Method for preventing or reducing contamination of an immersion type projection apparatus and an immersion type lithographic apparatus

A method for preventing or reducing contamination of an immersion type projection apparatus is provided. The apparatus includes at least one immersion space that is at least partially filled with a liquid when the apparatus projects a beam of radiation onto a substrate. The method includes rinsing at least part of the immersion space with a rinsing liquid before the apparatus is used to project the beam of radiation onto a substrate.

FIELD

The present invention relates to a method for preventing or reducing contamination of an immersion type projection apparatus. The present invention also relates to an immersion type lithographic apparatus.

BACKGROUND

It has been proposed to utilize immersion lithography, for example using an immersion type lithographic apparatus. As an example, it has been proposed to immerse the substrate in a lithographic projection apparatus in an immersion liquid having a relatively high refractive index, e.g. water, so as to fill the space between the final optical element of the projection lens and the substrate. The point of this is to enable imaging of smaller features because the exposure radiation will have a shorter wavelength in the liquid than in air or in a vacuum. (The effect of the liquid may also be regarded as increasing the effective NA of the system).

Submersing the substrate or substrate and substrate table in a bath of liquid (see for example U.S. Pat. No. 4,509,852) means that there is a large body of liquid that must be accelerated during a scanning exposure. This may require additional or more powerful motors and turbulence in the liquid may lead to undesirable and unpredictable effects.

It has also been proposed to apply a liquid supply system to provide liquid on only a localized area of the substrate and in between the final optical element of the projection system and the substrate (the substrate generally has a larger surface area than the final optical element of the projection system). Ways which have been proposed to arrange for this are disclosed, for example, in WO 99/49504 and EP 1 429 188 A2.

SUMMARY

It is desirable to prevent or reduce contamination in an immersion type projection apparatus.

According to an embodiment of the invention, there is provided a method for preventing or reducing contamination of an immersion type projection apparatus. The apparatus includes at least one immersion space that is at least partially filled with a liquid when the apparatus projects a beam of radiation onto a substrate. The method includes rinsing at least part of the immersion space with a rinsing liquid before the apparatus is used to project the beam of radiation onto a substrate.

According to another embodiment, there is provided a method for preventing or reducing contamination of a lithographic projection apparatus. The apparatus includes a substrate holder constructed to hold a substrate, a patterning device holder constructed to hold a patterning device, a projection system, and an immersion system configured to at least partially fill an immersion space of the apparatus with a liquid. The method includes moving at least one of the immersion system and at least part of the apparatus relative to each other, and rinsing the at least part of the apparatus with the liquid before the apparatus is used to project a patterned beam of radiation onto a target portion of a substrate.

According to another embodiment, there is provided a method for preventing or reducing contamination of a lithographic projection apparatus. The apparatus includes an immersion space. The method includes filling at least part of the immersion space with a rinsing liquid for at least one minute.

According to an embodiment, there is provided a method for preventing or reducing contamination of a lithographic projection apparatus. The apparatus includes a substrate holder constructed to hold a substrate, a patterning device holder constructed to hold a patterning device, a projection system, and an immersion space. The method includes filling at least part of the immersion space with a rinsing liquid during an idle time of the apparatus to prevent or reduce substrate contamination during at least one subsequent start-up run of the apparatus.

According to an embodiment, there is provided an immersion type lithographic apparatus that includes at least one immersion space, and an immersion system configured to at least partially fill the immersion space with a liquid. The apparatus is configured to rinse at least part of the immersion space with a rinsing liquid before the apparatus is used to project a patterned beam of radiation onto a substrate.

According to an embodiment, there is provided an immersion type lithographic apparatus that includes at least one storage space or compartment to store at least one dummy substrate or substrate shaped object in-situ.

According to an embodiment, there is provided an immersion type lithographic apparatus that includes at least one storage space or compartment to store at least one dummy patterning device or patterning device shaped object in-situ.

According to an embodiment, there is provided a computer program containing one or more sequences of machine-readable instructions configured to carry out a method for preventing or reducing contamination of an immersion type projection apparatus when the computer program is being executed by a computer. The apparatus includes at least one immersion space that is at least partially filled with a liquid when the apparatus projects a beam of radiation onto a substrate. The method includes rinsing at least part of the immersion space with a rinsing liquid before the apparatus is used to project the beam of radiation onto a substrate.

