Tunable optical system

Abstract

Systems and methods for providing variable spot size and variable focus at a substrate are described. Multiple sets of variable focal length lenses may be added to the alignment system to allow adjustment of the spot size and focus. A variable focal length lens is a liquid lens that is tunable based on the application of a voltage across the entire lens. Switching the voltage changes the water-oil interface in the liquid lens, in turn, the direction of light passing therethrough. For example, switching on the voltage across the entire lens shifts the light output direction to converge at a focal point. Thus, a variable focal length lens provides adjustments to compensate for the fixed spot size and focus defects of the prior art. In addition, a variable focal length lens may also be applied to compensate for spot shift and higher order diffraction orders.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. application No. 63 / 410,008, filed on September 26, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to a tunable optical system. Background Art

[0004] A lithographic apparatus is a machine that applies a desired pattern to a target portion of a substrate. For example, a lithographic apparatus can be used to manufacture integrated circuits (ICs). In this case, a patterning device (alternatively referred to as a mask or reticle) can be used to generate circuit patterns corresponding to the various layers of the IC, and the pattern can be imaged onto a target portion (e.g., including a portion of a die, a die, or several dies) on a substrate (e.g., a silicon wafer) having a layer of radiation-sensitive material (resist). Typically, a single substrate will contain a network of adjacent target portions that are exposed in succession. Known lithographic apparatus include so-called steppers (each target portion is irradiated by exposing the entire pattern to the target portion in one exposure) and so-called scanners (each target portion is irradiated by scanning the pattern through a beam in a given direction (the "scanning" direction) while synchronously scanning the substrate parallel or antiparallel to that direction). The pattern can also be transferred from the patterning device to the substrate by imprinting the pattern onto the substrate. Another lithographic system is an interferometric lithography system, in which there is no patterning device, and the beam is split into two beams, and the two beams are used to interfere at the target portion of the substrate by using a reflection system. The interference causes a line to be formed on a target portion of the substrate.

[0005] During a lithographic operation, different processing steps may require different layers to be sequentially formed on the substrate. Therefore, it may be necessary to position the substrate with a high degree of accuracy relative to a previous pattern formed thereon. Typically, alignment marks (which may include diffraction gratings, for example) are placed on the substrate to be aligned and positioned with reference to a second object. For example, a lithographic apparatus may use an alignment system for detecting the position of the alignment marks, and for aligning the substrate using the alignment marks to ensure accuracy in subsequent lithographic operations.

[0006] The alignment system typically has its own illumination system that can be used to illuminate the alignment marks during alignment measurements. Determining alignment typically includes determining the position of the alignment mark (or marks) and / or other targets in the semiconductor device structure layer. Alignment is typically determined by illuminating the alignment marks with radiation and comparing the characteristics of different diffraction order radiation reflected from the alignment marks. Similar techniques are used to measure overlay and / or other parameters. Current alignment sensors have a single measurement illumination spot projected onto a substrate (e.g., a wafer). A single illumination spot is used to measure multiple alignment parameters, phase and intensity detection. Current sensors measure metrology marks continuously. Thus, the number of measurement marks on a given substrate is limited by throughput considerations.

[0007] Alignment systems typically use a dual self-referencing interferometer (SRI) system to acquire the intensity as a function of the mark position. The phase of these sinusoidal signals is used to determine the alignment position of the mark. Each SRI has its dedicated polarization state, which is prepared using feed optics that separate the input light into x- and y-polarizations. These alignment systems are fixed optical systems.

[0008] However, current alignment systems have several limitations. The beam spot size illuminating the target mark at the wafer is fixed. Therefore, the size of the alignment mark is constrained. For example, alignment failures may occur for relatively thick resist and / or warped wafers. Another common problem is the undetectable ΔR effect, which is the re-weighting of the diffraction beam numerical aperture due to product wafer stacking. In addition, electromechanical components need to be used within a typical optical module to achieve higher order suppression. Mechatronics uses mechanical components that cause vibration and heat, and requires a lot of power, all of which are undesirable within an alignment system. Summary of the invention

[0009] A novel system and method are disclosed that facilitates variable spot size and variable focus at a substrate for alignment (and / or overlap) determination. Multiple sets of variable focal length lenses are provided in the alignment system to allow adjustment of the spot size and focus. The variable focal length lens is a liquid lens that is tunable based on applying a voltage across the entire lens. Switching the voltage changes the curvature of the water-oil interface in the liquid lens, thereby changing the direction of the light transmitted through. For example, turning on the voltage across the entire lens shifts the light output direction to converge at a focal point. Thus, the variable focal length lens provides adjustment to compensate for the fixed spot size and focus deficiencies of the prior art. In addition, the variable focal length lens can also be applied to compensate for spot shift and ΔR effects. Moreover, the variable focal length lens can be used instead of an electromechanical element to suppress higher diffraction orders.

[0010] According to an embodiment, a wafer alignment measurement system includes: an illumination source; a radiation beam output from the illumination source; a first group of variable focus lenses configured to receive the radiation beam, wherein the first group of variable focus lenses is controllable to control the illumination spot size at the wafer; a second group of variable focus lenses; and a third group of variable focus lenses positioned in a pupil plane downstream of the objective lens system, wherein the third group of variable focus lenses is controllable to control at least one of spot shift and higher diffraction orders.

[0011] In an embodiment, the first set of variable focus lenses is positioned in the illumination system.

[0012] In an embodiment, a first variable focus lens is offset from the optical axis of the illumination source output.

[0013] In an embodiment, there are "N" output channels and "N+1" second variable focus lenses, wherein there is one second variable focus lens in each output channel and one second variable focus lens in the objective system.

[0014] In an embodiment, said third group of variable focus lenses is positioned in a pupil plane.

[0015] In an embodiment, the first group of variable focus lenses, the second group of variable focus lenses, and the third group of variable focus lenses can be controlled by applying voltage to the first group of variable focus lenses, the second group of variable focus lenses, and the third group of variable focus lenses.

[0016] According to an embodiment, a wafer alignment measurement system includes: an illumination source; a radiation beam output from the illumination source; and at least two variable focus lenses configured to receive the radiation beam, wherein the variable focus lenses are controllable to control an illumination spot size at a wafer.

[0017] In an embodiment, the variable focus lens is positioned in the illumination system.

[0018] In an embodiment, the variable focus lens is positioned in the illumination system between an illumination relay lens and an aperture stop.

[0019] In an embodiment, the variable focus lens is controllable by applying a voltage to the variable focus lens.

[0020] In embodiments, a variable focus lens is offset from the optical axis of the illumination source output.

[0021] According to an embodiment, a wafer alignment measurement system includes: an illumination source; and at least two variable focus lenses, one variable focus lens positioned in an output channel and another variable focus lens positioned in an objective system, wherein the variable focus lenses are controllable to control the focus height of the output from the objective system.

[0022] In an embodiment, the illumination source output is a radiation beam reflected from the wafer.

[0023] In an embodiment, the radiation beam passes through the variable focus lens after reflection from the wafer.

[0024] In an embodiment, there are "N" output channels and "N+1" variable focus lenses, wherein there is one variable focus lens in each output channel and one variable focus lens in the objective system.

[0025] In an embodiment, the variable focus lens is controllable by applying a voltage to the variable focus lens.

[0026] According to an embodiment, a wafer alignment measurement system includes: an illumination source; a radiation beam output from the illumination source that travels to an objective system; and at least two variable focus lenses positioned in a pupil plane downstream of the objective system, wherein the variable focus lenses are controllable to control at least one of spot shift and higher diffraction orders.

[0027] In an embodiment, the variable focus lens is positioned in a pupil plane.

[0028] In an embodiment, the variable focus lens is positioned in the pupil plane between the objective system and the output lens.

[0029] In an embodiment, the variable focus lens compensates for spot shift.

[0030] In an embodiment, the variable focus lens compensates for higher diffraction orders.

[0031] In an embodiment, the variable focus lens is controllable by applying a voltage to the variable focus lens.

[0032] The structure and operation of the various embodiments of the present invention and the advantages and features 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. Based on the teachings included herein, other embodiments will be apparent to those skilled in the relevant art. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings, which are incorporated herein and form a part of this specification, illustrate the present invention and together with the description of the specification further serve to explain the principles of the invention and enable those skilled in the relevant art to make and use the invention.

[0034] Figure 1A is a schematic illustration of a reflective lithography apparatus according to an embodiment of the present disclosure.

[0035] Figure 1B is a schematic illustration of a transmissive lithography apparatus according to an embodiment of the present disclosure.

[0036] Figure 1C is a more detailed schematic illustration of a reflective lithography apparatus according to an embodiment of the present disclosure.

[0037] Figure 2A is a schematic illustration of a lithography cell according to an embodiment of the present disclosure.

[0038] Figure 2B is a schematic illustration of an inspection system according to an embodiment of the present disclosure.

[0039] Figure 2C is a schematic illustration of a measurement technique according to an embodiment of the present disclosure.

[0040] Figure 2D is a schematic diagram of the relationship between a radiation illumination spot and a measurement target of an inspection system according to an embodiment of the present disclosure.

[0041] Figure 3 is a schematic illustration of a state of the art alignment system according to an embodiment of the present disclosure.

[0042] Figure 4A is a schematic illustration of a variable focal length lens when no voltage is applied according to an embodiment of the present disclosure.

[0043] Figure 4B is a schematic illustration of a variable focus lens when a non-zero voltage is applied according to an embodiment of the present disclosure.

[0044] Figure 4C is a schematic illustration of an illumination system for an alignment system for a variable spot size according to an embodiment of the present disclosure.

[0045] Figure 4D is a schematic illustration of an alignment system for variable spot size according to an embodiment of the present disclosure.

[0046] Figure 4E is a schematic illustration of radiation beam spot sizes for a variable focus lens with a nominal voltage for a variable spot size according to an embodiment of the present disclosure.

[0047] Figure 4F is a schematic illustration of radiation beam spot size for a variable focus lens with an applied voltage for a variable spot size according to an embodiment of the present disclosure.

[0048] Figure 5A is a schematic illustration of an illumination system of an alignment system for beam steering according to an embodiment of the present disclosure.

[0049] Figure 5B is a schematic illustration of an alignment system for beam steering according to an embodiment of the present disclosure.

[0050] Figure 5C is a schematic illustration of the offset effect of a variable focal length lens for beam steering according to an embodiment of the present disclosure.

[0051] Figure 5D is another schematic illustration of the effect of a shift of a variable focal length lens for beam steering according to an embodiment of the present disclosure.

