JP4074368B2 - Heat generation type thin film element sensor and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heat generation type thin film element sensor including a heat generation type thin film element that detects relative humidity, relative flow rate, gas, and the like from a change in resistance value of a thin film element in a heat generation state, and a manufacturing method thereof.
[0002]
[Prior art]
As shown in FIG. 5, a conventional sensor equipped with this type of heat generating thin film element has a lower insulating film 2 formed on the upper surface of a semiconductor substrate 1 such as a silicon single crystal, and a heat generating portion and a current supply thereon. Some have provided a conductive film 3 made of a thin film including a portion and an electrode portion. A cavity 4 is formed in the semiconductor substrate 1 so as to open to the lower side opposite to the conductive film 3 and reach the lower insulating film 2. The cavity 4 is formed by anisotropic etching, and the heat generating thin film element 5 is constituted by the lower insulating film 2 in the cavity 4 and the conductive film 3 including the heat generating part. Further, an upper insulating film 6 was provided on the lower insulating film 2 so as to cover the heat generating portion of the conductive film 3.
[0003]
In the manufacture of the sensor including the heat generating thin film element 5, the lower insulating film 2 is formed by sputtering on the upper surface of the semiconductor substrate 1 such as silicon single crystal by SiO ₂ or Ta ₂ O ₅ , and Pt or the like is formed thereon. The conductive film 3 is formed and formed into a predetermined shape by etching or the like. An upper insulating film 6 such as SiO ₂ or Ta ₂ O ₅ is formed on the surface of the lower insulating film 2 by sputtering or the like so as to cover the conductive film 3 as necessary. Next, anisotropic etching was performed from below the semiconductor substrate 1 to the lower insulating film 2 to form the cavity 4.
[0004]
[Problems to be solved by the invention]
A sensor having such a conventional heat generation type thin film element has a lower insulating film 2 formed on a silicon wafer substrate 1 to detect a humidity and a flow rate from a change in the resistance value of the conductive film 3. In order to increase the temperature, the conductive film 3 is heated by flowing current, and the detection target data is detected from the resistance value in that state. However, since the heat distribution of the conductive film 3 becomes non-uniform, the temperature of a specific part is always likely to be high, so that the deterioration of that part is accelerated and it causes disconnection. Furthermore, it is easy to lead to a decrease in sensitivity and a decrease in life.
[0005]
The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide a heat-generating thin film element sensor with little bias in heat distribution, high durability and high detection accuracy, and a method for manufacturing the same. .
[0006]
[Means for Solving the Problems]
The exothermic thin film element sensor according to the present invention includes a cavity opened below a semiconductor substrate, a conductive film formed on the surface side of the substrate via an insulating layer, and the conductive film and the insulating layer interposed therebetween. A heating part formed in the cavity on the opposite side, and a soaking layer with good thermal conductivity such as polycrystalline Si provided through an insulating layer between the heating part and the conductive film Is. The substrate is a semiconductor single crystal wafer, and the heat generating portion is a diffusion portion in which predetermined impurities are diffused in the semiconductor. The conductive film and the electrode of the heat generating part are separately provided on the surface side of the substrate.
[0007]
In this heat generation type thin film element sensor, a conductive film as a detection part and a heat generation part for heating the conductive film are separately formed via an insulating layer and a soaking layer. At the time of detection, a predetermined current is detected by flowing a current through the heat generating portion and heating the conductive film to a predetermined temperature. Further, when dust or the like adheres to the surface, the conductive film is heated to a high temperature by the heat generating portion to remove the dust.
[0008]
According to the method of manufacturing the heat-generating thin film element sensor of the present invention, a heat generating portion having a predetermined pattern is formed on a substrate, an insulating layer is formed on the surface side of the heat generating portion, and the impurity diffusion portion is opposed to the surface of the insulating layer. Then, a soaking layer having a high thermal conductivity is formed by a vacuum thin film forming technique, a conductive film is further formed through an insulating layer, etching is performed from the back side of the substrate toward the heating portion, and the back side of the substrate is formed. This is a method for manufacturing a heat-generating thin film element sensor in which a hollow portion is formed and the heat generating portion is left in the hollow portion.
