Local purge within metrology and inspection systems

A purge system includes a purge gas distribution manifold that includes at least one port through which light beam from an optical metrology or inspection head is transmitted. The purge gas distribution manifold includes a bottom surface having one or more apertures through which purge gas is expelled. The bottom surface is held in close proximity to the top surface of the substrate and the apertures may be distributed over the bottom surface of the purge gas distribution manifold so that purge gas is uniformly distributed over the entirety of the top surface of the substrate at all measurement positions of the substrate with respect to the optical metrology or inspection head.

FIELD OF THE INVENTION

The present invention is related to optical metrology and inspection systems, and in particular to a localized purging of optical metrology and inspection systems.

BACKGROUND

To improve process control for some semiconductor manufacturing processes, optical metrology and substrate inspection systems are used to measure and quickly provide feedback for real-time control of the processes. Metrology and substrate inspection processes in semiconductor manufacturing, however, are vulnerable to Airborne Molecular Contamination (AMC) as well as moisture within the environment. Additionally, the substrates themselves are also vulnerable to AMC and moisture in the environment, which may produce contaminants on the surface of a substrate or form film growth or corrosion/oxidation. Moreover, the use of AMC filtration may reduce film growth rate, but does not address humidity control effectively enough to prevent corrosion/oxidation.

Purge systems are sometimes used to protect the metrology and substrate inspection systems and/or substrates under test. By way of example, purge systems sometimes use a purged chamber into which a purge gas or clean dry air is provided. Use of purged chamber, however, requires near vacuum chamber sealing integrity to the atmosphere, and significant safety controls to protect service personnel from asphyxiation hazards. Moreover, a significant amount of purge gas or air may be required to adequately purge a chamber. Other purge systems provide a purge gas or air to the beam path of the optical metrology or inspection device. Thus, purge gas or air contacts limited areas of the substrate during testing, but the remainder of the substrate may still be exposed to the atmosphere including AMC and humidity. Accordingly, improvements over conventional purge systems are desired.

SUMMARY

A purge system includes a purge gas distribution manifold that includes at least one port through which a light beam from an optical metrology or inspection head is transmitted. The purge gas distribution manifold includes a bottom surface having one or more apertures through which purge gas is expelled. The bottom surface is held in close proximity to the top surface of the substrate and the apertures are distributed over the bottom surface of the purge gas distribution manifold so that purge gas is uniformly distributed over the entirety of the top surface of the substrate at all measurement positions of the substrate with respect to the optical metrology or inspection head.

In one implementation, an apparatus includes an optical metrology or inspection head that produces a light beam that is incident on a substrate to be optically measured and is received by the optical metrology or inspection head after interacting with the substrate, a chuck for holding the substrate, wherein at least one of the chuck and the optical metrology or inspection head is movable to position the substrate at a plurality of measurement positions with respect to the optical metrology or inspection head, a purge gas distribution manifold coupled to a purge gas source, the purge gas distribution manifold having at least one port through which the light beam is transmitted, the purge gas distribution manifold having a bottom surface that is 25 mm or less from a top surface of the substrate and has a plurality of apertures through which purge gas is expelled over the top surface of the substrate, wherein the plurality of apertures are distributed over a surface area that is at least as large as a surface area of the top surface of the substrate to distribute the purge gas over an entirety of the top surface of the substrate at all measurement positions of the substrate with respect to the optical metrology or inspection head.

