WO2002103770A1

WO2002103770A1 - Apparatus and method for cleaning the surface of a substrate

Info

Publication number: WO2002103770A1
Application number: PCT/KR2002/001124
Authority: WO
Inventors: Hag-Joo Lee
Original assignee: Sem Technology Co., Ltd.
Priority date: 2001-06-15
Filing date: 2002-06-14
Publication date: 2002-12-27
Also published as: KR20020071694A; KR100491140B1

Abstract

There is provided an apparatus for cleaning the surface of a substrate and a method therefor. The apparatus does not require a means for impedance matching. In addition, the apparatus has a structure such that an atmospheric pressure plasma generated is derived to the outside of the apparatus and cleans the surface of the substrate at the outside of the apparatus.

Description

APPARATUSAND METHOD FORCLEANINGTHE SURFACE OFA

SUBSTRATE

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an apparatus and a method for cleaning the surface of a substrate. More specifically, the present invention relates to an apparatus which derives atmospheric pressure plasma to outside of the apparatus and then cleans the surface of a substrate located at the outside of the apparatus, and a method for the same.

BACKGROUND OF THE INVENTION

When contaminants are deposited and spread on or glued to a substrate, the degree of the removal of the contaminants from the substrate largely depends on adhesiveness and cohesiveness. Previously, cleaning had been performed with various chemicals. But, these methods are now seriously restricted because the chemicals used for cleaning have been proven to result in adverse effects on environment. Therefore, new cleaning methods have been intensively researched and studied. An example of these new cleaning methods is to use low temperature, low pressure plasma. This cleaning method generates plasma inside of low-pressure chamber, and then contacts ions or activated gases from the plasma with the surface of a substrate to remove contaminants deposited on or glued to the substrate. In spite of excellent cleaning performance, this method has not been popularly used because this method requires vacuum apparatus. That is, this method suffers from a disadvantage that its application to consecutive processes performed under atmospheric pressure environment is difficult. As thus, active researches have been progressed to generate plasma under atmospheric pressure environment and to use them for surface cleaning.

Although the atmospheric pressure plasma could be generated in many ways, the most common method is a silent discharge that has been used for ozone generating apparatus for a long time (Siemens W. 1857, Aim. Phys. Chem. 102, 66-122). As already well known, the principle of the silent discharge is to induce plasma discharge in the inner space between two metal electrodes by applying alternate current or pulse with high voltage to the metal electrodes insulated with at least one insulator. The plasma thus generated is used for the cleaning of the surface of a substrate located at the inner space between the two metal electrodes. When this electrode structure is actually used to clean the surface of a substrate, however, only very thin substrate can be treated because the substrate should be inserted between two electrodes. For this reason, its application is very limited. Further, when metal or semiconductor substrates are used for cleaning instead of a dielectric substrate, they are sometimes damaged by the high voltage applied to the electrodes.

Recently, generation of the atmospheric pressure plasma using RF power supply with 13.56 MHz is also researched to overcome the weaknesses of the silent discharge.

Japanese unexamined patent publication H06-108257 discloses a plasma reacting method and an apparatus for the same, comprising; introducing a mixed gas of rare gas and reactive gas into a reaction vessel having dielectric-coated electrodes wherein the surface of two or more electrodes located parallel with each other are provided with solid dielectric, and wherein a substrate is provided downstream of said electrodes; exciting said mixed gas with plasma at atmospheric pressure to produce an active species; and, treating the surface of said substrate with said active species. Although this method has a merit to generate atmospheric pressure plasma under relatively low voltage (about 70V), it still suffers from disadvantages that the RF electric power used in the method is expensive and its structure is complicated because impedance matching is necessarily required because the method uses high frequency (13.56 MHz) to generate plasma. This method also suffers form a disadvantage that expensive rare gas must be used. Furthermore, since this method requires reactive gas, the method is not used for cleaning (removing the contaminants (commonly organic contaminants) or photo-resister from the surface of a substrate) but for surface alternation or modification (forming another functional group on the surface of a substrate).

US 5,977,715 and 5,961,772 disclose another examples of atmospheric pressure plasma generation using 13.56 MHz RF power supply, while they still suffers from the weaknesses that the RF electric power apparatus is expensive and impedance matching is needed.

Japanese unexamined patent publication H08-321397 discloses an atmospheric pressure plasma generator using frequency of 50 Hz ~ several MHz and a method for generating atmospheric pressure plasma using the plasma generator. In this atmospheric pressure plasma generator, granulated objects obtained by coating the whole surface of a conducting material with an insulator, are packed between two electrodes. However, the granulated objects packed between two electrodes interrupt the flow of gases, namely, reactive gases, which reduces the efficiency of the cleaning. Further, the exposure of the conducting material of the granulated objects on the surrounding may result in serious risks.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to provide a novel surface cleaning apparatus that effectively generates atmospheric pressure plasma without impedance matching.

