JPH11273908A - Thin-film thermistor and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin-film thermistor, which can be reduced in 1/f noise and increased in electrical conductivity while its thermistor constant is increased, and consequently, can obtain a large S/N ratio with a small size, and a method for manufacturing the thermistor. SOLUTION: In a thin-film thermistor 10, a lower Cr electrode 11a and an upper Cr electrode 11b are respectively formed on both surfaces of a thermistor element 8 composed of a p-type a-SiC:H(hydrogenated amorphous SiC) thin film. The a-SiC:H thin film is formed by the plasma CVD method using monosilane and methane as gaseous starting materials and diborane as a dopant gas. the a-SiC:H thin film has a uniform carrier concentration in the thickness direction and is formed, so that the carrier concentration becomes higher than or equal to 3×<18> cm<-3> . When the carrier concentration is increased, the electrical conductivity σ of the thermistor 10 is increased, and at the same time, the 1/f noise is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thin film thermistor using an amorphous semiconductor thin film and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, infrared detectors capable of measuring temperature in a non-contact manner have been actively developed. As this type of infrared detecting element, for example, a pyroelectric element using a pyroelectric material and a thermopile element using a thermoelectromotive force have been developed. However, a pyroelectric infrared detecting element is a so-called differential type detecting element that absorbs infrared light as heat energy and detects a resulting change in the amount of charge (pyroelectric effect), and detects only a change in the infrared light. There was a problem that it was not possible. Further, the thermopile type infrared detecting element outputs a DC voltage proportional to the temperature, but has a disadvantage that the output is small.

On the other hand, it is known that a thermistor type infrared detecting element can obtain a high DC output and is suitable for miniaturization and high integration, and a thermistor is widely used as a temperature sensor for various devices. Used. A thermistor constant (B constant) is known as a value representing the characteristics of the thermistor. The B constant is a value indicating the relationship between the temperature change and the resistance change, and the larger the B constant, the larger the resistance change with respect to the temperature change. Therefore, it can be said that the larger the B constant is desirable as a thermistor.

By the way, an array sensor in which a large number of thermistors are two-dimensionally arranged to detect a temperature distribution has been proposed. If this type of array sensor is used, the temperature distribution can be handled in the same manner as image information. Will be possible. Since the thermistor used for this type of application needs to be highly integrated, each thermistor must be miniaturized. However, when the volume of the thermistor element is reduced, 1 /
There is a problem that the f noise increases in inverse proportion and the S / N ratio decreases as a result.

A small thermistor element used for an array sensor or the like cannot be manufactured by a conventional method of sintering a metal oxide.
A manufacturing method has been considered in which an amorphous semiconductor thin film is formed by a method and the amorphous semiconductor thin film functions as a thermistor element. Amorphous semiconductor thin films formed by the plasma CVD method are used for solar cells, thin film transistors, sensors, and the like, and in particular, a-Si: H (hydrogenated amorphous Si) and a-SiC: H formed by the plasma CVD method. (Hydrogenated amorphous SiC) has a larger optical band gap than crystalline silicon, a large light absorption coefficient in the visible light region, and can be easily formed into a thin film and large area. Application field. When an amorphous semiconductor thin film used for a solar cell is formed, the optical band gap becomes smaller as the impurity concentration becomes higher. Therefore, the amount of the dopant gas mixed with the source gas is generally reduced. Also, when a thermistor element is formed, the B constant is generally higher when the impurity concentration is lower, and from this viewpoint, it is better that the mixing amount of the dopant gas with respect to the source gas is smaller. In addition, when a-SiC: H is formed, it is general to increase the dilution ratio with hydrogen gas that dilutes the source gas.

[0006]

However, since the 1 / f noise is inversely proportional to the carrier concentration, the 1 / f noise increases when the doping concentration is low. That is,
To reduce the size and increase the B constant, 1 / f
This causes a problem that the noise increases and the S / N ratio decreases.