In one implementation, an apparatus includes an optical metrology or inspection head that produces a light beam that is incident on a substrate to be optically measured and is received by the optical metrology or inspection head after interacting with the substrate, a chuck for holding the substrate, wherein at least one of the chuck and the optical metrology or inspection head is movable to position the substrate at a plurality of measurement positions with respect to the optical metrology or inspection head, a purge gas distribution manifold coupled to a purge gas source, the purge gas distribution manifold having at least one port through which the light beam is transmitted, wherein there is relative motion between the purge gas distribution manifold and the substrate when the at least one of the chuck and the optical metrology or inspection head is moved to position the substrate at the plurality of measurement positions with respect to the optical metrology or inspection head, the purge gas distribution manifold having a plurality of apertures through which purge gas is expelled over a top surface of the substrate, wherein the plurality of apertures are distributed over a surface area that is larger than a surface area of the top surface of the substrate to distribute the purge gas over an entirety of the top surface of the substrate at all measurement positions of the substrate with respect to the optical metrology or inspection head.

In one implementation, an apparatus includes an optical metrology or inspection head that produces a light beam that is incident on a substrate to be optically measured and is received by the optical metrology or inspection head after interacting with the substrate, a chuck for holding the substrate, wherein at least one of the chuck and the optical metrology or inspection head is movable to position the substrate at a plurality of measurement positions with respect to the optical metrology or inspection head, a purge gas distribution manifold coupled to a purge gas source, the purge gas distribution manifold having at least one port through which the light beam is transmitted, the purge gas distribution manifold is held linearly stationary with respect to the substrate when the at least one of the chuck and the optical metrology or inspection head is moved to position the substrate at the plurality of measurement positions with respect to the optical metrology or inspection head, the purge gas distribution manifold having a plurality of apertures through which purge gas is expelled, wherein a distribution area of the plurality of apertures is within 25 percent of a surface area of a top surface of the substrate to distribute the purge gas over an entirety of the top surface of the substrate at all measurement positions of the substrate with respect to the optical metrology or inspection head.

In one implementation, an apparatus includes an optical metrology or inspection head that produces a light beam that is incident on a substrate to be optically measured and is received by the optical metrology or inspection head after interacting with the substrate, a chuck for holding the substrate, wherein at least one of the chuck and the optical metrology or inspection head is movable to position the substrate at a plurality of measurement positions with respect to the optical metrology or inspection head, a ceiling having at least one port through which the light beam is transmitted, the ceiling having a bottom surface that is 25 mm or less from a top surface of the substrate; and a fence surrounding the substrate on the chuck, wherein the fence is held linearly stationary with respect to the substrate when the at least one of the chuck and the optical metrology or inspection head is moved to position the substrate at the plurality of measurement positions with respect to the optical metrology or inspection head, the fence having one or more apertures below the top surface of the substrate and through which purge gas is expelled over the top surface of the substrate to distribute the purge gas over an entirety of the top surface of the substrate at all measurement positions of the substrate with respect to the optical metrology or inspection head.

DETAILED DESCRIPTION

FIG. 1illustrates a side view of a purge system100that provides a purged environment to the entirety of the top side of a substrate102being inspected or measured. The purged environment is localized to the surface of the substrate102, as opposed to the entire environment surrounding the substrate102or metrology or inspection device, e.g., as in a conventional purge chamber. The purge system100includes a purge gas distribution manifold110that distributes the purge gas and is positioned so that only a small gap is between a bottom surface118of the purge gas distribution manifold110and the top surface104of the substrate102. For example, the bottom surface118of the purge gas distribution manifold110may be 25 mm or less from the top surface104of the substrate102. The small gap between the purge gas distribution manifold110and the substrate102minimizes the purge gas consumption while providing good shielding purity in the local environment over the substrate102.

The purge gas distribution manifold110is fluidically coupled to a purge gas source112, which may supply an inert gas, such as nitrogen or argon or air, which is purified clean dry air, a combination thereof, or any other suitable inert gas. The purge gas distribution manifold110includes a distribution plenum114, which distributes the purge gas from the inlet116coupled to the purge gas source112and distributes the purge gas over a large area within the purge gas distribution manifold110. The bottom surface118of the purge gas distribution manifold110includes a plurality of apertures120through which the purge gas from the distribution plenum114is expelled, as illustrated by the arrows.

