JPH0885861A - Method of oxidizing the surface of an object to be treated or a substance on the surface under reduced pressure - Google Patents

Abstract

(57) [Abstract] [Purpose] A high concentration of ozone or active oxidative decomposition products can be obtained without using an ozone generator, so it is inexpensive, has a high processing speed, and from the light source to the object to be processed. To improve the wettability of the surface of the object to be treated, the method of oxidizing the surface of the object to be treated or the substance on the surface, the method of oxidizing and removing contaminants or unnecessary organic substances, or the wettability. Provide a way. [Structure] Oxygen or a fluid containing oxygen is irradiated under reduced pressure with vacuum ultraviolet light emitted from a dielectric barrier discharge lamp containing xenon or a gas containing xenon as a main component, and ozone and active oxidation are caused by a photochemical reaction. A oxidative decomposition product is generated, and the ozone and the active oxidative decomposition product are brought into contact with the surface of the object to be treated or a substance on the surface to oxidize the surface or the substance.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to the formation of an oxide film on the surface of a metal or semiconductor, removal of stains of organic compounds adhering to the surface of a metal or glass plate, ashing of unnecessary photoresist on a silicon wafer, and precision dry cleaning. Or an oxidation method of an object to be treated for improving wettability by modifying the surface of the object to be treated.

[0002]

2. Description of the Related Art Techniques related to the present invention are, for example,
There is Japanese Patent Laid-Open Publication No. 2-7353, in which a discharge vessel is filled with a discharge gas that forms excimer molecules, and a dielectric barrier discharge (also called ozonizer discharge or silent discharge. Revised new edition issued by the Institute of Electrical Engineers of Japan (discharge) Handbook)
This paper describes a radiator, that is, a dielectric barrier discharge lamp, which forms excimer molecules by taking out June 1993, Reprint 7th Edition, page 263, and extracts light emitted from the excimer molecules. On the other hand, in recent years, as a method for removing organic substances on the surface of the object to be processed, removing unnecessary resist, dry precision cleaning, forming an oxide layer on the metal surface, etc., UV / o
O ₃ treatment was developed and put to practical use. For "UV / O ₃ treatment", for example, the book "New technology of ozone utilization"
(Published by San-Yu Shobo, November 20, 1986) Chapter 9 (pages 301 to 313, (hereinafter referred to as Document 1))
The principle, equipment, cleaning effect, use, etc. are described in detail in the article. According to this, ozone emits vacuum ultraviolet light of 185 nm emitted from a low-pressure mercury lamp to air, oxygen-added air, It is generated by irradiating oxygen gas. And far-ultraviolet light 25 emitted from the same low-pressure mercury lamp
Part of the ozone is decomposed with 4 nm light, and ozone and ozone decomposition gas are brought into contact with the surface of the object to be treated to oxidize organic pollutants on the surface to oxidize low molecular weight compounds such as CO ₂ and H ₂ O. The surface is subjected to dry precision cleaning by changing it into an object and removing it.

As another method, ozone produced by an ozone generator is introduced into a processing chamber, and far ultraviolet light of 254 nm emitted from a low-pressure mercury lamp is irradiated on the ozone to decompose the ozone. By contacting the surface of the object to be treated, the organic contaminants on the surface are oxidized and removed.

In the technique described in the above-mentioned document 1, when the ozone generator is not used, the ozone concentration is low, and if an attempt is made to increase the absolute amount of ozone generated, it becomes 185 nm.
The value of the distance d (cm) through which the light is transmitted must be 10 cm or more when the oxygen partial pressure p (atmospheric pressure) is 0.2 atm, that is, the value of d × p must be larger than about 2. Therefore, there is a drawback that the apparatus becomes large, and at the same time, a high concentration of ozone cannot be obtained and the processing speed is slow. On the other hand, when an ozone generator is used, it is an expensive device itself, which causes economic problems and narrows the usable conditions.

The light source used in the method described above was a low pressure mercury lamp (wavelength 254 nm, 185 nm). On the other hand, Iso et al. In the 41st Japan Society of Applied Physics, Joint Lecture Lecture Summary 30p-ZE-2
/ O ₃ cleaning with 172n filled with xenon gas
It has been reported that the use of a dielectric barrier discharge lamp having a central wavelength in m enables a faster cleaning process than a low-pressure mercury lamp and enables a process process at a low temperature.

