Tunable Optics

Abstract

A system and method for providing a variable spot size and variable focus at a substrate is described. A set of variable focal length lenses can be added to an alignment system to enable 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 to the lens. Switching the voltage changes the water-oil interface within the liquid lens, which in turn changes the direction of light passing through the liquid lens. For example, turning on the voltage to the lens shifts the light output direction to converge to a focal point. As a result, the variable focal length lens provides adjustment to compensate for the drawbacks of the fixed spot size and focus of the prior art. Furthermore, the variable focal length lens can also be used to compensate for spot shift and higher diffraction orders.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS)

[0001] This application claims priority to U.S. Patent Application No. 63 / 410,008, filed September 26, 2022, which is incorporated herein by reference in its entirety.

[0002]

[0002] The present disclosure relates to tunable optical systems. [Background technology]

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

[0004]

[0004] During lithography operations, different layers may need to be formed sequentially on a substrate by different processing steps. Therefore, it may be necessary to position the substrate with high accuracy relative to previous patterns formed on the substrate. Typically, alignment marks, which may include, for example, a diffraction grating, are disposed on the substrate to be aligned and positioned relative to a second object. Lithography apparatuses may use alignment systems, for example, to detect the positions of the alignment marks and to align the substrate using the alignment marks to ensure the accuracy of subsequent lithography operations.

[0005]

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

[0006]

[0006] Alignment systems often use dual self-referencing interferometer (SRI) systems to acquire intensity as a function of mark position. The phase of these sinusoidal signals is used to determine the alignment position of the mark. Each SRI has a dedicated polarization state, which is prepared using feed optics that separates the input light into x- and y-polarized light. These alignment systems are fixed optics.

[0007] However, current alignment systems have several limitations. The beam spot size that illuminates the wafer target mark is fixed. As a result, the size of the alignment mark is constrained. For example, relatively thick resist and / or warped wafers can cause alignment failures. Another common problem is the undetectable delta-R effect, which is the re-counting of the diffracted beam numerical aperture due to the product wafer stack. Furthermore, high-order rejection necessitates the use of mechatronic elements inside a typical optical module. Mechatronics use mechanical elements that cause vibration and heat, as well as requiring a large amount of power, all of which are undesirable in an alignment system. Summary of the Invention

[0008]

[0008] Disclosed are novel systems and methods that facilitate variable spot size and variable focus on a substrate for alignment (and / or overlay) determination. An alignment system is provided with a set of variable focal length lenses to enable spot size and focus adjustment. The variable focal length lenses are liquid lenses that are tunable based on the application of a voltage to the lenses. Switching the voltage changes the curvature of the water-oil interface within the liquid lens, which in turn changes the direction of light passing through the liquid lens. For example, turning on the voltage to the lens shifts the light output direction to converge to a focal point. As a result, the variable focal length lenses provide adjustments to compensate for the shortcomings of fixed spot size and focus in the prior art. Furthermore, variable focal length lenses can also be used to compensate for spot shift and delta-R effects. Variable focal length lenses can also be used in place of mechatronic elements to reject higher diffraction orders.

[0009]

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

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

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

[0012]

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

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

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

[0015]

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

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

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

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

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

[0020]

[0020] According to one embodiment, a wafer alignment measurement system includes an illumination source and at least two variable focal length lenses, one positioned in the output channel and the other positioned in the objective system, which are controllable to control the focal height of the output from the objective system.

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

[0022] In one embodiment, the radiation beam passes through a variable focal length lens after reflecting off the wafer.

[0023]

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

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

[0025]

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

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

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

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

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

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

[0031]

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

[0032]

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

[0033] [Figure 1A]

[0033] FIG. 1 is a schematic diagram of a reflective lithographic apparatus according to one embodiment of the present disclosure. [Figure 1B]

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

[0035] 1 is a more detailed schematic diagram of a reflective lithographic apparatus according to an embodiment of the present disclosure; [Figure 2A]

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

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

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

[0039] FIG. 2 is a schematic diagram of the relationship between the radiant illumination spot of an inspection system and a metrology target, according to one embodiment of the present disclosure. [Figure 3]

[0040] FIG. 1 is a schematic diagram of a state-of-the-art alignment system according to one embodiment of the present disclosure. [Figure 4A]

[0041] FIG. 2 is a schematic diagram of a variable focal length lens with no voltage applied, according to one embodiment of the present disclosure. [Figure 4B]

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

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

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

[0045] FIG. 10 is a schematic diagram of a radiation beam spot size of a variable focal length lens with nominal voltage for variable spot size, according to an embodiment of the present disclosure. [Figure 4F]

[0046] FIG. 1 is a schematic diagram of a radiation beam spot size of a variable focal length lens with applied voltages for variable spot size, according to an embodiment of the present disclosure. [Figure 5A]

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

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

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

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

[0051] 5C illustrates a combined view of the elements shown in FIGS. 5A, 5C, and 5D that form part of the system of FIG. 5B, according to one embodiment of the present disclosure. [Figure 6A]

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

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

[0054] FIG. 10 is a schematic diagram of measuring overlay in a variable focus embodiment, according to one embodiment of the present disclosure. [Figure 6D]

[0055] FIG. 10 is another schematic diagram of measuring overlay with a variable focus embodiment, according to an embodiment of the present disclosure. [Figure 7A]