FIGS. 2A and 2Billustrate different implementations of the bottom surface118of the purge gas distribution manifold110relative to a substrate102.FIG. 2Aillustrates an implementation of the purge gas distribution manifold110, where the substrate is positioned for measurement using Cartesian coordinate plane (X,Y) directions andFIG. 2Billustrates an implementation where the substrate is moved in the Polar coordinate plane (R, θ). As illustrated, apertures120in the bottom surface may be holes uniformly or non-uniformly distributed over the area of the bottom surface118. If desired, as illustrated inFIG. 2B, distribution grooves122may be coupled to the holes in the bottom surface118in order to assist in a uniform distribution of the purge gas. By way of example, the holes may be 10 mm or less, e.g., 2 mm, in diameter, and there may be between 1 mm to 25 mm between the holes if there are no distribution grooves. With the use of distribution grooves, which may be, e.g., 2 mm-10 mm wide, fewer holes may be required and the spacing between holes may be increased, e.g., up to 50 mm-75 mm between holes. Moreover, with distribution grooves, a greater flow rate may be desired, and thus holes with a larger diameter, e.g., 10 mm, may be used. Additionally, the size of the holes may selected as a function of position in the bottom surface118of purge gas distribution manifold110to balance the flow rates for uniform protection over the entire surface of the substrate102. It should be understood, however, that while the general shape of the purge gas distribution manifold110may vary based on how the substrate moves, the specific implementation of the bottom surface of the purge gas distribution manifold110is not limited to movement of the substrate in any particular coordinate system.

In another implementation, the bottom surface118of the purge gas distribution manifold110or portions of the bottom surface118may be a porous media, such as a porous carbon or polymer, or sintered metal or polymer, where the purge gas is expelled through the apertures, i.e., pores, in the porous media. In some implementations, a porous media may be located within apertures, which may be 25 mm or less in diameter, in the bottom surface118to the throttle the flow of the purge gas and to provide a uniform distribution of gas over the substrate surface. The porous media, apertures and distribution grooves may be used together, or alternatively, the porous media and apertures, without distribution grooves, may be uniformly or non-uniformly distributed over the area of the bottom surface118.

By positioning the purge gas distribution manifold110close to the top surface104of the substrate102and the use of the plurality of apertures120distributed over the bottom surface118of the purge gas distribution manifold110, a uniform distribution of the purge gas over the entirety of the top surface104of the substrate102may be produced with only a modest flow rate of purge gas. By way of example, modeling has shown flow rates on the order of 1 cfm may reduce O2 levels below 0.02%, and further design optimization may yield even further reduced flow rates at similar O2 concentrations. For some applications, the flow rate may be controlled and reduced via a software recipe control, or by setting a lower flow rate passively. An exhaust port (not shown) may be provided, e.g., below the stage108, to remove the purge gas.

As illustrated inFIG. 1, the purge system100is used with an optical metrology or inspection head130that may include one or more metrology or inspection devices. Optical metrology or inspection head130is illustrated as including objective lenses131a,131b, which produce light beam132that is obliquely incident on the substrate102, and an objective lens131c, which produces light beam134that is normally incident on the substrate102. The objective lenses131a,131b, by way of example, may be part of an ellipsometer or other instrument that uses obliquely incident light. The light beam132may be emitted by objective lens131aand received by objective lens131bafter interacting with the substrate102. The object lens131c, by way of example, may be a reflectometer or other instrument that uses normally incident light. The light beam134is emitted by objective lens131cand received by objective lens131cafter interacting with the substrate102. For the sake of simplicity, the optical metrology or inspection head130is illustrated as only objective lenses, but it should be understood that additional optical elements, such as a light source, detector, polarizing elements, etc., are included in an optical metrology or inspection device, but illustrations of these additional elements are unnecessary for understanding the operation of the purge system100.

