JPH0740447B2 - Method for forming transparent conductive film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for forming a transparent conductive film, particularly to a method having excellent reproducibility and mass productivity at a relatively low temperature.
It can be widely used for manufacturing display elements such as EL, solid-state image pickup elements, or electric and electronic devices using a transparent conductive film such as a transparent touch panel which requires high transparency and low resistance.

_2. Description of the Related Art As a transparent conductive film, oxide semiconductors such as In ₂ O ₃ , ZnO and SnO ₂ are widely used, and the forming method thereof includes sputtering, vacuum deposition, CVD method and the like. The most commonly used sputtering methods are roughly classified into so-called reactive sputtering performed in a reactive gas atmosphere using a metal target, and a method using an oxide sintered body as a target. The former is capable of high-speed film formation as compared with the latter, and the target is inexpensive, but it is difficult in terms of reproducibility of film quality because it is a reaction system. on the other hand,
According to the latter method, the reproducibility is good, but the film formation rate is slow and the target is expensive.

Problems to be Solved by the Invention When a transparent conductive film is formed by sputtering in a mass production process, reactive sputtering is advantageous from the viewpoint of productivity, but a film with low resistance and high transmittance can be stably and well reproduced. You need some control to get it.
If it is a sputtering using only a normal inert gas,
A uniform film can be formed when parameters such as pressure and power are constant, but in the case of reactivity, the degree of oxidation of the target surface changes momentarily even if the parameters of sputtering are constant. Therefore, there is a problem that the film quality also changes accordingly.

Means for Solving the Problems In order to solve the above problems, the present invention uses an alloy made of a metal material for a transparent conductive film as a target,
The object to be processed on which the transparent conductive film is to be formed is heated to a temperature higher than room temperature and lower than the softening point of the object to be processed during the formation of the transparent conductive film to form the alloy target. The input power is controlled by feeding back the sputtering current so that the ratio of the emission peak intensity in the plasma of one kind of metal element and the sputtering current is kept constant, and in the mixed gas of inert gas and O ₂ . A forming method comprising: a step of performing sputtering; and a step of performing heat treatment on the object to be processed in the atmosphere or an atmosphere having a component equivalent to the atmosphere after the sputtering, wherein the step in the discharge for the sputtering is performed. As the current density increases, the relative intensity ratio of the emission peak of one kind of metal element constituting the alloy target and the current density Through the area change is large in the relative intensity ratio between the current density and the emission peak of a certain kind of metal element forming the alloy target from the area of small,
An emission peak of one kind of metal element constituting the alloy target and an emission peak of one kind of metal element constituting the alloy target, which changes to a different region where the change of the relative intensity ratio of the current density is small. In relation to the current density, sputtering is performed in a region where the change in relative intensity ratio between the emission peak of one kind of metal element constituting the alloy target and the current density is large.

In the formation of a transparent conductive film by reactive sputtering, the proportions of metal and oxygen in the film and the stability of their bonding are important. According to the method of the present invention, due to the change in the target surface state during sputtering, it is possible to eliminate the fluctuation of the amount of metal atom emission that causes a large variation in the film composition, and thus contributes greatly to keeping the film quality uniform. Also, heating during film formation strengthens the bonding force evenly from the bottom to the top of the film, and further heat treatment after film formation stabilizes the film surface and at the same time improves visible light transmittance. To do.

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

FIG. 1 is a schematic view showing an apparatus structure for forming a transparent conductive film according to the present invention. An In, Sn alloy target 2 (containing 10% Sn) and a glass substrate 3 (# 7059, manufactured by Corning Incorporated) as the object to be processed are opposed to each other in a vacuum chamber 1, and an exhaust device 5 is used for about 2 × 10 ⁻⁶ Torr. Exhaust to. Ar is used as an inert gas and is introduced into the vacuum chamber 1 together with O ₂ gas by the mass flow controllers 4a and 4b. The feedback system consists of a light-receiving part 6 for seeing plasma emission, a spectroscope 7,
It is configured by the controller 8 and DC
The input power from the power supply 9 is controlled.