In order to improve the B constant, the activation energy E of a semiconductor resistance layer made of an amorphous semiconductor thin film is increased.
It is necessary to increase a. Here, the activation energy E
The relationship between a and the electrical conductivity σ is generally expressed by the following equation near room temperature. σ = σ ₀ exp (−Ea / kT) = σ ₀ ^* exp (−Ea ₀ / k
T) where σ ₀ is a coefficient (pre-exponential pfactor), k
Is the Boltzmann constant, T is the absolute temperature σ ₀ ^* is the conductivity prefactor, and Ea ₀ is the activation energy at 0K. Further, the B constant is obtained by -Ea / k.
In other words, according to the above equation, when the activation energy Ea is increased to increase the B constant, the conductivity σ decreases. Therefore, to increase the B constant and increase the conductivity σ, the prefactor σ ₀ ^* Needs to be increased. However, the conventional thin-film thermistor has a problem that the value of prefactor σ ₀ ^* is small, and when the thermistor element is miniaturized, the resistance value becomes too high and measurement becomes difficult.

The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce the 1 / f noise and increase the conductivity while increasing the B constant, and consequently, to reduce the size and increase the S / F ratio.
An object of the present invention is to provide a thin film thermistor capable of obtaining an N ratio and a method for manufacturing the same.

[0009]

According to a first aspect of the present invention, there is provided a thin film thermistor in which an electrode is provided on a semiconductor resistance layer made of an amorphous semiconductor thin film, wherein the semiconductor resistance layer comprises a carrier. The density is 3 × 10 ¹⁸ c
m ⁻³ or more, and by setting the carrier concentration of the semiconductor resistance layer to 3 × 10 ¹⁸ cm ⁻³ or more, the conductivity increases and the 1 / f noise decreases, In addition, dangling bonds (unbonded hands) increase, the Fermi level does not easily move to the band edge, and a decrease in the B constant is suppressed.
The ratio can be improved.

According to a second aspect of the present invention, there is provided a method of manufacturing a thin film thermistor in which an electrode is provided on a semiconductor resistance layer made of an amorphous semiconductor thin film, wherein the semiconductor resistance layer has a carrier concentration of 3 × 10 ¹⁸ cm ^-3 or more. The semiconductor resistance layer has a carrier concentration of 3 × 10 ¹⁸
When the ^{density is not} less than cm ^-3 , the conductivity is increased and the 1 / f noise is reduced. In addition, dangling bonds (unbonded hands) are increased, and the Fermi level is less likely to move to the band edge. As a result, it is possible to provide a small-sized thin film thermistor having a high S / N ratio.

According to a third aspect of the present invention, there is provided a thin film thermistor in which electrodes are provided on a semiconductor resistance layer made of an amorphous semiconductor thin film, wherein the semiconductor resistance layer has one of a donor concentration and an acceptor concentration of 3 × 10 ¹⁸ cm. ^-3 or more, wherein one of the donor concentration or the acceptor concentration of the semiconductor resistance layer is 3 × 1
By setting it to 0 ¹⁸ cm ^-3 or more, the conductivity is increased, the 1 / f noise is reduced, dangling bonds (unbonded bonds) are increased, and the Fermi level is less likely to move to the band edge. Since the decrease in the constant is suppressed,
As a result, the S / N ratio can be improved with a small size.

According to a fourth aspect of the present invention, there is provided a method of manufacturing a thin film thermistor in which an electrode is provided on a semiconductor resistance layer comprising an amorphous semiconductor thin film, wherein one of a donor concentration and an acceptor concentration is 3 × 10 ¹⁸ cm ^-3
The conductivity is increased and the 1 / f noise is reduced when one of the donor concentration and the acceptor concentration of the semiconductor resistance layer is 3 × 10 ¹⁸ cm ⁻³ or more. As the dangling bonds (unbonded hands) increase, the Fermi level hardly moves to the band edge, and the decrease of the B constant is suppressed. As a result, a small-sized thin film thermistor having a high S / N ratio is obtained. Can be provided.