It is said that light having a wavelength of 175 nm or less can directly generate active oxygen O ( ¹ D) having a strong oxidizing ability from oxygen molecule O _2, and a central wavelength of 172 nm emitted from a dielectric barrier discharge lamp. Vacuum ultraviolet light can directly generate active oxygen O ( ¹ D). On the other hand, a low-pressure mercury lamp cannot be directly generated, and once it emits ozone O _{3 with} light of 185 nm.
To generate active oxygen O by decomposing it with light of 254 nm.
It is generating ⁽¹ D). However, the luminous efficiency at 185 nm is considerably lower than that of the barrier discharge lamp, and therefore the generation efficiency of active oxygen O ( ¹ D) is inferior. Further, the absorption coefficient of light due to atmospheric oxygen is as large as 0.8 cm ^-1 at 185 nm and 15 cm ^-1 at 172 nm. Therefore, the dielectric barrier discharge lamp is
It can be said that the concentrations of ozone and active oxygen near the light source are extremely high. As described above, the dielectric barrier discharge lamp has an excellent oxidizing ability as compared with the low-pressure mercury lamp, but (1) the distance from the light source to the object to be treated is too short in the conventional treatment under atmospheric pressure. However, there are drawbacks or problems such as (2) the effect is not sufficiently exerted depending on the unevenness of the surface of the object to be treated, and (3) the optimum treatment condition is not achieved.

[0007]

The present invention has been made in view of the above circumstances, and an object thereof is to obtain a high concentration of ozone or an active oxidative decomposition product without using an ozone generator. Therefore, it is inexpensive, the processing speed is high, the distance from the light source to the object to be processed is increased, and unevenness on the surface of the object to be processed can be uniformly processed. Another object of the present invention is to provide a method of oxidizing and removing contaminants and unnecessary organic substances, or a method of improving wettability.

[0008]

In order to achieve the object of the present invention, the following oxidation method is adopted in the present invention. (1) Oxygen or a fluid containing oxygen is irradiated under reduced pressure with vacuum ultraviolet light emitted from a dielectric barrier discharge lamp containing xenon or a gas containing xenon as a main component, and ozone and active oxidation are caused by a photochemical reaction. A oxidative decomposition product is generated, and the ozone and the active oxidative decomposition product are brought into contact with the surface of the object to be treated or a substance on the surface to oxidize the surface or the substance. (2) Oxygen or a fluid containing oxygen is irradiated with vacuum ultraviolet light emitted from a dielectric barrier discharge lamp containing xenon or a gas containing xenon as a main component under reduced pressure, and ozone and active oxidation are caused by a photochemical reaction. Oxidative decomposition product is generated, and the ozone and the active oxidative decomposition product are brought into contact with the surface of the object to be treated or a substance on the surface, and the ultraviolet light is also applied to the surface or the substance, and their cooperative action. Then, the surface or the substance is oxidized.

Here, as the shape of the dielectric barrier discharge lamp, in particular, a double cylinder type or a flat type is easy to use, and synthetic quartz glass or sapphire is used for all or part of the vacuum ultraviolet light extraction portion. It can be said that a material selected from alkali metal halides and alkaline earth metal halides is good.

Practically, when the oxygen partial pressure of oxygen or a fluid containing oxygen is set to p (atmospheric pressure) under reduced pressure, 1 × 10 ^{−5 is set} in order to make the treatment rate faster than the conventional atmospheric pressure. <P
<0.2 is preferable, and in order to obtain a more remarkable effect, the above specified range is further 0.005 <p <
It is better to limit it to 0.05. In the case of removing unnecessary photoresist, when oxidizing the surface of the object to be treated or the substance on the surface, the surface layer of the surface or the oxide of the substance is efficiently released from the surface as a gas because the evaporation rate is accelerated. Alternatively, it can be oxidized so that it is removed.

[0011]

[Function] A radiator, that is, a dielectric barrier discharge lamp, which is filled with a discharge gas for forming excimer molecules in the discharge vessel to form excimer molecules by dielectric barrier discharge and takes out light emitted from the excimer molecules, , It has various features that conventional low pressure mercury lamps and high pressure arc discharge lamps do not have. This lamp itself is, for example, Japanese Patent Laid-Open No. 2-735.
3 etc. In the present invention, xenon or a gas containing xenon as a main component is designated as the discharge gas.

As described above, conventionally, the light (center wavelength 172 nm) generated when the excimer (Xe ₂ *) of xenon excited by the dielectric barrier discharge lamp is dissociated into xenon atoms is oxygen or oxygen. Ultraviolet light emitted from a low-pressure mercury lamp when irradiated with contained fluid.
It has been known that a higher concentration of ozone and an active oxidative decomposition product can be obtained than in the case of 5 nm.

In the present invention, in the UV / O ₃ cleaning, optimization in an atmosphere of general conditions which has been conventionally performed was examined, and pressure dependency of the cleaning was investigated and an experiment was conducted. As a result, it was found that the cleaning rate was improved under the reduced pressure as compared with the conventional method, and the optimum conditions were obtained.

