Reticle load lock system and method

Abstract

A reticle load lock having a valve with a variable size orifice, or servo valving, is described. Servo valving can continually adjust the size of the orifice such that the reticle load lock can pump or vent at an optimal level. The servo valving pressure profile follows an optimized pressure rate to protect the structural integrity of the pellicle. The optimized servo valving curves minimize the evacuation and vent times without exceeding the pressure rate (dP / dt) limits. By following the optimized pressure rate curve, servo valving significantly reduces the time to pump down and vent and prevents breakage of the pellicle.

Description

RETICLE LOAD LOCK SYSTEM AND METHODCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 602,717 which was filed on November 27, 2023 and which is incorporated herein in its entirety by reference.TECHNICAL FIELD

[0002] The description herein relates generally to a reticle load lock system and method.BACKGROUND

[0003] A lithography (e.g., projection) apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device (e.g., a mask) may contain or provide a pattern corresponding to an individual layer of the IC (“design layout”), and this pattern can be transferred onto a target portion (e.g. comprising one or more dies) on a substrate (e.g., silicon wafer) that has been coated with a layer of radiation-sensitive material (“resist”), by methods such as irradiating the target portion through the pattern on the patterning device. In general, a single substrate contains a plurality of adjacent target portions to which the pattern is transferred successively by the lithographic projection apparatus, one target portion at a time. In one type of lithographic projection apparatus, the pattern on the entire patterning device is transferred onto one target portion in one operation. Such an apparatus is commonly referred to as a stepper. In an alternative apparatus, commonly referred to as a step-and-scan apparatus, a projection beam scans over the patterning device in a given reference direction (the “scanning” direction) while synchronously moving the substrate parallel or anti-parallel to this reference direction. Different portions of the pattern on the patterning device are transferred to one target portion progressively. In these lithography apparatuses, a patterning device is held by a patterning device chuck with an optically contacted clamp.SUMMARY

[0004] Some lithography apparatuses are used at vacuum pressure. In order for a reticle to be introduced into or removed from an apparatus, it requires the environment surrounding the reticle to be pumped down or vented, respectively. Traditional pump down or venting methods use three discrete valves and orifices, which are inefficient. In the present systems and methods, a valve having an orifice with variable size is used for optimal pump down and venting operations. This valve is part of a reticle load lock, as described below. By controlling the orifice size, an ideal pressure rate curve for the fastest pump speeds can be followed, without sacrificing the structural integrity of the reticle pellicle. As a result, the pump down and venting times are reduced significantly for the reticle loadlock.

[0005] According to an embodiment, there is provided a reticle load lock. The reticle load lock comprises a load lock chamber, wherein the chamber has a closure movable between an open and a closed position, wherein when the closure is in the open position, a reticle can be inserted or removed from the chamber. The reticle load lock comprises a pump system configured to evacuate the chamber. The reticle load lock comprises a venting system configured to pressurize the chamber. The reticle load lock comprises a first valve having an orifice of variable size and configured to communicate the pump system with the chamber. The reticle load lock comprises a second valve having an orifice of variable size and configured to communicate the venting system with the chamber. The reticle load lock comprises a controller operatively connected with the first and second valves and configured to control the size of the orifice to control a pressure in the chamber over time based on a desired pressure profile.

[0006] In some embodiments, the reticle load lock further comprises a pressure sensor operatively connected with the controller and configured to monitor pressure within the chamber, and to provide pressure signals to the controller indicative of the pressure within the chamber.

[0007] In some embodiments, the controller controls the orifice size based on the pressure signals.

[0008] In some embodiments, the controller is pre-programmed to control the orifice size based on a predetermined pressure over time profile.

[0009] In some embodiments, the reticle comprises a pellicle, wherein the reticle is separated from the pellicle by a small air gap.

[0010] In some embodiments, the small air gap is between 50 pm to 1 mm wide.

[0011] In some embodiments, the evacuating the gas out of the chamber brings the chamber to a vacuum environment.

[0012] In some embodiments, the controller is configured to control the second valve to allow gas into the chamber to bring the chamber to a non-vacuum environment.

[0013] In some embodiments, the non-vacuum environment is at atmospheric pressure.

[0014] In some embodiments, the first and second valves are servo control valves having orifice size control.

[0015] In some embodiments, the closure is a gate valve.

[0016] According to an embodiment, there is provided a lithography apparatus. The lithography apparatus comprises an illumination system that provides a beam of radiation. The lithography apparatus comprises a support structure that supports a reticle, wherein the reticle is configured to impart the beam of radiation with a pattern in its cross-section. The lithography apparatus comprises a substrate support that supports a substrate. The lithography apparatus comprises a projection system that projects the patterned beam onto a target portion of the substrate. The lithography apparatus comprises a reticle load lock. The reticle load lock comprises a load lock chamber, wherein the chamber has a closure movable between an open and a closed position, wherein when the closure is inthe open position, the reticle can be inserted or removed from the chamber. The reticle load lock comprises a pump system configured to evacuate the chamber. The reticle load lock comprises a venting system configured to pressurize the chamber. The reticle load lock comprises a first valve having an orifice of variable size and configured to communicate the pump system with the chamber. The reticle load lock comprises a second valve having an orifice of variable size and configured to communicate the venting system with the chamber. The reticle load lock comprises a controller operatively connected with the first and second valves and configured to control the size of the orifice to control a pressure in the chamber over time based on a desired pressure profile.

[0017] In some embodiments, the reticle load lock further comprises a pressure sensor operatively connected with the controller and configured to monitor pressure within the chamber, and to provide pressure signals to the controller indicative of the pressure within the chamber.

[0018] In some embodiments, the controller controls the orifice size based on the pressure signals.

[0019] In some embodiments, the controller is pre-programmed to control the orifice size based on a predetermined pressure over time profile.

[0020] In some embodiments, the reticle comprises a pellicle, wherein the reticle is separated from the pellicle by a small air gap.

[0021] In some embodiments, the small air gap is between 50 pm to 1 mm wide.

[0022] In some embodiments, the evacuating the gas out of the chamber brings the chamber to a vacuum environment.

[0023] In some embodiments, the controller is configured to control the second valve to allow gas into the chamber to bring the chamber to a non-vacuum environment.

[0024] In some embodiments, the non-vacuum environment is at atmospheric pressure.

[0025] In some embodiments, the first and second valves are servo control valves having orifice size control.

[0026] In some embodiments, the closure is a gate valve.

[0027] According to an embodiment, there is provided a method of using a reticle load lock. The method comprises inserting or removing a reticle into a closure of a load lock chamber when the closure is in an open position, wherein the closure is movable between the open and a closed position. The method comprises evacuating the chamber using a pump system. The method comprises pressurizing the chamber using a venting system. The method comprises communicating the pump system with the chamber using a first valve having an orifice of variable size. The method comprises communicating the venting system with the chamber using a second valve having an orifice of variable size. The method comprises controlling the size of the orifice to control a pressure in the chamber over time based on a desired pressure profile using a controller operatively connected with the first and second valves.

[0028] In some embodiments, the method further comprises monitoring pressure within the chamber using a pressure sensor operatively connected with the controller and providing pressuresignals using the pressure sensor to the controller indicative of the pressure within the chamber.

[0029] In some embodiments, the method further comprises controlling the orifice size using the controller based on the pressure signals.

[0030] In some embodiments, the method further comprises pre-programming the controller to control the orifice size based on a predetermined pressure over time profile.

[0031] In some embodiments, the reticle comprises a pellicle, wherein the reticle is separated from the pellicle by a small air gap.

[0032] In some embodiments, the small air gap is between 50 pm to 1 mm wide.

[0033] In some embodiments, the evacuating the gas out of the chamber brings the chamber to a vacuum environment.

[0034] In some embodiments, the method further comprises controlling the second valve using the controller to allow gas into the chamber to bring the chamber to a non-vacuum environment.

[0035] In some embodiments, the non-vacuum environment is at atmospheric pressure.

[0036] In some embodiments, the first and second valves are servo control valves having orifice size control.

[0037] In some embodiments, the closure is a gate valve.

[0038] According to an embodiment, there is provided a method of using a reticle load lock. The method comprises inserting a reticle into a load lock chamber through a closure when the closure is in an open position, wherein the closure is movable between the open and a closed position. The method comprises evacuating the load lock chamber using a pump system with a first valve having an orifice of variable size by controlling the size of the orifice to control a pressure in the chamber over time based on a desired pump down pressure profile using a controller operatively connected with the first valve. The method comprises moving the reticle from the load lock chamber to a lithography apparatus. The method comprises exposing a substrate using the pattern of the reticle in the lithography apparatus. The method comprises moving the reticle from the lithography apparatus to the load lock chamber. The method comprises venting the load lock chamber using a venting system with a second valve having the orifice of variable size by controlling the size of the orifice to control a pressure in the chamber over time based on a desired venting pressure profile using the controller operatively connected with the second valve. The method comprises removing the reticle from the load lock chamber via the closure when the closure is in the open position.

[0039] In some embodiments, the method further comprises monitoring pressure within the chamber using a pressure sensor operatively connected with the controller and providing pressure signals using the pressure sensor to the controller indicative of the pressure within the chamber.

