JPH0630343B2 - Amorphous silicon thin film conductor containing microcrystalline phase - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a conductor for use in an electronic circuit,
Especially belongs to the microelectronics range,
The present invention relates to a thin film conductor having a special new atomic structure.
Despite being made of a semiconductor material, this new special semiconductor thin-film conductor has a relatively large electric conductivity and a small temperature coefficient, while the thermoelectric power (Seebeck coefficient) is similar to that of a semiconductor. Since it was discovered that it has a large feature, it is possible to form a fine thermoelectric effect element and to use it as a constituent material of a power sensor for power measurement. Further, since it has an elastoresistance effect (or piezoresistance effect) whose resistance changes due to mechanical strain (or stress), it can be used as a constituent material of a strain or force sensor. That is, it provides various materials for sensor electronics.

[Conventional technology]

Sensors As materials for electronics, various metals,
Many alloys, single element semiconductors, compound semiconductors, semi-metals, amorphous materials, etc. are known. Looking at the characteristics of conventional materials of this kind, it was found that each one had its own characteristics and had other drawbacks. For example, the piezoresistive effect of p-type silicon, which is a single element semiconductor, is 10 ² times as large as that of nickel chrome alloy, but the temperature coefficient of resistance is 10 ³ times as large. The same applies to the Seebeck coefficient and the conductivity or the temperature coefficient thereof.

[Problems to be solved by the invention]

A characteristic of semiconductors, which has both excellent characteristics to be used in sensor electronics, low resistance (high conductivity) and a small temperature coefficient, can be deposited on any substrate including glass substrates, and is easy to process. It is an object of the present invention to realize a conductor for microelectronics that meets all the technical requirements.

[Means for solving problems]

In the present invention, as a thin film conductor, a phase material such as a mixture of a silicon microcrystalline phase and an amorphous phase has a high conductivity, a small temperature coefficient, and a large Seebeck effect and an elast resistance (piezoresistance). ) Utilizing the fact discovered by the inventor that it is effective. That is, a thin film of silicon in which the amorphous phase and the microcrystalline phase are mixed is formed on a substrate having an insulating property by a microelectronic technique (for example, plasma CVD).
Method, photo-CVD method, etc.) and a pair of electrodes provided at both ends of the thin film to form current input / output terminals, so that the current phenomenon (transport phenomenon) of the above material can be used for a sensor. To do.

[Work]

The silicon thin film conductor thus produced has, for example, a crystallinity (volume ratio of microcrystals in the whole) of 10% to 99%.
It is estimated that the microcrystals are silicon, the average grain size is expected to be about 50Å to 500Å, the conductivity is at least 0.1 S · cm ⁻¹ , and the temperature coefficient of conductivity is It is 1% / K or less. Moreover, the magnitude of thermoelectric power (Seebeck coefficient) is at least 10 μV / K, and the gauge rate (rate of resistance change / strain) indicating the magnitude of elastoresistance effect (piezoresistance effect) is at least 4.

〔Example〕

The thin-film conductor of the present invention is a CVD (Chemical Vapor Deposition) which is one of the microelectronic techniques.
The method of manufacturing by the method will be described. Commercially available plasma CV
A D furnace is used. A thermal CVD furnace or a photo CVD furnace may be used, and the manufacturing apparatus may be any as long as it can form an amorphous phase. In the example described here, p
Form a conductor. The n-type can also be formed by the same method.

Silane gas is used as the raw material gas introduced into the furnace. Hydrogen diluted diborane (B ₂ H ₆ ) is added as a p-type dopant.
Table 1 shows an example of deposition conditions. As the substrate, a substrate having at least an insulating surface, for example, a glass substrate, mica, a polymide film, various semiconductor substrates, or a metal plate whose surface is covered with an insulating material is used.

FIG. 1 is a diagram showing an X-ray diffraction waveform of an amorphous silicon thin film deposited on a glass substrate under the conditions of Table-1.
In the figure, the horizontal axis represents the diffraction angle 2θ, and the vertical axis represents the diffraction intensity (arbitrary unit). Further, waveforms A and B, the discharge power density magnitude is respectively 0.15 W / cm ^2, is the X-ray diffraction pattern when deposited at 4.0 W / cm ^2. It is shown that as the discharge power increases, the deposited amorphous silicon film changes from a completely amorphous phase to a phase in which a microcrystalline phase and an amorphous phase are mixed. Further, sharp diffraction peaks appear at (111), (110) and (311), indicating that (111), (110) and (311) are strongly oriented. Further, it is shown that it is composed of silicon from the peak waveform and the diffraction angle of the peak value of each diffraction pattern. The crystallinity of an amorphous silicon thin film in which a microcrystalline phase and an amorphous phase are mixed can be calculated by separating the X-ray diffraction pattern into the amorphous phase and the microcrystalline phase. The description of the procedure is omitted.