[0052] Figure 5E The embodiment according to the present disclosure is illustrated Figure 5A , 5C and 5D, which form a combined view of the elements shown Figure 5B part of the system.

[0053] Fig. 6A is a schematic illustration of an alignment system for variable focusing according to an embodiment of the present disclosure.

[0054] Figure 6B is a schematic illustration of a thick resist substrate and variable focus according to an embodiment of the present disclosure.

[0055] Figure 6C is a schematic illustration of the overlap in a measurement variable focus embodiment according to an embodiment of the present disclosure.

[0056] Fig.6D is another schematic illustration of measuring overlap in a variable focus embodiment according to an embodiment of the present disclosure.

[0057] Fig. 7A is a schematic illustration of an alignment system for spot shift and higher order suppression according to an embodiment of the present disclosure.

[0058] Figure 7B is a schematic illustration of beam size in a calibrated spot shift embodiment according to an embodiment of the present disclosure.

[0059] Figure 7C is another schematic illustration of calibrating the beam size in a spot shifting embodiment according to an embodiment of the present disclosure.

[0060] Fig.7D is another schematic illustration of calibrating the beam size in a spot shifting embodiment according to an embodiment of the present disclosure.

[0061] Fig. 7E is a schematic illustration of shifting higher diffraction orders in a higher order suppression embodiment according to an embodiment of the present disclosure.

[0062] Figure 8 A wafer alignment measurement method according to an embodiment is illustrated.

[0063] Fig. 9 is a block diagram of an example computer system according to an embodiment. DETAILED DESCRIPTION

[0064] For semiconductor manufacturing and / or other applications, self-reference interferometers (SRI) can be used in alignment systems to obtain the intensity of reflected radiation as a function of the position of alignment marks on a substrate (e.g., such as a wafer). The phase of these signals is used to determine the alignment position of the mark. However, the SRI method has limitations. The beam spot size that illuminates the alignment mark on the substrate is fixed, such as a thick resist and / or a warped substrate (e.g., a wafer) may inadvertently cause alignment failure. Moreover, with the SRI method, electromechanical elements are often used within an optical module (OM) to achieve higher-order suppression, but these electromechanical elements may cause vibrations, leading to measurement inaccuracies and / or other problems. In some embodiments, the optical module consists of a plurality of passive and active optical components, whose function is to direct illumination, such as light, to the wafer under investigation. The optical module also collects diffracted light from the mark on the wafer and directs the light toward a demultiplexer and an optical detector. For example, the optical module can illuminate a target on the wafer by directing light from a light source to the target, and collect a return signal. The return signal can be sent to a detection electronic device to calculate the target position on the wafer.

[0065] Among other advantages, the present system and method provide solutions to these and other problems, allowing for variable spot sizes and smaller alignment marks. The present system and method also improves the performance of thick stack measurements and allows for non-mechanical scanning within the OM. As described below, to provide a variable spot size, the typical input fiber assembly fixed lens is replaced with a set of liquid lenses to provide afocal functionality. A voltage applied to two variable focus lenses provides an increased focal length. In another embodiment, two variable focus lenses are used to maintain the numerical aperture to account for thick stacks and maintain the spot size at different focal points.

[0066] By way of brief introduction, the following description relates to semiconductor device manufacturing and patterning processes. The following paragraphs also describe several components of systems and / or methods for semiconductor device measurement. For example, these systems and methods can be used to measure alignment, overlay, etc. during semiconductor device manufacturing, or for other operations.

[0067] Example Reflective and Transmissive Lithography Systems

[0068] Figure 1A and 1B is a schematic illustration of a lithographic apparatus 100 and a lithographic apparatus 100', in which or for which embodiments of the present disclosure may be implemented. The lithographic apparatus 100 and the lithographic apparatus 100' respectively include the following: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., deep ultraviolet or extreme ultraviolet radiation); a support structure (e.g., a mask stage) MT configured to support a pattern forming device (e.g., a mask, a reticle, or a dynamic pattern forming device) MA and connected to a first positioner PM configured to accurately position the pattern forming device MA; and a substrate stage (e.g., a wafer stage) WT configured to hold a substrate (e.g., a wafer coated with resist) W and connected to a second positioner PW configured to accurately position the substrate W. The lithographic apparatus 100 and 100' also have a projection system PS, which is configured to project a pattern imparted to the radiation beam B by the pattern forming device MA onto a target portion (e.g., including one or more dies) C 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.

[0069] The illumination system IL may include various types of optical components for directing, shaping or controlling the radiation beam B, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof.

[0070] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA relative to the reference frame, the design of at least one of the 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 may be a frame or a stage, for example, which may be fixed or movable as desired. For example, by using sensors, the support structure MT may ensure that the patterning device MA is at a desired position relative to the projection system PS.

[0071] The term “patterning device” MA should be broadly interpreted as referring to any device that can be used to impart a radiation beam B with a pattern in its cross-section, such as to create a pattern in a target portion C of a substrate W. The pattern imparted to the radiation beam B may correspond to a specific functional layer in the device created in the target portion C to form an integrated circuit.

[0072] The pattern forming device MA may be transmissive (e.g. Figure 1B lithographic apparatus 100') or reflective (as in Figure 1A 100). Examples of pattern forming 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 mask types, alternating phase-shift mask types, and attenuated phase-shift mask types, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam B that is reflected by the array of small mirrors.

[0073] The term "projection system" PS may cover any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems or any combination thereof, as appropriate for the exposure radiation used or other factors such as the use of an immersion liquid or the use of a vacuum on the substrate W. A vacuum environment may be used for EUV or electron beam radiation, as other gases may absorb too much radiation or electrons. Therefore, by means of vacuum walls and a vacuum pump, a vacuum environment may be provided for the entire beam path.

[0074] The lithographic apparatus 100 and / or the lithographic apparatus 100' may be of a type having two (dual stage) or more substrate tables WT (and / or two or more mask tables). In such a "multi-stage" machine, the additional substrate tables WT may be used in parallel, or preparatory steps may be performed on one or more tables while one or more other substrate tables WT are being used for exposure. In some cases, the additional tables may not be substrate tables WT.

[0075] Reference Figure 1A and 1B , the illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus 100, 100' may be separate physical entities, for example when the source SO is an excimer laser. In this case, the source SO is not considered to form part of the lithographic apparatus 100 or 100', and is provided with the aid of a beam delivery system BD (in the case of a laser) comprising, for example, suitable directional mirrors and / or a beam expander. Figure 1B), the radiation beam B is delivered from the source SO to the illuminator IL. In other cases, the source SO may be an integral part of the lithographic apparatus 100, 100' - for example when the source SO is a mercury lamp. The source SO and the illuminator IL and, if required, the beam delivery system BD may be referred to as a radiation system.

[0076] The illuminator IL may include an adjuster AD (in Figure 1B ), for adjusting the angular intensity distribution of the radiation beam. Typically, 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 can be adjusted. In addition, the illuminator IL may include various other components (in Figure 1B ), such as an integrator IN and a condenser CO. The illuminator IL can be used to condition the radiation beam B so as to have a desired uniformity and intensity distribution in its cross-section.

[0077] Reference Figure 1A , the radiation beam B is incident on and patterned by the pattern forming device (e.g. mask) MA, which is held on a support structure (e.g. mask table) MT. In the lithographic apparatus 100, the radiation beam B is reflected from the pattern forming device (e.g. mask) MA. After reflection from the pattern forming device (e.g. mask) MA, the radiation beam B passes through the projection system PS, which focuses the radiation beam B onto a target portion C of the substrate W. With the help of a second positioner PW and a position sensor IF2 (e.g. an interferometric measurement device, a linear encoder or a capacitive sensor), the substrate table WT can be accurately moved (e.g. in order to position different target portions C in the path of the radiation beam B). Similarly, a first positioner PM and a further position sensor IF1 can be used to accurately position the pattern forming device (e.g. mask) MA relative to the path of the radiation beam B. The pattern forming device (e.g. mask) MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0078] Reference Figure 1B , the radiation beam B is incident on a patterning device (e.g. a mask MA) which is held on a support structure (e.g. a mask table MT) and 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 the substrate W. The projection system has a pupil PPU conjugate to an illumination system pupil IPU. Part of the radiation emanates from the intensity distribution at the illumination system pupil IPU and traverses the mask pattern without being affected by diffraction at the mask pattern and creates an image of the intensity distribution at the illumination system pupil IPU.

[0079] With the aid of a second positioner PW and a position sensor IF (e.g. an interferometric device, a linear encoder or a capacitive sensor), the substrate table WT can be accurately moved (e.g. in order to position a different target portion C in the path of the radiation beam B). Similarly, a first positioner PM and a further position sensor (not shown) can be used. Figure 1B ) can be used to accurately position the mask MA relative to the path of the radiation beam B (for example after mechanical retrieval from a mask library, or during scanning).

[0080] Typically, movement of the mask table MT can be achieved with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning) forming part of the first positioner PM. Similarly, movement of the substrate table WT can be achieved using a long-stroke module and a short-stroke module forming part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask table MT may be connected only to a short-stroke actuator, or may be fixed. The mask MA and the substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks (as illustrated) occupy dedicated target portions, they may be located in the space between target portions (referred to as scribe alignment marks). Similarly, in the case where more than one die is provided on the mask MA, the mask alignment marks may be located between the dies.

[0081] The mask table MT and patterning device MA can be in a vacuum chamber, wherein 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, when the mask table MT and patterning device MA are outside the vacuum chamber, an out-of-vacuum robot can be used for various transport operations, similar to the in-vacuum robot IVR. Both in-vacuum and out-of-vacuum robots need to be calibrated in order to smoothly transfer any payload, such as a mask, to the fixed kinematic base of the transfer station.

[0082] The lithographic apparatus 100 and 100' may be used in at least one of the following modes:

[0083] 1. In step mode, the support structure (e.g. mask table) MT and the substrate table WT remain substantially stationary while the entire pattern imparted to the radiation beam B is projected at one time onto a target portion C (i.e. a single static exposure). The substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed.

[0084] 2. In scan mode, the support structure (e.g. mask table) MT and substrate table WT are scanned synchronously while a pattern imparted to the radiation beam B is projected onto a target portion C (i.e. a single dynamic exposure). The speed and direction of the substrate table WT relative to the support structure (e.g. mask table) MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS.

[0085] 3. In another mode, the support structure (e.g. mask table) MT remains essentially stationary, thereby holding the programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. A pulsed radiation source SO may be employed and the programmable patterning device updated as required after each movement of the substrate table WT or between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography, which makes use of a programmable patterning device (such as a programmable mirror array).