[0040] In some embodiments, the method further comprises controlling the orifice size using the controller based on the pressure signals.

[0041] In some embodiments, the method further comprises pre-programming the controller to control the orifice size based on a predetermined pressure over time profile.

[0042] In some embodiments, the reticle comprises a pellicle, wherein the reticle is separated from the pellicle by a small air gap.

[0043] In some embodiments, the small air gap is between 50 pm to 1 mm wide.

[0044] In some embodiments, the evacuating the gas out of the chamber brings the chamber to a vacuum environment.

[0045] In some embodiments, the method further comprises controlling the second valve using the controller to allow gas into the chamber to bring the chamber to a non-vacuum environment.

[0046] In some embodiments, the non-vacuum environment is at atmospheric pressure.

[0047] In some embodiments, the first and second valves are servo control valves having orifice size control.

[0048] In some embodiments, the closure is a gate valve.BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. Embodiments will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0050] FIG. 1A is a schematic illustration of a reflective lithographic apparatus, according to an embodiment of the present disclosure.

[0051] FIG. IB is a schematic illustration of a transmissive lithographic apparatus, according to an embodiment of the present disclosure.

[0052] FIG. 1C is a more detailed schematic illustration of the reflective lithographic apparatus, according to an embodiment of the present disclosure.

[0053] FIG. 2 schematically depicts an embodiment of a lithographic cell or cluster, according to an embodiment.

[0054] FIG. 3A is a schematic illustration of a reticle load lock, according to an embodiment of the present disclosure.

[0055] FIG. 3B is a perspective illustration of a reticle load lock, according to an embodiment of the present disclosure.

[0056] FIG. 4A is a pressure rate curve for venting, according to an embodiment of the present disclosure.

[0057] FIG. 4B is a pressure rate curve for pump down, according to an embodiment of the present disclosure.

[0058] FIG. 5 illustrates a method for using the reticle load lock, according to an embodiment.

[0059] FIG. 6 is a block diagram of an example computer system, according to an embodiment.DETAILED DESCRIPTION

[0060] In photolithography, there is a need to perform exposure at vacuum pressure. With the recent technological advancements in extreme ultraviolet (EUV) lithography, the EUV radiation source requires vacuum conditions. As a result, the entire EUV lithography system is kept at vacuum pressure. Additionally, exposure requires the use of many different reticles to form the desired pattern on the substrate. An environment around a reticle can be pumped down in a reticle load lock before entering the EUV lithography system.

[0061] However, a conventional reticle load lock is inefficient and is not optimized for throughput. A conventional reticle load lock typically uses three discrete valves and orifices. These reticle load locks pump down or vent to a certain pressure using a first valve having a small orifice size, at which point a second valve with a medium orifice size will take over. After pumping down or venting to a second pressure, the third valve with a large orifice size will replace the second valve. The third valve will pump down or vent the reticle load lock to vacuum or atmospheric pressure, respectively. The orifice sizes will increase in size as reticle load lock is further pumped down. An issue with this typical three discrete valve system is that the three valves and orifices each pump at a certain rate that cannot be adjusted. In general, pump or vent speed can only be altered when the orifice size is changed. Since the size of the three orifices are fixed, no adjustment, and hence change to the pump or vent speed, can be made other than switching between the three orifices. As a result, the typical three discrete valve system limits how quickly the load lock can be pumped down or vented.Alternatively, the conventional reticle load lock has only one valve of a fixed size. This load lock will pump down even more slowly than that of the three discrete valves and orifices.

[0062] In contrast, the reticle load lock described herein, having a valve with a variable size orifice, or servo valving, solves problems associated with the three discrete valve system. A servo control valve, or a proportioning valve, can continually adjust the size of the orifice such that the reticle load lock can pump at an optimal level. The servo valving pressure profile follows a greater pressurization rate compared to prior systems yet maintains the structural integrity of a pellicle attached to the reticle. The pellicle is a thin, transparent membrane that covers the reticle to prevent contaminants from reaching the reticle surface. Optimized servo valving curves minimize the pump and vent times without exceeding pressure rate (dP / dt) limits. By following the optimized pressure rate curves, servo valving significantly reduces the time needed to pump down and / or vent the load lock chamber compared to conventional methods. Further, the servo valve systems and methods described herein allow for greater flexibility by adjusting the orifice to any size and can be easily programmed for different pumping and / or venting speeds.

[0063] Although specific reference may be made in this text to the manufacture of integrated circuits (ICs), it should be understood that the description herein has many other possible applications. For example, it may be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid-crystal display panels, thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “reticle”, “wafer” or “die” in this text should be considered as interchangeable with the more general terms “mask”, “substrate” and “target portion”, respectively. In addition, any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.”

[0064] As an introduction, prior to transferring a pattern from a patterning device such as a mask to a substrate, the substrate may undergo various procedures, such as priming, resist coating and a soft bake. After exposure, the substrate may be subjected to other procedures (“post-exposure procedures”), such as a post-exposure bake (PEB), development, a hard bake and measurement and / or other inspection of the transferred pattern. This array of procedures is used as a basis to make an individual layer of a device, e.g., an IC. The substrate may then undergo various processes such as etching, ion-implantation (doping), metallization, oxidation, chemical mechanical polishing, etc., all intended to finish an individual layer of the device. If several layers are required in the device, then the whole procedure, or a variant thereof, is repeated for each layer. Eventually, a device will be present in each target portion on the substrate. These devices are then separated from one another by a technique such as dicing or sawing, whence the individual devices can be mounted on a carrier, connected to pins, etc.

[0065] Manufacturing devices, such as semiconductor devices, typically involves processing a substrate (e.g., a semiconductor wafer) using a number of fabrication processes to form various features and multiple layers of the devices. Such layers and features are typically manufactured and processed using, e.g., deposition, lithography, etch, chemical mechanical polishing, ion implantation, and / or other processes. Multiple devices may be fabricated on a plurality of dies on a substrate and then separated into individual devices. This device manufacturing process may be considered a patterning process. A patterning process involves a patterning step, such as optical and / or nanoimprint lithography using a patterning device in a lithographic apparatus, to transfer a pattern on the patterning device to a substrate and typically, but optionally, involves one or more related pattern processing steps, such as resist development by a development apparatus, baking of the substrate using a bake tool, etching using the pattern using an etch apparatus, etc. One or more metrology processes are typically involved in the patterning process.

[0066] Lithography is a step in the manufacturing of devices such as ICs, where patterns formed on substrates define functional elements of the devices, such as microprocessors, memory chips, etc. Similar lithographic techniques are also used in the formation of flat panel displays, micro-electro mechanical systems (MEMS) and other devices.

[0067] As semiconductor manufacturing processes continue to advance, the dimensions of functional elements have continually been reduced while the number of functional elements, such as transistors, per device has been steadily increasing over decades, following a trend commonly referred to as “Moore’s law”. At the current state of technology, layers of devices are manufactured usinglithographic projection apparatuses that project a design layout onto a substrate using illumination from a deep-ultraviolet illumination source, creating individual functional elements having dimensions well below 100 nm, i.e. less than half the wavelength of the radiation from the illumination source (e.g., a 193 nm illumination source).

[0068] This process in which features with dimensions smaller than the classical resolution limit of a lithographic projection apparatus are printed, is commonly known as low-kl lithography, according to the resolution formula CD = k I X / . / NA, where X is the wavelength of radiation employed (currently in most cases 248nm or 193nm), NA is the numerical aperture of projection optics in the lithographic projection apparatus, CD is the “critical dimension’ -generally the smallest feature size printed-and kl is an empirical resolution factor. In general, the smaller kl the more difficult it becomes to reproduce a pattern on the substrate that resembles the shape and dimensions planned by a designer in order to achieve particular electrical functionality and performance. To overcome these difficulties, sophisticated fine-tuning steps are applied to the lithographic projection apparatus, the design layout, or the patterning device. These include, for example, but not limited to, optimization of NA and optical coherence settings, customized illumination schemes, use of phase shifting patterning devices, optical proximity correction (OPC, sometimes also referred to as “optical and process correction”) in the design layout, overlay measurement, or other methods generally defined as “resolution enhancement techniques” (RET).

[0069] The term “projection optics” as used herein should be broadly interpreted as encompassing various types of optical systems, including refractive optics, reflective optics, apertures and catadioptric optics, for example. The term “projection optics” may also include components operating according to any of these design types for directing, shaping, or controlling the projection beam of radiation, collectively or singularly. The term “projection optics” may include any optical component in the lithographic projection apparatus, no matter where the optical component is located on an optical path of the lithographic projection apparatus. Projection optics may include optical components for shaping, adjusting and / or projecting radiation from the source before the radiation passes the patterning device, and / or optical components for shaping, adjusting and / or projecting the radiation after the radiation passes the patterning device. The projection optics generally exclude the source and the patterning device.

