JP3085128B2 - Light cleaning method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called light cleaning method for cleaning and removing contaminants from several molecules to several tens of nanometers from glass, silicon semiconductor wafers, semiconductor photomasks, ceramics, plastics, etc. The removal of the photoresist.

[0002]

2. Description of the Related Art As a technique related to the present invention, there is, for example, Japanese Patent Laid-Open Publication No. 1-144560.
It describes a lamp using a dielectric barrier discharge (also known as an ozonizer discharge or a silent discharge. See the revised edition of the “Discharge Handbook” published by the Institute of Electrical Engineers of Japan, June 1991, 7th edition, page 263). In this lamp, it is known that a dielectric barrier discharge lamp having a center wavelength of 172 nm containing xenon has a higher ability to generate active oxygen species having a higher oxidizing power than a low-pressure mercury lamp.

On the other hand, in recent years, as a method for removing organic contaminants on the surface of an object to be irradiated without contacting the object, removing unnecessary photoresist, and performing dry precision cleaning, etc., a method using the synergistic action of ultraviolet light and ozone has been proposed. / O ₃ treatment ”has been developed and is now in practical use. The “UV / O ₃ ” treatment is described, for example, in Chapter 9 of the book “New Technology of Ozone Utilization” (published by Sanyu Shobo, November 20, 1986).
The principle, equipment, cleaning effect, and application are described in detail on page 13). According to the report, ozone emits 185 nm vacuum ultraviolet light emitted from a low-pressure mercury lamp to air or air added with oxygen. Alternatively, it is generated by irradiating oxygen gas. Then, a part of the ozone is decomposed by 254 nm far ultraviolet light emitted from the same low-pressure mercury lamp, and the ozone and the ozone decomposed gas are brought into contact with the surface of the object to be treated to remove organic contaminants on the surface. The surface is dry-precisely cleaned by oxidizing, changing to low molecular oxides such as carbon dioxide and water, and removing it.

The above-described method is a method of continuously irradiating a low-pressure mercury lamp (wavelengths of 254 nm and 185 nm), but has the following disadvantages. (1) The cleaning efficiency is insufficient and the cleaning speed is insufficient. (2) It is difficult to control the amount of ultraviolet light, and the object to be processed is damaged by excessive ultraviolet light. (3) Thermal damage to the irradiated object is inevitable due to the large amount of heat generated. (4) The lamp can only be turned on continuously, and the lamp must be turned on even when the object to be irradiated is not irradiated, so that power consumption is large and lamp replacement is frequent. (5) It is difficult to uniformly clean a large area because unevenness in cleaning occurs and a plurality of lamps cannot be turned on and off with one power supply at a time.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object a high cleaning efficiency.
It is an object of the present invention to provide an optical cleaning method which is capable of performing precision cleaning of a large area with less damage by ultraviolet rays and heat, less frequent lamp replacement.

[0006]

In order to solve the above-mentioned problems, an object of the present invention is to dispose an object to be irradiated in an atmosphere containing oxygen, and to apply oxygen and ultraviolet light from an ultraviolet lamp to the object to be irradiated. In the UV / O ₃ cleaning method of irradiating UV light, the ultraviolet lamp is turned on and off during cleaning by repeating input and cutoff of an electric input to the ultraviolet lamp.

[0007] The invention of claim 2 of the present invention is the invention of claim 1, wherein a dielectric barrier discharge lamp is used as the ultraviolet lamp.

According to a third aspect of the present invention, in any one of the first and second aspects, the light-off time is set to 30 minutes.
This is done in less than a second.

The invention according to claim 4 of the present invention relates to claims 1 and 2
Alternatively, in any one of the third to third aspects of the present invention, the amount of ultraviolet light per cycle is adjusted by changing the ratio between the light-off time and the light-on time.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, the amount of ultraviolet irradiation at the end of cleaning is smaller than the amount of ultraviolet irradiation at the beginning of cleaning.

The invention according to claim 6 of the present invention is directed to claim 2,
The invention according to any one of the third, fourth and fifth aspects, wherein a plurality of the dielectric barrier discharge lamps are connected in parallel to one power supply.