According to an embodiment, there is provided a method for preventing or reducing contamination of a lithographic projection apparatus. The apparatus includes a space that is to be provided with a liquid through which a beam of radiation can be transmitted. The method includes operating the lithographic apparatus, and subsequently rinsing at least part of the space with a rinsing liquid.

DETAILED DESCRIPTION

In the present application, the same or similar features are generally denoted by the same or similar reference signs.

FIG. 1schematically depicts a projection apparatus1according to one embodiment of the invention.

According to an embodiment of the invention, the apparatus1is a lithographic apparatus, and is arranged to project a pattern from a patterning device MA onto a substrate W.

In an embodiment of the present invention, the projection apparatus1is of a type wherein at least a portion of the substrate is covered by a liquid having a relatively high refractive index, e.g. water or an other suitable liquid, so as to fill an immersion space10between the projection system and the substrate (seeFIG. 2). An immersion liquid may also be applied to other spaces10′ in the lithographic apparatus1, for example, between the mask MA and the projection system PS (seeFIG. 4). Immersion techniques as such are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but generally only means that liquid is located between the projection system on one side and the substrate and/or mask MA on an opposite side during exposure. For example, the apparatus can have a similar construction as the apparatus described in EP 1 429 188 A2, which has been incorporated in the present application by reference in its entirety, or a different construction.

FIG. 2shows a detail of the apparatus ofFIG. 1.FIG. 2depicts an immersion space10which abuts at least part of a projection system PS. Particularly, inFIG. 2, the immersion space10extends between a final optical element PL of the projection system PS and a substrate W or substrate shaped object W, which is positioned on a substrate table WT. The apparatus1includes an immersion system, comprising inlet/outlet ducts13. During use, the immersion system fills the immersion space10with a liquid11having a relatively high refractive index, e.g. water, via inlet/outlet ducts13. The liquid has the effect that the radiation of the projection beam has a shorter wavelength in the liquid than in air or in a vacuum, allowing smaller features to be resolved. It is well known that the resolution limit of a projection system is determined, inter alia, by the wavelength of the projection beam and the numerical aperture of the system. The presence of the liquid may also be regarded as increasing the effective numerical aperture. Furthermore, at fixed numerical aperture, the liquid is effective to increase the depth of field.

The configuration of the apparatus can be such that a substantially contactless seal is formed to the substrate W around the image field of the final optical element PL so that the liquid is confined to fill the space between the substrate's primary surface, which faces the projection system PS, and the final optical element PL of the projection system PS. A reservoir, providing the immersion space10, can be formed by a seal member12, for example an ‘immersion hood’, positioned below and surrounding the final optical element PL of the projection system PS. Thus, the immersion system can be arranged to provide immersion liquid on only a localized area of the substrate W. The seal member12can form part of the liquid supply system for filling the space between the final optical element PL of the projection system PS and the substrate W with a liquid. This liquid is brought into the space below the final optical element PL and within the seal member12. The seal member12preferably extends a little above the final optical element PL of the projection system PS and the liquid rises above the final optical element PL so that a buffer of liquid is provided. The seal member12can have an inner periphery that at the upper end closely conforms to the shape of the projection system PS or the final optical element PL thereof and may, e.g. be round. At the bottom the inner periphery closely conforms to the shape of the image field, e.g. rectangular, though this is not necessarily so. The seal member12can be substantially stationary in the XY plane relative to the projection system PS though there may be some relative movement in the Z direction (in the direction of the optical axis). A seal can be formed between the seal member12and the surface of the substrate W, to confine immersion liquid11in the immersion space10. This seal is preferably a contactless seal and may be a gas seal (not shown).

Also, the substrate table WT can be provided with a cover plate or edge seal member17. Such an edge seal member17can have an upper (as illustrated) primary surface substantially co-planar with the upper primary surface of substrate W and is closely adjacent to the edge of the substrate W so that there is no sudden loss of liquid as the edge of the substrate moves under the final optical element PL. Some liquid loss into the gap may still occur.