[0070] FIGS. 1A and IB are schematic illustrations of a lithographic apparatus 100 and lithographic apparatus 100’, in or for which embodiments of the present disclosure may be implemented. Lithographic apparatus 100 and lithographic apparatus 100’ each include the following: an illumination system (illuminator) IL configured to condition a radiation beam B (for example, ultraviolet (UV), deep ultraviolet (DUV) or extreme ultraviolet (EUV) radiation); a support structure (for example, a mask table) MT configured to support a patterning device (for example, a mask, a reticle, or a dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA; and, a substrate table (for example, a wafer table) WT(e.g., WTa, WTb or both) configured to hold a substrate (for example, a resist coated wafer) W and connected to a second positioner PW configured to accurately position the substrate W. Lithographic apparatus 100 and 100’ also have a projection system PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion (for example, comprising one or more dies) C of the substrate W. In lithographic apparatus 100, the patterning device MA and the projection system PS are reflective. In lithographic apparatus 100’, the patterning device MA and the projection system PS are transmissive.

[0071] The illumination system IL may include various types of optical components, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for directing, shaping, or controlling the radiation beam B.

[0072] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA, the design of at least one of the lithographic apparatus 100 and 100’, and other conditions, such as whether or not the patterning device MA is held in a vacuum environment. The support structure MT may use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device MA. The support structure MT can be a frame or a table, for example, which can be fixed or movable, as required. By using sensors, the support structure MT can ensure that the patterning device MA is at a desired position, for example, with respect to the projection system PS.

[0073] The term “patterning device” MA should be broadly interpreted as referring to any device that can be used to impart a radiation beam B with a pattern in its cross-section, such as to create a pattern in the target portion C of the substrate W. The pattern imparted to the radiation beam B can correspond to a particular functional layer in a device being created in the target portion C to form an integrated circuit.

[0074] The patterning device MA may be transmissive (as in lithographic apparatus 100’ of FIG. IB) or reflective (as in lithographic apparatus 100 of FIG. 1 A). Examples of patterning devices MA include reticles, masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase shift, and attenuated phase shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam B which is reflected by a matrix of small mirrors.

[0075] The term “projection system” PS can encompass any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors, such as the use of an immersion liquid on the substrate W or the use of a vacuum. A vacuum environment can be used for EUV or electron beam radiation since other gases can absorb too much radiation or electrons. A vacuum environment can therefore be provided to the whole beam path with the aid of avacuum wall and vacuum pumps.

[0076] Lithographic apparatus 100 and / or lithographic apparatus 100’ can be of a type having two (dual stage) or more substrate tables WT (and / or two or more mask tables). In such “multiple stage” machines, the additional substrate tables WT can be used in parallel, or preparatory steps can be carried out on one or more tables while one or more other substrate tables WT are being used for exposure. In some situations, the additional table may not be a substrate table WT. For example, alignment measurements using an alignment sensor AS and / or level (height, tilt, etc.) measurements using a level sensor LS may be made (in FIG. IB).

[0077] Referring to FIGS. 1 A and IB, the illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus 100, 100’ can be separate physical entities, for example, when the source SO is an excimer laser. In such cases, the source SO is not considered to form part of the lithographic apparatus 100 or 100’, and the radiation beam B passes from the source SO to the illuminator IL with the aid of a beam delivery system BD (in FIG. IB) including, for example, suitable directing mirrors and / or a beam expander. In other cases, the source SO can be an integral part of the lithographic apparatus 100, 100’ — for example when the source SO is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD, if required, can be referred to as a radiation system.

[0078] The illuminator IL may alter the intensity distribution of the beam. The illuminator may be arranged to limit the radial extent of the radiation beam such that the intensity distribution is non- zero within an annular region in a pupil plane of the illuminator IL. Additionally or alternatively, the illuminator IL may be operable to limit the distribution of the beam in the pupil plane such that the intensity distribution is non-zero in a plurality of equally spaced sectors in the pupil plane. The intensity distribution of the radiation beam in a pupil plane of the illuminator IL may be referred to as an illumination mode.

[0079] The illuminator IL can include an adjuster AD (in FIG. IB) for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radial extent (commonly referred to as “o-outcr” and “o-inner,” respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL can comprise various other components (in FIG. IB), such as an integrator IN and a condenser CN. The illuminator IL can be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross section.

[0080] Referring to FIG. 1A, the radiation beam B is incident on the patterning device (for example, mask) MA, which is held on the support structure (for example, mask table) MT, and is patterned by the patterning device MA. In lithographic apparatus 100, the radiation beam B is reflected from the patterning device (for example, mask) MA. After being reflected from the patterning device (for example, mask) MA, the radiation beam B passes through the projection system PS, which focuses the radiation beam B onto a target portion C of the substrate W. With the aid of thesecond positioner PW and position sensor IF2 (for example, an interferometric device, linear encoder, or capacitive sensor), the substrate table WT can be moved accurately (for example, so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor IF1 (for example, an interferometric device, linear encoder, or capacitive sensor) can be used to accurately position the patterning device (for example, mask) MA with respect to the path of the radiation beam B. Patterning device (for example, mask) MA and substrate W can be aligned using mask alignment marks Ml, M2 and substrate alignment marks Pl, P2.

[0081] Referring to FIG. IB, the radiation beam B is incident on the patterning device (for example, mask MA), which is held on the support structure (for example, mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. The projection system PS is supported on a reference frame RF.

[0082] The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) or deep ultraviolet (DUV) radiation (e.g. having a wavelength of 365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams.

[0083] With the aid of the second positioner PW and position sensor IF2 (for example, an interferometric device, linear encoder, or capacitive sensor), the substrate table WT can be moved accurately (for example, so as to position different target portions C in the path of the radiation beam B). The position sensor IF2 measures the substrate table WT in three dimensions. In this example, the position sensor IF2 is an interferometric device. The z-direction interferometers are positioned to the side of the substrate table WT. The interferometric mirrors have 45-degree angled surfaces attached to the left and the right side of the substrate table WT. The interferometric lasers are mounted such that the laser light is incident upon the interferometric mirrors. FIG. IB shows the relationship between the interferometric lasers and the mirrors of the position sensor IF2. Similarly, the first positioner PM and another position sensor IF1 (shown in FIG. 1 A) can be used to accurately position the mask MA with respect to the path of the radiation beam B (for example, after mechanical retrieval from a mask library or during a scan). The position sensor IF1 measures the mask table MT in three dimensions. In this example, the position sensor IF1 is an interferometric device. The z- direction interferometers are positioned to the side of the mask table MT. The interferometric mirrors have 45-degree angled surfaces attached to the left and the right side of the mask table MT. The interferometric lasers are mounted such that the laser light is incident upon the interferometric mirrors.

[0084] In general, movement of the mask table MT can be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT can be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of astepper (as opposed to a scanner), the mask table MT can be connected to a short-stroke actuator only or can be fixed. Mask MA and substrate W can be aligned using mask alignment marks Ml, M2, and substrate alignment marks Pl, P2. Although the substrate alignment marks (as illustrated) occupy dedicated target portions, they can be located in spaces between target portions (known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks can be located between the dies.

[0085] The lithographic apparatus 100 and 100’ can be used in at least one of the following modes:

[0086] 1. In step mode, the support structure (for example, mask table) MT and the substrate tableWT are kept essentially stationary, while an entire pattern imparted to the radiation beam B is projected onto a target portion C at one time (i.e., a single static exposure). The substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed.

[0087] 2. In scan mode, the support structure (for example, mask table) MT and the substrate tableWT are scanned synchronously while a pattern imparted to the radiation beam B is projected onto a target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (for example, mask table) MT can be determined by the (de-)magnification and image reversal characteristics of the projection system PS.

[0088] 3. In another mode, the support structure (for example, mask table) MT is kept substantially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. A pulsed radiation source SO can be employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes a programmable patterning device, such as a programmable mirror array.

[0089] Combinations and / or variations on the described modes of use or entirely different modes of use can also be employed.

[0090] In some embodiments, lithographic apparatus 100 includes an extreme ultraviolet (EUV) source, which is configured to generate a beam of EUV radiation for EUV lithography. In general, the EUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV source.

[0091] FIG. 1C shows the lithographic apparatus 100 in more detail, including the source collector apparatus SO, the illumination system IL, and the projection system PS. The source collector apparatus SO is constructed and arranged such that a vacuum environment can be maintained in an enclosing structure 120 of the source collector apparatus SO. An EUV radiation emitting plasma 110 may be formed by a discharge produced plasma source. EUV radiation may be produced by a gas or vapor, for example Xe gas, Li vapor or Sn vapor in which the hot plasma 110 is created to emit radiation in the EUV range of the electromagnetic spectrum. The hot plasma 110 is created by, for example, an electrical discharge causing an at least partially ionized plasma. Partial pressures of, forexample, 10 Pa of Xe, Li, Sn vapor or any other suitable gas or vapor may be required for efficient generation of the radiation. In an embodiment, a plasma of excited tin (Sn) is provided to produce EUV radiation.

[0092] The radiation emitted by the hot plasma 110 is passed from a source chamber 111 into a collector chamber 112 via an optional gas barrier or contaminant trap 113 (in some cases also referred to as contaminant barrier or foil trap) which is positioned in or behind an opening in source chamber 111. The contaminant trap 113 may include a channel structure. Contamination trap 113 may also include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap 113 further indicated herein at least includes a channel structure, as known in the art.