The improvement of the cleaning rate under reduced pressure can be estimated as follows. UV / O ₃ cleaning is considered to be performed in the next step. (1) Generation of ozone and active oxygen O ₂ + hν → O ( ¹ D) + O ( ³ P) O ( ³ P) + O ₂ → O ₃ O ₃ + hν → O ( ¹ D) + O ₂ → O ( ³ P) + O ₂ (2) Diffusion of O ₂ excited molecules, O ( ³ P), and O ( ¹ D) into the surface to be cleaned (3) Oxidation reaction of organic compounds and oxygen active species on the surface Detachment from the surface due to vaporization (cleaning)

It is considered that which of these processes becomes the rate-determining process depends on the pressure of the atmosphere. That is, it is considered that the process rate is determined by the rate of generation of active oxygen in the low pressure region, the rate of diffusion of active oxygen in the high pressure region, and the ratio of the two in the intermediate region. Since the lifetime and diffusion rate of active oxygen greatly depend on the pressure, it is considered that optimum cleaning conditions can be achieved in the region shown in the above specified range. On the other hand,
It is considered that the reduced pressure also accelerates the evaporation rate of the oxidized substance and contributes to further increase in the cleaning rate. This is considered to be more effective when a large amount of vaporized substances such as ashing are present.

[0016]

1 is a schematic view of a dielectric barrier discharge lamp used in the present invention. In FIG. 1, the discharge vessel 1 is made of synthetic quartz with a total length of about 150 mm and has an outer diameter of 14 mm and a wall thickness of 1 mm.
The inner tube 2 and the outer tube 3 having an inner diameter of about 24 mm and a wall thickness of 1 mm are coaxially arranged to form a hollow cylindrical discharge space 7. The outer tube 3 also serves as a dielectric barrier for dielectric barrier discharge and a light extraction window member, and is provided with a mesh electrode 4. On the inner surface of the inner tube is provided an aluminum thin film electrode 5 which also serves as a light reflecting plate and an electrode for dielectric barrier discharge. 250 as a discharge gas in the discharge space 7 of the discharge vessel
Tall xenon gas was enclosed. A getter 6 is provided in the getter chamber 8. If necessary, a cooling fluid, for example, cooling nitrogen gas, can flow into the inner space 9 of the lamp. Here, the power supply 10 turned on the dielectric barrier discharge lamp with an input of 20 watts. As a result, the ultraviolet light having the maximum emission value at the wavelength of 172 nm was efficiently emitted.

FIG. 2 is an explanatory diagram of a method for cleaning the surface of a slide glass using the above lamp. In FIG. 2, 1
Reference numeral 1 denotes a processing chamber, in which a sample table 12 and a slide glass 13 having an area of 1 cm × 2 cm mounted on the table are arranged, and the above-mentioned lamp is provided with an irradiation window made of synthetic quartz. It is arranged through 14. The processing chamber 11 is provided with an oxidizing fluid inlet 15 and an outlet 16 for oxygen or a gas containing oxygen, and the outlet is provided with a valve 2
It is connected to the vacuum exhaust device 22 via 1 and can be depressurized to an arbitrary pressure. At the entrance,
For example, a nitrogen gas source 19 and an oxygen gas source 20 are connected via a mixing chamber 17 and a valve 18.

Using such an irradiation device, the electric input of the lamp is set to 20 watts, the distance d (cm) between the irradiation window and the surface of the slide glass and the partial pressure p of oxygen in the processing chamber are set.
(Atmospheric pressure) was changed and the washing rate was examined. The slide glass used for the evaluation was pretreated by ultrasonic cleaning in isopropyl alcohol (hereinafter referred to as IPA) for 5 minutes, naturally dried, and allowed to stand in the atmosphere for a few days. To evaluate the cleaning rate, the contact angle of pure water was measured with a contact angle meter. The thicker the surface organic contamination layer is, the larger the contact angle is, and it is said that the contact angle is 3 degrees and about 0.1 molecular layer or less. The unirradiated contact angle of the sample this time was about 49 degrees.

The results are shown in the table of FIG. FIG.
FIG. 4 is an explanatory diagram of data on a contact angle (degree). Irradiation time is 5
Fixed to second, change irradiation distance d (mm), oxygen partial pressure p
The results of measuring the contact angle (degree) by shaking (atmospheric pressure) are summarized. According to this result, first, the irradiation distance is 1 m under atmospheric pressure.
It can be seen that when m, the contact angle is 30 degrees. Further, it can be seen that when the irradiation distance is made larger than 1 mm and the oxygen partial pressure is reduced under reduced pressure, the contact angle also becomes smaller. Even at a place where the oxygen partial pressure is quite low, 10 ^-3 to 10 -4 atm,
By increasing the irradiation distance, the contact angle can be made smaller than that at atmospheric pressure. From this, it can be seen that the cleaning speed is improved by appropriately selecting the irradiation distance under reduced pressure, as compared with the conventional cleaning under atmospheric pressure.
Further, when the oxygen partial pressure is limited to the range of 0.005 atm to 0.05 atm, the contact angle becomes about half at atmospheric pressure, and the cleaning effect is remarkable.

