JPH06318577A - Etching method for thin film - Google Patents

Abstract

PURPOSE:To prevent a film from being left on the side wall part on a step- difference, and avoid short-circuiting the picture elements, by a method wherein, after a transparent conductive thin film is formed on a thin film of at least one layer, etching is performed by an ion beam milling method while the ion beam incident angle is changed by two steps. CONSTITUTION:A substrate holder 3 for retaining a substrate 2 is fixed to the depth of a vacuum vessel 1. A plasma chamber 5 is installed in the front side via a leading-out electrode 4. A permanent magnet 6 for generating magnetic field is fixed around the plasma chamber. A gas introducing port 7 connected with a gas cylinder 8, and a filament 9 are installed in the inlet of the plasma chamber. The vacuum vessel 1 is equipped with an exhaust opening 10 for evacuation. Thereby a film is prevented from being left on the side wall part of a step-difference in a substratum, and short circuit between picture elements can be prevented, so that display quality and yield can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dry etching a transparent conductive thin film which is formed on an insulating film such as an insulating transparent substrate and functions as a transparent electrode of a liquid crystal display device or the like.

[0002]

2. Description of the Related Art In a liquid crystal display device, an ITO (Indium Tin Oxid) is used as a transparent conductive thin film on a pixel electrode.
e) A film is generally used, and the wet method is the mainstream as the etching method. The reason is that the etching rate is faster than dry etching, the area can be easily increased, the management is relatively simple, and the throughput is high. The method of forming this ITO film is
A general method is to perform sputtering using an ITO metal oxide as a target in an atmosphere of an inert gas such as argon containing a very small amount of oxygen. The amount of oxygen in the sputtering gas taken into the thin film during the film formation and the crystal state greatly affect the film quality. These depend on the temperature during film formation, the oxygen / argon flow rate ratio, and the electric power applied to the electrodes. For example, when the temperature is higher, the oxidation reaction is more likely to proceed, the transparency of the film is increased, and the crystal grains are also grown larger, which has the advantage of lowering the specific resistance, while the etching rate is lower and the patterning property is worse. There is a disadvantage that In addition, since the composition of the target surface changes with time even if sputtering is performed under the same film forming conditions, the film quality of the transparent conductive thin film is very unstable.

[0003]

However, since the transparency and the specific resistance are important even though the film characteristics of the transparent conductive thin film are unstable, film forming conditions have been adopted in which the etching property is sacrificed to some extent. For this reason, in wet etching, the end point is time-controlled, so that etching residues and over-etch defects frequently occur.

As a solution to this problem, a method has been adopted in which the photolithography and wet etching steps are repeated twice in the patterning of ITO. However, in this method, the number of steps is doubled, so that there is a drawback in that the greatest merit of wet etching is impaired mass productivity. As another problem, since a wet etchant for the ITO thin film uses a hydrochloric acid-based etchant, if the base film is a metal thin film such as aluminum that is affected by acid, an insulating film or the like is interposed between the thin film and the ITO thin film. There was a need. Also in that case, the etching solution permeated from the pinhole of the film interposed between the ITO thin film and the metal thin film, so that it was not a fundamental countermeasure. As a measure against this,
The dry etching method was examined. However, when dry etching by the RIE (reactive ion etching) method is performed, there is a problem that a film residue is generated on the side wall at the underlying step due to strong anisotropy, which causes a short circuit between pixels and causes a display defect. Become. Further, in the conventional milling method in which the incident angle of the ion beam is constant, the ITO film in the flat portion is redeposited on the sidewall during etching, which also causes a short circuit between pixels. Occur.

[0005]

According to the present invention, a transparent conductive thin film is formed directly or through an insulating film on at least one thin film patterned in a predetermined manner on a transparent insulating substrate, and then a predetermined shape is formed. When the etching is performed, the ion beam milling method is used to change the incident angle of the ion beam in two steps.

[0006]

In the method of manufacturing a liquid crystal display device according to the present invention, when the transparent conductive thin film formed on the step is dry-etched by the ion beam milling method, the incident angle of the ion beam is changed in two steps. It is possible to prevent the film from remaining on the side wall portion, prevent short circuits between pixels, and eliminate display defects, which is effective in improving display quality and yield.

[0007]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows a schematic view of an ion beam milling device used in the present invention. A substrate holder-3 that supports the substrate 2 is attached to the inner side of the vacuum container 1 with a predetermined inclination. And on the front side of the vacuum container 1,
A plasma chamber 5 is provided via the extraction electrode 4. A magnetic field generating permanent magnet 6 is attached around the plasma chamber, and a gas inlet 7 and a filament 9 connected from a gas cylinder 8 are installed at the inlet of the plasma chamber. Further, the vacuum container 1 is further provided with an exhaust port 10 for vacuum exhaust.

In the processing method, the inside of the vacuum container 1 is first evacuated from the exhaust port 10. When the inside of the vacuum container 1 reaches a predetermined pressure, argon gas is introduced from the gas introduction port 7 and voltage is applied to the filament 9 to cause glow discharge. Further, the magnetic field generated by the permanent magnet 6 excites the argon atoms, and becomes a plasma state to become argon ions. The argon ions are attracted to the extraction electrode 4 to which a negative charge is applied and accelerated to reach the substrate surface at a predetermined angle,
The thin film on the surface of the substrate is etched. The substrate holder has a predetermined inclination, the incident angle of the ion beam is determined by the inclination of the substrate holder, and the substrate holder itself is also rotating.