[0013]

FIG. 1 is a cross-sectional view of an infrared detecting element using a thin film thermistor of the present invention, and shows Si on a main surface and a back surface of a support substrate 1 made of a single crystal silicon substrate.
A dielectric film 2 made of an O ₂ / Si ₃ N ₄ film is formed, and a recess 6 having a V-shaped cross section is formed from the main surface side of the support substrate 1.
To provide a thin film portion 2a made of the dielectric film 2
Is formed, and the thin film thermistor 1 is formed on the thin film portion 2a.
0 is formed. The thin film thermistor 10 includes the thin film portion 2
a lower electrode 1 made of a chromium (Cr) film formed on
1a and a p-type a-Si formed on the lower electrode 11a.
A thermistor element 8 is formed of a C: H thin film, and an upper electrode 11b is formed on the thermistor element 8 and formed of a Cr film. SiON on the thin film thermistor 10
An infrared absorbing film 5 is formed with a second protective film 4 made of. Here, the thin film portion 2a and the thin film thermistor 1
0, the detection unit A constituted by the infrared absorbing film 5 and the like,
It is supported on the support substrate 1 by a plurality of support beams 7. The lower electrode 11a has a first pad electrode 14a.
Is connected to the upper electrode 11b, and the second pad electrode 14
b is connected. Incidentally, reference numeral 3 in FIG. 1 denotes a first protective film made of a SiO ₂ film.

Hereinafter, the manufacturing method will be described. First,
SiO ₂ / Si on the main surface and the back surface of the support substrate 1, respectively.
_A dielectric film 2 of ₃ N ₄ film is formed (that is, Si ₃
After forming the N ₄ film, the SiO ₂ film is formed), a Cr film is formed on the entire surface of the dielectric film 2 on the main surface side of the support substrate 1 by a vapor deposition device (for example, an EB vapor deposition device), and photolithography is performed. A lower electrode 11a made of a Cr film having a predetermined shape is formed by a technique and an etching technique. next,
P-type a-Si using a plasma CVD apparatus (see FIG. 2)
A C: H thin film is formed so as to cover the entire surface on the main surface side, and p-type a is formed by photolithography and etching.
-Thermistor element 8 is formed by removing an unnecessary portion of the SiC: H thin film, and thereafter, an SiO ₂ film is formed so as to cover the entire main surface side of the support substrate 1, and the photolithography technique and the etching technique are used. first made of the SiO ₂ film by removing unnecessary portions of the SiO ₂ film
Is formed. Thereafter, a Cr film is formed so as to cover the entire surface on the main surface side of the support substrate 1, and an upper electrode 11b made of a Cr film having a predetermined shape is formed by a photolithography technique and an etching technique. Thereafter, a second protective film 4 made of a SiON film is formed so as to cover the entire surface on the main surface side of the support substrate 1, an infrared absorbing film 5 is formed on the second protective film 4, and photolithography technology and Unnecessary portions of the infrared absorbing film 5 are removed by an etching technique. Thereafter, a part of the second protective film 4 and the first protective film 3 is etched to form a contact hole exposing a part of the surface of each of the lower electrode 11a and the upper electrode 11b, and the contact hole is buried. Thus, a metal film such as an aluminum film is formed on the entire surface on the main surface side of the support substrate 1 by a vapor deposition apparatus, and unnecessary portions of the metal film are removed to form pad electrodes 14a and 14b made of the metal film. Further, thereafter, a plurality of support beams 7 for supporting the detection unit A are formed apart from each other by photolithography technology and etching technology, and the support substrate 1 is mainly moved through slits formed between the support beams 7. The recess 6 is formed by etching from the front side. The infrared detecting element having the structure shown in FIG. 1 is formed by the manufacturing method described above.

FIG. 2 shows a film forming apparatus comprising the plasma CVD apparatus used for forming the p-type a-SiC: H thin film. The support substrate 1 on which the dielectric film 2 and the lower electrode 11a are formed is housed in a chamber 22, and is heated to, for example, 270 ° C. by a heater 23. The chamber 22 is provided with an outlet 24 for evacuating the inside to a vacuum and an inlet 25 for introducing a gas for film formation. The support substrate 1 is placed on a grounded electrode 26a together with the chamber 22, and a high frequency voltage (13.56 MHz) is applied from a high frequency power supply 27 to an electrode 26b facing the electrode 26a. As a result, plasma is generated between the two electrodes 26a and 26b by glow discharge, the gas for film formation is decomposed to generate active species, and the support substrate 1 is vaporized by the active species.
A p-type a-SiC: H thin film is formed on the main surface side of. Here, in the present embodiment, monosilane (S
A mixed gas of iH ₄ ) and methane (CH ₄ ) is used, hydrogen gas (H ₂ ) is used as a gas for diluting a source gas, and diborane (B ₂ H ₆ ) diluted with H ₂ is used as a dopant gas.
Is used.