FIG. 2 is a diagram showing that the crystallinity of the amorphous silicon thin film depends on the magnitude of the discharge power density, and is an example of the experimental result obtained from the X-ray diffraction pattern. In the figure, the horizontal axis represents the discharge power density Pd (W / cm ² ) and the vertical axis represents the crystallinity V.V. F (%) is shown. This experimental result shows that the crystallinity increases sharply when the discharge power density becomes larger than about 0.3 W / cm ² .

FIG. 3 is a diagram showing an example of a laser Raman spectrum of an amorphous silicon thin film deposited on a glass substrate under the conditions of Table 1 above. The right angle scattering method was used as the measuring method. In the figure, the horizontal axis represents the Raman shift (cm ^-1 ) and the vertical axis represents the Raman intensity (arbitrary unit). Also, the waveform A
And B are Raman spectra when deposited at discharge power density magnitudes of 0.15 W / cm ² and 4.0 W / cm ² , respectively. The waveform A shows a broad pattern, which indicates that the amorphous silicon thin film deposited on the glass substrate is composed of a completely amorphous phase, and the waveform B has a sharp peak. Are shown to be mixed.
These results correspond well with the results obtained with the X-ray diffraction pattern shown in FIG. Further, each Raman shift amount of the peak value in the waveform B is obtained in the vicinity of 520 cm ^-1 , which indicates that the amorphous silicon thin film is composed of a silicon-silicon bond.

FIG. 4 is a diagram showing a sample shape used for measuring the dark conductivity and Seebeck coefficient of an amorphous silicon thin film deposited on a glass substrate under the conditions shown in Table 1, where 1 is a glass substrate and 2 is an amorphous material. Silicon thin film, 3 is a platinum thin film, and 4 is a Seebeck coefficient measurement sample. The thickness of the amorphous silicon thin film used for measurement is approximately
0.3 μm. Further, T + ΔT represents the hot junction temperature, and T represents the cold junction temperature. An ordinary photolithography technique was used for pattern formation, and a vacuum deposition method was used for platinum thin film formation.

FIG. 5 is a diagram showing an example of the temperature characteristic of dark conductivity of the amorphous silicon thin film obtained by using the Seebeck coefficient measurement sample 4 shown in FIG. In the figure, the horizontal axis is
The reciprocal of absolute temperature (1 / T) and the vertical axis represent dark conductivity (σ _D ), respectively. Waveform A shows the magnitude of the discharge power density.
A graph showing the temperature characteristic of dark conductivity of an amorphous silicon thin film composed only of an amorphous phase deposited at 15 W / cm ² , which is proportional to (1 / T) ^1/4 in the low temperature region and 1 / T in the high temperature region.
Therefore, the electric conduction mechanism is dominated by the hopping conduction in the low temperature region and the band conduction in the high temperature region. This shows the same tendency as the example of the temperature characteristic obtained by the conventional amorphous silicon thin film, but it can be said that the great feature is that the magnitude of the absolute value of dark conductivity is improved by 1 to 2 digits. . Waveform B is a graph showing temperature characteristics of dark conductivity of an amorphous silicon thin film containing a microcrystalline phase having a crystallinity of 70% deposited at a discharge power density of 4.0 W / cm ² . It can be said that the dark conductivity is as large as 30 S · cm ⁻¹ or more, and the change with temperature is very small as 1% / K or less. As described above, the fact that the dark conductivity is hardly affected by the temperature change is extremely advantageous in forming a minute resistor or the like on the IC chip or the like. Although not shown, the amorphous silicon thin film formed under the deposition conditions shown in Table-1 has a dark conductivity of 0.
It has been confirmed that the temperature coefficient of 1 S · cm ⁻¹ or more is extremely small at 1% / K or less.

FIG. 6 is a diagram showing the dark conductivity-Seebeck coefficient characteristics of an amorphous silicon thin film measured using the Seebeck coefficient measurement sample 4 shown in FIG. 4, with the horizontal axis representing the dark conductivity σ _D (S · cm). ^-1 ) and the Seebeck coefficient α (μV /
The size of K) is shown. In the figure, white circles indicate the Seebeck coefficient of the amorphous silicon thin film. The amorphous silicon thin film shows a large value of 100 to 350 (μV / K) as the Seebeck coefficient when the dark conductivity σ _D is 0.1 S · cm ⁻¹ or more. If this amorphous silicon thin film is used, a high-performance thermocouple, a high-frequency power sensor, an infrared sensor, a temperature sensor, etc. can be configured, and application to a wide range of sensors can be expected.

