WO2004051702A2

WO2004051702A2 - Apparatus for treating surfaces of a substrate with atmospheric pressure plasma

Info

Publication number: WO2004051702A2
Application number: PCT/KR2003/002485
Authority: WO
Inventors: Hag-Joo Lee
Original assignee: Sem Technology Co., Ltd
Priority date: 2002-12-02
Filing date: 2003-11-19
Publication date: 2004-06-17
Also published as: KR100476136B1; JP4409439B2; TWI227951B; JP2006509331A; WO2004051702A3; AU2003279587A8; KR20040048272A; TW200414577A; AU2003279587A1; CN1720349A; CN100471993C

Abstract

There is provided a surface treatment apparatus with atmospheric pressure plasma. The surface treatment apparatus is comprised of a processing gas storage part and a plasma generating part located below the processing gas storage part in which a) the processing gas storage part comprises a first inlet port through which a processing gas is introduced, and b) the plasma generating part comprising an upper electrode and a lower electrode facing each other, a plasma generating space formed between the electrodes, at least one dielectric insulating the upper electrode and the lower electrode, a radiator lowering the surface temperature of the electrode, a second inlet port through which the processing gas is introduced from the processing gas storage part into the plasma generating space, an outlet port through which a plasma and the processing gas which has not been converted into the plasma are driven to outside of the plasma generating space, and an alternating current supply applying an alternating current voltage, wherein both the upper electrode and the lower electrode are flat-panel electrodes, the outlet port is formed on the lower electrode, and a substrate is located below the lower electrode. The apparatus is not limited to a shape of the substrate, and makes it possible to widen effective processing area of the substrate as well as to perform consecutive processes under atmospheric pressure.

Description

APPARATUS FOR TREATING SURFACES OF A SUBSTRATE WITH ATMOSPHERIC PRESSURE PLASMA

TECHNICAL FIELD OF THE INVENTION The present invention relates to a surface treatment apparatus (or plasma treatment apparatus) , more specifically, to a surface treatment apparatus that generates a plasma under atmospheric pressure and drives the plasma to outside of a plasma generating space (or discharging space) to contact the plasma with the surface of a substrate to be treated.

BACKGROUND OF THE INVENTION

Surface treatments, such as removing contaminants such as organic substances from surfaces of a substrate, stripping resists, improving adhesion of organic films, surface modification, film formation, reducing metal oxides, or cleaning glass substrates for liquid crystal, can be divided into chemical surface treatments and plasma surface treatments. Of the surface treatments, the chemical surface treatments suffered from a disadvantage that chemicals cause adverse effects on an environment .

One of the plasma surface treatment methods is a surface treatment with a low temperature, low pressure plasma. The method generates plasma inside a low pressure chamber, and then the low pressure plasma contacts with a substrate to treat the surface thereof. Despite its excellent performance, the method has not been popularly used because it requires a vacuum apparatus to maintain low pressure, and thus, it is hard to apply the method to consecutive processes performed under atmospheric pressure. As a result, active researches have been progressed to generate plasmas under atmospheric pressure and to use them for surface treatment .

Japanese unexamined patent publication No. 2-15171, 3- 241739 or 1-306569 discloses surface treatment method and apparatus in which a substrate is located inside a plasma generating space. More specifically, the method comprises arranging a pair of metal electrodes parallel each other and insulated with at least one dielectric, introducing a processing gas into a plasma generating space formed between the electrodes, applying an alternating current between the electrodes to generate a plasma from the processing gas, and treating the surface of a substrate located inside the plasma generating space with the generated plasma. According to the methods and apparatuses described in the documents, however, only very thin substrates can be treated because the substrate should be positioned between the two electrodes. For this reason, its application is very limited. Further, when the substrate is not a dielectric but a conductive metal or a semiconductor, there is high risk of substrate damage due to high voltage applied to the electrodes .

To overcome the disadvantages, there was proposed a method, wherein the plasma generated within a plasma generating space is driven to outside of the plasma generating space, and there, contacts with a substrate to treat the surface thereof.

