JP4438072B2 - Method for cleaning lens of exposure apparatus - Google Patents

Description

  The present invention relates to an exposure apparatus that uses an ultraviolet ray such as an excimer laser or a short wavelength electromagnetic wave such as an X-ray as an exposure beam. Furthermore, the present invention relates to a device manufacturing method using the exposure apparatus and an optical element cleaning method of the exposure apparatus.

  Conventionally, in a projection exposure apparatus for the purpose of manufacturing a semiconductor integrated circuit, light in various wavelength bands is irradiated onto a substrate as an exposure beam. The exposure beam includes e-line (wavelength λ = 546 nm), g-line (λ = 436 nm), h-line (λ = 405 nm), i-line (λ = 365 nm), KrF excimer laser (λ = 248 nm), ArF excimer laser ( 193 nm) or X-rays are used.

  The exposure beam emitted from the light source is exposed and transferred onto the photosensitive substrate by an illumination optical system that illuminates the reticle and a projection optical system (projection lens) that forms an image of the fine pattern formed on the reticle on the photosensitive substrate. is doing. In the conventional exposure apparatus as described above, as the pattern line width becomes finer, it is required to improve the throughput and resolution, and accordingly, an exposure beam with higher power is required. At the same time, the wavelength of the exposure beam is being shortened.

  However, when i-line (wavelength λ = 365 nm) or an exposure beam with a shorter wavelength is used, it is known that the exposure beam causes photochemical reaction of impurities in the air with oxygen due to the shorter wavelength. The product (cloudy substance) adheres to the optical elements (lenses and mirrors) of the optical system, resulting in an inconvenience that an opaque “cloudy” occurs.

As this cloudy substance, for example, ammonium sulfate (NH ₄ ) ₂ SO ₄ generated by reacting (oxidizing) with oxygen in the air when sulfite SO ₂ absorbs light energy and becomes excited is typically mentioned. This ammonium sulfate has a white color, and when it adheres to the surface of an optical member such as a lens or a mirror, it becomes the “cloudy” state. As a result, the transmittance of the optical system is reduced as a result of the exposure beam being scattered or absorbed by ammonium sulfate, so that the amount of light (transmittance) until reaching the photosensitive substrate is greatly reduced, which may cause a reduction in throughput. .

  In particular, in the shorter wavelength region such as ArF excimer laser (193 nm) and X-rays, the exposure beam causes a stronger photochemical reaction.

And the proposal for solving this problem is made | formed (for example, refer patent document 1 and 2).
JP-A-6-216000 Japanese Patent Laid-Open No. 7-209569

  On the other hand, in the apparatus disclosed in Patent Document 1, a lens barrel having a glass member such as a lens is disposed in a sealed housing, and the inside of the housing is filled with an inert gas. We are solving the above problem.

  However, even in the above example using an inert gas, it has been found that the housing of the illumination optical system and the optical element inside the lens barrel are contaminated with organic molecules. These molecules are the chemicals used in the production and processing of the parts that make up each part of the illumination optical system, or the adhesive used on the housing and lens barrel. It is thought that a part of the agent was generated by evaporation.

  Furthermore, even in the manufacturing situation, the surrounding air is contaminated by organic molecules generated from the adhesive layer between the substrate and the photoresist, for example, and these molecules may enter the housing or the lens barrel. There is. Even if the concentration of organic molecules is small, the particles decompose due to the influence of the ultraviolet beam and precipitate on the optical element, and a carbon film or a film containing carbon is formed on these surfaces.

  In order to solve this, in the apparatus disclosed in Patent Document 2, when supplying an inert gas to the projection optical system, a small amount of ozone is mixed into the inert gas, and the inert gas containing ozone is removed from the optical system. To supply. Since the optical element is irradiated with an exposure beam in a gas containing ozone, decomposition of organic particles on the surface of the optical element and generation of deposits of decomposition products are prevented by a so-called ozone cleaning effect.