Of course there are arrangements in which the whole construction illustrated inFIG. 2is positioned upside down so that it is the lower surfaces of the edge seal member and the substrate which face the projection system and which are substantially co-planar. The surfaces are therefore be referred to as the primary surfaces which face the projection system PS rather than upper surfaces. References herein to upper surfaces and lower surfaces may be also appropriately considered as references to lower and upper surfaces respectively in an upside-down configuration.

With such an apparatus, a liquid supply system (e.g. immersion space10) can be positioned over the edge of the substrate W and can even be moved completely off the substrate W. This enables edge portions of the substrate W to be imaged during a device manufacturing method, carried out by the apparatus.

The edge seal member17can be provided in various ways, and may, for example, form an integral part of the substrate table WT or may be temporarily mounted relative to the remainder of the substrate table by the use of, for example, vacuum suction or through use of electromagnetic forces. Also, the edge seal member17may be formed of several individual segments, each of which surrounds a portion of the edge of the substrate W.

According to an embodiment, the projection apparatus comprises at least one said immersion space10and a respective immersion system which is configured to at least partially fill the immersion space10with an immersion liquid11. The apparatus can be configured to rinse at least part of the immersion space10with a rinsing liquid11before the apparatus is used to project the patterned beam of radiation onto a substrate W. For example, in an embodiment, the apparatus is being configured to rinse at least part of the immersion space during a relatively long idle operational mode of the apparatus. The apparatus can be configured to rinse the immersion space substantially continuously until the apparatus projects a patterned radiation beam onto a substrate.

It is advantageous when the apparatus is configured to rinse the immersion space with said immersion liquid11. Then, the immersion liquid and rinsing liquid are simply the same liquid11, so that the apparatus does not have to be provided with a special cleaning device to supply a particular cleaning liquid to the immersion space.

In an embodiment, the apparatus can be configured to provide an object in said immersion space10and/or in an adjoining position with respect to the immersion space10during the rinsing of that space10, and to remove said object before the apparatus is used to project a patterned radiation beam onto a target portion of a substrate. Said object can include, for example, a virgin (non-coated) wafer, a dummy wafer or a wafer shaped object. For example, as is shown inFIG. 1, the apparatus can include at least one storage space or compartment22, H to store said object when the apparatus is used to project a patterned radiation beam onto a target portion of a normal (resist coated) substrate. Said storage space or compartment22, H can be provided at various different locations of or near the apparatus. For example, such a storage space or compartment can be located in or near the substrate stage2of the apparatus, as has been schematically depicted by box22inFIG. 1. Such a storage space or compartment can be arranged in various ways, and can include a closable container, a substrate storage box, a substrate robot gripper or any other suitable substrate holder or substrate storing means. Such a storage space or compartment is preferably located within the apparatus1, for example near said immersion system (in substrate handler is described in the following).

Alternatively, said storage space or compartment can include or be part of a substrate handler H, which is located outside the substrate stage2of the apparatus1. Such a substrate handler H as such is known to the skilled person. Usually, such a substrate handler H can be configured to receive one or more substrates from an environment of the apparatus1, to temporarily store the one or more substrates and to transfer the one or more substrates to the substrate support WT, to be subsequently illuminated by the projection system PS. In the present embodiment, for example, the substrate handler H can be configured to hold or store one or more substrates, dummy substrates and/or substrate shaped objects during a desired period of time, before such a substrate, dummy substrate and/or substrate shaped object is located on a respective substrate table WT during a rinsing process, for example during an idle operational period of the apparatus1.

Besides, the apparatus1can include a mechanism (not specifically shown) which is arranged or configured to transfer substrates W from such a storage space or compartment22, H to a substrate holder WT, and vice-versa. Such a mechanism is known to the skilled person. For example, the substrate handler H and substrate support WT can be arranged or configured in various ways to transfer substrates therebetween. For example, one or more robot arms, conveyors, transport means or other transfer mechanisms can be provided to move substrates, dummy substrates or substrate shaped objects from and to desired substrate positions.

Further, the apparatus can include at least one ultra violet radiation source to illuminate the immersion space10with ultraviolet radiation during the rinsing of that space, before the apparatus is actually used to transfer a patterned radiation beam onto a normal (resist coated) substrate. For example, the above-mentioned radiation source SO may be arranged and configured to be such an ultra violet radiation source. On the other hand, one or more different radiation sources can be provided to illuminate the immersion space10with ultraviolet radiation during the rinsing.

