JPS62133770A - Ohmic-junction device - Google Patents

Abstract

PURPOSE:To realize an amorphous semiconductor thin film ohmic junction free of diffusion- or eutectic-caused degradation even at a temperature of 400 deg.C or higher by a method wherein thin films of such a high-melting metal as Pt, Cr, Ti, Mo, or W are used for the formation of an ohmic-junction device. CONSTITUTION:In an ohmic-junction device built of an amorphous semiconductor 2 and a metal thin film electrode 3 provided thereon, Pt is the metal that constitutes the electrode 3. The Pt electrode 3 is connected directly, or through the intermediary of a Cr thin film 4, to the amorphous semiconductor 2. For the construction of the metal thin film electrode 3, high-melting Ti, Mo, or W may be employed. Pt not only melts at a high temperature but also well resists diffusion into an amorphous semiconductor. An ohmic-junction device incorporating Pt is affected little by the passage of time, capable of withstanding fusion, and excellent in heat-withstanding features. Use of Pt in a device improves the device in its functions and reliability.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to electronic devices constructed using amorphous semiconductors containing silicon, germanium, or both as main components, such as amorphous solar cells, amorphous transistors, and amorphous semiconductors. The present invention relates to an ohmic junction device required for the construction of thermocouple elements, amorphous strain sensors, amorphous image sensors, and the like.

Here, an amorphous semiconductor refers to a substance excluding liquids and gases, which does not exhibit three-dimensional periodicity in terms of crystallography, and is irregular and non-crystalline. The so-called "
By containing "amorphous semiconductor" and microcrystalline phase,
So-called "microcrystallization" (also known as microcrystalline m1cro), which shows diffraction peaks that can be specified in the X-ray diffraction pattern.
-crystalline) amorphous semiconductor”
It refers to something that includes both.

[Conventional technology]

Including plasma CVD method, sputtering method, photo CVD method,
In constructing a device using an amorphous semiconductor film formed at low temperature using an ECR plasma method or the like, it is essential to form electrodes with good ohmic properties. Conventionally, ohmic electrodes include: 1. T, O(Indiwm in C)xide) thin film and aluminum (AA)
, a method of depositing a metal thin film such as gold (Au)/nichrome (NiCr) on an amorphous semiconductor thin film has been used.

Vacuum evaporation and sputtering methods are generally used as a method for depositing metal thin films on amorphous semiconductor substrates. For example, a NiCr alloy is deposited using a vacuum evaporation method, and then A method has been used in which an ohmic electrode is formed by depositing Au on the substrate. However, when an ohmic junction device is formed using a multi-metal thin film by such a method, there is a problem in that the ohmic properties are impaired at high temperatures. For example, if an ohmic junction device is formed using a metal thin film such as Au/NiCr on an amorphous semiconductor containing germanium,
At temperatures above 00° C., Au diffuses into the amorphous semiconductor thin film, resulting in a change in junction resistance.

Due to this change, the magnitude of the junction resistance becomes non-uniform within the junction surface, and when external stain pressure is applied and current flows, the current concentrates locally within the junction surface, causing the ohmic junction device to melt. There was a problem of bringing

[Problem 9 to be Solved by the Invention As described above, the conventional ohmic bonding device using a metal thin film has the following drawbacks. When exposed to high temperatures of 400°C or higher, (1) metals such as Au and AL diffuse into the amorphous semiconductor film, causing
(2) electrical characteristics such as resistance value change greatly; As a result, the reliability of the device was significantly reduced.

Generally, amorphous semiconductor devices have a wide variety of applications, and are often locally exposed to high temperatures due to use at high temperatures or heat generation within the device. For example, such a situation occurs when using space. Therefore, in the present invention, it is necessary to form an ohmic bonding device using a metal thin film mainly made of a high-melting point metal such as platinum (PT). This provides a good ohmic bonding device.