  However, in this apparatus, an ozone generator including a mercury lamp is provided in the middle of the inert gas supply line, and ozone is generated in advance by the ozone generator, and then ozone is supplied into the lens holder. Therefore, the exposure light source and two ozone generation light sources are necessary, and the apparatus is complicated. In addition, there are also the following risks. In other words, because ozone has the property of deteriorating objects, there is a problem that the ozone generator itself is likely to deteriorate due to the influence of ozone, and there is a risk that harmful ozone will leak out from the deteriorated ozone generator I am involved.

  SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the conventional apparatus, and it is an object of the present invention to solve the problem of contamination of optical elements due to organic molecules, and to provide an exposure apparatus that can solve it more easily and effectively. To do. Furthermore, it aims at providing the device manufacturing method using this exposure apparatus, and the optical element cleaning method of this exposure apparatus.

In order to achieve the above object, an optical element cleaning method for an exposure apparatus according to one aspect of the present invention is a method for cleaning a lens of an exposure apparatus that exposes a substrate with an exposure beam, the mirror being sandwiched between the lenses. Oxygen or clean air and an inert gas are supplied to the internal space of the tube and irradiated with the exposure beam to generate ozone in the internal space, and the photochemical reaction between the generated ozone and the exposure beam causes the lens to removing the organic compounds adhering, characterized in that it and a step of reducing the oxygen in the internal space by performing exhaust and supply of the inert gas to the interior space.

  According to the exposure apparatus of the present invention, the problem that organic molecules adhere to the surface of the optical element and the illuminance decreases can be solved. At this time, the exposure beam itself used for exposure is also used for ozone generation. Therefore, it can be realized without providing a large additional mechanism. In addition, since ozone is generated only in a closed space where the optical element is placed, there is no risk of harmful ozone leaking out.

  Since this exposure apparatus can always obtain high throughput, high productivity can be achieved in device manufacturing.

  Specific embodiments of the present invention will be described with reference to the drawings. The exposure apparatus of this example is a reduction projection type semiconductor exposure apparatus generally called a stepper or a scanner.

  The exposure apparatus main body A1 is roughly a light source 1 (ArF excimer laser light source) and a light source lens system 2 that is an illumination optical system that forms laser light L1 that is illumination light emitted from the light source 1 into a light east of a predetermined shape. And a projection lens system 5 that is a projection optical system that forms an image of the laser light L1 shaped into a predetermined shape by the light source lens system 2 on a wafer 4 that is a substrate through a reticle 3. The light source 1 has a laser control device 6 that controls its laser output, and the laser control device 6 is controlled by a controller 7 as control means. As will be described later, the laser control device 6 can change the oscillation laser wavelength band.

  In this example, an ArF excimer laser light source that generates ultraviolet rays is used as a light source. However, a KrF excimer laser light source or an X-ray having a shorter wavelength (generally called soft X-rays or vacuum ultraviolet rays are called X-rays) is generated. It may be an X-ray source such as a laser plasma radiation source or a synchrotron radiation source.

  The light source lens system 2 includes lens barrels 2h and 2i in which a plurality of lenses 2a to 2d for shaping the laser light L1 into a light beam having a predetermined shape are arranged, and these lens barrels are accommodated in a container 2g. On both sides, mirrors 4a and 4b for accommodating the laser beam by bending are accommodated. The container 2g of the illumination optical system is provided with a detachable window 2e at the entrance facing the light source L, and a window 2f at the entrance facing the reticle 3.

  In the projection optical system 5, a plurality of lenses 5a and 5b for reducing and projecting a pattern on a reticle onto a wafer are built in a lens barrel, and the lens barrel has a surface facing the reticle and a surface facing the wafer. Windows 5c and 5d are provided, respectively.

