WO2004074915A1

WO2004074915A1 - Method for selectively removing polyimide alignment layer coated on negative photoresist formed on a substrate and recycling the same using plasma

Info

Publication number: WO2004074915A1
Application number: PCT/KR2003/001138
Authority: WO
Inventors: Seung-Ho Lee
Original assignee: Innovation For Creative Devices Co., Ltd.
Priority date: 2003-02-18
Filing date: 2003-06-10
Publication date: 2004-09-02
Also published as: AU2003237047A1; JP2006514328A; KR20040074428A; TW200416458A; CN1742226A

Abstract

Disclosed is a method for selectively removing polyimide organic alignment layer coated on negative photoresist formed on a glass substrate and recycling the glass substrate by use of a plasma device having a reaction chamber generating plasma by a high frequency power applied to an electrode, which includes the steps of putting the negative photoresist-formed glass substrate coated with the polyimide organic alignment layer into the reaction chamber and then keeping a pressure to 100 ~ 900 mTorr, keeping the pressure with putting a mixed gas O2/N2 into the reaction chamber, and applying a power of 1 ~ 20 kwatt to the electrode of the plasma device to generate plasma so that the polyimide organic alignment layer is selectively resolved.

Description

METHOD FOR SELECTIVELY REMOVING POLYIMIDE ALIGNMENT

LAYER COATED ON NEGATIVE PHOTORESIST FORMED ON A

SUBSTRATE AND RECYCLING THE SAME USING PLASMA

TECHNICAL FIELD

The present invention relates to a method for recycling a glass substrate used for

LCD or TFT(Thin Film Transistor)-LCD, and more particularly to a method for

recycling a glass substrate by selectively removing a polyimide organic alignment layer

coated on negative photoresist formed on the glass substrate by use of plasma.

BACKGROUND ART

As various flat display elements develop, LCDs and TFT-LCDs are more

developed and produced. Such an LCD element is basically composed of a glass substrate, and electrodes formed on faced inner sides of the substrate. A post spacer,

protrusion or resin black matrix (or, resin BM) is formed on the electrodes, and a

polyimide organic alignment layer is again coated thereon. And then, a liquid crystal is

injected into the substrate, and the substrate is sealed to make the LCD element.

Among the above procedures, the alignment layer coating process is as follows.

At first, after washing the glass substrate coated with the post spacer, polyimide is

printed thereon and then precured. Then, a state of the alignment layer is examined,

and then the alignment layer is secondarily cured if the alignment layer is in a good state.

Subsequently, the alignment layer is rubbed for liquid crystal alignment. In the above

process, if the precured substrate is examined to be inferior, the substrate is passed to a substrate recycling process and used for recycling. An inferior substrate is also passed

for recycling even after the secondary curing.

As described above, in the liquid crystal display element manufacturing process,

there are often found inferior substrates which need recycling after coating the

polyimide organic alignment layer on the substrate. To recycle the substrate, the

polyimide alignment layer coated on the post spacer formed on the glass substrate

should be removed. Conventionally, the polyimide organic alignment layer is removed

wholly using a wet method.

In other words, as for the conventional wet method for removing the polyimide

alignment layer, a solvent such as Tetra Methyl Ammonium Hydroxide is applied to the

polyimide alignment layer coated on the substrate to be recycled in order to separate the polyimide alignment layer (called 'a stripping process'). Subsequently, the alignment

layer-stripped substrate is brushed and washed with a neutral solution, and then dried by

the spin dry to recycle the substrate.

However, such a conventional wet method has some problems as below.

First, the method for stripping the polyimide organic alignment layer using a

solvent as described above cannot remove the alignment layer completely, thereby not

giving a sufficient quality to the recycled substrate. Generally, the solvent applied to

the recycled substrate in the wet method is penetrated between the substrate and the

polyimide for the stripping. However in the above procedure, a stripping amount at a portion where the solvent is initially penetrated is not equal to that at a portion where the

solvent is penetrated later. Thus, the stripping of the polyimide alignment layer

becomes not uniform. In particular, the polyimide alignment layer is relatively easily stripped when the substrate is recycled in the procuring process after the polyimide is

coated, but the alignment layer is hardly eliminated after the secondary curing since the

alignment layer is firmly stuck to the substrate. Thus, after the secondary curing, it is impossible to recycle the substrate as it was.