[0086] Combinations and / or variations on the described modes of use or entirely different modes of use may also be employed.

[0087] In some embodiments, the lithographic apparatus 100 includes an extreme ultraviolet (EUV) source configured to generate an EUV radiation beam 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.

[0088] Figure 1C The lithographic apparatus 100 is shown in more detail, including a source collector device SO, an illumination system IL and a projection system PS. The source collector device SO is constructed and arranged so that a vacuum environment can be maintained in an enclosed structure 120 of the source collector device SO. The EUV radiation emitting plasma 110 can be formed by a plasma source produced by a discharge. EUV radiation can be generated by a gas or vapor, such as xenon, lithium vapor or tin vapor, wherein a hot plasma 110 is created to emit radiation in the EUV range of the electromagnetic spectrum. The hot plasma 110 is created by, for example, a discharge that results in an at least partially ionized plasma. In order to efficiently generate radiation, a partial pressure of, for example, 10 Pa of Xe, Li, Sn vapor or any other suitable gas or vapor may be required. In an embodiment, a plasma that excites tin (Sn) is provided to produce EUV radiation.

[0089] Radiation emitted by the hot plasma 110 is transferred from the source chamber 111 to the collector chamber 112 via an optional gas barrier or contaminant trap 113 (also referred to as a contaminant barrier or fin trap in some cases) positioned in or behind an opening in 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. As known in the art, the contaminant trap 113 further indicated herein includes at least a channel structure.

[0090] 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 side 151 and a downstream radiation collector side 152. Radiation traversing the collector CO may be reflected from the grating spectral filter 140 to be focused in a virtual source point IF. The virtual source point IF is generally referred to as an intermediate focus, and the source collector device is arranged so that the intermediate focus IF is located at or near the opening 119 in the enclosure 120. The virtual source point IF is an image of the radiation emitting plasma 110. The grating spectral filter 140 is particularly used to suppress infrared (IR) radiation.

[0091] The radiation then traverses an illumination system IL which may include a faceted field mirror arrangement 122 and a faceted pupil mirror arrangement 124 which are arranged to provide a desired angular distribution of the radiation beam 121 at the patterning device MA and a desired uniformity of radiation intensity at the patterning device MA. Upon reflection of the radiation beam 121 at the patterning device MA held by the support structure MT, a patterned beam 126 is formed and the patterned beam 126 is imaged by the projection system PS via reflective elements 128, 130 onto a substrate W held by a wafer stage or substrate table WT.

[0092] More elements than shown may typically be present in the illumination optics unit IL and the projection system PS. Depending on the type of lithographic apparatus, a grating spectral filter 140 may optionally be present. Further, there may be more mirrors than shown in the figures, for example with Figure 1C Compared to that shown, there may be 1 to 6 additional reflective elements in the projection system PS.

[0093] like Figure 1C As illustrated, the collector optics CO is depicted as a nested collector with grazing incidence reflectors 153, 154 and 155, merely as an example of a collector (or collector mirror). The grazing incidence reflectors 153, 154 and 155 are arranged axially symmetrically around the optical axis O, and preferably, this type of collector optics CO is used in combination with a discharge produced plasma source, generally referred to as a DPP source.

[0094] Example Lithography Cell

[0095] Figure 2A A lithography unit 200 is shown, sometimes also referred to as a lithography unit or cluster. The lithography apparatus 100 or 100' may form part of the lithography unit 200. The lithography unit 200 may also include equipment 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 the exposed resist, a cooling plate CH, and a baking plate BK. A substrate handler or robot RO picks up substrates from input / output ports I / O1, I / O2, moves them between different processing equipment, and then delivers them to a feed station LB of the lithography apparatus. These devices, which are generally referred to as tracks, are controlled by a track control unit TCU, which itself is controlled by a monitoring system SCS, which also controls the lithography apparatus via a lithography control unit LACU. Therefore, different equipment can be operated to maximize throughput and processing efficiency.

[0096] The manufacturing facility in which the lithography unit 200 is located typically also includes a metrology system that measures some or all of the substrates W that have been processed in the lithography unit ( Figure 1A , 1B , 1C) or other objects in a lithography cell. For example, the metrology system may be part of a lithography cell, or it may be part of a lithography apparatus. One or more measurement parameters may include, for example, overlap between consecutive layers formed in or on a patterned substrate, alignment, for example, critical dimensions (CD) of features formed in or on a patterned substrate (e.g., critical line width), focus or focus error of an optical lithography step, dose or dose error of an optical lithography step, optical aberration of an optical lithography step, etc. The measurement is typically performed on one or more dedicated metrology targets provided on the substrate. The measurement may be performed after resist development but before etching, after etching, after deposition, and / or at other times.

[0097] There are a variety of techniques for measuring structures formed during the patterning process, including the use of scanning electron microscopes, image-based measurement tools, and / or various specialized tools. A rapid and non-invasive form of specialized measurement tool is one in which a radiation beam is directed onto a target on the surface of a substrate and the properties of the scattered (diffraction / reflection) beam are measured. By evaluating one or more properties of the radiation scattered by the substrate, one or more properties of the substrate can be determined. Traditionally, this can be referred to as diffraction-based measurement. Applications of such diffraction-based measurement include measurement of alignment, overlay, etc. For example, alignment and / or overlay can be measured by comparing portions of the diffraction spectrum (e.g., comparing different diffraction orders in the diffraction spectrum of a periodic grating).

[0098] Thus, in a device fabrication 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 and equipment used in the process (e.g., aligning two layers on a substrate or aligning a patterning device to a substrate), may measure the performance of the process and equipment, or may be used for other purposes. Examples of measurements include optical imaging (e.g., optical microscopy), non-imaging optical measurements (e.g., diffraction-based measurements, such as ASML YieldStar metrology tools, ASML SMASH metrology systems), mechanical measurements (e.g., profiling using a stylus, atomic force microscopy (AFM)), and / or non-optical imaging (e.g., scanning electron microscopy (SEM)).

[0099] The measurement results may be provided directly or indirectly to the monitoring system SCS. If an error is detected, adjustments may be made to the exposure of subsequent substrates (particularly if the inspection can be completed quickly enough so that one or more other substrates of the batch are still to be exposed) and / or to subsequent exposures of the exposed substrate. Furthermore, already exposed substrates may be stripped and reworked to improve yield, or discarded to avoid further processing of substrates known to be faulty. In the event that only some target portions of the substrate are faulty, further exposures may be performed only on those target portions that meet the specification. Other manufacturing process adjustments are also under consideration.

[0100] The metrology system may be used to determine one or more characteristics of a substrate structure, in particular how one or more characteristics of different substrate structures vary or how different layers of the same substrate structure vary from layer to layer. The metrology system may be integrated into the lithography apparatus 100 and 100' or the lithography apparatus 200, or may be a stand-alone device.

[0101] Alignment System Embodiments

[0102] One or more targets may be specifically provided on the substrate to enable alignment. Typically, the targets are specifically designed and may include periodic structures. For example, the target on the substrate may include one or more 1D periodic structures (e.g., geometric features, such as gratings) that are printed so that after development, the periodic structural features are formed by solid resist lines. As another example, the target may include one or more 2D periodic structures (e.g., gratings) that are printed so that after development, the one or more periodic structures are formed by solid resist pillars or vias in the resist. Alternatively, the bars, pillars, or vias may be etched into the substrate (e.g., etched into one or more layers on the substrate).

[0103] Figure 2BAn example alignment system 10 is depicted that can be used to detect alignment and overlay and / or perform other metrology operations. It includes a radiation or illumination source 2 that projects or otherwise illuminates radiation onto a substrate W (which may typically include metrology marks, for example). 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, such as e.g. Figure 2C The sensor may generate an alignment signal conveying alignment data indicative of the characteristics of the reflected radiation. From this data, the structure or profile that produced the detected spectrum may be reconstructed by one or more processors PRO, a generalized example of which is as follows: Figure 2C as shown, or may be reconstructed by other operations.

[0104] and Figure 1A and 1B As with the lithographic apparatus 100 and 100', one or more substrate tables may be provided for holding a substrate W during measurement operations. The one or more substrate tables may be similar in form to the Figure 1A and 1B The substrate table WT of the inspection system 10 is similar or identical to that of the substrate table WT. In examples where the inspection system 10 is integrated with a lithographic apparatus, they may even be the same substrate table. Coarse and fine positioners may be provided and configured to accurately position the substrate with respect to the measuring optical system. Various sensors and actuators are provided, for example to acquire the position of a target portion of interest of the structure (e.g. a measurement mark) and place it in position under the objective lens. Typically, many measurements will be made of the target portion of the structure at different locations on the substrate W. The substrate support may be moved in the X and Y directions to acquire different targets, and in the Z direction to acquire the desired location of the target portion relative to the focus of the optical system. When, for example, in practice the optical system may remain substantially stationary (usually 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 is placed at different locations relative to the substrate. As long as the relative position of substrate and optical system is correct, it is in principle unimportant which of these is moving, or whether both are moving, or a combination in which part of the optical system is moving (e.g. in Z and / or tilt direction) while the rest of the optical system is stationary and the substrate is moving (e.g. in X and Y direction, but optionally also in Z and / or tilt direction).

[0105] For typical alignment measurements, the target (portion) 30 on the substrate W may be a 1D grating, which is printed so that after development, the grating bars are formed by solid resist lines (which may be covered by a deposited layer, for example) and / or other materials. Alternatively, the target 30 may be a 2D grating, which is printed so that after development, the grating is formed by solid resist pillars and / or other features in the resist.

[0106] The bars, pillars, vias, and / or other features may be etched into or onto the substrate (e.g., etched into one or more layers on the substrate), deposited on the substrate, covered by a deposited layer, and / or have other characteristics. The target (portion) 30 (e.g., bars, pillars, vias, etc.) is sensitive to process variations during the patterning process (e.g., optical aberrations in a lithographic projection device (such as a projection system), focus variations, dose variations, etc.), so that process variations appear as variations in the target 30. Therefore, measurement data from the target 30 can be used to determine adjustments to one or more manufacturing processes, and / or used as a basis for making actual adjustments.

[0107] For example, the measurement data from the target 30 may indicate an overlap of semiconductor device layers. The measurement data from the 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 overlap, and to determine adjustments to semiconductor device manufacturing equipment based on one or more determined semiconductor device manufacturing process parameters. In some embodiments, this may include, for example, stage position adjustments, or this may include determining adjustments to mask design, measurement target design, semiconductor device design, radiation intensity, radiation incident angle, radiation wavelength, pupil size and / or shape, resist material, and / or other process parameters.

[0108] Figure 2D A plan view of a typical target (e.g., a measurement mark) 30 and the extent of a typical radiation illumination spot S are illustrated. Typically, in order to obtain a diffraction spectrum that is not interfered with by surrounding structures, in an embodiment, the target 30 is a periodic structure (e.g., a grating) that is 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 illuminated 'underfilled' or underfilled, and the diffraction signal is substantially unaffected by any signal from product features, etc., other than the target itself. For example, the illumination arrangement may be configured to provide illumination of uniform intensity across the entire back focal plane of the objective. Alternatively, the illumination may be limited to an on-axis direction or an off-axis direction, for example, by including an aperture in the illumination path.

[0109] State-of-the-art alignment systems

[0110] Figure 3A schematic diagram of an alignment system 300 of the current state of the art according to an embodiment is illustrated, which can be implemented as part of or otherwise combined with a lithographic apparatus 100 or 100' and / or other lithographic apparatus. In this example of an embodiment, the alignment system 300 can be configured to align a substrate (e.g., a semiconductor wafer, the substrate W described above, etc.) relative to a patterning device (e.g., the patterning device MA described above). The alignment system 300 can also be configured to detect the position of alignment marks on the substrate, and use the detected position of the alignment marks to align the substrate relative to the patterning device or other components of the lithographic apparatus 100 or 100'. Such alignment of the substrate can ensure accurate exposure of one or more patterns on the substrate.

[0111] According to an embodiment, the alignment system 300 may include an illumination source 305, an input optical fiber 307, an illumination system 310, a spot reflector 320, an objective lens 330, a self-referencing interferometer (SRI) 340, polarization beam splitters 341a and 341b, and an output system 350. The optical module 399 of the system 300 may include any optical components in or along the radiation path that are used to guide or control radiation in the system 300. The illumination source 305 may be configured to provide an electromagnetic narrowband radiation beam 306 having a first polarization state (such as a linear polarization state). In an example, the narrowband radiation beam 306 may be within a wavelength spectrum between about 500 nm and about 900 nm. In another example, the narrowband radiation beam 306 includes a discrete narrow passband within a wavelength spectrum between about 500 nm and about 900 nm. In yet another example, the radiation beam 306 may be monochromatic, for example provided by a monochromatic light source (such as a laser source in the illumination source 305). A polychromatic light source such as an LED may also be used for the illumination source 305 to provide the polychromatic radiation beam 306 .

[0112] The illumination system 310 may be configured to receive the radiation beam 306. In this example of an embodiment, the illumination system 310 may also be configured to direct the radiation beam 306 onto the substrate W. The illumination system 310 may include an illumination relay lens 312, a fixed lens input fiber assembly (IFA) 311, and an aperture stop 313. The illumination system 310 may also include an optical device that generates additional illumination beams that are split or replicated from the radiation beam 306 and directs them toward alignment marks (not shown) on the substrate W.

[0113] The substrate W may be placed on a platform WT that is movable along the direction (see Figure 1A , 1Band 1C). The radiation beam 306 may be configured to illuminate an alignment mark located on the substrate W. In this example of an embodiment, the alignment mark may be coated with a radiation sensitive film. In another example, the alignment mark may have 180° symmetry. That is, when the alignment mark is rotated 180° around an axis of symmetry perpendicular to the plane of the alignment mark, the rotated alignment mark may be substantially the same as the unrotated alignment mark.

[0114] like Figure 3 As illustrated, according to an embodiment, the objective 330 can be configured to direct the diffracted radiation beam 335 toward the self-referencing interferometer 340. The objective 330 can include any appropriate number of optical elements suitable for directing the diffracted radiation beam 335. The objective 330 can also include a field stop 331. In an example embodiment, the diffracted radiation beam 335 can be at least a portion of the radiation beam 306 that is diffracted from the alignment mark. The spot mirror 320 is substantially transparent to the diffracted radiation beam 355 and can allow the diffracted radiation beam 335 to pass through it without substantially changing the characteristics of the diffracted radiation beam 335. It should be further noted that although the objective 330 is shown as directing the radiation beam 335 toward the self-referencing interferometer 340, the present disclosure is not limited to this. Other optical arrangements can be used to obtain similar results of detecting the diffraction signal from the alignment mark.

[0115] In some embodiments, the self-referencing interferometer 340 may include any suitable set of optical components, such as a combination of a prism, a half-wave plate, and a compensator, which may be configured to form two images of the alignment mark based on the received diffracted radiation beam 335. It should be understood that good quality images need not be formed, but features of the alignment mark should be resolved. The self-referencing interferometer 340 may also be configured to rotate one of the two images by 180° relative to the other of the two images, and interferometrically reconstruct the rotated and unrotated images.

[0116] After passing through the self-referencing interferometer 340, the diffracted radiation beam 335 is incident on polarizing beam splitters 341a and 341b. Polarizing beam splitters 341a and 341b redirect the diffracted radiation beam 335 to the output system 350. The first output channel 351a includes an output lens 352a and an output field stop 353a for passing the diffracted radiation beam 335 to a detector (not shown) for measuring the sum of the y-component of the beam. The second output channel 351b includes an output lens 352b and an output field stop 353b and a second detector (not shown) for measuring the difference of the y-component of the beam. The third output channel 351c includes an output lens 352c and an output field stop 353c and a third detector (not shown) for measuring the sum of the x-component of the beam. The fourth output channel 351d includes an output lens 352d and an output field stop 353d and a fourth detector (not shown) for measuring the difference of the x-component of the beam.

[0117] The above detector can be configured to receive the recombined image and detect interference due to the recombined image when the alignment axis of the alignment system 300 passes through the symmetry center of the alignment mark (not shown). According to an example embodiment, this interference may be due to the alignment mark being 180° symmetrical and the recombined image being constructively or destructively interfering. Based on the detected interference, the detector can also be configured to determine the position of the symmetry center of the alignment mark and thus detect the position of the substrate W. According to an example, the alignment axis can be aligned with an optical beam that is perpendicular to the substrate 420 and passes through the center of the self-referencing interferometer 340.

[0118] Variable focal length lens

[0119] Figures 4A to 4B A schematic diagram of a variable focal length lens 420 is shown. As described below, the lens 420 is shown as "closed" ( Figure 4A ) and Open ( Figure 4B ) configuration. The variable focus lens 420 is a liquid lens including water 404 and oil 405 and forming a water-oil interface 406, and an interface film 427 forms a seal therebetween. Figure 4A and 4B Other components of lens 420 are also shown, including an optical window 421 configured to transmit light beam 403 (and / or other radiation), a metal structural component 423, and a lens 420 that is configured to transmit light beam 403 (and / or other radiation) when lens 420 is "open" ( Figure 4B ) is provided with an electrostatic pressure 425.

[0120] By applying a specified voltage 408 to the lens 420, the focal length of the lens 420 can be finely tuned and modified. Figure 4A The water-oil interface 406 is shown when no voltage is applied (ie, "off"). When the lens 420 is connected to ground 407, Figure 4AIn one example, in the absence of voltage, water 404 and oil 405 naturally form a slightly concave curvature at interface 406, causing the incident light beam 403 parallel to the optical axis OA to diverge slightly when leaving the variable focus lens 420. As another example, Figure 4B The water-oil interface 406 is shown when a non-zero voltage 408 is applied (i.e., "ON"). The applied voltage 408 in the liquid lens 420 generates an electrostatic pressure 425 at or near the edge 429, resulting in a buildup of positive charge (see Figure 4B Therefore, the negative charge in water 404 (see Figure 4B The water 404 thus moves to the edge 429 of the lens 420, which displaces the oil 405 into the center 431 of the lens 420. Figure 4B It is shown that the curvature of the interface 406 has now changed to a convex shape which converges the incident light beam 403 to a focus 433 on the optical axis OA.

[0121] The variable focus lens 420 can replace (as described below) the input fiber assembly in a typical state-of-the-art alignment system, such as the system 300 described above. Compared to typical state-of-the-art alignment systems, the variable focus lens 420 described herein provides a fast response (e.g., on the order of milliseconds), has a compact design, low heat dissipation at the lens, low power consumption of approximately 1 mW (+ / - 20%), and allows for tunability of optical module 399 functionality, among other advantages.

[0122] Variable spot size alignment system

[0123] Figure 4C Variable focal length lenses 401 and 402 (eg, similar and / or identical to focal length lens 420 described above, respectively) are shown incorporated into illumination system 410. Illumination system 410 may be Figure 4D A portion of a variable spot size alignment system 400 is shown. Figure 4D As shown, Figure 3 The irradiation system 310 is Figure 4C In one embodiment, the variable spot size alignment system 400 (eg Figure 4D shown) utilized Figure 3 The remaining components of the alignment system 300. Figure 4C In the illumination system 410, the illumination system variable focal length lenses 401 and 402 replace Figure 3 The alignment system 400 may be configured to achieve a variable spot size at the substrate W by removing the IFA 311 and inserting the lenses 401 and 402.

[0124] According to an embodiment, the illumination system 410 (eg Figure 4C and 4D 4. The illumination system 410 is configured to receive a radiation beam 306, for example, from an input optical fiber 307, along an optical axis AX (the optical axis AX may be similar and / or identical to the optical axis OA described above). The illumination system 410 includes a fixed lens, such as an illumination relay lens 312, which receives the radiation beam 306 before the radiation is passed to the first variable focus lens 401, and then receives the second variable focus lens 402 before reaching the aperture stop 313.

[0125] The set of variable focal length lenses (in this case, a pair of variable focal length lenses 401 and 402) are usually used in pairs to manipulate the focal length. However, a set of variable focal length lenses is not limited to two lenses.

[0126] In one embodiment, a nominal amount of voltage is applied to the variable focal length lenses 401 and 402 to achieve no curvature of the film(s) 435, 437 (similar and / or identical to the film 427 described above). In one embodiment, when increasing voltage is applied, an increased focal length is achieved and the spot size of the radiation on the substrate changes. The configuration can be such that a negative voltage is applied to achieve a decreased focal length (and a different spot size of the radiation on the substrate). If desired, the polarity of the voltage can be reversed to achieve a different curvature to increase or decrease the focal length.

[0127] Figure 4D The diagram shows Figure 3 The Input Fiber Assembly (IFA) 311 is Figure 4C By replacing the input fiber assembly (IFA) 311 with an illumination system 410 including variable focus lenses 401 and 402, a variable spot size on the substrate W can be achieved. By applying different voltages across the lenses 401, 402, the spot size on the substrate W can be enlarged or reduced. Depending on the size of the alignment mark, the spot size can be enlarged or reduced. By using the above voltages to change the spot size of the radiation on the substrate to match the size of the alignment (or other measurement) mark, alignment marks of various sizes can be more easily measured.

[0128] exist Figure 4E and 4F The change in size of the light spot 491 is shown in FIG. Figure 4ESchematic diagram of the size of the spot 491 of the radiation beam 306 when a nominal voltage is applied to the variable focal length lenses 401 and 402. Upon leaving the input optical fiber 307, the radiation beam 306 expands in size 481 until it reaches the illumination relay lens 312. The illumination relay lens 312 changes the incoming beam into a parallel radiation beam 483. With a nominal voltage applied to each of the variable focal length lenses 401 and 402, the water-oil interface 406 (see Figure 4A and 4B ) has no curvature. Therefore, the parallel radiation beam 306 remains the same when leaving each lens 401 and 402. The parallel radiation beam 306 then travels through the aperture stop 313, and the diameter of the spot 491 is D1.

[0129] Figure 4F Schematic diagram showing the size of the spot 491 of the radiation beam 306 when voltage is applied to the variable focus lenses 401 and 402. Figure 4E , upon leaving the input fiber 307, the radiation beam 306 expands in size 481 until it reaches the illumination relay lens 312. The illumination relay lens 312 changes the incoming beam into a parallel radiation beam 483. With a voltage applied to each of the variable focus lenses 401 and 402, at the water-oil interface 406 (see Figure 4A and 4B ). Therefore, the increased focal length of the lenses 401 and 402 increases 489 the size of the parallel radiation beam 306 when leaving the second lens 402. Finally, the amplified radiation beam 306 travels through the aperture stop 313, and the spot 491 has an enlarged diameter D2.

[0130] Currently, state-of-the-art alignment systems such as Figure 3 The system 300 shown in FIG. 3 can achieve an illumination spot size as small as about 30 μm to measure a 30 μm × 80 μm alignment mark. However, by using an alignment system with a variable spot size Figure 4C The illumination system 410 can achieve a variable spot size that can be fine-tuned to a range of 10 μm to 40 μm or less to measure alignment marks as small as 10 μm × 10 μm or less.

[0131] Beam Steering Alignment System

[0132] Figure 5A A schematic diagram of an illumination system 510 of a beam steering alignment system is shown. The illumination system 510 includes a relay lens 312 (e.g., Figure 4C312 is similar and / or the same as the relay lens 312 shown in FIG. 31 ), a first variable focal length lens 501 and a second variable focal length lens 502 (similar to the relay lens 312 shown in FIG. 31 ). Figure 4C The lenses 401 and 402 are similar and / or identical) and the aperture stop 313 (similar to Figure 4C 313 as shown). Figure 5A As shown, the illumination system 510 can be configured to receive the radiation beam 306 from the optical fiber 307. The illumination system 510 includes an illumination relay lens 312 that receives the radiation beam 306, a first variable focal length lens 501, a second variable focal length lens 502, and an 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.

[0133] Figure 5B A beam steering alignment system 500 is illustrated including an illumination system 510. Figure 5B middle, Figure 3 The illumination system 310 is shown as Figure 5A In one embodiment, the beam steering alignment system 500 (eg, Figure 5B shown) utilized Figure 3 The remaining components of the alignment system 300.

[0134] Figures 5C to 5D A schematic diagram illustrating the effect of the variable focal length lens 502 being offset from the optical axis AX is shown. Figure 5C The diagram shows that when the variable focal length lens 502 is not offset from the optical axis AX, the illumination spot 333 on the substrate W coincides with the optical axis AX. Figure 5D It is shown that when the variable focal length lens 502 is offset from the optical axis AX, the illumination spot 333 on the substrate W also becomes offset from the optical axis AX. Figure 5D As shown, the offset from the optical axis AX of the variable focus lens 502 causes the radiation beam 306 to reflect from the spot mirror 320 at a different angle, which in turn results in an illumination spot 333 that is offset from the optical axis AX. For example, a beam steering angle of 1.8 mrad tilt results in a scan length of ±24 μm.

[0135] By offsetting the variable focus lens 502 from the optical axis AX, the beam can be displaced laterally at the substrate W. In beam steering, the substrate W is stationary and the lens 502 is moved, which in turn modifies the beam 306. The beam can be steered in the x and / or y direction. Beam steering can be used to compensate for lateral scanning offsets due to the substrate table WT (the substrate table WT is as shown and described above). Since beam steering is easier to perform than accelerating and decelerating the substrate table WT, beam steering can be used to measure alignment. Therefore, beam steering can be used to perform alignment diagnostics. Further, beam steering allows non-mechanical scanning within the optical module 399 (see Figure 5B ).

[0136] For clarity, Figure 5E Pictured Figure 5A , 5C and 5D, forming a combined view 591 of the elements shown in FIG. Figure 5B is part of a larger alignment system 500. For example, Figure 5E Tunable lenses 501 and 502 are illustrated, wherein lens 502 is offset from the optical axis AX and lens 501. When lens 502 is not offset from the optical axis AX, the illumination spot 333 on substrate W coincides with the optical axis AX. When variable focal length lens 502 is offset from the optical axis AX, the illumination spot 333 on substrate W is also offset from the optical axis AX. The offset of the optical axis AX of variable focal length lens 502 causes the radiation beam 306 to be reflected from the spot reflector 320 at a different angle, which in turn results in an illumination spot 333 that is offset from the optical axis AX.

[0137] Non-mechanical beam scanning of the optical module for the alignment mark, Figure 5E The design shown ensures that the beam steering will still fall within the spot mirror 320. The current spot size and spot mirror size ensure that the 0th order blocking is maintained. Even if the beam 306 is offset from the optical axis AX when incident on the substrate W, the 0th order of the diffracted radiation beam 335 is still blocked by the spot mirror 320. Therefore, since the 0th order beam is blocked, dark field measurement is still possible. Further, without the use of mechanical elements, regular and angled raster scanning can be achieved. In addition, there is a combined bidirectional angled scanning. Then, the lateral scanning offset is compensated.

[0138] In other embodiments, beam steering can be used in combination with a high bandwidth detector and a constant high speed substrate stage WT for more marks to account for the Doppler shift of different marks. In addition, additional coherent illumination spots can be generated at the substrate W and beam steering provided on the original beam spot. The alignment position as a function of the beam steering angle can be achieved. Alternatively, the direct beam can be directly illuminated on the detector.

[0139] Variable focus alignment system

[0140] Fig. 6A 1 and 2. The variable focus alignment system 600 is similar to the variable focus alignment system 600 except that the input fiber assembly (IFA) 311 is removed and a first variable focus lens 601 is added to the objective lens 330 and second variable focus lenses 602a to 602d are added to the output channels 351a to 351d, respectively. Figure 3 The alignment system 300 is the same as in FIG.

[0141] According to an embodiment, the first variable focus lens 601 is positioned in the objective lens 330. Second variable focus lenses 602a, 602b, 602c and 602d are positioned in the output channels 351a, 351b, 351c and 351d, respectively. Therefore, each output channel radiation beam will travel through a pair of variable focus lenses, namely, the first variable focus lens 601 and one of the second variable focus lenses 602a to 602d of the output channel. These variable focus lenses are positioned in the collection path of the sensor. Therefore, when there are "N" output channels, then there are "N+1" variable focus lenses in the alignment system. Fig. 6A In the example of , there are 4 (N) output channels and 5 (N+1) variable focus lenses. There is a first variable focus lens 601 in the objective lens 330, and there are four second variable focus lenses 602a to 602d in the output channels 351a to 351d, that is, there are 5 variable focus lenses in total.

[0142] By having a first variable focus lens 601 in the objective 330 and second variable focus lenses 602a to 602d in the output channels 351a to 351d, respectively, the focus of the radiation beam at the substrate W can be varied. Changing the focus allows for measurements of alignment marks positioned at different z levels. Thus, the alignment system 600 has the ability to align on warped substrates or thick resist layers and perform overlay. Further, variable focus by overlay measurement allows for thick overlay measurements and diffraction-based overlay within the alignment sensor.

[0143] For example, Figure 6B The variable focus alignment system 600 ( Fig. 6A ) is a schematic diagram of a thick resist substrate W in FIG. The substrate W includes an alignment mark 610 positioned below a resist layer 611. Despite the thickness of the multiple layers of photoresist 611, the alignment mark 610 layer below remains in focus. By focusing the variable focal length lenses 601 and 602a to 602d (such as Fig. 6A By applying a voltage (as shown), the focus of the radiation beam 306 can be changed so that the radiation beam 306 is focused at the level of the alignment mark 610. In some embodiments, the variable focus alignment system 600 can be used to align thick 3D NAND stacks with thick resist and warped wafers.

[0144] Figures 6C to 6D A schematic diagram of measuring the overlap (eg, offset "d") of alignment marks 610a and 610b in the variable focus alignment system is shown. Figure 6C In , the top alignment mark 610a (grating) can be measured by focusing the radiation beam 306 at the surface of the alignment mark 610a. Fig.6DIn the embodiment of the present invention, the bottom alignment mark 610b (grating) can be measured by focusing the radiation beam 306 at the surface of the alignment mark 610b. Therefore, the offset "d" between the alignment mark gratings can be determined. For example, variable focusing can be applied to a Z-Star system with diffraction gratings at different z levels.

[0145] Variable focus alignment system 600 ( Fig. 6A ) can maintain the same marking pitch range. The numerical aperture pitch is between 0.118 and 0.7. Variable focus accounts for typical thick stacks on the order of millimeters. Further, variable focus lenses 401 and 402 are used at the IFA (such as in Figure 4C Variable focus can be used with variable focus to maintain spot size at different focal points. The overlap capability in the variable focus alignment system 600 is achieved by using alignment signals at multiple z levels. Further, variable focus can be used in the alignment system 600 to provide an adjustable working distance at commercially proven aperture sizes. Variable focus can also be deployed in YieldStar for overlay measurements.

[0146] Spot shift and higher order suppression alignment system

[0147] Fig. 7A A schematic diagram of an alignment system 700 for spot shifting and higher order suppression is shown. The alignment system 700 is similar to the alignment system 700 except that the input fiber assembly (IFA) 311 is removed and a first variable focus lens 701 and a second variable focus lens 702 are added in the pupil plane. Figure 3 The alignment system 300 is the same as in FIG.

[0148] 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 the lens 420 described above) are positioned in the pupil plane downstream of the objective lens 330 and upstream of the self-referencing interferometer 340. Positioning the variable focal length lenses 701 and 702 at the pupil plane provides spot shift calibration and higher order suppression. For example, by applying different voltages to the variable focal length lenses 701 and 702, calibrating the spot shift of the diffracted radiation beam 335 can be achieved.

[0149] Figures 7B to 7D A schematic diagram for calibrating spot shift using variable focal length lenses 701 and 702 is illustrated. Figure 7BThe diffracted radiation beam 335 spot shift is illustrated for the variable focal length lenses 701 and 702 with nominal voltage. The diffracted radiation beam 335 is reflected from the alignment mark on the substrate W. As the light changes to parallelism, the diffracted radiation beam 335 expands until it reaches the objective lens 330. With nominal voltage applied to each of the variable focal length lenses 701 and 702, there is no curvature in the water-oil interface 406 (see Figure 4A and 4B ). Therefore, the parallel diffracted radiation beam 335 remains the same when leaving each lens 701 and 702. Thereafter, the beam 335 travels to the self-referencing interferometer 340.

[0150] Figure 7C The diagram shows the spot shift for a diffracted radiation beam 335 using lenses 701 and 702 with a medium voltage. The diffracted radiation beam 335 is reflected from an alignment mark on a substrate W. The diffracted radiation beam 335 expands until it reaches the objective lens 330, i.e. when the rays become parallel. With the medium voltage applied, a curvature is formed at the interface 406 (see Figure 4A and 4B ). As a result, the diffracted radiation beam 335 has been shifted to a smaller spot size when leaving the second lens 702. Thereafter, the beam 335 is incident on the self-referencing interferometer 340.

[0151] Fig.7D The spot shift is illustrated for a diffracted radiation beam 335 using lenses 701 and 702 with a high voltage. Fig.7D Similar to Figure 7C , except for the degree of voltage applied. As a result of the use of higher voltages, interface 406 (see Figure 4A and 4B ) has a steeper curvature. Therefore, the diffracted radiation beam 335 has shifted to a smaller spot size when leaving the second lens 702.

[0152] By positioning the afocal lens system (lenses 701 and 702) in the pupil plane (see Fig. 7A 701 and 702 in the image), pupil measurement compensation can be performed. Pupil measurement can be used to account for product crosstalk. Product crosstalk is the signal that leaks from the surrounding structure of the target mark to the detection system. Crosstalk occurs when the spot size changes (such as in Figure 4CIn the alignment system 400 of FIG. 4 , the aperture field stop (such as aperture stop 313) and the illumination field stop remain the same. If the alignment mark is not underfilled or underfilled, then signal leakage from adjacent structures to the alignment diffraction 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 metrology can mitigate product crosstalk.

[0153] Further, the spot shift can be used to compensate for the ΔR effect. The ΔR effect is a re-weighing of the diffracted beam NA due to product wafer stacking. Since there is no explicit pupil measurement to help measure the shift of the spot in the pupil, the ΔR effect cannot be detected. The ΔR effect may occur when the diffracted radiation beam 335 from the substrate W is shifted due to stacking on the alignment mark. The ΔR effect can be compensated by calibrating the changes in the wavefront sample caused by stacking changes. The calibration can be performed by generating a return signal as a function of the spot shift. This curve can be compared with a calibration curve measured for the same target mark pitch on the benchmark. The tunable system facilitates the implementation of spot shift. Therefore, pupil measurement allows stacking measurement and facilitates smaller marks (for example as described above Figures 7B to 7D described).

[0154] Next, variable focus lenses 701 and 702 are inserted into the pupil plane (see Fig. 7A Higher order suppression can be performed at positions 701 and 702 in the image processing apparatus. Fig. 7E The application of voltages to the variable focus lenses 701 and 702 in the pupil plane to suppress higher diffraction orders is illustrated.The diffracted radiation beam 335 is reflected from the surface of the substrate W and split into diffracted beam spots. Fig. 7E The first and third order diffraction beam spots are shown. The objective lens 330 receives the beam spots and transmits the beam spots to the variable focal length lenses 701 and 702. A voltage is applied to the lenses 701 and 702 at the interface 406 (see Figure 4A and 4B ) creates a curvature in the optical axis (not shown) that pushes the beam spot radially outward away from the optical axis. Upon exiting the second lens 702, the third order diffraction beams are directed radially outward so that they are outside the clear aperture of the lens 336. Thus, the +3 and -3 diffraction order beam spots are filtered out and are not transmitted through the lens 336. On the other hand, despite being pushed outward, the +1 and -1 diffraction order beams remain within the aperture of the lens 336 and are thus transmitted therethrough.

[0155] The tunable beam shift as a function of the mark pitch allows to suppress higher orders within the optical module (e.g. the Nth higher order (N>1) can be suppressed). Fig. 7EIn the case of , it is desirable to remove the third order diffraction beams; otherwise, they will contaminate the signal. Therefore, the higher diffraction orders of the mark pitch can be filtered out. Using a single pixel detector, it is not possible to separate the higher diffraction order contributions from the mark (e.g., I +总 =I +1 +I +2 +I +3 …). In previous systems, only the total dc signal I +总 and I -总 The algorithm used to correct the aligned position error requires knowledge of a pair of diffraction orders, such as +1 and -1, +2 and -2, etc. Removing the higher order signals and calculating the aligned position based only on the detected orders results in higher accuracy and reduced noise to the o / p position.

[0156] Alignment System 700 ( Fig. 7A ) is a non-electromechanical alternative to suppress unwanted orders. Instead of using mechatronics to remove higher diffraction orders, variable focus lenses 701 and 702 can be applied. Therefore, by using variable focus lenses 701 and 702 instead of electromechanical elements, the alignment system 700 can be improved.

[0157] Multiple Alignment System Embodiments That Can Be Used Together

[0158] Figures 4A to 7E One or more of the components and / or systems shown may be Figure 3 In other words, for example, the alignment system 300 can be adjusted to include Figure 4A and 5A The illumination systems 410 and 510, the objective lens 330 Fig. 6A The first variable focal length lens 601, and the output channels 351a to 351d Fig. 6A The second variable focal length lenses 602a to 602d, and the Fig. 7A Variable focal length lenses 701 and 702. This results in three sets of variable focal length lenses being positioned in alignment system 300. In this embodiment, the variable focal length lenses in alignment system 300 can be positioned on optical axis AX, such as Figure 4C 401 and 402, or may be positioned offset from the optical axis AX, such as Figure 5A 502 of them.

[0159] Further, the two embodiments can be used together. For example, Figure 4C The irradiation system 410 and Fig. 6A The variable focal length lenses 601 and 602a to 602d can be Figure 3 The alignment system 300 is used together. Alternatively, Figure 5A The illumination system 510 and Fig. 7A The variable focal length lenses 701 and 702 can be used together. Needless to say, any combination of the embodiments can be used together in the alignment system 300. The above-mentioned benefits and advantages will exist in such an embodiment.

[0160] Figure 8 An alignment method 800 is illustrated. In some embodiments, for example, the method 800 is performed as part of an alignment sensing operation in a semiconductor device manufacturing process. In some embodiments, one or more operations of the method 800 may be implemented in or by a system described herein, including a computer system (e.g., Fig. 9 In some embodiments, the method 800 includes generating (802) an output radiation beam with an illumination source; receiving (804) the radiation beam with a first set of variable focus lenses; controlling (806) the first set of variable focus lenses to change the illumination spot size at the wafer; positioning (808) a second set of variable focus lenses, one of which is positioned in an output channel and another of which is positioned in an objective system; controlling (810) the second set of variable focus lenses to change the focus height of the output from the objective system; positioning (812) a third set of variable focus lenses in a pupil plane downstream of the objective system; controlling (814) the third set of variable focus lenses to change at least one of a spot shift and a higher order diffraction order, and / or other operations.

[0161] The operation of method 800 is intended to be illustrative. In some embodiments, method 800 may be completed with one or more additional operations not described and / or without one or more operations discussed. For example, in some embodiments, method 800 may include additional operations, which include determining adjustments for 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 a measurement signal and / or other similar systems and / or other information. The one or more parameters may include parameters of the radiation (radiation used for measurement), overlap values, alignment values, measurement inspection locations on semiconductor device structure layers, radiation beam tracks across a target, and / or other parameters. In some embodiments, process parameters may be broadly interpreted as including platform position, mask design, measurement target design, semiconductor device design, intensity of the radiation (used for exposing resist, etc.), incident angle of the radiation (used for exposing resist, etc.), wavelength of the radiation (used for exposing resist, etc.), pupil size and / or shape, resist material, and / or other parameters.

[0162] In some embodiments, method 800 includes determining a process adjustment based on one or more determined semiconductor device manufacturing process parameters, adjusting semiconductor device manufacturing equipment based on the determined adjustment, and / or other operations. For example, if the determined alignment measurement value is not within the process tolerance, the out-of-tolerance measurement value may be caused by one or more manufacturing processes whose process parameters have drifted and / or otherwise changed such that the process no longer produces an acceptable device or apparatus (e.g., the measurement value may exceed a threshold for acceptability). One or more new or adjusted process parameters may be determined based on the measurement determination. The new or adjusted process parameters may be configured to cause the manufacturing process to once again produce an acceptable device or apparatus.

[0163] For example, a new or adjusted process parameter may cause a previously unacceptable measurement to be adjusted back into an acceptable range. The new or adjusted process parameter may be compared to the existing parameters for a given process. For example, if there is a difference, the difference may be used to determine an adjustment to the equipment used to produce the device or apparatus (e.g., parameter "x" should be increased / decreased / changed so that it matches a 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 parameter). Electronically adjusting the equipment may include sending an electronic signal and / or other communication to the equipment, which may result in a change to the equipment, for example. Electronic adjustments may include, for example, changing settings on the equipment and / or other adjustments.

[0164] Additionally, the operation of method 800 is Figure 8 The order illustrated in and described herein is not intended to be limiting.

[0165] 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 stored electronically on an electronic storage medium. The one or more processing devices may include devices that are configured by hardware, firmware, and / or software to be specifically designed to perform one or more operations of method 800 (e.g., see the instructions described below). Fig. 9 Related discussion) of one or more devices.

[0166] Fig. 9 1 is a diagram of an example computer system CS that can be used for one or more operations described herein. The computer system CS includes a bus BS or other communication mechanism for transferring information and a processor PRO (or multiple processors, coupled to the bus BS) for processing information. Figure 3 The computer system CS further comprises a main memory MM, such as a random access memory (RAM) or other dynamic storage means, which is coupled to the bus BS for storing information and instructions to be executed by the processor PRO. The main memory MM can also be used for storing temporary variables or other intermediate information during the execution of instructions by the processor PRO. The computer system CS further comprises a read-only memory (ROM) ROM or other static storage means coupled to the bus BS for storing static information and instructions for the processor PRO. Storage means SD, such as a magnetic disk or optical disk, are provided and coupled to the bus BS for storing information and instructions.

[0167] The computer system CS can be coupled to a display DS via a bus BS, such as a flat or touch panel display or a cathode ray tube (CRT), for displaying information to a computer user. An input device ID including alphanumeric keys and other keys is coupled to the bus BS for passing information and command selections to the processor PRO. Another type of user input device is a cursor control CC, such as a mouse, a trackball, or cursor direction keys, for passing direction information and command selections to the processor PRO and controlling cursor movement on the display DS. The input device typically has two degrees of freedom on two axes, a first axis (e.g., x) and a second axis (e.g., y), allowing the device to specify a position in a plane. A touch panel (screen) display can also be used as an input device.

[0168] In some embodiments, in response to the processor PRO executing one or more sequences of one or more instructions contained in the main memory MM, all or some of the one or more operations described herein can be performed by the computer system CS. Such instructions can be read from another computer-readable medium (such as a storage device SD) into the main memory MM. Executing the instruction sequence contained in the main memory MM causes the processor PRO to perform the process steps (operations) described herein. One or more processors in a multi-processing arrangement can also be adopted to execute the instruction sequence contained in the main memory MM. In some embodiments, a hard-wired circuit system can be used instead of a software instruction or in combination with a software instruction. Therefore, the description herein is not limited to any specific combination of hardware circuit system and software.

[0169] The term "computer-readable medium" or "machine-readable medium" used herein refers to any medium that participates in providing instructions to the processor PRO for execution. Such a medium can take many forms, including but not limited to non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical disks or disks, such as storage devices SD. Volatile media include dynamic memory, such as main memory MM. Transmission media include coaxial cables, copper wires, and optical fibers, including wires that constitute the bus BS. Transmission media can also take the form of sound waves or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Computer-readable media can be non-temporary, such as floppy disks, foldable disks, hard disks, tapes, any other magnetic media, CD-ROMs, DVDs, any other optical media, punch cards, paper tapes, any other physical media with hole patterns, RAM, PROMs and EPROMs, flash EPROMs, any other memory chips, or memory cartridges. Non-temporary computer-readable media can have instructions recorded thereon. When executed by a computer, instructions can implement any operation described herein. For example, a temporary computer-readable medium can include a carrier or other propagating electromagnetic signal.

[0170] Various forms of computer-readable media may be involved in carrying one or more sequences of one or more instructions to the processor PRO for execution. For example, the instructions may initially be carried on a disk of a remote computer. The remote computer may load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. The modem local to the computer system CS may receive data on the telephone line and convert the data into an infrared signal using an infrared transmitter. An infrared detector coupled to the bus BS may receive the data carried in the infrared signal and place the data on the bus BS. The bus BS carries the data to the main memory MM, from which the processor PRO retrieves and executes the instructions. Before or after execution by the processor PRO, the instructions received by the main memory MM may optionally be stored on a storage device SD.

[0171] The computer system CS may also include a communication interface CI coupled to the bus BS. The communication interface CI provides a bidirectional data communication coupling with a network link NDL connected to the local network LAN. For example, the communication interface CI may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection with a corresponding type of telephone line. As another example, the communication interface CI may be a local area network (LAN) card to provide a data communication connection with a compatible LAN. A wireless link may also be implemented. In any such implementation, the communication interface CI sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information.

[0172] The network link NDL usually provides data communication to other data devices through one or more networks. For example, the network link NDL can provide a connection to the host computer HC through a local network LAN. This can include data communication services provided through the global packet data communication network (now generally called the "Internet" INT). The local network LAN (Internet) can use electrical signals, electromagnetic signals or optical signals that carry digital data streams. The signals through the various networks and the signals on the network data link NDL and through the communication interface CI (carrying digital data to and from the computer system CS) are exemplary forms of carrier waves that transport information.

[0173] The computer system CS can send messages and receive data, including program code, through (multiple) networks, network data links NDL and communication interfaces CI. In the Internet example, the host computer HC can send the request code of the application program through the Internet INT, the network data link NDL, the local network LAN and the communication interface CI. For example, one such download application can provide all or part of the method described herein. The received code can be executed by the processor PRO when it is received, and / or stored in the storage device SD or other non-volatile storage device for later execution. In this way, the computer system CS can obtain the application code in the form of a carrier wave.

[0174] This specification discloses one or more embodiments that incorporate the features of the present invention. The disclosed (multiple) embodiments merely illustrate the present invention. The scope of the present invention is not limited to the disclosed (multiple) embodiments. The present invention is defined by the appended claims.

[0175] The described embodiment(s) and references in the specification to "one embodiment," "an embodiment," "an example embodiment," etc. indicate that the described embodiment(s) may include a particular feature, structure, or characteristic, but each embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Further, when a particular feature, structure, or characteristic is described in conjunction with an embodiment, it is understood that it is within the knowledge of those skilled in the art to implement such feature, structure, or characteristic in conjunction with other embodiments, whether or not explicitly described.

[0176] 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 in the manufacture of guidance and detection patterns for integrated optical systems, magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, and the like. Those skilled in the art will appreciate 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" or "target portion", respectively. The substrates referenced herein may be processed before or after exposure, such as in a track or coating development system (a tool that typically applies a resist layer to a substrate and develops the exposed resist), a metrology tool, and / or an inspection tool. Where applicable, the present disclosure herein may be applied to such and other substrate processing tools. Further, a substrate may be processed more than once, such as to create a multi-layer IC, such that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

[0177] Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications, such as imprint lithography, and is not limited to optical lithography where the context permits. In imprint lithography, a topography in a patterning device defines a pattern created on a substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate, whereupon the resist is cured by application of electromagnetic radiation, heat, pressure, or a combination thereof. After the resist is cured, the patterning device is removed from the resist, leaving a pattern therein.

[0178] It is to be understood that the phraseology or terminology herein is for the purpose of description rather than limitation, so that the phraseology or terminology of the specification is interpreted by those skilled in the relevant art(s) in light of the teachings herein.

[0179] In the embodiments described herein, the terms "lens" and "lens element," as the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic, and electrostatic optical components.

[0180] Further, 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 range of 5 to 20 nm, such as, for example, 13.5 nm), or hard X-rays operating at less than 5 nm, and particle beams (such as ion beams or electron beams). Generally, radiation with wavelengths between about 400 and about 700 nm is considered visible radiation; radiation with wavelengths between about 780 and 3000 nm (or greater) is considered IR radiation. UV refers to radiation with wavelengths of approximately 100 to 400 nm. Within 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 UV or VUV (i.e., UV absorbed by gases) refers to radiation with wavelengths of approximately 100 to 200 nm. Deep UV (DUV) generally refers to radiation having a wavelength range from 126 nm to 428 nm, and in embodiments, an excimer laser may generate DUV radiation for use within a lithographic apparatus. It should be understood that radiation having a wavelength in the range of, for example, 5 to 20 nm refers to radiation having a wavelength band, at least a portion of which is in the range of 5 to 20 nm.

[0181] As used herein, the term "substrate" generally describes a material to which subsequent layers of material are added. In embodiments, the substrate itself may be patterned, and the material added thereon may also be patterned, or may remain unpatterned.

[0182] As used herein, the term "substantially in contact" generally describes elements or structures that are in physical contact with each other, with only a slight separation from each other, which is generally due to misalignment tolerances. It should be understood that the relative spatial descriptions between one or more specific features, structures, or characteristics (e.g., "vertically aligned," "substantially in contact," etc.) used herein are for illustration purposes only, and actual implementations of the structures described herein may include misalignment tolerances without departing from the spirit and scope of the present disclosure.

[0183] As used herein, the term "optically coupled" generally refers to one coupling element being configured to impart light to another coupling element, either directly or indirectly.

[0184] As used herein, the term "optical material" generally refers to a material that allows light or optical energy to propagate therein or through it.

[0185] Although specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. This description is not intended to limit the invention.

[0186] It will be appreciated that the Detailed Description section, rather than the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more but not all exemplary embodiments of the present invention as contemplated by the inventor(s), and thus, are not intended to limit the present invention and the appended claims in any way.

[0187] The present invention has been described above with the aid of functional building blocks that illustrate the implementation of specified functions and their relationships. For ease of description, the boundaries of these functional building blocks are arbitrarily defined in this article. Alternating boundaries can be defined as long as the specified functions and their relationships are properly performed.

[0188] Various embodiments of the present system and method are disclosed in the list of subsequent numbered aspects. In the following, additional features, characteristics and exemplary technical solutions of the present disclosure will be described according to aspects that can be optionally claimed in any combination:

[0189] 1. A wafer alignment measurement system, comprising: an illumination source; a radiation beam output from the illumination source; a first set of variable focus lenses configured to receive the radiation beam, wherein the first set of variable focus lenses is controllable to control the illumination spot size at the wafer; a second set of variable focus lenses, one variable focus lens being positioned in an output channel and the other variable focus lens being positioned in an objective lens system, wherein the second set of variable focus lenses is controllable to control the focus height of the output from the objective lens system; and a third set of variable focus lenses being positioned in a pupil plane downstream of the objective lens system, wherein the third set of variable focus lenses is controllable to control at least one of spot shift and higher diffraction orders.

[0190] 2. The wafer alignment measurement system of clause 1, wherein the first set of variable focus lenses is positioned in an illumination system.

[0191] 3. The wafer alignment measurement system according to any of the preceding aspects, wherein a first variable focus lens is offset from an optical axis of the radiation beam.

[0192] 4. A wafer alignment measurement system according to any one of the preceding aspects, wherein there are "N" output channels and "N+1" second variable focus lenses, wherein there is one second variable focus lens in each output channel and one second variable focus lens in the objective lens system.

[0193] 5. The wafer alignment measurement system according to any one of the preceding aspects, wherein the third group of variable focus lenses is positioned in a pupil plane.

[0194] 6. A wafer alignment measurement system according to any one of the preceding aspects, wherein the first group of variable focus lenses, the second group of variable focus lenses and the third group of variable focus lenses can be controlled by applying voltage to the first group of variable focus lenses, the second group of variable focus lenses and the third group of variable focus lenses.

[0195] 7. A wafer alignment measurement system, comprising: an illumination source; a radiation beam output from the illumination source; and at least two variable focus lenses configured to receive the radiation beam, wherein the variable focus lenses are controllable to control the illumination spot size at the wafer.

