JPH04307977A - Manufacture of thermal type infrared sensor - Google Patents

Abstract

PURPOSE:To increase constant of a thermistor and electric resistance value at the sensing part of a thermal type infrared sensor, to improve the controllability of the sensor, to enhance the sensitivity of response of the sensor as well as to improve the yield of a product. CONSTITUTION:A silicon oxynitride film 12 is formed on a silicon substrate 11 by a plasma CVD method and thereafter, a temperature-sensing film 14 consisting of amorphous silicon (a-Si) is formed on the film 12 and the substrate 11. Subsequently, ion implantation of impurities, such as phosphorus (P), is performed in the film 14 for making the film 14 have an intrinsic property. In this ion implantation, the phosphorus is implanted at a dose of 1X10<13> piece/cm<2> and after that, a heat treatment of one hour is performed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a thermal infrared sensor that measures the temperature of an object in a non-contact manner.

0002

2. Description of the Related Art Recently, various techniques have been developed for producing thermal infrared sensors suitable for use in non-contact thermometers and the like using semiconductor microfabrication. This thermal infrared sensor has a structure in which a bridge is formed on a support substrate, and a temperature sensitive film is further formed on the bridge. That is,
A temperature-sensitive film receives infrared rays, and the temperature rise caused by the infrared rays is measured by changes in electrical resistance to determine the amount of infrared rays (heat amount).

In this thermal infrared sensor, the temperature sensitive film has a small heat capacity with respect to a small amount of infrared rays, and moreover, the smaller the amount of heat transferred from the film to the outside, the larger the temperature rise and the higher the response sensitivity. For this reason, generally
The thermal capacity is reduced by forming the temperature sensitive membrane into a small cross-linked structure or a thin diaphragm structure, thereby improving sensitivity. This temperature sensitive film is composed of a temperature sensitive film formed on the bridge, an electrode formed on this sensitive film, and wiring from this electrode to a bonding pad. Here, not only the temperature-sensitive film but also the electrodes and wiring contribute to heat capacity and heat transfer, so it is necessary to make these as small, fine, and thin as possible.

[0004] Also, among infrared sensors, bolometer-type sensors utilize the thermistor effect in a temperature-sensitive film made of a semiconductor, but theoretically, this thermistor effect is caused by thermal excitation when heat is applied to the semiconductor. This is a phenomenon in which the number of free carriers increases and the electrical resistance of a semiconductor decreases. For this reason, it is desirable to use a single crystal semiconductor thin film such as silicon, which is easy to microfabricate and has a large thermistor effect, as the temperature sensitive film. Formation of this silicon single crystal film is generally performed by epitaxial growth, but it is difficult to provide a single crystal silicon film on a fine crosslinked structure, and even if it is possible, it is costly. For this reason, conventionally, amorphous silicon (a-Si) or amorphous germanium (a-Ge) was used as a temperature-sensitive film by sputtering or CVD.
It was formed into a thin film with a thickness of about 1 μm using a chemical vapor deposition method.

By the way, in order to make silicon semiconductor temperature sensitive films conductive, certain impurities such as arsenic (As) and phosphorus (P) are generally doped.
This forms a shallow impurity level and decreases the thermistor constant (B constant), resulting in a problem that the sensitivity of the thermistor decreases. In order to increase the thermistor constant, it is better to use an intrinsic semiconductor as the temperature sensitive film. For this purpose, the Fermi level Ef of the semiconductor is
If it contains a large number of acceptors, it can be compensated for by introducing a donor near the center of the forbidden band, or an impurity with a deep level (for example, for silicon, gold ( It is possible to fix the Fermi level Ef at a deep level formed by these impurities by introducing materials such as Au) or copper (Cu).However, the amount of these impurities is extremely large in terms of compensation. It must be precisely controlled. Conventionally, doping with this impurity has been carried out by a thermal diffusion method at a high temperature (1000° C. or higher).

[0006]

[Problems to be Solved by the Invention] However, in conventional thermal infrared sensors, the temperature sensitive film is formed on a crosslinked structure, so when doping with impurities is carried out by the high temperature thermal diffusion method as described above, The controllability of the doping amount is poor, and as a result, the controllability of the thermistor constant and the resistance value of the temperature-sensitive film of the semiconductor is poor, and the temperature-sensitive film is deformed, and the contact between the film and the electrode is poor, resulting in poor response. There was a problem that the sensitivity was lowered and the yield of the product was lowered.