Second, the wet method requires a lot of costs for line installation and

processing in each procedure as well as a large workspace. In addition, since the web

method uses a large amount of organic solvent, a huge sum of money is also required for

equipments used to treat and reuse wasted water, without which an environmental

pollution is caused. Third, with the organic solvent used in the wet method, it is impossible to

selectively remove only the polyimide alignment layer with retaining the post spacer,

protrusion or resin BM existing entirely or partially under the alignment layer. Thus, after recycling the substrate by the wet method, it is required to form the negative

photoresist such as the post spacer again on the recycled substrate.

DISCLOSURE OF INVENTION

The present invention is designed to solve such problems of the prior art, and therefore an object of the present invention is to provide a method for efficiently

recycling a substrate by selectively removing only a polyimide organic alignment layer

coated on negative photoresist formed on a glass substrate such as LCD and TFT-LCD

by using not a conventional wet method but the dry plasma method.

According to the present invention, the polyimide alignment layer may be easily

removed even after the secondary curing. In addition, the polyimide alignment layer may be efficiently removed by means of a dry method using plasma, not an organic

solvent. Moreover, the method of the present invention is capable of retaining the negative photoresist existing under the polyimide alignment layer at the same time,

thereby improving the substrate recycling efficiency.

In order to accomplish the above object, the present invention provides a method

for selectively removing a polyimide organic alignment layer coated on negative

photoresist coated on a glass substrate and recycling the glass substrate by use of a

plasma device having a reaction chamber for generating plasma by a high frequency

power applied to an electrode, in which the method includes the steps of: putting the

negative photoresist-formed glass substrate coated with the polyimide organic alignment layer into the reaction chamber and then keeping a pressure thereof to 100 ~ 900mTorr;

keeping the pressure with putting a mixed gas O₂/N₂ into the reaction chamber; and applying a power of 1 ~- 20 kwatt to the electrode of the plasma device to generate

plasma so that the polyimide organic alignment layer is selectively resolved. At this

time, a mixed ratio of the mixed gas O₂/N₂ is preferably in a range of 2:1 to 1:2 by volume.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of preferred embodiments of the present invention will be more fully described in the following detailed description,

taken accompanying drawings. In the drawings:

FIG. 1 shows an example of a plasma device adopted for removing a polyimide

alignment layer and recycling a substrate according to the present invention. BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a plasma device for adopting a method for removing an alignment

layer of a substrate and recycling the substrate by use of plasma according to the present invention. The plasma device of the present invention is not limited to that, but it

should be understood that the plasma device might be variously changed within the

scope capable of accomplishing the object of the invention.

Seeing the plasma reaction device illustrated in this embodiment in brief, a first

electrode 11 which is one of parallel plate electrodes is installed in a reaction chamber 10, and a second electrode 12 is installed at an upper portion faced with the first electrode 11. On the first electrode 11, a workpiece 100 to be processed is placed.

The workpiece 100 is for example a glass substrate 101 which is judged as an inferior

one requiring the recycling in a TFT-LCD substrate manufacturing procedure. On this glass substrate 101, formed is negative photoresist 103 such as a plurality of post

spacers for keeping a space with a faced substrate (not shown) in an assembling process,

a protrusion in an MVA mode for obtaining an optical viewing angle, or a resin black

matrix (or, resin BM). This negative photoresist 103 may be made by a

photolithography using commonly applied photoresist.

The first electrode 11 is connected to a drawing electrode 13 extended out of the

reaction chamber 10, and this drawing electrode 13 is also connected to a power source

15 to receive a high frequency power for generating plasma. The drawing electrode 13 is insulated from the reaction chamber 10 by means of an insulating unit 14.

In addition, the second electrode 12 is installed to an opposite side to the first electrode 11 in Ike reaction chamber 10 and excites reaction gas in the reaction chamber 10 to generate plasma as described below.

