JP2004183038A - METHOD FOR FORMING ELECTRODE WITH LOW CONTACT RESISTANCE ONTO n-TYPE CONDUCTIVE ZINC OXIDE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form an electrode with low contact resistance onto zinc oxide which is useful as an electronic material including an electric resistor and a sensor material. <P>SOLUTION: The method for forming the electrode comprises heating/vaporizing indium metal and fixing the vapor on the surface of the zinc oxide. In the above step, direct current plasma is used in particular for the purpose of avoiding increase of contact resistance by oxidation of indium metal, to improve adhesiveness of vapor deposited indium. The method further comprises stopping generation of the direct-current plasma after the vapor deposition of the indium metal, and without breaking the vacuum, preferably vapor depositing a noble metal on the indium metal electrode so as to form a film for preventing the oxidation. Because the film acquires higher adhesiveness of the indium metal than that by pressure bonding or normal vapor deposition, the film realizes a more stable ohmic property and lower resistance. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention forms a metal electrode having low resistance and good ohmic properties on zinc oxide of electric and electronic devices such as electric resistors, sensors, varistors, and transparent electrodes using zinc oxide characterized by n-type conductivity. On how to do it.
[0002]
[Prior art]
Generally, at the junction between a metal and a semiconductor, an energy barrier determined by the work function of the metal and the electron affinity of the semiconductor is formed. Therefore, various efforts have been made to form a low-resistance electrode having excellent ohmic properties. It has been done. Until now, ohmic electrodes on zinc oxide used for electric and electronic devices have been formed by applying and baking a paste in which fine metal particles such as a silver paste are dispersed, or by sputter deposition of a metal such as gold. Was.
[0003]
Also, it has been known that indium can be used as a low-resistance electrode. In particular, indium is effective for n-type doped zinc oxide (for example, see Non-Patent Document 1). For forming the indium electrode, a method of pressing an indium foil, a method of applying an indium-gallium-based amalgam, or a method of using an indium-based metal as solder is used.
[0004]
[Non-patent document 1]
N. Ohashi et al. , Japanese Journal of Applied Physics Vol. 38, pp5028-5032, 1999
[0005]
[Problems to be solved by the invention]
In the method of forming an indium electrode on zinc oxide, when an indium-gallium-based amalgam is applied, a reaction with zinc oxide occurs, which may damage the surface of the zinc oxide single crystal. Further, in an electrode that requires baking, the defect structure of zinc oxide that is sensitive to the temperature history may be altered. Further, it is difficult to form an electrode on a minute element by a coating method.
[0006]
As described in Non-Patent Document 1, when indium diffuses at a high concentration with respect to zinc oxide, there is a possibility that a complex oxide composed of zinc and indium may be formed. It has the property of easily becoming.
[0007]
In normal indium deposition, indium can diffuse into zinc oxide and cause such problems. In addition, the properties of the electrode may be lost due to oxidation of the indium.
[0008]
An object of the present invention is to form an indium metal electrode having a low contact resistance with zinc oxide characterized by n-type conductivity used in electric and electronic devices and having excellent oxidation resistance by a vapor deposition method. is there. In particular, a small high-quality indium metal electrode having a size of less than 1 mm is formed on the n-type conductive zinc oxide film, and the defect structure and impurity state of the zinc oxide material can be reduced without heat treatment. It is an object of the present invention to provide a technique for forming a small electrode without changing it.
[0009]
[Means for Solving the Problems]
The present inventor has found a method of depositing indium, which is a metal that realizes low contact resistance, under conditions that do not diffuse into zinc oxide and adhere well.
According to this method, it is possible to cover only a necessary portion with a mask so that the indium metal is not adhered, and to vapor-deposit only a necessary portion, so that a small electrode can be easily formed.
[0010]
Furthermore, the deposited film is thin, and when zinc oxide is deposited at room temperature and then exposed to the atmosphere, indium is oxidized and the characteristics as an electrode are impaired, so a film with excellent oxidation resistance is continuously deposited. It was found that this problem could be solved by doing so.