[0196] 8. The wafer alignment measurement system according to any of the preceding aspects, wherein the variable focus lens is positioned in an illumination system.

[0197] 9. The wafer alignment measurement system according to any one of the preceding aspects, wherein the variable focus lens is positioned between an illumination relay lens and an aperture stop in the illumination system.

[0198] 10. The wafer alignment measurement system according to any one of the preceding aspects, wherein the variable focus lens is controllable by applying a voltage to the variable focus lens.

[0199] 11. The wafer alignment measurement system according to any of the preceding aspects, wherein a variable focus lens is offset from an optical axis of the radiation beam.

[0200] 12. A wafer alignment measurement system comprising: an illumination source; and at least two variable focus lenses, one variable focus lens positioned in an output channel and another variable focus lens positioned in an objective system, wherein the variable focus lenses are controllable to control the focus height of an output from the objective system.

[0201] 13. A wafer alignment measurement system according to any one of the preceding aspects, wherein the output of the illumination source is a radiation beam reflected from the wafer.

[0202] 14. The wafer alignment measurement system according to any of the preceding aspects, wherein the radiation beam passes through the variable focus lens after reflecting off the wafer.

[0203] 15. A wafer alignment measurement system according to any one of the preceding aspects, wherein there are "N" output channels and "N+1" variable focus lenses, wherein there is one variable focus lens in each output channel and one variable focus lens in the objective lens system.

[0204] 16. The wafer alignment measurement system according to any one of the preceding aspects, wherein the variable focus lens is controllable by applying a voltage to the variable focus lens.

[0205] 17. A wafer alignment measurement system comprising: an illumination source; a radiation beam output from the illumination source that travels to an objective system; and at least two variable focus lenses positioned in a pupil plane downstream of the objective system, wherein the variable focus lenses are controllable to control at least one of spot shift and higher diffraction orders.

[0206] 18. The wafer alignment measurement system according to any of the preceding aspects, wherein the variable focus lens is positioned in a pupil plane.

[0207] 19. The wafer alignment measurement system according to any of the preceding aspects, wherein the variable focus lens is positioned in the pupil plane between the objective lens system and the self-referencing interferometer.

[0208] 20. The wafer alignment measurement system according to any one of the preceding aspects, wherein the variable focus lens compensates for spot shift.

[0209] 21. The wafer alignment measurement system according to any of the preceding aspects, wherein the variable focus lens compensates for higher diffraction orders.

[0210] 22. The wafer alignment measurement system according to any one of the preceding aspects, wherein the variable focus lens is controllable by applying a voltage to the variable focus lens.

[0211] 23. A wafer alignment measurement method, the wafer alignment measurement method comprising: generating an output radiation beam using an illumination source; receiving the radiation beam using a first group of variable focus lenses; controlling the first group of variable focus lenses to change the illumination spot size at the wafer; positioning a second group of variable focus lenses, one of the second group of variable focus lenses being positioned in an output channel and another of the second group of variable focus lenses being positioned in an objective system; controlling the second group of variable focus lenses to change the focus height of the output from the objective system; positioning a third group of variable focus lenses in a pupil plane downstream of the objective system; and controlling the third group of variable focus lenses to change at least one of a spot shift and a higher order diffraction order.

[0212] 24. The wafer alignment measurement method according to clause 23, wherein the first set of variable focus lenses is positioned in an illumination system.

[0213] 25. A wafer alignment measurement method according to any one of the preceding aspects, wherein a first variable focus lens is offset from an optical axis of the radiation beam.

[0214] 26. A wafer alignment measurement method according to any one of the preceding aspects, wherein there are "N" output channels and "N+1" second variable focal length lenses, wherein there is one second variable focal length lens in each output channel and one second variable focal length lens in the objective lens system.

[0215] 27. The wafer alignment measurement method according to any one of the preceding aspects, wherein the third group of variable focus lenses is positioned in a pupil plane.

[0216] 28. The wafer alignment measurement method according to any one of the preceding aspects, wherein the first group of variable focus lenses, the second group of variable focus lenses, and the third group of variable focus lenses can be controlled by applying voltage to the first group of variable focus lenses, the second group of variable focus lenses, and the third group of variable focus lenses.

[0217] 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 focus lenses; and controlling the variable focus lenses to change an illumination spot size at a wafer.

[0218] 30. The wafer alignment measurement method according to any one of the preceding aspects, wherein the variable focus lens is positioned in an illumination system.

[0219] 31. The wafer alignment measurement method according to any one of the preceding aspects, wherein the variable focus lens is positioned between an illumination relay lens and an aperture stop in an illumination system.

[0220] 32. The wafer alignment measurement method according to any one of the preceding aspects, wherein the variable focus lens can be controlled by applying a voltage to the variable focus lens.

[0221] 33. A wafer alignment measurement method according to any one of the preceding aspects, wherein a variable focus lens is offset from an optical axis of the radiation beam.

[0222] 34. A wafer alignment measurement method, the wafer alignment measurement method comprising: an illumination source; and at least two variable focus lenses, one variable focus lens positioned in an output channel and another variable focus lens positioned in an objective lens system, wherein the variable focus lenses are controllable to control the focus height of an output from the objective lens system.

[0223] 35. A wafer alignment measurement method according to any one of the preceding aspects, wherein the output of the illumination source is a radiation beam reflected from the wafer.

[0224] 36. A wafer alignment measurement method according to any one of the preceding aspects, wherein the radiation beam passes through the variable focus lens after reflecting from the wafer.

[0225] 37. A wafer alignment measurement method according to any one of the preceding aspects, wherein there are "N" output channels and "N+1" variable focus lenses, wherein there is one variable focus lens in each output channel and there is one variable focus lens in the objective lens system.

[0226] 38. The wafer alignment measurement method according to any one of the preceding aspects, wherein the variable focus lens can be controlled by applying a voltage to the variable focus lens.

[0227] 39. A wafer alignment measurement method, the wafer alignment measurement method comprising: generating a radiation beam output from an illumination source, the radiation beam traveling to an objective system; positioning at least two variable focus lenses in a pupil plane downstream of the objective system; and controlling the variable focus lenses to vary at least one of a spot shift and higher diffraction orders.

[0228] 40. The wafer alignment measurement method according to any one of the preceding aspects, wherein the variable focus lens is positioned in a pupil plane.

[0229] 41. A wafer alignment measurement method according to any one of the preceding aspects, wherein the variable focus lens is positioned in the pupil plane between the objective lens system and a self-referencing interferometer.

[0230] 42. The wafer alignment measurement method according to any one of the preceding aspects, wherein the variable focus lens compensates for spot shift.

[0231] 43. A wafer alignment measurement method according to any one of the preceding aspects, wherein the variable focus lens compensates for higher diffraction orders.

[0232] 44. The wafer alignment measurement method according to any one of the preceding aspects, wherein the variable focus lens can be controlled by applying a voltage to the variable focus lens.

[0233] The foregoing description of specific embodiments will fully demonstrate the generality of the present invention, and by applying the knowledge within the prior art, others can easily modify and / or adapt various applications of these specific embodiments without undue experimentation and without departing from the general concept of the present invention. Therefore, based on the teachings and guidance presented herein, such adaptations and modifications are intended to fall within the meaning and scope of equivalents to the disclosed embodiments.

[0234] 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. A wafer alignment measurement system, comprising: Irradiation source; a radiation beam output from the illumination source; a first set of variable focus lenses configured to receive the radiation beam, wherein the first set of variable focus lenses is controllable to control an illumination spot size at the wafer; a second set of variable focus lenses, one variable focus lens being positioned in the output channel and the other variable focus lens being positioned in the objective lens system, wherein the second set of variable focus lenses is controllable to control the focus height of the output from the objective lens system; as well as A third set of variable focus lenses is positioned in a pupil plane downstream of the objective system, wherein the third set of variable focus lenses is controllable to control at least one of spot shift and higher diffraction orders.

2. The wafer alignment measurement system of claim 1, wherein the first set of variable focus lenses is positioned in an illumination system.

3. The wafer alignment measurement system of claim 2, wherein a first variable focus lens is offset from an optical axis of the radiation beam.

4. The wafer alignment measurement system of claim 1 , wherein there are "N" output channels and "N+1" second variable focus lenses, wherein there is one second variable focus lens in each output channel and one second variable focus lens in the objective lens system.

5. The wafer alignment measurement system of claim 1, wherein the third set of variable focus lenses is positioned in a pupil plane.

6. The wafer alignment measurement system according to claim 1, wherein the first group of variable focus lenses, the second group of variable focus lenses, and the third group of variable focus lenses can be controlled by applying voltage to the first group of variable focus lenses, the second group of variable focus lenses, and the third group of variable focus lenses.

7. A wafer alignment measurement system comprising: Irradiation source; a radiation beam output from the illumination source; as well as At least two variable focus lenses are configured to receive the radiation beam, wherein the variable focus lenses are controllable to control an illumination spot size at the wafer.

8. The wafer alignment measurement system of claim 7, wherein the variable focus lens is positioned in an illumination system.

9. The wafer alignment measurement system of claim 8, wherein the variable focus lens is positioned between an illumination relay lens and an aperture stop in the illumination system.

10. The wafer alignment measurement system of claim 7, wherein the variable focus lens is controllable by applying a voltage to the variable focus lens.

11. The wafer alignment measurement system of claim 7, wherein a variable focus lens is offset from an optical axis of the radiation beam.

12. A wafer alignment measurement method, the wafer alignment measurement method comprising: generating an output radiation beam using an illumination source; receiving the radiation beam using a first set of variable focus lenses; controlling the first set of variable focus lenses to change the size of the illumination spot at the wafer; positioning a second group of variable focus lenses, one of the second group of variable focus lenses being positioned in the output channel and another of the second group of variable focus lenses being positioned in the objective lens system; controlling the second group of variable focus lenses to change the focus height of the output from the objective lens system; positioning a third variable focus lens group in a pupil plane downstream of the objective lens system; as well as The third group of variable focus lenses is controlled to vary at least one of a spot shift and a higher order diffraction order.

13. The wafer alignment measurement method according to claim 12, wherein the first set of variable focus lenses is positioned in an illumination system.

14. The wafer alignment measurement method of claim 13, wherein a first variable focus lens is offset from an optical axis of the radiation beam.

15. The wafer alignment measurement method of claim 12, wherein there are "N" output channels and "N+1" second variable focus lenses, wherein there is one second variable focus lens in each output channel and one second variable focus lens in the objective lens system.

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