The reaction chamber 10 has an inlet hole 16 for putting in the reaction gas to generate plasma and an outlet hole 17 for discharging the gas after reaction.

Now, a process for removing an alignment layer on the substrate according to

the present invention using the above device is described.

First, the workpiece 100 is put in the reaction chamber 10. At this time, a

pressure in the reaction chamber 10 is kept to about 100 mTorr ~ 900 mTorr.

Subsequently, reaction gas is flowed in the reaction chamber 10 through the inlet hole

16. At this time, the reaction gas uses a mixed gas of O and N₂. While flowing in

the gas, the pressure in the reaction chamber 10 is kept as it is.

Then, a high frequency power of 1 ~ 20 kwatt is applied from the power source

15 to the electrcde 11 to generate O /N₂ plasma. This high reactive gas is dissociated,

excited and ionized as follows.

Chemical Formula 1

O₂ →O+ O O + e→O' + e

O₂ + e → O₂ ^* + e O₂ → O ⁺+ e

O₂ → 2O⁺ + 2e 2O₂ ⁺ + 3e → O^" + O₃

O + e → O^" 0 + 2e → 0^2"

N₂ → M + N N + e → N^* + e N + e → N₂ + e N₂ N?

N₂ → 2N⁺ + 2e N + e → N^"

N + 2e → W N + 3e → N^J

In such reaction procedures, it is shown that secondary and thirdly reactions are

mixed. In addition, O₂ ⁺, O^", O , N^", N^2", N^J" instantly obtain electrons to generate

unstable and high reactive radicals such as O^*, O₂ , O₃ , N , N₂ .

The generated radicals destruct the molecular couplings of the polyimide composing the alignment layer 102 of the workpiece 100 and resolve it into organic

molecules such as nitrogen, oxygen and carbon. The resolved polyimide organic molecules are combined with oxygen and nitrogen existing in the reaction chamber and

changed into CO, CO₂, NO, NO₂, H₂O, which is then discharged through the outlet hole 17. At this time, the chemical formula is as follows.

Chemical Formula 2

C + O⁺ → CO

O^" + 0⁺ → O₂

N^" + O₂ ⁺ → NO₂

N- + O⁺ → NO

According to the present invention, this reaction is generated uniformly on the

entire substrate.

On the other hand, the radical ions show restricted reactivity to the negative photoresist 103 such as post spacers, a protrusion in an MVA mode for obtaining an

optical viewing angle, or a resin black matrix (or, resin BM) existing partially or wholly

under the alignment layer 102 of the substrate. In other words, the negative photoresist 103 is a composition including a binder, an optical crosslink agent, an optical initiator, a

solvent or other additives. This negative photoresist 103 shows dramatically improved thermal characteristics, chemical resistance and reactive stability as a molecular weight

of the binder greatly increases due to' the crosslink reaction or the photodimerization

reaction caused by light exposure, differently from the positive photoresist. Thus, the

negative photoresist 103 is not easily resolved by the radicals, and N₂ gas mixed therein

further improves the resistance of the negative photoresist against the resolution by the

radical ions, thereby retaining the negative photoresist. As for the binder which is a main component of the formed negative photoresist, (meta-)acrylate polymer is mainly

used in addition to polyvinyl alcohol polymer and polyisoprene polymer. Besides them,

various kinds of polymers as disclosed in Korean Laid-open Patent Publication No.

1998-22330 may be used, and all kinds of negative photoresist which improves

resistance against resolution by radicals due to crosslink reaction caused by light

exposure conforming to the object of the present invention may be used. Considering

the resolvability for the polyimide alignment layer and the resolution resistance of the

negative photoresist, a most suitable mixing ratio of the O₂/N₂ mixed gas is ranged in

2:1 - 1:2 by volume.

As described above, the polyimide alignment layer 102 coated on the glass

substrate may be selectively uniformly removed using the O₂/N₂ plasma etching with retaining the negative photoresist existing partially or wholly under the alignment layer. Effects of the present invention will be more clearly understood from the following experiment.