[Purpose of the invention]

As described above, the present invention is based on the conventional At or Au/N
In order to improve the problems of ohmic junction devices formed with thin metal films such as iCr and amorphous semiconductors, we focus on PT, which is a typical high-melting point metal, and provide a good and stable ohmic junction device. It is something to do.

The purpose of the ohmic bonding device according to the present invention is (1) 40
(2) To prevent the ohmic bonding device from deteriorating even at high temperatures of 400°C or higher; (3) To make electrode formation easy and electrically good. (4) It must be able to withstand use at high temperatures, such as in automobile engines and in environments different from those on Earth, such as space.

[Means for solving problems]

In an ohmic junction device consisting of an amorphous semiconductor and a metal thin film electrode provided thereon.

PT was used as the material for the metal thin film electrode, and the resulting PT thin film electrode was connected either directly to the amorphous semiconductor or via a chromium (Cr) thin film. Incidentally, in place of ptO, any one of high melting point metals such as titanium (Ti), molybdenum (Mo), or tungsten (W) may be used as a metal thin film electrode. The PT thin film can be easily formed by a vacuum evaporation method using an electron beam.

[For production]

The inventor's experiments have revealed that pt has a high melting point and is difficult to diffuse into an amorphous semiconductor. Therefore, a device equipped with an ohmic bonding device constructed using PT has almost no change over time, is difficult to blow out, and has excellent heat resistance, so that the device 17) has higher functionality and higher reliability. .

〔Example〕

The amorphous semiconductor thin film used in the ohmic junction device according to the present invention can be produced by ordinary plasma CVD method, thermal CVD method, etc.
It can be easily formed by a method such as a method, a photo-CVD method, or a sputtering method. For example, in the plasma CVD method, a hydride raw material gas such as silane or germane is decomposed by plasma discharge, and silicon (8
1) or a method of depositing an amorphous semiconductor thin film mainly made of germanium (Ge), which has the feature of being able to form a uniform, high-quality film over a large area. As the raw material gas, in addition to hydrides, halogen group fluorides such as 7-sokasilane and hookahgermanium are used.

In addition, in order to control p-type and n-type, a trace amount of diborane (B
2H6), phosphine (PH3) and althane (AlH3)
) and other hydrides are added. In the photoCVD method, a mercury sensitization method or a direct excitation method is generally used by using light energy to decompose a source gas, and since there is no ion damage, good film formation can be achieved even at a substrate temperature of 200°C or less. . However, the deposition rate is slow (~IA/see or less) and it is difficult to form a thick film (up to a few dozen at most).
It has the following problems.

Therefore, in order to compensate for this drawback, the optical CVD method can be used in combination with the plasma CVD method to bring out the advantages of each other.

FIG. 1 shows an embodiment of a thermocouple element constructed using an ohmic junction device according to the present invention. The thermocouple element includes an insulating substrate 1, an amorphous semiconductor thin film 2 formed on this substrate, and an amorphous semiconductor It consists of a metal thin film electrode 3 and a metal thin layer 4 provided so as to cover a part of the thin film.

Here, the illustrated thermocouple element is an example of a structure that reveals the influence on the film characteristics of the amorphous semiconductor thin film of the ohmic junction device, and similar results can be obtained using electronic devices with other structures.

As the insulating substrate 1, a solid material having low thermal conductivity and exhibiting electrical insulation, such as a glass plate, mica, or poly(A) madder film, is used. In this example, ↓ indicates the case where Corning 70+9 is used. The amorphous semiconductor thin film 2 was made of silicon-germanium as its main components. In addition, the metal thin film electrode 3 has
PT was deposited using electron beam evaporation in ultra-high vacuum. Further, several hundred holes of Mo, Ti, Cr, etc. were deposited on the metal thin layer 4 by electron beam evaporation or sputtering. A photoetching method and a metal mask method were used to form the pattern. Although FIG. 1 shows an example in which a thin metal layer 4 is inserted between the amorphous semiconductor thin film 2 and the metal thin film electrode 3 in order to increase adhesion, the following can be achieved without using the metal thin layer 4. Similar results were obtained in the examples described in .

