JPH10221144A - Micro heater and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a micro heater of high detection accuracy wherein an internal stress is not applied to a heater wire and the heater wire is not distorted. SOLUTION: A heater wire 14 and a lead-out wire 15 are set at an upper face of a silicon substrate 10 which has a recessed part 10a with an opened upper face. At this time, an oxidization film 12 is formed at a lower face of each wire, thereby securing insulation from the substrate. The heater wire 14 is set at a position confronting to the recessed part and supported in a cantilever state to the substrate. The heater wire 14 is formed of single crystal silicon. Single crystal silicon is bonded via the oxidization film 12 to the silicon substrate, and therefore no internal stress is brought about. Surfaces of the heater wire 14, lead-out wire 15 are coated with a protecting film 16 of an oxidization film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects a change in the temperature of a thin-film heater (detection section) due to the surrounding environment as a change in an electric signal, and measures a physical quantity such as a flow rate, a flow rate, and a humidity of a gas or liquid. And a method for manufacturing the same.

[0002]

2. Description of the Related Art FIG. 1 shows an example of a conventional micro heater. As shown in FIG. 1, a sheet-shaped dielectric film 2 is formed on an upper surface of a flat rectangular substrate 1 having an opening vertically penetrating at a predetermined position, and the opening is covered with the dielectric film 2. The lower part is an open recess 1a. Further, a heater wire 3 made of a polycrystalline silicon thin film is built in the dielectric film 2.

In the flow sensor having such a configuration, the heater wire 3
, The heater wire 3 generates heat. On the other hand, if a fluid flows around the sensor, the heat generated in the heater wire 3 is taken away, and the resistance value of the heater wire 3 changes. Since the temperature coefficient of the resistance of the heater wire 3 is known, a change in temperature can be obtained from a change in the resistance value, and a flow velocity or the like is obtained from the change in temperature (the amount of heat taken). Both ends of the heater wire 3 become wide terminal electrodes 3a. Above the terminal electrodes 3a, an oxide film is not formed and is exposed, and can be connected to an external device. A predetermined metal is formed on the exposed surface of the terminal electrode 3a to form an electrode pad.

In the illustrated example, the change in heat of the heater wire (change in resistance) is directly measured.
For example, as disclosed in Japanese Patent Application Laid-Open No. 7-58346, there is a device in which a detection resistor is formed near a heater wire, and a predetermined physical quantity is measured from a change in the resistance value of the detection resistor. The detection resistor is also made of polycrystalline silicon, and is patterned at the same time as the heater wire.

In order to manufacture the above-described micro heaters, a flat silicon substrate is prepared, and an oxide film is formed on the surface of the silicon substrate. Further, a polycrystalline silicon thin film is patterned on the surface of the oxide film, and an oxide film is further laminated on the surface. As a result, the polycrystalline silicon thin film constitutes the heater wires 3 and the terminal electrodes 3a and the like.
Thus, the dielectric film 2 is formed.

Thereafter, a predetermined position on the lower surface of the silicon substrate 1,
That is, the heater line forming region is removed by etching to form the concave portion 1a. Oxide film 2 is exposed through recess 1a. In this etching, the masked silicon substrate 1 is immersed in a predetermined etching solution, so that the silicon substrate portion exposed without being masked is removed by wet etching.

In the micro heater manufactured in this manner, since the silicon substrate 1 does not exist below the heater wire 3 and is a space (recess 1a), the heat insulation between the micro heater and the silicon substrate 1 is good. Become. Further, the volume of the silicon substrate 1 is reduced, and the heat capacity is also reduced.

[0008]

However, the above-mentioned conventional micro heater has the following problems. That is, since the detection section including the heater wire is composed of an insulator film 2 (thin film) such as an oxide film formed on a silicon substrate and a thin polycrystalline silicon film formed thereon, the thin film has the same composition. Large internal stress occurs at the time of film formation. as a result,
When the concave portion 1a in which a predetermined position on the lower surface of the silicon substrate 1 is finally removed is formed, there is a problem that the portion of the dielectric film 2 facing the concave portion 1a is warped due to internal stress. Further, when such a warp occurs, the heater wire 3 existing inside the dielectric film 2 also warps. Then, since the heater wire 3 is a polycrystalline silicon thin film, the resistance value changes due to the strain applied to the polycrystalline silicon thin film. Then, the degree of warpage changes depending on the magnitude of the generated internal stress and the external environment at the time of use, so that the detection accuracy decreases.

