Photocopying – Projection printing and copying cameras – With temperature or foreign particle control
Reexamination Certificate
1999-03-12
2003-03-18
Nguyen, Hung Henry (Department: 2851)
Photocopying
Projection printing and copying cameras
With temperature or foreign particle control
C355S053000
Reexamination Certificate
active
06535270
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an exposure apparatus used for generating fine patterns for various products including semiconductor circuits (Ics), liquid crystal displays (LCDs) and the like, as well as to air-conditioning apparatus for use with such exposure apparatus. More particularly, the present invention relates to apparatus for effecting air-conditioning of a chamber which houses all or some of the components of an exposure apparatus for transferring a pattern formed on a mask onto a photosensitized substrate by exposure, including a light source, an illumination optical system, an exposure unit and others, in order to eliminate or minimize any harmful effects of impurities in the chamber.
A clean room used in fabrication of semiconductor devices is provided with an air purification system for removing particulate contaminants from the air in the room, and such air purification system typially uses high efficiency particulate air (HEPA) filters and/or ultra low penetration air (ULPA) filters. Various equipment and apparatus are used in the fabrication of semiconductor devices, among which exposure apparatus using ultraviolet (UV) light or deep-ultraviolet (DUV) light for exposure have been commonly used. In an exposure apparatus of this type, gaseous impurities in the surrounding atmosphere may undergo certain chemical and/or physical changes and form adhesive substances that tend to adhere to the surface of glass optical elements such as lenses and mirrors, resulting in blurring and/or reduced transmittance of the elements. For example, ammonium ions (NH
4
) and sulfur oxides (SOx), two typical, harmful gaseous impurities, form an adhesive layer of ammonium sulfate ((NH
4
)
2
SO
4
) on a surface of a glass optical element.
Thus, for long-term, continuous and effective operation of an exposure apparatus using a UV or DUV light source, it is required that the space along the light path of the light beam from the light source be filled with a gas having no sensitivity to UV or DUV radiation such as nitrogen and helium, or with an environmental gas (ambient air) having any harmful gaseous impurities removed therefrom. A known technique used for this purpose is to confine the space along the light path of the exposure light beam to an airtight chamber, and fill the chamber with a gas having no sensitivity to exposure radiation. The gas is supplied from a suitable gas supply device such as a gas cylinder or a gas storage tank. Another known technique used for this purpose is to supply ambient air outside the exposure apparatus to the illumination optical system in the exposure apparatus, after the air has been passed through an impurity-removing filter such as a chemical filter to remove any harmful gaseous impurities from the air.
Chemical filters can remove, unlike HEPA and ULPA filters, gaseous impurities from the environmental gas. Various chemical filters are commonly used, including those using fibrous or granulate activated carbon, those utilizing ion exchange reaction provided by various ion exchange resins, and those using fibrous activated carbon with some sort of agent added. Examples of chemical filters utilizing an ion exchange reaction are products bearing a trademark “EPIX” available from Ebara Corporation in Japan. Examples of chemical filters using fibrous activated carbon with some sort of agent added are products bearing a trademark “CLEAN SORB” available from Kondo Kogyo Co, Ltd. in Japan.
Various resists are used in photolithographic process in order to form patterns on a substrate, among which chemically sensitized resists have become common recently. In general, chemically sensitized resists consist of a resin, a photosensitive acid generator (PAG), and either a dissolution promotor (for positive resists) or a cross-linking agent (for negative resists). When exposed to exposure radiation, the photosensitive acid generator generates an acid. During the post-exposure baking process, the acid acts as a catalyst. In the case of a positive resist, the catalyst increases the activity of the dissolution promotor to break cross-links between the polymer molecules. In the case of a negative resist, the catalyst increases the activity of the cross-linking agent to form cross-links between the polymer molecules. In both cases, a pattern is formed with the aid of the catalyst during the following development process, in which a positive resist using a dissolution promotor forms positive patterns while a negative resist using a cross-linking agent forms negative patterns on the substrate. Examples of the positive chemically amplified resists are products bearing a trademark “FH-EX1” available from Fuji-Hunt Corporation. Examples of negative chemically amplified resists are products bearing a trademark “XP” available from Shipray Corporation.
When a chemically sensitized resist is used, some basic gaseous impurities (ammonia and amines, for example) in the local atmosphere around the substrate and acid generated from the photosensitive acid generator may cause a neutralization reaction during the time interval between exposure to post-exposure baking, resulting in reduced sensitivity. Further, in the case of a positive resist this also results in the formation of a dissolution-resistant surface layer, which may affect the pattern transfer process. A commonly used technique used to avoid the adverse effects of such gaseous impurities is to fill the process atmosphere for the sequence of processes from the application process of chemically sensitized resist on a substrate (or from the exposure process of a substrate applied with chemically amplified resist) to post-exposure baking with a clean gas containing no impurities.
More specifically, where this technique is used to avoid adverse effects of gaseous impurities, a chamber is used to house the entire exposure apparatus or at least a critical part thereof. The chamber has an air inlet through which ambient air is introduced into the chamber. The air inlet is provided with a gaseous-impurity-removing device, such as a chemical filter, for preventing any gaseous impurities from entering the chamber. In addition, the chamber is provided with a second chemical filter for removing any gaseous impurities from a gas stream recirculating in the chamber.
However, the above prior art technique suffers from several problems as described below. First, a problem arises relating to the filters used. Chemical filters are commonly used as gaseous-impurity-removing devices. The impurity removal efficiency of a chemical filter, however, tends to gradually decrease as more gaseous impurities are caught and removed by the filter. The rate of decrease in the impurity removal efficiency depends on several factors including the concentrations of the gaseous impurities contained in the environmental gas in which the chemical filter is used, as well as the humidity of the environmental gas. An even rate of operation of the semiconductor device factory equipped with an exposure apparatus may cause significant changes in the concentrations of the gaseous impurities in the environmental air of the exposure apparatus.
An impurity-removing filter element has to be replaced when its impurity removal efficiency has dropped below a minimum acceptable level. Typically, the life of a filter element is defined as the point of time when its impurity removal efficiency has decreased to a predetermined threshold level. However, the rate of degradation of a filter element depends on environmental conditions as described above, and impurity concentrations in different environments of respective filter elements are quite different from each other, so that it is difficult to predict with precision when a particular filter element has reached the end of its effective life.
In order to determine the impurity removal efficiency of a filter element used with an exposure apparatus, it is required to set a gas-concentration-measuring device on the exposure apparatus for measurement at regular intervals. However, this may result in
Armstrong Westerman & Hattori, LLP.
Nguyen Hung Henry
Nikon Corporation
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