FIG. 2 is an oscilloscope photograph showing the ohmic characteristics of a thermocouple element constructed using the ohmic junction device according to the present invention shown in FIG. As a method for evaluating the ohmic characteristics, the ohmic junction device is formed between point A, which is formed so as to cover one end of the amorphous semiconductor 2, and point B, which is the take-out electrode of the ohmic junction device, which is formed so as to cover the other end of the amorphous semiconductor 2. υ was determined by examining the voltage dependence of the magnitude of the flowing current. In FIG. 2, the horizontal axis represents the applied voltage and the vertical axis represents the magnitude of the flowing current. As can be seen from the diagram, the magnitude of the applied voltage and the magnitude of the flowing current are directly proportional. It was confirmed that the ohmic junction device according to the present invention exhibits good ohmic properties.

FIG. 3 shows the rate of change in resistance value of the thermocouple element shown in FIG. 1 due to heat treatment. For the heat treatment, a method was used in which the thermocouple element was held at a high temperature for 3 minutes in a nitrogen atmosphere, and then returned to room temperature. The horizontal axis shows the height of the heat treatment temperature, and
The vertical axis indicates the rate of change (%) of the resistance value due to heat treatment with respect to the initial value (before heat treatment). In Fig. 3, the black circles indicate the magnitude of the change rate (%) of the resistance value of the thermocouple element equipped with the ohmic junction device formed using Pt/Cr t& according to the present invention, and the white circles indicate the rate of change (%) of the conventional thermocouple element. The magnitude of the rate of change (chi) in the resistance value of a thermocouple element equipped with an ohmic junction device formed using an Au/NiCr electrode, which is said to be able to withstand the highest temperatures, is shown. Au/
When using a NiCr electrode, when heat treated at 500°C or higher, the resistance value begins to change due to the heat treatment, and
℃, the resistance value decreases rapidly (22 cm),
It has been shown that when a Pt/Cr electrode is used, the resistance value begins to change at 600° C. and then slowly decreases thereafter.

FIG. 4 is a diagram showing the rate of change of the Seebeck coefficient, measured using the thermocouple element shown in FIG. 1, due to heat treatment.

As a force method for measuring the Seebeck coefficient, point C at the junction between the amorphous semiconductor thin film 2 and metal electrode 3 in FIG.
A method was used in which a temperature difference was given between the hot junction and the cold junction, and the magnitude of the DC voltage generated between the points A and B of each electrode section was divided by the temperature difference. The horizontal axis indicates the height of the heat treatment temperature, and the vertical axis indicates the rate of change (%) of the Seebeck coefficient with respect to the initial value (before heat treatment) due to heat treatment. In Fig. 4, the black circles indicate the rate of change (%) in the Beck coefficient of the ohmic junction formed using the uninvented Pt/Cr electrode.
) are shown respectively.

When using Au/NiCr electrodes, the heat treatment temperature is 40°C.
The Seebeck coefficient begins to change above 0°C, and as the heat treatment temperature increases to 500°C and 600°C, the rate of change increases by approximately 2.
It increases rapidly to 0% and 40chi. On the other hand, it has been shown that when a Pt/Cr electrode is used, the heat treatment temperature hardly changes up to 900°C.

The difference in the rate of change (ch) of the resistance value and Seebeck coefficient due to heat treatment due to the difference in electrode materials in the ohmic junction device shown in the above experimental results is due to the diffusion coefficient of the electrode material into the amorphous semiconductor film. By observing the diffusion phenomenon under a microscope, it was confirmed that this was due to the difference in .

5 and 6 show enlarged microscopic photographs of the D portion of the thermocouple element shown in FIG. 1, viewed from the glass substrate 1 side. Figure 5 shows the state after heat treatment at 400°C using Au/NiCr metal thin film as the electrode material, and Figure 6 shows the state after heat treatment at 400°C.
/Cr metal thin films are photographed after heat treatment at 600°C.