The present invention has been made in view of the above problems, and its purpose is to increase the thermistor constant and electric resistance value by making the temperature sensitive film made of a semiconductor thin film intrinsic, and to improve the manufacturing efficiency. Good controllability,
An object of the present invention is to provide a method for manufacturing a thermal infrared sensor that has high response sensitivity and can improve product yield.

[0008]

[Means for Solving the Problems] A method for manufacturing a thermal infrared sensor according to the present invention includes the steps of forming a temperature sensitive film on a crosslinked portion formed on a semiconductor substrate, and implanting ions into the temperature sensitive film. a step of introducing an impurity that becomes an intrinsic semiconductor or a near-intrinsic semiconductor; a heat treatment step of heating the semiconductor substrate into which the impurity has been introduced at a predetermined temperature; and a step of forming an electrode on the temperature sensitive film. It is equipped with

In the method for manufacturing a thermal infrared sensor of the present invention, since it is possible to set the dose and introduction depth of impurities more accurately than in the thermal diffusion method, it is possible to easily impart intrinsic semiconductor properties to the sensor. Through the subsequent short-time heat treatment step, the impurities can be uniformly diffused into the thin temperature-sensitive film, making it easier to obtain an intrinsic semiconductor or a near-intrinsic semiconductor with uniform impurities. Furthermore, the thermistor constant and electrical resistance value are increased, controllability is improved, response sensitivity is improved, and reproducibility of electrical characteristics is improved.

The temperature sensitive film is made of amorphous silicon (a-
Si) or amorphous germanium (a-Ge)
is formed by a sputtering method, and is made polycrystalline or single crystallized by heat treatment or the like. Alternatively, it may be formed by polycrystallization using a CVD method, and it is preferable to form a thin film with a thickness of about 1 μm.

The conditions for ion implantation into this temperature sensitive film are as follows:
As a result of the subsequent heat treatment, the temperature sensitive film made of a semiconductor thin film is made to have properties like an intrinsic semiconductor or close to an intrinsic semiconductor. If the temperature sensitive film is a silicon semiconductor, p-type impurities can be implanted to make it a compensated semiconductor.If the temperature sensitive film is a silicon semiconductor, gold (Au) or copper (Cu) can be used to make it close to an intrinsic semiconductor. The Fermi level of the semiconductor may be pinned near the center of the forbidden band width by ion-implanting an impurity that forms a deep level as shown in FIG.

For example, if the acceptor concentration of a 1 μm thick silicon temperature sensitive film is 1×10 16 /cm 3 after a heat treatment process is performed without ion implantation, phosphorus (P), which is an n-type impurity, 1×1013 pieces/c
Ion implantation may be performed at a dose of m2. Generally, 8
Since the doping efficiency becomes 100% with heat treatment at 50° C. or higher, the doping efficiency is assumed to be 100% in the above calculation, but in reality, it is necessary to adjust it experimentally. In addition, as mentioned above, the acceptor concentration is 1 × 1016 pieces/cm
3, gold or copper is added to a concentration of 1 x 1016 pieces/cm3 or more, for example, 5 x 1013 pieces/cm2.
Ion implantation may be performed at a dose of .

The heat treatment step has three purposes. One is to uniformly diffuse ion-implanted impurities into a thin temperature-sensitive film of about 1 μm.
, about 30 minutes is sufficient. The other reason is to activate the implanted impurity by 100%, that is, to make the doping efficiency 100%, and for this purpose, the temperature should be 850° C. or higher. Another method is to crystallize the amorphous layer on the surface of the temperature-sensitive film that has been roughened by ion implantation, and to crystallize the sputter-formed temperature-sensitive film, which is generally in an amorphous state. It can be crystallized by heat treatment at 1050°C for about 1 hour. In order to achieve these three purposes at once, heat treatment at 1100°C for 1 hour is sufficient.