[0093] The collector chamber 112 may include a radiation collector CO which may be a so-called grazing incidence collector. Radiation collector CO has an upstream radiation collector side 151 and a downstream radiation collector side 152. Radiation that traverses collector CO can be reflected off a grating spectral filter 140 to be focused at a virtual source point IFP. The virtual source point IFP is commonly referred to as the intermediate focus, and the source collector apparatus is arranged such that the intermediate focus IFP is located at or near an opening 119 in the enclosing structure 120. The virtual source point IFP is an image of the radiation emitting plasma 110. Grating spectral filter 140 is used in particular for suppressing infra-red (IR) radiation.

[0094] Subsequently the radiation traverses the illumination system IL, which may include a facetted field mirror device 122 and a facetted pupil mirror device 124 arranged to provide a desired angular distribution of the radiation beam 121, at the patterning device MA, as well as a desired uniformity of radiation intensity at the patterning device MA. Upon reflection of the radiation beam 121 at the patterning device MA, held by the support structure MT, a patterned beam 126 is formed and the patterned beam 126 is imaged by the projection system PS via reflective elements 128, 130 onto a substrate W held by the wafer stage or substrate table WT.

[0095] More elements than shown may generally be present in illumination optics unit IL and projection system PS. The grating spectral filter 140 may optionally be present, depending upon the type of lithographic apparatus. Further, there may be more mirrors present than those shown in the FIGS., for example there may be 1-6 additional reflective elements present in the projection system PS than shown in FIG. 1C.

[0096] Collector optic CO, as illustrated in FIG. 1C, is depicted as a nested collector with grazing incidence reflectors 153, 154 and 155, just as an example of a collector (or collector mirror). The grazing incidence reflectors 153, 154 and 155 are disposed axially symmetric around an optical axis O and a collector optic CO of this type is preferably used in combination with a discharge produced plasma source, often called a DPP source.

[0097] As shown in FIG. 2, the lithographic apparatus 100 or 100’ (indicated as “LA” in Fig. 2) may form part of a lithographic cell LC, also sometimes referred to as a lithocell or cluster, which also includes apparatuses to perform pre- and post-exposure processes on a substrate. Conventionallythese include one or more spin coaters SC to deposit one or more resist layers, one or more developers to develop exposed resist, one or more chill plates CH and / or one or more bake plates BK. A substrate handler, or robot, RO picks up one or more substrates from input / output port I / O I , I / O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus. These apparatuses, which are often collectively referred to as the track, are under the control of a track control unit TCU which is itself controlled by the supervisory control system SCS, which also controls the lithographic apparatus via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

[0098] In order that a substrate that is exposed by the lithographic apparatus is exposed correctly and consistently and / or in order to monitor a part of the patterning process (e.g., a device manufacturing process) that includes at least one pattern transfer step (e.g., an optical lithography step), it is desirable to inspect a substrate or other object to measure or determine one or more properties such as alignment, overlay (which can be, for example, between structures in overlying layers or between structures in a same layer that have been provided separately to the layer by, for example, a double patterning process), line thickness, critical dimension (CD), focus offset, a material property, etc. For example, contamination on reticle clamp membranes (e.g., as described herein) may adversely affect overlay because clamping a reticle over such contamination will distort the reticle. Accordingly, a manufacturing facility in which lithocell LC is located also typically includes a metrology system that measures some or all of the substrates W (FIGS. 1A-1C) that have been processed in the lithocell or other objects in the lithocell. The metrology system may be part of the lithocell LC, for example it may be part of the lithographic apparatus 100 or 100’.

[0099] The one or more measured parameters may include, for example, alignment, overlay between successive layers formed in or on the patterned substrate, critical dimension (CD) (e.g., critical linewidth) of, for example, features formed in or on the patterned substrate, focus or focus error of an optical lithography step, dose or dose error of an optical lithography step, optical aberrations of an optical lithography step, etc. This measurement may be performed on a target of the product substrate itself and / or on a dedicated metrology target provided on the substrate. The measurement can be performed after-development of a resist but before etching, after-etching, after deposition, and / or at other times.

[0100] There are various techniques for making measurements of the structures formed in the patterning process, including the use of a scanning electron microscope, an image-based measurement tool and / or various specialized tools. As discussed above, a fast and non-invasive form of specialized metrology tool is one in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered (diffracted / reflected) beam are measured. By evaluating one or more properties of the radiation scattered by the substrate, one or more properties of the substrate can be determined. This may be termed diffraction-based metrology. One such application of this diffraction-based metrology is in the measurement of feature asymmetry within a target. This can beused as a measure of overlay, for example, but other applications are also known. For example, asymmetry can be measured by comparing opposite parts of the diffraction spectrum (for example, comparing the -1stand +lstorders in the diffraction spectrum of a periodic grating). Another application of diffraction-based metrology is in the measurement of feature width (CD) within a target.

[0101] Thus, in a device fabrication process (e.g., a patterning process, a lithography process, etc.), a substrate or other objects may be subjected to various types of measurement during or after the process. The measurement may determine whether a particular substrate is defective, may establish adjustments to the process and apparatuses used in the process (e.g., aligning two layers on the substrate or aligning the patterning device to the substrate), may measure the performance of the process and the apparatuses, or may be for other purposes. Examples of measurement include optical imaging (e.g., optical microscope), non-imaging optical measurement (e.g., measurement based on diffraction such as the ASML YieldStar metrology tool, the ASML SMASH metrology system), mechanical measurement (e.g., profiling using a stylus, atomic force microscopy (AFM)), and / or non- optical imaging (e.g., scanning electron microscopy (SEM)).

[0102] Metrology results may be provided directly or indirectly to the supervisory control system SCS. If an error is detected, an adjustment may be made to exposure of a subsequent substrate (especially if the inspection can be done soon and fast enough that one or more other substrates of the batch are still to be exposed) and / or to subsequent exposure of the exposed substrate. Also, an already exposed substrate may be stripped and reworked to improve yield, or discarded, thereby avoiding performing further processing on a substrate known to be faulty. In a case where only some target portions of a substrate are faulty, further exposures may be performed only on those target portions which meet specifications.

[0103] Within a metrology system, a metrology apparatus is used to determine one or more properties of the substrate, and in particular, how one or more properties of different substrates vary, or different layers of the same substrate vary from layer to layer. As noted above, the metrology apparatus may be integrated into the lithographic apparatus LA or the lithocell LC or may be a standalone device.

[0104] To enable the metrology, one or more targets can be provided on the substrate. In an embodiment, the target is specially designed and may comprise a periodic structure. In an embodiment, the target is a part of a device pattern, e.g., a periodic structure of the device pattern. In an embodiment, the device pattern is a periodic structure of a memory device (e.g., a Bipolar Transistor (BPT), a Bit Line Contact (BLC), etc. structure).

[0105] In an embodiment, the target on a substrate may comprise one or more 1-D periodic structures (e.g., gratings), which are printed such that after development, the periodic structural features are formed of solid resist lines. In an embodiment, the target may comprise one or more 2-D periodic structures (e.g., gratings), which are printed such that after development, the one or moreperiodic structures are formed of solid resist pillars or vias in the resist. The bars, pillars, or vias may alternatively be etched into the substrate (e.g., into one or more layers on the substrate).

[0106] In an embodiment, one of the parameters of interest of a patterning process is overlay. Overlay can be measured using dark field scatterometry in which the zeroth order of diffraction (corresponding to a specular reflection) is blocked, and only higher orders processed. Diffractionbased overlay using dark-field detection of the diffraction orders enables overlay measurements on smaller targets. These targets can be smaller than the illumination spot and may be surrounded by device product structures on a substrate. In an embodiment, multiple targets can be measured in one radiation capture.

[0107] As lithography nodes keep shrinking, more and more complicated wafer designs may be implemented. Various tools and / or techniques may be used by designers to ensure complex designs are accurately transferred to physical wafers. These tools and techniques may include mask optimization, source mask optimization (SMO), OPC, design for control, and / or other tools and / or techniques. For example, a source mask optimization process is described in United States Patent No. 9,588,438 titled “Optimization Flows of Source, Mask and Projection Optics”, which is incorporated in its entirety by reference.

[0108] The present systems, and / or methods may be used as stand-alone tools and / or techniques, and / or or used in conjunction with semiconductor manufacturing processes, to enhance the accurate transfer of complex designs to physical wafers.

[0109] FIG. 3A illustrates a reticle load lock 300. The reticle load lock 300 includes a load lock chamber 301, closures 302A and 302B, a pump system 303 A, a venting system 303B, controllers 304A and 304B, valves 305A and 305B, a pressure sensor 306, closure drives 307A and 307B, robots 308A and 308B, vacuum chamber 310A, and atmospheric chamber 310B. The load lock chamber 301 comprises an enclosed housing, or space, that is pumped down to vacuum conditions or vented back to atmospheric conditions. The load lock chamber 301 has closures 302 A and 302B configured to facilitate insertion or removal of the reticle or mask MA. Closures 302A and 302B are movable between an open and a closed position. FIG. 3A shows closures 302A and 302B in the closed position. Closures 302A and 302B can be moved to the open position using the closure drives 307A and 307B, respectively. In some embodiments, the closures 302A and 302B are gate valves. In another embodiment, the closures 302A and 302B are doors that move between open and closed positions. In another embodiment, a different type of valve can be used for the closures 302A and 302B. The vacuum closure 302A is an opening that can be opened to connect the load lock chamber 301 to the vacuum chamber 310A, and the atmospheric closure 302B is an opening that can be opened to connect the load lock chamber 301 to the atmospheric chamber 310B. The insertion or removal of the reticle MA can be performed by the robots 308A and 308B, such as robot arms (shown as arrows in FIG. 3A; more detail shown in FIG. 3B).