[0009]
In particular, in the method for manufacturing a heat-generating thin film element sensor according to the present invention, an impurity diffusion portion serving as a heat generating portion having a predetermined pattern is formed on a semiconductor substrate. Then, an insulating layer is formed on the surface of the substrate where the impurity diffusion portion is formed, and a soaking layer such as Si having high thermal conductivity is formed on the surface of the insulating layer so as to face the impurity diffusion portion. A conductive film is formed by a technique and further through an insulating layer. Then, an insulating layer that covers and protects the conductive film is formed. Thereafter, anisotropic etching is performed from the substrate rear surface side toward the impurity diffusion portion to form a cavity in the substrate rear surface. At this time, the anisotropic etching is performed so that the impurity diffusion portion remains selectively without being etched.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a heat generation type thin film element sensor of the present invention will be described with reference to the drawings. The heat generation type thin film element sensor of this embodiment includes a silicon (Si) single crystal semiconductor substrate 10, and a cavity portion 14 opened downward is formed in the semiconductor substrate 10. , Covered with a thin insulating layer 12 of about ₂ μm of SiO ₂ .
[0011]
The insulating layer 12 is further laminated with a thin insulating layer 13 of SiO ₂ of about 1 μm, and a soaking layer 15 made of a polycrystalline Si thin film is sandwiched between the insulating layers 12 and 13. The thickness of the heat equalizing layer 15 is, for example, a thickness of about 5000～10000A.
[0012]
On the surface side of the insulating layer 13, a conductive film 16 having a thickness of about 4000 to 5000 mm is formed in a U shape. The conductive film 16 is made of a metal thin film having a large temperature coefficient such as platinum (Pt) or titanium (Ti). Electrodes (not shown) formed on the sides of the surface of the substrate 10 are formed at both ends of the conductive film 16. Further, a thin SiO ₂ insulating layer 18 having a thickness of about 1 μm, which is a protective film, is laminated on the surface of the conductive film 16.
[0013]
On the back side of the insulating layer 12 in the cavity 14, a U-shaped heat generating portion 20 having a shape facing the conductive film 16 is formed. The heat generating part 20 is composed of P ⁺ Si obtained by diffusing boron (B) as an impurity at a high concentration in silicon. The boron concentration of the heat generating portion 20 as the impurity diffusion portion is, for example, about 10 ²⁰ cm ⁻³ . Diffusion portions continuing from both end portions of the U-shaped heat generating portion 20 reach the side of the substrate 10 along the back surface of the insulating layer 12 and are connected to electrodes formed on the surface of the substrate 10. The electrode of the conductive film 16 and the electrode of the heat generating part 20 are separately located on the surface side of the substrate 10.
[0014]
Next, a method for manufacturing the heat-generating thin film element sensor of this embodiment will be described with reference to FIG. In this manufacturing method, first, as shown in FIG. 3A, an oxide film 22 is formed on the surface of an N-type Si single crystal substrate 10 and a window 24 is opened in a pattern that forms the shape of the heat generating portion 20. Then, a P-type dopant such as boron is diffused in the Si substrate 10 at a high concentration. Thereby, the impurity diffusion part 26 is formed in a predetermined shape, for example, a U-shape.
[0015]
Thereafter, the oxide film 22 is removed, and as shown in FIG. 3B, the insulating layer 12 is formed on the surface of the substrate 10 by sputtering or the like. Further, as shown in FIG. 4 and the like, a soaking layer 15 made of a polycrystalline thin film is formed at the center of the insulating layer 12 by sputtering. The shape of the soaking layer 15 is formed using a mask. Then, the insulating layer 13 is formed by sputtering or the like so as to cover the soaking layer 15 and the surrounding insulating layer 12.
[0016]
Further, a conductive film 16 of a metal thin film is formed so as to be positioned inside the soaking layer 15 on the surface of the insulating layer 13. As a method for forming the conductive film 16, a metal thin film is formed on the entire surface by vapor deposition or sputtering and then etched to form the conductive film 16 in a predetermined shape as shown in FIGS. Then, an insulating layer 18 as a protective film is formed by sputtering or the like so as to cover the conductive film 16 and the surrounding insulating layer 13.
[0017]
Next, anisotropic etching is performed from the rear surface side of the substrate 10 so that the impurity diffusion portion 26 forming the heat generating portion 20 remains selectively as shown in FIG. The impurity diffusion portion 26 remains without being selectively etched when Si is anisotropically etched with an alkaline etching solution such as KOH (potassium hydroxide) or TMAH (tetramethylammonium hydroxide).