When a mixed gas of monosilane and methane is used as a source gas, the bandgap Eg shown in FIG. 3 is increased due to the inclusion of carbon in the amorphous semiconductor thin film, and a decrease in the B constant is suppressed. This is because that. E _C and E _V is the band edge in FIG. 3 (mobility edge), E _F is the Fermi level, Ea denotes activation energy. 30 and 40 represent shallow levels, respectively.
50 indicates a deep level.

In the present invention, the 1 / f noise of the thin film thermistor 10 is reduced by making the carrier concentration in the thickness direction of the thermistor element 8 uniform and adjusting the carrier concentration of the thermistor element 8. Therefore, the activation energy Ea with respect to the mixing ratio of the dopant gas to the source gas,
Changes in conductivity σ, prefactor σ ₀ ^* , and 1 / f noise were measured. The results are shown in FIGS. here,
4 to 7 show the results when the high-frequency power applied to the electrode 26b is 100 W (high-frequency power density is 110 mW / cm ² ) as the conditions for forming the p-type a-SiC: H. It is well known that increasing the high frequency power promotes gas decomposition, and the value of 100 W is a relatively large value.

The horizontal axis of FIG. 4 shows the mixing ratio of diborane to monosilane, and the vertical axis shows the activation energy Ea. In FIG. 4, ◆ indicates that the mixing ratio of methane to monosilane is 0.3, ▼ indicates 0.5, Δ indicates 1.0, ● indicates 1.7, and ▲ indicates 3. The case where it is set to 0 is shown. As is apparent from FIG. 4, the activation energy E increases when the mixing ratio of the dopant gas to the source gas is increased.
a decreases. That is, when the mixing ratio of the dopant gas to the source gas is increased, the B constant decreases. The activation energy Ea is increased by increasing the mixing ratio of methane to monosilane.

The horizontal axis of FIG. 5 shows the mixing ratio of diborane to monosilane, and the vertical axis shows the conductivity σ. In FIG. 5, ▼ indicates that the mixing ratio of methane to monosilane is 0.5,
The symbol “を” indicates the case where it is set to 1.0, and the symbol “△” indicates the case where it is set to 3.0.
As is clear from FIG. 5, the conductivity σ increases as the mixing ratio of the dopant gas to the source gas (monosilane and methane) increases.

The abscissa in FIG. 6 corresponds to diborane monosilane.
Vertical axis is the prefactor σ₀ ^*Is shown. Figure 6
● indicates that the mixing ratio of methane to monosilane is 0.3
, ▲ indicates 0.5, and △ indicates 1.
You. As is clear from FIG.
Prefactor σ₀ ^*
Indicates a generally upward trend. However, FIG. 5 and FIG.
Therefore, as is clear, the conductivity σ, the prefactor σ₀ ^*To
From the viewpoint of enlargement, methane to monosilane
Is not so high, the desired B
It is advisable to mix methane in an appropriate amount to obtain a constant.
I can say that.

The horizontal axis of FIG. 7 shows the activation energy Ea, and the vertical axis shows 1 / f noise. In FIG. 7, ▲ indicates that the mixing ratio of diborane to monosilane is 0.25 vol%.
(2) shows the case where 1.0 vol%, and ● shows the case where 2.0 vol%. As is clear from FIG. 7, when compared at the same activation energy Ea, the 1 / f noise decreases as the mixing ratio of the dopant gas to the source gas increases. Since the activation energy Ea decreases as described above by increasing the mixing ratio of diborane to monosilane, the flow rate of methane is increased as a formation condition when viewed at the same activation energy Ea in FIG. . For example, when the mixing ratio is 0.25 vol% and the activation energy Ea is 0.42 eV, the flow rate of methane is 10
When the mixing ratio is 2.0% and the activation energy Ea is 0.42 eV, the flow rate of methane is increased from 170 sccm to 300 sccm.