[0011]
That is, the present invention provides: (1) an anode electrode for enabling direct-current plasma discharge, a cathode electrode disposed opposite to the anode electrode, and a high temperature sufficient for realizing vacuum heating deposition of indium metal in a vacuum chamber. And a heating vessel filled with indium metal capable of realizing the above, an electronic element using n-type conductive zinc oxide is arranged on the cathode electrode, and the inside of the vacuum chamber is evacuated. Introduced into a vacuum chamber and maintained at an appropriate pressure to generate DC plasma.In a state where DC plasma was generated, indium metal was heated and evaporated, and plasma was applied to the surface of the n-type conductive zinc oxide under a DC electric field. A method for forming a low contact resistance electrode on n-type conductive zinc oxide, characterized by forming indium metal electrode by depositing indium while irradiating.
[0012]
The present invention also provides (2) the method for forming a low contact resistance electrode on zinc oxide according to (1) above, wherein after indium metal deposition, the generation of DC plasma is stopped, and the vacuum is not broken. A method for forming a low contact resistance electrode on n-type conductive zinc oxide, comprising depositing a noble metal film for preventing oxidation on an indium metal electrode.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
In order to carry out the method of the present invention, the following DC plasma vacuum deposition apparatus is used. In the vacuum chamber, an anode electrode and a cathode electrode for enabling direct-current plasma discharge and irradiating plasma to the surface of the n-type conductive zinc oxide under a direct-current electric field are provided opposite to each other. An electric or electronic device using n-type conductive zinc oxide is disposed on a cathode electrode such that the surface of the zinc oxide film faces the anode electrode.
[0014]
A resistance wire heating or a heating mechanism equivalent thereto is installed in the vacuum chamber. This heating mechanism is a heating mechanism capable of generating a high temperature sufficient for vacuum deposition of indium. The heating vessel heated by this heating mechanism is desirably a basket formed by molding a resistance heating heater, but any mechanism capable of heating and evaporating indium, such as resistance wire heating of a porcelain crucible, is preferred. Not limited. The heating vessel is filled with indium metal to be evaporated.
[0015]
The heating vessel filled with indium is preferably installed between opposed electrodes for direct-current plasma discharge.However, as long as the evaporated indium is arranged to be deposited on the surface of the zinc oxide film, it can be installed in other installation places. I do not care.
[0016]
As described above, an anode electrode, a cathode electrode, and a heating vessel filled with indium are arranged in a vacuum chamber, and after the electric and electronic elements using n-type conductive zinc oxide are arranged on the cathode electrode, the vacuum chamber is evacuated. . An appropriate evacuation mechanism for the vacuum chamber can be used. It is desirable that the inside of the vacuum chamber is purged with argon gas before the evacuation and purged to remove oxygen components in the vacuum chamber and prevent oxidation of indium metal.
[0017]
After the evacuation of the vacuum chamber is completed, argon gas is introduced into the vacuum chamber to maintain an appropriate pressure for stably generating DC plasma. The pressure (degree of vacuum) at this time is about several pascals, but an appropriate degree of vacuum is selected depending on the vacuum tank to be used, the shape of the discharge electrode, and the discharge voltage.
[0018]
Under a condition in which the degree of vacuum is stable, a voltage is applied to the discharge electrode to form argon plasma in the vacuum chamber. After the generation of the argon plasma, evaporation of indium metal is started by the above-described heating device filled with indium. After depositing enough indium to form an electrode having a desired thickness, the temperature of the heating device is lowered to stop the generation of DC plasma.
[0019]
By performing the deposition under the irradiation of the DC plasma, the adhesion strength of the indium metal electrode to the electric or electronic device using zinc oxide to which the electrode is to be attached is increased. The exact mechanism is unknown. In the indium metal electrode which was not subjected to plasma irradiation, fluorescence which was easily oxidized in the atmosphere was observed, and the value of the contact resistance of the electrode varied. On the other hand, when the indium metal electrode was formed under plasma irradiation, an electrode having little variation and being relatively resistant to oxidation was obtained.
