JPH0869858A - Hot-wire type microheater - Google Patents

Abstract

PURPOSE: To simplify a manufacturing process, reduce mechanical fatigue of a hot-wire part even if a high temperature heat cycle is received, and lengthen the service life by constituting an overhang part of a material having heat resistance and a thermal expansion coefficient extremely close to a thermal expansion coefficient of a hot-wire. CONSTITUTION: A TiO2 film 11 being an overhang part to support a hot-wire is formed on an Si board 10 by using a semiconductor fine processing technology, and a Pt film 12 being the hot-wire is formed on it. A lower part of the TiO2 film 11 is removed by etching, and becomes a space 13, and it is formed as a cantilever structure. A thermal expansion coefficient (for example, 9.0×10<-6> at 20 deg.C) of the TiO2 film 11 is extremely close to a thermal expansion coefficient (For example, 8.8×10<-6> at 20 deg.C) of Pt.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot wire type microheater formed by using a semiconductor fine processing technique.

[0002]

2. Description of the Related Art A heat ray is formed on a semiconductor substrate by using a semiconductor microfabrication technique and heated by energizing the heat ray to cause a chemical reaction between the gas sensitive substance and the gas to detect the presence or absence or concentration of the gas. Known are a gas sensor for detecting, a flow sensor for detecting the flow rate of gas by converting the amount of heat taken by the gas from the heat ray into an electric quantity, and a hot wire micro-heater for heating a minute local area.

As an example, Japanese Patent Publication No. 5-3894 discloses a gas detecting device of this type suitable for a gas leak alarm device. The gas sensor of this type has a heat capacity as small as possible to improve response characteristics. In order to reduce power consumption, an aerial overhang structure such as a bridge structure or a cantilever structure in which a heating wire part overhangs in the air is adopted. The heat wire formed on the air overhang is made of Pt, SiC, NiCr or the like, which is a stable material for a long period of time. The air overhang which supports the heat wire has heat resistance and leakage current when energized. In order to prevent this, a material having a high electric insulation property, such as SiO ₂ , Al ₂ O ₃ or MgO, is used.

[0004]

By the way, when gas is detected by a gas sensor or a flow rate sensor using a micro heater, the temperature of the hot wire is not so high when the target gas is hydrogen or carbon monoxide, but In case of 400 ℃ -5
The temperature is as high as 00 ° C., and adoption of a pulse driving method is being considered to enable battery driving. In this case, the hot wire and the overhanging portion that supports the hot wire are repeatedly subjected to a high temperature heat cycle to change the thermal stress, which increases mechanical fatigue of the hot wire and shortens the life of the sensor. In this case, it is considered that the magnitude of the thermal stress is greatly affected by the difference between the coefficient of thermal expansion of the heat wire and the coefficient of thermal expansion of the overhanging portion that supports it.

On the other hand, the inventors of the present invention recognize that the overhanging portion supporting the heat wire does not have to have a high electrical insulation property, and the thermal expansion coefficient of the overhanging portion supporting the heat wire and the heat ray. By selecting the material of the overhanging portion from the viewpoint of the above, it is an object to provide a hot wire type micro-heater that has a simple manufacturing process, has a small mechanical fatigue of the hot wire portion even when subjected to a high temperature heat cycle, and has a long life. .

[0006]

According to the first aspect of the present invention, in order to achieve the above object, a heat wire is formed on an overhang formed on a semiconductor substrate by using a semiconductor fine processing technique. The protruding portion of the hot wire micro-heater was made of a material having heat resistance and a coefficient of thermal expansion very close to that of the wire.

According to the second aspect of the present invention, in order to achieve the above object, a heat ray is formed on an overhanging portion formed on a semiconductor substrate using a semiconductor fine processing technique via an insulating film. The protruding part of the heat wire type micro heater,
It was made of a material having a heat resistance and a coefficient of thermal expansion extremely close to that of a heat ray.

