JPS63909A - Formation of transparent conducting film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for forming a transparent conductive film, particularly a method that is relatively low temperature and has excellent reproducibility and mass production.
It can be widely used in the production of display devices such as EL, solid-state imaging devices, and electrical and electronic devices using transparent conductive films that require high transparency and low resistance, such as transparent touch panels.

As a conventional transparent conductive film, I n203 + Z no +
Oxide semiconductors such as S no 2 are widely used,
In addition, methods for forming it include subsotering, vacuum deposition, and CVD. The most commonly used sputtering methods can be roughly divided into so-called reactive sputtering, which is performed using a metal target in a reactive gas atmosphere, and a method using a sintered oxide as a target. The former method allows for faster film formation than the latter method, and the target is less expensive, but since it is a reaction system, it is difficult to reproduce the film quality. On the other hand, if the latter method is used, the reproducibility is good, but the film formation rate is slow and the target is expensive.

Problems to be Solved by the Invention When forming a transparent conductive film by sputtering in a mass production process, reactive sputtering is advantageous in terms of productivity, but it is not possible to form a film with low resistance and high transmittance stably and reproducibly. To obtain [ requires some kind of control.

If it is spanotaring using only normal inert gas,
When parameters such as pressure and power are constant, a nearly homogeneous film can be formed, but in the case of reactive sputtering, even if each sputtering parameter is constant, the degree of oxidation on the target surface changes every moment. Therefore, there is a problem in that the film quality changes accordingly.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention heats the object to be processed during film formation, controls the sputtering power, and performs heat treatment after film formation.

Power control is one of the elements that make up target 1.
This is done by calculating the ratio between the emission peak intensity of each type and the sputtering discharge current, and applying feedback to the sputtering power source so as to keep the value constant in a region where the ratio changes significantly.

In the formation of a transparent conductive film by action-reactive spanotaring, the proportions of metal and oxygen in the film and the stability of their bonds are important. According to the method of the present invention, it is possible to eliminate fluctuations in the amount of metal atoms released, which are caused by changes in the target surface state during spa sottering and which cause large fluctuations in the film composition, which greatly contributes to maintaining uniform film quality. In addition, heating during film formation strengthens the bonding strength evenly from the bottom to the top of the film, and heat treatment after film formation stabilizes the film surface and simultaneously improves visible light transmittance. do.

Example Hereinafter, details of the present invention will be explained based on Examples.

FIG. 1 is a schematic diagram showing the configuration of an apparatus for forming a transparent conductive film according to the present invention. An alloy target 2 of In and Sn (containing 10 parts of Sn) and a glass substrate 3 (manufactured by Corning Inc., 4=7o59) as a workpiece were placed facing each other in a vacuum chamber 1, and the vacuum was heated to about 2×10 Torr using an exhaust system i5K.
exhaust to. Ar is used as an inert gas, and both gases and gases are introduced into the empty tank 1 by mass flow controllers 4a and +b, respectively. The feed and dovanok system is composed of a light receiving section 6 for observing plasma emission, a spectrometer 7, and a controller 8, which controls the input power from a DC power source 9.

When forming an ITO thin film on the glass substrate 3 using the apparatus having the above configuration, the luminescence peak intensity of In is monitored. In this example, In accounts for 90% of the target composition, and since In has a sharp emission peak around a wavelength of 461 nm, it is suitable for monitoring power control.

FIG. 2 shows the relationship between discharge current and In emission peak intensity. When DC discharge is performed in a mixed gas of Ar +02, the luminescence peak intensity of In is in the low current region D.
), the area above it (■
), it increases rapidly, and in the high current region (DI), it becomes gradual again, showing a tendency to saturate.

FIG. 3 shows how the film properties change as the emission peak intensity changes. The resistance exhibits a characteristic with a valley in region (II), and the transmittance in visible light (550 nm for example) is almost the same in regions (1) and (II), but As we enter area (III),
It gradually declines.

The reason why the IT◯ film produced by reactive sputtering exhibits the above-mentioned change in characteristics is as follows.

The weaker the region of In emission peak intensity, the more I
It contains less n and Sn and more 02, and has a higher transmittance. On the other hand, as the amount of 02 increases, the resistance becomes higher because it approaches an insulating film-like injection. Conversely, when the In emission peak intensity is very strong, that is, in region (III), ITO
The transmittance decreases because the film contains a large amount of In and Sn. Further, the resistance is also high due to the properties of metals containing a large amount of impurities, in this case In and Sn containing 02. However, the intermediate region (n) contains oxygen to the extent necessary to maintain high transmittance and is not a complete oxide, so vacancies contribute to electrical conduction and exhibit low resistance.