In the embodiment shown in theFIGS. 1 and 2, said immersion space10can extend between at least part of a substrate, a dummy substrate, a substrate-shaped object W and/or substrate table or holder WT,17on one side and a projection system PS on an opposite side during use. Said dummy substrate can be, for example, a bare silicon wafer, which has not been provided with a resist coating layer. For example, as has been mentioned above, the apparatus can be configured to place a dummy substrate or a substrate-shaped object on said substrate holder WT, and to subsequently rinse the respective immersion space10. Also, the apparatus can be configured to have the immersion space10at least reach or include an outer contour of a substrate, dummy substrate or substrate-shaped object W, being held by said substrate holder WT, during the rinsing. This is shown inFIG. 3. For example, the apparatus can be configured to rinse at least an area of the substrate support WT (using said rinsing liquid), which area extends along and/or around an edge of a substrate, dummy substrate or substrate-shaped object, being held by the substrate holder WT. In that case, relatively low particle per substrate counts can be obtained when the apparatus is used subsequently to illuminate normal substrates as part of a lithography process. For example, the apparatus can be configured to rinse at least part of a surface of the substrate holder WT and/or at least part of a surface of the substrate edge seal member17of the substrate holder WT, using said immersion space10and said rinsing liquid.

Besides, in an embodiment, the apparatus can be configured to move said substrate holder WT with respect to said projection system PS during the rinsing or cleaning process, such that the position of the immersion space10changes with respect to the substrate holder during the rinsing. This is shown inFIGS. 2 and 3by arrows Q and R. InFIG. 2, the arrow Q indicated a lateral movement of the substrate holder WT with respect to the projection system PS and immersion space10.

InFIG. 3, the arrow R indicates the scanning of the immersion space10along an edge of the substrate or substrate shaped object W, circumferentially with respect to the substrate or substrate shaped object W, from a first position101of the immersion space10to a second position102. In this way, the inner part of the surface of the substrate holder WT, or of the respective substrate edge seal member17, that extends near a substrate W during a lithography use of the apparatus, can be rinsed with rinsing liquid. Also, in this way, contamination can be removed from an edge slit E extending between the substrate or substrate shaped object W on one side and the substrate holder, or optional edge seal member17, on an opposite side relatively well.

Besides, the surface of the substrate holder WT surrounding the substrate W during use can include other components21, such as sensors, positioning devices, mirror elements and/or other components, as has been schematically depicted inFIG. 3. In an embodiment of the invention, the scanning of the immersion space is such, that those components21can also be reached by the immersion system, to rinse the outer surfaces of these components21.

Movement of the substrate holder WT to scan the immersion space10with respect to the substrate holder WT can be carried out in various directions, for example in the directions Q, R as shown inFIGS. 2 and 3and/or in various other scanning directions, as will be clear to the skilled person.

In an embodiment of the invention, the apparatus is configured to start said rinsing automatically after a predetermined amount of idle time of the apparatus. Also, the apparatus can be configured to start said rinsing automatically after a predetermined number of lithographic substrate exposures (when a patterned radiation beam is being projected onto the substrates). Moreover, in an embodiment, the apparatus can be configured to determine or estimate whether at least part of said apparatus has reached a certain threshold amount of contamination, and to rinse said apparatus part when it has been determined or estimated that that apparatus part has reached the threshold amount of contamination. Besides, as has been shown schematically inFIG. 1, the apparatus can comprise a computer control CU to control the apparatus, or to at least control said rinsing. Such a computer control CU can be configured, for example, to control the timing of the starting of the rinsing process, to count numbers of substrate exposures in order to start the rinsing process and/or to estimate or determine when a certain apparatus part has reached said threshold amount of contamination. The computer control can be provided by suitable computer software. For example, an embodiment of the invention provides a computer program containing one or more sequences of machine-readable instructions which are configured to carry out a method as disclosed in this patent application, when the computer program is being executed by a computer.

In an alternative embodiment, schematically depicted inFIG. 4, the immersion space10′ formed by a seal member12′ and filled via inlet/outlet ducts13′ can extend at least between a patterning device MA and/or patterning device holder MT on one side and the projection system on an opposite side. In that case, for example, the apparatus can be configured to place a dummy patterning device or a patterning device shaped object on said patterning device holder MT, and to subsequently rinse the respective immersion space10′. It will be clear that the apparatus can also include an immersion space at the wafer stage and an immersion stage at the patterning device stage, for example by combining the embodiments ofFIGS. 2 and 4.