US 5,185,132 discloses a surface treatment method comprising introducing a mixed gas of rare gas and reactive gas into a reaction vessel having dielectric-coated flat-panel 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. Fig. la is a perspective view illustrating a surface treatment apparatus used in the method, and Fig. lb is a cross-sectional view illustrating an electrode structure used in the apparatus shown in Fig. la. As shown in Figs, la and lb, the surface treatment apparatus comprises two flat-panel electrodes (101a, 101b) parallel each other and insulated with dielectrics (106a, 106b) , a processing gas inlet port (103) installed on one side of a plasma generating space (102) formed between the electrodes (101a, 101b) , and an outlet port (104) installed on an opposite side of the plasma generating space (102) . A processing gas is firstly introduced through the inlet port (103) into the plasma generating space (102) , and there, is converted to plasma with an alternating current voltage applied to the electrodes (101a, 101b) . The plasma and the processing gas, which is not converted to the plasma, are driven through the outlet port (104) to outside of the plasma generating space (102) , and then contacts with the surface of a substrate (105) to treat it. However, the surface treatment apparatus suffers from a disadvantage that the effective processing width (W) of the surface is restricted since the outlet port (104) is installed on one side of the plasma generating space (102) . Widening the width (W) requires sudden rise of the alternating current voltage applied.

To overcome the above mentioned disadvantage, US 6,424,091 discloses a surface treatment apparatus comprising: a) at least one pair of electrodes, at least one of said pair of electrodes having a dielectric layer at an outer surface thereof; b) a gas supply means for supplying a gas for plasma generation to said discharging space defined between said electrodes wherein said gas supply means provides a flow of the gas for plasma generation from said discharging space toward a substrate; and c) a power supply for applying an AC voltage between said electrodes to generate said plasma of the gas for plasma generation in said discharging space, wherein at least one of said pair of electrodes has a curved surface jutting into said discharging space which is configured to spread out said plasma outwardly from said discharging space toward said substrate. Fig. 2 is a cross-sectional view showing a preferred embodiment of the electrode structure used in the surface treatment apparatus, wherein a plasma is generated between two cylindrical electrodes

(201a, 201b) insulated with dielectrics (202a, 202b) , the plasma thus generated contacts with and treats the surface of a substrate (204) located outside of the surface treatment apparatus. The surface treatment apparatus having the cylindrical electrodes makes it possible to widen the processing width. However, the apparatus still suffers from low plasma conversion efficiency because the plasma generating space per unit area of the electrode is remarkably reduced compared to the flat-panel electrode structure. That is, the effective area of the electrode to convert the processing gas into plasma is remarkably reduced, which reduces plasma conversion efficiency and lowers the processing efficiency of a substrate. Furthermore, the surface treatment apparatus requires more power than the flat panel electrode due to wasted power as a result of the low plasma conversion efficiency.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a surface treatment apparatus which solves the narrow width of the effective processing area caused by the conventional flat -panel electrode structure, and which addresses the reduction of the plasma discharging space caused by the cylindrical electrode structure.

Another object of the present invention is to provide a surface treatment apparatus that makes it possible to treat surfaces of substrates in a continuous manner while increasing the overall processing area of the substrates.

The above objects and others which will be described in the detailed description of the present invention will be accomplished by provision of a surface treatment apparatus comprised of a processing gas storage part and a plasma generating part located below the processing gas storage part in which a) the processing gas storage part comprises a first inlet port through which a processing gas is introduced, and b) the plasma generating part comprising an upper electrode and a lower electrode facing each other, a plasma generating space formed between the electrodes, at least one dielectric insulating the upper electrode and the lower electrode, a radiator lowering the surface temperature of the electrodes, a second inlet port through which the processing gas is introduced from the processing gas storage part into the plasma generating space, an outlet port through which a plasma and the processing gas which has not been converted into the plasma are driven to outside of the plasma generating space, and an alternating current supply applying an alternating current voltage, wherein both the upper electrode and the lower electrode are flat -panel electrodes, the outlet port is formed on the lower electrode, and a substrate is located below the lower electrode.