That is, as can be seen from FIGS. 5 to 7, when the mixing ratio of the dopant gas to the source gas is increased, in other words, when the doping concentration is increased, the conductivity σ and the prefactor σ ₀ ^*
Increases, and the 1 / f noise decreases.
It can be said that it is desirable to mix methane in an appropriate amount so as to obtain a desired B constant. In order to increase the S / N ratio, it is desirable to increase the mixing ratio of the dopant gas to the source gas, for example, it is desirable to set the mixing ratio to 1% or more.

In an amorphous semiconductor thin film on which active species generated by plasma of a mixed gas of a source gas and a dopant gas are deposited, the doping efficiency is proportional to the square root of the volume ratio of the dopant gas to the source gas. Is known, and is represented by the following relational expression. Nd = 3 × 10 ¹⁹ × Cg ^0.5 (cm ⁻³ ) where Nd is the dangling bond density and Cg is the volume ratio of the dopant gas to the source gas. When the conductivity type of the amorphous semiconductor thin film is p-type, the acceptor concentration N _A and the dangling bond density N d are N _A ≒ N
The carrier concentration n _bt of the shallow level 40 in FIG. 3 is represented by the following equation. The n _bt = N _A -Nd present invention, as described above, the volume ratio of the dopant gas to the source gas when 1% or more, 1 / f high-performance thin-film thermistor 10 lower noise is realized. When the volume ratio of the dopant gas to the source gas is 1%, the carrier concentration is Nd = 3 × 10 ¹⁹ × 0.01 ^0.5 = 3 × 10 ¹⁸ (cm
^-3 ) Since shallow level carrier concentration n _bt in 40 is negligibly small relative to the acceptor concentration N _A, the acceptor concentration N _A is substantially equal to 3 × 10 ¹⁸ cm ^-3. Therefore, in the present embodiment, it is desirable that the carrier concentration and the acceptor concentration be 3 × 10 ¹⁸ cm ⁻³ or more.

As shown in FIG. 3, the carriers in the amorphous semiconductor thin film are divided into a deep level 50 (electronic state in the gap) and shallow levels 30 and 40 (tail state), and are frozen. In this state, the number of carriers at shallow levels 30, 40 gradually changes. That is, shallow level 30,
When there are many carriers of 40, the characteristics change with time greatly and exhibit unstable characteristics. Therefore, when most of the carriers exist at the deep level 50, such a change with time is suppressed to a small extent, and the B constant, the conductivity σ, and the 1 / f noise are stabilized.

It should be noted, increasing the doping concentration of the amorphous semiconductor thin film, an increase in dangling bonds in the film (dangling bonds), since the Fermi level E _F is less likely to move to the mobility edge, reduction of B constant Is suppressed. It is known that dangling bonds in the film are reduced by hydrogen dilution. However, by lowering the hydrogen dilution concentration, a decrease in the B constant can be suppressed.

In the above embodiment, the source gas and
Using a mixed gas of monosilane and methane gas
Although diborane is used as a punt gas,
Is a gas mixture of silicon-containing gas and carbon-containing gas
If so, other combinations can be used. Also do
Various well-known substances can be used for pantogas.
Thermistor element made of n-type a-SiC: H thin film
8 is formed, for example, as dopant gas
Sphine (PH_Three) May be used. In this case,
Carrier concentration of 3 × 10¹⁸cm^-3Above (donor concentration
3 × 10¹⁸cm ^-3Above).

[0027]

According to a first aspect of the present invention, there is provided a thin film thermistor having an electrode provided on a semiconductor resistance layer made of an amorphous semiconductor thin film, wherein the semiconductor resistance layer has a carrier concentration of 3 ×.
Since it is 10 ¹⁸ cm ⁻³ or more, the conductivity of the semiconductor resistance layer increases, and 1 / f noise decreases. In addition, dangling bonds (unbonded hands) of the semiconductor resistance layer increase, and the Fermi level increases in the band. Hard to move to the end B
Since the decrease in the constant is suppressed, there is an effect that as a result, the S / N ratio can be improved with a small size.

