JPS63471A - Method for forming transparent conductive 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.

Background Art As transparent conductive films, oxide semiconductors such as In2O, ZnO, SnO2, etc. are widely used, and methods for forming them include sputtering and vacuum evaporation.

There are CVD methods, etc. The most commonly used sputtering methods can be roughly divided into so-called reactive sputtering, which is performed in a reactive gas atmosphere using a metal target, 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. You need some kind of control to get it. If sputtering is performed using only ordinary inert gas, a nearly homogeneous film can be formed when parameters such as pressure and power are constant, but in the case of reactive sputtering, each parameter of sputtering is constant. Even though
There is a problem in that as the degree of oxidation on the target surface changes moment by moment, the film quality also changes accordingly.

Means for Solving the Problem The present invention solves this problem by using In, Sn
.

An alloy made of a metal material for a transparent conductive film such as Zn is used as a target, and the workpiece on which the transparent conductive film is to be formed is kept at a temperature higher than room temperature during the formation of the transparent conductive film, and When heating to a temperature lower than the softening point and performing sputtering in a mixed gas of an inert gas and 02, the emission peak of one type of metal element and inert gas element constituting the target alloy in the plasma. In the formation of a transparent conductive film in which input power is controlled by applying feedback to a sputtering power source so as to maintain a constant intensity ratio, and then heat treatment is applied to the object to be processed, the relationship between the emission peak intensity ratio and the input power is determined. The method is characterized in that sputtering is performed in a region where the ratio changes greatly.

In forming a transparent conductive film by action-reactive sputtering, 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 release of gold atoms, which are caused by changes in the target surface state during sputtering and cause significant fluctuations in the film composition, which greatly contributes to maintaining uniform film quality. In addition, the heating during film formation strengthens the bonding strength evenly from the bottom to the top of the film, and the heat treatment after film formation stabilizes the film surface, and at the same time improves the visible light transmittance. It also improves.

Example Hereinafter, the present invention will be explained in detail 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. In the vacuum chamber 1.

A Sn alloy target 2 (containing 10% Sn) and a glass substrate 3 as a processing object (Corning Corp. g p 7
059) facing each other, and approximately 2×
Exhaust at 10 Torr4. Ar as an inert gas
are introduced into the vacuum chamber 1 together with the 02 gas by the mass flow controller 4a14b. The feed bank system is composed of a light receiving section 69 for observing plasma emission, spectrometers 7a and 7b, and a controller 8, which controls the input power from the DC power source 9.

When forming an ITO thin film using the apparatus configured as described above, the luminescence peak intensities of In and Ar are 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 purposes for power control.

FIG. 2 shows the relationship between the input power and the emission peak intensity of In and Ar. When a DC discharge is performed in a mixed gas of Ar and 02, the emission peak intensity 1o of Ar increases gradually almost linearly, but as I
The emission peak intensity 11 of n increases gradually in the low power region I, increases rapidly in the middle power region 11,
In the high power region li1, it becomes gradual again and becomes saturated.
Show trends. FIG. 3 shows how the film properties change as the emission peak intensity changes. Looking at the resistance, it shows a characteristic with a valley in the region 3, and the transmittance in visible light (for example, λ=saonm) is in the region 1. In If, the transmittance is almost the same, but it gradually decreases as it enters region (3).

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

Where is the region of weak In emission peak intensity?
It contains less n and Sn, more oxygen, and has a higher transmittance. On the other hand, the more oxygen there is, the more the properties approach those of an insulating film, and the higher the resistance. On the other hand, when the In emission peak intensity is very strong, that is, for area use, ITO
The transmittance decreases because the film contains a large amount of In and Sn. Furthermore, 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... 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 0□ in the 02 mixed gas, abnormal discharge during sputtering, and pinhole density in the formed 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 this purpose, the 02 mixture ratio must be approximately 20 or less. This is because an increase in 02 promotes oxidation of the target surface, so that if an attempt is made to maintain In 2 light emission at a certain level, the current will be significantly increased, causing the discharge to deviate from the stable discharge region. On the other hand, the reduction in 02 acts to keep the target surface in a metallic state, making the discharge itself stable, but the reduction in 02 in the formed film prevents the appropriate oxidation necessary to maintain film stability. This causes an increase in pinholes. Furthermore, when such an oxygen-deficient film is subjected to heat treatment, it becomes cloudy, leading to a decrease in visible light transmittance, and has poor durability against subsequent device fabrication processes, such as cleaning and etching. It is eroded during the process and becomes unusable. Therefore, the 02 mixing ratio must be approximately 1° or more.