BRIEF DESCRIPTION OF THE INVENTION

Fig. la is a perspective view illustrating a conventional surface treatment apparatus having a flat-panel electrode structure.

Fig. lb is a cross-sectional view illustrating an electrode structure used in the apparatus shown in Fig. la.

Fig. 2 is a cross-sectional view showing an electrode structure used in the conventional surface treatment apparatus having a cylindrical electrode structure.

Fig. 3 is a cross-sectional view showing a surface treatment apparatus in accordance with the present invention.

Figs. 4a and 4b are perspective views illustrating preferred embodiments of an electrode structure which can be used in the surface treatment apparatus shown in Fig. 3.

DESCRIPTION TO REFERENCE NUMERALS OF THE MAIN PARTS ON DRAWINGS

101a, 101b: Flat panel electrodes 102 : Plasma generating space 103 : Inlet port 104: Outlet port 105: Substrate

106a, 106b: Dielectrics 201a, 201b: Cylindrical electrodes 202a, 202b: Dielectrics 203: Plasma 204: Substrate

300: Processing gas storage part 301a, 301b: first inlet ports 400: Plasma generating part 401a: Flat-panel upper electrode 401b: Flat-panel lower electrode 402: Plasma generating space 403a, 404b: Dielectrics 404a, 404b: Radiators

405a, 405b: Second inlet ports

406 (406a, 406b, 406c, 406d, 406e) : Outlet port (s) 407: Alternating current supply 408: Substrate

DETAILED DESCRIPTION OF THE INVENTION

Fig. 3 is a cross-sectional view showing a preferred embodiment of a surface treatment apparatus in accordance with the present invention. As shown in Fig. 3, the surface treatment apparatus is comprised of a processing gas storage part (300) and a plasma generating part (400) located below the processing gas storage part. The processing gas storage part (300) has a role to stably supply a processing gas into the plasma generating part (400) , as thus, the volume thereof can be suitably chosen regarding processing capacity and conversion efficiency. The plasma generating part (400) has a role to convert the processing gas into plasma.

First inlet ports (301a, 301b) through which the processing gas for plasma generation is introduced into the processing gas storage part (300) are placed on one side of the processing gas storage part (300) . Although two first inlet ports (301a, 301b) are exemplified to introduce the processing gas into the processing gas storage part (300) , it should be interpreted that the number of the first inlet ports is not limited thereto. Four first inlet ports could be located, if required, on four sides of the processing gas storage part (300) , or only one inlet port could be located on the center of the upper wall in the processing gas storage part (300) .

The plasma generating part (400) is comprised of a upper flat panel electrode (401a) and a lower flat panel electrode (401b) , a plasma generating space (402) formed between the electrodes (401a, 401b) , dielectrics (403a, 403b) insulating the electrodes (401a, 401b) , radiators (404a, 404b) that lower the surface temperature of the electrodes (401a, 401b) , second inlet ports (405a, 405b) that introduce the processing gas from the processing gas storage part (300) to the plasma generating part

(400) and outlet ports (406a, 406b 406c, 406d, 406e, totally "406") that drive the generated plasma as well as the remaining unconverted processing gas to outside of the plasma generating space (402) . Below the lower electrode (401b) , a substrate (408) is located. The upper electrode (401a) is connected to an alternating current supply (407) and the lower electrode (401b) is grounded. The processing gas is firstly introduced into the processing gas storage part (300) through the first inlet ports (301a, 301b) installed on side walls of the processing gas storage part (300) . The processing gas introduced is then supplied through the second inlet ports (405a, 405b) located on the dielectric (403a) to the' plasma generating space (402) , and there, converted to plasma with an aid of the alternating current voltage supplied from the alternating current supply (407) . The plasma and the remaining unconverted processing gas are driven to outside of the plasma generating space (402) through the outlet ports (406) located on the lower electrode (401b) , to make contacts with the surface of the substrate (408) to be treated.