[0009] Focusing on the manufacturing process, the silicon substrate 1 is etched after forming the dielectric film 2, the heater wire 3, and the terminal electrode 3a to form the concave portion 1a. The formed electrode pad needs to be formed of a metal having resistance to an etching solution. Since the etching solution for silicon is generally an alkaline aqueous solution (KOH or the like), the electrode pad is usually formed using a noble metal such as gold. Therefore, the cost is increased.

SUMMARY OF THE INVENTION The present invention has been made in view of the above background, and has as its object to solve the above-mentioned problems, and to apply an internal stress to a detection portion such as a thin film heater (heater wire) at the time of manufacturing. Another object of the present invention is to provide a micro-heater which is mechanically strong, prevents a detection portion from being damaged during manufacturing or use, and has high detection accuracy. It is another object of the present invention to provide a micro heater having a structure that can be easily manufactured at a low cost.
It is a further object to provide a manufacturing method suitable for achieving each of the above objects.

[0011]

According to the present invention, there is provided a thin-film heater comprising: a thin-film heater; and a substrate supporting an end of the thin-film heater, wherein a space exists around the thin-film heater. Micro heater (claim 1),
A thin-film heater, a thin-film resistor for resistance detection, and a substrate supporting end portions of the thin-film heater and the thin-film resistor, wherein a space exists around the thin-film heater and the thin-film resistor On the premise of a microheater (claim 2), the thin film heater and / or the thin film resistor are made of single crystal silicon, and the single crystal silicon is joined to the substrate in an electrically insulated state. .

Since the thin-film heater and the like are formed of single-crystal silicon, unlike a conventional method in which a dielectric film is formed on a silicon substrate and a polycrystalline silicon thin film is formed thereon, a single-crystal silicon film is formed. Internal stress does not occur at all when bonding silicon is provided or when a thin film heater or the like is formed in a pattern. Therefore, since no distortion or bending occurs, the resistance value is also as desired, and there is no breakage.

In the above structure, for example, the substrate is made of single crystal silicon, and the crystal direction of the single crystal silicon forming the substrate and at least one of the thin film heater and the thin film resistor are formed. The crystal direction of the single crystal silicon can be matched (claim 3). In this case, as a specific crystal direction, for example, the substrate has a rectangular shape, and the direction of each side of the substrate and the direction in which the thin film heater and the thin film resistor are arranged are in the <110> direction. They can be formed in parallel (claim 4). With this configuration, the semiconductor device can be manufactured by a normal semiconductor manufacturing process / semiconductor manufacturing apparatus, mass production is possible, the price is low, and the reliability is further increased.

Further, in the manufacturing method according to the present invention, the substrate having an opening formed at a predetermined position on the bonding surface and the single crystal silicon substrate are integrated by heating and bonding with an insulator film interposed therebetween. Next, a predetermined amount of the surface of the single crystal silicon substrate opposite to the bonding surface is removed to form a single crystal silicon thin film having a desired thickness. Thereafter, a step of patterning the single crystal silicon thin film and forming a thin film heater made of the single crystal silicon thin film at a position facing the opening is included.

[0015] This makes it possible to easily manufacture the above-described structure having the structure described in claims 1 to 4 (a manufacturing process of the thin-film resistor is also required to manufacture the structure of claim 2). When a single crystal silicon substrate is bonded, an opening is already formed in the bonding surface of the substrate. Then, since the thin-film heater and the thin-film resistor are patterned thereafter, there is no step of immersing in an etching solution after manufacturing the electrode pad continuous thereto. Therefore, the electrode pad can be manufactured using an inexpensive material such as aluminum.

* Relationship between Terms in Claims and Embodiments "Thin film heater" corresponds to "heater wire 14" in the embodiment. The “thin film resistor” corresponds to the “detection resistance line 22” in the embodiment. “Substrate” corresponds to “silicon substrate 10” in the embodiment. Although a single-crystal silicon substrate is used in the embodiment, the substrate may not necessarily be formed of such a material. However, by using a single crystal silicon substrate, a micro heater can be manufactured by a simple semiconductor manufacturing process.