The purge gas distribution manifold110includes one or more ports124through which the light beams132and134from an optical metrology or inspection head130is transmitted to and from the substrate102. The purge gas distribution manifold110may include two separate ports124that are slanted with respect to the bottom surface118to accommodate the obliquely incident light from the optical metrology or inspection head130and a port124that is perpendicular to the bottom surface118to accommodate the normally incident beam134. If desired, a single large port124may be used with the obliquely incident light beam132and normally incident light beam134of the optical metrology or inspection head130, but this may affect distribution of the purge gas over the substrate102.

The port(s)124in the purge gas distribution manifold110may be, e.g., apertures passing through the purge gas distribution manifold110. For example, as illustrated in a closer view of the ports124inFIG. 3, the ports124may pass through and may be fluidically coupled to the distribution plenum114and, thus, purge gas may be expelled through the port(s)124as illustrated by arrows126. In another implementation, as illustrated in a closer view of the ports124inFIG. 4, the ports124may not be fluidically coupled to the distribution plenum114.

The substrate102is held by a chuck106that may be coupled to a stage108. Additionally, or alternatively, the optical metrology or inspection head130may be coupled to a stage (not shown). The stage108(and/or the stage coupled to the optical metrology or inspection head130, produces relative motion between the chuck106(with substrate102) and the optical metrology or inspection head130so that at least one of the chuck106and the optical metrology or inspection head130is movable to position the substrate102at a plurality of measurement positions with respect to the optical metrology or inspection head130. For example, the stage108may move the substrate102linearly, e.g., within the Cartesian coordinate plane (X,Y) directions, or may rotate and linearly move the substrate102, e.g., in Polar coordinate plane (R, θ). If desired, the substrate102and the optical metrology or inspection head130may both be moved, e.g., the substrate102may rotate while the optical metrology or inspection head130moves linearly. Alternatively, the optical metrology or inspection head130may move while the substrate102is held stationary. In implementations where the optical metrology or inspection head130moves linearly, it should be understood that the purge gas distribution manifold110may move with the optical metrology or inspection head130.

As illustrated inFIG. 1, the bottom surface118of the purge gas distribution manifold110may be significantly larger than the substrate102. The plurality of apertures120are distributed over a surface area that is larger than the surface area of a top surface of the substrate in order to distribute the purge gas over an entirety of the top surface of the substrate at all measurement positions of the substrate with respect to the optical metrology or inspection head. In one implementation, e.g., where Cartesian coordinate are used as illustrated byFIG. 2A, diameter of the purge gas distribution manifold110may be twice that of the substrate102or more, e.g., the plurality of apertures120may be distributed over a surface area that is at least four times the surface area of the substrate102. In an implementation in which Polar coordinates are used as illustrated byFIG. 2B, the size of the purge gas distribution manifold110may be reduced so that the plurality of apertures120may be distributed over a surface area that is approximately 2.3 times the surface area of the substrate102. Accordingly, as the relative motion between the substrate102and the optical metrology or inspection head130to place the substrate102in different measurement positions with respect to the optical metrology or inspection head130, the entirety of the substrate102remains under the distribution of apertures120in the purge gas distribution manifold110at all measurement positions of the substrate102. Thus, the purge gas distribution manifold110uniformly distributes the purge gas over the entire top surface104of the substrate102at all measurement positions resulting in an effective coverage protecting the top surface104of the substrate102from environmental chemical, humidity, or particle contaminants, with minimal flow of the purge gas.

Additionally, as illustrated inFIG. 1, a reference chip140may be coupled to the stage108. The reference chip140may be, e.g., a bare silicon chip, or other appropriate chip that may be used to calibrate the optical metrology or inspection device. As optical metrology or inspection device may be sensitive to any changes in the optical properties of the reference chip140, the purge gas distribution manifold110may be used to additionally provide purge gas to the reference chip140. If desired, however, a separate purge system may be used with the reference chip140.

