JP2006249540A - Method for forming transparent electroconductive thin-film with low resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a transparent thin-film superior in electroconductivity on a glass substrate with a plasma sputtering vapor-deposition technique. <P>SOLUTION: The method for forming the transparent thin-film with high functionality comprises the steps of: introducing an inert gas comprising at least one element of Ar or heavier in the group 0 in the periodic table into a vacuum vessel with a pressure of 3×10<SP>-5</SP>Pa or lower, till the pressure reaches 0.7×10<SP>-1</SP>Pa to 1.8×10<SP>-1</SP>Pa; arranging the alkali-free glass substrate so as to face a target, in an atmosphere containing the inert gas and 0.6 to 1% hydrogen and/or deuterium; setting the substrate to an electrically floating state in plasma; and forming the thin film with a thickness of 100 nm or more on the substrate, in the presence of a metallic filament with a low gas-pressure plasma sputtering technique. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for forming a transparent conductive thin film having a low electrical resistance, such as an ITO (indium tin oxide) thin film, on a glass substrate.

For example, a transparent conductive thin film such as an ITO thin film formed on a glass substrate is used as an electronic material that requires high light transmission and conductivity, such as an electrode substrate in a liquid crystal display. As a means for forming a transparent conductive thin film on a glass substrate, a thin film forming method by plasma sputter deposition is often employed (for example, see Patent Document 1).
JP 2001-131741 A

  However, since a transparent conductive thin film such as an ITO thin film to be formed on a glass substrate has a complicated crystal structure, a method for controlling its physical properties such as electrical conductivity has not yet been established. As an electrode substrate in a liquid crystal display, a substrate in which a thin film having excellent light transmittance and a low electric resistance value is formed on a glass substrate is required. As described above, as a means for forming a transparent conductive thin film such as an ITO thin film on a glass substrate, many film forming methods using sputter deposition are employed. However, the main parameters that make it possible to reduce the resistance of a transparent conductive thin film, for example, an ITO thin film, and its control method are not clear.

  An object of the present invention is to provide a method for forming a transparent thin film having excellent conductivity on a glass substrate by plasma sputtering deposition.

The invention described in claim 1 for solving the above-mentioned problem is a non- ^volatile substance composed of at least one element of group 0 element in the periodic table and argon or more in a vacuum vessel having a pressure of 3 × 10 ⁻⁵ Pa or less. An active gas is introduced until a pressure of 0.7 × 10 ⁻¹ Pa to 1.8 × 10 ⁻¹ Pa is reached, and 0.6% to 1% of hydrogen and / or deuterium is contained in the inert gas. In an atmosphere, an alkali-free glass substrate is placed opposite to the target to be in an electrically floating state in the plasma, and a highly functional transparent film with a thickness of 100 nm or more is formed on the substrate by low gas pressure plasma sputtering in the presence of a metal filament This is a method for forming a low-resistance transparent conductive thin film in which a conductive thin film is formed.

  Invention of Claim 2 is a formation method of the low resistance transparent conductive thin film of Claim 1 whose highly functional transparent conductive thin film is an ITO thin film.

  According to the present invention, by containing 0.6% to 1% hydrogen and / or deuterium in the atmosphere, oxygen is extracted from the film during film formation, thereby generating oxygen defects. A conductivity improvement of 30% is provided. The effect of improving the conductivity (lowering the resistance of the film) by adding hydrogen increases as the thickness of the transparent conductive thin film, for example, the ITO thin film increases, and is particularly large in the region of thickness 200 nm to 300 nm useful as an electronic material.

As the transparent conductive thin film formed on the glass substrate, a metal oxide such as ZnO, SnO ₂ , or ITO can be used, but ITO has the highest conductivity. By the way, in order to further reduce the resistance of the ITO film, an increase in carrier density due to generation of oxygen defects is one of the problems. Therefore, the inventor worked on the formation of an ITO thin film on a glass substrate by a film formation method by low-pressure plasma sputter deposition, and 0.6% of hydrogen and / or deuterium was added to the atmosphere during film formation by low-pressure plasma sputter deposition. It has been found that by containing ˜1%, oxygen defects can be generated during film formation and the carrier density can be increased, thereby completing the present invention.