Experimental Example

A workpiece in which a color filter layer composed of pigment-dispersed

negative photoresist (containing benzyl methacrylate/methacrylic acid manufactured by Fuji Film Arch in Japanese as a binder)" having a color in a spin coating method and a

polyimide alignment layer having a thickness of 500 A are subsequently formed on a

glass substrate having a size of 600 X 700 0.7mm³ is put in the plasma reaction device

having a volume of 100 liters, which is then made vacuum. While putting a O₂ N₂ mixed gas (1 : 1) into the vacuum plasma reaction device at l,500sccm (Standard Cubic

Centimeter per Minute; 0°C, latm), a power of 2 kwatts is applied thereto for generating

plasma and then the reaction is proceeded for 40 seconds.

After the reaction, the substrate is pulled out of the reaction device, and then its

surface is checked. As a result of the checking, it is found that the polyimide

alignment layer is entirely removed and the 1024X 765 cells of the substrate have no

defect, j In addition, after measuring the color sensitivity of the color filter layer formed

below the alignment layer of the substrate, it is checked that the color sensitivity is less

than 2%, which is substantially retained as it is.

INDUSTRIAL APPLICABILITY

The method for removing an organic alignment layer of the substrate according

to the present invention has advantages as follows. First, because of removing the polyimide organic alignment layer by the dry

method in the plasma reaction device, the present invention does not need a large-scaled equipment and the removal of the alignment layer may be performed at lower costs. In

addition, the dry method is more easily operated and maintained rather than the conventional wet method.

Second, though the conventional wet method may hardly remove the polyimide

alignment layer after the secondary curing, the dry method adopted m the present

invention may completely remove the polyimide alignment layer even after the

secondary curing. This shows that the present invention enables to effectively recycle

the substrates, which was conventionally disused due to the difficulty in removing the

alignment layer.

Third, since removing the polyimide alignment layer by the plasma dry method,

the present invention need not use a large amount of organic solvent, which was

required in the conventional wet method, and thereby is capable of preventing

environmental pollutions.

Fourth, since the polyimide organic alignment layer resolved according to the

present invention is removed in a vapor state, there are not required additional processes

for washing the recycled substrate with a neutral solution and drying the washed

substrate.

Fifth, though the conventional wet method shows irregular recycling and high inferiority rate since the removal degree of the alignment layer at edges is different from

that at the center of the substrate in which the alignment layer is separated due to the

organic solvent, the present invention shows no difference in the removal of the alignment layer and thereby is capable of dramatically decreasing the inferiority rate

since the alignment layer is removed at once by means of the chemical reaction using plasma.

Sixth, though the conventional wet method removes not only the polyimide

alignment layer but also the negative photoresist substances such as spacers existing

partially or wholly below the alignment layer because of using a large amount of organic

solvent showing strong solubility, the present invention may selectively remove only the

alignment layer by restricting the reactivity with the negative photoresist by use of the O₂/N₂ mixed gas. Thereby, the present invention may improve the substrate recycling

efficiency and reduce the following manufacturing procedures.

The present invention has been described in detail. However, it should be

understood that the detailed description and specific examples, while indicating

preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will

become apparent to those skilled in the art from this detailed description.

Claims

What is claimed is:

1. A method for selectively removing a polyimide organic alignment layer coated on negative photoresist coated on a glass substrate and recycling the glass

substrate by use of a plasma device having a reaction chamber for generating plasma by

a high frequency power applied to an electrode, the method comprising the steps of: putting the negative photoresist-formed glass substrate coated with the

polyimide organic alignment layer into the reaction chamber and then keeping a

pressure thereof to 100 ~ 900 mTorr;

keeping the pressure with putting a mixed gas O₂/N₂ into the reaction chamber; and applying a power of 1 ~ 20 kwatt to the electrode of the plasma device to

generate plasma so that the polyimide organic alignment layer is selectively resolved.

2. A method for selectively removing a polyimide organic alignment layer

coated on negative photoresist coated on a glass substrate and recycling the glass

substrate according to claim 1,

wherein a mixed ratio of the mixed gas O₂/N₂ is in a range of 2:1 to 1 :2 by volume.