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

[0057] FIG. 10 is a schematic diagram of calibrating beam size in a spot-shifting embodiment, according to one embodiment of the present disclosure. [Figure 7C]

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

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

[0060] FIG. 10 is a schematic diagram of shifting high diffraction orders in a high order rejection embodiment, according to an embodiment of the present disclosure. [Figure 8]

[0061] 1 illustrates a wafer alignment measurement method according to one embodiment. [Figure 9]

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

[0034]

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

[0035]

[0064] Among other advantages, the present system and method provide a solution to these and other problems, allowing for variable spot size and alignment mark miniaturization. The present system and method also improve performance for measuring thick stacks and enable non-mechanical scanning within the OM. To provide the variable spot size, as described below, a set of liquid lenses replaces the fixed lens of a typical input fiber assembly to provide afocal functionality. A voltage applied to two variable focal length lenses increases the focal length. In another embodiment, two variable focal length lenses are used to maintain a numerical aperture that accommodates thick stacks while maintaining a variety of focal spot sizes.

[0036]

[0065] Briefly, the following description relates to semiconductor device measurement and patterning processes. The following paragraphs also describe some components of systems and / or methods for semiconductor device metrology. These systems and methods can be used, for example, to measure alignment, overlay, and the like, or for other operations in the semiconductor device manufacturing process.

[0037]

[0066] Exemplary Reflective and Transmissive Lithography Systems

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

[0038]

[0068] The illumination system IL may include various types of optical components, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping or controlling the radiation beam B.

[0039]

[0069] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA relative to a reference frame, the design of at least one of lithographic apparatuses 100 and 100′, and other conditions, such as whether or not the patterning device 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, for example, a frame or a table, which may be fixed or movable as required. By using sensors, the support structure MT can ensure that the patterning device MA is at a desired position, for example with respect to the projection system PS.

[0040]

[0070] The term "patterning device" MA should be interpreted broadly to refer 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 particular functional layer in a device being created in the target portion C to form an integrated circuit.

[0041]

[0071] Patterning device MA may be transmissive (as in lithographic apparatus 100′ of FIG. 1B) or reflective (as in lithographic apparatus 100 of FIG. 1A). Examples of patterning devices MA include reticles, masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam B in different directions. The tilted mirrors impart a pattern to a radiation beam B that is reflected by the matrix of small mirrors.

[0042]

[0072] The term "projection system" PS may include any type of projection system, including refractive, reflective, refractive-reflective, magnetic, electromagnetic, electrostatic optical systems, or any combination thereof, appropriate to 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 be too absorbing of the radiation or electrons. A vacuum environment may therefore be provided throughout the beam path using a vacuum wall and vacuum pumps.

[0043]

[0073] Lithographic apparatus 100 and / or 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 one or more substrate tables WT may be used for exposure while preparation steps are performed on one or more other tables. In some circumstances, the additional tables may not be substrate tables WT.

[0044]

[0074] 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 if 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 the radiation beam B passes from the source SO to the illuminator IL via a beam delivery system BD (FIG. 1B), which may comprise, for example, suitable directing mirrors and / or beam expanders. In other cases, the source SO may be an integral part of the lithographic apparatus 100, 100', for example if the source SO is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD, if required, may be referred to as a radiation system.

[0045]

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

[0046]

[0076] Referring to Figure 1A, a radiation beam B is incident on a patterning device (e.g., mask) MA, which is held on a support structure (e.g., mask table) MT, and is patterned by the patterning device MA. In lithographic apparatus 100, the radiation beam B is reflected from the patterning device (e.g., mask) MA. After reflecting from the patterning device (e.g., mask) MA, the radiation beam B passes through a projection system PS, which focuses the radiation beam B onto a target portion C of a substrate W. With the aid of a second positioner PW and a position sensor IF2 (e.g., an interferometric device, a linear encoder, or a capacitive sensor), the substrate table WT can be accurately moved (e.g., to position different target portions C in the path of the radiation beam B). Similarly, a first positioner PM and another position sensor IF1 can be used to accurately position the patterning device (e.g., mask) MA relative to the path of the radiation beam B. Patterning device (eg mask) MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0047]

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

[0048]

[0078] 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. to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and a further position sensor (not shown in FIG. 1B) can be used to accurately position the mask MA with respect to the path of the radiation beam B (e.g. after mechanical removal of a mask library or during a scan).

[0049]

[0079] In general, movement of the mask table MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask table MT may be connected to a short-stroke actuator only, or may be fixed. The mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. The substrate alignment marks (as shown) occupy dedicated target portions, but may be located in spaces between the target portions (known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks may be located between the dies.

[0050]

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

[0051]

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

[0052]

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

[0053]

[0083] 2. In scan mode, the support structure (e.g. mask table) MT and the 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 velocity and direction of the substrate table WT relative to the support structure (e.g. mask table) MT can be determined by the (de-)magnification and image reversal characteristics of the projection system PS.

[0054]

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

[0055]

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

[0056]

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

[0057]

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

[0058]

[0088] Radiation emitted by the hot plasma 110 is delivered from the source chamber 111 into the collector chamber 112 through an optional gas barrier or contaminant trap 113 (sometimes referred to as a contaminant barrier or foil trap) 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. The contaminant trap 113 further illustrated herein includes at least a channel structure known in the art.