As a result of investigating the influence of the plasma atmosphere on the electrical characteristics of the thin film on the glass substrate, the inventor has found that the specific resistance value of the thin film is dependent on hydrogen in the plasma atmosphere. The result is shown in FIG. As is clear from FIG. 1, the specific resistance value of the ITO thin film decreases as the hydrogen partial pressure increases, and the hydrogen content: 1% (hydrogen partial pressure: 1 × 10 ⁻⁵ Torr shows a minimum value, In the experiment, an ITO thin film is formed on a glass substrate by an electron-excited plasma sputtering method operating at a low gas pressure (1.33 × 10 ⁻¹ Pa). As a target, a sintered body of In ₂ O ₃ / SnO ₂ = 95/5 (wt%) was used, and 99.9999% Ar gas was used as a plasma excitation gas.

  The inventor further formed an ITO thin film on the glass substrate by plasma sputter deposition in an Ar atmosphere containing 0.6% hydrogen and / or deuterium, and the electrical properties of the ITO thin film on the glass substrate were The thickness of the ITO thin film was examined as a parameter. The result is shown in FIG. FIG. 2 also shows a case where no hydrogen is added to the atmosphere (circles).

  As is apparent from FIG. 2, the resistivity value of the ITO thin film decreases exponentially regardless of the presence or absence of hydrogen until the thickness of the ITO thin film is about 20 nm, but in the atmosphere when the film thickness exceeds 20 nm. When there is no hydrogen content, a monotonic decrease is observed after a significant increase in specific resistance value as the film thickness increases. On the other hand, in the case where 0.6% hydrogen was contained in the atmosphere (one embodiment of the present invention) (marked with ●), even if the thickness of the ITO thin film increased beyond 20 nm, The specific resistance value continues to decrease monotonously.

  In addition, in the case where 0.6% hydrogen was contained in the atmosphere (invention), the thickness was about 30% compared to the case where hydrogen was not added to the atmosphere (circle mark) in the region of 100 nm or more. The resistance value is decreasing. From this and the relationship (measurement result) between the hydrogen partial pressure and the carrier density shown in FIG. 3, when 0.6% to 1% hydrogen is present in the atmosphere, the hydrogen is reduced by oxygen during the ITO film formation. It can be concluded that it is related to defect generation, resulting in an increase in carrier density and a decrease in the resistivity value of the ITO thin film. When the hydrogen gas content is less than 0.6%, oxygen defects are not sufficiently generated. When the hydrogen gas content exceeds 1%, excessive oxygen defects are generated, leading to precipitation of In metal and light-transmitting properties. Bring about a decline.

  On the other hand, in the present invention, the glass substrate must have an alkali-free composition. If an alkali metal or alkaline earth metal such as K, Na, or Ca is present in the glass substrate composition, the electrical properties (specific resistance value) of the ITO thin film are deteriorated.

As the plasma excitation gas (atmosphere), a group 0 element in the periodic table, that is, a gas composed of at least one of Ar, Kr, Xe, and Rn can be used. In particular, heavy elements such as Kr (krypton) and Xe (xenon) are preferable, but Ar (argon) is preferable in consideration of cost. For example when introducing argon gas into the vacuum container is introduced up to a pressure of ^{0.7 × 10 -1 Pa~1.8 × 10 -1} Pa. An Ar partial pressure of at least 0.7 × 10 ⁻¹ Pa is necessary for film formation of ITO or the like by plasma sputter deposition, and if it exceeds 1.8 × 10 ⁻¹ Pa, the electrical characteristics of the film deteriorate. Let

  For example, hydrogen and / or deuterium can be used as hydrogen added to the argon atmosphere. In this embodiment, hydrogen is introduced into the plasma generating vacuum vessel by a diffusion method using a palladium tube. Palladium passes only hydrogen, and the palladium permeation amount of hydrogen is a function of temperature and pressure. Thus, the hydrogen content can be precisely controlled by control using temperature and / or pressure as operating parameters.