[0014] The process of forming electrodes on the temperature sensitive film is performed using, for example, titanium (Ti), platinum (Pt), molybdenum (M
It is possible to form an ohmic electrode by forming a low-resistance silicide such as (o). For example, titanium is deposited to a thickness of about 500 Å, patterned into the required electrode shape by photolithography, sintered at 650°C, unreacted titanium and its oxides are etched away, and aluminum or other electrodes are formed. It is recommended to form a

[0015] As the semiconductor substrate, a semiconductor substrate made of silicon, germanium, etc. can be used, but it is preferable to use a single crystal silicon substrate, which can be easily and inexpensively obtained. Further, it is preferable to use a silicon oxynitride (SiOxNy) film as the bridge portion. This silicon oxynitride film has the properties of both a silicon oxide film and a silicon nitride film, and therefore has a good stress balance and can form a stable crosslinked structure. The thickness of this silicon oxynitride film is preferably 0.1 to 50 μm. If it is less than 0.1 μm, it will be too thin to obtain sufficient strength, while if it is thicker than 50 μm, the heat capacity will increase and the sensitivity will decrease for the above-mentioned reason. Specifically, the silicon oxynitride film is formed by, for example, a plasma CVD method. In this method, the gases used are monosilane (SiH4), nitrogen (N
2) and laughing gas (N2O) is used. Here, the gas flow rate ratio of N2 and N2 O (N2 / (N2
+N2O)) The stoichiometric composition x,y of the silicon oxynitride film can be controlled, and the difference in thermal expansion coefficient between it and the supporting substrate, especially the silicon substrate, can be substantially reduced. This prevents damage due to stress.

[0016]

Embodiments Hereinafter, embodiments of the present invention will be explained in detail with reference to the drawings.

FIG. 2 schematically shows a planar structure of a thermal infrared sensor according to an embodiment of the present invention, and FIG. 1 is a perspective view showing a temperature sensitive film, which is an essential part thereof.

In this thermal infrared sensor, a cavity 13 is formed in the center of a silicon substrate 11 that serves as a support, and a cavity 13 with a width of 100 μm and a length of 100 μm is formed on the surface of the silicon substrate 11 above the cavity 13. 2 mm, film thickness 2 μm 2
A silicon oxynitride film 12 having book bridge portions 12a, 12a is formed. Bridge parts 12a, 12
A temperature sensitive film 14 is formed at the upper center of each of the portions a. The temperature sensitive film 14 is formed by polycrystallizing sputtered amorphous silicon (a-Si) by heat treatment, and is doped with an impurity such as phosphorus (P) to give it intrinsic properties. Further, on the temperature sensitive film 14, two electrodes 15a,
15b are formed facing each other. These electrodes 15a and 15b are formed of, for example, a titanium silicide film. Further, one end of a wiring 16 is connected to each of the electrodes 15a and 15b, and the other end of this wiring 16 is connected to bonding pads 17 at both ends of the bridge portion 12a.
It is connected to the. These wiring lines 16 are made of aluminum (Al), for example.

In this thermal infrared sensor, the electrical resistance value of the temperature sensitive film 14 changes depending on the amount of infrared rays (heat amount) incident on it, and the electrode 15 and the wiring 16 change depending on the change in resistance value. A signal processing circuit (not shown as it is publicly known) determines the flowing current value or the voltage value between the bonding pads 17.
By measuring the amount of infrared rays, it is possible to detect the amount of infrared rays.

FIGS. 3(a)-(d) and FIGS. 4(e)-(
g) represents the manufacturing process of this thermal infrared sensor. In addition, FIGS. 3(a) to (d) and FIGS. 4(e) to (g
) represents a cross-sectional structure taken along line A-A in FIG.

First, the plane orientation (1
10) The silicon substrate 11 was prepared. Next, on this silicon substrate 11, a silicon oxynitride film 12 having a thickness of 2 .mu.m as shown in FIG. 3(b) was formed by plasma CVD. That is, the silicon substrate 11 is
℃, and the pressure was set to 0.45 toor as a film forming condition.
, the high frequency output was 400 W, and the reaction gases were 15 SCCM of monosilane (Si H4) and nitrogen (N2
) to 203SCCM, laughing gas (N2O) to 32SCCM
CM was flowed to grow silicon oxynitride on the silicon substrate 11 in a vapor phase.

Next, sputtering is performed using silicon as a target to form a temperature sensitive film 14 made of amorphous silicon (a-Si) on the silicon oxynitride film 12 and the silicon substrate 11, as shown in FIG. Formed. This sputtering is performed using gas flow rates of argon (Ar) = 2SCCM and hydrogen (H2) = 1SCCM.
CM was performed for 10 minutes at a film forming pressure of 3 x 10-3 Torr and a high frequency pressure of 200W.