When the ITO thin film is formed on the glass substrate 3 by the apparatus having the above-described configuration, the emission peak intensity of In is monitored. In this example, 90% of the target composition is occupied, and In has a sharp emission peak near the wavelength of 451 nm, and is suitable for a monitor for power control.

It is also possible to utilize the light emission of Sn, which is the other constituent element of the target, but in the present example, In was used for monitoring for the above reason. Of course, in the case of a target containing a large amount of Sn, it is advantageous to monitor with Sn.

FIG. 2 shows the relationship between the discharge current and the In emission peak intensity. When direct current discharge is carried out in a mixed gas of Ar and O ₂ , the emission peak intensity of In rises gently in the low current region (I) and increases sharply in the region (II) above it. In the high current region (III), it becomes gentle again and shows a saturation tendency.

FIG. 3 shows the state of the film characteristics associated with such changes in the emission peak intensity. Regarding the resistance, it has a characteristic that it has a valley in the region (II), and the transmittance in the visible light (550 nm as an example) is almost the same in the regions (I) and (II). As it enters (III), it gradually decreases.

The ITO film formed by reactive sputtering exhibits the above-mentioned characteristic changes for the following reasons. In the region where the In emission peak intensity is weaker, the ITO film contains less In and Sn and contains more O ₂ , and the transmittance becomes higher. On the other hand, as the content of O ₂ increases, the resistance becomes higher because the properties of the insulating film become closer. On the contrary, when the In emission peak intensity is very strong, that is, in the region (III), the ITO film contains a large amount of In and Sn, and thus the transmittance decreases. Further, the resistance is also high due to the property of metal containing a large amount of impurities, here In and Sn containing O ₂ . However, in the intermediate region (II), oxygen is contained to the extent necessary to maintain a high transmittance, and since it is not a perfect oxide, vacancies contribute to electric conduction and show low resistance.

FIG. 4 shows the relationship between the proportion of O _{2 in} the Ar, O ₂ mixed gas, the abnormal discharge during sputtering, and the pinhole density of the formed ITO film. The discharge itself can be performed at any mixing ratio, but a certain limited range is suitable from the viewpoint of film characteristics. In case of abnormal discharge or arc, flake-like things should adhere to the film,
In addition, there is a problem that the abnormal discharge is further induced by leaving a granular material due to high temperature melting on a part of the target surface, and therefore it is necessary to eliminate these phenomena. Therefore, the O ₂ mixing ratio must be about 20% or less. This is because an increase in O ₂ promotes the oxidation of the target surface, resulting in a large increase in the current when trying to keep the In emission at a certain level, which is outside the stable discharge region. On the other hand, the reduction of O ₂ acts to keep the target surface in a metallic state and stabilizes the discharge itself, but the reduction of O ₂ in the formed film reduces the amount of O ₂ required to maintain the stability of the film. Is not done, causing an increase in pinholes. Further, when such a film deficient in oxygen is subjected to a heat treatment, white turbidity occurs, which leads to a decrease in the visible light transmittance, and further, the durability against a subsequent device manufacturing process is poor, such as cleaning and etching. It is eroded in the process and unusable. Therefore, the O ₂ mixing ratio must be about 10% or more.

FIG. 5 shows the relationship between the discharge gas pressure during film formation and the abnormal discharge frequency and resistance. A certain level or more of pressure is required to stably maintain the discharge, and about 3 × 10 ⁻³ Torr or more is desirable from the viewpoint of eliminating abnormal discharge.

On the other hand, when the pressure is high, the mean free path becomes small, the degree of oxidation in the gas phase becomes high, and the resistance of the formed film becomes high, which is not preferable. Therefore, it is suitable to form the film at a pressure of about 2 × 10 ^-2 Torr or less.