[0110] On a vacuum side of the load lock chamber 301, the robot 308A is an in-vacuum robot(IVR) that transports the reticle MA from the load lock chamber 301 to a vacuum chamber 310A and vice versa. The transport of the reticle MA by the robot 308A is done through the vacuum closure 302A. The closure 302A is only open when the reticle MA is ready to move between the chambers. The vacuum closure 302A is opened and closed by the vacuum closure drive 307A. The pump system 303A is a vacuum pump configured to pump down the load lock chamber 301 from atmospheric pressure to vacuum pressure. The pump system 303A evacuates the load lock chamber 301 by pumping air out of the chamber 301 until it reaches vacuum levels. The speed at which the load lock chamber 301 is pumped down is controlled by the vacuum valve 305A and the vacuum controller 304A. The vacuum valve 305A has an orifice of variable size that is controlled by the vacuum controller 304A. The vacuum valve 305A is configured to communicate the pump system 303A with the chamber 301 such that the pump system 303A can be used to pump gas out of the chamber 301. The vacuum valve 305 A can be a servo control valve, proportioning valve, or any other type of suitable valve. For example, the valve 305A can be a servo-controlled variable flow valve for pump down. The orifice size of the vacuum valve 305 A affects the rate at which the chamber 301 can be pumped down. The larger the orifice size is, the greater the evacuation rate of the pump system 303 A, and the faster that the chamber 301 reaches vacuum conditions. The controller 304A is capable of enlarging the orifice size of the valve 305A to increase the vacuum pump down speed. Alternatively, the controller 304A can also reduce the orifice size of the valve 305A to decrease the pump down speed. The vacuum controller 304A is operatively connected with the vacuum valve 305A and configured to control the size of the orifice to control a pressure in the chamber 301 over time based on a desired pressure profile.

[0111] On an atmospheric side of the load lock chamber 301, the robot 308B is an out of vacuum robot (OVR) that transports the reticle MA from the load lock chamber 301 to an atmospheric chamber 310B and vice versa. The transport of the reticle MA by the robot 308B is done through the atmospheric closure 302B. The closure 302B is only open when the reticle MA is ready to move between the chambers. The atmospheric closure 302B is opened and closed by the atmospheric closure drive 307B. The venting system 303B introduces air into the load lock chamber 301 to bring the chamber 301 from vacuum pressure to atmospheric pressure. The venting system 303B delivers pressurized clean dry air (CD A) into the chamber 301, but other suitable gases can also be used. The speed at which the load lock chamber 301 is vented is controlled by the atmospheric valve 305B and the atmospheric controller 304B. The atmospheric valve 305B has an orifice of variable size that is controlled by the atmospheric controller 304B. The atmospheric valve 305B is configured to communicate the venting system 303B with the chamber 301 such that the venting system 303B can be used to introduce gas into the chamber 301. The atmospheric valve 305B can be a servo control valve, proportioning valve, or any other type of suitable valve. For example, the valve 305B can be a servo-controlled variable flow valve for venting. The orifice size of the atmospheric valve 305B affects the rate at which the chamber 301 can be vented. The larger the orifice size is, the greater theventing rate of the venting system 303B, and the faster that the chamber 301 reaches atmospheric conditions. The controller 304B is capable of enlarging the orifice size of the valve 305B to increase the venting speed. Alternatively, the controller 304B can also reduce the orifice size of the valve 305B to decrease the venting speed. The atmospheric controller 304B is operatively connected with the atmospheric valve 305B and configured to control the size of the orifice to control a pressure in the chamber 301 over time based on a desired pressure profile.

[0112] The reticle arrangement shown in FIG. 3A will now be described. A pellicle PEL can be attached to the reticle MA to prevent particulates from reaching the reticle MA. The pellicle PEL is a thin, transparent membrane that covers the reticle MA to prevent contaminants from reaching the reticle surface. The pellicle PEL acts as a protective shield to or filter to prevent dust or contaminant particles from interfering with the imaging of the reticle MA pattern and thereby cause defects in an imaged wafer. The surface of the pellicle PEL is not flush with the pattern of the reticle MA so that the dust particles that attach to the pellicle PEL will remain out of focus during exposure. When attached, there remains a small air gap AG between the pellicle PEL and the reticle MA. The air gap AG is approximately 200 pm wide but can range between 100 to 300 pm wide or between 50 pm to 1 mm wide.

[0113] FIG. 3B shows a perspective illustration of the reticle load lock 300. On the vacuum side, the load lock chamber 301 is used for pumping down or venting the reticle MA. After pump down, the reticle MA is transferred through the closure 302A (not shown in FIG. 3B; see FIG. 3 A) on the right side of the load lock chamber 301 by the in-vacuum robot (IVR) 308A to an in-vacuum library (IVL) 331 for temporarily storing the reticle MA before use. Thereafter, the IVR 308 A retrieves the desired reticle MA from the IVL 331 and provides the reticle MA to a reticle exchange device (RED) 332. The RED 332 is used to change reticles during the lithography process in the least possible amount of time. On the atmosphere side, a load port 320 serves as an entry point to the lithography apparatus 100 or 100’ (FIGS. 1A-1C) via which the reticle MA is introduced into the lithography apparatus 100 or 100’. The out of vacuum robot (OVR) 308B retrieves the reticle MA from the load port 320 and brings the reticle MA to the load lock chamber 301 through the closure 302B (not shown in FIG. 3B; see FIG. 3A) on the left side of the load lock chamber 301 to be pumped down.

[0114] The right side of FIG. 3B shows that the RED 332, exchanges the reticle MA, to which the pellicle PEL is attached, that rests on the support structure MT. The air gap AG is not pictured between the reticle MA and the pellicle PEL but is still present. The RED 332 removes one reticle MA and pellicle PEL from the support structure MT and replaces it with another reticle MA and pellicle PEL on the support structure MT.

[0115] When the reticle MA is placed in the chamber 301, the gas in the chamber 301 can be evacuated to bring the reticle MA in the chamber 301 to a vacuum environment. From the vacuum environment, gas can be allowed back into the chamber 301 to bring the chamber 301 to a nonvacuum environment, which is at atmospheric pressure. The pump system 303A and the ventingsystem 303B are configured to evacuate or pressurize the chamber 301, respectively. The pressure sensor 306 is operatively connected with the controllers 304A and 304B and configured to monitor pressure within the chamber 301, and to provide pressure signals to the controllers 304A and 304B indicative of the pressure within the chamber 301. As a result, the controllers 304 A and 304B control the orifice size based on the pressure signals. Further, the controllers 304A and 304B are preprogrammed to control the orifice size based on a predetermined pressure over time profile. The pressure sensor 306 can be a pressure transducer or any other type of detector that can measure the pressure within the chamber 301.

[0116] The reticle load lock 300 shown in FIGS. 3 A and 3B can be part of the lithography apparatus 100 or 100’ shown in FIGS. 1A-1C. Alternatively, the reticle load lock 300 can be separate from yet connected to the lithography apparatus 100 or 100’.

[0117] Pumping down is the process of bringing the chamber 301 initially at atmospheric pressure to vacuum pressure. This is done by evacuating the gas out of the chamber 301 with the pump system 303A. The process of continuously removing gas from the chamber 301 will eventually bring the chamber 301 to vacuum conditions. Pump down is performed to bring the reticle MA from the ambient environment to the vacuum conditions of the lithography apparatus 100 or 100’. On the other hand, venting is done with the venting system 303B and is the process of bringing the chamber 301 from vacuum pressure to atmospheric pressure. Venting introduces gas back into the chamber 301 to increase the pressure. The process of continuously introducing gas into the chamber 301 will eventually bring the chamber 301 to atmospheric conditions. Venting is typically performed after pump down.

[0118] Due to the small air gap AG between the reticle MA and the pellicle PEL, the change of pressure over time produced by the pump system 303A or the venting system 303B in the chamber 301 cannot exceed a certain value, lest the pellicle PEL will break. If the pressure changes too quickly, then the air gap AG will expand or contract so much that the thin membrane of the pellicle PEL will rupture. As a result, the rate of pressure change must be monitored by the pressure sensor 306 to ensure that it stays under a predetermined threshold. By reducing the pressure change, the air gap AG expands or contracts more slowly, which minimizes the stress acting on the pellicle PEL. A pressure over time profile has been determined for venting or pumping down to minimize venting and / or pumping time yet maintain the structural integrity of the pellicle PEL. From modeling and / or testing, an optimal pressure over time profile has been determined. By closely following this pressure over time profile, it can be assured that the chamber 301 is being pumped down or vented at the highest speed possible without damaging the pellicle PEL.