[0012]

According to the first aspect of the present invention, there is provided a UV / O ₃ cleaning method in which an object to be irradiated is placed in an atmosphere containing oxygen and the object to be irradiated is irradiated with ultraviolet rays. The lamp is turned on and off during cleaning by repeatedly inputting and shutting off the input.
The cleaning is performed by the same operation as the conventional light cleaning. in addition,
The reaction and decomposition of the remaining active oxygen species and contaminants occur even when the light is turned off, and cleaning is performed. Active oxygen species lifetime O ⁽¹ D) is 110 seconds, O ₂ ^{* (1} Δg) is known to be a few minutes, to react with contaminants these reactive oxygen species even in off, Decomposition and cleaning are performed. Therefore, if the blinking is repeated, the washing speed increases with the same electric input.

In the second aspect of the present invention, since the dielectric barrier discharge lamp containing xenon or a mixed gas of argon and chlorine as a discharge gas is used as the ultraviolet lamp in the first aspect of the invention, the wavelength is 172 nm.
Or vacuum ultraviolet rays having a wavelength of 175nm emits light with high efficiency, the following UV wavelength 175nm oxygen molecule O ₂
⁽³ Σg ^-) is dissociated directly, O ⁽¹ D) having a strong oxidizing power with high efficiency in addition to ozone ^{_{O 3, O 2 * (1}} Δg)
Since the reactive oxygen species such as the above can be generated, the cleaning rate is further increased.

The present inventors have also found that the lamp life is not shortened even if the dielectric barrier discharge lamp is repeatedly turned on and off. That is, since the dielectric barrier discharge lamp is used even if the above-mentioned blinking is repeated, a long-life lamp device can be obtained.

According to a third aspect of the present invention, in any one of the first and second aspects, the light-off time is set to 30 seconds or less. Are sufficiently present, and a sufficient cleaning speed can be obtained even when the light is turned off. The present inventors have found that when compared with the total lighting time when the light-off time is within 30 seconds, the cleaning efficiency is higher than that of a low-pressure mercury lamp or a dielectric barrier discharge lamp of continuous lighting. The above effects and effects were particularly remarkable when the light-off time was between 0.1 seconds and 5 seconds.

According to a fourth aspect of the present invention, in any one of the first, second and third aspects of the present invention, the amount of ultraviolet light per cycle is changed by changing the ratio of the extinguishing time to the lighting time. Since it is adjustable, the amount of ultraviolet irradiation can be changed according to the type of the object to be cleaned, and the amount of ultraviolet irradiation can be changed in the process of cleaning,
Low-damage cleaning without excessive or insufficient amount of ultraviolet light can be easily performed. Further, it contributes to reduction of damage due to heat.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, the amount of ultraviolet radiation at the end of cleaning is smaller than the amount of ultraviolet radiation at the beginning of cleaning. As a result, cleaning proceeds and contaminants are removed, reducing the amount of ultraviolet light at the time when the irradiation object is exposed, controlling the amount of ultraviolet light on the irradiation object and reducing damage to the irradiation object, Optimized cleaning without excess and shortage, and low damage cleaning.

According to a sixth aspect of the present invention, in the light cleaning method according to any one of the second to third aspects, the plurality of dielectric barrier discharge lamps are provided for one power supply. Are turned on in parallel, this lamp can be turned on and off by inputting and shutting off one power supply, so that irradiation of a large area can be performed, and the power supply device is inexpensive.

The method of dimming by blinking is applied to plasma displays, liquid crystal backlights, and the like, and is well known. However, the present invention is based on the discovery that cleaning is performed even while the lamp is turned off. In particular, the light cleaning method by flashing and lighting the dielectric barrier discharge lamp according to claims 2 to 5 is a new method described below. It is based on discovery. (1) Vacuum ultraviolet rays having a center wavelength of 172 nm or 175 nm are radiated by using a dielectric barrier discharge lamp filled with xenon or a mixed gas of argon and chlorine. These vacuum ultraviolet rays have 18 times the absorption coefficient of oxygen molecules in the air at the center wavelength of 172 nm with xenon compared to the ultraviolet rays with a wavelength of 185 nm emitted by the low-pressure mercury lamp. 12 at the center wavelength of 175 nm
Twice as large, and the density of active oxygen species is extremely high in a very narrow range near the lamp. Therefore, when the irradiation target is disposed near the lamp, the frequency of collision of the active oxygen species with the contaminants on the irradiation target is extremely high, and the active oxygen species is easily diffused onto the irradiation target during turning off the light, As a result, the efficiency of the reaction, decomposition, and washing becomes extremely high. (2) The life of the lamp is not shortened by blinking. (3) The shape of the emission spectrum does not change depending on the blinking ratio. (4) A large number of lamps can be lit in parallel and uniformly with one power supply. (5) Since vacuum ultraviolet rays can be emitted with high efficiency, thermal damage to the irradiation object is extremely small. By applying the above items (1) to (5) to the light cleaning method, which could not be realized by the conventional discharge lamp, a completely new high-performance light cleaning has become possible.