[0059]

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

[0060]

[0090] The radiation then traverses an illumination system IL, which may include a faceted field mirror device 122 and a facetted pupil mirror device 124 arranged to provide a desired angular distribution of the radiation beam 121 at the patterning device MA and to provide a desired radiation intensity uniformity at the patterning device MA. When the radiation beam 121 is reflected from the patterning device MA, which is held by a support structure MT, a patterned beam 126 is formed which 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.

[0061]

[0091] In general, there may be more elements in the illumination optics unit IL and the projection system PS than are shown. Optionally, a grating spectral filter 140 may be present, depending on the type of lithographic apparatus. Furthermore, there may be more mirrors than are shown. For example, there may be one to six additional reflective elements in the projection system PS compared to what is shown in FIG. 1C .

[0062]

[0092] 1C is shown as merely one example of a collector (or collector mirror), as a nested collector with grazing incidence reflectors 153, 154, and 155. Grazing incidence reflectors 153, 154, and 155 are arranged axially symmetrically about optical axis O, and this type of collector optic CO is suitable for use in combination with a discharge-produced plasma source, often referred to as a DPP source.

[0063]

[0093] Exemplary Lithography Cell

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

[0064]

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

[0065]

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

[0066]

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

[0067]

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

[0068]

[0099] A metrology system can be used to determine one or more properties of a substrate structure, specifically how one or more properties of different substrate structures differ, or how different layers of the same substrate structure differ from one another. The metrology system can be integrated into lithographic apparatus 100 or 100′ or lithography apparatus 200, or can be a stand-alone device.

[0069]

[0100] Alignment System Embodiments

[0101] In particular, one or more targets can be provided on the substrate to enable alignment. Typically, the targets are specially designed and can include periodic structures. For example, the target on the substrate can include one or more 1D periodic structures (e.g., geometric features such as gratings) that are printed such that, after development, the periodic structure features are formed of solid resist lines. As another example, the target can include one or more 2D periodic structures (e.g., gratings) that are printed such that, after development, the periodic structures are formed of solid resist pillars or vias in the resist. Alternatively, bars, pillars, or vias can be etched into the substrate (e.g., in one or more layers on the substrate).

[0070]

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

[0071]

[0103] Similar to lithographic apparatus 100 and 100′ of FIGS. 1A and 1B, one or more substrate tables may be provided to hold substrate W during measurement operations. The one or more substrate tables may be similar to or identical to substrate table WT of FIGS. 1A and 1B. In examples where inspection system 10 is integrated with the lithographic apparatus, they may be the same substrate table. Coarse and fine positioners may be provided and configured to accurately position the substrate relative to the measurement optics. Various sensors and actuators are provided, for example, to acquire the position of a target portion of a structure of interest (e.g., a metrology mark) and move it to a predetermined position under the objective lens. Typically, many measurements are made on target portions of the structure at different positions across the substrate W. The substrate support can be moved in the X and Y directions to acquire various targets, and in the Z direction to obtain the desired position of the target portion relative to the focus of the optics. For example, it is convenient to describe operation in terms of moving an objective lens to various positions relative to the substrate, even though in reality the optics remain substantially fixed (typically in X and Y, but possibly also in Z) and the substrate moves. Provided the relative positions of the substrate and optics are correct, it is in principle immaterial whether one of them moves, or both, or whether part of the optics moves (e.g., in Z and / or tilt) while the rest of the optics remains fixed and the substrate moves (e.g., in X and Y, but optionally in Z and / or tilt).

[0072]

[0104] In a typical alignment measurement, the target (portion) 30 on the substrate W may be a 1D grating that is printed such that after development the bars are formed of solid resist lines (which may be covered, for example, by a deposition layer) and / or other material. Alternatively, the target 30 may be a 2D grating that is printed such that after development the grating is formed of solid resist pillars or other features in the resist.

[0073]

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

[0074]

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

[0075]

[0107] FIG. 2D shows a plan view of a typical target (e.g., metrology mark) 30 and the extent of a typical emitted illumination spot S. To obtain a diffraction spectrum typically free of interference from surrounding structures, the target 30 in one embodiment 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 can be smaller than the width and length of the target. In other words, the target is "underfilled" by the illumination. The diffraction signal is substantially free of signal from product features outside the target itself. The illumination setup can be configured to provide uniform-intensity illumination, for example, at the back focal plane of the objective. Alternatively, the illumination can be limited to an on-axis or off-axis direction, for example, by including an aperture in the illumination path.

[0076]

[0108] Latest Alignment System

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

[0077]

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

[0078]

[0111] The illumination system 310 may be configured to receive the radiation beam 306. In this example embodiment, the illumination system 310 may further 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 optics to generate additional illumination beams that are split or replicated from the radiation beam 306 and direct them towards alignment marks (not shown) on the substrate W.

[0079]

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

[0080]

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

[0081]

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

[0082]

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

[0083]

[0116] If the alignment axis of the alignment system 300 passes through the center of symmetry of the alignment mark (not shown), the detectors described above may be configured to receive the recombined image and detect interference resulting from the recombined image. According to exemplary embodiments, such interference may be due to the 180-degree symmetry of the alignment mark and the recombined images interfering constructively or destructively. Based on the detected interference, the detectors may be further configured to determine the position of the center of symmetry of the alignment mark and, consequently, detect the position of the substrate W. According to one example, the alignment axis may be aligned with a light beam that is perpendicular to the substrate 420 and passes through the center of the self-referencing interferometer 340.

[0084]

[0117] Variable focal length lens

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

[0085]

[0119] The focal length of the lens 420 can be fine-tuned and changed by applying a specified voltage 408. FIG. 4A shows the water-oil interface 406 when no voltage is applied (“off”). In FIG. 4A, no voltage is shown applied because the lens 420 is connected to ground 407. In one example, in the absence of voltage, the water 404 and oil 405 naturally form a slight concave curvature at the interface 406, so that an incident light beam 403 parallel to the optical axis OA diverges slightly upon exiting the variable focal length lens 420. As another example, FIG. 4B shows the water-oil interface 406 when a non-zero voltage 408 is applied (“on”). The applied voltage 408 on the liquid lens 420 generates an electrostatic voltage 425 at or near the edge 429, resulting in the accumulation of positive charge (see the “+” sign shown in FIG. 4B). Thus, the negative charges (see the "-" sign shown in FIG. 4B) in the water 404 are attracted to the positive charges. As a result, the water 404 moves to the edge 429 of the lens 420, and the oil 405 is displaced to the center 431 of the lens 420. FIG. 4B shows that the curvature of the interface 406 changes to a convex shape, which causes the incident light beam 403 to converge to a focal point 433 on the optical axis OA.

[0086]

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

[0087]

[0121] Variable Spot Size Alignment System

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

[0088]

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

[0089]

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

[0090]

[0125] In one embodiment, a nominal amount of voltage is applied to variable focal length lenses 401 and 402 to achieve one or more films 435, 437 (similar and / or identical to film 427 described above) with no curvature. In one embodiment, as the applied voltage is increased, a longer focal length is achieved, changing the spot size of the radiation on the substrate. This configuration can be such that applying a negative voltage shortens the focal length (and results in a different radiation spot size on the substrate). If desired, the polarity of the voltage to achieve different curvatures can be reversed to increase or decrease the focal length.

[0091]

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

[0092]

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

[0093]

[0128] Figure 4F shows a schematic of the size of spot 491 of radiation beam 306 when voltages are applied to variable focal length lenses 401 and 402. Similar to Figure 4E, as radiation beam 306 emerges from input fiber 307, it expands in size (481) until it reaches illumination relay lens 312, which transforms the incident beam into a collimated radiation beam 483. With voltages applied to each of variable focal length lenses 401 and 402, a curvature is formed at the water-oil interface 406 of lenses 401 and 402 (see Figures 4A and 4B). This results in an increase in the size of collimated radiation beam 306 as it emerges from second lens 402 due to the increase in focal length of lenses 401 and 402 (489). Finally, the enlarged radiation beam 306 passes through aperture stop 313, with spot 491 having an expanded diameter D2.

[0094]

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

[0095]

[0130] Beam Steering Alignment System

[0131]

[0033] Figure 5A shows a schematic of an illumination system 510 of the beam steering alignment system. The illumination system 510 includes a relay lens 312 (e.g., similar to and / or identical to the relay lens 312 shown in Figure 4C), first and second variable focal length lenses 501 and 502 (e.g., similar to and / or identical to the lenses 401 and 402 shown in Figure 4C), and an aperture stop 313 (e.g., similar to and / or identical to the aperture stop 313 shown in Figure 4C). As shown in Figure 5A, the illumination system 510 may be configured to receive the radiation beam 306 from the fiber 307. The illumination system 510 includes the illumination relay lens 312 that receives the radiation beam 306, the first variable focal length lens 501, the second variable focal length lens 502, and the aperture stop 313. The second variable focal length lens 502 is offset (503) from the first variable focal length lens 501 and the optical axis AX.

[0096]

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

[0097]

[0133] 5C-5D show a schematic representation of the effect of the variable focal length lens 502 being offset from the optical axis AX. FIG. 5C 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 is coincident with the optical axis AX. However, FIG. 5D shows that when the variable focal length lens 502 is offset from the optical axis AX, the illumination spot 333 on the substrate W is also offset from the optical axis AX. Due to the offset of the variable focal length lens 502 from the optical axis AX, the radiation beam 306 reflects from the spot mirror 320 at a different angle, resulting in an illumination spot 333 that is offset from the optical axis AX, as shown in FIG. 5D. For example, a beam steering angle of tilt of 1.8 milliradians results in a scan length of ±24 μm.

[0098]

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

[0099]

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

[0100]

[0136] Due to the non-mechanical beam scanning of the alignment marks, the design shown in FIG. 5E ensures that the beam steering still fits within the spot mirror 320. The current spot size and spot mirror size ensure that the zeroth order blocking is maintained. Even if the beam 306 is offset from the optical axis AX when it is incident on the substrate W, the zeroth order of the diffracted radiation beam 335 is still blocked by the spot mirror 320. As a result, dark-field measurements are still possible because the zeroth order beam is blocked. Furthermore, regular diagonal raster scanning can be achieved without using mechanical elements. Furthermore, bidirectional diagonal scanning is combined. Lateral scan offsets are then compensated for.

