JPS6051559B2 - Etching method for transparent conductive film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an etching method for a transparent conductive film, and particularly to an etching method that can be used semi-permanently even in mass production.

Transparent conductive films are widely used in displays such as liquid crystal display panels, and most of them are used with some kind of patterning.

It is no exaggeration to say that the accuracy, yield, etc. of this patterning greatly influence the specifications and costs of products using these. Commonly used transparent conductive films include indium oxide and tin oxide.

The former is expensive and has inferior electrochemical stability to the latter. The latter is inexpensive, but has the disadvantage that patterning is difficult. The Zn powder/HCl method has long been used for the latter patterning, or etching, but it is difficult to control the reaction speed, and there are problems such as resist peeling off due to physical contact.
It is no longer compatible with recent fine patterning. On the other hand, an immersion etching technique using a Cr゜゛/Cr' redox system is described in US Pat. No. 4,009,061, but this method causes severe deterioration of the etching solution and is not industrially applicable at all. Therefore, the present inventor first developed Cr″゛/C
We investigated a method of separating the r'゛redox system with an electrolytic diaphragm and causing the reaction Cr'゛-Cr゛ under electrolysis. It was found that it gradually deteriorated. As a result of analysis of the etching solution, Sn of O, lg/l or more was detected, and it was found that this had a significant effect on the reduction in etching speed. Originally Cr'
It is supposed to be electrodeposited as metal tin on the cathode in the cathode compartment where Cr24 is carried out, but because the current density is too high, it is formed as an electrolytic powder and is missing from the electrode, so it is not recovered. On the other hand, if the current density is lowered, the efficiency of Cr゜゛→Cr゛ decreases and the etching speed cannot be kept constant. In addition to the density electrode hair, it is equipped with a hair electrode that electrolyzes at a lower current density to recover each metal from tin ions, iron ions, nickel ions, copper ions, etc. that cause a reduction in etching speed. The present invention will be explained below using the drawings.

FIG. 1 is a cross-sectional view of the basic etching bath of the present invention.
3 is a diaphragm that separates the cathode compartment 1 and the anode compartment 2;
Consists of Teflon filters, etc.

In the cathode conversion, there is a Cr2+/Cr3+ redox system dissolved in mineral acid.

Examples of the mineral acids include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, hydrofluoric acid, hydroiodic acid, and hydrobromic acid, and they may be used alone or in a mixture of any of these. The concentration is 0.1
N or more is usually used. Among these acids, especially hydrochloric acid,
Hydrohalic acids such as hydrobromic acid have excellent etching properties. In the Cr2+/Cr3+ redox system, chromium salts such as Crcl3.61120, Cr2(SO4)3, or metallic chromium are dissolved in these mineral acids, and 4 is applied between the electrodes 4 and 5.
This is obtained by applying one potential of 0.30 V (υS-RHE). This potential difference may be determined by using a potentiostat or by using a DC power source. By immersing the transparent conductive film in the Cr2+/Cr3+ redox-based cathode conversion 1 thus formed, the transparent conductive film can be easily etched. As for electrode 4, the one with larger hydrogen overvoltage is Cr3+→Cr
2+ reduction efficiency is good.

Carbon, Pb, Fe, Sn, Hg, Hg amalgam,
Stainless steel etc. are good, but especially cheap ones,
Pb is superior. 5 has a good insoluble electrode, carbon, P
t, Rh, Tj-Pt, Ti-Rh, Ti-RhO, T
i-RuO etc. are good.

In Figure 2, electrode 5 is a carbon electrode, electrode 4 is a Pb electrode, and cathode conversion 1 is CrCl3.61120 at 100 g/E. The solution temperature and etching speed when the etching speed reached a steady state after electrolysis was performed for 5 hours at 5 A/Dm2 using 6N hydrochloric acid and an unglazed separator as the diaphragm 3 are shown.

Note that the transparent conductive film is tin oxide. If such etching is continued for about 20,000 sheets (10 cm x 20 c71 x 500 A), the steady state etching speed will drop to about half. As a result of liquid analysis, it was found that etched tin ions were responsible for preventing damage. When the tin ion concentration exceeds 0.1 g/', a significant decrease occurs.

Originally, tin ions should be electrodeposited on the electrode 4 as metal tin, but at temperatures above 50'C, almost no electrodeposition occurs. This is thought to be because the current density is too high and the electrolytic powder is missing from the electrode, or because the adhesion to carbon, Pb, etc. is poor. Therefore, the present inventor used sub-electrode bare electrodes 6 and 7, and by removing impurities (metal ions that adversely affect etching speed) with these bare electrodes, 50,000 sheets and 10
Invented a permanent etching method that can print up to 10,000 sheets.
The electrode used in 6 is selected to have good adhesion to these impurities during electrodeposition, and is preferably a plate or mesh of Pt, Au, Rh, or P sown. 7 may be any insoluble electrode and may be made of the same material as 5. The DC electric field applied between 6 and 7 is 0.1
A-5A/Dm2 is good, more preferably 0.2A-2
A/Dm2. If the current density is too low, electrodeposition will not be possible, and if the current density is too high, the adhesion will be poor and the effect will be lost. A system for stably maintaining such a Cr2+/Cr3+ redox system does not necessarily have to be used as an etching bath.
There is no problem even if the solution in tank 1 is introduced into a separate tank and etching is performed in that tank. However, the system of the present invention is indispensable when this type of etching is carried out industrially.

[Brief explanation of drawings]

Fig. 1: A sectional view of an etching tank of the present invention, Fig. 2: Relationship between temperature and etching speed in an embodiment of the present invention.

Claims (1)

[Claims] 1 The Cr^2^+/Cr^3^+ redox system formed in the mineral acid is introduced into the cathode compartment of the electrolytic cell.
In a method of etching a transparent conductive film which is maintained under electrolysis so that the cathode potential is -0.3 V (US/RHE) or lower, in addition to the pair of electrodes that hold the redox system, one pair of electrodes is further provided. A method for etching a transparent conductive film, characterized in that it is maintained under weak electrolysis of 0.1 A to 5 A/dm^2.