Next, a method of forming a display element of a liquid crystal display device having a thin film transistor (hereinafter abbreviated as TFT) used in this embodiment will be described.

First, a polycrystalline silicon film 22 is deposited on the transparent insulating substrate 21 shown in FIG. 2 by a low pressure chemical vapor deposition method (hereinafter abbreviated as LPCVD method) to a thickness of about 1000 Å and patterned into a predetermined shape by photolithography. . Next, part of the polycrystalline silicon film 22 is heated to 1000 ° C. to 1200 ° C. in an oxygen atmosphere or a mixed atmosphere of oxygen and nitrogen.
It is thermally oxidized at the temperature of about 1000 Å to form an oxide film. Then, a polycrystalline silicon film 24 to be a gate electrode is deposited on the upper layer by the LPCVD method at 3000Å to 4000Å, and phosphorus is doped by thermal diffusion and patterned by photolithography into a predetermined shape. Next, using the polycrystalline silicon film 24 as a mask, the polycrystalline silicon film 22 is doped with phosphorus by ion implantation (boron in the case of P type) to form the source and drain regions by self-alignment. Further thereon, a SiO ₂ film is formed as an interlayer insulating film 25 by atmospheric pressure chemical vapor deposition (APCVD) or LPCV.
Deposit 5000 Å to 10,000 Å by method D. Next, after opening a contact hole 26 in the source region by photolithography, Al is formed by a sputtering method.
The film is deposited in the range of 6000 Å to 10000 Å, the source wiring 27 having a predetermined shape is formed by photolithography, and the source wiring 27 is connected by the contact hole 26. Again, an SiO ₂ film is deposited as the interlayer insulating film 28 by the APCVD method or the LPCVD method at 5000Å to 10000Å. Next, contact holes 2 are formed in the drain region by photolithography.
After opening 9, open the ITO film 1 by sputtering.
000Å to 2000Å are deposited, a predetermined shape is exposed by photolithography, a transparent electrode 30 is formed by dry etching, and a contact hole 29 is connected to a switching element.

The dry etching conditions of the transparent electrode in the display element thus formed by ion beam milling will be described in detail below. The transparent conductive thin film was etched by the apparatus shown in FIG. Argon was used as the etching gas and the gas pressure was 0.
Electric power of 2 mTorr and 40 W was applied to the electrodes. The etching rate is about 400 Å / min, and the etching time of the transparent conductive thin film (CITO) is
The just etch for removing the film was 3 minutes and 50 seconds, and was set to 5 minutes including the over etch amount (30%) for the just etch. The rotation speed of the substrate holder is 20 rp.
m. The incident angle of the ion beam when etching the flat portion can be etched within the range of 60 ° to 90 ° with respect to the substrate, but this time, the etching rate is the fastest.
Etched at an angle of 0 °. At this angle, since the ITO may slightly remain on the side wall of the step, the second step etching is performed. The side wall can be etched in the range of 10 ° to 40 °, but this time, it was etched at an angle of 10 °, which is the fastest etching rate. The same effect can be obtained by first etching the side wall portion at an angle of 10 ° to 40 ° and then etching the flat portion at an angle of 60 ° to 90 °. Although the liquid crystal display device using the TFT is used in this embodiment, the present invention can be applied to any liquid crystal display device using the transparent conductive thin film.

[0012]

In the thin film etching method of the present invention, when the transparent conductive thin film formed on the step is dry-etched by the ion beam milling method, the angle of incidence of the ion beam is changed in two steps to form the base. Since it is possible to prevent the film from remaining on the side wall of the step and to prevent a short circuit between pixels, display defects are eliminated, which is effective in improving display quality and yield.

[Brief description of drawings]

FIG. 1 is a view showing an ion beam milling device of the present invention.

FIG. 2 is a diagram showing a cross-sectional structure of a display element of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vacuum container 2 Substrate 3 Substrate holder-4 Extraction electrode 5 Plasma chamber 6 Permanent magnet for generating magnetic field 7 Gas inlet 8 Gas cylinder 9 Filament 10 Exhaust port 21 Transparent insulating substrate 22 Polycrystalline silicon film 23 Gate oxide film 24 Gate Electrode 25 Interlayer insulating film 26 Contact hole 27 Source wiring 28 Interlayer insulating film 29 Contact hole 30 Pixel electrode

Claims (2)

[Claims] 1. Ion beam milling when a transparent conductive thin film is formed directly or through an insulating film on at least one thin film patterned in a predetermined manner on a transparent insulating substrate and then etched into a predetermined shape. Etching method by changing the incident angle of the ion beam in two steps by the method. 2. The first ion beam is made to have an incident angle of 60 ° to 90 ° with respect to the substrate, and the flat portion is etched first.
Next, the incident angle of the second ion beam is set to 1 with respect to the substrate.
2. The method for etching a thin film according to claim 1, wherein the side wall portion of the underlying step is etched at an angle of 0 to 40 degrees.