FIG. 4 is an explanatory view of the data of the result of comparing the change of the contact angle (degree) with the irradiation time (second) under the conventional condition and the optimum condition under reduced pressure found in the present invention. . According to this result, the irradiation time of about 30 seconds was conventionally required for the contact angle to be 10 degrees or less, but in the present invention, the contact angle is reduced to 4 degrees with the irradiation time of 10 seconds. . Therefore, it can be seen that the present invention has a triple cleaning rate.

[0021]

EFFECTS OF THE INVENTION A method of oxidizing a surface of an object to be treated or a substance on the surface using a dielectric barrier discharge lamp is conventionally known in a narrow area between the lamp and the surface of the object to be treated, particularly in the vicinity of the surface of the object to be treated. As compared with the case of using the low-pressure mercury lamp described above, ozone and an active oxidative decomposition product having a concentration 10 times or more higher than that of the low-pressure mercury lamp are generated, so that the speed of oxidizing the surface of the object to be processed or the object on the surface is remarkably high. It is recognized that the effect is further improved under reduced pressure, and a more remarkable effect is recognized under certain conditions. In addition, since the irradiation distance, which was a drawback in processing under atmospheric pressure, cannot be reduced, the cleaning speed is not impaired even if the irradiation distance is considerable. Similarly, it is possible to effectively clean deep irregularities on the surface.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an example of a double cylindrical dielectric barrier discharge lamp used in the present invention.

FIG. 2 is an explanatory view of a method for cleaning the surface of a slide glass.

FIG. 3 is an explanatory diagram of data of a surface cleaning result.

FIG. 4 is an explanatory diagram of data of surface cleaning results.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Discharge container 2 Inner tube 3 Outer tube 4 Mesh electrode 5 Aluminum thin film electrode 6 Getter 7 Discharge space 8 Getter chamber 9 Inner cavity 10 Power supply 11 Processing chamber 12 Sample stand 13 Slide glass 14 Irradiation window 15 Oxidizing fluid inlet 16 Oxidizing property Fluid outlet 17 Mixing chamber 18 Valve 19 Nitrogen gas source 20 Oxygen gas source 21 Valve 22 Vacuum exhaust device

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hiromitsu Matsuno 1194 Sado, Bessho-cho, Himeji-shi, Hyogo Ushio Electric Co., Ltd.

Claims (4)

[Claims] 1. A vacuum ultraviolet light emitted from a dielectric barrier discharge lamp in which xenon or a gas containing xenon as a main component is filled, is irradiated with oxygen or a fluid containing oxygen under reduced pressure to generate ozone and ozone by a photochemical reaction. An object to be treated, characterized in that an active oxidative decomposition product is produced, and the ozone and the active oxidative decomposition product are brought into contact with the surface of the object to be processed or a substance on the surface to oxidize the surface or the substance. A method of oxidizing a surface or a substance on the surface under reduced pressure. 2. A vacuum ultraviolet light emitted from a dielectric barrier discharge lamp containing xenon or a gas containing xenon as a main component is irradiated under reduced pressure on oxygen or a fluid containing oxygen to generate ozone and ozone by a photochemical reaction. The active oxidative decomposition product is generated, and the ozone and the active oxidative decomposition product are brought into contact with the surface of the object to be treated or a substance on the surface, and the ultraviolet light is also applied to the surface or the substance, and their cooperation is performed. A method for oxidizing a surface of an object to be treated or a substance on the surface under reduced pressure, which comprises oxidizing the surface or the substance by an action. 3. The method according to claim 1, wherein the oxygen partial pressure of oxygen or a fluid containing oxygen is defined as 1 × 10 ⁻⁵ <p <0.2 when the oxygen partial pressure is p (atmospheric pressure). Item 3. The method according to Item 2, wherein the surface of the object to be treated or the substance on the surface is oxidized under reduced pressure. 4. When oxidizing a surface of an object to be treated or a substance on the surface, the surface layer of the surface or an oxide of the substance is oxidized so as to be released or removed from the surface as a gas. The method for oxidizing a surface of an object to be treated or a substance on the surface under reduced pressure according to any one of claims 1 to 3.