From the above, when forming ITO as a transparent conductive film, under the above gas conditions, the emission peak intensity of In (II), that is, the emission peak intensity of In in FIG. 2 and FIG. A region where the ratio to the current changes rapidly, and a current density of 1 to 2.5 A / cm ² is suitable. Therefore, film formation should be performed under the optimized conditions in region (II). However, some control is performed because this region is greatly affected by the subtle changes in the target surface condition, especially the oxidation degree. Unless it is constant, it is difficult to maintain certain characteristics. Therefore, the optimum value of the ratio of the emission peak intensity of In to the discharge current is obtained, and the input power is controlled by feeding back to the sputtering power source so as to maintain the optimum value. By doing so, the reproducibility of the film quality is significantly improved, and ITO with low resistance and high transmittance can be obtained.

If the substrate heating during film formation and the heat treatment after film formation are performed in addition to the above control, the film characteristics and stability are further improved.

When the ITO 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 thereon to form a transistor array or the like. The process includes a high temperature process such as CVD.

Therefore, the heat treatment of ITO needs to be performed at the maximum temperature or higher thereafter, or if it is not, it causes an unintended change in film quality during the subsequent process. Considering the generally used plasma CVD method and the like, it is desirable that the heat treatment of ITO is performed at least at 250 ° C. or 300 ° C. or higher.

EFFECTS OF THE INVENTION According to the method of the present invention, it is possible to form a film in a region which has been difficult to control under conditions suitable for forming a transparent conductive film in the related art, and which has low resistance and high visible light transmittance. It is possible to obtain a conductive film and to maintain high-quality transparent conductivity even after passing through a high-temperature process that is usually required for producing an element.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a sputtering apparatus in an embodiment of the present invention, FIG. 2 is a characteristic diagram showing a relationship between a sputtering current density and an emission peak intensity of In in plasma, and FIG. 3 is a sputtering current density. A characteristic diagram showing the relationship between the sheet resistance and the visible light transmittance of the formed ITO film. Fig. 4 shows the proportion of O ₂ contained in the discharge gas (Ar, O ₂ ) and the abnormal discharge frequency during film formation. FIG. 5 is a characteristic diagram showing the relationship with the pinhole density of the film, and FIG. 5 is a characteristic diagram showing the relationship between the discharge gas pressure, the abnormal discharge frequency during film formation, and the sheet resistance of the film. 1 ... Vacuum tank, 2 ... Target, 3 ... Substrate, 4a, 4b
…… Mass flow controller, 6 …… Light receiving part.

Claims (2)

[Claims] 1. An object to be processed for forming a transparent conductive film, which is at a temperature higher than room temperature during the formation of the transparent conductive film, and which is processed by using an alloy made of a metal material for a transparent conductive film as a target. Heating to a temperature below the softening point of the material,
The input power is controlled by feeding back the sputtering current so as to keep the ratio of the emission peak intensity in plasma of one alloy element constituting the alloy target and the sputtering current constant, and the inert gas and O 2 _A step of performing sputtering in a mixed gas of ₂ ,
A method of performing heat treatment on the object to be processed in the atmosphere or an atmosphere having a component equivalent to the atmosphere after the sputtering, the increase in the current density in the discharge for the sputtering. From the region where the change in the relative intensity ratio between the emission peak of one type of metal element forming the alloy target and the current density is small, the emission peak of one type of metal element forming the alloy target and the current density Through the region where the change in the relative intensity ratio of the alloy target is large, and to the different region where the change in the relative intensity ratio of the emission density of one kind of metal element constituting the alloy target and the current density is small. In the relationship between the emission peak and the current density of one kind of constituent metal element, one kind of constituent of the alloy target The method for forming a transparent conductive film, which comprises sputtering of at the area change is large in the relative intensity ratio between the emission peak the current density of the metal element. 2. A target composed of In and Sn and containing a large amount of In is used, and O ₂ is mixed in an amount of 10 to 20% with respect to Ar. The emission peak intensity of the target component is In, and the sputtering current density is 1 to 10. The method for forming a transparent conductive film according to claim 1, wherein the film is formed at ^2.5 mA / cm ² , and the heat treatment is performed at a temperature higher than the highest temperature in the subsequent step.