[0119] Further, there is a finely controlled orifice size to keep the pressure in the load lock close to the determined pressure profile of the graph during venting and pump down. This requires close monitoring of the pressure with the pressure sensor 306, such as a pressure transducer, which sends pressure signals to the controllers 304A and 304B, and the controllers 304A and 304B closely controlvalve opening size (making it bigger or smaller) to make sure pressure stays within a plus or minus range of the pressure profile curve. This is an iterative / continuous process.

[0120] The pressure sensor 306 provides real-time feedback to the controllers 304A and 304B regarding the pressure within the chamber 301. As such, an iterative and continuous process is performed to ensure that the pressure stays within a ±5% range of the pressure profile curve. As a result, the orifice size of the valves 305A and 305B can be enlarged, reduced, or kept at the same size to optimize pressure rates. Based on the pressure signals measured by the pressure sensor 306, the controllers 304A and 304B can determine how the orifice size should be adjusted, if at all. The orifice sizes of the valves 305A and 305B are changed to maximize pumping / venting speed as well as protect the pellicle integrity.

[0121] On the other hand, if the reticle MA does not use a pellicle PEL, then the reticle MA can be pumped down and vented in the reticle load lock 300 faster than if a pellicle PEL was used. Since there is no pellicle PEL or air gap AG to be concerned with, the reticle MA can be evacuated or vented much quicker.

[0122] FIG. 4A shows the pressure rate curve for venting, and FIG. 4B shows the pressure profile for pump down. The pressure rate curves illustrate the pressure rate (dP / dt) as a function of pressure. Pressure rate (dP / dt) is a change of pressure over time. The more that the pressure changes over a short period of time, the higher the pressure rate will be. A higher pressure rate will allow for faster pump down or venting. However, too high of a pressure rate, and the pellicle PEL will burst due to the air gap AG (FIG. 3A). Consequently, the limiting factor in pressure rate is ensuring the structural integrity of the pellicle PEL. The pressure sensor 306 measures the pressure within the load lock chamber 301. That value is measured in pascals (Pa) in this example. Further, pressure rate (dP / dt) can be calculated by taking the change of the pressure measured by the pressure sensor 306 over a certain length of time. For example, if the pressure is measured by the pressure sensor 306 every second, then the difference between the two measurements will be the pressure rate.

[0123] As described above, the reticle load lock 300 is configured to facilitate the use of a servo control valve. Servo valving is accomplished by using an orifice of variable size to quickly pump the load lock chamber 301 down to a vacuum level, or vent that chamber 301 back to atmospheric pressure. Discrete valving is the conventional method of using three discrete valves and orifices for pump down and / or venting. Venting has a different pressure profile than pump down. The venting graph shown in FIG. 4A brings the pressure from 0.1 Pa (vacuum pressure) to 105Pa (atmospheric pressure). The venting curve of FIG. 4A should be read from left (0.1 Pa) to right (105Pa). Conversely, the pump down graph shown in FIG. 4B pumps the pressure from 105Pa (atmospheric pressure) down to 0.1 Pa (vacuum pressure). The pump down curve of FIG. 4B should be read from right (105Pa) to left (0.1 Pa). Although the pressure profiles are different, each process in servo valving takes about 90 seconds. The combined times are cut significantly compared to typical discrete valving. For example, discrete valving usually takes approximately 220 seconds for ventingand 160 seconds for pump down. Discrete valving uses three discrete valves and orifices, which can be seen in the graph as three distinct steps. In FIG. 4A, the three discrete steps are shown as Al, A2, and A3. Al is venting at one orifice size, which is followed with A2 venting at a different orifice size, and finally A3 brings the pressure to atmosphere at a third orifice size. The orifice sizes increase as the venting progresses from Al to A3. In other words, the size of the orifice is smallest for Al, medium for A2, and largest for A3. For FIG. 4B, the three discrete steps are shown as Bl, B2, and B3. Similarly, Bl pumps down at a first orifice size, then B2 pumps down at a second orifice size, and finally B3 pumps the chamber 301 to a vacuum pressure at a third orifice size. The orifice sizes increase as the pumping progresses from Bl to B3. In other words, the size of the orifice is smallest for Bl, medium for B2, and largest for B3. Discrete valving is not optimized, because the load lock can pump faster without breaking the pellicle. However, since there are only three valves, each of fixed orifice size, there is no way to take advantage of pumping and / or venting at optimal speeds. Therefore, servo valving is faster because the orifice is incrementally adjusted. The servo valving pressure profile follows a greater pressure rate yet maintains the structural integrity of the pellicle. The optimized servo valving curves minimize the pump and vent times without exceeding the pressure rate (dP / dt) limits. The areas between the servo valve graph and the discrete valve graph are the wasted throughput. As a result, servo valving significantly reduces the pump times within the reticle load lock. Using the servo valving method doubles the throughput through the load lock.

[0124] Further, by using a servo valve or a proportioning valve, updates can be easily made to implement multiple pressure rate curves or change the curve through software changes. There is no need to create more valves and orifices. Rather, the servo valve having an orifice of variable size can be programmed to a desired size. As a result, any desired pumping or venting speed can be achieved.

[0125] FIG. 5 illustrates a method 500 for using the reticle load lock. In some embodiments, one or more operations of method 500 may be controlled by one or more processors and / or a computing system, as described below (see FIG. 6). The operations of method 500 presented below are intended to be illustrative. In some embodiments, method 500 may be accomplished with one or more additional operations not described, and / or without one or more of the operations discussed. Additionally, the order in which the operations of method 500 are illustrated in FIG. 5 and described below is not intended to be limiting.

[0126] In some embodiments, one or more operations of method 500 may be implemented in and / or controlled by one or more processing devices (e.g., a digital processor, an analog processor, a digital circuit designed to process information, an analog circuit designed to process information, a state machine, and / or other mechanisms for electronically processing information, as described with respect to FIG. 6 below). The one or more processing devices may include one or more devices executing some or all of the operations of method 500 in response to instructions stored electronically on an electronic storage medium. The one or more processing devices may include one or more devices configured through hardware, firmware, and / or software to be specifically designed forexecution of one or more of the operations of method 500 (e.g., see discussion related to FIG. 6 below).

[0127] At an operation 501, the reticle MA is inserted into the load lock chamber 301 from the atmospheric chamber 310B through the closure 302B, as shown in FIG. 3A. The insertion can be performed by the robot 308B. When the reticle MA is inserted, the load lock chamber 301 is at atmospheric, or ambient, pressure. In other words, the pressure inside the load lock chamber 301 is the same as the pressure in the room.

[0128] At an operation 502, gas is evacuated from the load lock chamber 301 using the pump system 303A via the vacuum valve 305A having an orifice of variable size, as shown in FIG. 3A. By controlling the size of the orifice, the pressure in the chamber 301 can be controlled over time. The size of the orifice is directly proportional to the speed at which the load lock chamber 301 is pumped down. The larger the orifice size is, the faster that gas is removed from the chamber 301. The orifice can be sized based on known pressure profiles that maintain the structural integrity of the pellicle PEL attached to the reticle MA. The vacuum controller 304A operatively connected to the valve 305A pumps down the chamber 301 based on a desired pump down pressure profile. The desired pump down pressure rate curve is shown as the servo valving curve in FIG. 4B. By closely following the pressure rate curve, the pump down time can be optimized without destroying the pellicle PEL. The pumping down ends when the desired pressure has been reached, which is, in this example, vacuum pressure.

[0129] At an operation 503, the reticle MA is moved from the load lock chamber 301 in FIG. 3A to a lithography apparatus 100 or 100’ in FIGS. 1A-1C. This is performed by the robot 308A or the like. The reticle MA, which is at vacuum pressure, will be entering the lithography apparatus 100 or 100’ which is also at vacuum pressure. The reticle MA will be positioned on the mask table MT, as shown in FIGS. 1A-1C.

[0130] At an operation 504, a substrate W in the lithography apparatus 100 or 100’ in FIGS. 1A- 1C is exposed to the pattern of the reticle MA. A radiation beam B emitted from a source SO is incident on the reticle MA and exposes the substrate W using the reticle pattern. As a result, the pattern of the reticle MA is patterned onto the substrate W. All of the target portions C of the substrate W are exposed to the reticle MA before exposure is complete.

[0131] At an operation 505, the reticle MA is moved from the lithography apparatus 100 or 100’ in FIGS. 1A-1C to the load lock chamber 301 in FIG. 3 A. This is performed by the robot 308 A or the like. This can be done by the same robot arm in operation 503 or a different robot arm. At this point, the load lock chamber 301 is still at vacuum pressure.

[0132] After operation 505 is complete, operation 506 is performed. Operation 506 involves venting the load lock chamber 301 using the venting system 303B with the venting valve 305B having the orifice of variable size, as shown in FIG. 3A. By controlling the size of the orifice, the pressure in the chamber 301 can be controlled over time. The size of the orifice is directly proportional to thespeed at which the load lock chamber 301 is vented. The larger the orifice size is, the faster that gas enters the chamber 301. The orifice can be sized based on known pressure profiles that maintain the structural integrity of the pellicle PEL attached to the reticle MA. The venting controller 304B operatively connected to the valve 305B vents the chamber 301 based on a desired venting pressure profile. The desired venting pressure rate curve is shown as the servo valving curve in FIG. 4A. By closely following the pressure rate curve, the venting time can be optimized without destroying the pellicle PEL. The venting ends when the desired pressure has been reached, which is, in this example, atmospheric pressure.