[0101]

[0137] In other embodiments, beam steering can be used with a high bandwidth detector and a constant high speed substrate table WT for more marks to accommodate the Doppler shift of different marks. Furthermore, additional coherent illumination spots on the substrate W can be generated to provide beam steering on the original beam spot. Aligned positions can be achieved as a function of the beam steering angle. Alternatively, the beam can be positioned directly on the detector.

[0102]

[0138] Variable Focus Alignment System

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

[0103]

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

[0104]

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

[0105]

[0142] For example, Figure 6B shows a schematic of a thick resist substrate W in a variable focus alignment system 600 (Figure 6A). The substrate W includes an alignment mark 610 positioned below a resist layer 611. Despite the thickness of the multiple photoresist layers 611, the alignment mark 610 underneath remains in focus. By applying voltages to the variable focal length lenses 601 and 602a-602d (shown in Figure 6A), the focal length of the radiation beam 306 can be changed so that the radiation beam 306 is focused at the alignment mark 610 level. In some embodiments, the variable focus alignment system 600 can be used to align thick 3D NAND stacks with thick resist and warped wafers.

[0106]

[0143] Figures 6C-6D show a schematic for measuring the overlay (e.g., the amount of offset "d") of alignment marks 610a and 610b in a variable focus alignment system. In Figure 6C, the top alignment mark 610a (grating) can be measured by focusing the radiation beam 306 on the surface of alignment mark 610a. In Figure 6D, the bottom alignment mark 610b (grating) can be measured by focusing the radiation beam 306 on the surface of alignment mark 610b. As a result, the offset "d" between the alignment mark gratings can be determined. For example, variable focus can be used in a Z-Star system, which uses different gratings at different z levels.

[0107]

[0144] The variable-focus alignment system 600 (Figure 6A) can maintain the same mark pitch range. The numerical aperture pitch is 0.118 to 0.7. The variable focus accommodates typical thick stacks on the order of millimeters. Furthermore, variable focal length lenses 401 and 402 in the IFA can be used with the variable focus to maintain spot size at various foci, as shown in Figure 4C. The overlay function in the variable-focus alignment system 600 is achieved by using multi-z-level alignment signals. Furthermore, the variable focus in the alignment system 600 can provide adjustable working distances with commercially proven aperture sizes. The variable focus can also be deployed in the YieldStar for overlay metrology.

[0108]

[0145] Spot shift and high-order rejection alignment system

[0146] Figure 7A shows a schematic of an alignment system 700 for spot shift and high-order rejection. Alignment system 700 is the same as alignment system 300 of Figure 3 except for the removal of input fiber assembly (IFA) 311 and the addition of first and second variable focal length lenses 701 and 702 at the pupil plane.

[0109]

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

[0110]

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

[0111]

[0149] Figure 7C shows the spot shift of the diffracted radiation beam 335 using lenses 701 and 702 with an intermediate voltage. The diffracted radiation beam 335 reflects off an alignment mark on the substrate W. The diffracted radiation beam 335 expands until it reaches the objective system 330, where the rays become parallel. With the intermediate voltage applied, a curvature is formed at the interface 406 (see Figures 4A and 4B). This causes the diffracted radiation beam 335 to be shifted to a smaller spot size when it exits the second lens 702. The beam 335 then enters the self-referencing interferometer 340.

[0112]

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

[0113]

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

[0114]

[0152] Additionally, spot shift can be used to compensate for the delta-R effect. The delta-R effect is a re-metering of the diffracted beam NA due to the product wafer stack. Because there is no explicit pupil metrology that can help measure the shift of the spot in the pupil, the delta-R effect cannot be detected. The delta-R effect can occur when the diffracted radiation beam 335 from the substrate W shifts due to stacking on the alignment marks. The delta-R effect can be compensated for by calibrating the change in the wavefront sample due to stack variations. Calibration can be performed by generating a return signal as a function of spot shift. This curve can be compared to a calibration curve measured for the same target mark pitch on a reference. Spot shift is facilitated by a tunable system. This allows stack measurements to be made using pupil metrology, facilitating smaller marks (e.g., as described above with respect to Figures 7B-7D).

[0115]

[0153] Second, inserting variable focal length lenses 701 and 702 in the pupil plane (see the positions of 701 and 702 in Figure 7A) results in higher order rejection. Figure 7E shows applying a voltage to variable focal length lenses 701 and 702 in the pupil plane to reject higher diffraction orders. The diffracted radiation beam 335 reflects off the surface of the substrate W and splits into multiple diffracted beam spots. Figure 7E shows the first and third order diffracted beam spots. The objective system 330 receives the beam spots and delivers them to the variable focal length lenses 701 and 702. Applying a voltage to lenses 701 and 702 creates a curvature at interface 406 (see Figures 4A and 4B), pushing the beam spot radially outward, away from the optical axis (not shown). The third order diffracted beam is radially outward as it emerges from the second lens 702, and therefore outside the aperture of lens 336. As a result, the +3rd and -3rd order diffracted beam spots are eliminated and do not pass through lens 336. Meanwhile, the +1st and -1st order diffracted beams, despite being pushed outward, are still within the aperture of lens 336 and pass through it.