In the figure, 12.16 is a silicon germanium thin film, 13
14 represents a portion where Au is diffused into a silicon germanium thin film, 15 and 18 represent a glass substrate, and 17 represents a Pt/Cr metal thin film. As is clear from the photograph in FIG. 5, when an Au/NiCr metal thin film is used, Au is diffused into the silicon-germanium thin film by heat treatment at 400°C.

In the figure, the band-shaped diffusion part is due to the diffusion of Au.
This shows that when a silicon-germanium thin film is used and is inhibited by iCr, no diffusion occurs even after heat treatment at 600°C.

From the above, it has been shown that the cause of changes in resistance value and Seebeck coefficient due to heat treatment is the diffusion of Au into the silicon germanium thin film. Therefore, as a metal thin film material for ohmic junction devices that has excellent heat resistance and does not change element characteristics, PT
It was confirmed that metals with a high melting point, such as those represented by , and which have a small diffusion coefficient into an amorphous semiconductor are good.

Above, we have explained in detail that improvements in heat resistance and reliability can be achieved when using silicon/germanium thin films as amorphous semiconductor thin films and Pt/Cr f as metal thin films. In each amorphous semiconductor such as amorphous silicon, amorphous kermanium, amorphous silicon carbide, Pt/Cr, Pt, Mo, Ti
By forming an ohmic junction device using any of the high melting point metal thin films such as , W, etc., it was possible to improve the heat resistance and reliability of the amorphous device.

By improving the heat resistance and reliability of amorphous semiconductor devices according to the present invention, it has been possible to expand the conventionally limited applications of amorphous semiconductor devices. In particular, the application of amorphous solar cells to the space field and power generation field, and [Effects of the Invention] Next, the effects of the present invention will be described.

(1) Pt, Or, Ti + M as metal materials
Since we formed an ohmic bonding device using a metal thin film made of a high melting point metal such as +W, we achieved 4.
It has been possible to realize an ohmic junction device for an amorphous semiconductor thin film containing silicon or germanium or both as main components, which does not deteriorate due to diffusion, eutectic, etc. even at high temperatures of 00° C. or higher.

(2) By using an ohmic bonding device with excellent heat resistance and little deterioration, a highly reliable amorphous device was realized.

(3) By using an ohmic bonding device that has excellent heat resistance and minimal deterioration, we have been able to create amorphous solar cells that can be used in space and power generation, as well as amorphous sensors that can be used in harsh environments.

[Brief explanation of drawings]

FIG. 1 shows a thermocouple element using an ohmic junction device. FIG. 2 is an oscilloscope photograph showing the ohmic characteristics of an ohmic junction device consisting of a PT thin film and an amorphous semiconductor thin film with a Cr thin layer interposed therebetween. FIG. 3 shows the rate of change in resistance before and after heat treatment plotted against each heat treatment temperature. FIG. 4 shows the rate of change in the Seebeck coefficient before and after heat treatment plotted against each heat treatment temperature. FIG. 5 is a micrograph showing the thermal diffusion phenomenon of Au into an amorphous semiconductor when heat treated at 400°C. FIG. 6 is a micrograph showing the state of a Pt/Cr metal thin film after heat treatment at 600c. In the figure, 2 is an amorphous semiconductor thin film mainly composed of silicon or germanium, or both, 3 is a metal thin film electrode, and 4 is a metal thin layer. Patent Applicant Anritsu Corporation Agent Patent Attorney Battery Ryutabe 1...Insulating Substrate 2...Amorphous Semiconductor Thin Film 3...Metal Thin Film Electrode 4...Metal Thin Testing Paperback 1111. ~1- 1 0.1) History of the entire review ω Procedural amendment (voluntary) January 2nd, 1985

Claims (1)

[Claims] In an ohmic junction device comprising an amorphous semiconductor (2) mainly composed of silicon or germanium or both, and a metal thin film electrode (3) provided on the semiconductor: the metal thin film electrode is made of platinum, and the platinum An ohmic junction device characterized in that a thin film electrode made of the above is connected to the semiconductor directly or via a thin metal layer (4).