Another object of the present invention is to provide a surface cleaning apparatus utilizing nitrogen gas only or a mixture of nitrogen and oxygen as a processing gas.

Other object of the present invention is to provide a surface cleaning apparatus that has simple structure and makes it possible to clean the surface of a substrate in a continuous manner. Other object of present invention is to provide a surface cleaning method using the surface cleaning apparatus.

BRIEF DISCRIPTION OF THE DRAWINGS

Fig. 1 is a cross-sectional view of the surface cleaning apparatus according to the present invention using atmospheric pressure plasma.

Fig. 2 is a graph showing water contact angles of glass substrates, which is cleaned with the atmospheric pressure nitrogen plasma generated from the surface cleaning apparatus according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a surface cleaning apparatus and a surface cleaning method. The surface cleaning apparatus according to the present invention comprises: a) two metal electrodes insulated with at least one insulator, located parallel with each other; b) an inverter applying 15kHz - 100 kHz of frequency and 2kV - 6 kV of voltage to the metal electrodes; c) a plasma generating space formed between the metal electrodes, which converts a processing gas introduced into the plasma generating space to plasma with the high voltage applied to the metal electrodes under atmospheric pressure environment; d) an inlet port and an outlet port formed on the side of the plasma generating space; e) a gas supply which supplies the processing gas through the inlet port; f) a mass flow controller between the inlet port and the gas supply, which controls the mass flow of the processing gas; and g) a flow homogenizer installed at the inlet port, which ensures uniform flow of the processing gas inside the plasma generating space.

The apparatus of the present invention has a structure such that it converts a processing gas into plasma, pushes out the plasma thus generated to outside of the apparatus, and then removes contaminants (commonly organic contaminant) deposited or glued to a substrate, or a photo resistor from semiconductor by contacting the plasma with the contaminants or photo resister. The processing gas used for cleaning is preferably selected from the group consisting of nitrogen, a mixture of nitrogen and oxygen, and a mixture of nitrogen and an air. According to the specific embodiment of the present invention, there was no remarkable difference between the system that adopts only nitrogen (25 1pm) as a processing gas and the system that adopts a mixture of nitrogen (25 1pm) and an air (1 1pm) in terms of efficiency of the removal of contaminants. Therefore, the system adopting only nitrogen gas is preferable for removing contaminants. Meanwhile, it is desirable to use a mixture of nitrogen and oxygen or a mixture of nitrogen and an air for the removal of photo-resister, because the oxygen present in the mixture could improve the removal efficiency of the photo- resister of the semiconductor. The mixed gas of nitrogen is, in general, obtained by mixing with nitrogen gas, no more than 20%, preferably 1-10%, most preferably 5-10% of air (or oxygen)

Fig. 1 shows a cross-sectional view of the surface cleaning apparatus according to the present invention using atmospheric pressure plasma. The apparatus 1 comprises two metal electrodes 102 insulated with insulators 101, a high voltage inverter 103 connected to the one of the metal electrodes 102, a plasma generating space 104 formed between the metal electrodes 102 insulated with insulators 101, an inlet port 105 and an outlet port 106 confronted each other on the side of the plasma generating space 104, a gas supply 107 supplying an processing gas through the inlet port 105, a mass flow controller 108 between the inlet port 105 and the gas supply 107 which controls the flow of the processing gas, and a flow homogenizer 109 which ensures uniform flow of the processing gas inside the plasma generating space 104. According to the specific embodiment of the present invention, without the flow homogenizer 109, uniform surface cleaning was not accomplished. Therefore, remarkably long processing time would be taken to get sufficient cleaning without the flow homogenizer 109.

The high voltage inverter 103 produces an alternate current or pulse with 15 kHz - 100 kHz of frequency and 2 kV - 6 kV of voltage and applies the high voltage to the metal electrodes 101. The type and kind of the inverter is not limited as long as the frequency and the voltage can be produced and applied to the metal electrodes. Impedance matching is not necessary in this range of frequency and voltage, therefore the apparatus can be simplified and expensive RF power supply is not required.