Fig. 4a is a perspective view showing the electrode structure used in the surface treatment apparatus shown in Fig. 3. As mentioned above, the electrode structure is composed of the upper flat panel electrode (401a) and the lower flat panel electrode (401b) facing each other, the plasma generating space (402) formed between the electrodes (401a, 401b) , the dielectrics (403a, 403b) insulating the electrodes (401a, 401b) . On the dielectric (403a), the second inlet ports (405, 405b) through which the processing gas is supplied from the processing gas storage part (300) to the plasma generating space (402) is formed. The processing gas introduced into the plasma generating space (402) is converted to a plasma with the alternating current voltage applied by the alternating current supply. The generated plasma and the remaining processing gas that has not converted to the plasma, are driven to outside of the plasma generating space (402) through the outlet ports (406a to 406e, "406") formed on the lower electrode (401b), and then the plasma contacts with the surface of the substrate (408) to treat it. In this embodiment, the total processing width (D1+D2+D3+D4+D5) of the outlet ports (406) could be increased significantly more than the processing width (W) of the conventional flat-panel electrode structure, thereby greatly increasing the possible width of the substrate to be processed. Furthermore, another advantage of the present invention is that while the processing width (W) is highly limited by the voltage applied, the length of the electrode (D) is not noticeably affected. In other words, the processing width (W) is typically limited to 0.01 mm ~ 30 mm by the voltage applied, but the length of the electrode (D) is hardly affected by the voltage such that its length can be sufficiently increased. As a result, the total processing width (D1+D2+D3+D4+D5) can be also remarkably increased. In addition, according to the conventional case, change of the shape of the outlet port was difficult because many modifications of the apparatus are required. According to the present invention, the shape of the outlet ports (406) can be variously changed in a form of circular, triangular, oval or any other shape without any change of any part of the apparatus except for the radiator. Therefore, an advantage that the shape of the outlet ports (406) can be changed depending on the shape of the substrate (408) to be processed is attained. Fig. 4b shows such an exemplary embodiment in which the outlet ports are formed as multiple holes. Furthermore, although the second inlet ports (405a, 405b) are located on two edges of the dielectric (403a) in Fig. 4a, it would be evident that the second inlet ports could be located on all four edges of the dielectric (403a) regarding the total volume of the plasma generating space (402) .

The present invention does not specifically limit to the kind of the processing gas for plasma generation and the processing gases generally used in this field can be widely used. For example, nitrogen, oxygen, a rare gas, carbon dioxide, nitric oxide, perfluorinated gas, hydrogen, ammonia, chloride gas, ozone or mixtures thereof can be mentioned. As a rare gas, helium, argon, neon or xenon can be used. As a Perfluorinated gas, CF₄, C₂F₆, CF₃CF=CF₂, CC1F₃ and SF₆ may be mentioned.

The processing gas can be suitably chosen regarding the purpose of the plasma treatment, which is well known to a person of ordinary to which the present invention pertains. For example, when cleaning organic substances on the substrate (408) , it is preferred to use nitrogen gas, a mixture of nitrogen and oxygen, a mixture of nitrogen and an air, a rare gas or a mixture of nitrogen and rare gas. From an economic point of view, nitrogen, a mixture of nitrogen and oxygen, a mixture of nitrogen and air are more preferable. When removing resists, or etching organic films, it is preferred to use oxygen, ozone, an air, carbon dioxide (C0₂) , a steam or nitric oxide (N₂0) . In addition, when etching silicon, it is effective to use nitrogen or a rare gas in combination with a fluorine-based gas such as CF₄ or a chlorinated gas. When reducing metal oxides, it is possible to use a reducing gas such as hydrogen or ammonia.