Next, in order to give the temperature sensitive film 14 intrinsic properties, as shown in FIG.
4, an impurity such as phosphorus (P) was ion-implanted. This ion implantation is carried out at a rate of, for example, 1×1013 phosphorus/cm.
After that, heat treatment was performed at 1100°C for 1 hour.

Next, as shown in FIG. 4(e), the temperature sensitive film 14 was patterned. Subsequently, as shown in FIG. 4F, a titanium film was formed on the surface of the temperature sensitive film 14 and the silicon substrate 11 by, for example, a vapor deposition method, and then patterned to form electrodes 15a and 15b facing each other. Subsequently, a titanium silicide film was formed by sintering at 650°C for 5 minutes, and unreacted titanium and its oxide film were removed using an etching solution.

[0025] Next, aluminum was deposited by vacuum evaporation to a thickness of about 1
000 Å thick, and patterned by etching to form the wiring 16 as shown in FIG. 2(g).

Next, silicon oxynitride film 1
2 is patterned to form a bridge portion 12a as shown in FIG.
, 12a were formed. This patterning was performed, for example, by reactive ion etching (RIE) until the underlying silicon substrate 11 was exposed. This etching uses methane trifluoride (CHF) as an etching gas.
3), using Freon 14 (CF4) and oxygen (O2), the flow rates are CHF3 = 30SCCM, CF4 =
The etching pressure was 0.075 Torr, the high frequency output was 300 W, and the etching time was 40 minutes.

Finally, the silicon substrate 11 under the bridge parts 12a, 12a is selectively etched away to form the cavity 1.
3 was formed. This etching was performed by anisotropic etching using a hydrazine aqueous solution. Note that this anisotropic etching may be performed using an aqueous potassium hydroxide solution.

As described above, in this embodiment, when introducing impurities into the temperature sensitive film 14, the dose amount and introduction depth of the impurities can be set more accurately than in the thermal diffusion method.
It can be easily imparted with intrinsic semiconductor properties and can be introduced uniformly. Therefore, the thermistor constant and electrical resistance value can be increased, controllability is improved, response sensitivity is improved, and reproducibility of electrical characteristics is improved.

The present invention has been explained above with reference to examples.
The present invention is not limited to the above-mentioned embodiments, but can be modified in various ways without changing the gist thereof. For example, in the above embodiment, after ion implantation into the temperature sensitive film 14, anisotropic etching is performed to form the bridge portion 12a, but it is preferable to perform ion implantation after forming the bridge portion 12a. You can also do this.

[0030]

[Effects of the Invention] As explained above, according to the method of manufacturing a thermal infrared sensor of the present invention, since the ion implantation method is used to introduce impurities into the temperature sensitive film, the dose amount can be set accurately. Therefore, the semiconductor tends to become intrinsic, and impurities tend to be uniformly distributed in the thin temperature-sensitive film. Therefore, the thermistor constant and electrical resistance value become larger, controllability becomes better, response sensitivity improves, reproducibility of electrical characteristics improves, and manufacturing yield improves.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the configuration of a sensitive part of a thermal infrared sensor according to an embodiment of the present invention.

FIG. 2 is a plan view showing the configuration of a thermal infrared sensor according to an embodiment of the present invention.

3 is a longitudinal cross-sectional view showing the manufacturing process of the thermal infrared sensor of FIG. 1 along line AA of FIG. 2; FIG.

4 is a longitudinal sectional view showing the manufacturing process of the thermal infrared sensor of FIG. 1 along the line AA of FIG. 2; FIG.

[Explanation of symbols]

11-Silicon substrate 12-Silicon oxynitride film 12a - Crosslinked part 13─Cavity part 14-Temperature sensitive membrane 15, 15b - electrode 16─Wiring

Claims (1)

[Claims] 1. A step of forming a temperature sensitive film on a crosslinked portion formed on a semiconductor substrate, and introducing an impurity that becomes an intrinsic semiconductor or a near-intrinsic semiconductor by implanting ions into the temperature sensitive film. a heat treatment step of heating the semiconductor substrate into which the impurity has been introduced at a predetermined temperature; and a step of forming an electrode on the temperature sensitive film.