The structure in which “single-crystal silicon is bonded to the substrate in an electrically insulated state” is realized in the embodiment by “interposing oxide film 12”. This is because the substrate is a silicon substrate, and a separate insulating film such as the oxide film 12 is not indispensable as long as the substrate itself (at least a portion that contacts the thin film heater or the like) has an insulating property. However, if there is nothing on the bonding surface side, the lower surface of the thin film heater or the like will be exposed at the portion located in the space such as the concave portion 10a. Is preferred.

The space secured around the thin film heater and the like is as follows:
This is for achieving thermal insulation between the substrate and the substrate, and in the embodiment, is realized by the concave portion 10a formed on the surface of the silicon substrate. However, it is not necessary that the recess is a bottomed recess, and a through hole vertically penetrating may be used. Further, a thin film heater or the like may project outward from a side edge of the substrate.

In the method according to the fifth aspect of the present invention, the opening may be any shape as long as it is open at least on the joint surface side. That is, it may be a concave part with a bottom or a through hole without a bottom. Further, the area and shape of the opening are also arbitrary.

In the embodiment, an insulating film (oxide film 12) is formed on the junction side surface of the single-crystal silicon substrate in order to realize “across the insulating film”.
The present invention is not limited to this. Further, the step of forming a single-crystal silicon thin film having a predetermined thickness can be performed by etching or polishing. When etching is performed, an etch stop layer is formed in advance on the junction side of the single crystal silicon thin film, and etching is performed from the surface of the single crystal silicon thin film by electrochemical etching or the like. Stop. Therefore, by setting the thickness of the etch stop layer to the thickness of a thin film heater or the like, highly accurate dimensioning can be performed.

[0021]

FIG. 2 shows an embodiment of a micro-heater according to the present invention. As shown in the figure,
An oxide film 12 is provided on the upper surface of a rectangular silicon substrate 10,
On the upper surface of the oxide film 12, a heater wire 14 formed of a single crystal silicon thin film having a predetermined pattern and appropriately bent in a linear shape, and lead wires 15 connected to both ends of the heater wire 14 are joined and arranged. . Further, a protective film 16 made of an oxide film is formed so as to cover the heater wire 14 and the lead wire 15. This allows
The heater wire 14 and the lead wire 15 have an oxide film 12 disposed on the lower surface thereof and a protective film (oxide film) on the upper surface and side surfaces.
Since 16 is arranged, the entire periphery is covered with an oxide film.

A recess 10a is formed on the upper surface of the silicon substrate 10 facing the heater wire 14, and the heater wire 1
A predetermined space is created between the lower part of the silicon substrate 4 and the silicon substrate 10 to obtain thermal insulation. Further, in this example, the heater wire 14 is in contact with the periphery of the concave portion 10a only at both ends continuous with the lead wire 15, and at other portions, the concave portion 10a.
It is located in the air without touching the periphery of a. That is, the heater wires 14 are cantilevered with respect to the silicon substrate 10. As a result, in the conventional device shown in FIG. 1, the dielectric film 2 is connected all around the concave portion 1a, and the heat generated in the heater wire 3 is thermally diffused (transmitted) to the silicon substrate 1 via the dielectric film 2. However, in this example, since the contact area with the silicon substrate 10 is very small, the loss and decrease in measurement accuracy due to thermal diffusion can be suppressed as much as possible.

Since the heater wire 14 is formed of a single-crystal silicon thin film, no warpage occurs during manufacturing.
There is no internal stress and the mechanical strength is high. Therefore, there is no problem in strength even with the cantilever support type as in this example. Also,
Since there is no warpage, there is no change in resistance value due to the warpage, which is a problem of the conventional polycrystalline silicon, and highly accurate measurement can be performed.

The lead 15 connected to the heater wire 14 is
In this embodiment, since both are formed of single crystal silicon, patterns can be formed at the same time, and the shape is wider than the heater wire 14. Thus, even if the same material is formed simultaneously, the resistance value of the portion of the lead wire 15 can be made extremely smaller than the resistance value of the portion of the heater wire 14, and the resistance value accompanying the flow (flow velocity) of the fluid can be reduced. The amount of change can be increased and the detection sensitivity can be increased.