Pt, Pt-Rh (rhodium), Pt-Ir (iridium), or Pd (palladium), Pd-Rh, Pd-Ir is used as the heat ray material, and TiO ₂ is used as the material of the overhang portion. , TiN, YSZ (yttria-stabilized zirconia) are used.

[0009]

[Function] Since the thermal expansion coefficients of the overhanging portion and the heat wire held on it are extremely close to each other, the thermal stress applied to the overhanging portion and the heat wire is small even when subjected to repeated thermal cycles due to energization of the heat wire, so that mechanical fatigue is reduced. Get smaller.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing the structure of an embodiment of a hot wire type micro-heater according to the present invention.

In the first embodiment, a TiO ₂ film 11 serving as an overhang portion for supporting heat rays is formed on a silicon substrate 10 by using a semiconductor fine processing technique, and a Pt film 12 serving as heat rays is formed thereon. To be done. The lower part of the TiO ₂ film 11 on which heat rays are formed by the Pt film 12 is removed by etching to become a space 13 and has a cantilever structure.

FIG. 2 is a sectional view showing the structure of another embodiment of the hot wire type micro-heater according to the present invention.

In the second embodiment, a TiO ₂ film 11 serving as an overhang portion for supporting the heat rays is formed on a silicon substrate 10 by using a semiconductor fine processing technique, and a film thickness of several hundred Å is formed on the TiO ₂ film 11. SiO ₂ film 14 which is a thin insulating film
Is formed, and the Pt film 12 which becomes a heat ray is formed thereon. TiO ₂ film 11 in which heat rays are formed by the Pt film 12
Is removed by etching to form a space 13 having a cantilever structure.

In the second embodiment, the TiO ₂ film 11 and Pt are
Since the SiO ₂ film 14 having high electric insulation is present between the film 12 and the film 12, there is no fear of leakage current when the heat wire is energized, and the material of the overhanging portion becomes the heat wire without considering the electric insulation. It is more advantageous because the selection can be made only from the viewpoint of the coefficient of thermal expansion of the Pt film 12. Even if the SiO ₂ film 14 is subjected to a heat cycle when electricity is applied to the heating wire, it is not likely to be peeled off for a long time because it receives substantially the same thermal stress from the upper and lower Pt films 12 and TiO ₂ film 11 having extremely close thermal expansion coefficients.

FIG. 3 shows the thermal expansion coefficients of main metals including Pt and the materials used for the overhanging portion of the microheater.

As can be seen from FIG. 3, the thermal expansion coefficient (for example, 9.0 × 10 ^-6 at 20 ° C.) of the TiO ₂ film 11 used for the overhang portion in this embodiment is Si, which is conventionally used.
O ₂ (for example, 0.4 to 0.55 × 10 ⁻⁶ at 20 ° C.),
Compared with Al ₂ O ₃ and MgO, it is extremely close to the thermal expansion coefficient of Pt which is a heat wire material (for example, 8.8 × 10 ⁻⁶ at 20 ° C.). Further, comparing the electric insulation between the two, the conductivity of the TiO ₂ film 11 used in this example is 1.2 × 10 ² Ω.
・ Since the conductivity of SiO ₂ used conventionally is 1 × 10 ¹³ Ω · cm, the TiO ₂ film 1
1 is much less electrically insulating than SiO _2, but
Still, since the conductivity is 9 orders of magnitude smaller than the conductivity of Pt, which is a heat wire, of 1 × 10 ⁻⁷ Ω · cm, it is considered that the leakage current when the heat wire is energized does not pose any problem.

Next, the manufacturing process of the hot wire type micro-heater according to the present invention will be described with reference to FIG. The example described below is a micro-heater corresponding to the embodiment shown in FIG. 1 in which the projecting portion has a cantilever structure. Step 1: Using a load-lock type multi-source sputtering apparatus, first, as shown in FIG. 4 (A), TiO ₂ by:
The film 11 was formed. The load-lock type multi-source sputtering device was used to obtain a resistivity close to the specific resistance without being affected by moisture.

