed on the thermal oxide film 9 to a thickness of 2.0 im by a sputtering method.

(3) For example, a platinum film is formed to a thickness of 0.5 μm on the aluminum oxide film by a sputtering method.

(4) As the protective film 4, an aluminum oxide film 4b is formed to a thickness of about 0 by, for example, a sputtering method.

(5) Using a heat treatment furnace, perform heat treatment in air at a temperature of 1200 ° C for 1 hour.

(6) Using a photolithography method, the platinum film 6a is patterned together with the aluminum oxide protective film 4b as shown in the plan view of (a) in FIG. 1 to form the thermal resistor 6 and the wiring portion ( The wiring is not shown).

(7) As the protective film 4, a silicon nitride film is formed to a thickness of about 0.8 zm by, for example, a sputtering method so as to cover the base film 3 and the thermal resistor 6.

(8) The pad portion 11 for wire bonding is opened by dry etching, and the aluminum oxide 4b of the protective film is removed.

(9) Open the oxide film on the back surface, remove the silicon base material by jet etching to form the diaphragm 12, and remove the silicon oxide film under the diaphragm to form the cavity 2 and complete .

The platinum thin film resistor thus produced has the same effect as described in the first embodiment, so that the platinum thin film can have a temperature coefficient of resistance of more than 350 ppm / ° C.

In addition, although stress control is possible even with silicon oxide, The use of a silicon nitride film, which facilitates stress control for the protective film, makes it easier to control the stress in the diaphragm.

Here, an example was shown in which aluminum oxide was used immediately under and immediately above the platinum film during the process, but it goes without saying that the same effect can be obtained by using aluminum nitride or zirconium oxide / zirconium nitride as the aluminum oxide. Embodiment 5.

FIG. 7 is a view for explaining a thermal sensor equipped with a platinum thin film according to one embodiment of the present invention, and is a partial cross-sectional view of the thermal sensor.

In the figure, 1 is a flat substrate made of silicon, on which a thermal oxide film 9 is formed, and 3 is an insulating base film provided on the surface of the flat substrate 1, which is made of aluminum oxide 3a and nitrided. It consists of two layers of silicon 3b. Reference numeral 6 denotes a thin-film heat-sensitive resistor made of platinum disposed on the base film 3. The heat-sensitive resistor 6 or the base film 3 is an insulating protective film 4 made of a silicon nitride film 4c. Covered with. Further, the flat substrate 1 below the portion where the thermal resistor 6 is formed is removed to form the cavity 2. Here, the insulating (underlying) film functions as a supporting film.

Although the structure is similar to that shown in FIG. 4 of Embodiment 2, in this embodiment, the protective film 4 is formed of aluminum oxide 4b once, heat-treated, and then patterned together with the thermal resistor. A film formed with another film as a protective film can be used.

Next, the manufacturing process of this embodiment will be briefly described.

(1) A silicon wafer 1 (thickness: 380 zm) having a plane orientation (100) with a thermal oxide film 9 having a thickness of 0.5 μm is prepared. (2) For example, after a silicon nitride film is formed to a thickness of 1.8 μm by a sputtering method, an aluminum oxide film is formed on the thermal oxide film 9 to a thickness of 0.2 μm.

(3) A platinum film is formed on the aluminum oxide film to a thickness of 0.2 μm by, for example, a sputtering method.

(4) As the protective film 4, an aluminum oxide film 4b is formed to a thickness of about 0.2 μm by, for example, a sputtering method.

(5) Heat treatment in air at 900 ° C for 1 hour using a heat treatment furnace.

(6) Using a photolithography method, pattern the platinum film 6a together with the protective film 4b of aluminum oxide as shown in the plan view (a) in Fig. 1 to form the thermal resistor 6 and the wiring part (The wiring is not shown).

(7) As the protective film 4, a silicon nitride film 4 c is formed to a thickness of about 0.8 μm by, for example, a sputtering method so as to cover the base film 3 and the thermal resistor 6.

(8) The pad portion 11 for wire bonding is opened by dry etching, and at this time, the aluminum oxide 4b of the protective film is removed.

(9) Open the oxide film on the back surface, remove the silicon substrate by photo-etching to form the diaphragm 12, and remove the silicon oxide film under the diaphragm to form the cavity 2. Complete.

The platinum thin film resistor thus produced has the same effect as described in the first embodiment, so that the platinum thin film can have a temperature coefficient of resistance of 3500 ppm / ° C or more.