The high voltage with an alternating current or pulse generated from high voltage inverter 103 is applied onto one of the metal electrodes 102. The metal electrodes 102 are desirably manufactured by coating an electrically conductive material onto the surface of the insulator 101. The ceramic (for example, alumina) or glass is used as an insulator 101 and the silver-palladium alloy, copper or aluminum is used as an electrically conductive coating material. Although the type of the metal electrode is not specifically restricted, the square shape is desirable. The voltage which is applied onto one of the metal electrodes 102, converts the processing gas, which is introduced into the plasma generating space 104 from the gas supply 107 through the mass flow controller 108 and the inlet port 105, into plasma 110 by silent discharge under atmospheric pressure environment. The plasma 110 thus generated is pushed out to outside of the plasma generating space 104 through the outlet port 106 with aid of the continuous flow of the processing gas into the plasma generating space 104. The plasma 110 that was pushed out to outside of the plasma generating space 104 contacts with contaminants or photo-resisters and removes them from the resting or moving surface of the substrate 113.

The atmospheric pressure plasma generating apparatus 1 is equipped with radiator 111 in order to removes the heat generated during plasma discharge. It should be understood that the radiator 111 is not specifically limited to a particular type, as long as the radiator 111 ensures the removal of sufficient heat produced during plasma discharge. Meanwhile, one of electrodes 112 is earthed for safety on its use.

After the processing gas passes through the mass flow controller 108, a flow homogenizer 109 located at the opening of the inlet port 105 thrusts the injected gas through the innumerable fine holes with less than 1 mm of diameter so that the processing gas has uniform flow inside the plasma generating space 104 and that the uniformity of the plasma which contacts with the substrate is improved.

The gap distance of the plasma generating space 104 between the two electrodes 102 insulated with insulators 101 is preferably adjusted in the range from 0.1mm to 1mm, but is not limited thereto. If the gap distance is less than 0.1mm, the gas flow is not smooth, that is, uniform flow of plasma is not attained. For larger than 1mm gap, the voltage required to induce plasma discharge is higher than 6 kV, therefore safety on its use is not ensured and substrate damage by the high voltage may occur.

The surface cleaning apparatus 1 according to the present invention could be widely applied to the surfaces (for example, TFT LCD) to be cleaned. Especially, it could be applied to PCB strip, leadframe or packaging such as bonding, molding, soldering, chip attaching, dipping or marking process.

The atmospheric pressure plasma generating apparatus could be equipped with two or more generators shown on Fig, 1 with series or parallel connection type. Parallel connection of two or more atmospheric pressure plasma generators is more desirable to improve the efficiency of the substrate cleaning. Preferably, 2-7, most preferably 3-5 atmospheric pressure plasma generators are connected in parallel.

The present invention also relates to a method for cleaning the surface of a substrate with the plasma generated by the atmospheric pressure plasma generating apparatus, comprising:

(a) supplying an processing gas from a gas supply into a plasma generating space through an inlet port via a mass flow controller and a flow homogenizer; (b) applying to one of two metal electrodes insulated with at least one insulator an alternating current or pulse with 15kHz - 100 kHz of frequency and 2kV - 6 kV of voltage produced by an inverter;

(c) generating atmospheric pressure plasma by converting the processing gas to plasma with the high voltage applied to the electrodes under atmospheric pressure environment;

(d) pushing out the atmospheric pressure plasma thus generated to outside of the plasma generating space with aid of the flow of the processing gas introduced into the plasma generating space; and (e) cleaning the surface of a substrate by contacting the pushed-out atmospheric pressure plasma with containments deposited on or glued to the substrate to remove the contaminants from the resting or moving substrate.

If required, the apparatus can be comiected in parallel to improve the surface cleaning efficiency.

Referring to Examples, the present invention will be more fully explained in the following.

Example 1

To test the efficiency of the removal of containments from the surface of a substrate with the atmospheric pressure plasma generated apparatus of the present invention, a glass panel is used and degree of surface cleaning is quantified by measuring water contact angle, which is the direct evidence of the surface cleaning.

The atmospheric pressure plasma generating apparatus described in Fig. 1 had 0.635 mm thick alumina as an insulator and metal strip formed by coating silver (Ag)- palladium (Pd) on the one surface of the alumina for the metal electrode. The gap distance of the discharging space was 0.4 mm and the mass flow of nitrogen gas for discharge was adjusted to 25 liter/min. The voltage, frequency and power of the inverter were set to 4 kV, 20 kHz, and 100 W, respectively. The distance between the plasma generating apparatus and substrate panel to be cleaned was varied from 0.5 mm to 2 mm. The velocity of the moving substrate is varied from 10 cm/min to 50 cm/min. The results of the removal of the contaminants measured are summarized in Fig. 2.