The substrate102may be loaded onto the chuck106, e.g., by lowering the chuck106to allow an end effector to place the substrate102on pins in the chuck106, and the chuck106may then be raised to a desired height to hold the substrate102on the chuck surface. Alternatively, the purge gas distribution manifold110may have a step with greater clearance at the location where the substrate102is loaded onto the chuck, where the step has sufficient height to allow the end effector to place the substrate102on the chuck106. With the presence of a step in a portion of the purge gas distribution manifold110, an increased flow rate may be used in the location of the step in order to maintain purge purity.

In one implementation, the purge gas distribution manifold may be partitioned into a plurality of zones, where the flow of purge gas is switched on or off at different zones depending on whether the substrate is present or absent from each zone when the substrate is moved to different measurement positions.FIG. 5, by way of example, illustrates a side view of a purge system200that includes a plurality of zones to provide a localized clean environment for the top side of a substrate102when the substrate102is present within any zone, while the remaining zones have a reduced flow of purge gas. Purge system200is similar to purge system100shown inFIG. 1, like designated elements being the same. Purge system200includes a purge gas distribution manifold220that is positioned, e.g., 25 mm or less, from the top surface104of the substrate102. The purge gas distribution manifold220includes a distribution plenum224that includes multiple zones Z1, Z2, Z3, each of which is fluidically coupled to a purge gas source112through valves226Z1,226Z2,226Z3(sometimes collectively referred to as valves226) that independently control the flow of purge gas to their associated zones. Each valve226may be controlled to reduce or stop the flow of purge gas to an associated zone, for example, when the substrate102is not present under an associated zone. Additionally, associated with each valve226Z1,226Z2,226Z3is a bypass valve228Z1,228Z2,228Z3(sometimes collectively referred to as bypass valves228). Each bypass valve228provides a reduced flow of purge gas to the associated zones in the distribution plenum224to maintain a charge of purge gas within the associated zone of the distribution plenum224when the valve to the associated zone is turned off. If a reference chip140is included, the valves226and bypass valves228may be controlled to provide purge gas to any zone in which the reference chip is present.

The valves226and bypass valves228may be controlled by controller240, e.g., based on the known position of the stage108. The controller240may be, e.g., a processor that controls movement of the stage108, and thus, the substrate102to its different measurement positions. In another implementation, the valves226and bypass valves228may be controlled based on sensors, e.g., light sensors (not shown), that detect the presence of the substrate102within each zone. For some applications, the flow rate may be controlled via a software recipe control or by setting a lower flow rate passively.

FIG. 6is a plan view of the purge gas distribution manifold220illustrating a plurality of zones Z1, Z2, Z3, Z4, Z5, Z6, Z7, Z8, and Z9. The substrate102is illustrated inFIG. 6with dotted lines at a measurement position. The optical metrology or inspection head130is not illustrated inFIG. 6, but the location that measurements are performed by the optical metrology or inspection head130is illustrated at the center of the purge gas distribution manifold220and is illustrated with spot131. The substrate102is positioned for a measurement at the outer diameter of the substrate102. As can be seen, the substrate102is present only in zones Z2, Z3, Z6and Z7. Accordingly, valves226associated with zones Z2, Z3, Z6and Z7are controlled to produce a flow of purge gas. The valves226at the remaining zones, i.e., zones Z1, Z4, Z5, Z8, and Z9may be controlled to reduce or stop the flow of purge gas. The bypass valves228at the remaining zones, i.e., zones Z1, Z4, Z5, Z8, and Z9, may be controlled to provide a minimum flow rate to keep gas purity high in the distribution plenum224.

It should be understood that whileFIGS. 5 and 6illustrate three and nine zones, respectively, of the purge gas distribution manifold220, additional or fewer zones may be used to minimize the amount of purge gas used, while maintaining an effective coverage protecting the substrate102.