In addition, although stress control is possible even with silicon oxide, the use of a silicon nitride film, which facilitates stress control for the underlying film and the protective film, makes it easier to control the stress in the diaphragm.

Here, aluminum oxide was used just below and directly above the platinum film during the process. Although an example has been shown, it goes without saying that the same effect can be obtained even when the aluminum oxide is aluminum nitride or zirconium oxide / zirconium nitride.

Although not shown in Examples 1 to 5 above, a temperature detecting section (temperature sensor) for compensating the temperature of the sensor is formed near the heat-sensitive resistor as in the past. In the present invention, the platinum thin film of the present invention can also be used as a heat-sensitive resistor for the temperature detecting section. Embodiment 6.

FIG. 8 and FIG. 9 are diagrams illustrating the configuration of a flow sensor in a thermal sensor according to one embodiment of the present invention, and are diagrams arranged in a fluid passage.

In the figure, 21 is a flow detecting element using a platinum thin film resistor having a TCR of 3500 ppm / ^ C shown in Examples 1 to 5 above, 22 is a detecting pipe, and 23 is a detecting pipe. Is a main passage which is a fluid passage, 24 is a grid-like rectifier, 25 is a case in which a control circuit is housed, and 26 is a connector for supplying power to the flow sensor and taking out an output. Note that the arrow 10 indicates the direction of the air flow during normal times.

For example, in the case of in-vehicle flow sensors, the idling flow rate has been reduced in order to reduce gasoline consumption due to environmental concerns, and low flow measurement of lg / s or less is required. If a membrane with a TCR of 310 ppm / ° C is applied to such a flow sensor, the accuracy for detecting a flow rate of 1 g / s will deteriorate due to insufficient sensitivity at low flow rates.

FIG. 10 shows the relationship between TCR and flow rate drift. In other words, in the figure, the flow rate and flow rate drift at different resistance temperature coefficients (the flow rate measured by forcibly changing the resistance value of the temperature sensing resistor by 1%) Initial measurement flow rate χιοο [%], the range where the resistance fluctuation after endurance evaluation is 0.1% or less and the flow rate drift at that time is 3% or less can be guaranteed accuracy. The results of investigating the relationship are shown below. This drift amount can be read as sensitivity, and the lower the drift value, the higher the sensitivity. If the flow drift value is about 30% or less, reliability and accuracy can be secured. At a TCR of 3 100 ppm / ° C, the flow drift of 2 g / s is 31%, but the TCR is 3500 ppm. In the case of C, the flow drift of lg / s is 30%, which enables measurement of a lower flow rate.

As described above, the sensitivity of the thermal type flow sensor equipped with the platinum thin film resistor according to the present invention is improved as compared with the related art.

Although the thermal type flow sensor has been described here, if the platinum thin film resistors according to Examples 1 to 5 are incorporated in other thermal type sensors such as a pressure sensor, the resistance change with respect to temperature change can be increased. Thus, a thermal sensor with improved sensor sensitivity can be obtained. Industrial applicability

The platinum thin film according to the present invention is mounted on a thermal sensor, and this thermal sensor is used for a flow rate sensor or a pressure sensor for measuring an intake air amount of an internal combustion engine for a vehicle or the like.

Claims

The scope of the claims

1. A platinum thin film formed on an insulating film on a flat silicon substrate, wherein the platinum thin film has a temperature coefficient of resistance of 350 ppm / ° C or more.

2. A platinum thin film formed on an insulating film on a flat silicon substrate, wherein a material of the insulating film that is in contact with the platinum thin film is an intermetallic compound of the material and platinum. A platinum thin film, which is a material having a eutectic point with platinum of less than 850 ° C or less.

3. The platinum thin film according to claim 1 or 2, wherein a material of the insulating film that is in contact with the platinum thin film is aluminum or zirconium oxide or nitride. .

3. The platinum thin film according to claim 1, wherein a second insulating film made of an oxide or a nitride of aluminum or zirconium is further formed on the platinum thin film.

5. An insulating support film disposed on the first surface of the flat silicon substrate, a heat-sensitive resistor composed of a heat-sensitive resistive film and a temperature detecting portion were formed on the support film, and the heat-sensitive resistor was formed. In the thermal sensor in which the diaphragm is formed by partially removing the base material below the region, the platinum thin film according to claim 1 or 2 is used as at least a heat-sensitive resistor. A thermal sensor characterized by the following.