As shown in Fig. 2, very low water contact angle was obtained under 10 cm/min of the low speed of a substrate, which indicates almost perfect surface cleaning was accomplished. As the substrate moved faster and the distance from the outlet of the plasma generator to the substrate was farer, the surface cleaning was worse. However, such a declination of the surface cleaning can be easily solved by connecting two or more atmospheric pressure plasma generators in parallel. Further, parallel connecting of two or more atmospheric pressure plasma generator would make it possible to clean large area substrates.

The atmospheric pressure plasma generating apparatus of the present invention has various advantages, for example, simple structure that provides economic cleaning of a substrate, and easy applicability to various kinds of application. Specifically, it could be applied to the cleaning of PCB strip and leadframe or packaging such as bonding, molding, soldering, chip attaching, dipping or marking process.

Further, the surface cleaning method of the present invention uses the plasma generated from silent discharge at the outside of the narrow discharging space, which provides wide application and excellent cleaning. The surface cleaning method of the present invention is not limited to the type of a substrate because the substrate is not needed to situate inside the narrow discharging space. In addition, the damage of the substrate due to the high voltage can be prevented because the substrate locates at the outside of the region into which high electric field is applied. Meanwhile, by moving the substrate relatively to the atmospheric pressure plasma generator of the present invention, the substrate could be cleaned in a continuous manner. That is, such a continuous cleaning can be accomplished by moving the substrate under atmospheric pressure environment or for the moving atmospheric pressure plasma generator.

Claims

1. An apparatus for cleaning the surface of a substrate, wherein the apparatus does not requires impedance matching and comprises: a) two metal electrodes insulated with at least one insulator, located parallel with each other; b) an inverter applying 15kHz - 100 kHz of frequency and 2kV - 6 kV of voltage to the metal electrodes; c) a plasma generating space formed between the metal electrodes insulated with at least one insulator, which converts a processing gas introduced into the plasma generating space to plasma with the high voltage applied to the metal electrodes under atmospheric pressure environment; d) an inlet port and an outlet port formed on the side of the plasma generating space; e) a gas supply which supplies the processing gas through the inlet port; f) a mass flow controller between the inlet port and the gas supply, which controls the mass flow of the processing gas; and g) a flow homogenizer installed at the inlet port, which ensures uniform flow of the processing gas inside the plasma generating space.

2. The apparatus as set forth in claim 1, wherein the metal electrodes are formed on the insulator by coating electrically conductive material on the surface of the insulator.

3. The apparatus as set forth in claim 1, wherein the gap of the plasma generating space is in a range of from 0.1 mm to 1mm.

4. The apparatus as set forth in claim 1, wherein the insulator is formed of insulating ceramic or glass.

5. The apparatus as set forth in claim 1, wherein the processing gas is selected from the group consisting of nitrogen, a mixture of nitrogen and oxygen, and a mixture of nitrogen and an air.

6. The apparatus as set forth in claim 1, wherein the apparatus is connected in parallel in a range of from 2 to 7.

7. The apparatus as set forth in claim 1, wherein the apparatus is applied to the cleaning of PCB strip, leadframe or packaging.

8. The apparatus as set forth in claim 1, wherein the apparatus is applied to the process selected from the group consisting of bonding, molding, soldering, chip attaching, dipping, or marking process of PCB strip, leadframe or packaging.

9. The apparatus as set forth in claim 1, wherein the apparatus is applied to the pre- cleaning of the large area glass for TFT-LCD.

10. The apparatus as set forth in claim 1, wherein the apparatus is applied to the removal of photo-resister coated on the large area glass for TFT-LCD.

11. The apparatus as set forth in claim 1, wherein apparatus is applied to the cleaning of semiconductor or removal of photo-resister.

12. A method for cleaning a surface of a substrate with the plasma generated by the apparatus of claim 1, comprising:

a) supplying an processing gas from a gas supply into a plasma generating space through an inlet port via a mass flow controller and a flow homogenizer; b) applying to one of two metal electrodes insulated with at least one insulator an alternating current or pulse with 15kHz - 100 kHz of frequency and 2kV - 6 kV of voltage produced by an inverter; c) generating atmospheric pressure plasma by converting the processing gas to plasma with the high voltage applied to the electrodes under atmospheric pressure environment; d) pushing out the atmospheric pressure plasma thus generated to outside of the plasma generating space with aid of the flow of the processing gas introduced into the plasma generating space; and e) cleaning the surface of a substrate by contacting the pushed-out atmospheric pressure plasma with containments deposited on or glued to the substrate to remove the contaminants from the resting or moving substrate.