Method and device for replacing objective parts

This is a Continuation of International Application PCT/EP2007/061563, with an international filing date of Oct. 26, 2007, which was published under PCT Article 21(2) in German, and the complete disclosure of which, including amendments, is incorporated into this application by reference.

The present invention relates to a method and a device for replacing objective parts, especially of a projection or illumination objective for microlithography.

Modern lenses in lithography increasingly have replaceable or exchangeable elements, such as replaceable or exchangeable lenses, filters, diaphragms and the like. US 2006/0176460 A1 describes, for example, an EUV (extreme ultraviolet) lithography system having optical elements, such as mirrors and the like, which are individually selectable for use, wherein the optical elements are not replaced, in the sense of being moved into and out of the objective, but rather are exchanged only in the form of a rotatable turret. However, this imposes a very high space requirement.

WO 2006/069755 A1 describes, in contrast, a replaceable optical element of an objective module of a lithography system, which can be completely removed from the objective, wherein a proposal is made to avoid contamination of the objective room by providing a load-lock chamber.

When parts located in the highly clean, gas-flushed or evacuated objective interior are replaced, there is a problem that the process of replacement can introduce impurities into the objective. In addition to contamination via the gas room during the replacement, contaminants adhering to the replaceable components can be introduced into the objective, said contaminants subsequently capable of leading to a deterioration of the objective characteristics. Possible contaminants in this context are particularly hydrocarbons, water deposits and other particles.

The hydrocarbons, which are mostly present in the form of monolayers on the surface of the replacement parts, mostly do not become detached until irradiation with the objective light used for imaging, for example, UV laser light. Accordingly, unless further cleaning takes place, this means that hydrocarbons are present in the objective and can then enter into chemical reactions at undesirable regions, and so lead to deposits on the optical elements. As a result, the imaging properties of the objective are impaired.

Similar considerations apply to monolayers of water, which are also present on replacement parts that are exposed to the ambient atmosphere. In the normally extremely dry environment within the objective, the water monolayers desorb or evaporate and are then also in the objective, as a result of which ozone, which is highly reactive, can form due to UV light. The water molecules, too, can then enter into reactions, for example, with hydrocarbons that are also present in the objective interior or with other components in the objective interior, such that, due to the monolayers of water as well, deposits can form on the surfaces of the optical elements, especially salts. To prevent imaging damage, US 2006/0001854 A1 accordingly proposes the provision of optical elements having several usable areas in the objective, such that, following contamination of one area, a different, clean area can be moved into the beam, while the contaminated area can be cleaned.

JP 11288870 A proposes exchanging contaminated areas and subsequent cleaning of the contaminated areas for a protective device between the projection objective and the wafer of a lithography system.

A further problem of replaceable components of the optical system of a lithography system is that particles adhering to the replacement parts can become detached from the replacement parts and precipitate on the surfaces of the optical elements, a fact which also impairs the imaging properties.

These problems have so far been counteracted by cleaning the replaced objective parts or the objective interior with cleaning gas for an adequate length of time. As a result, the desorbed or evaporated water monolayers or the hydrocarbons or residual parts thereof which have been transferred into the gas phase during illumination are driven out of the objective, such that the corresponding negative deposits are avoided.

However, this approach has the disadvantage that, first, the contaminants are introduced into the objective interior and there is a risk that, on account of the subsequent cleaning, said contaminants are not completely removed from the objective interior, such that, for example, a device according to US 2006/0001854 A1 is required. Furthermore, this approach means that the objective is inoperable for a long period because, during this time, cleaning takes place after the corresponding parts of the objective have been replaced.

Accordingly, the proposed solution was to avoid contamination of replaceable objective parts by preventing the parts for installation into the objective from being exposed to the ambient atmosphere after production and cleaning. This means, however, that the entire transport chain from storage to transport right into the objective must be carried out in a correspondingly clean atmosphere, a fact which represents considerable outlay. Moreover, there is a risk that, in storage, tiny amounts of contaminants in the sealed atmosphere around the replaceable objective part will in turn lead to deposits.

It is therefore an object of the present invention to provide a method and a device to replace objective parts for the purpose of largely avoiding introduction of contaminants into the objective interior, wherein the replacement is to be conducted in an effective and easy way. Especially, rapid replacement of objective parts with short downtimes for the objective is to be made possible while the problems of the prior art are avoided.

The above-mentioned objects are achieved, in whole or in part by methods, cleaning devices, objectives and systems as disclosed and claimed herein. Advantageous embodiments are also disclosed and claimed in particular through dependent claims.

The present invention proceeds from the insight that the introduction of contaminants into the objective interior can be effectively prevented during objective parts replacement by cleaning the replaceable objective part outside the objective interior immediately prior to installation into the objective and immediately installing it in the objective after the cleaning and without contact with the normal ambient atmosphere. Instead of downstream cleaning of optical elements which become contaminated by contaminants present in the objective, as is proposed in US 2006/0001854 A1, the approach of the present invention is pre-emptive avoidance of contamination. The immediate installation of the replaceable objective part in the objective immediately after cleaning, without further contact with the normal ambient atmosphere, has the advantage of minimising the effort of handling the cleaned objective part under exclusion of the normal ambient atmosphere, and also prevents contaminant deposits from recurring on the replaceable objective part after cleaning. Similarly, immediate installation directly after cleaning means that only as much time is available until commencement of transfer into the objective as is necessary for the stages of the transfer process, or, that less time remains than is required for appreciable deposition of contaminants. Essentially, therefore, the immediate installation proceeds without any time delay directly after cleaning of the replaceable objective part. However, in isolated cases, short intermediate storage times ranging from a few minutes to several hours are possible. In normal circumstances, however, installation of the replaceable objective part is commenced or completed less than 30 minutes, preferably less than 15 minutes, especially from a few minutes to several seconds after cleaning.

The replaceable objective parts can be all parts present in an objective or optical system, particularly optical lenses, mirrors, mirror elements, filters, diaphragms, membranes and the like.

By replaceable is particularly understood that the corresponding objective part can be removed completely from the objective interior, i.e. completely leaves a housing that seals the objective interior. Accordingly, replaceable objective parts differ from merely exchangeable objective parts in that, in the removed state, they are completely separate from the objective or can be simply separated from it.

By objective is understood any optical system, even where no object is imaged onto an image plane, for example, illumination systems of microlithography systems. The corresponding objectives or optical systems can be operated at all kinds of wavelengths, especially the wavelengths used for microlithography in the range of 248 nm, 193 nm, 157 nm as well as in the extreme ultraviolet light range of wavelengths less than 30 nm, especially in the range of 13 nm and 13.5 nm. Generally, the invention can be realized for optical systems that use all kinds of wavelengths.

Cleaning of the replaceable objective part takes place in a sealed cleaning room to ensure that defined cleaning can take place. Preferably, the cleaning room has a cleaning atmosphere different from that of the ambient atmosphere, such that precisely the contaminants in the ambient atmosphere, such as water, hydrocarbons and particles can be removed effectively from the objective part to be cleaned. The cleaning atmosphere can be formed by vacuum, dry air, nitrogen, dry nitrogen, argon, oxygen, helium, hydrogen, general inert gases or noble gases and combinations thereof.