FIG. 4 shows the relationship between the proportion of 02 in the Ar,02 mixed gas, abnormal discharge during sputtering, and pinhole density in the formed ITO film. Although the discharge itself is possible at any mixing ratio, a certain limited range is suitable from the viewpoint of film characteristics. If an abnormal discharge or arc occurs, problems such as flakes adhering to the film and particles left on a part of the target surface due to high temperature melting may induce further abnormal discharge. It is necessary to eliminate these phenomena. For that purpose, the 02 mixing ratio is approximately 2
It must be below 0:/t. This is because an increase in 02 promotes oxidation of the target surface, which results in a significant increase in current when trying to maintain In 2 light emission at a certain level, resulting in a departure from the stable discharge region. On the other hand, a decrease in O2 acts to keep the target surface in a metallic state, making the discharge itself stable, but as O2 in the formed film decreases, the appropriate oxidation required to maintain film stability is not carried out. This causes an increase in pinhonyl.

In addition, when heat treatment is applied to such an oxygen-deficient film, it becomes cloudy, leading to a decrease in visible light transmittance.
Furthermore, it has poor durability against subsequent device manufacturing processes, and is eroded during cleaning, etching, etc. processes, making it unusable. Therefore, the 02 mixing ratio must be approximately IQ% or higher.

FIG. 5 shows the relationship between discharge gas pressure, abnormal discharge frequency, and resistance during film formation. In order to maintain stable discharge, a certain level of pressure or higher is required, and from the standpoint of eliminating abnormal discharge, a pressure of about 2 to 3×10 Torr or higher is desirable.

On the other hand, when the pressure is high, the mean free path becomes small, the degree of oxidation in the gas phase is high, and the resistance of the formed film becomes high, which is not preferable. Therefore, 2×1 0'−2Tor
It is appropriate to form a film at a temperature of about r or less.

From the above, when forming ITO as a transparent conductive film, under the above gas conditions, the area (■) in Figures 2 and 3, that is, the luminescence peak intensity of In and the discharge of spa sotering A region where the ratio to the current changes rapidly, the current density is 1 to 2. csA/cA is suitable. Therefore, it is sufficient to perform film formation under conditions optimized in the region (If), but since this region is greatly affected by subtle changes in the target surface condition, especially the degree of oxidation, some kind of control is required. It is difficult to maintain constant characteristics unless Therefore, the optimum value of the ratio between the luminescence peak intensity of In 2 and the discharge current is determined, and the input power is controlled by applying a feed control to the spanottering source so as to maintain this value. By doing this, the reproducibility of the film quality has been greatly improved, and IT○ with low resistance and high transmittance has been achieved.
is obtained.

If, in addition to the above-mentioned control, substrate heating during film formation and heat treatment after film formation are performed, the film properties and stability will be further improved.

When ITO formed on a substrate is used as a transparent electrode in a display element such as a liquid crystal panel, a functional film is laminated thereon to form a transistor array, etc., but these formation steps are includes high temperature processes such as CVD.

Therefore, when heat-treating ITO, it is necessary to carry out the heat treatment at or above the maximum temperature that will elapse thereafter, otherwise unintended changes in film quality will occur during subsequent processes. Plasma CV used in one step
Considering method D, etc., it is desirable that the heat treatment of ITO be performed at at least 250'C to 300°C or higher.

Effects of the Invention According to the method of the present invention, it is possible to form a transparent 4-electroelectric film in a region where it was difficult to control despite the conditions suitable for forming the film, and it has low resistance and high visible light transmittance. It becomes possible to obtain a transparent conductive film.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a sputtering device in an embodiment of the present invention, and FIG. 2 is a characteristic diagram showing the relationship between the sputtering current density and the luminescence peak intensity in In plasma.
Figure 3 shows the spa sotering current density and the formed ITO.
A custom-made diagram showing the relationship between film sheet resistance and visible light transmittance, Figure 4 shows 0 in discharge gas (Ar, 02).
Figure 5 shows the relationship between discharge gas pressure, abnormal discharge frequency during film formation, and film sheet resistance. FIG. 1... Vacuum chamber, 2...--Target, 3
. . . Substrate, 4h, 4b . . . Mass flow controller, 6 . . . Light receiving section. Name of agent: Patent attorney Toshio Nakao and 1 other person 1st
Figure 2 lθ 2,0 3.0 electric R
'M l'J (mA/cm') Figure 3 t. oz. o3. ofQ
20 02 Engagement 之

Claims (2)

[Claims] (1) Using an alloy made of a metal material for a transparent conductive film as a target, the workpiece on which the transparent conductive film is to be formed is heated to a temperature higher than room temperature during the formation of the transparent conductive film, and the workpiece is When heating to a temperature lower than the softening point and performing sputtering in a mixed gas of an inert gas and O_2, the ratio of the plasma emission peak intensity of one type of target constituent element to the sputtering current is kept constant. controlling the input power by applying feedback to the sputtering power source, and then performing the sputtering in a region where the ratio of the emission peak intensity to the current changes greatly in forming a transparent conductive film in which the object to be treated is subjected to heat treatment; A method for forming a transparent conductive film characterized by: (2) Using a target made of In and Sn and containing a large amount of In, 10 to 20% O_2 is mixed with Ar, the emission peak intensity of the target component is determined by In, and the sputtering current density is 1 to 2.5 mA. 2. The method of forming a transparent conductive film according to claim 1, wherein the film is formed at a temperature of /cm^2 and then heat-treated at a temperature higher than the highest temperature during the subsequent steps.