The frequency of the AC power supply is preferably within a range of 50 Hz to 200 MHz. When the frequency is less than 50 Hz, there is a possibility that the discharge can not be stabilized. When the frequency is more than 200 MHz, arc discharge can occur due to considerable temperature rise of the plasma. Preferably, the frequency is in a range of 1kHz ~ 100MHz, and most preferably, the frequency is in a range of 5kHz ~ 100kHz. The applied voltage could be suitably chosen with regard to the distance between the two electrodes (401a, 401b) , the area of the electrodes, the plasma conversion efficiency and the type of the dielectrics used. Generally, the voltage is adjusted within a range of lkV ~ 40kV. Plasma discharge hardly occurs at a voltage of below than lkV and the dielectrics could be damaged at voltages greater than 40kV. The preferable voltage is in a range of 2kV - lOkV and the most preferable voltage is in a range of 2kV ~ 8kV. When the frequency and the voltage are adjusted in a range of 5kHz ~ 100kHz and 2kV ~ lOkV, respectively, impedance matching for applying higher frequency and voltage is not required such that simplicity of the apparatus and economical earnings can be attained. The shape of the wave generated by the alternating current supply (407) is not particularly limited, both pulse waves and sine waves can be used.

It is preferred that the surface temperature of the electrodes (401a, 401b) is maintained at 250°C or less, and particularly 200°C or less during the plasma treatment. When the electrode temperature is more than 250°C, arc discharge may occur. There is no limitation as to a lower- limit value of the electrode temperature, while additional cooling is required when the temperature is maintained below room temperature. The surface cooling of the electrodes (401a, 401b) is performed by installing the radiators (404a, 404b) around the electrodes (401a, 401b) . Although shape of the radiator (404a) for the upper electrode (401a) is not specifically limited, shape of the radiator (404b) for the lower electrode (401b) needs to be defined according to the shape of the outlet port (406) . More specifically, the shape of the radiator (404b) for the lower electrode (401b) has a shape such that it does not adversely affect the outflow of the plasma through the lower electrode

(401b) . The surface cooling of the electrodes (401a, 401b) can be performed by circulation of air, water or refrigerant. Air circulation is preferable for low electric power, and water or refrigerant circulation is preferable for high electric power.

Although the radiators (404a, 404b) for the upper electrode

(401a) and for the lower electrode (401b) could be cooled independently, it is preferable to connect the radiator (404a, 404b) with a connection pipe (not shown) . Moreover, the radiator (404b) for the lower electrode (401b) may not be required when low power is applied.

The upper electrode (401a) and the lower electrode (401b) are insulated by the dielectrics (403a, 403b) . Although two dielectrics (403a, 403b) are used in Figs. 3 and 4, the upper electrode (401a) and the lower electrode (401b) can be insulated with only one dielectric, which is well known to a person to which the present invention pertains. The dielectrics (403a, 403b) are preferably made of an insulating material having a dielectric constant of 2000 or less, but are not limited thereto.

For example, MgF₂, CaF₂, LiF, alumina, glass and ceramic can be used. In particular, it is preferred to use magnesium oxide

(magnesia) to maintain the stability. As a dielectric material containing magnesium oxide, for example, it is possible to use a sintered body produced by preparing a mixture of a ceramic powder such as alumina and a small amount (0.01-5 vol%) of magnesium oxide and sintering the mixture. As an alternative example, the dielectric material containing magnesium oxide may be prepared by coating MgO film on a surface of a dielectric substrate such as alumina or quartz by means of sputtering, electron-beam deposition, or thermal spraying. The thickness of the dielectrics (403a, 403b) is preferably within a range of 0.1 to 2 mm. When the thickness is less than 0.1 mm, a withstand voltage of the dielectric layer may lower. In addition, crack or peeling may occur, so that it becomes difficult to maintain uniform glow discharge. When the thickness is more than 2 mm, the withstand voltage may increase excessively.

Connection between the dielectrics (403a, 403b) and the electrodes (401a, 401b) could be achieved by well known techniques such as fusion-bonding, ceramic spraying, or chemical or physical vapor deposition of the electrode material .

While the outlet ports (406) could be formed on the lower electrode (401b) by cutting out specific regions after connecting the dielectric (403b) to the lower electrode (401b) , it is preferable to deposit or spray the electrode materials

(for example, copper, silver, aluminum, gold, platinum, palladium, molybdenum, tungsten or alloys thereof) on the dielectric on which the outlet ports (406) has already been formed by cutting out the specific regions.