As an example, if the line width of the heater wire 14 is 10
μm, the film thickness is 3 μm, the total length is 1600 μm, and the resistivity of the heater is about 0.002 Ω · cm.
The resistance value of the four parts becomes 1 kΩ. In contrast, Leader 1
Assuming that the line width of No. 5 is 800 μm, the film thickness is the same as that of the heater wire 14, so that even if the length is the same, the resistance value of the lead wire 15 is 1/80 of the resistance value of the heater wire 14. , The lead wire 15 is linear, and the heater wire 1
4 can be shorter than the overall length. As a result, the resistance values of the two are different by one or more digits, and the resistance value of the lead wire 15 can be ignored. By appropriately changing the pattern shape (line width and length), the resistance value of the heater wire 14 and the lead wire 15 can be set to an arbitrary value.

The protection film 16 is not formed above the end portion 15a of the lead wire 15 on the side opposite to the heater wire 14, and the electrode pad 20 is formed on the exposed surface. This electrode pad 20
Can be manufactured after the formation of the concave portion 10a, as will be described later, so that aluminum or the like can be used, and can be manufactured at a lower cost than noble metals used in conventional products. Then, it can be electrically connected to an external device via the electrode pad 20. Accordingly, a predetermined current is applied between the electrode pads 20 and 20 to cause the heater wire 14 to generate heat. In this state, the resistance value between the electrode pads 20 and 20 is determined to determine the flow rate of the fluid flowing on the heater wire 14.・ Detects flow velocity.

The single-crystal silicon thin film constituting the heater wire 14 and the lead wire 15 may be one doped with a predetermined impurity. At this time, by appropriately setting the doping amount and the material, the resistance value of each line 14 and 15 can be set to an arbitrary value. As a result, as shown in FIG. 3, when the specific resistance value R1 of the heater wire portion 14 'and the specific resistance value R2 of the lead wire portion 15' are satisfied, it is possible to satisfy R2 <R1. As described above, since the specific resistance value itself partially differs, by performing the above-described adjustment based on the pattern shape, it is possible to accurately set a desired resistance value while reducing the size. The structure, operation, and effect of the embodiment shown in FIG. 3 are the same as those of the embodiment shown in FIG. 2 except that the specific resistance is adjusted by doping. The detailed description is omitted.

On the other hand, in each of the above two examples, the heater wire is attached to the silicon substrate 10 in a cantilevered manner, but the present invention is not limited to this, and as shown in FIG. The heater wire 14 may be supported on the opposite side of 10a. That is, in the above example, only the portion shown in FIG. 4 is supported by the silicon substrate 10, but in this example, the portion shown on the opposite side is connected to the silicon substrate 10 via the oxide film 12 and supported. I am trying to be. Further, in this example, the center turn portion of the heater wire 14 shown in FIG.
It is connected to and supported. By doing so, the mechanical strength is higher. Note that as the number of contact portions increases, the rate at which heat generated by the heater wires 14 is radiated to the silicon substrate 10 side increases (still sufficiently lower than conventional ones). Therefore, an appropriate structure may be adopted according to the specifications in consideration of strength and thermal insulation. Since other configurations and operational effects are the same as those of the above-described embodiments, the same reference numerals are given and the detailed description is omitted.

Further, in each of the above embodiments, the flow velocity of the fluid around the heater wire 14 is determined based on the change in the resistance value of the heater wire 14, but the present invention is not limited to this. As shown in (1), a structure in which the detection resistance wire 22 is provided in the vicinity of the heater wire 14 may be adopted. The structure of the detection resistor line 22 is also made of single-crystal silicon similarly to the heater line 14, an oxide film is located on the lower surface, and the protective film 16 is formed on the upper surface. The heater wire 14 and the detection resistor wire 22 are both located above the concave portion 10a, and most of them are not in contact with the silicon substrate 10 at a predetermined space, so that desired thermal insulation can be secured.