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 is required, and from the viewpoint of eliminating abnormal discharge, approximately 3×10 Torr or more 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, 2X10Torr
It is appropriate to form a film at a level below this level.

From the above, when forming ITO as a transparent conductive film, under the above gas conditions, the change in the emission peak intensity ratio of In and Ar in region 11 in FIGS. 2 and 3 is Rapid region, power density o
, 30 to 0.90 W/d is suitable. Therefore, it is sufficient to perform film formation under conditions optimized in region H, but this region is greatly affected by subtle changes in the target surface condition, especially the degree of oxidation, so unless some kind of control is performed, It is difficult to maintain certain characteristics. Therefore, the optimal value of the emission peak intensity ratio of In and Ar is determined, and feedback is applied to the sputtering power source to control the input power so as to maintain that value. By doing so, the reproducibility of the film quality is greatly improved, and ITO with low resistance and high transmittance can be 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. During film formation, the substrate was heated to 20oC and the pressure was 6X.
103 Torr, o2 mixing ratio 15%.

Sputtering was performed at a power density of 0.45 W/ci, and after film formation, heat treatment was performed in the air at 450°C. As a result, the resistance was 50 ± 5 Ω, the core, and the transmittance was 93% (sson m
) films were obtained with good reproducibility.

When the TO formed on the substrate is used as a transparent electrode in a display element such as a liquid crystal panel, a functional film is laminated on it to form a transistor array, etc. The process 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. Commonly used plasma CV
Considering the D method etc., ITOO heat treatment is at least 25
It is desirable to carry out the process at a temperature of 0°C to 300°C or higher.

Effects of the Invention According to the method of the present invention, although the conditions are suitable for forming a transparent conductive film, it is possible to form a film in a region where it was difficult to control conventionally, and it has low resistance and high visible light transmittance. A transparent conductive film can be provided.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a sputtering apparatus in an embodiment of the present invention, Figure 2 is a diagram showing the relationship between sputtering power density and luminescence peak intensity in In and Ar plasma, and Figure 3 is a diagram showing the relationship between sputtering power density and luminescence peak intensity in In and Ar plasma. formed I
A diagram showing the relationship between the sheet resistance and visible light transmittance of the TO film. Figure 4 shows the relationship between the proportion of 02 in the discharge gas (Ar, O□), the abnormal discharge frequency during film formation, and the pinhole density of the film. FIG. 5 is a diagram showing the relationship between the discharge gas pressure, the frequency of abnormal discharge during film formation, and the sheet resistance of the film. 1... Vacuum chamber, 2... Target, 3...
..... Board, 4a, 4b... mass flow controller, e... light receiving section. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2, 20. Otsu l-θ no Vfu density (W/cπpi) Fig. 3 no Vw color sequence [Fig.

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 Feedback is applied to the sputtering power source to control the input power so as to keep the intensity ratio constant, and then heat treatment is applied to the object to be processed.When forming a transparent conductive film, the difference between the emission peak intensity ratio and the input power is controlled. A method for forming a transparent conductive film, characterized in that sputtering is performed in a region where the ratio in the relationship has a large change. (2) Using a target consisting of In and Sn and containing a large amount of In, 10% to 20% O_2 is mixed with Ar,
It is characterized by taking the emission peak intensity of the target component with In, forming a film at a sputtering power density of 0.30 to 0.90 W/cm^3, and then performing heat treatment at a temperature higher than the highest temperature during the subsequent steps. Claim 1:
A method for forming a transparent conductive film as described in .