Further, as a result of forming the strain gauge measurement sample 9 shown in FIG. 7 and measuring the gauge ratio, 4 to 60 or more were obtained. In the figure, 5 is a glass substrate, 6 is an amorphous silicon thin film, 7 and 7'are ohmic electrodes, and 8 and 8'are
Au ribbon lines are shown respectively. As the ohmic electrode material, a nichrome / gold multilayer thin film is used. Further, the arrow indicates the direction of the stress applied from the outside for the strain gauge measurement.

Plasma CV of amorphous silicon thin film described above
The deposition conditions by the D method are SiH ₄ / H ₂ flow rate ratio, discharge pressure,
It has been confirmed that it depends on the discharge power and the substrate temperature, and it can be formed by other than those shown in Table 1. Within the range shown below, for example, SiH ₄ / H ₂ = 0.003 to 1, discharge pressure 0.01 to
10 (Torr), discharge power density 0.01 to 10W / cm ² , substrate temperature 1
It can be formed at 50 to 500 ° C. Further, in the photo CVD method,
It can be formed at a low temperature, for example, even when the substrate temperature is around 200 ° C.

[Effect]

As described above in detail, the amorphous silicon thin film conductor according to the present invention has the following unique effects by mixing the amorphous phase made of a silicon mixed crystal and the microcrystalline phase.

(1) Since a large dark conductivity of 0.1 S · cm ⁻¹ or more (maximum value 100 S · cm ⁻¹ ) can be obtained, a small resistor can be formed on the insulating substrate.

(2) Seebeck coefficient is 100 even when the dark conductivity is 0.1 S ・ cm ^-1 or more.
Since it is ~ 350 μV / K or more, high-performance thermocouples, high-frequency power sensors, infrared sensors, temperature sensors, etc. can be constructed.

(3) Despite the large dark conductivity of 0.1 Scm ^-1 or more,
Since the gauge factor is as large as 4 to 60 or more, high-performance strain sensor, pressure sensor, load cell, and touch sensor can be configured.

(4) Since the temperature coefficient of dark conductivity is as small as 1% / K or less, resistors, high frequency power sensors, infrared sensors, strain sensors, pressure sensors, load cells, etc. that do not require temperature compensation can be configured.

(5) It can be formed by a relatively simple method such as plasma CVD,
And, the crystallinity, dark conductivity, etc. can be easily controlled, and
Since it is compatible with the IC process, a temperature sensor, a strain sensor, a pressure sensor, and the like can be easily incorporated in the conventional IC, so that a high-performance IC can be configured. Further, a three-dimensional sensor in which a temperature sensor, a strain sensor, etc. are combined can be easily and inexpensively constructed.

(6) By the thin film forming technology, a conductor can be formed on a wide variety of insulating substrates over a wide area and in a planar shape.

[Brief description of drawings]

FIG. 1 is a diagram showing an X-ray diffraction pattern of an amorphous silicon thin film, FIG. 2 is a diagram showing discharge power dependence of crystallinity, FIG. 3 is a diagram showing laser Raman spectrum, and FIG. 4 is a Seebeck coefficient. The figure which shows the sample 4 for a measurement, 5th
FIG. 6 is a diagram showing the temperature dependence of dark conductivity, FIG. 6 is a diagram showing dark conductivity-Seebeck coefficient characteristics, and FIG. 7 is a diagram showing a strain gauge measurement sample 9 . In the figure, 1 and 5 are glass substrates, 2 and 6 are amorphous silicon thin films, 3 is a platinum electrode, 4 is a Seebeck coefficient measurement sample, 7 and 7 ′ are ohmic electrodes, and 8 and 8 ′ are Au ribbon wires, 9 Indicate samples for strain gauge measurement.

Claims (4)

[Claims] 1. An insulating substrate, a thin film formed on the substrate and made of silicon in which an amorphous phase and a microcrystalline phase are mixed, and a pair of electrodes for inputting and outputting an electric current to and from the thin film. Silicon thin film conductor with. 2. The silicon thin film conductor according to claim 1, wherein the thin film has a conductivity of at least 0.1 S · cm ⁻¹ . 3. The silicon thin film conductor according to claim 1, wherein the thin film has a thermoelectric power of at least 10 μV / K. 4. The silicon thin film conductor according to claim 1, wherein the temperature coefficient of conductivity of the thin film is 1% / K or less.