[0020]

FIG. 1 is a schematic view of a light cleaning method according to a first embodiment of the present invention. Five dielectric barrier discharge lamps 4 were connected to one power supply 10 in parallel. In the cleaning duct 3, five dielectric barrier discharge lamps 4 are provided close to the object 8 to be cleaned. The object to be cleaned 8 is supported by a support 5, which is a conventional means for changing the temperature of the object 8 to be cleaned, for example, an electric heater, the object to be cleaned and a dielectric barrier discharge lamp. 4 has a moving mechanism for adjusting the distance between them.

FIG. 2 is a schematic explanatory view of a dielectric barrier discharge lamp used in the present invention. In FIG. 2, a discharge vessel 13 is made of synthetic quartz having a total length of 250 mm, and an inner tube 14 having an outer diameter of 14 mm and a thickness of 1 mm and an outer tube 15 having an inner diameter of 24 mm and a thickness of 1 mm are coaxially arranged to form a hollow cylindrical discharge space 20. It is the structure which did. The outer tube 15 also serves as a dielectric barrier for the dielectric barrier discharge and a light extraction window member, and is provided with a mesh electrode 17. On the inner surface of the inner tube 14, there is provided an aluminum thin film electrode 16 which also serves as a light reflection plate and an electrode for dielectric barrier discharge. Xenon gas of 250 torr was sealed in the discharge space 20 of the discharge vessel. A getter 18 is provided in the getter room. A cooling fluid, for example, a cooling nitrogen gas can be supplied to the inner space 19 of the lamp as needed. The power supply 21 turned on the dielectric barrier discharge lamp at an input of 50 W per unit. As a result, the wavelength 172
Ultraviolet light having a maximum emission value in nm was emitted efficiently.

Using such an irradiating apparatus, the cleaning speed with respect to the total irradiation time of ultraviolet rays was examined when the electric input per lamp of the above lamp was set to 50 W and the blinking interval was changed. For evaluation, a quartz glass pre-treated, subjected to ultrasonic cleaning in isopropyl alcohol for 5 minutes, air-dried, and left in the air for a few days was used. Also,
The total irradiation time was the total lighting time, and the cleaning rate was evaluated by measuring the contact angle of pure water with a contact angle meter. It is said that the thicker the organic contaminant layer on the surface is, the larger the contact angle is, and the contact angle is 3 degrees and about 0.1 molecular layer or less. In addition, the contact angle of the quartz glass not irradiated with ultraviolet light in this case was 56 degrees.

For comparison, one high-efficiency low-pressure mercury lamp was continuously turned on using one power supply of 450 W input, and the same cleaning was performed to obtain data. At this time, the temperature of the glass surface of the object to be cleaned was heated by heat radiation from the lamp, and the surface temperature became 48 ° C.

The results are as shown in FIG. FIG. 3 is an explanatory diagram of data obtained by evaluating the cleaning rate with respect to the total irradiation time by the contact angle of water. When comparing the total irradiation time from the results, comparing the required time from the unirradiated contact angle to the contact angle of 3 degrees at which the cleaning is considered to be completely completed, the low-pressure mercury lamp is lit continuously for 240 seconds. In the dielectric barrier discharge lamp of the present invention, the cleaning is performed in 120 seconds, and in the blinking dielectric barrier discharge lamp of the present invention, the cleaning is performed in 47 seconds when the ratio between the lighting time and the extinguishing time is 1: 3, and 77 seconds when the ratio is 1: 1. It can be seen that cleaning can be performed with significantly higher cleaning efficiency than the lighting low-pressure mercury lamp or the dielectric barrier discharge lamp.

Further, in the case of the dielectric barrier discharge lamp, no temperature rise is observed on the quartz glass surface, and the object to be cleaned is not damaged by heating.

In the second embodiment of the present invention, the structure of the cleaning apparatus is the same as that of the first embodiment. In this case, the amount of ultraviolet irradiation per unit was reduced to about 50% of the amount of irradiation in the first two third steps. The result was little damage. In general, semiconductor silicon wafers are considered to be significantly damaged by ultraviolet light having a short wavelength. However, according to the present invention, a light cleaning method with almost no damage by ultraviolet rays was realized.