The micro-heater having this configuration is disclosed in
It has a measurement principle similar to that disclosed in Japanese Patent No. 58346, and generates heat by energizing the heater wire 14, thereby heating the detection resistor wire 22. In this state, the fluid to be measured flows above the heater wire 14 and the detection resistance wire 22. Then, since the heat of the detection resistance wire 22 is removed and the resistance value changes, the fluid value is detected by detecting the resistance value of the detection resistance wire 22 via the electrode pad 20 ′ connected to the detection resistance wire 22. Can be determined.

In the illustrated example, the heater wires 14 are supported on both sides of the silicon substrate 10 and the detection resistor wires 22 are supported on the silicon substrate 10 in a cantilever manner. Alternatively, the detection resistance wire 22 may be supported at both ends.

Next, an embodiment of a method for manufacturing a micro heater having a heater wire or the like using single crystal silicon will be described. For example, the method can be realized by the method shown in FIGS.

That is, first, as shown in FIG.
A first substrate having a concave portion 10a formed at a predetermined position on the surface of a silicon substrate 10 and a second substrate having an oxide film 12 formed on the surface of a single crystal silicon substrate 24 are prepared as shown in FIG. The concave portion 10a in the first substrate can be manufactured by etching with a predetermined region masked by photolithography. Further, the second substrate can be manufactured by thermally oxidizing the surface of the single crystal silicon substrate 24. Both can be easily performed by a normal semiconductor manufacturing process.

Next, the first substrate and the second
The substrates are bonded to each other with the oxide film 12 side facing each other while the relative positions of the two substrates are aligned, and the substrates are joined by heating at about 1000 ° C. to integrate the two substrates (see FIG. 3C). Next, the surface of the single-crystal silicon substrate 24 on the second substrate side is polished or etched and removed to form a single-crystal silicon thin film 24 ′ having a thickness equal to the thickness of the heater wire 14 or the lead wire 15 ( FIG. The desired thickness can be controlled by, for example, time control in the case of etching. In the case of polishing, for example, the polishing can be performed with high accuracy by repeating the polishing step and the film thickness measuring step. Of course, other film thickness control may be used.

Next, if necessary, the single-crystal silicon thin film 2
Phosphorus as an impurity is diffused into 4 'to obtain a desired specific resistance value. Then, dry etching is performed on the single-crystal silicon thin film to form a pattern of the heater wire 14 and the lead wire 15 (see FIG. 7A). Next, an oxide film 16 is formed on the surface of the single-crystal silicon thin film (the heater wire 14 and the lead wire 15) (see FIG. 1B).
5 is removed to remove the oxide film facing the end 15a.
Is exposed, and an aluminum film is formed on the exposed surface to form an electrode pad 20 (see FIG. 3C). In addition,
The patterning is not limited to dry etching as described above, but may be anisotropic etching or the like.

Note that the above-described steps are actually performed using a plurality of heater elements formed on a silicon wafer, and a predetermined portion is finally cut to simultaneously manufacture a plurality of micro heaters. Become. At this time, when bonding the first substrate and the second substrate, the crystal directions (crystal directions) of the silicon substrate 10 and the single-crystal silicon substrate 24 should be matched as shown in FIG. preferable.

As shown in FIG. 9, the direction of each side of the silicon substrate 10 and the direction in which the heater wires 14 and the detection resistor wires 15 are arranged are as follows.
That is, it is to be parallel to the <110> direction.

Further, as another manufacturing method, a step as shown in FIG. 9 can be taken instead of the step shown in FIG. That is, as shown in FIG.
The first substrate is formed by providing the concave portion 10a at a predetermined position of zero. In another step, an etch stop layer 24a is formed on the surface of the single crystal silicon substrate 24 as shown in FIG. The thickness of the etch stop layer 24a is made to match the thickness of the heater wire 14 and the lead wire 15. Of course, the etch stop layer 24a is also a conductive layer made of single crystal silicon. Next, an oxide film 12 is formed on the upper surface of the etch stop layer 24a, and this becomes the second substrate (FIG. 2C).