FIG. 7illustrates a side view of another purge system300that is similar to purge system100shown inFIG. 1, like designated elements being the same. The purge system300includes a purge gas distribution manifold320that is approximately the same size as the substrate102and moves linearly with the substrate102so that the purge gas distribution manifold320is stationary relative to the substrate102for all linear movement of the substrate102, i.e., the purge gas distribution manifold320is linearly stationary with respect to the substrate102, but there may be relative rotational movement between the substrate102and the purge gas distribution manifold320, e.g., as in a Polar coordinate (R, θ) movement. As illustrated inFIG. 7, the purge gas distribution manifold320includes a distribution plenum324that is fluidically coupled to a purge gas source112by a flexible connector326. The purge gas distribution manifold320may be coupled to the chuck106through the stage108so that the purge gas distribution manifold320is held linearly stationary with respect to the substrate102when at least one of the chuck and the optical metrology or inspection head is moved to position the substrate at the plurality of measurement positions with respect to the optical metrology or inspection head. If desired, the substrate102may rotate with respect to the purge gas distribution manifold320, e.g., when Polar coordinate motion is used. The flexible connector326may be routed through the connection between the stage108and the purge gas distribution manifold320.

It should be understood that the optical metrology or inspection head130may move in addition to or instead of the substrate102, but the purge gas distribution manifold320will remain stationary with respect to the substrate102for all linear movement. For example, as discussed above, the substrate102and the optical metrology or inspection head130may both be moved, e.g., the substrate102may rotate while the optical metrology or inspection head130moves linearly. Alternatively, the optical metrology or inspection head130may move while the substrate102is held stationary. The purge gas distribution manifold320may include elongated ports (or slots) or additional ports to accommodate movement of the optical metrology or inspection head130or substrate102to different measurement positions.

With the purge gas distribution manifold320held stationary with respect to the substrate102for all linear movement, the purge gas distribution manifold320does not need to be larger than the substrate102to cover the entire top surface104at all measurement positions of the substrate102. The purge gas distribution manifold320may be approximately the same size as the substrate102to achieve the desired localized purged environment. If desired, the purge gas distribution manifold320may be slightly smaller than the substrate102and an adequate localized purged environment over the substrate102may be maintained for all measurement positions.

FIG. 8, by way of example, illustrates a side view of portions of the purge gas distribution manifold320and the substrate102and illustrates a possible size relationship between the purge gas distribution manifold320and the substrate102. As illustrated inFIG. 8, the purge gas distribution manifold320is positioned a height H above the top surface of the substrate102, which may be, e.g., 25 mm or less. The closer the purge gas distribution manifold320is to the substrate102, i.e., a smaller height H, the smaller the purge gas distribution manifold320may be relative to the substrate102and less purge gas will be required to produce a desired localized purge environment over the entire surface of the substrate102. With use of a small height H, however, loading the substrate102onto the chuck may require additional actions, such as lowering and raising the chuck to accommodate an end effector, which will increase the time that the substrate102is not within the localized purged environment and is exposed to the atmosphere.

As illustrated inFIG. 8, the substrate102may include an edge exclusion zone402, which may be a distance D402, typically 2 mm, between the edge of the substrate102and the area103on the substrate where dies are fabricated. Thus, it should be clear that the purge gas distribution manifold320need not extend to the edge of the substrate102in order to provide an adequate localized purged environment over the usable area of the substrate102. As illustrated, the end of the purge gas distribution manifold320may, but is not necessarily required to, extend past the usable area of the substrate102, i.e., over the edge exclusion zone402. Thus, the end of the purge gas distribution manifold320may be a distance D320from the edge of the substrate102, which for a 300 mm substrate may be 0 mm or up to 5 mm, e.g., specifically may be 2 mm (i.e., to the edge exclusion zone402). Thus, the purge gas distribution manifold320may be the same size as the substrate102or may have a diameter that is up to 10 mm, or may be approximately 10%, smaller than the substrate102. It should be understood that, if desired, the purge gas distribution manifold320may be larger than the substrate102, but this may utilize more purge gas.