FIG. 4 is an explanatory view of the ultraviolet lamp device used in the third embodiment of the present invention. The ultraviolet lamp device comprises a conventional low-pressure mercury lamp 40, electrode devices 42a and 42b for electrically heating electrodes 41a and 41b, and a main power supply 43 for supplying lamp power to the low-pressure mercury lamp. When the low-pressure mercury lamp 40 is repeatedly turned on and off, the electrodes 41a and 41b are preheated in advance by the power supplies for heating 42a and 42b before the main power supply 43 supplies the lamp voltage. By such means, the electrodes 41a, 42b at the start of discharge of the lamp
A low-pressure mercury lamp device is obtained in which the wear of the lamp is small and the life thereof is not shortened even if the light is repeatedly blinked.

When the low-pressure mercury lamp 40 is turned on and off,
Mercury adheres to the tube wall at the center of the lamp, and the mercury absorbs ultraviolet rays, and as a result, the ultraviolet output may be reduced. The present inventors, as a result of trial and error, when performing flashing lighting of the low-pressure mercury lamp 40, when the temperature of the tube wall at the center of the lamp in the lighting state is maintained at 100 ° C or higher, preferably 150 ° C or higher. Discovered that the above-mentioned mercury adhesion phenomenon disappeared.

The light cleaning apparatus is the same as the light cleaning apparatus of the first embodiment except that the dielectric barrier discharge lamp and its power supply are replaced with the low-pressure mercury lamp and its power supply shown in FIG.
After the object to be cleaned was set in the cleaning device, the lighting of the low-pressure mercury lamp 40 was started. The main power supply 43 and the power supplies 42a and 42b for energization and heating are high-frequency power supplies of 40 kHz,
During the light cleaning step, the electrodes 41a and 41b are constantly turned on while being energized and heated, and are repeatedly turned on and off for 50 ms and off for 50 ms. The tube wall temperature during lighting was set to 100 ° C. or higher by setting the power to 0.2 W / cm ² . As a result, a sufficient cleaning speed can be obtained, and since the low-pressure mercury lamp is turned off while the object to be irradiated is being installed in the optical cleaning device, the worker may be exposed to harmful ultraviolet rays. There was also the advantage of being less.

[0030]

As described above, according to the present invention,
By performing blinking lighting, it is possible to provide an optical cleaning method capable of cleaning a large area with a high cleaning speed, less damage due to ultraviolet rays and heat, less frequent lamp replacement.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an outline of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an example of a dielectric barrier discharge lamp used in the present invention.

FIG. 3 is an explanatory diagram of data of a contact angle of water with respect to a total irradiation time according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram of another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Processing fluid air 2 Processing fluid supply port 3 Cleaning duct 4 Dielectric barrier discharge lamp 5 Support 8 Irradiated object 10 Power supply 14 Inner tube 15 Outer tube 16, 17 Electrode 19 Cooling fluid 20 Discharge space 21 AC power supply 40 Low pressure mercury lamps 41a, 41b Electrodes 42a, 42b Power supply for energization and heating 43 Main power supply

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tatsumi Hiramoto 1194 Sado, Bessho-cho, Himeji-shi, Hyogo Ushio Electric Co., Ltd. Examiner Makoto Yagi (56) References JP-A-2-28032 (JP, A) JP-A-6-312130 (JP, A) JP-A-6-231735 (JP, A) JP-A-7-78751 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) ) H01L 21 / 304,21 / 302 B08B 5/00-13/00

Claims (6)

(57) [Claims] 1. A UV / O ₃ cleaning method in which an object to be irradiated is placed in an atmosphere containing oxygen and the object and the object to be irradiated are irradiated with ultraviolet rays from an ultraviolet lamp. A light cleaning method, wherein the ultraviolet lamp is turned on and off during cleaning by repeating the above. 2. The light cleaning method according to claim 1, wherein a dielectric barrier discharge lamp is used as said ultraviolet lamp. 3. The light cleaning method according to claim 1, wherein the light-off time is 30 seconds or less. 4. The optical cleaning method according to claim 1, wherein the amount of ultraviolet light per cycle can be adjusted by changing a ratio between the light-off time and the light-on time. 5. The method according to claim 4, wherein the amount of ultraviolet radiation at the end of cleaning is smaller than the amount of ultraviolet radiation at the beginning of cleaning.
3. The light cleaning method according to 1. 6. A plurality of said dielectric barrier discharge lamps are connected in parallel to one power supply.
The light cleaning method according to claim 3, 4, or 5.