Sputtering device: high frequency power source, output is 200 to 1000 W Pressure: 1 to 100 mTorr Temperature: Room temperature to 500 ° C. Film thickness: 5000 to 30000 Å TiO ₂ film 11 is continuously formed without being exposed to the atmosphere. The Pt film 12 was formed under the following conditions.

Sputtering device: DC power supply, output 500 to 1500
W pressure: 1 to 100 mTorr Temperature: 300 to 500 ° C. Film thickness: 500 to 5000 Å In this step, the sputtering temperature is 300 to 5
It was confirmed that by setting the temperature to 00 ° C., the Pt film 12 does not need an adhesive material and is bonded to the TiO ₂ film 11 with sufficient force. Step 2: Next, as shown in FIG. 4B, patterning of heat rays was performed using a known photolithography technique. In the figure, 15 is a resist. Step 3: Subsequently, as shown in FIG. 4C, a Pt film 1 is formed under the following conditions using a load-lock type plasma etching apparatus.
2 was etched to form a heat ray.

Etching apparatus: high frequency power supply, output 50 to 200 W Etching gas: Ar Pressure: 1 to 50 mTorr Temperature: -30 ° C. to chamber temperature Step 4: After removing the resist 15, as shown in FIG. Then, a resist 16 was applied using a known photolithography technique, and then patterning was performed to form holes and overhangs for anisotropic etching later. Step 5: In the next step, as shown in FIG. 4E, a load-lock type reactive ion etching apparatus is used to form a hole 17 and an overhanging portion for later anisotropic etching. The TiO ₂ film 11 was etched under the above conditions.

Ion etching apparatus: high frequency power supply, output 50 to 200
W etching gas: SF ₆ pressure: 1 to 50 mTorr temperature: −40 ° C. to room temperature Other etching gases such as CF ₄ , CF ₄ + O ₂ ,
CCl ₄ or the like can be used. Step 6: Finally, as shown in FIG. 4 (F), the silicon substrate 10 is anisotropically etched from the hole 17 formed in Step 5 to leave a space 13 at the bottom to form a projecting portion having a cantilever structure. did. Although TMAH (tetramethylammonium hydroxide) solution was used as the etching solution, KOH, EDP (ethylenediaminepyrocatechol), TEAH (tetraethylammonium hydroxide), or the like can be used in addition to this.

The above is the manufacturing process of the micro-heater of the embodiment shown in FIG. 1, but the manufacturing process of the micro-heater of the embodiment shown in FIG. 2 is the same as described above except for the following two points. (1) In the step 1 shown in FIG. 3A, the number of films having an electrical insulating property between the TiO ₂ film 11 and the Pt film 12 is 1
A step of forming the SiO ₂ film 14 of 00Å is added. (2) Pt film 12 which becomes a heat ray on the SiO ₂ film 14
The temperature at which is formed by sputtering is set to 500 to 700 ° C., which is higher than the above temperature. It has been confirmed that at this temperature, the adhesion material is not required to attach the Pt wire 12 on the SiO ₂ film 14.

Although Pt was used as the heat-ray material in the above-mentioned examples, Pt-Rh (rhodium) and Pt-Ir are also used.
(Iridium), or Pd (palladium), Pd-R
It is also possible to use h, Pd-Ir. In addition to the TiO ₂ used in the examples, Ti ₃
N ₄ or YSZ (yttria-stabilized zirconia) can be used. The coefficient of thermal expansion of these materials (eg P
Since the thermal expansion coefficient of d is about 11.8 × 10 ⁻⁶ ) at 20 ° C., good results can be obtained regardless of the combination of the heat wire material and the material of the overhang portion.
t, Pt-Rh, combining the TiO ₂ and one of Pt-Ir, or Pd, Pd-Rh, the combination of the YSZ and either Pd-Ir, obtained good effect since the difference in thermal expansion coefficient is small To be The conductivity of Pd as a heat wire material is almost equal to that of Pt.