Additionally, as illustrated inFIG. 8, the purge gas distribution manifold320includes a surface area404over which the plurality of apertures are distributed, which may be smaller than the usable area of the substrate102, i.e., the distribution area404of the apertures may not extend over the edge exclusion zone402. As illustrated, the distribution area404of the apertures may be a distance D404from the edge of the substrate102, which for a 300 mm substrate may be from 0 mm to 10 mm or from 0 mm to 20 mm. Thus, the distribution area404of the apertures may be the same size as the substrate102or may have a diameter that is up to 40 mm, or approximately 25%, smaller than the substrate102. Moreover, with sufficiently small clearance between the purge gas distribution manifold320and the substrate102, i.e., height H, it may be possible for the distribution area404of the apertures to be approximately 50% smaller than the substrate102, while still providing an adequate localized purged environment to the entire surface of the substrate in all measurement positions. For example, some applications may benefit even from modest improvements in dryness, Airborne Molecular Contamination (AMC) cleanliness or O2 reduction. It should be understood that, if desired, the distribution area404of the apertures of the purge gas distribution manifold320may be larger than the substrate102, but this may utilize more purge gas.

FIG. 9illustrates a top plan view of purge gas distribution manifold320and a substrate102and its edge exclusion zone402shown with broken lines. As illustrated, the purge gas distribution manifold320may include one or more linear ports322or slots that are the length of a full radius of the substrate102, which permits the light beams, such as obliquely incident light beam132and normally incident light beam134, to access the substrate102. The purge gas distribution manifold320and a substrate102are held linearly stationary with respect to each other, so that as the substrate102is moved linearly to different measurement positions, or alternatively, as the optical metrology or inspection head130is moved linearly with respect to the substrate102and the purge gas distribution manifold320, the purge gas distribution manifold320remains stationary with respect to the substrate102and, accordingly, will continue to provide a localized purge environment to the entire surface of the substrate102at all measurement positions. Moreover, because the size of the purge gas distribution manifold320is much reduced compared to the purge gas distribution manifold110shown inFIG. 1, less purge gas is required by the purge gas distribution manifold320.

Additionally, as illustrated inFIG. 9, the reference chip140may be used with the purge system300where, for example, the purge gas distribution manifold320is extended to cover the reference chip140. If desired, one or more purge apertures120in the purge gas distribution manifold320may be located over the reference chip140.

If desired, additional components may be included with the purge system300, which may assist in providing a localized purge environment while minimizing the purge gas flow rate. For example, a fence may surround the substrate102to contain and direct the purge gas.FIG. 10A, by way of example, illustrates a side view of a portion of a fence340that surrounds the substrate102. If a reference chip is present (not shown inFIG. 10A), both the substrate102and the reference chip may be surrounded by the fence340. The fence340may have a fixed height and may be coupled to the stage108so that the fence340moves linearly with the chuck106and substrate102. As with the purge gas distribution manifold320, if desired, the chuck106and substrate102may be permitted to rotate with respect to the fence340. During substrate load and unload, the fence340may move downward with the stage108to allow an end effector to place the substrate102on or remove the substrate102from pins in the chuck106, and the chuck106may then be raised to a desired height. If desired, the fence340may move independently of the Z stage.

The fence340may include an upper surface342that is positioned near the bottom surface318of the purge gas distribution manifold320. For example, the vertical gap341between the upper surface342of the fence340and the bottom surface318of the purge gas distribution manifold320may be 10 mm or less. The fence340may include one or more, e.g., 1 to 150, apertures344, which may be, e.g., up to 25 mm in diameter, through which the purge gas may be exhausted passively or actively, e.g., using a pump. By way of example, the apertures344may be located below the top surface of the substrate102, such as on a bottom surface346of the fence340.