Also, in an embodiment, the apparatus can include at least two substrate holders WT. Then, the apparatus can be configured to move each substrate holder WT at least to a first position, wherein said immersion space extends between at least part of the substrate holder WT on one side and the projection system PS on an opposite side, and to a respective second position, away from said projection system PS. Said second position can be, for example, near said substrate handler H, to transfer substrates between the respective substrate holder and the substrate handler H (seeFIG. 1). According to a further embodiment, the apparatus can be configured to subsequently move said various substrate holders WT to said first position, to be at least partially rinsed in or near that position by said rinsing liquid. Alternatively, the apparatus can comprise one or more cleaning devices which are configured to at least partially clean a substrate holder when that substrate holder is in said second position. Such a cleaning device20is schematically depicted inFIG. 1, and may be arranged, for example to rinse a substrate holder with rinsing fluid when the substrate holder is in or near said second position. Such a cleaning device20can function similarly to said immersion system, by creating and applying a respective immersion space, or in a different way. Besides, such a cleaning device20might be arranged to immerse a respective substrate holder completely in a suitable cleaning liquid.

Besides, the apparatus can be configured to determine which of said various substrate holders is most likely to be contaminated and is to be rinsed or cleaned first, wherein the apparatus is configured to rinse or clean that substrate holder first which is found to be most likely to be contaminated.

During use, the immersion type projection apparatus shown inFIGS. 1-3can carry out a method for preventing or reducing contamination. To that aim, at least part of the immersion space10is being rinsed with a rinsing liquid, preferably being said immersion liquid, before the apparatus is used to project the patterned beam of radiation onto a resist coated substrate. As follows from the above, the immersion space10can simply be rinsed substantially continuously during an idle operational mode of the apparatus, until the apparatus is used to carry out a lithography process to transfer a patterned radiation beam onto a target portion of a substrate. Optionally, at least part of the immersion space and/or the rinsing liquid is being illuminated by ultraviolet radiation, for example to disable or kill bacteria. In one embodiment, the immersion liquid can be transformed into an ultrasonic cleaning bath. In an other embodiment, the immersion liquid is not transformed into an ultrasonic cleaning bath, i.e. an embodiment wherein the apparatus1does not include an ultrasonic transmitter configured to turn immersion liquid into an ultrasonic cleaning liquid.

Said idle operational mode of the apparatus1can include various idle times. For example, the apparatus can be idle in a device manufacturing plant due to various circumstances, such as the instantaneous substrate throughput of the plant, a temporary halt in the supply of substrates to the apparatus1, a downtime of the plant, a certain maintenance period of the apparatus and/or a different period.

As is shown inFIGS. 2 and 3, a dummy substrate or a substrate-shaped object W can be provided on said substrate holder WT when the immersion space is being rinsed with said rinsing liquid, for example to rinse at least part of the substrate holder WT. For example, during use, before staring the rinsing, said dummy substrate or substrate shaped object W can be transferred from the in-situ compartment22, or alternatively from the substrate handler H, to the substrate holder WT.

Also, the substrate holder WT can be provided with said edge seal member17. In that case, an upper surface, or part thereof, of the edge seal member17of the substrate holder WT can be rinsed by the immersion system.

After such rinsing, the dummy substrate or the substrate-shaped object can be replaced by a true substrate which is to be illuminated by the projection system PS in a lithography manufacturing method. For example, the dummy substrate or substrate shaped object W can be stored in a suitable storage compartment, for example said in-situ compartment22or said substrate handler H, during said lithography manufacturing method. After the lithography manufacturing method, for example, when the apparatus is being put into a relatively long idle operational mode, the dummy substrate or substrate shaped object can again be placed onto the substrate holder WT, and the substantially continuous rinsing can be repeated.