The surface treatment apparatus according to the present invention could be modified in a various form. For example, the electrode structures shown in Fig. 4 could be connected each other in a parallel structure. Furthermore, the surface temperature of the electrode could be controlled by installing a thermometer to measure the surface temperature of the electrode, a monitor to display the measured electrode temperature and a controller to control the surface temperature. Regarding such a modification, please refer to US 6,424,091. More uniform supply of the processing gas could be achieved by installing a flow homogenizer or a multi -port plate inside the processing gas storage part as shown in US 5,185,132. The surface treatment apparatus according to the present invention can be used for removing contaminants such as organic substances from surfaces of a substrate, stripping resists, improving adhesion of organic films, surface modification, film formation, reducing metal oxides, cleaning glass substrates for liquid crystal, etching oxide films or etching silicone or metal. For instance, it could be applied to cleaning of PCB strip and lead frame, pre-cleaning of large area glasses used for TFT-LCD, and stripping resist loaded on the large area glasses used for TFT-LCD. Moreover, it could be applied to all packaging steps of the semiconductor manufacturing process such as bonding, molding, soldering, chip attaching, dipping and marking processes. Furthermore, it could be applied to removal of metal oxide materials from a semiconductor, formation of hydrophilic surfaces or formation of water repellent surfaces.

The surface treatment apparatus according to the present invention makes it possible to continuously treat the surfaces of substrates at atmospheric pressure. In other words, it can be applied to continuous processes by moving the substrate relative to the surface treatment apparatus according to the present invention.

The surface treatment apparatus according to the present invention has flat-panel type electrodes for the upper electrode and the lower electrode, but it solves the narrow width of the effective processing area caused by the conventional flat -panel electrode structure, and addresses the reduction of the plasma discharging space caused by the cylindrical electrode structure. In addition, the apparatus is not limited to the shape of the substrate and can treat the surfaces of substrates in a continuous manner at atmosphere pressure.

Claims

1. A surface treatment apparatus comprising a processing gas storage part and a plasma generating part located below the processing gas storage part in which a) the processing gas storage part comprises a first inlet port through which a processing gas is introduced, and b) the plasma generating part comprising an upper electrode and a lower electrode facing each other, a plasma generating space formed between the electrodes, at least one dielectric insulating the upper electrode and the lower electrode, a radiator lowering the surface temperature of the electrodes, a second inlet port through which the processing gas is introduced from the processing gas storage part into the plasma generating space, an outlet port through which a plasma and the processing gas which has not been converted into the plasma are driven to outside of the plasma generating space, and an alternating current supply applying an alternating current voltage, wherein both the upper electrode and the lower electrode are flat-panel electrodes, the outlet port is formed on the lower electrode, and a substrate is located below the lower electrode.

2. The apparatus as set forth in claim 1, wherein the outlet port has rectangular, circular, triangular or oval shape.

3. The apparatus as set forth in claim 1, wherein the frequency of the alternating current supply is in a range of 50HZ ~ 200MHz and the voltage thereof is in a range of lkV ~ 40kV.

4. The apparatus as set forth in claim 1, wherein the frequency of the alternating current supply is in a range of 5kHZ ~ 100kHz and the voltage thereof is in a range of 2kV ~ lOkV.

5. The apparatus as set forth in claim 1, further comprising a flow homogenizer.

6. The apparatus as set forth in claim 1, wherein the processing gas is selected from nitrogen, oxygen, a rare gas, carbon dioxide, nitric oxide, perfluorinated gas, hydrogen, ammonia, chloride gas, ozone and a mixture thereof.

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

8. The apparatus as set forth in claim 1, wherein the substrate is a semiconductor.

9. The apparatus as set forth in claim 1, wherein the substrate is PCB strip or lead frame.

10. The apparatus as set forth in claim 1, wherein the substrate is a large area glass for TFT-LCD.

11. The apparatus as set forth in claim 1, wherein the apparatus is used for removing contaminants from surfaces of a substrate, stripping resists, improving adhesion of organic films, surface modification, film formation, reducing metal oxides, cleaning glass substrates for liquid crystal, etching oxide films, or etching silicone or metal.