According to a second aspect of the present invention, there is provided a method of manufacturing a thin film thermistor in which an electrode is provided on a semiconductor resistance layer made of an amorphous semiconductor thin film, wherein the semiconductor resistance layer has a carrier concentration of 3 × 10 ¹⁸ cm ^-3 or more. As a result, the 1 / f noise is reduced while the conductivity of the semiconductor resistance layer is increased, and the dangling bonds (unbonded hands) of the semiconductor resistance layer are increased, and the Fermi level moves to the band edge. And the decrease of the B constant is suppressed,
As a result, it is possible to provide a small-sized thin film thermistor having a high S / N ratio.

According to a third aspect of the present invention, there is provided a thin film thermistor in which electrodes are provided on a semiconductor resistance layer made of an amorphous semiconductor thin film, wherein the semiconductor resistance layer has a donor concentration or an acceptor concentration of 3 × 10 ¹⁸ cm. ^-3 or more, the conductivity of the semiconductor resistance layer is increased and 1 /
f noise is reduced, dangling bonds (unbonded bonds) of the semiconductor resistance layer are increased, the Fermi level is less likely to move to the band edge, and a decrease in the B constant is suppressed. There is an effect that the S / N ratio can be improved.

According to a fourth aspect of the present invention, there is provided a method of manufacturing a thin film thermistor in which an electrode is provided on a semiconductor resistance layer made of an amorphous semiconductor thin film, wherein one of a donor concentration and an acceptor concentration is 3 × 10 ¹⁸ cm ^-3
Since the semiconductor resistance layer is formed as described above, the conductivity of the semiconductor resistance layer is increased and 1 / f noise is reduced, and dangling bonds (unbonded hands) of the semiconductor resistance layer are formed.
Increases, the Fermi level is less likely to move to the band edge, and a decrease in the B constant is suppressed.
There is an effect that it is possible to provide a thin film thermistor having a / N ratio.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an infrared detecting element using a thin film thermistor of the present invention.

FIG. 2 is a schematic configuration diagram showing an apparatus for manufacturing an amorphous semiconductor thin film according to the present invention.

FIG. 3 is an explanatory diagram of a state density of an amorphous semiconductor thin film.

FIG. 4 is a diagram showing a relationship between a mixing ratio of a dopant gas to a source gas and an activation energy in the embodiment.

FIG. 5 is a diagram showing a relationship between a mixing ratio of a dopant gas to a source gas and an electric conductivity in the embodiment.

FIG. 6 is a diagram illustrating a relationship between a mixing ratio of a dopant gas to a source gas and a prefactor according to the embodiment.

FIG. 7 is a diagram showing a relationship between activation energy and 1 / f noise in the embodiment.

[Explanation of symbols]

 Reference Signs List 8 thermistor element 10 thin film thermistor 11a lower electrode 11b upper electrode

Claims (4)

[Claims] 1. A thin-film thermistor in which electrodes are provided on a semiconductor resistance layer made of an amorphous semiconductor thin film, wherein the semiconductor resistance layer has a carrier concentration of 3 × 10 ¹⁸ cm ⁻³ or more. . 2. A method for manufacturing a thin film thermistor having an electrode provided on a semiconductor resistance layer made of an amorphous semiconductor thin film, wherein the semiconductor resistance layer has a carrier concentration of 3 × 10 ¹⁸ cm.
^A method for manufacturing a thin film thermistor, characterized in that the thin film thermistor is formed to have a ^{thickness of -3} or more. 3. A thin film thermistor in which an electrode is provided on a semiconductor resistance layer made of an amorphous semiconductor thin film, wherein the semiconductor resistance layer has a donor concentration or an acceptor concentration of 3 × 10 ¹⁸ cm ⁻³ or more. A thin film thermistor characterized by the above. 4. A method of manufacturing a thin film thermistor in which an electrode is provided on a semiconductor resistance layer made of an amorphous semiconductor thin film, wherein one of a donor concentration and an acceptor concentration is 3 × 10 ¹⁸ cm ⁻³ or more. A method for manufacturing a thin-film thermistor, characterized in that: