Adjustable optics

Abstract

A system and method are described that provides variable spot size and variable focus at a substrate. Adding a set of variable focal length lenses to an alignment system allows for adjustment of spot size and focus. The variable focal length lens is a liquid lens that is adjustable based on the application of a voltage to the lens. Switching the voltage changes the water-oil interface of the liquid lens, changing the direction of light passing through. For example, turning on the voltage to the lens shifts the output direction of the light toward a focal point. As a result, the variable focal length lens provides adjustment to compensate for the shortcomings of the fixed spot size and focus of the prior art. Furthermore, the variable focal length lens can also be applied to compensate for spot shift and higher diffraction orders.

Description

[Technical Field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims priority to U.S. Application No. 63 / 412,822, filed October 3, 2022, which is incorporated herein by reference in its entirety.

[0002] [Technical field] TECHNICAL FIELD The present disclosure relates to adjustable optical systems. [Background technology]

[0003] A lithographic apparatus is a machine that applies a desired pattern to a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a context, a patterning device, also known as a mask or reticle, can be used to create a circuit pattern that corresponds to an individual layer of the IC, and then image this pattern onto a target portion (e.g., comprising part of a die, or several dies) on a substrate (e.g., a silicon wafer) that has a layer of radiation-sensitive material (resist) on it. Typically, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing the entire pattern onto the target portion in a single exposure, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a beam in a predetermined direction (the "scan" direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate. Another lithography system is an interference lithography system that does not have a patterning device, but instead splits a light beam into two beams and uses a reflection system to cause the two beams to interfere at a target portion of the substrate, which interference forms a line in the target portion of the substrate.

[0004] During lithography operations, different processing steps may require sequentially forming different layers on a substrate. Therefore, the substrate may need to be positioned with high precision relative to a previous pattern to be formed thereon. Typically, alignment marks, which may comprise, for example, a diffraction grating, are placed on the substrate to be aligned and are positioned relative to a second object. Lithography apparatus may use alignment systems to detect the positions of the alignment marks and align the substrate using the alignment marks, for example, to ensure precision in subsequent lithography operations.

[0005] Alignment systems typically have their own illumination system that can be used to illuminate alignment marks during alignment measurements. Determining alignment typically involves determining the position of an alignment mark (or marks) and / or other targets in a layer of a semiconductor device structure. Alignment is usually determined by illuminating the alignment mark with radiation and comparing the characteristics of different diffraction orders of the radiation reflected from the alignment mark. Similar techniques are used to measure overlay and other parameters. Current alignment sensors have a single measurement illumination spot projected onto a substrate (e.g., a wafer). The single illumination spot is used to measure multiple alignment parameters, including phase and intensity detection. Current sensors measure metrology marks sequentially. Therefore, the number of metrology marks on a given substrate is limited by throughput considerations.

[0006] Alignment systems often use dual self-referencing interferometer (SRI) systems to acquire intensity as a function of mark position. The phase of these sinusoidal signals is used to determine the alignment position of the mark. Each SRI has its own polarization state and is prepared using feed optics that separate the input light into X and Y polarizations. These alignment systems are fixed optics.

[0007] However, current alignment systems have several limitations. The size of the beam spot that illuminates the wafer target mark is fixed. As a result, the size of the alignment mark is constrained. For example, alignment may fail in the case of relatively thick resist or warped wafers. Another common problem is the undetectable delta-R effect, which is the re-metering of the diffracted beam numerical aperture caused by the product wafer stack. Furthermore, inside a typical optical module, mechatronic elements must be used for high-order rejection. Mechatronics are undesirable within an alignment system because they use mechanical elements that cause vibration and heat and require a large amount of power. Summary of the Invention

[0008] A novel system and method are disclosed that supports variable spot size and variable focus on a substrate for alignment (and / or overlay) determination. A set of variable focal length lenses is provided in an alignment system to enable spot size and focus adjustment. The variable focal length lens is a liquid lens that is adjustable based on the application of a voltage to the lens. Switching the voltage changes the curvature of the water-oil interface within the liquid lens, changing the direction of light passing through. For example, turning on the voltage to the lens shifts the output direction of the light toward the focal point. As a result, the variable focal length lens provides adjustment to compensate for the drawbacks of fixed spot size and focus in the prior art. Furthermore, the variable focal length lens can also be applied to correct spot shift and delta-R effects. The variable focal length lens can also be used in place of mechatronic elements to eliminate higher diffraction orders.

[0009] According to one embodiment, a wafer alignment measurement system comprises an illumination source, a radiation beam output from the illumination source, a first set of variable focal length lenses configured to receive the radiation beam, the first set of variable focal length lenses being controllable to control the illumination spot size at the wafer, a second set of variable focal length lenses, and a third set of variable focal length lenses located in a pupil plane downstream of the objective system, the third set of variable focal length lenses being controllable to control at least one of spot shift and higher diffraction orders.

[0010] In one embodiment, a first set of variable focal length lenses is located in the illumination system.

[0011] In one embodiment, one of the first variable focal length lenses is offset from the optical axis of the illumination source output.

[0012] In one embodiment, there are N output channels and N+1 second variable focal length lenses, one second variable focal length lens in each output channel and one second variable focal length lens in the objective.

[0013] In one embodiment, a third set of variable focal length lenses is located in the pupil plane.

[0014] In one embodiment, the first, second and third sets of variable focal length lenses are controllable by applying voltages to the first, second and third sets of variable focal length lenses.

[0015] According to one embodiment, a wafer alignment measurement system comprises an illumination source, a radiation beam output from the illumination source, and at least two variable focal length lenses configured to receive the radiation beam, the variable focal length lenses being controllable to control the illumination spot size on the wafer.

[0016] In one embodiment, a variable focal length lens is located in the illumination system.

[0017] In one embodiment, the variable focal length lens is located in the illumination system between the illumination relay lens and the aperture stop.

[0018] In one embodiment, the variable focal length lens is controllable by applying a voltage to the variable focal length lens.

[0019] In one embodiment, one of the variable focal length lenses is offset from the optical axis of the illumination source output.

[0020] According to one embodiment, a wafer alignment measurement system comprises an illumination source and at least two variable focal length lenses, one of the variable focal length lenses located in an output channel and another of the variable focal length lenses located in an objective system, the variable focal length lenses being controllable to control the focus height of the output from the objective system.

[0021] In one embodiment, the illumination source output is a radiation beam that is reflected from the wafer.

[0022] In an embodiment, the radiation beam passes through a variable focal length lens after being reflected from the wafer.

[0023] In one embodiment, there are N output channels and N+1 variable focal length lenses, one variable focal length lens in each output channel and one variable focal length lens in the objective.

[0024] In one embodiment, the variable focal length lens is controllable by applying a voltage to the variable focal length lens.

[0025] According to one embodiment, a wafer alignment measurement system comprises an illumination source, a radiation beam output from the illumination source and directed towards an objective system, and at least two variable focal length lenses positioned in a pupil plane downstream of the objective system, the variable focal length lenses being controllable to control at least one of spot shift and higher diffraction orders.

[0026] In one embodiment, the variable focal length lens is located in the pupil plane.

[0027] In one embodiment, the variable focal length lens is located in the pupil plane between the objective and the output lens.

[0028] In one embodiment, a variable focal length lens compensates for spot shift.

[0029] In one embodiment, the variable focal length lens compensates for higher diffraction orders.

[0030] In one embodiment, the variable focal length lens is controllable by applying a voltage to the variable focal length lens.

[0031] Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. It should be noted that the present invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to those skilled in the relevant art based on the teachings contained herein. [Brief explanation of the drawings]

[0032] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate the invention and, together with the description, further serve to explain the principles of the invention and to enable one skilled in the relevant art to make and use the invention.

[0033] [Figure 1A] 1 is a schematic diagram of a reflective lithographic apparatus according to an embodiment of the present disclosure;

[0034] [Figure 1B] 1 is a schematic diagram of a transmissive lithographic apparatus according to an embodiment of the present disclosure;

[0035] [Figure 1C] 1 is a schematic diagram illustrating a reflective lithographic apparatus in greater detail, according to an embodiment of the present disclosure;

[0036] [Figure 2A] FIG. 1 is a schematic diagram illustrating a lithography cell according to an embodiment of the present disclosure.

[0037] [Figure 2B] 1 is a schematic diagram illustrating an inspection system according to an embodiment of the present disclosure.

[0038] [Figure 2C] FIG. 1 is a schematic diagram illustrating a metrology technique according to an embodiment of the present disclosure.

[0039] [Figure 2D] FIG. 2 is a schematic diagram illustrating the relationship between the radiation illumination spot and the metrology target of an inspection system in accordance with an embodiment of the present disclosure.

[0040] [Figure 3] FIG. 1 is a schematic diagram illustrating a state-of-the-art alignment system according to an embodiment of the present disclosure.

[0041] [Figure 4A] FIG. 2 is a schematic diagram illustrating a variable focal length lens when no voltage is applied, according to an embodiment of the present disclosure.

[0042] [Figure 4B] FIG. 2 is a schematic diagram illustrating a variable focal length lens when a non-zero voltage is applied, according to an embodiment of the present disclosure.

[0043] [Figure 4C] FIG. 1 is a schematic diagram illustrating an illumination system of an alignment system for variable spot size, according to an embodiment of the present disclosure.

[0044] [Figure 4D]FIG. 1 is a schematic diagram illustrating an alignment system for variable spot size according to an embodiment of the present disclosure.

[0045] [Figure 4E] 1 is a schematic diagram illustrating a radiation beam spot size at a variable focal length lens with nominal voltages for variable spot size, according to an embodiment of the present disclosure.

[0046] [Figure 4F] 1 is a schematic diagram illustrating a radiation beam spot size in a variable focal length lens with applied voltages for variable spot size, according to an embodiment of the present disclosure.

[0047] [Figure 5A] FIG. 1 is a schematic diagram illustrating an illumination system of an alignment system for beam steering, according to an embodiment of the present disclosure.

[0048] [Figure 5B] FIG. 1 is a schematic diagram illustrating an alignment system for beam steering, according to an embodiment of the present disclosure.

[0049] [Figure 5C] FIG. 10 is a schematic diagram illustrating the effect of offset of a variable focal length lens for beam steering, according to an embodiment of the present disclosure.

[0050] [Figure 5D] FIG. 10 is another schematic diagram illustrating the effect of offset of a variable focal length lens for beam steering, according to an embodiment of the present disclosure.

[0051] [Figure 5E] FIG. 5C illustrates a combination of the elements shown in FIGS. 5A, 5C, and 5D that form part of the system of FIG. 5B, according to an embodiment of the present disclosure.

[0052] [Figure 6A]FIG. 1 is a schematic diagram illustrating an alignment system for variable focus, according to one embodiment of the present disclosure.

[0053] [Figure 6B] FIG. 1 is a schematic diagram illustrating a thick resist substrate and variable focus according to an embodiment of the present disclosure.

[0054] [Figure 6C] FIG. 10 is a schematic diagram illustrating overlay measurement in a variable focus embodiment according to an embodiment of the present disclosure.

[0055] [Figure 6D] FIG. 10 is another schematic diagram illustrating overlay measurement in a variable focus embodiment, according to an embodiment of the present disclosure.

[0056] [Figure 7A] FIG. 1 is a schematic diagram illustrating an alignment system for spot shifting and high order rejection, according to an embodiment of the present disclosure.

[0057] [Figure 7B] FIG. 10 is a schematic diagram illustrating beam size calibration in a spot shifting embodiment according to an embodiment of the present disclosure.

[0058] [Figure 7C] FIG. 10 is another schematic diagram illustrating beam size calibration in a spot-shifting embodiment according to an embodiment of the present disclosure.

[0059] [Figure 7D] FIG. 10 is another schematic diagram illustrating beam size calibration in a spot-shifting embodiment according to an embodiment of the present disclosure.

[0060] [Figure 7E] FIG. 10 is a schematic diagram illustrating shifts in higher diffraction orders in a high order rejection embodiment, according to certain embodiments of the present disclosure.

[0061] [Figure 8] 1 illustrates a wafer alignment measurement method according to an embodiment.

[0062] [Figure 9] FIG. 1 is a block diagram illustrating an exemplary computer system according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0063] For semiconductor manufacturing and / or other applications, self-referencing interferometers (SRIs) can be used in alignment systems to acquire the intensity of reflected radiation as a function of the position of an alignment mark on a substrate (e.g., a wafer). The phase of these signals is used to determine the alignment position of the mark. However, the SRI approach has limitations. Because the beam spot size illuminating the alignment mark on the substrate is fixed, for example, thick resist and / or a warped substrate (e.g., a wafer) can inadvertently cause misalignment. Additionally, in SRI approaches, mechatronic elements are often used in the optical module (OM) for high-order rejection, but these mechatronic elements can introduce vibrations that can lead to inaccurate measurements and / or other problems. In some embodiments, the optical module, comprised of multiple passive and active optical components, functions to direct illumination, such as light, onto the wafer under investigation. The optical module also collects diffracted light from the marks on the wafer and directs the light to a demultiplexer and optical detector. For example, the optics module may illuminate a target on the wafer by directing light from a light source onto the target and collect a return signal, which may be sent to detection electronics to calculate the target position on the wafer.

[0064] Among other advantages, the present system and method provide a solution to these and other problems, enabling variable spot sizes and smaller alignment marks. The present system and method also improves thick stack measurement performance and enables non-mechanical scanning within the optical module (OM). As described below, to provide the variable spot size, the fixed lens of a typical input fiber assembly is replaced with a pair of liquid lenses to provide afocal functionality. Voltages applied to two variable focal length lenses result in an increase in focal length. In another embodiment, two variable focal length lenses are used to maintain the numerical aperture to account for thick stacks and maintain spot sizes at different focuses.

[0065] As a brief introduction, the following description relates to semiconductor device fabrication and patterning processes. Also, the following paragraphs describe some components of systems and / or methods for semiconductor device metrology. These systems and methods may be used, for example, to measure alignment, overlay, or other steps in the semiconductor device fabrication process.

[0066] Examples of reflective and transmissive lithography systems

[0067] 1A and 1B are schematic diagrams of lithographic apparatus 100 and lithographic apparatus 100' in which embodiments of the present disclosure can be implemented. Lithographic apparatus 100 and lithographic apparatus 100' each include an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., deep ultraviolet radiation or extreme ultraviolet radiation); a support structure (e.g., a mask table) MT configured to support a patterning device (e.g., a mask, reticle, or dynamic patterning device) MA and connected to a first positioner PM configured to precisely position the patterning device MA; and a substrate table (e.g., a wafer table) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to precisely position the substrate W. Lithographic apparatus 100 and 100' also include a projection system PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W. In lithographic apparatus 100, patterning device MA and projection system PS are reflective. In lithographic apparatus 100', patterning device MA and projection system PS are transmissive.

[0068] 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.

[0069] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA relative to a reference frame, the design of at least one of lithographic apparatuses 100 and 100′, and other conditions, such as whether 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, for example, a frame or a table, and 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.

[0070] The term "patterning device" MA should be interpreted broadly as referring to any device that can be used to impart a radiation beam B having a pattern in its cross-section to create a pattern in a target portion C of a substrate W. The pattern imparted to the radiation beam B may correspond to a particular functional layer in a device being created in the target portion C to form an integrated circuit.

[0071] Patterning device MA may be transmissive (such as lithographic apparatus 100' in FIG. 1B) or reflective (such as lithographic apparatus 100 in FIG. 1A). 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 current, and attenuated, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each individually tiltable so as to reflect an incoming radiation beam B in different directions. The tilted mirrors impart a pattern to a radiation beam B, which is reflected by the matrix of small mirrors.

[0072] 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, where appropriate for the exposure radiation used or for other factors such as the use of an immersion liquid or a vacuum on the substrate W. A vacuum environment can be used for EUV radiation or electron beam radiation, as other gases may be too absorbing for the radiation or electrons. Therefore, a vacuum environment can be provided along the entire beam path with the aid of a vacuum wall or vacuum pumps.

[0073] Lithographic apparatus 100 and / or lithographic apparatus 100' can be of a type having two (dual stage) or more than two substrate tables WT (and / or two or more mask tables). In such "multi-stage" machines, the additional substrate tables WT can be used in parallel, or preparatory steps can be performed on one or more tables while one or more other substrate tables WT are being used for exposure. In some circumstances, the additional tables need not be substrate tables WT.

[0074] 1A and 1B, the illuminator IL receives a radiation beam from a radiation source SO. The radiation source SO and the lithographic apparatus 100, 100' may be separate physical entities, for example, when the radiation source SO is an excimer laser. In such cases, the radiation source SO is not considered to form part of the lithographic apparatus 100 or 100', and the radiation beam B passes from the radiation source SO to the illuminator IL with the aid of a beam delivery system BD (in FIG. 1B) that may include, for example, appropriate directing mirrors and / or beam expanders. In other cases, the radiation source SO may be an integral part of the lithographic apparatus 100, 100', such as when the radiation source SO is a mercury lamp. The radiation source SO and the illuminator IL, together with the beam delivery system BD, if required, may be referred to as a radiation system.

[0075] The illuminator IL may include an adjuster AD (FIG. 1B) for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radial extent (commonly referred to as "σ-outer" and "σ-inner," respectively) of the intensity distribution in a pupil plane of the illuminator may be adjusted. In addition, the illuminator IL may comprise various other components (FIG. 1B), such as an integrator IN and a condenser CO. The illuminator IL can be used to condition the radiation beam B so that it has a desired uniformity and intensity distribution in its cross-section.

[0076] Referring to Figure 1A, a radiation beam B is incident on a patterning device (e.g., mask) MA, which is held on a support structure (e.g., 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 (e.g., mask) MA. After reflecting from the patterning device (e.g., mask) MA, the radiation beam B passes through a projection system PS, which focuses the radiation beam B onto a target portion C of a substrate W. With the aid of a second positioner PW and a position sensor IF2 (e.g., an interferometer device, a linear encoder, or a capacitive sensor), the substrate table WT can be precisely moved (e.g., to position different target portions C in the path of the radiation beam B). Similarly, a first positioner PM and another position sensor IF1 can be used to accurately position the patterning device (e.g., mask) MA relative to the path of the radiation beam B. Patterning device (eg mask) MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0077] Referring to Figure 1B, a radiation beam B is incident on a patterning device (e.g., mask MA), which is held on a support structure (e.g., mask table MT), and is patterned by the patterning device. After traversing the mask MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. The projection system has a pupil PPU that is conjugate with the illumination system pupil IPU. A portion of the radiation arises from the intensity distribution at the illumination system pupil IPU and traverses the mask pattern without being affected by diffraction at the mask pattern, producing an image of the intensity distribution at the illumination system pupil IPU.

[0078] With the aid of the second positioner PW and a position sensor IF (e.g. an interferometer device, a linear encoder or a capacitive sensor), the substrate table WT can be precisely moved (e.g. to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and a further position sensor (not shown in Figure 1B) can be used to precisely position the mask MA with respect to the path of the radiation beam B (e.g. after machine retrieval from a mask library or during a scan).

[0079] In general, movement of the mask table MT may 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 may be realized by means of a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask table MT may be connected to a short-stroke actuator only, or may be fixed. The mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. The substrate alignment marks occupy dedicated target portions (as shown) but may be located in spaces between the 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 may be located between the dies.

[0080] The mask table MT and patterning device MA can be inside a vacuum chamber, and an in-vacuum robot IVR can be used to move the patterning device, such as a mask, into and out of the vacuum chamber. Alternatively, if the mask table MT and patterning device MA are outside the vacuum chamber, an out-of-vacuum robot can be used for various transfer tasks similar to the in-vacuum robot IVR. Both the in-vacuum robot and the out-of-vacuum robot need to be calibrated for smooth transfer of any load (e.g., a mask) towards the fixed kinematic mounts of the transfer station.

[0081] Lithographic apparatus 100 and 100' can be used in at least one of the following modes:

[0082] 1. In step mode, the support structure (e.g. mask table) MT and substrate table WT are kept substantially stationary and an entire pattern imparted to the radiation beam B is projected onto a target portion C in one go (i.e. a single static exposure), where the substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed.

[0083] 2. In scan mode, the support structure (e.g. mask table) MT and the substrate table WT are scanned synchronously (i.e. single dynamic exposure) while a pattern imparted to the radiation beam B is projected onto a target portion C. The velocity and direction of the substrate table WT relative to the support structure (e.g. mask table) MT can be determined by the (de-)magnification and image reversal characteristics of the projection system PS.

[0084] 3. In another mode, the support structure (e.g. mask table) MT holds a programmable patterning device and is kept substantially stationary, while the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. Pulsed radiation SO can be employed, the programmable patterning device being updated as required with each movement of the substrate table WT, or in between successive radiation pulses during a scan. This mode of operation is readily adaptable to maskless lithography employing a programmable patterning device, such as a programmable mirror array.

[0085] Combinations and / or variations on the described modes of use may be employed or entirely different modes of use may also be employed.

[0086] In some embodiments, the lithographic apparatus 100 includes an extreme ultraviolet (EUV) source configured to generate a beam of EUV radiation for EUV lithography. Typically, 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.

[0087] FIG. 1C shows a lithographic apparatus 100 in more detail, including a source collector apparatus SO, an illumination system IL, and a projection system PS. The source collector apparatus SO is constructed and arranged to maintain a vacuum environment in an enclosure 120 of the source collector apparatus SO. The EUV-emitting plasma 110 may be formed by a discharge-produced plasma source. EUV radiation may be generated by a gas or vapor, such as Xe gas, Li vapor, or Sn vapor, in which the generated high-temperature plasma 110 emits radiation in the EUV range of the electromagnetic spectrum. The high-temperature plasma 110 may be generated, for example, by a discharge that produces an at least partially ionized plasma. A partial pressure of, for example, 10 Pa, of Xe, Li, Sn vapor, or any other suitable gas or vapor may be required for efficient generation of radiation. In one embodiment, a plasma of excited tin (Sn) is provided to generate EUV radiation.

[0088] Radiation emitted by the high-temperature plasma 110 passes from the source chamber 111 to the collector chamber 112 through an optional gas barrier or contaminant trap 113 (sometimes also referred to as a contaminant barrier or foil trap) located at or behind the opening of the source chamber 111. The contaminant trap 113 may include a channel structure. The contaminant trap 113 may also include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap 113 described further herein includes at least a channel structure, as known in the art.

[0089] The collector chamber 112 may include a radiation collector CO, which may be a so-called grazing incidence collector. The radiation collector CO has an upstream radiation collector surface 151 and a downstream radiation collector surface 152. Radiation traversing the collector CO may be reflected from a grating spectral filter 140 and focused at a virtual source point IF. The virtual source point IF is commonly also called an intermediate focus, and the source collector arrangement is positioned such that the intermediate focus IF is located at or near an opening 119 in the enclosing structure 120. The virtual source point IF is an image of the radiation-emitting plasma 110. The grating spectral filter 140 is used to suppress, in particular, infrared (IR) radiation.

[0090] The radiation then traverses the illumination system IL, which may include a faceted field mirror device 122 and a faceted pupil mirror device 124 that are positioned to provide a desired angular distribution of the radiation beam 121 at the patterning device MA, and to provide a desired uniformity of the radiation intensity at the patterning device MA. Upon reflection of the radiation beam 121 off the patterning device MA, which is held by the support structure MT, a patterned beam 126 is formed which is imaged by the projection system PS via reflective elements 128, 130 onto the substrate W, which is held by a wafer stage or substrate table WT.

[0091] More elements than shown may typically be present in illumination optics unit IL and projection system PS. Grating spectral filter 140 may optionally be present depending on the type of lithographic apparatus. Furthermore, more mirrors than shown may be present, for example, 1 to 6 additional reflective elements may be present in projection system PS compared to what is shown in Figure 1C.

[0092] 1C, collector optic CO is depicted as a nested collector with grazing incidence reflectors 153, 154, and 155, just as an example of a collector (or collector mirror). Grazing incidence reflectors 153, 154, and 155 are arranged axisymmetrically about optical axis O, and this type of collector optic CO is preferably used in combination with a discharge-produced plasma source, often referred to as a DPP source.

[0093] Lithography Cell Example

[0094] FIG. 2A illustrates a lithography cell 200, sometimes referred to as a lithocell or cluster. Lithography apparatus 100 or 100′ may form part of lithography cell 200. Lithography cell 200 may also include apparatus for performing pre-exposure and post-exposure processes on a substrate. Conventionally, these include a spin coater SC for depositing a resist layer, a developer DE for developing exposed resist, a chill plate CH, and a bake plate BK. A substrate handler (robot) RO picks up substrates from input / output ports I / O1 and I / O2, moves them between different process tools, and delivers them to the loading bay LB of the lithography apparatus. These tools, often collectively referred to as a track, are under the control of a track control unit TCU, which itself is controlled by a supervisory control system SCS, which also controls the lithography apparatus via a lithography control unit LACU. In this way, the different tools can be operated to maximize throughput and processing efficiency.

[0095] The manufacturing facility in which the lithography cell 200 is located typically also includes a metrology system that measures some or all of the substrate W (FIGS. 1A, 1B, 1C) processed in the lithocell or other objects in the lithocell. The metrology system may be part of the lithography cell, for example, or may be part of the lithography apparatus. The one or more measured parameters may include, for example, alignment, overlay between successive layers in or formed on the patterned substrate, critical dimension (CD) (e.g., critical linewidth) of features in or formed 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. The measurements are often performed on one or more dedicated metrology targets provided on the substrate. Measurements can be performed after resist development, before etch, after etch, after deposition, and / or at other times.

[0096] There are various techniques for making measurements of structures formed in patterning processes, including the use of scanning electron microscopes, image-based metrology tools, and / or various specialized tools. One rapid, non-invasive form of specialized metrology tool directs a beam of radiation toward a target on the substrate surface and measures the properties of the scattered (diffracted / reflected) beam. By evaluating one or more properties of the radiation scattered by the substrate, one or more properties of the substrate can be determined. Traditionally, this might be referred to as diffraction-based metrology. Applications of this diffraction-based metrology include measuring alignment, overlay, etc. For example, alignment and / or overlay can be measured by comparing portions of the diffraction spectrum (e.g., by comparing different diffraction orders in the diffraction spectrum of a periodic grating).

[0097] Thus, during a device manufacturing process (e.g., a patterning process or a lithography process), a substrate or other object may be subjected to various types of measurements during or after the process. The measurements may determine whether a particular substrate is defective, may establish adjustments to the process or equipment used in the process (e.g., the alignment of two layers on the substrate or the alignment of a patterning device relative to the substrate), may measure the performance of the process or equipment, or may be performed for other purposes. Examples of measurements include optical imaging (e.g., optical microscopy), non-imaging optical measurements (e.g., diffraction-based measurements such as the ASML YieldStar metrology tool or the ASML-SMASH metrology system), mechanical measurements (e.g., profiling using a stylus or an atomic force microscope (AFM)), and / or non-optical imaging (e.g., scanning electron microscope (SEM)).

[0098] The metrology results may be provided directly or indirectly to the supervisory control system SCS. If an error is detected, adjustments may be made to the exposure of subsequent substrates (especially if the inspection is performed early enough that one or more other substrates in the batch are still being exposed) and / or to subsequent exposures of exposed substrates. Also, already exposed substrates may be stripped and reworked to improve yield, or may be discarded, thereby avoiding performing further processing on substrates known to be defective. If only some target portions of a substrate are defective, further exposures may be performed only on those target portions that meet specifications. Other manufacturing process adjustments are also possible.

[0099] The metrology system may be used to determine one or more properties of a substrate structure, in particular how one or more properties vary between different substrate structures or between different layers of the same substrate structure. The metrology system may be integrated into lithographic apparatus 100 or 100', or lithography cell 200, or may be a stand-alone apparatus.

[0100] Alignment System Embodiments

[0101] One or more targets may be specially provided on the substrate to enable alignment. Typically, the targets are specially designed and may comprise periodic structures. For example, a target on the substrate may comprise one or more one-dimensional periodic structures (e.g., geometric features such as gratings) that are printed such that, after development, the features of the periodic structures are formed of solid resist lines. As another example, a target may comprise one or more two-dimensional periodic structures (e.g., gratings) that are printed such that, after development, the features of the periodic 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).

[0102] FIG. 2B shows an exemplary alignment system 10 that may be used to detect alignment and overlay and / or perform other metrology operations. It includes a radiation or illumination source 2 that projects or illuminates radiation onto a substrate W (e.g., which may typically include metrology marks). The redirected radiation is passed to a sensor, such as a spectrometer detector 4 and / or other sensor, which measures the spectrum (intensity as a function of wavelength) of the specularly reflected and / or diffracted radiation, as shown, for example, in the graph on the left of FIG. 2C. The sensor may generate alignment signals that convey alignment data characteristic of the reflected radiation. From this data, the structure or profile giving rise to the detected spectrum may be reconstructed by one or more processors PRO or other operations, a generalized example of which is shown in FIG. 2C.

[0103] As in lithographic apparatus 100 and 100′ of FIGS. 1A and 1B, one or more substrate tables may be provided to hold a substrate W during measurement operations. The one or more substrate tables may be of a form similar to or identical to substrate table WT of FIGS. 1A and 1B. In examples where inspection system 10 is integrated with the lithographic apparatus, these may be the same substrate table. Coarse and fine positioners may be configured to accurately position the substrate relative to the measurement optics. Various sensors and actuators may be configured, for example, to acquire the position of a target portion of interest on the structure (e.g., a metrology mark) and bring it under the objective lens. Typically, many measurements will be made on target portions of the structure at different locations on the substrate W. The substrate support may move in the X and Y directions to acquire different targets and in the Z direction to acquire desired locations of the target portions relative to the focus of the optics. For example, if the optics actually remain substantially stationary (typically in the X and Y directions, but possibly also in the Z direction) and the substrate moves, it is convenient to think of and describe the operation as if the objective lens moves to different locations relative to the substrate. As long as the relative positions of the substrate and the optics are correct, it does not matter in principle whether one or both move, or even a combination where part of the optics moves (e.g., in the Z direction and / or tilt direction) while the rest of the optics remains stationary and the substrate moves (e.g., in the X and Y directions, but optionally also in the Z direction and / or tilt direction).

[0104] For a typical alignment measurement, the target (portion) 30 on the substrate W may be a one-dimensional grating that is printed such that, after development, the bars are formed of solid resist lines (which may be covered, for example, by a deposition layer) and / or other material. Alternatively, the target 30 may be a two-dimensional grating that, after development, the grating is formed of solid resist pillars and / or other features in the resist.

[0105] The bars, pillars, vias, and / or other features may be etched into or on the substrate (e.g., in one or more layers on the substrate), deposited on the substrate, covered by a deposited layer, and / or have other properties. Target (portion) 30 (e.g., comprised of bars, pillars, vias, etc.) is sensitive to processing variations in the patterning process (e.g., optical aberrations in a lithographic projection apparatus, such as a projection system, changes in focus, changes in dose, etc.), such that process variations manifest themselves in variations in target 30. Therefore, measurement data from target 30 may be used to determine one or more adjustments to the manufacturing process and / or may be used as a basis for making the actual adjustments.

[0106] For example, metrology data from target 30 may indicate overlay of layers of a semiconductor device. The metrology data from target 30 may be used (e.g., by one or more processors PRO and / or other processors) to determine one or more semiconductor device manufacturing process parameters based on the overlay, and to determine adjustments to semiconductor device manufacturing equipment based on the one or more determined semiconductor device manufacturing process parameters. In some embodiments, this may include, for example, adjusting stage position, which may include determining adjustments to mask design, metrology target design, semiconductor device design, intensity of radiation, angle of incidence of radiation, wavelength of radiation, pupil size and / or shape, resist material, and / or other process parameters.

[0107] FIG. 2D shows a plan view of a typical target (e.g., metrology mark) 30 and the extent of a typical radiation illumination spot S. Typically, to obtain a diffraction spectrum free of interference from surrounding structures, in one embodiment, the target 30 is a periodic structure (e.g., a grating) larger than the width (e.g., diameter) of the illumination spot S. The width of the spot S may be smaller than the width and length of the target. In other words, the target is "underfilled" by the illumination, and the diffraction signal is essentially unconstrained from signals from product features outside the target itself. The illumination arrangement may be configured to provide uniform-intensity illumination across the entire back focal plane of the objective lens, for example. Alternatively, illumination may be constrained in an on-axis or off-axis direction, for example, by including an aperture in the illumination path.

[0108] State-of-the-art alignment system

[0109] 3 shows a schematic diagram of a state-of-the-art alignment system 300 that can be implemented as part of or in combination with lithographic apparatus 100 or 100′ and / or other lithographic apparatuses, according to an embodiment. In one example of this embodiment, alignment system 300 may be configured to align a substrate (e.g., the aforementioned semiconductor wafer, substrate W, etc.) with respect to a patterning device (e.g., the aforementioned patterning device MA). Alignment system 300 may be further configured to detect the positions of alignment marks on the substrate and use the detected positions of the alignment marks to align the substrate with respect to the patterning device or other components of lithographic apparatus 100 or 100′. Aligning the substrate in this manner may ensure accurate exposure of one or more patterns on the substrate.

[0110] According to one embodiment, alignment system 300 may include illumination source 305, input fiber 307, illumination system 310, spot mirror 320, objective lens 330, self-referencing interferometer (SRI) 340, polarizing beam splitters 341a and 341b, and output system 350. Optical module 399 of system 300 may include any optical elements in or along the radiation path used to direct or control radiation within system 300. Illumination source 305 may be configured to provide narrowband electromagnetic radiation beam 306 having a first polarization state, such as a linear polarization state. In one example, narrowband radiation beam 306 may be in a spectral range of wavelengths between about 500 nm and about 900 nm. In another example, narrowband radiation beam 306 comprises discrete narrow passbands within the spectral range of wavelengths between about 500 nm and about 900 nm. In yet another example, radiation beam 306 may be monochromatic, for example provided by a monochromatic light source such as a laser light source in illumination source 305. Polychromatic light sources, such as LEDs, may also be used in illumination source 305 to provide polychromatic radiation beam 306.

[0111] Illumination system 310 may be configured to receive radiation beam 306. In this example embodiment, illumination system 310 may be further configured to direct radiation beam 306 onto substrate W. Illumination system 310 may include an illumination relay lens 312, a fixed lens input fiber assembly (IFA) 311, and an aperture stop 313. Illumination system 310 may also include optics to generate additional illumination beams split or replicated from radiation beam 306 and direct them towards alignment marks (not shown) on substrate W.

[0112] The substrate W may be disposed on a stage WT (see Figures 1A, 1B and 1C) that is movable along a direction. The radiation beam 306 may be configured to illuminate alignment marks located on the substrate W, which in this example embodiment may be coated with a radiation sensitive film. In another example, the alignment marks may have 180° symmetry, i.e., when the alignment mark is rotated 180° about an axis of symmetry perpendicular to the plane of the alignment mark, the rotated alignment mark may be substantially identical to the un-rotated alignment mark.

[0113] As shown in FIG. 3 , according to an embodiment, objective lens 330 may be configured to direct diffracted radiation beam 335 towards self-referencing interferometer 340. Objective lens 330 may comprise any suitable number of optical elements suitable for directing diffracted radiation beam 335. Objective lens 330 may also include aperture stop 331. In an exemplary embodiment, diffracted radiation beam 335 may be at least a portion of radiation beam 306 diffracted from the alignment mark. Spot mirror 320 may be substantially transparent to diffracted radiation beam 335 or may be able to pass diffracted radiation beam 335 without substantially changing the properties of diffracted radiation beam 335. It should further be noted that although objective lens 330 is shown directing radiation beam 335 towards self-referencing interferometer 340, the present disclosure is not so limited. Other optical arrangements may be used to achieve similar results of detecting a diffraction signal from an alignment mark.

[0114] In some embodiments, the self-referencing interferometer 340 may comprise any suitable set of optical elements, such as a combination of prisms, half-wave plates, and compensators, and may be configured to form two images of the alignment mark based on the received diffracted radiation beam 335. It should be understood that high quality images need not be formed, but they must be able to resolve features of the alignment mark. The self-referencing interferometer 340 may further be configured to rotate one of the two images by 180° relative to the other of the two images, and interferometrically recombine the rotated and un-rotated images.

[0115] After passing through self-referencing interferometer 340, diffracted radiation beam 335 is incident on polarizing beam splitters 341a and 341b, which redirect diffracted radiation beam 335 to output system 350. First output channel 351a comprises output lens 352a and output aperture stop 353a, and passes diffracted beam 335 to a detector (not shown) to measure the sum of the y-components of the beam. Second output channel 351b comprises output lens 352b and output aperture stop 353b, and a second detector (not shown) for measuring the difference of the y-components of the beam. Third output channel 351c comprises output lens 352c and output aperture stop 353c, and a third detector (not shown) for measuring the sum of the x-components of the beam. A fourth output channel 351d includes an output lens 352d and an output aperture stop 353d, and a fourth detector (not shown) for measuring the difference in the x-components of the beams.

[0116] The detector may be configured to receive the recombined image and detect interference resulting from the recombined image when the alignment axis of the alignment system 300 passes through the center of symmetry (not shown) of the alignment mark. Such interference may result from the alignment mark being 180° symmetric, according to an exemplary embodiment, causing the recombined image to interfere constructively or destructively. Based on the detected interference, the detector may be further configured to determine the position of the center of symmetry of the alignment mark and, consequently, detect the position of the substrate W. According to one example, the alignment axis may be perpendicular to the substrate 420 and aligned with a light beam passing through the center of the self-referencing interferometer 340.

[0117] Variable focal length lens

[0118] 4A-4B show schematic diagrams of a variable focal length lens 420. The lens 420 is shown in an "off" ( FIG. 4A ) and "on" ( FIG. 4B ) configuration, as described below. The variable focal length lens 420 is a liquid lens comprising water 404 and oil 405, forming a water-oil interface 406, with an interface membrane 427 forming a seal therebetween. FIGS. 4A and 4B also show other components of the lens 420, including an optical window 421 configured to transmit the light beam 403 (and / or other radiation), a metal structural component 423, and an electrostatic pressure 425 applied when the lens 420 is "on" ( FIG. 4B ).

[0119] The focal length of the lens 420 can be finely adjusted and changed by applying a specified voltage 408. FIG. 4A shows the water-oil interface 406 when no voltage is applied (“off”). The no-voltage state is shown in FIG. 4A as the lens 420 connected to ground 407. In one example, with no voltage, the water 404 and oil 405 naturally form a slight concave curvature at the interface 406, causing an incident light beam 403 parallel to the optical axis OA to diverge slightly as it exits the variable focal length lens 420. As another example, FIG. 4B shows the water-oil interface 406 when a non-zero voltage 408 is applied (“on”). The voltage 408 applied to the liquid lens 420 generates an electrostatic pressure 425 at or near the edge 429, resulting in the accumulation of a positive charge (see the “+” sign in FIG. 4B). As a result, the negative charges (see the "-" signs in FIG. 4B) in the water 404 are attracted to the positive charges. As a result, the water 404 migrates to the edge 429 of the lens 420, displacing the oil 405 to the center 431 of the lens 420. FIG. 4B shows that the curvature of the interface 406 has changed to a convex shape, focusing the incident light beam 403 to a focal point 433 on the optical axis OA.

[0120] The variable focal length lens 420 may replace the input fiber assembly in a typical state-of-the-art alignment system (e.g., system 300 described above) (as described below). Compared to a typical state-of-the-art alignment system, the variable focal length lens 420 described herein provides, among other advantages, a fast response (e.g., on the order of milliseconds), a compact design, low heat dissipation in the lens, low power consumption of approximately 1 mW (±20%), and allows for adjustment of the functionality of the optical module 399.

[0121] Variable Spot Size Alignment System

[0122] FIG. 4C shows variable focal length lenses 401 and 402 (e.g., similar and / or the same as focal length lens 420, respectively, described above) incorporated into illumination system 410. Illumination system 410 may be part of variable spot size alignment system 400, as shown in FIG. 4D. As shown in FIG. 4D, illumination system 310 of FIG. 3 is replaced with illumination system 410 of FIG. 4C. In one embodiment, variable spot size alignment system 400 (as shown in FIG. 4D) utilizes the remaining components of alignment system 300 of FIG. 3. In illumination system 410 of FIG. 4C, illumination system variable focus lenses 401 and 402 replace fixed lens IFA 311 of illumination system 310 of FIG. 3. By removing IFA 311 and inserting lenses 401 and 402, alignment system 400 can achieve a variable spot size at substrate W.

[0123] According to one embodiment, illumination system 410 (as shown in FIGS. 4C and 4D ) is configured to receive radiation beam 306 from input fiber 307, for example along optical axis AX (which may be similar and / or the same as optical axis OA described above). Illumination system 410 includes a fixed lens, such as illumination relay lens 312, that receives radiation beam 306 before passing the radiation to first variable focal length lens 401, then to second variable focal length lens 402, and then to aperture stop 313.

[0124] A variable focal length lens set (in this case, the pair of variable focal length lenses 401 and 402) is typically used in pairs to manipulate focal length, but the variable focal length lens set is not limited to two lenses.

[0125] In one embodiment, a nominal amount of voltage is applied to variable focal length lenses 401 and 402 to achieve no curvature of membranes 435, 437 (similar and / or the same as membrane 427 described above). When an increased voltage is applied, in one embodiment, an increased focal length is achieved, resulting in a change in the spot size of the radiation on the substrate. A negative voltage can also be applied to achieve a decreased focal length (and a different spot size of the radiation on the substrate). The polarity of the voltage to achieve different curvatures and increase or decrease the focal length can be reversed as desired.

[0126] Figure 4D shows the input fiber assembly (IFA) 311 of Figure 3 replaced by the illumination system 410 shown in Figure 4C. By replacing the input fiber assembly (IFA) 311 with the illumination system 410, which includes variable focal length lenses 401 and 402, a variable spot size on the substrate W can be achieved. The spot size on the substrate W can be enlarged or reduced by applying different voltages to the lenses 401, 402. Depending on the size of the alignment mark, the spot size can be enlarged or reduced. By using the voltages described above to vary the spot size of the radiation on the substrate to match the size of the alignment mark (or other metrology mark), alignment marks of various sizes can be more easily measured.

[0127] The change in size of spot 491 is shown in Figures 4E and 4F. Figure 4E shows a schematic diagram of the size of spot 491 of radiation beam 306 when a nominal voltage is applied to variable focal length lenses 401 and 402. As radiation beam 306 exits input fiber 307, it expands to a size of 481 until it reaches illumination relay lens 312. Illumination relay lens 312 changes the incident beam into a collimated radiation beam 483. When a nominal voltage is applied to each of variable focal length lenses 401 and 402, there is no curvature at the water-oil interface 406 of lenses 401 and 402 (see Figures 4A and 4B). As a result, collimated radiation beam 306 remains the same as it exits each of lenses 401 and 402. Next, collimated radiation beam 306 passes through aperture stop 313, and spot 491 has a diameter D1.

[0128] Figure 4F shows a schematic diagram of the size of spot 491 of radiation beam 306 when voltage is applied to variable focal length lenses 401 and 402. Similar to Figure 4E, when radiation beam 306 exits input fiber 307, it expands to a size of 481 until it reaches illumination relay lens 312, which changes the incident beam into a collimated radiation beam 483. When voltage is applied to each of variable focal length lenses 401 and 402, a curvature is formed at the water-oil interface 406 of lenses 401 and 402 (see Figures 4A and 4B). As a result, the increased focal lengths of lenses 401 and 402 increase the size 489 of collimated radiation beam 306 when it exits second lens 402. Finally, the expanded radiation beam 306 passes through aperture stop 313, and spot 491 has an expanded diameter D2.

[0129] Currently, state-of-the-art alignment systems, such as system 300 shown in Figure 3, can achieve an illumination spot size as small as approximately 30 μm to measure a 30 μm by 80 μm alignment mark. However, by using illumination system 410 of Figure 4C in an alignment system with a variable spot size, a variable spot size can be achieved that can be finely adjusted to range from 10 μm to 40 μm or less to measure alignment marks as small as 10 μm by 10 μm or less.

[0130] Beam Steering Alignment System

[0131] FIG. 5A shows a schematic diagram of an illumination system 510 of a beam steering alignment system. The illumination system 510 includes a relay lens 312 (e.g., similar and / or the same as the relay lens 312 shown in FIG. 4C ), first and second variable focal length lenses 501 and 502 (similar and / or the same as the lenses 401 and 402 shown in FIG. 4C ), and an aperture stop 313 (similar and / or the same as the aperture stop 313 shown in FIG. 4C ). As shown in FIG. 5A , the illumination system 510 may be configured to receive the radiation beam 306 from the fiber 307. The illumination system 510 includes the illumination relay lens 312 that receives the radiation beam 306, the first variable focal length lens 501, the second variable focal length lens 502, and the aperture stop 313. The second variable focal length lens 502 is offset 503 from the first variable focal length lens 501 and the optical axis AX.

[0132] Figure 5B shows a beam steering alignment system 500 that includes an illumination system 510. In Figure 5B, the illumination system 310 shown in Figure 3 replaces the illumination system 510 of Figure 5A. In one embodiment, the beam steering alignment system 500 (as shown in Figure 5B) utilizes the remaining components of the alignment system 300 of Figure 3.

[0133] 5C-5D show schematic diagrams of the effect of offsetting the variable focal length lens 502 from the optical axis AX. FIG. 5C shows the case where the variable focal length lens 502 is not offset from the optical axis AX, and the illumination spot 333 on the substrate W is aligned with the optical axis AX. Meanwhile, FIG. 5D shows the case where the variable focal length lens 502 is offset from the optical axis AX, and the illumination spot 333 on the substrate W is also offset from the optical axis AX. The offset of the variable focal length lens 502 from the optical axis AX causes the radiation beam 306 to reflect off the spot mirror 320 at a different angle, resulting in the illumination spot 333 being offset from the optical axis AX, as shown in FIG. 5D. For example, a beam steering angle of 1.8 mrad tilt results in a scan length of ±24 μm.

[0134] By offsetting the variable focal length lens 502 from the optical axis AX, the beam can be shifted laterally at the substrate W. In beam steering, the lens 502 moves while the substrate W remains stationary, thereby varying the beam 306. The beam can be steered in the x and / or y directions. Beam steering can be used to compensate for lateral scan offsets due to the substrate table WT (the substrate table WT is shown and described above). Because beam steering is easier to perform than accelerating and decelerating the substrate table WT, beam steering can be used to measure alignment. As a result, beam steering can be used to perform alignment diagnostics. Additionally, beam steering allows for non-mechanical scanning within the optical module 399 (see FIG. 5B).

[0135] 5A, 5C, and 5D, forming part of the larger alignment system 500 of FIG. 5B. For example, FIG. 5E shows adjustable lenses 501 and 502, with lens 502 offset from optical axis AX and lens 501. When lens 502 is not offset from optical axis AX, the illumination spot 333 on substrate W coincides with optical axis AX. When variable focal length lens 502 is offset from optical axis AX, the illumination spot 333 on substrate W also becomes offset from optical axis AX. The offset of variable focal length lens 502 from optical axis AX causes radiation beam 306 to reflect off spot mirror 320 at a different angle, resulting in illumination spot 333 that is offset from optical axis AX.

[0136] To non-mechanically beam scan the alignment mark with the optical module, the design shown in FIG. 5E ensures that beam steering still fits within the spot mirror 320. The current spot size and spot mirror size ensure that zero-order blocking is maintained. Even if the beam 306 is offset from the optical axis AX when incident on the substrate W, the zero-order of the diffracted radiation beam 335 is still blocked by the spot mirror 320. As a result, dark-field measurements are still possible because the zero-order beam is blocked. Furthermore, both normal raster scanning and angled raster scanning can be achieved without employing mechanical elements. In addition, there is a combination of bidirectional angled scanning. As a result, lateral scan offsets are compensated for.

[0137] In other embodiments, beam steering can be used in combination with a high bandwidth detector for more marks and a constant high speed substrate table WT to take into account the Doppler shift of different marks. Furthermore, an additional coherent illumination spot can be generated at the substrate W, providing beam steering relative to the original beam spot. An aligned position can be achieved as a function of the beam steering angle. Alternatively, the beam can be directed directly onto the detector.

[0138] Variable Focus Alignment System

[0139] Figure 6A shows a schematic diagram of a variable focus alignment system 600. Variable focus alignment system 600 is the same as alignment system 300 of Figure 3 except that input fiber assembly (IFA) 311 is removed and a first variable focal length lens 601 is added to objective lens 330 and second variable focal length lenses 602a-602d are added to output channels 351a-351d, respectively.

[0140] According to one embodiment, a first variable focal length lens 601 is located in the objective lens 330. Second variable focal length lenses 602a, 602b, 602c, and 602d are located in the output channels 351a, 351b, 351c, and 351d, respectively. As a result, the radiation beam of each output channel passes through a pair of variable focal length lenses: the first variable focal length lens 601 and the second variable focal length lens of one of the output channels 602a-602d. These variable focal length lenses are located in the collection path of the sensor. Thus, if there are "N" output channels, there are "N+1" variable focal length lenses in the alignment system. In the example of FIG. 6A, there are four (N) output channels and five (N+1) variable focal length lenses. A first variable focal length lens 601 is located in the objective lens 330, and four second variable focal length lenses 602a-602d are located in the output channels 351a-351d, for a total of five variable focal length lenses.

[0141] By including a first variable focal length lens 601 in the objective lens 330 and second variable focal length lenses 602a-602d in the output channels 351a-351d, respectively, the focus of the radiation beam at the substrate W can be varied. The variation in focus allows measurements to be made on alignment marks located at different z-levels. As a result, the alignment system 600 has the ability to align and perform overlay over warped substrates or thick resist layers. Furthermore, the variable focus for through-stack measurements enables thick stack measurements and diffraction-based overlay in the alignment sensor.

[0142] For example, Figure 6B shows a schematic diagram of a thick resist substrate W in a variable focus alignment system 600 (Figure 6A). The substrate W comprises an alignment mark 610 located below a resist layer 611. Despite the thickness of the multiple layers of photoresist 611, the underlying alignment mark 610 layer remains in focus. By applying a voltage to variable focal length lenses 601 and 602a-d (shown in Figure 6A), the focal length of the radiation beam 306 can be changed to focus the radiation beam 306 to the level of the alignment mark 610. In some embodiments, thick 3D NAND stacks with thick resist and warped wafers can be aligned using the variable focus alignment system 600.

[0143] 6C-6D show schematic diagrams of measuring the overlay (e.g., offset "d") of alignment marks 610a and 610b in a variable focus alignment system. In FIG. 6C, the upper alignment mark 610a (grating) can be measured by focusing the radiation beam 306 on the surface of alignment mark 610a. In FIG. 6D, the lower alignment mark 610b (grating) can be measured by focusing the radiation beam 306 on the surface of alignment mark 610b. As a result, the offset "d" between the alignment mark gratings can be determined. For example, variable focus can be applied in a Z-star system with diffraction gratings at different z levels.

[0144] The variable focus alignment system 600 (Figure 6A) has the ability to maintain the same mark pitch range. The numerical aperture pitch is between 0.118 and 0.7. The variable focus accounts for typical thick stacks on the order of millimeters. Furthermore, the use of variable focal length lenses 401 and 402 in an IFA like that shown in Figure 4C can be used in conjunction with the variable focus to maintain spot sizes at different foci. The overlay capability in the variable focus alignment system 600 is achieved by using a multi-Z level alignment signal. Furthermore, the variable focus can be used in the alignment system 600 to provide an adjustable working distance with commercially proven aperture sizes. The variable focus can also be deployed on a yield star for overlay metrology.

[0145] Spot shift and high order exclusion alignment system

[0146] 7A shows a schematic diagram of an alignment system 700 for spot shift and high-order rejection. Except for removing the input fiber assembly (IFA) 311 and adding a first variable focal length lens 701 and a second variable focal length lens 702 in the pupil plane, alignment system 700 is the same as alignment system 300 of FIG.

[0147] According to an embodiment, a first variable focal length lens 701 and a second variable focal length lens 702 (each similar and / or identical to lens 420 described above) are located in a pupil plane downstream of objective lens 330 and upstream of self-referencing interferometer 340. Locating variable focal length lenses 701 and 702 in the pupil plane allows for spot shift calibration and high order rejection. For example, calibration of the spot shift of diffracted radiation beam 335 can be achieved by applying different voltages to variable focal length lenses 701 and 702.

[0148] Figures 7B-7D show a schematic diagram for calibrating spot shift using variable focal length lenses 701 and 702. Figure 7B shows the spot shift of diffracted radiation beam 335 at variable focal length lenses 701 and 702 with nominal voltages. Diffracted radiation beam 335 reflects from an alignment mark on substrate W. Diffracted radiation beam 335 expands until it reaches objective lens 330, where its rays become parallel. With nominal voltages applied to each of variable focal length lenses 701 and 702, there is no curvature at water-oil interface 406 (see Figures 4A and 4B). As a result, the parallel diffracted radiation beam 335 remains the same as it exits each lens 701 and 702. The beam 335 then travels towards self-referencing interferometer 340.

[0149] Figure 7C shows the spot shift of the diffracted radiation beam 335 when lenses 701 and 702 have a medium voltage. The diffracted radiation beam 335 reflects from an alignment mark on the substrate W. The diffracted radiation beam 335 expands until it reaches the objective lens 330, causing the rays to become parallel. When a medium voltage is applied, a curvature is formed at the interface 406 (see Figures 4A and 4B). As a result, the diffracted radiation beam 335 has shifted to a smaller spot size when it exits the second lens 702. The beam 335 then enters the self-referencing interferometer 340.

[0150] Figure 7D shows the spot shift of diffracted radiation beam 335 when lenses 701 and 702 have a high voltage. Figure 7D is similar to Figure 7C except for the magnitude of the voltage applied. Because a higher voltage is used, the curvature of interface 406 (see Figures 4A and 4B) becomes sharper. As a result, diffracted radiation beam 335 has shifted to an even smaller spot size when it exits second lens 702.

[0151] Pupil measurement compensation can be performed by positioning the afocal lens system (lenses 701 and 702) in the pupil plane (see the locations of 701 and 702 in Figure 7A). Pupil measurement can be used to account for product crosstalk. Product crosstalk is signal leakage into the detection system from structures surrounding the target mark. Crosstalk occurs when the aperture stop (e.g., aperture stop 313) and the illumination aperture stop remain the same while the spot size varies (as in alignment system 400 in Figure 4C). If the alignment mark is not underfilled, signal leakage from adjacent structures onto the alignment grating on the substrate W will be captured. In other words, increasing the spot size will illuminate not only the alignment mark but also surrounding structures adjacent to the alignment grating. However, using spot shift calibration in pupil measurement can mitigate product crosstalk.

[0152] Additionally, spot shift can be used to compensate for the delta-R effect. The delta-R effect is a re-metering of the diffracted beam NA due to the product wafer stack. Because there is no explicit pupil metrology to help measure the spot shift in the pupil plane, the delta-R effect would be undetectable. The delta-R effect can occur when the diffracted radiation beam 335 from the substrate W shifts due to stacking on the alignment marks. The delta-R effect can be compensated for by calibrating the change in the wavefront sample due to stacking variations. Calibration can be performed by generating a return signal as a function of spot shift. This curve can be compared to a calibration curve measured for the same target mark pitch on a fiducial. Spot shift is facilitated by an adjustable system. As a result, pupil metrology enables stack measurements (e.g., as described above in connection with Figures 7B-7D) and facilitates smaller marks.

[0153] Second, inserting variable focal length lenses 701 and 702 in the pupil plane (see the locations of 701 and 702 in Figure 7A) provides high-order rejection. Figure 7E shows applying voltages to variable focal length lenses 701 and 702 in the pupil plane to reject higher diffraction orders. The diffracted radiation beam 335 reflects from the surface of the substrate W and splits into diffracted beam spots. Figure 7E shows the first and third diffracted beam spots. The objective lens 330 receives the beam spots and passes them to the variable focal length lenses 701 and 702. Applying voltages to the lenses 701 and 702 induces a curvature at interface 406 (see Figures 4A and 4B), pushing the beam spots radially outward from the optical axis (not shown). Upon exiting the second lens 702, the third-order diffracted beam is radially outward, enough to be outside the clear aperture of lens 336. As a result, the +3rd and -3rd order diffracted beam spots are filtered out and do not pass through lens 336. On the other hand, the +1st and -1st order diffracted beams, despite being pushed outward, are still within the aperture of lens 336 and therefore pass through that aperture.

[0154] Adjustable beam shift as a function of mark pitch allows for higher-order rejection within the optical module (e.g., Nth order or higher can be rejected (N>1)). In the case of Figure 7E, it is desirable to reject the third diffraction order beam, which would otherwise contaminate the signal. Therefore, diffraction orders higher than the mark pitch can be filtered. The contributions of higher diffraction orders from the mark cannot be separated using a single-pixel detector (e.g., I+total = I+1 + I+2 + I+3). Conventional systems can only measure the sum dc signals of I+total and I-total. Algorithms to correct aligned position errors require knowledge of pairs of diffraction orders, such as +1 and -1, +2 and -2, etc. Removing the higher-order signals and calculating the alignment position based only on the detected orders provides high accuracy and reduces noise in the O / P position.

[0155] Alignment system 700 (FIG. 7A) is an alternative that does not use mechatronics to remove unwanted orders. Instead of using mechatronics to remove higher diffraction orders, variable focal length lenses 701 and 702 can be applied. As a result, alignment system 700 can be improved by the use of variable focal length lenses 701 and 702 rather than mechatronic elements.

[0156] Embodiments of Multiple Alignment Systems Usable Together

[0157] One or more of the components and / or systems shown in Figures 4A-7E can be used together in alignment system 300 of Figure 3. In other words, for example, alignment system 300 can be arranged to include illumination systems 410 and 510 of Figures 4A and 5A, respectively, first variable focal length lens 601 in objective lens 330 of Figure 6A and second variable focal length lenses 602a-602d in output channels 351a-351d of Figure 6A, respectively, and variable focal length lenses 701 and 702 in the pupil plane of Figure 7A. This results in three sets of variable focal length lenses being located in alignment system 300. In this embodiment, the variable focal length lenses in alignment system 300 can be located on optical axis AX, such as 401 and 402 of Figure 4C, or one can be located offset from optical axis AX, such as 502 of Figure 5A.

[0158] Furthermore, two embodiments can be used together. For example, illumination system 410 of FIG. 4C and variable focal length lenses 601 and 602a-602d of FIG. 6A can be used together in alignment system 300 of FIG. 3. Alternatively, illumination system 510 of FIG. 5A and variable focal length lenses 701 and 702 of FIG. 7A can be used together. Of course, any combination of embodiments can be used with alignment system 300. The benefits and advantages described above would also be present in this embodiment.

[0159] 8 illustrates an alignment method 800. In some embodiments, method 800 is performed, for example, as part of an alignment sensing operation in a semiconductor device manufacturing process. In some embodiments, one or more operations of method 800 may be implemented in or by a system described herein, including, for example, a computer system (e.g., shown in FIG. 9 and described below), and / or may be implemented in or by another system. In some embodiments, method 800 comprises generating an output radiation beam using an illumination source (802); receiving the radiation beam using a first set of variable focal length lenses (804); controlling the first set of variable focal length lenses (806) to vary the illumination spot size at the wafer; positioning a second set of variable focal length lenses (808) such that one lens of the second set of variable focal length lenses is located in the output channel and another lens of the second set of variable focal length lenses is located in the objective system; controlling the second set of variable focal length lenses (810) to vary the focus height of the output from the objective system; positioning a third set of variable focal length lenses in a pupil plane downstream of the objective system (812); and controlling the third set of variable focal length lenses (814) to vary at least one of the spot shift and higher diffraction orders, and / or for other operations.

[0160] The operations of method 800 are intended to be exemplary. In some embodiments, method 800 may be implemented with one or more additional operations not described and / or without one or more operations described. For example, in some embodiments, method 800 may include an additional operation comprising determining an adjustment to a semiconductor device manufacturing process. In some embodiments, method 800 includes determining one or more semiconductor device manufacturing process parameters. The one or more semiconductor device manufacturing process parameters may be determined based on alignment values ​​indicated by metrology signals and / or other similar systems and / or other information. The one or more parameters may include parameters of the radiation (radiation used for metrology), overlay values, alignment values, metrology inspection locations on layers of a semiconductor device structure, trajectories of the radiation beam across the target, and / or other parameters. In some embodiments, process parameters may be broadly interpreted to include stage position, mask design, metrology target design, semiconductor device design, intensity of radiation (used to expose resist, etc.), angle of incidence of radiation (used to expose resist, etc.), wavelength of radiation (used to expose resist, etc.), pupil size and / or pupil shape, resist material, and / or other parameters.

[0161] In some embodiments, method 800 includes determining process adjustments based on one or more determined semiconductor device manufacturing process parameters, adjusting semiconductor device manufacturing equipment based on the determined adjustments, and / or other operations. For example, if the determined alignment measurements are not within process tolerances, the out-of-tolerance measurements may be caused by one or more manufacturing process parameters having drifted and / or otherwise changed, such that the process no longer produces acceptable devices (e.g., the measurements may breach a threshold of acceptability). One or more new or adjusted process parameters may be determined based on determining the measurements. The new or adjusted process parameters may be configured to once again produce acceptable devices in the manufacturing process.

[0162] For example, new or adjusted process parameters may be adjusted to bring previously unacceptable measurements back into an acceptable range. The new or adjusted process parameters may be compared to existing parameters for a given process. If there are differences, the differences may be used, for example, to determine adjustments to equipment used to manufacture the device (e.g., parameter "x" should be increased / decreased / changed to match the new or adjusted version of parameter "x" determined as part of method 800). In some embodiments, method 800 may include electronically adjusting the equipment (e.g., based on the determined process parameters). Electronically adjusting the equipment may include, for example, sending an electronic signal and / or other communication to the equipment that causes a change in the equipment. Electronic adjustments may include, for example, changing settings and / or other adjustments to the equipment.

[0163] Additionally, the order of operations of method 800 shown in FIG. 8 and described herein is not intended to be limiting.

[0164] In some embodiments, one or more portions of method 800 may be implemented in and / or controlled by one or more processing devices (e.g., digital processors, analog processors, digital circuits designed to process information, analog circuits designed to process information, state machines, and / or other mechanisms for electronically processing information). The one or more processing devices may include one or more devices that perform some or all of the operations of method 800 in response to instructions electronically stored 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 specially designed for performing one or more operations of method 800 (e.g., see the discussion related to FIG. 9 below).

[0165] 9 is a block diagram of an exemplary computer system CS that may be used for one or more operations described herein. The computer system CS includes a bus BS or other communication mechanism for communicating information and a processor PRO (or multiple processors similar and / or identical to the processor PRO shown in FIG. 3) coupled to the bus BS for processing information. The computer system CS also includes a main memory MM, such as a random access memory (RAM) or other dynamic storage device, coupled to the bus BS for storing information and instructions executed by the processor PRO. The main memory MM may also be used to store temporary variables or other intermediate information during execution of instructions by the processor PRO. The computer system CS further includes a read-only memory (ROM) ROM or other static storage device coupled to the bus BS for storing static information and instructions for the processor PRO. A storage device SD, such as a magnetic or optical disk, is provided and coupled to the bus BS for storing information and instructions.

[0166] The computer system CS may be coupled via a bus BS to a display DS, such as a flat-panel or touch-sensitive display or cathode ray tube (CRT), for displaying information to a computer user. An input device ID, including alphanumeric and other keys, is coupled to the bus BS for communicating information and command selections to the processor PRO. Another type of user input device is a cursor control CC, such as a mouse, trackball, or cursor direction keys, for communicating directional information and command selections to the processor PRO and for controlling cursor movement on the display DS. This input device typically has two degrees of freedom, a first axis (e.g., x) and a second axis (e.g., y), allowing for the specification of a position in a plane. A touch-sensitive (screen) display may also be used as an input device.

[0167] In some embodiments, all or some of one or more operations described herein may be performed by computer system CS in response to processor PRO 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 PRO to perform the process steps (operations) described herein. One or more processors in a multi-processing arrangement may be employed to execute the sequences of instructions contained in main memory MM. In some embodiments, 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.

[0168] As used herein, the terms "computer-readable medium" or "machine-readable medium" refer to any medium that participates in providing instructions to a processor PRO for execution. Such media 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 devices SD. Volatile media include dynamic memory, such as main memory MM. Transmission media include the wires that comprise the bus BS, including coaxial cables, copper wire, and optical fibers. 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. Computer-readable media can be non-transitory, such as, for example, floppy disks, flexible disks, hard disks, magnetic tape, other magnetic media, CD-ROMs, DVDs, other optical media, punch cards, paper tape, other physical media with patterns of holes, RAM, PROM, EPROM, FLASH-EPROM, and other memory chips or cartridges. Non-transitory computer-readable media can have instructions recorded on them. The instructions, when executed by a computer, can implement any of the operations described herein. The transitory computer-readable medium can include, for example, a carrier wave or other propagated electromagnetic signal.

[0169] Various forms of computer-readable media may be involved in carrying one or more sequences of one or more instructions to processor PRO for execution. For example, the instructions may initially be carried 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 telephone line using a modem. A modem local to computer system CS can receive the data on the telephone line and convert the data to an infrared signal using an infrared transmitter. An infrared detector coupled to bus BS receives the data transmitted in the infrared signal and places the data on bus BS. Bus BS carries the data to main memory MM, from which processor PRO 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 PRO.

[0170] The computer system CS may also include a communications interface CI coupled to the bus BS. The communications interface CI provides a bidirectional data communications coupling to a network link NDL connected to a local network LAN. For example, the communications interface CI may be an Integrated Services Digital Network (ISDN) card or modem for providing a data communications connection to a corresponding type of telephone line. As another example, the communications interface CI may be a local area network (LAN) card providing a data communications connection to a compatible LAN. A wireless link may also be implemented. In such implementations, the communications interface CI sends and receives electrical, electromagnetic, or optical signals that carry digital data streams representing various types of information.

[0171] The network link NDL typically provides data communication through one or more networks to other data devices. For example, the network link NDL may provide a connection to a host computer HC through a local network LAN. This may include data communication services provided through the worldwide packet data communication network now commonly referred to as the "Internet" INT. The local network LAN (Internet) may use electrical, electromagnetic, or optical signals that carry digital data streams. The signals through the various networks, the signals on the network data link NDL, and the signals through the communication interface CI that carry digital data to and from the computer system CS are exemplary forms of carrier waves conveying information.

[0172] The computer system CS can send messages and receive data, including program code, via the network, the network data link NDL, and the communication interface CI. In the Internet example, the host computer HC may transmit requested code for an application program via the Internet INT, the network data link NDL, the local network LAN, and the communication interface CI. One such downloaded application may, for example, provide all or part of the methods described herein. The received code may be executed by the processor PRO as it is received and / or may be stored in the storage device SD or other non-volatile storage for later execution. In this manner, the computer system CS may obtain application code in the form of a carrier wave.

[0173] This specification discloses one or more embodiments that incorporate the features of the present invention. The disclosed embodiments are merely exemplary of the present invention. The scope of the present invention is not limited to the disclosed embodiments. The present invention is defined by the appended claims.

[0174] References to the described embodiments, and to "one embodiment," "an embodiment," "an exemplary embodiment," etc. throughout the specification, indicate that the described embodiment may include a particular feature, structure, or characteristic, but that not all embodiments necessarily include the particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with an embodiment, it will be understood that it is within the knowledge of one of ordinary skill in the art to affect such feature, structure, or characteristic in connection with other embodiments, whether or not explicitly stated.

[0175] Although specific reference may be made herein to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, magnetic domain memory guidance and detection patterns, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc. Those skilled in the art will recognize that, in the context of such alternative applications, any use of the terms "wafer" or "die" herein may be considered synonymous with the more general terms "substrate" and "target portion," respectively. Substrates referred to herein may be processed, pre- or post-exposure, for example, in a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool, and / or an inspection tool. Where applicable, the disclosure herein may apply to such and other substrate processing tools. Furthermore, a substrate may be processed multiple times, for example to produce a multi-layer IC, and the term substrate, as used herein, may refer to a substrate already including multiple processed layers.

[0176] While specific reference may be made above to the use of embodiments of the present invention in the context of optical lithography, it will be appreciated that the present invention may be used in other applications, for example imprint lithography, and is not limited to optical lithography where the context allows. In imprint lithography, a topography of a patterning device defines the pattern to be created on a substrate. The topography of the patterning device is pressed into a layer of resist supplied to the substrate and the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist is cured, the patterning device is removed from the resist leaving the pattern behind.

[0177] It is to be understood that the terms or phraseology used herein are for the purpose of description and not of limitation, as interpreted by those skilled in the relevant art in light of the teachings herein.

[0178] In the embodiments described herein, where the context allows, the terms "lens" and "lens element" may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.

[0179] Furthermore, the terms "radiation" and "beam" as used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength λ of 365, 248, 193, 157, or 126 nm), extreme ultraviolet (EUV or soft X-ray) radiation (e.g., having a wavelength in the 5-20 nm range, such as 13.5 nm), or hard X-rays operating below 5 nm, as well as particle beams such as ion beams or electron beams. Generally, radiation having a wavelength of about 400 to about 700 nm is considered visible radiation, and radiation having a wavelength of about 780 to 3000 nm (or longer) is considered infrared radiation. UV refers to radiation having a wavelength of about 100 to 400 nm. In the field of lithography, the term "UV" also applies to wavelengths that can be produced by mercury discharge lamps: G-line 436 nm, H-line 405 nm, and / or I-line 365 nm. Vacuum ultraviolet or VUV (i.e., UV absorbed by gases) refers to radiation having a wavelength of approximately 100-200 nm. Deep ultraviolet (DUV) generally refers to radiation having a wavelength in the range of 126 nm to 428 nm, and in certain embodiments, excimer lasers can generate DUV radiation for use in lithography equipment. It will be understood that radiation having a wavelength in the range of, for example, 5-20 nm, refers to radiation having a particular wavelength band, at least a portion of which is in the 5-20 nm range.

[0180] As used herein, the term "substrate" generally describes a material onto which subsequent layers of material are added. In embodiments, the substrate itself may be patterned, or the materials added onto it may also be patterned or left unpatterned.

[0181] As used herein, the term "substantially contacting" describes elements or structures that are in physical contact with one another, typically with only a small separation relative to one another due to misalignment tolerances. It will be understood that any relative spatial descriptions between one or more particular features, structures, or characteristics used herein (e.g., "vertically aligned," "substantially contacting," etc.) are for illustrative purposes only, and that actual implementations of the structures described herein may include misalignment tolerances without departing from the spirit and scope of the present disclosure.

[0182] As used herein, the term "optically coupled" generally refers to a configuration in which one coupled element is configured to transmit light directly or indirectly to another coupled element.

[0183] As used herein, the term "optical material" generally refers to a material that allows light or optical energy to propagate therethrough.

[0184] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described, and this description is not intended to limit the invention.

[0185] It is understood that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. While the Summary and Abstract sections may describe one or more exemplary embodiments of the invention contemplated by the inventors, they are not exhaustive and therefore are not intended to limit the scope of the invention and the appended claims in any way.

[0186] The present invention has been described above using functional building blocks that illustrate the implementation of specific functions and their relationships. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of explanation. Alternative boundaries may be defined as long as the specific functions and their relationships are appropriately performed.

[0187] Various embodiments of the present system and method are disclosed in the following numbered clause list. Hereinafter, further features, characteristics, and exemplary technical solutions of the present disclosure are described by clauses which may be optionally claimed in any combination. (Item 1) A wafer alignment measurement system comprising: an illumination source; a radiation beam output from the illumination source; a first set of variable focal length lenses configured to receive the radiation beam, the first set of variable focal length lenses being controllable to control an illumination spot size at a wafer; a second set of variable focal length lenses, one of which is located in an output channel and another of which is located in an objective system, the second set of variable focal length lenses being controllable to control a focus height of an output from the objective system; and a third set of variable focal length lenses located in a pupil plane downstream of the objective system, the third set of variable focal length lenses being controllable to control at least one of a spot shift and a higher diffraction order. (Item 2) The wafer alignment measurement system according to item 1, wherein the first set of variable focal length lenses is located in an illumination system. (Item 3) A wafer alignment measurement system according to any one of the above items, wherein one of the first variable focal length lenses is offset from the optical axis of the radiation beam. (Item 4) A wafer alignment measurement system according to any one of the above items, wherein there are N output channels and N+1 second variable focal length lenses, one second variable focal length lens in each output channel, and one second variable focal length lens in the objective system. (Item 5) A wafer alignment measurement system according to any one of the above items, wherein the third set of variable focal length lenses is located in a pupil plane. (Item 6) A wafer alignment measurement system according to any one of the above items, wherein the first set, the second set, and the third set of variable focal length lenses are controllable by applying voltages to the first set, the second set, and the third set of variable focal length lenses. (Item 7) A wafer alignment measurement system comprising: an illumination source; a radiation beam output from the illumination source; and at least two variable focal length lenses configured to receive the radiation beam, wherein the variable focal length lenses are controllable to control the illumination spot size on the wafer. (Item 8) A wafer alignment measurement system according to any one of the above items, wherein the variable focal length lens is located in an illumination system. (Item 9) A wafer alignment measurement system according to any one of the above items, wherein the variable focal length lens is located in the illumination system between the illumination relay lens and the aperture stop. (Item 10) A wafer alignment measurement system according to any one of the above items, wherein the variable focal length lens is controllable by applying a voltage to the variable focal length lens. (Item 11) A wafer alignment measurement system according to any one of the preceding items, wherein one variable focal length lens is offset from the optical axis of the radiation beam. (Item 12) A wafer alignment measurement system comprising: an illumination source; and at least two variable focal length lenses, one of the variable focal length lenses being located in an output channel and another of the variable focal length lenses being located in an objective system, the variable focal length lenses being controllable to control the focus height of the output from the objective system. (Item 13) A wafer alignment measurement system according to any one of the above items, wherein the output of the illumination source is a radiation beam that is reflected from the wafer. (Item 14) A wafer alignment measurement system according to any one of the preceding items, wherein the radiation beam passes through the variable focal length lens after being reflected from the wafer. (Item 15) A wafer alignment measurement system according to any one of the above items, having N output channels and N+1 variable focal length lenses, one variable focal length lens in each output channel, and one variable focal length lens in the objective system. (Item 16) A wafer alignment measurement system according to any one of the above items, wherein the variable focal length lens is controllable by applying a voltage to the variable focal length lens. (Item 17) A wafer alignment measurement system comprising: an illumination source; a radiation beam output from the illumination source and directed toward an objective system; and at least two variable focal length lenses positioned in a pupil plane downstream of the objective system, the variable focal length lenses being controllable to control at least one of spot shift and higher diffraction orders. (Item 18) A wafer alignment measurement system according to any one of the above items, wherein the variable focal length lens is located in a pupil plane. (Item 19) A wafer alignment measurement system according to any one of the above items, wherein the variable focal length lens is located in a pupil plane between the objective system and a self-referencing interferometer. (Item 20) A wafer alignment measurement system according to any one of the above items, wherein the variable focal length lens compensates for spot shift. (Item 21) A wafer alignment measurement system according to any one of the above items, wherein the variable focal length lens compensates for higher diffraction orders. (Item 22) A wafer alignment measurement system according to any one of the above items, wherein the variable focal length lens is controllable by applying a voltage to the variable focal length lens. (Item 23) A wafer alignment measurement method comprising: generating a radiation beam using an illumination source; receiving the radiation beam using a first set of variable focal length lenses; controlling the first set of variable focal length lenses to vary the illumination spot size on the wafer; positioning a second set of variable focal length lenses, with one lens of the second set of variable focal length lenses positioned in an output channel and another lens of the second set of variable focal length lenses positioned in an objective system; controlling the second set of variable focal length lenses to vary the focus height of the output from the objective system; positioning a third set of variable focal length lenses in a pupil plane downstream of the objective system; and controlling the third set of variable focal length lenses to vary at least one of the spot shift and higher diffraction orders. (Item 24) The wafer alignment measurement method according to Item 23, wherein the first set of variable focal length lenses is located in an illumination system. (Item 25) A wafer alignment measurement method according to any one of the preceding items, wherein one of the first set of variable focal length lenses is offset from the optical axis of the radiation beam. (Item 26) A wafer alignment measurement method according to any one of the above items, wherein there are N output channels and N+1 second variable focal length lenses, one second variable focal length lens in each output channel, and one second variable focal length lens in the objective system. (Item 27) A wafer alignment measurement method according to any one of the above items, wherein the third set of variable focal length lenses is located in a pupil plane. (Item 28) A wafer alignment measurement method according to any one of the above items, wherein the first set, the second set, and the third set of variable focal length lenses are controllable by applying voltages to the first set, the second set, and the third set of variable focal length lenses. (Item 29) A wafer alignment measurement method comprising: generating a radiation beam output from an illumination source; receiving the radiation beam using at least two variable focal length lenses; and controlling the variable focal length lenses to vary the illumination spot size on the wafer. (Item 30) A wafer alignment measurement method according to any one of the above items, wherein the variable focal length lens is located in an illumination system. (Item 31) A wafer alignment measurement method according to any one of the above items, wherein the variable focal length lens is located in the illumination system between an illumination relay lens and an aperture stop. (Item 32) A wafer alignment measurement method according to any one of the above items, wherein the variable focal length lens is controllable by applying a voltage to the variable focal length lens. (Item 33) A wafer alignment measurement method according to any one of the preceding items, wherein one variable focal length lens is offset from the optical axis of the radiation beam. (Item 34) A wafer alignment measurement method comprising: an illumination source; and at least two variable focal length lenses, one of the variable focal length lenses being located in an output channel and another of the variable focal length lenses being located in an objective system, the variable focal length lenses being controllable to control the focus height of the output from the objective system. (Item 35) A wafer alignment measurement method according to any one of the preceding items, wherein the output of the illumination source is a radiation beam that is reflected from the wafer. (Item 36) A wafer alignment measurement method according to any one of the preceding items, wherein the radiation beam passes through the variable focal length lens after being reflected from the wafer. (Item 37) A wafer alignment measurement method according to any one of the above items, wherein there are N output channels and N+1 variable focal length lenses, each output channel having one variable focal length lens, and the objective system having one variable focal length lens. (Item 38) A wafer alignment measurement method according to any one of the above items, wherein the variable focal length lens is controllable by applying a voltage to the variable focal length lens. (Item 39) A wafer alignment measurement method comprising: generating a radiation beam output from an illumination source and directed toward an objective system; positioning at least two variable focal length lenses in a pupil plane downstream of the objective system; and controlling the variable focal length lenses to vary at least one of spot shift and higher diffraction orders. (Item 40) A wafer alignment measurement method according to any one of the above items, wherein the variable focal length lens is located within a pupil plane. (Item 41) A wafer alignment measurement method according to any one of the above items, wherein the variable focal length lens is located in a pupil plane between the objective system and a self-referencing interferometer. (Item 42) A wafer alignment measurement method according to any one of the above items, wherein the variable focal length lens compensates for spot shift. (Item 43) A wafer alignment measurement method according to any one of the above items, wherein the variable focal length lens compensates for higher diffraction orders. (Item 44) A wafer alignment measurement method according to any one of the above items, wherein the variable focal length lens is controllable by applying a voltage to the variable focal length lens.

[0188] The foregoing description of specific embodiments fully reveals the general nature of the invention, and those skilled in the art may readily modify and / or adapt such specific embodiments for various applications without undue experimentation and without departing from the general inventive concept. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein.

[0189] The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. an illumination source; at least two variable focal length lenses; one of the variable focal length lenses is located in the output channel; another one of the variable focal length lenses is located in the objective system; the variable focal length lens is controllable to control the height of the focus of the output from the objective. Wafer alignment measurement system.

2. the output of the illumination source is a radiation beam that is reflected from the wafer; The wafer alignment measurement system according to claim 1 .

3. the radiation beam passes through the variable focal length lens after being reflected from the wafer; The wafer alignment measurement system according to claim 2 .

4. There are N output channels and N+1 variable focal length lenses, There is one variable focal length lens for each output channel, The objective system has one variable focal length lens. The wafer alignment measurement system according to claim 3 .

5. the variable focal length lens is controllable by applying a voltage to the variable focal length lens; The wafer alignment measurement system according to claim 3 .

6. an illumination source; a radiation beam output from the illumination source and directed towards an objective; at least two variable focal length lenses located in a pupil plane downstream of the objective; the variable focal length lens is controllable to control at least one of spot shift and higher diffraction orders; Wafer alignment measurement system.

7. The variable focal length lens is located in a pupil plane.

7. The wafer alignment measurement system according to claim 6.

8. the variable focal length lens is located in a pupil plane between the objective and a self-referencing interferometer; 7. The wafer alignment measurement system according to claim 6.

9. The variable focal length lens compensates for spot shift.

7. The wafer alignment measurement system according to claim 6.

10. the variable focal length lens compensates for higher diffraction orders; 7. The wafer alignment measurement system according to claim 6.

11. the variable focal length lens is controllable by applying a voltage to the variable focal length lens; 7. The wafer alignment measurement system according to claim 6.

12. an illumination source; at least two variable focal length lenses; one of the variable focal length lenses is located in the output channel; another one of the variable focal length lenses is located in the objective system; the variable focal length lens is controllable to control the height of the focus of the output from the objective. Wafer alignment measurement method.

13. the output of the illumination source is a radiation beam that is reflected from the wafer; The wafer alignment measurement method according to claim 12.

14. the radiation beam passes through the variable focal length lens after being reflected from the wafer; The wafer alignment measurement method according to claim 13.

15. There are N output channels and N+1 variable focal length lenses, There is one variable focal length lens for each output channel, The objective system has one variable focal length lens. The wafer alignment measurement method according to claim 14.

Images