In the first embodiment described above, the structure of the overhanging portion for supporting the heat rays is exemplified as the cantilever structure, but it goes without saying that it may be a bridge structure or other hollow structure.

In the second embodiment, the extremely thin electric insulating film formed between the TiO ₂ film 11 and the Pt film 12 is S.
Si ₃ N ₄ may be used in addition to iO ₂ .

Further, in the above-mentioned embodiment, sputtering was used to form the TiO ₂ film to be the overhang portion and the Pt film to be the heat ray on the silicon substrate, but in addition to this, vapor deposition, CVD, PVD, laser deposition are used. The method etc. can also be used.

[0028]

As described above, according to the present invention,
Since the thermal expansion coefficient of the heat wire material and the overhanging portion supporting the heat wire are very close to each other, even if the heat cycle is repeated while the heater is driven, the thermal stress caused by the heat cycle is reduced, and the mechanical fatigue of the microheater is also reduced. The life of the heater is longer than that of the conventional one. For example, when Pt is used as the heat-ray material, if TiO ₂ having a coefficient of thermal expansion extremely close to that of Pt is selected for the overhanging portion, leakage current during energization is not a problem and mechanical fatigue is reduced. can do. Sputtering is used to form the hot wire material on the overhang portion, and the temperature is set to 300
If the temperature is higher than 0 ° C., the bonding is performed without using an adhesive material, so that the number of manufacturing processes does not increase. If an extremely thin insulating film is provided between the heat wire and the projecting portion, the material of the projecting portion does not need to consider the insulating property at all, so it is sufficient to select it only from the viewpoint of the coefficient of thermal expansion. Greater freedom.

Although the present invention is a hot wire type micro heater,
It goes without saying that this micro heater can be used for a gas sensor or a flow rate sensor.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of an embodiment of a hot-wire micro-heater according to the present invention.

FIG. 2 is a sectional view showing the structure of another embodiment of the hot-wire micro-heater according to the present invention.

FIG. 3 shows coefficients of thermal expansion of main metals including Pt and materials used for an overhang portion of a microheater.

4 (A) to (F) show a manufacturing process of a hot wire type micro-heater according to the present invention.

[Explanation of symbols]

10 Silicon Substrate 11 TiO ₂ Film 12 Pt Film 13 Space 14 SiO ₂ Film 15, 16 Resist 17 Hole

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H05B 3/20 328

Claims (8)

[Claims] 1. A hot-wire type micro-heater comprising a heating wire formed on a protruding portion formed on a semiconductor substrate by using a semiconductor fine processing technique, wherein the protruding portion has a heat resistance and a thermal expansion coefficient extremely close to that of the heating wire. A hot wire type micro-heater characterized by being made of a material having an expansion coefficient. 2. The hot wire micro-heater according to claim 1, wherein the hot wire material is Pt and the material of the overhanging portion is TiO ₂ . 3. A hot wire micro-heater comprising a heating wire formed on a protruding portion formed on a semiconductor substrate by a semiconductor microfabrication technique through an insulating film, wherein the protruding portion has heat resistance and thermal expansion of the heating wire. A hot-wire micro-heater characterized by being made of a material having a coefficient of thermal expansion extremely close to the coefficient. 4. The insulating film is a SiO ₂ film, the heat ray material is Pt, and the material of the projecting portion is TiO ₂
The hot wire micro-heater according to claim 3. 5. Pt which becomes a heat ray by sputtering at 300 ° C. or higher on the TiO ₂ film forming the projecting portion.
The hot wire micro-heater according to claim 2, wherein a film is formed. 6. The hot wire micro-heater according to claim 4, wherein a Pt film which becomes a hot wire is formed on the SiO ₂ film by sputtering at 500 ° C. or higher. 7. The hot wire micro-heater according to claim 1, wherein the projecting portion has a cross-linking structure. 8. The hot wire micro-heater according to claim 1, wherein the projecting portion has a cantilever structure.