  Here, each of the internal space 2j of the container 2g of the illumination optical system 2, the internal space of the lens barrels 2h and 2i, and the space delimited by the lenses in the lens barrel of the projection lens 5 is an inert gas. Nitrogen gas (may be helium or neon) is supplied. For this purpose, an inert gas supply device 8a is provided. The inert gas supply device 8a is connected to each space via an inert gas supply line 8b and an electromagnetic valve 8c which is an on-off valve provided in the middle of the inert gas supply line 8b. Further, an oxygen supply line 10b is branched and connected in the middle of the inert gas supply line 8b, and an oxygen supply device 10a is connected via an electromagnetic valve 10c that is an on-off valve provided in the middle. This makes it possible to mix a small amount of oxygen into the inert gas supplied. Note that clean air containing oxygen may be mixed instead of pure oxygen.

  Further, in order to discharge gas from each of the above-mentioned spaces to which an inert gas is supplied, a gas exhaust device 9a is provided, and a gas exhaust line 9b from each space and an electromagnetic valve 9c which is an on-off valve provided in the middle of the line. And is connected to the gas exhaust device 9a.

  The gas recovered by the gas exhaust means contains a small amount of residual ozone. A converter for reconverting this into oxygen is provided in the gas exhaust device 9a, and the reconverted oxygen is passed through a filter. After removing the impurities, the oxygen supply device 10a may be refluxed and reused.

  The solenoid valves 8c and 9c provided in the middle of the lines of these inert gas supply means and gas exhaust means are controlled by a program preset in the controller 7, and each space is used during normal use (exposure) and The state filled with the inert gas is maintained during standby.

  Specifically, at a preset timing, the electromagnetic valve 10c on the oxygen supply line is opened at the time of standby of the apparatus, and a small amount of oxygen is mixed into the nitrogen gas. Is supplied into the barrel of the projection optical system. The opening and closing of the solenoid valve is controlled so that the supply amount of oxygen is not more than a predetermined concentration (several grams or less per 1 m3). After this mixed gas is supplied, the solenoid valves 8c and 9c are closed. Laser light irradiation is performed while the nitrogen gas is filled with a gas in which a small amount of oxygen is mixed. Thereby, oxygen in the inert gas filled in each space is converted into ozone by a photochemical reaction, and ozone is generated only in each space. In this state, further irradiation with laser light is continued to oxidize the organic compound deposited on the optical element (lens, mirror, window, etc.) constituting the optical system. Thereby, organic molecules on the optical element are removed and cleaned by ozone cleaning.

  Thereafter, the solenoid valves on the inert gas supply line and the gas exhaust line are opened, and the supply and exhaust of the inert gas are continued continuously or intermittently until the gas is completely replaced with nitrogen gas. These series of operations are performed based on a program preset in the controller. Note that it is preferable to clean the optical element when the exposure apparatus is not in operation because it does not affect the throughput. Further, cleaning may be performed during actual operation of the apparatus.

  By the way, the efficiency of generating ozone from oxygen by light irradiation greatly depends on the wavelength of the irradiation light. Therefore, it is preferable to change the exposure beam wavelength between when the substrate is exposed and when the optical element is cleaned so that ozone is generated more efficiently. That is, it is preferable to continuously shift the wavelength band during cleaning, or to switch to a shorter wavelength side to increase the ozone generation efficiency and hence the cleaning ability. Changing the wavelength can be achieved by controlling the driving of the light source or inserting a wavelength conversion means (such as a harmonic generation element) in the optical path.

  FIG. 2 is an enlarged view of the vicinity of the outlet of the inert gas supply line in the lens barrel 2h of the illumination optical system. In particular, the optical elements 13a and 13b, which are expected to have a large amount of organic molecules, are configured such that an inert gas is directly blown onto the optical elements. Thereby, the effect of ozone cleaning is further enhanced.

  Note that a flow rate switching means as shown in Patent Document 1 or the like may be provided in the inert gas supply line so as to supply a large flow rate of nitrogen during the impurity removal operation.

  As an optical element of the exposure apparatus, a filter that transmits only a desired wavelength from a wide wavelength band emitted from a light source such as a mercury lamp or a synchrotron radiation source is used in addition to the lens, mirror, and window described above. In some cases, the effect of the present invention can be expected as described above.