[0133] At an operation 507, the reticle MA is removed from the load lock chamber 301 to the atmospheric chamber 310B through the atmospheric closure 302B, as shown in FIG. 3A. The removal can be performed by the robot 308B. When the reticle is removed, the load lock chamber 301 is at atmospheric, or ambient, pressure. In other words, the pressure inside the load lock chamber 301 is the same as the pressure in the room.

[0134] The reticle load lock 300 is not limited to reticles. Other components that need to be brought to vacuum pressure can also use the load lock, such as the substrate W, components of the source SO, components of the illuminator IL, or components of the projection system PS.

[0135] FIG. 6 is a block diagram that illustrates a computer system CS that can assist in implementing the methods, flows, or the system(s) disclosed herein. Computer system CS may be included in and / or electronically coupled to the lithography apparatus 100 or 100’ described above (FIGS. 1 A-1C). Computer system CS includes a bus BS or other communication mechanism for communicating information, and a processor PRO1 (or multiple processors PRO1, PRO2, etc.) coupled with bus BS for processing information. Computer system CS also includes a main memory MM, such as a random access memory (RAM) or other dynamic storage device, coupled to bus BS for storing information and instructions to be executed by processor PRO1. Main memory MM also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by processor PRO1. Computer system CS further includes a read only memory ROM or other static storage device coupled to bus BS for storing static information and instructions for processor PRO1. A storage device SD, such as a magnetic disk or optical disk, is provided and coupled to bus BS for storing information and instructions.

[0136] Computer system CS may be coupled via bus BS to a display DS, such as a cathode ray tube (CRT) or flat panel or touch panel display for displaying information to a computer user. An input device ID, including alphanumeric and other keys, is coupled to bus BS for communicating information and command selections to processor PRO1. Another type of user input device is cursor control CC, such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to processor ROM and for controlling cursor movement on display DS. This input device typically has two degrees of freedom in two axes, a first axis (e.g., X) and a second axis (e.g., Y), that allows the device to specify positions in a plane. A touch panel(screen) display may also be used as an input device.

[0137] According to one embodiment, portions of one or more flows and / or methods described herein may be performed by computer system CS in response to processor PRO1 executing one or more sequences of one or more instructions contained in main memory MM. Such instructions may be read into main memory MM from another computer-readable medium, such as storage device SD. Execution of the sequences of instructions contained in main memory MM causes processor PRO1 to perform the flows and / or process steps described herein. One or more processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in main memory MM. In an alternative embodiment, hard-wired circuitry may be used in place of or in combination with software instructions. Thus, the description herein is not limited to any specific combination of hardware circuitry and software.

[0138] The term “computer-readable medium” or “machine readable medium” as used herein refers to any medium that participates in providing instructions to processor PRO1 for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as storage device SD. Volatile media include dynamic memory, such as main memory MM. Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise bus BS. Transmission media can also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH- EPROM, any other memory chip or cartridge, a carrier wave as described hereinafter, or any other medium from which a computer can read.

[0139] Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to processor PRO1 for execution. For example, the instructions may initially be borne on a magnetic disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a network such as the internet. A modem local to computer system CS can receive the data and use an infrared transmitter to convert the data to an infrared signal. An infrared detector coupled to bus BS can receive the data carried in the infrared signal and place the data on bus BS. Bus BS carries the data to main memory MM, from which processor PRO1 retrieves and executes the instructions. The instructions received by main memory MM may optionally be stored on storage device SD either before or after execution by processor PRO1.

[0140] Computer system CS may also include a communication interface CI coupled to bus BS. Communication interface CI provides a two-way data communication coupling to a network link NL that is connected to a local network LAN. For example, communication interface CI may be anintegrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, communication interface CI may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links may also be implemented. In any such implementation, communication interface CI sends and receives electrical, electromagnetic, or optical signals that carry digital data streams representing various types of information.

[0141] Network link NL typically provides data communication through one or more networks to other data devices. For example, network link NL may provide a connection through local network LAN to a host computer HC or to data equipment operated by an Internet Service Provider ISP. Internet Service Provider ISP in turn provides data communication services through the worldwide packet data communication network, now commonly referred to as the “Internet” INT. Local network LAN and Internet INT both use electrical, electromagnetic, or optical signals that carry digital data streams. The signals through the various networks and the signals on network link NL and through communication interface CI, which carry the digital data to and from computer system CS, are exemplary forms of carrier waves transporting the information.

[0142] Computer system CS can send messages and receive data, including program code, through the network(s), network link NL, and communication interface CL In the Internet example, a server SV might transmit a requested code for an application program through Internet INT, Internet Service Provider ISP, local network LAN and communication interface CL One such downloaded application may provide all or part of a method described herein, for example. The received code may be executed by processor PRO1 as it is received, and / or stored in storage device SD, or other nonvolatile storage for later execution. In this manner, computer system CS may obtain application code in the form of a carrier wave.

[0143] Various embodiments of the present systems and methods are disclosed in the subsequent list of numbered clauses:1. A reticle load lock, comprising: a load lock chamber, wherein the chamber has a closure movable between an open and a closed position, wherein when the closure is in the open position, a reticle can be inserted or removed from the chamber; a pump system configured to evacuate the chamber; a venting system configured to pressurize the chamber; a first valve having an orifice of variable size and configured to communicate the pump system with the chamber; a second valve having an orifice of variable size and configured to communicate the venting system with the chamber; and a controller operatively connected with the first and second valves and configured to control the size of the orifice to control a pressure in the chamber over time based on a desired pressure profile.2. The reticle load lock of any of the previous clauses, further comprising a pressure sensor operatively connected with the controller and configured to monitor pressure within the chamber, and to provide pressure signals to the controller indicative of the pressure within the chamber.3. The reticle load lock of any of the previous clauses, wherein the controller controls the orifice size based on the pressure signals.4. The reticle load lock of any of the previous clauses, wherein the controller is pre-programmed to control the orifice size based on a predetermined pressure over time profile.5. The reticle load lock of any of the previous clauses, wherein the reticle comprises a pellicle, wherein the reticle is separated from the pellicle by a small air gap.6. The reticle load lock of any of the previous clauses, wherein the small air gap is between 50 pm to 1 mm wide.7. The reticle load lock of any of the previous clauses, wherein the evacuating the gas out of the chamber brings the chamber to a vacuum environment.8. The reticle load lock of any of the previous clauses, wherein the controller is configured to control the second valve to allow gas into the chamber to bring the chamber to a non-vacuum environment.9. The reticle load lock of any of the previous clauses, wherein the non-vacuum environment is at atmospheric pressure.10. The reticle load lock of any of the previous clauses, wherein the first and second valves are servo control valves having orifice size control.11. The reticle load lock of any of the previous clauses, wherein the closure is a gate valve.12. A lithography apparatus, comprising: an illumination system that provides a beam of radiation; a support structure that supports a reticle, wherein the reticle is configured to impart the beam of radiation with a pattern in its cross-section; a substrate support that supports a substrate; a projection system that projects the patterned beam onto a target portion of the substrate; and a reticle load lock, comprising: a load lock chamber, wherein the chamber has a closure movable between an open and a closed position, wherein when the closure is in the open position, the reticle can be inserted or removed from the chamber; a pump system configured to evacuate the chamber; a venting system configured to pressurize the chamber; a first valve having an orifice of variable size and configured to communicate the pump system with the chamber; a second valve having an orifice of variable size and configured to communicate the venting system with the chamber; and a controller operatively connected with the first and second valves and configured to control the size of the orifice to control a pressure in the chamber over time based on a desired pressure profile.13. The lithography apparatus of any of the previous clauses, further comprising a pressure sensor operatively connected with the controller and configured to monitor pressure within the chamber, and to provide pressure signals to the controller indicative of the pressure within the chamber.14. The lithography apparatus of any of the previous clauses, wherein the controller controls the orifice size based on the pressure signals.15. The lithography apparatus of any of the previous clauses, wherein the controller is preprogrammed to control the orifice size based on a predetermined pressure over time profile.16. The lithography apparatus of any of the previous clauses, wherein the reticle comprises a pellicle, wherein the reticle is separated from the pellicle by a small air gap.17. The lithography apparatus of any of the previous clauses, wherein the small air gap is between 50 pm to 1 mm wide.18. The lithography apparatus of any of the previous clauses, wherein the evacuating the gas out of the chamber brings the chamber to a vacuum environment.19. The lithography apparatus of any of the previous clauses, wherein the controller is configured to control the second valve to allow gas into the chamber to bring the chamber to a non-vacuum environment.20. The lithography apparatus of any of the previous clauses, wherein the non-vacuum environment is at atmospheric pressure.21. The lithography apparatus of any of the previous clauses, wherein the first and second valves are servo control valves having orifice size control.22. The lithography apparatus of any of the previous clauses, wherein the closure is a gate valve.23. A method of using a reticle load lock, comprising: inserting or removing a reticle into a closure of a load lock chamber when the closure is in an open position, wherein the closure is movable between the open and a closed position; evacuating the chamber using a pump system; pressurizing the chamber using a venting system; communicating the pump system with the chamber using a valve having an orifice of variable size; communicating the venting system with the chamber using a second valve having an orifice of variable size; and controlling the size of the orifice to control a pressure in the chamber over time based on a desired pressure profile using a controller operatively connected with the first and second valves.24. The method of any of the previous clauses, further comprising monitoring pressure within the chamber using a pressure sensor operatively connected with the controller and providing pressure signals using the pressure sensor to the controller indicative of the pressure within the chamber.25. The method of any of the previous clauses, further comprising controlling the orifice size using the controller based on the pressure signals.26. The method of any of the previous clauses, further comprising pre-programming the controller to control the orifice size based on a predetermined pressure over time profile.27. The method of any of the previous clauses, wherein the reticle comprises a pellicle, wherein the reticle is separated from the pellicle by a small air gap.28. The method of any of the previous clauses, wherein the small air gap is between 50 pm to 1 mm wide.29. The method of any of the previous clauses, wherein the evacuating the gas out of the chamber brings the chamber to a vacuum environment.30. The method of any of the previous clauses, further comprising controlling the second valve using the controller to allow gas into the chamber to bring the chamber to a non-vacuum environment.31. The method of any of the previous clauses, wherein the non-vacuum environment is at atmospheric pressure.32. The method of any of the previous clauses, wherein the first and second valvse are servo control valves having orifice size control.33. The method of any of the previous clauses, wherein the closure is a gate valve.34. A method of using a reticle load lock, comprising: inserting a reticle into a load lock chamber through a closure when the closure is in an open position, wherein the closure is movable between the open and a closed position; evacuating the load lock chamber using a pump system with a first valve having an orifice of variable size by controlling the size of the orifice to control a pressure in the chamber over time based on a desired pump down pressure profile using a controller operatively connected with the first valve; moving the reticle from the load lock chamber to a lithography apparatus; exposing a substrate using the pattern of the reticle in the lithography apparatus; moving the reticle from the lithography apparatus to the load lock chamber; venting the load lock chamber using a venting system with a second valve having the orifice of variable size by controlling the size of the orifice to control a pressure in the chamber over time based on a desired venting pressure profile using the controller operatively connected with the second valve; and removing the reticle from the load lock chamber via the closure when the closure is in the open position.35. The method of any of the previous clauses, further comprising monitoring pressure within the chamber using a pressure sensor operatively connected with the controller and providing pressure signals using the pressure sensor to the controller indicative of the pressure within the chamber.36. The method of any of the previous clauses, further comprising controlling the orifice size using the controller based on the pressure signals.37. The method of any of the previous clauses, further comprising pre-programming the controller to control the orifice size based on a predetermined pressure over time profile.38. The method of any of the previous clauses, wherein the reticle comprises a pellicle, wherein the reticle is separated from the pellicle by a small air gap.39. The method of any of the previous clauses, wherein the small air gap is between 50 pm to 1 mm wide.40. The method of any of the previous clauses, wherein the evacuating the gas out of the chamber brings the chamber to a vacuum environment.41. The method of any of the previous clauses, further comprising controlling the second valve using the controller to allow gas into the chamber to bring the chamber to a non-vacuum environment.42. The method of any of the previous clauses, wherein the non-vacuum environment is at atmospheric pressure.43. The method of any of the previous clauses, wherein the first and second valves are servo control valves having orifice size control.44. The method of any of the previous clauses, wherein the closure is a gate valve