FIG. 10Billustrates a portion of a side view of another implementation of the fence340that surrounds the substrate102. As illustrated inFIG. 10B, the apertures344may be fluidically coupled to a purge gas source350(which may be the same or a different purge gas source that is fluidically coupled to the purge gas distribution manifold320. Purge gas may be emitted by the one or more apertures344, which may be located below the top surface of the substrate102, e.g., on the bottom surface346of the fence340. Alternatively, the fence340may not include apertures344. The purge gas that is emitted by the purge gas distribution manifold320may not be exhausted through apertures in the bottom surface346of the fence340, but rather through the vertical gap341between the upper surface342of the fence340and the bottom surface318of the purge gas distribution manifold320, as illustrated by the arrows. Purge gas emitted by the apertures344in the fence340, if used, may likewise be exhausted through the vertical gap341.

FIG. 11illustrates a top plan view of purge gas distribution manifold320with the fence340, where the substrate102and its edge exclusion zone402are shown with broken lines.FIG. 11is similarFIG. 9, like designated elements being the same. As illustrated, fence340surrounds the substrate102, as well as the reference chip140, if used. The purge gas distribution manifold320may extend beyond the outside edge of the upper surface342of the fence340. The apertures344in the bottom surface346of the fence340may be underneath the substrate102. The fence340, along with the purge gas distribution manifold320may be held linearly stationary with respect to the substrate102, i.e., so that they are held stationary with respect to each other during linear movement, but there may be relative rotational movement. Thus, the fence340and purge gas distribution manifold320will provide a localized purge environment to the entire surface of the substrate102at all measurement positions.

If desired, the purge gas may be provided through the fence to produce a localized purge environment above the substrate102.FIG. 12, by way of example, illustrates a side view of a purge system400in which purge gas is provided into the localized environment around the substrate102through a fence410. The purge system400shown inFIG. 12, is similar to that shown inFIGS. 10A and 10B, like designated elements being the same. As illustrated, purge gas may be provided from a purge gas source430through one or more apertures414(e.g., 1 to 150 apertures) in the fence410which surrounds the substrate102to contain and direct the purge gas over the top surface of the substrate102. The apertures414may be, e.g., up to 25 mm in diameter and may be located below the top surface of the substrate102, e.g., on the bottom surface416of the fence410. Similar to the fence shown inFIGS. 10A and 10B, the fence410may have a fixed height and may be coupled to the stage108so that the fence410moves linearly with the chuck106and substrate102. The fence410may include an upper surface412that is positioned near the bottom surface422of a ceiling420, e.g., 10 mm or less. Similar to the purge gas distribution manifold320, the bottom surface422of the ceiling420may be positioned 25 mm or less from the top surface104of the substrate102to minimize the purge gas consumption while providing good shielding purity in the local environment over the substrate102.

The ceiling420may be coupled to the stage108and may be linearly stationary with respect to the chuck106, substrate102and fence410, i.e., there is no relative movement between the ceiling420and the chuck106, substrate102and fence410during linear motion, but relative rotational movement may be permitted. Alternatively, the ceiling420may be coupled to the optical metrology or inspection head130so that there is relative linear and rotational movement between the ceiling420and the chuck106, substrate102, and fence410. Thus, relative movement using Cartesian coordinates or Polar coordinates is possible. The ceiling420may include apertures424(or slots) through which light beams132and134from the optical metrology or inspection head130may be transmitted. As illustrated by the arrow, the purge gas may be exhausted through apertures424, or may be exhausted through other apertures (not shown) above the top surface of the substrate102. Similar to fence340, during substrate load and unload, the fence410may move downward with the stage108to allow an end effector to place the substrate102on or remove the substrate102from pins in the chuck106, and the chuck106may then be raised to a desired height. If desired, the fence410may move independently of the Z stage.

Although the present invention is illustrated in connection with specific embodiments for instructional purposes, the present invention is not limited thereto. Various adaptations and modifications may be made without departing from the scope of the invention. Therefore, the spirit and scope of the appended claims should not be limited to the foregoing description.