[0020]
The effect of this plasma irradiation is that the ions in the plasma are accelerated by the DC electrode, increase the ion density and are beaten against the indium being deposited on the zinc oxide surface, so that the kinetic energy of the ions is converted into thermal energy as the indium being deposited. It is understood that, due to the effect, indium deposited on the zinc oxide surface does not become isolated fine particles, but becomes a polycrystalline state in which bonds between particles are formed, thereby enhancing adhesion. Is done.
[0021]
However, on the other hand, if a species having excessive energy collides with the zinc oxide surface or the indium thin film being deposited, excessive thermal energy is applied, and the indium during the formation of defects or deposition in the zinc oxide is reduced. The problem of reacting with zinc oxide arises. In reality, r. f. It is known that zinc oxide synthesized by a sputtering method has a high defect density ("Microstructure of Zinc Oxide Growth by rf Magnetron Sputtering; Aspect of Oxygen Vacancy", T.O.K.Og. S. Hista, N. Ohashi, T. Takenaka, K. Oki, N. Kuwano and H. Haneda, Key Engineering Materials, Vol. 181-182, (2000) pp 101-104, Trans. Using high-frequency plasma of AC will damage the zinc oxide, so high-frequency AC plasma Although it is effective to use high-energy particles to increase adhesion by irradiating them with high-energy particles, a high-output AC plasma is used when there is a fear of introducing damage to zinc oxide, which is an object on which an electrode is to be formed. Its use is not preferred.
[0022]
The adhesion between indium metal and zinc oxide can also be increased by subjecting the sample with the indium metal electrode to heat treatment in an oxygen-free atmosphere, but in that case, the temperature of the zinc oxide element itself also increases. , Zinc oxide may be deteriorated. It is understood that ion irradiation from plasma has an advantage that local heating of only the electrode portion is realized.
[0023]
After the formation of the indium metal electrode, the use of the zinc oxide with the electrode in an oxidizing atmosphere, or a step in an oxidizing atmosphere, the surface of the formed indium metal electrode is oxidized, and the indium itself has an electric power. Conductivity may be impaired. To avoid this, after forming the indium metal electrode, a noble metal having high oxidation resistance such as gold is formed as an antioxidant film on the indium metal electrode.
[0024]
For this purpose, if a heating vessel for heating and evaporating gold or the like is provided in the vacuum chamber in addition to a heating vessel for heating and evaporating indium, the antioxidant film can be formed on the indium metal without breaking the vacuum in the vacuum evaporation apparatus. Can be deposited on electrodes. In addition, even if a method in which high-energy particles are poured down by plasma is used to form the metal film for forming the antioxidant film, direct damage to the zinc oxide is small because the zinc oxide is covered with indium. Become.
[0025]
【Example】
Example 1
In the vacuum evaporation apparatus having the structure shown in FIG. 1, a mask made of stainless steel having a thickness of 0.2 mm and having a plurality of circular holes each having a diameter of 0.2 mm provided with electric and electronic elements 3 using n-type conductive zinc oxide. 4 and placed on the lower cathode electrode plate 2 installed for plasma generation. A first resistance heater 5 shaped like a basket was arranged between the upper anode electrode plate 1 and the lower cathode electrode plate 2 for plasma generation, and connected to a heating power supply 7 provided outside the vacuum chamber 9. . The basket portion of the resistance heater 5 was filled with metal indium particles.
[0026]
After these preparations were completed, the vacuum chamber was evacuated by the exhaust device 10 and evacuated to 10 ^-3 Pascal. Thereafter, argon gas was introduced into the vacuum chamber 9 through a flow control valve, and the degree of vacuum was maintained at about 10 Pascal to maintain a stable state. After the degree of vacuum was stabilized, a voltage was applied to a DC plasma generating power source 8 installed outside the vacuum chamber 9 to generate DC plasma.