[0018]
In the heat generation type thin film element sensor of this embodiment, the conductive film 16 and the heat generating part 20 which are detection parts are provided separately via the insulating layers 12 and 13, and the heat generating part 20 is also provided when the conductive film 16 becomes dirty. The conductive film 16 may be heated by, for example, generating heat at about 700 ° C., and the heating is performed uniformly and appropriately, and the heat generation is not concentrated on a part of the conductive film 16 and is not disconnected. In addition, since the soaking layer 15 having a relatively high thermal conductivity is provided between the insulating layers 12 and 13 and the heat of the heat generating portion 20 is spread uniformly around, the conductive film 16 is heated more uniformly. It is. This makes it difficult for heating unevenness to occur in the conductive film 16, enabling uniform heating, extending the life, and improving the measurement accuracy.
[0019]
Furthermore, since the conductive film 16 is indirectly heated to, for example, 200 to 300 ° C. by the heat generating unit 20 for heating at the time of detection, it is not necessary to constantly flow a large current necessary for heat generation through the conductive film 16. It is only necessary to pass a necessary small amount of current, and the durability of the conductive film 16 becomes higher.
[0020]
The heat-generating thin film element sensor and the manufacturing method thereof according to the present invention are not limited to the above embodiment, and the substrate may be made of other semiconductors or insulators besides Si single crystal. The insulating layer can be appropriately selected from SiO ₂ , Ta ₂ O _{5 and the} like. In addition to diffusing boron, the heat generating part may be diffused by other impurities. In addition to selective etching by diffusion, the heat generating part is formed in a predetermined shape on the substrate surface by vapor deposition or the like to form an insulating layer. Thereafter, the substrate may be etched to form a heat generating portion in a predetermined shape on the back surface of the insulating layer. Further, the soaking layer may be a metal or other material having a relatively high thermal conductivity other than silicon.
[0021]
【The invention's effect】
According to the heat generation type thin film element sensor of the present invention, it is not necessary to flow a large current directly to the conductive film to be detected to generate heat, and the conductive film is indirectly heated by the heat generating portion. In addition, the durability of the sensor is improved without being locally heated. Furthermore, the heat of the heat generating portion is more uniformly transmitted to the conductive film by the soaking layer, temperature unevenness due to the position of the conductive film can be suppressed, and the measurement accuracy can be increased.
[Brief description of the drawings]
FIG. 1 is a partial cutaway perspective view of an embodiment of a heat generation type thin film element sensor of the present invention.
FIG. 2 is a longitudinal sectional view of a heat generation type thin film element sensor of this embodiment.
FIG. 3 is a longitudinal sectional view showing a manufacturing process of the heat generating thin film element sensor of this embodiment.
FIG. 4 is a partially broken plan view of a soaking layer of the heat generation type thin film element sensor of this embodiment.
FIG. 5 is a longitudinal sectional view of a conventional heat-generating thin film element sensor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Board | substrate 12, 13, 18 Insulating layer 14 Cavity part 15 Soaking | uniform-heating layer 16 Conductive film 20 Heat generating part

Claims (2)

A cavity opened below the substrate of the semiconductor single crystal, a conductive film formed on the surface side of the substrate via an insulating layer, and formed in the cavity on the opposite side via the conductive film and the insulating layer A heat generating part which is a diffusion part in which a predetermined impurity is diffused in the semiconductor, and a soaking layer made of a polycrystalline semiconductor having a good thermal conductivity provided between the heat generating part and the conductive film via an insulating layer A heat-generating thin film element sensor. An impurity diffusion portion serving as a heat generating portion having a predetermined pattern is formed on a semiconductor single crystal substrate, an insulating layer is formed on the surface of the substrate on which the impurity diffusion portion is formed, and the impurity diffusion portion and the surface of the insulating layer are formed. A soaking layer of a polycrystalline thin film having high thermal conductivity facing the pattern is formed by a vacuum thin film forming technique, and a conductive film is further formed through an insulating layer. Etching toward the impurity diffusion portion to form a cavity on the back surface of the substrate and selectively leaving the impurity diffusion portion to form the heat generating thin film element sensor.

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