[0144] The concepts disclosed herein may be associated with any generic imaging system for imaging sub wavelength features, and may be especially useful with emerging imaging technologies capable of producing increasingly shorter wavelengths. Emerging technologies already in use include EUV (extreme ultra violet), DUV lithography that is capable of producing a 193nm wavelength with the use of an ArF laser, and even a 157nm wavelength with the use of a Fluorine laser. Moreover, EUV lithography is capable of producing wavelengths within a range of 20-5nm by using a synchrotron or by hitting a material (either solid or a plasma) with high energy electrons in order to produce photons within this range.

[0145] While the concepts disclosed herein may be used for wafer manufacturing on a substrate such as a silicon wafer, it shall be understood that the disclosed concepts may be used with any type of manufacturing system, e.g., those used for manufacturing on substrates other than silicon wafers. In addition, the combination and sub-combinations of disclosed elements may comprise separate embodiments. For example, the cleaning system and / or method, and the associated lithography apparatus may comprise separate embodiments, and / or these features may be used together in the same embodiment.

[0146] The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made as described without departing from the scope of the claims set out below.

Claims

CLAIMS1. A reticle load lock, comprising: a load lock chamber, wherein the chamber has a closure movable between an open and a closed position, wherein when the closure is in the open position, a reticle can be inserted or removed from the chamber; a pump system configured to evacuate the chamber; a venting system configured to pressurize the chamber; a first valve having an orifice of variable size and configured to communicate the pump system with the chamber; a second valve having an orifice of variable size and configured to communicate the venting system with the chamber; and a controller operatively connected with the first and second valves and configured to control the size of the orifice to control a pressure in the chamber over time based on a desired pressure profile.

2. The reticle load lock of claim 1, further comprising a pressure sensor operatively connected with the controller and configured to monitor pressure within the chamber, and to provide pressure signals to the controller indicative of the pressure within the chamber, wherein: the controller controls the orifice size based on the pressure signals; and the controller is pre-programmed to control the orifice size based on a predetermined pressure over time profile.

3. The reticle load lock of claim 1, wherein: the reticle comprises a pellicle, wherein the reticle is separated from the pellicle by a small air gap between 50 pm to 1 mm wide; the evacuating the gas out of the chamber brings the chamber to a vacuum environment; the controller is configured to control the second valve to allow gas into the chamber to bring the chamber to a non-vacuum environment; and the non-vacuum environment is at atmospheric pressure.

4. The reticle load lock of claim 1, wherein: the first and second valves are servo control valves having orifice size control; and the closure is a gate valve.

5. A lithography apparatus, comprising: an illumination system that provides a beam of radiation;a support structure that supports a reticle, wherein the reticle is configured to impart the beam of radiation with a pattern in its cross-section; a substrate support that supports a substrate; a projection system that projects the patterned beam onto a target portion of the substrate; and a reticle load lock, comprising: a load lock chamber, wherein the chamber has a closure movable between an open and a closed position, wherein when the closure is in the open position, the reticle can be inserted or removed from the chamber; a pump system configured to evacuate the chamber; a venting system configured to pressurize the chamber; a first valve having an orifice of variable size and configured to communicate the pump system with the chamber; a second valve having an orifice of variable size and configured to communicate the venting system with the chamber; and a controller operatively connected with the first and second valves and configured to control the size of the orifice to control a pressure in the chamber over time based on a desired pressure profile.

6. The lithography apparatus of claim 5, further comprising a pressure sensor operatively connected with the controller and configured to monitor pressure within the chamber, and to provide pressure signals to the controller indicative of the pressure within the chamber, wherein: the controller controls the orifice size based on the pressure signals; and the controller is pre-programmed to control the orifice size based on a predetermined pressure over time profile.

7. The lithography apparatus of claim 5, wherein: the reticle comprises a pellicle, wherein the reticle is separated from the pellicle by a small air gap between 50 pm to 1 mm wide; the evacuating the gas out of the chamber brings the chamber to a vacuum environment; the controller is configured to control the second valve to allow gas into the chamber to bring the chamber to a non-vacuum environment; and the non-vacuum environment is at atmospheric pressure.

8. The lithography apparatus of claim 5, wherein: the first and second valves are servo control valves having orifice size control; and the closure is a gate valve.

9. A method of using a reticle load lock, comprising: inserting or removing a reticle into a closure of a load lock chamber when the closure is in an open position, wherein the closure is movable between the open and a closed position; evacuating the chamber using a pump system; pressurizing the chamber using a venting system; communicating the pump system with the chamber using a first valve having an orifice of variable size; communicating the venting system with the chamber using a second valve having an orifice of variable size; and controlling the size of the orifice to control a pressure in the chamber over time based on a desired pressure profile using a controller operatively connected with the first and second valves.

10. The method of claim 9, further comprising: monitoring pressure within the chamber using a pressure sensor operatively connected with the controller and providing pressure signals using the pressure sensor to the controller indicative of the pressure within the chamber; controlling the orifice size using the controller based on the pressure signals; and pre-programming the controller to control the orifice size based on a predetermined pressure over time profile.

11. The method of claim 9, wherein: the reticle comprises a pellicle, wherein the reticle is separated from the pellicle by a small air gap between 50 pm to 1 mm wide; and the evacuating the gas out of the chamber brings the chamber to a vacuum environment.

12. The method of claim 9, further comprising controlling the second valve using the controller to allow gas into the chamber to bring the chamber to a non-vacuum environment, wherein the non-vacuum environment is at atmospheric pressure.

13. The method of claim 9, wherein: the first and second valves are servo control valves having orifice size control; and the closure is a gate valve.

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