Then, in the same manner as described above, the first and second substrates are bonded to each other in a predetermined positional relationship, and are bonded by heating and integrated (FIG. 3D). Next, the process shifts to a single-crystal silicon film formation process of a predetermined thickness. In this example, since the etch stop layer 24a is provided in the process of FIG. Is performed, only the surface of the single crystal silicon substrate is removed by etching, and the etch stop layer 24a is not removed. Therefore, a desired film thickness can be obtained by a simple process.

[0040]

As described above, in the micro-heater and the method of manufacturing the same according to the present invention, the detection portion such as the thin film heater (heater wire) is formed of single crystal silicon, and the heater wire or the like is bonded to the substrate. (It is not necessary to form a predetermined pattern at the time of bonding), so that the application of internal stress to the single crystal silicon thin film during manufacturing can be suppressed as much as possible. Therefore, it is possible to prevent the detection portion or the like from being damaged mechanically during manufacture or use. In addition, since there is no internal stress, no distortion occurs, so that there is no change in resistance value due to the distortion, a micro-heater can be manufactured as designed, and variation between products is small, and detection accuracy can be increased. In addition, since the electrode pad and the like at the portion to be connected to the external device can be manufactured after the etching process for the substrate, the manufacturing process is easy and can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing a conventional example.

FIG. 2A is a plan view illustrating an embodiment of a micro heater according to the present invention. FIG. 3B is a cross-sectional view taken along line BB in FIG. (C) is a sectional view taken along line CC in FIG.

FIG. 3 is a view showing another embodiment of the micro heater according to the present invention.

FIG. 4A is a plan view showing still another embodiment of the micro heater according to the present invention. FIG. 2B is a cross-sectional view taken along line BB in FIG.

FIG. 5 is a plan view showing still another embodiment of the micro heater according to the present invention.

FIG. 6 is a process chart (1) showing one embodiment of a method for manufacturing a micro heater according to the present invention.

FIG. 7 is a process diagram (part 2) showing one embodiment of a method for manufacturing a micro heater according to the present invention.

FIG. 8 is a diagram showing a state in the middle of a manufacturing process.

FIG. 9 is a view showing another embodiment of the micro heater according to the present invention.

FIG. 10 is a part of a process view showing another embodiment of the method for manufacturing a micro heater according to the present invention and is a view corresponding to FIG. 6;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Silicon substrate 10a Depression 12 Oxide film 14 Heater wire 16 Protective film

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Fumihiko Sato 10 Okayama Todocho, Ukyo-ku, Kyoto, Kyoto Prefecture (72) Inventor Kenichi Nakamura 1-5-20 Kaigan, Minato-ku, Tokyo Tokyo Gas (72) Inventor Tokudai Neda 1-5-20 Kaigan, Minato-ku, Tokyo Tokyo Gas Co., Ltd.

Claims (5)

[Claims] 1. A micro-heater comprising: a thin-film heater; and a substrate that supports an end of the thin-film heater, wherein a space exists around the thin-film heater, wherein the thin-film heater is made of single-crystal silicon. And the single crystal silicon is bonded to the substrate in an electrically insulated state. 2. A thin-film heater, a thin-film resistor for detecting resistance, and a substrate supporting end portions of the thin-film heater and the thin-film resistor, and a space around the thin-film heater and the thin-film resistor. Wherein at least one of the thin film heater and the thin film resistor is made of single crystal silicon, and the single crystal silicon is joined to the substrate in an electrically insulated state. A micro heater characterized in that: 3. The substrate is made of single crystal silicon, the crystal direction of single crystal silicon forming the substrate, and the single crystal silicon crystal forming at least one of the thin film heater and the thin film resistor. The micro-heater according to claim 1, wherein the direction is made to coincide with the direction. 4. The substrate has a rectangular shape, and the direction of each side of the substrate and the direction in which the thin film heater and the thin film resistor are arranged are formed in parallel to the <110> direction. The micro heater according to claim 3, wherein 5. A substrate having an opening formed at a predetermined position on a bonding surface side and a single crystal silicon substrate are integrated by heating and bonding with an insulating film interposed therebetween, and then opposite to the bonding surface of the single crystal silicon substrate. Forming a single-crystal silicon thin film of a desired thickness by removing a predetermined amount of the surface on the side, patterning the single-crystal silicon thin film,
Forming a thin-film heater made of a single-crystal silicon thin film at a position facing the opening.