  FIG. 4 shows a film forming apparatus by plasma sputter deposition used in the low resistance transparent conductive thin film forming method according to one embodiment of the present invention. In FIG. 4, 1 is a metal filament, and in this embodiment a tungsten filament, which functions as a thermoelectron source that generates thermoelectrons by energization heating. The metal filament 1 is not limited to tungsten, and for example, a molybdenum wire can be used. A cylindrical anode (anode) 2 is applied with a voltage to accelerate electrons. At this time, plasma is not generated unless the amount of accelerated electrons exceeds a certain value. In this embodiment, plasma is generated at a low pressure by accelerating thermoelectrons from a metal filament (tungsten filament) in a magnetic field.

3 is a permanent magnet for plasma control, and 4 is a cylindrical lens for plasma control. Reference numeral 5 denotes plasma, which is generated between the cylindrical anode (anode) 2 and the target 6. In this embodiment, the target 6 is obtained by mixing powder of In ₂ O ₃ / SnO ₂ = 95/5 (wt%), and sintering and forming it into a disk shape having a thickness of 5 mm and a diameter of 75 mm. Used. Reference numeral 7 denotes a substrate holder for forming a thin film, which is equipped with an alkali-free glass substrate. The alkali-free glass substrate is disposed so as to face the target 6 and performs film formation by electrically floating the substrate in plasma.

Reference numeral 8 denotes an argon gas introduction port (leak valve), which is in a vacuum container (film formation chamber) 11 having a vacuum of 3 × 10 ⁻⁵ Pa or less from 0.7 × 10 ⁻¹ Pa to 1.8 × 10 8. ^In this embodiment, argon gas is introduced until a pressure of ⁻¹ Pa (deposition pressure by sputter deposition) is reached. At that time, argon having a purity of 99.9999% is used. Reference numeral 9 denotes a hydrogen inlet (palladium tube), which introduces hydrogen and / or deuterium so that the argon gas atmosphere in the vacuum vessel (film formation chamber) 11 has a content of 0.6% to 1%. To do. Reference numeral 10 denotes a plasma control electromagnet.

  Next, a process when the low resistance transparent conductive thin film forming method of this embodiment is carried out will be described.

(1) Ensuring vacuum conditions 1) The inside of the vacuum vessel (film formation chamber) 11 is evacuated to a pressure of 3 × 10 ⁻⁵ Pa using a rotary pump and a molecular pump.
2) Next, a gas containing argon as a main component is introduced into the vacuum vessel (film formation chamber) 11 up to a film formation pressure of 1.33 × 10 ⁻¹ Pa by sputtering deposition. At that time, argon having a purity of 99.9999% is prepared and introduced while adjusting the pressure regulator and the needle valve.
3) Prepare another container for hydrogen, and introduce it to a desired amount, for example, 0.8% by using a pressure regulator and a hydrogen inlet (palladium tube) 9.
4) The pressure in the vacuum vessel (film formation chamber) 11 is constantly monitored with an ionization vacuum gauge.

(2) Ensuring film formation conditions by sputter deposition 1) After confirming that the inside of the vacuum vessel (film formation chamber) 11 has reached a pressure of 1.33 × 10 ⁻¹ Pa, ⁷⁵ V is applied to the cylindrical anode (anode) 2. While applying a voltage, the metal (tungsten) filament 1 is energized, and the metal filament 1 is slowly heated until the current value of the cylindrical anode (anode) 2 becomes 0.8 A. At this time, plasma is excited.
2) In order to further increase the density of the excited plasma, the plasma control electromagnet 10 is energized (0.8 A).
3) A negative voltage of 200 V for film formation by sputter deposition is applied to the target 6.
4) Current of about 15 mA flows through the target 6 at a target 6 negative voltage of 200V.
5) Sputtering for about 10 minutes before film formation by sputter deposition is performed to clean the surface of the target 6.
6) The substrate holder 7 for forming a thin film on which the alkali-free glass substrate is mounted is slowly moved to the center of the plasma 5 as shown in FIG. At that time, the thin film forming substrate holder 7 is rotated about the horizontal axis so that the film forming substrate surface faces the surface of the target 6. At this time, the distance from the surface of the target 6 to the surface of the alkali-free glass substrate was about 50 mm.
7) Thereafter, the target 6 current decreases to 7 mA to 8 mA, and film formation starts.
8) Although the temperature control heater was not attached to the thin film formation substrate holder 7, the temperature of the alkali-free glass substrate rose to 250 ° C. due to the radiant heat from the plasma 5 during film formation.