[0116]

[0154] Tunable beam shift as a function of mark pitch enables higher-order rejection within the optical module (e.g., high N orders can be rejected (N>1)). In the case of Figure 7E, it is desirable to remove the third-order diffraction beam, which would otherwise corrupt the signal. Therefore, diffraction orders higher than the mark pitch can be removed. The contributions of higher diffraction orders from the mark cannot be separated using a single-pixel detector (e.g., I+total = I+1 + I+2 + I+3...). In conventional systems, only the total dc signal, I+total, and I-total can be measured. Algorithms for correcting errors in the aligned position require knowledge of diffraction order pairs, such as +1 and -1, +2 and -2, etc. By removing the higher-order signals and calculating the alignment position based only on the detected orders, improved accuracy and noise reduction for the o / p position are obtained.

[0117]

[0155] Alignment system 700 (FIG. 7A) is a non-mechatronic alternative for rejecting unwanted orders. Instead of using mechatronics to remove high diffraction orders, variable focal length lenses 701 and 702 can be used. As a result, alignment system 700 can be improved by using variable focal length lenses 701 and 702 rather than mechatronic elements.

[0118]

[0156] Embodiments of Multiple Alignment Systems That Can Be Used Together

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

[0119]

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

[0120]

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

[0121]

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

[0122]

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

[0123]

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

[0124]

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

[0125]

[0164] In some embodiments, one or more portions of method 800 may be implemented in and / or 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 processing information electronically). The one or more processing devices may include one or more devices that perform some or all of the operations of method 800 in accordance with instructions electronically stored on an electronic storage medium. The one or more processing devices may include one or more devices configured with hardware, firmware, and / or software specifically designed to perform one or more of the operations of method 800 (see, e.g., the discussion of FIG. 9 below).

[0126]

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

[0127]

[0166] The computer system CS can be coupled via a bus BS to a display DS, such as a flat panel display, a touch panel display, or a cathode ray tube (CRT), for displaying information to a computer user. An input device ID, including alphanumeric and other keys for communicating information and command selections to the processor PRO, is coupled to the bus BS. Another type of user input device is a cursor control CC, such as a mouse, trackball, or cursor direction keys, for communicating directional information and command selections to the processor PRO and for controlling cursor movement on the display DS. This input device typically has two degrees of freedom in 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. Touch panel (screen) displays can also be used as input devices.

[0128]

[0167] In some embodiments, all or a portion of one or more operations described herein may be performed by computer system CS in response to processor PRO executing one or more sequences of one or more instructions contained in main memory MM. Such instructions may be read into main memory MM from another computer-readable medium, such as storage device SD. Execution of the sequences of instructions contained in main memory MM causes processor PRO to perform the process steps (operations) described herein. One or more processors in a multi-processing arrangement may also be used to execute the sequences of instructions contained in main memory MM. In some embodiments, hardwired circuitry may be used in place of or in combination with software instructions. Thus, the description herein is not limited to any specific combination of hardware circuitry and software.

[0129]

[0168] As used herein, the terms "computer-readable medium" or "machine-readable medium" refer to any medium that participates in providing instructions to a processor PRO for execution. Such media may take many forms, including, but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media include optical or magnetic disks, such as a storage device SD. Volatile media include dynamic memory, such as main memory MM. Transmission media include coaxial cables, copper wire, and optical fibers, including the wires that comprise the bus BS. Transmission media may also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Computer-readable media may be non-transitory, such as a floppy disk, a flexible disk, a hard disk, magnetic tape, any other magnetic medium, a CD-ROM, a DVD, any other optical medium, punch cards, paper tape, any other physical medium with a pattern of holes, RAM, PROM, EPROM, FLASH-EPROM, or any other memory chip or cartridge. Non-transitory computer-readable media may have instructions recorded on it. The instructions, when executed by a computer, can perform any of the operations described herein. The transitory computer-readable medium may include, for example, a carrier wave or other propagating electromagnetic signal.

[0130]

[0169] Various forms of computer-readable media may be involved in carrying one or more sequences of one or more instructions to processor PRO for execution. For example, the instructions may initially be carried on a magnetic disk of a remote computer. The remote computer may load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to computer system CS may receive the data on the telephone line and convert the data to an infrared signal using an infrared transmitter. An infrared detector coupled to bus BS may receive the data transmitted in the infrared signal and place the data on bus BS. Bus BS transmits the data to main memory MM, from which processor PRO retrieves and executes the instructions. The instructions received by main memory MM may optionally be stored on storage device SD either before or after execution by processor PRO.

[0131]

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

[0132]

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

[0133]

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

[0134]

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

[0135]

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

[0136]

[0175] Although specific reference is made herein to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc. In light of these alternative applications, those skilled in the art will recognize that when the terms "wafer" or "die" are used herein, they may be considered synonymous with the more general terms "substrate" or "target portion," respectively. The substrates described herein may be processed, before or after exposure, in, for example, a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool, and / or an inspection tool. Where appropriate, the disclosure herein may be applied to these and other substrate processing tools. Furthermore, a substrate may be processed multiple times, for example to produce multi-layer ICs, and thus the term substrate, as used herein, may also refer to a substrate that already includes multiple processed layers.

[0137]

[0176] Although specific reference has been made above to the use of embodiments of the invention in the context of optical lithography, it should be understood that the invention can be used in other applications, such as imprint lithography, and is not limited to optical lithography where the context allows. In imprint lithography, a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device is imprinted into a layer of resist supplied to the substrate and the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. Once the resist is cured, the patterning device is removed from the resist leaving a pattern in it.