Also, the location of the immersion space10can be being varied during the rinsing treatment. For example, the apparatus can move the substrate holder WT with respect to the immersion system and/or projection system PS, such that the immersion space10can subsequently reach different locations of the substrate holder (and/or substrate edge seal17or other components21), to remove contamination therefrom. In this way, at least part of the apparatus can be washed or rinsed by the immersion system, preferably simply using the immersion liquid which is also used during lithography use of the apparatus. As follows from the above, in an embodiment, the immersion system can wash or rinse at least one slit or aperture E extending in or near the substrate holder WT, particularly said edge slit E extending between the substrate or substrate shaped object W on one side and the substrate holder, or optional edge seal member17, on an opposite side relatively well.

In an embodiment, the immersion space is at least partially being filled or flushed with a rinsing liquid, preferably said immersion liquid, for example for at least one minute, at least one hour, or a different time period. For example, the immersion space10can at least partially be filled or flushed with a rinsing liquid substantially continuously for at least one day, including at least one idle operational period or part thereof. Also, different rinsing periods can be utilized, if desired. Also, the immersion space10can be at least partially being filled or flushed with a rinsing liquid during an idle time of the apparatus, to prevent or reduce substrate contamination during at least one subsequent start-up run of the apparatus. Besides, the method can include circulating an immersion liquid through an immersion space of the apparatus. To provide a substantially contamination free immersion liquid, the immersion liquid can be filtered and/or treated in a suitable manner, as will be clear to the skilled person.

When the apparatus includes at least two substrate holders WT, see for example European Patent Application No. 03257072.3, the substrate holders WT might be moved subsequently to said first position, to be cleaned by the immersion system. Alternatively, one or more of those substrate holders might be cleaned by said optional cleaning device20, when that substrate holder is in said second position. Also, during idle time, one or more of the substrate holders might be submerged completely in a suitable liquid, to clean the holder and/or to keep the holder uncontaminated. Besides, the computer control CU and/or the software may determine which of said various substrate holders is most likely to be contaminated and is to be rinsed or cleaned, or submerged, first.

In an alternative method, as has been described above and has been depicted inFIG. 4, a respective immersion space10′ at least extends between a patterning device, a dummy patterning device or a patterning device shaped object MA and/or patterning device holder MT on one side and a projection system PS on an opposite side. For example, a dummy patterning device or a patterning device shaped object MA can be placed on the patterning device holder MT, whereafter the respective immersion space10′ is being rinsed, for example during idle mode of the apparatus. Preferably, the apparatus includes an in-situ storage space or compartment (not shown) to store such a dummy patterning device or a patterning device shaped object MA, when that patterning device or object is not being located on the patterning device holder. After the rinsing, the dummy patterning device or the patterning device shaped object can be replaced by a true patterning device, which is to be used to pattern radiation before the radiation enters the projection system PS. For example, the immersion system can wash or rinse at least part of the patterning device holder. Also, the immersion system can wash or rinse at least one slit or aperture E′ extending in or near the patterning device holder WT (seeFIG. 4). In case the apparatus includes at least two patterning device holders, the various patterning device holders can be treated similarly to the above-described method for preventing or reducing contamination with respect to multiple substrate holders WT.

In case the apparatus1includes at least two patterning device supports MT, the supports MT might be moved subsequently to respective first position, to be cleaned by the respective immersion system, similar to the above described treatment of at least two substrate holders WT. Also, one or more of those patterning device supports MT might be cleaned by an optional cleaning device (not shown), when those supports MT are in respective second positions. Besides, the computer control CU and/or the software may determine which of said various patterning device supports MT is most likely to be contaminated and is to be rinsed or cleaned first.

The invention can be aimed at reducing contamination during start-up of the lithographic apparatus and/or reducing contamination on the first substrate(s) of a batch of substrates. For example, the first substrates being processed by the apparatus after a machine idle time may show a contamination peak, for example in the number of particles. Said number can be expressed as the “Particle per Wafer Pass” (PWP) number. Besides, the invention can achieve a reduction of potential bacteria growth. For example, said rinsing can provide a continuous flow of fluid over a respective apparatus part (for example a substrate holder), which can prevent bacteria growth. Besides, by applying the optional in-situ UV-light cleaning procedure, the utilization of a H2O2cleaning method to remove bacteria can be avoided. The use of H2O2is not compatible with TiN, which might be present in certain components of the apparatus.