[0027]
After the generation of plasma is confirmed, current is passed from the heating power supply 7 to the resistance heater 5 filled with indium metal to heat, melt, and evaporate the indium metal. The film was vapor-deposited on the zinc oxide film of the electric / electronic element 3 so as to have a thickness of about 300 nm along the mask. After this vapor deposition, the power supply to the resistance heater 5 was stopped, the evaporation of indium metal was terminated, the power supply for plasma generation was cut off, and the formation of the indium metal electrode was terminated.
[0028]
The ohmic characteristics of the obtained indium metal electrode were evaluated. As a result, linearity of the electrode resistance was observed in the range of 1 nA to 0.1 A, and it was confirmed that a good ohmic contact was formed.
[0029]
Example 2
After the formation of the indium metal electrode was completed in the same manner as in Example 1, electric power was supplied to the second resistance heater 6 formed into a basket shape for evaporating gold, and gold was evaporated to deposit the indium metal previously deposited. A gold thin film was deposited on the electrode so as to have a thickness of about 300 nanometers.
With respect to the indium metal electrode coated with the obtained gold thin film, the ohmic characteristics were evaluated. As a result, in the range of 1 nA to 0.1 A, the linearity of the electrode resistance was recognized, and a good ohmic contact was formed. confirmed.
[0030]
Comparative Example 1
An indium metal electrode was formed on a zinc oxide film in the same manner as in Example 1 except that no DC plasma was generated without applying a voltage to the DC plasma generating power supply 8 installed outside the vacuum chamber 9. did.
[0031]
When the electric or electronic device on which the indium metal electrode was formed was taken out to the atmosphere, the metal luster of the indium metal portion was lost and the indium metal became white. Along with this whitening, the surface of the indium metal was increased in resistance, and the electrode characteristics obtained in Examples 1 and 2 were not realized, and a high-resistance contact resistance was recognized.
[0032]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the method of this invention, the adhesiveness of an electrode which becomes a problem when the method of forming an indium metal electrode by vacuum vapor deposition on the n-type conductive zinc oxide film used for an electric and electronic element, an indium metal electrode By improving the low oxidation resistance of the indium metal electrode, it is possible to form a stable low-resistance indium metal electrode with excellent ohmic properties, reduce the heat generated by the contact resistance of the indium metal electrode, and reduce the resistance of the indium metal electrode. Noise can be reduced, and stable operation of electric and electronic elements can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic view of a DC plasma vacuum deposition apparatus for performing the method of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Anode electrode 2 Cathode electrode 3 Electric and electronic element 4 using n-type conductive zinc oxide 4 Mask 5 First resistance heating heater formed in basket shape 6 Second resistance heating heater formed in basket shape 7 Resistance heating heater Heating power supply 8 DC plasma power supply 9 Vacuum chamber 10 Exhaust device

Claims (2)

A vacuum chamber is filled with an anode electrode for enabling DC plasma discharge, a cathode electrode disposed opposite to the anode electrode, and an indium metal filling capable of realizing a high temperature sufficient for realizing vacuum heating vapor deposition of indium metal. And an electric and electronic device using n-type conductive zinc oxide on the cathode electrode, evacuating the vacuum chamber, and then introducing argon gas into the vacuum chamber, While maintaining a suitable pressure for generating plasma, in a state where DC plasma is generated, indium metal is heated and evaporated, and indium is deposited while irradiating the plasma on the surface of the n-type conductive zinc oxide under a DC electric field. Forming a low contact resistance electrode on the n-type conductive zinc oxide by forming an indium metal electrode. 2. The method for forming a low contact resistance electrode on zinc oxide according to claim 1, wherein after the indium metal is deposited, the generation of DC plasma is stopped, and the oxidation is prevented on the indium metal electrode without breaking the vacuum. A method for forming a low contact resistance electrode on n-type conductive zinc oxide, comprising depositing a noble metal film for the purpose.

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