[0138]

[0177] It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, and thus should be interpreted by one of ordinary skill in the art in light of the teachings herein.

[0139]

[0178] The terms "lens" and "lens element", where 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.

[0140]

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

[0141]

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

[0142]

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

[0143]

[0182] As used herein, the term "optically coupled" generally refers to one coupled element being configured to impart light directly or indirectly to another coupled element.

[0144]

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

[0145]

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

[0146]

[0185] It is understood that the "Description of the Invention" section, and not the "Summary" and "Abstract" sections, are intended to be used to interpret the claims. The "Summary" and "Abstract" sections may describe one or more exemplary embodiments of the invention as envisioned by the inventors, but cannot describe all exemplary embodiments, and therefore are not intended to limit the scope of the invention and the appended claims in any way.

[0147]

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

[0148]

[0187] Various embodiments of the present system and method are disclosed in the following list of numbered clauses: Further features, characteristics, and exemplary technical solutions of the present disclosure are described below in terms of clauses that may optionally be claimed in any combination.

[0149] 1. A wafer alignment measurement system comprising: an illumination source; a radiation beam output from the illumination source; a first set of variable focal length lenses configured to receive the radiation beam, the first set of variable focal length lenses being controllable to control the illumination spot size at the wafer; a second set of variable focal length lenses, one of which is positioned in the output channel and the other of which is positioned in the objective system, the second set of variable focal length lenses being controllable to control the focal height of the output from the objective system; and a third set of variable focal length lenses positioned in a pupil plane downstream of the objective system, the third set of variable focal length lenses being controllable to control at least one of spot shift and higher diffraction orders. 2. A wafer alignment measurement system as described in clause 1, wherein the first set of variable focal length lenses is positioned within the illumination system. 3. A wafer alignment measurement system according to any of the preceding clauses, wherein the first variable focal length lens is offset from the optical axis of the radiation beam. 4. A wafer alignment measurement system according to any of the preceding clauses, wherein there are "N" output channels and "N+1" second variable focal length lenses, one second variable focal length lens in each output channel and one second variable focal length lens in the objective system. 5. A wafer alignment measurement system according to any preceding clause, wherein a third set of variable focal length lenses is positioned at a pupil plane. 6. A wafer alignment measurement system according to any preceding clause, wherein the first, second, and third sets of variable focal length lenses are controllable by applying voltages to the first, second, and third sets of variable focal length lenses. 7. A wafer alignment measurement system comprising an illumination source, a radiation beam output from the illumination source, and at least two variable focal length lenses configured to receive the radiation beam, the at least two variable focal length lenses being controllable to control the illumination spot size at the wafer. 8. A wafer alignment measurement system according to any preceding clause, wherein the variable focal length lens is positioned within the illumination system. 9. A wafer alignment measurement system according to any preceding clause, wherein the variable focal length lens is positioned within the illumination system between the illumination relay lens and the aperture stop. 10. A wafer alignment measurement system according to any preceding clause, wherein the variable focal length lens is controllable by applying a voltage to the variable focal length lens. 11. A wafer alignment measurement system according to any of the preceding clauses, wherein one variable focal length lens is offset from the optical axis of the radiation beam. 12. A wafer alignment measurement system comprising an illumination source and at least two variable focal length lenses, one positioned in the output channel and one positioned in the objective, the at least two variable focal length lenses being controllable to control the focal height of the output from the objective. 13. A wafer alignment measurement system according to any preceding clause, wherein the output of the illumination source is a beam of radiation that reflects off the wafer. 14. A wafer alignment measurement system according to any preceding clause, wherein the radiation beam passes through a variable focal length lens after reflecting off the wafer. 15. A wafer alignment measurement system according to any of the preceding clauses, wherein there are "N" output channels and "N+1" variable focal length lenses, one variable focal length lens in each output channel and one variable focal length lens in the objective system. 16. A wafer alignment measurement system according to any preceding clause, wherein the variable focal length lens is controllable by applying a voltage to the variable focal length lens. 17. A wafer alignment measurement system comprising an illumination source, a radiation beam output from the illumination source and traveling to an objective system, and at least two variable focal length lenses positioned in a pupil plane downstream of the objective system, the at least two variable focal length lenses being controllable to control at least one of spot shift and higher diffraction orders. 18. A wafer alignment measurement system according to any of the preceding clauses, wherein the variable focal length lens is positioned at a pupil plane. 19. A wafer alignment measurement system according to any preceding clause, wherein the variable focal length lens is positioned at a pupil plane between the objective and the self-referencing interferometer. 20. A wafer alignment measurement system according to any preceding clause, wherein the variable focal length lens compensates for spot shift. 21. A wafer alignment measurement system according to any preceding clause, wherein the variable focal length lens compensates for higher diffraction orders. 22. A wafer alignment measurement system according to any preceding clause, wherein the variable focal length lens is controllable by applying a voltage to the variable focal length lens. 23. A wafer alignment measurement method comprising: generating a radiation beam output by an illumination source; receiving the radiation beam by a first set of variable focal length lenses; controlling the first set of variable focal length lenses to vary an illumination spot size at the wafer; positioning a second set of variable focal length lenses, wherein one lens in the second set of variable focal length lenses is positioned in an output channel and another lens in the second set of variable focal length lenses is positioned in an objective system; controlling the second set of variable focal length lenses to vary a focal height of an output from the objective system; positioning a third set of variable focal length lenses in a pupil plane downstream of the objective system; and controlling the third set of variable focal length lenses to vary at least one of a spot shift and higher diffraction orders. 24. The wafer alignment measurement method of clause 23, wherein a first set of variable focal length lenses is positioned within the illumination system. 25. A wafer alignment measurement method according to any preceding clause, wherein the first variable focal length lens is offset from the optical axis of the radiation beam. 26. A wafer alignment measurement method according to any of the preceding clauses, wherein there are "N" output channels and "N+1" second variable focal length lenses, one second variable focal length lens in each output channel and one second variable focal length lens in the objective system. 27. A wafer alignment measurement method according to any preceding clause, wherein a third set of variable focal length lenses is positioned at the pupil plane. 28. A wafer alignment measurement method described in any of the preceding clauses, wherein the first, second, and third sets of variable focal length lenses are controllable by applying voltages to the first, second, and third sets of variable focal length lenses. 29. A wafer alignment measurement method comprising: generating a radiation beam output from an illumination source; receiving the radiation beam by at least two variable focal length lenses; and controlling the variable focal length lenses to vary an illumination spot size at the wafer. 30. A wafer alignment measurement method according to any preceding clause, wherein the variable focal length lens is positioned within the illumination system. 31. A wafer alignment measurement method according to any preceding clause, wherein the variable focal length lens is positioned within the illumination system between the illumination relay lens and the aperture stop. 32. A wafer alignment measurement method according to any preceding clause, wherein the variable focal length lens is controllable by applying a voltage to the variable focal length lens. 33. A wafer alignment measurement method according to any of the preceding clauses, wherein one variable focal length lens is offset from the optical axis of the radiation beam. 34. A wafer alignment measurement method including an illumination source and at least two variable focal length lenses, one positioned in the output channel and one positioned in the objective system, the at least two variable focal length lenses being controllable to control the focal height of the output from the objective system. 35. A wafer alignment measurement method according to any preceding clause, wherein the output of the illumination source is a radiation beam that reflects off the wafer. 36. A wafer alignment measurement method according to any preceding clause, wherein the radiation beam passes through a variable focal length lens after reflecting off the wafer. 37. A wafer alignment measurement method according to any of the preceding clauses, wherein there are "N" output channels and "N+1" variable focal length lenses, one variable focal length lens in each output channel and one variable focal length lens in the objective system. 38. A wafer alignment measurement method according to any preceding clause, wherein the variable focal length lens is controllable by applying a voltage to the variable focal length lens. 39. A wafer alignment measurement method comprising: generating a radiation beam output from an illumination source and traveling to an objective; positioning at least two variable focal length lenses in a pupil plane downstream of the objective; and controlling the variable focal length lenses to vary at least one of a spot shift and higher diffraction orders. 40. A wafer alignment measurement method according to any of the preceding clauses, wherein the variable focal length lens is positioned at the pupil plane. 41. A wafer alignment measurement method according to any preceding clause, wherein the variable focal length lens is positioned at a pupil plane between the objective and the self-referencing interferometer. 42. A wafer alignment measurement method according to any of the preceding clauses, wherein a variable focal length lens compensates for spot shift. 43. A wafer alignment measurement method according to any preceding clause, wherein the variable focal length lens compensates for higher diffraction orders. 44. A wafer alignment measurement method according to any preceding clause, wherein the variable focal length lens is controllable by applying a voltage to the variable focal length lens.