Usually, in a device manufacturing method, resist coated wafers are to be illuminated by the apparatus. The use of resist coated wafers may increase the contamination level PWP, depending for example on the resist and the way it is applied to the substrate. This has been depicted inFIG. 5.FIG. 5shows results of different experimental test runs concerning the substrate stage of the immersion type apparatus. First, a PWP value was being determined using a bare silicon wafer, which had been loaded and unloaded to and from the substrate holder WT of the apparatus. The respective value was relatively low, and has been plotted by a circle AA inFIG. 5.

Shortly after that, a batch of resist coated wafers (zero dose) was exposed by the apparatus. Next, the PWP was again tested, using a further 8 bare Si wafers. The respective 8 results, depicted inFIG. 5by diamonds BB, show an increase of the PWP.

Then, the rinsing of the immersion space was started, utilizing the immersion system and immersion liquid, during a subsequent idle period of the apparatus of about 9½ hrs. After that, a further 5 bare wafers were used to test the PWP again. Their results, depicted by triangles CC inFIG. 5, shown that the rinsing of the immersion space10led to a desired low PWP

Particularly, the PWP of a first wafer to be exposed in an operational period of the apparatus can typically be much higher than of any subsequently exposed wafers. Following the present invention, prolonged or substantially continuous wet hovering by the immersion system over the substrate holder WT and/or patterning device holder MT, and/or parts thereof such as said edge seal member17, slits E, E′, sensors and other components, has been demonstrated to reduce the PWP.

In an embodiment, the apparatus can be configured to load bare silicon wafers on the substrate holder or substrate holders (or chucks of parts thereof), and to start wet hovering over the substrate holder(s). For example, such a rinsing can be carried out with a minimal number of Closing Disk Exchanges, in case the apparatus has been provided with a so called closing disk or suitable closing member to close fluid supplies13of said immersion system. The rinsing procedure can be started automatically after a given time of “machine idle” (compare with a “screen-saver”), and/or after a certain number of exposures. For example, a number of virgin wafers stored in a “pizza box shaped container” in the Wafer Handler H, or in a different location, can be used for such cleaning actions.

When the apparatus includes two or more substrate holders or chucks, each of the substrate holders or chucks may be cleaned by swapping the substrate holders or chucks after a certain time frame. In addition, said computer control CU and/or said software might keep track of the substrate holder or chuck which was cleaned last, and start with the other one next time.

Also, to prevent bacteria growth on or near the substrate holder or the chuck, preferably during idle time of the apparatus, the substrate holder or chuck can be flushed continuously with the immersion liquid, for example with ultra pure water (UPW). Preferably, puddles of not-moving water which are exposed to air are avoided. In addition, said radiation source SO might be switched on for a certain period of time during the flushing with the water, which can provide a UV-light induced ozone cleaning of the substrate holder or chuck. Such an ozone cleaning can be effective for chemical contamination with an organic nature such as spilled resist and to “kill” bacteria. During such a cleaning procedure, preferably, a bare substrate or substrate shaped object is present on the substrate holder under treatment.

For example, during idle time of the apparatus, each substrate holder or chuck can be continuously flushed with UPW water to decrease particle contamination and to avoid bacteria growth. Preferably, the immersion liquid is running at all times.

Also, during idle time, the radiation source SO light might be used to perform an in-situ cleaning, particularly when the source is an UV-light radiation source. Ozone generated in the water is an effective means to remove organic and bacteria growth.

Also, bare dummy substrates, or objects with similar geometry to a bare wafer, can be placed on the substrate holder WT during said idle time cleaning procedure. The immersion type apparatus can be equipped with a dedicated in-situ storage compartment22for the dummy substrates.

One or more embodiments of the present invention may be applied to any immersion lithographic apparatus, such as those types mentioned above, and whether the immersion liquid is provided in the form of a bath or only on a localized surface area of the substrate. An immersion system can be any mechanism that provides a liquid to a space between the projection system and the substrate and/or substrate table. It may comprise any combination of one or more structures, one or more liquid inlets, one or more gas inlets, one or more gas outlets, and/or one or more liquid outlets, the combination providing and confining the immersion liquid to the space. In an embodiment, a surface of the space may be limited to a portion of the substrate and/or substrate table, a surface of the space may completely cover a surface of the substrate and/or substrate table, or the space may envelop the substrate and/or substrate table.

Also, an immersion system can be any mechanism that provides a liquid to a space between the projection system and the patterning device and/or patterning device support.