(3) Composition and shape of target 6 1) In ₂ O ₃ powder and SnO ₂ powder were mixed at a weight ratio of 95: 5 and sintered and formed into a disk shape having a thickness of 5 mm and a diameter of 75 mm. A thing was used.

(4) Composition of glass substrate and treatment before film formation 1) Alkali-free glass having a size of 20 mm × 20 mm × 0.6 mm (thickness) was used.
2) The glass surface was not pretreated (as purchased).

(5) Method of introducing hydrogen 1) Deuterium was charged at a pressure of 3.5 × 10 ⁴ Pa into a palladium tube 9 having a closed tip: 0.1 mm, diameter (outer diameter): 3 mm, and heavy at room temperature. Hydrogen is diffused and introduced into the vacuum container (film formation chamber) 11.

(6) Ensuring the ratio of hydrogen in the plasma 1) After evacuating the vacuum vessel (film formation chamber) 11 in advance to a vacuum degree of 2 × 10 ⁻⁵ Pa, first, deuterium is added (5) The hydrogen is introduced into the vacuum container (film formation chamber) 11 by the hydrogen introduction method described in the item 1, for example, and the partial pressure of deuterium is set to 1.33 × 10 ⁻³ Pa. Subsequently, argon gas (purity: 99.9999%) is introduced using an argon gas inlet (leak valve) 8 to obtain a pressure of 1.33 × 10 ⁻¹ Pa.
2) By introducing the above deuterium and argon gas, the inside of the vacuum vessel (film formation chamber) 11 is made an argon gas atmosphere containing 1% deuterium.

(7) Other requirements for film formation 1) No other gas is introduced except that deuterium is mixed with argon gas. For example, no oxygen is introduced.
2) During film formation, the film thickness is monitored with a film thickness monitor.
3) High-performance transparent conductive film, in this embodiment, the absolute value of the ITO film thickness is measured on the alkali-free glass substrate by multiple optical interferometry, and the film thickness monitor and film thickness I'm investigating the relationship.

The graph which shows the influence of the hydrogen partial pressure which acts on the specific resistance value of ITO thin film based on one Example of this invention The graph which shows the relationship between the specific resistance value and film thickness of the ITO thin film on the glass substrate based on one Example of this invention The graph which shows the relationship between the hydrogen partial pressure in the atmosphere at the time of film-forming, and the carrier density of a film | membrane based on one Example of this invention The schematic diagram which shows the apparatus when enforcing the formation method of the low resistance transparent conductive thin film based on one Example of this invention

Explanation of symbols

1 Metal filament 2 Cylindrical anode (anode)
3 Permanent magnet for plasma control 4 Cylindrical lens for plasma control 5 Plasma 6 Target 7 Substrate holder for thin film formation 8 Argon gas inlet (leak valve)
9 Hydrogen inlet (palladium tube)
10 Electromagnet for plasma control 11 Vacuum container (deposition chamber)

Claims (2)

Pressure: 0.7 × 10 ⁻¹ Pa to 1.8 × inert gas consisting of at least one element of group 0 element in the periodic table and more than argon in a vacuum vessel of 3 × 10 ⁻⁵ Pa or less. Introduced until a pressure of 10 ⁻¹ Pa is reached and an alkali-free glass substrate is placed opposite the target in an atmosphere containing 0.6% to 1% hydrogen and / or deuterium in the inert gas. Low resistance, characterized in that a highly functional transparent conductive thin film having a thickness of 100 nm or more is formed on a substrate by low gas pressure plasma sputtering in the presence of a metal filament in an electrically floating state A method for forming a transparent conductive thin film. The method for forming a low-resistance transparent conductive thin film according to claim 1, wherein the high-functional transparent conductive thin film is an ITO thin film.

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