[0150]

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

[0151]

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

Claims

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

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

3. The wafer alignment measurement system of claim 2 , wherein one first variable focal length lens is offset from the optical axis of the radiation beam.

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

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

6. 2. The wafer alignment measurement system of claim 1, wherein the first, second, and third sets of variable focal length lenses are controllable by applying voltages to the first, second, and third sets of variable focal length lenses.

7. an illumination source; a radiation beam output from the illumination source; and at least two variable focal length lenses configured to receive the radiation beam, the at least two variable focal length lenses being controllable to control an illumination spot size at the wafer; A wafer alignment measurement system comprising:

8. The wafer alignment measurement system of claim 7 , wherein the variable focal length lens is positioned within an illumination system.

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

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

11. The wafer alignment measurement system of claim 7 , wherein one variable focal length lens is offset from the optical axis of the radiation beam.

12. generating a radiation beam output by an illumination source; receiving the radiation beam with a first set of variable focal length lenses; controlling the first set of variable focal length lenses to vary an illumination spot size at a wafer; positioning a second set of variable focal length lenses, wherein one lens of the second set of variable focal length lenses is positioned in the output channel and another lens of the second set of variable focal length lenses is positioned in the objective; controlling the second set of variable focal length lenses to vary the focal height of the output from the objective; positioning a third set of variable focal length lenses in a pupil plane downstream of the objective; controlling the third set of variable focal length lenses to vary at least one of spot shift and higher diffraction orders; A wafer alignment measurement method comprising:

13. The wafer alignment measurement method of claim 12 , wherein the first set of variable focal length lenses is positioned within an illumination system.

14. 14. The wafer alignment measurement method of claim 13, wherein one first variable focal length lens is offset from the optical axis of the radiation beam.

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

Images