  Next, an example of a device manufacturing method using the above-described exposure apparatus will be described. FIG. 9 shows a flow of manufacturing a microdevice (a semiconductor chip such as an IC or LSI, a liquid crystal panel, a CCD, a thin film magnetic head, a micromachine, etc.). In step 1 (circuit design), a device pattern is designed. In step 2 (mask production), a mask on which the designed pattern is formed is produced. On the other hand, in step 3 (wafer manufacture), a wafer is manufactured using a material such as silicon or glass. Step 4 (wafer process) is called a pre-process, and an actual circuit is formed on the wafer by lithography using the prepared mask and wafer. The next step 5 (assembly) is referred to as a post-process, and is a process for forming a semiconductor chip using the wafer produced in step 4, such as an assembly process (dicing, bonding), a packaging process (chip encapsulation), and the like. including. In step 6 (inspection), inspections such as an operation confirmation test and a durability test of the semiconductor device manufactured in step 5 are performed. Through these steps, the semiconductor device is completed and shipped (step 7).

  FIG. 10 shows a detailed flow of the wafer process. In step 11 (oxidation), the wafer surface is oxidized. In step 12 (CVD), an insulating film is formed on the wafer surface. In step 13 (electrode formation), an electrode is formed on the wafer by vapor deposition. In step 14 (ion implantation), ions are implanted into the wafer. In step 15 (resist process), a resist is applied to the wafer. In step 16 (exposure), the circuit pattern of the mask is arranged in a plurality of shot areas on the wafer and printed by the exposure apparatus described above. In step 17 (development), the exposed wafer is developed. In step 18 (etching), portions other than the developed resist image are removed. In step 19 (resist stripping), unnecessary resist after etching is removed. By repeating these steps, multiple circuit patterns are formed on the wafer. By using the production method of this embodiment, it is possible to produce a high-precision device that has been difficult to produce with high productivity.

It is explanatory drawing explaining the whole structure of an Example. It is a figure explaining the example inside a lens-barrel. It is a figure which shows the flow of a device manufacturing method. It is a figure which shows the detailed flow of a wafer process.

Explanation of symbols

A1 exposure apparatus 1 excimer laser 2 illumination optical system 2a to 2d lens 2e, 2f window 2g container 2h, 2i barrel 2j container inner space 3 reticle 4 wafer 5 projection optical system (projection lens barrel)
5a, 5b Lens 5c, 5d Window 6 Laser control device 7 Controller 8a Inert gas supply device 8b Inert gas supply line 8c Solenoid valve 9a Gas exhaust device 9b Gas exhaust line 9c Electromagnetic valve 10a Oxygen supply device 10b Oxygen supply line 10c Electromagnetic Valve 11 Lens barrel 12 Inert gas supply line

Claims (4)

A method of cleaning a lens of an exposure apparatus that exposes a substrate with an exposure beam,
Oxygen or clean air and an inert gas are supplied to the inner space of the lens barrel sandwiched between the lenses to irradiate the exposure beam to generate ozone in the inner space, and the generated ozone and the exposure beam Removing an organic compound adhering to the lens by a photochemical reaction of
A method for reducing the oxygen in the internal space by supplying and exhausting an inert gas to the internal space, and a lens cleaning method for an exposure apparatus. The method according to claim 1, wherein the wavelength of the exposure beam is changed between when the substrate is exposed and when the lens is cleaned. The method according to claim 1, wherein the wavelength of the exposure beam is continuously changed when the lens is cleaned. An exposure apparatus that exposes a substrate with an exposure beam,
A lens for guiding the exposure beam to the substrate;
An inert gas supply device for supplying an inert gas to the internal space of the lens barrel sandwiched between the lenses ;
An oxygen supply device for supplying oxygen or clean air to the internal space;
A gas discharge device for discharging gas from the internal space,
Attached to the lens by photochemical reaction of the inner space and supplying oxygen or clean air and an inert gas ozone to generate in its interior space by irradiating the exposure beam, wherein the exposure beam and the generated ozone Removing organic compounds,
An exposure apparatus comprising: supplying and exhausting an inert gas to the internal space to reduce oxygen in the internal space.

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