Design of Multiple Off-Axis Illumination Beams for Wafer Alignment Sensors

Abstract

A novel approach for an alignment system by generating off-axis illumination beams using glass plates is described. To generate a pair of off-axis illumination beams, a pair of glass plates are inserted into the alignment system. The off-axis illumination beams pass through an aperture stop. A transmissive optical system with a plurality of total reflection mirrors reflects the beams towards the objective system. Then, the objective system focuses the beams onto alignment marks on the substrate. Next, the diffracted beams are detected and analyzed to determine the alignment of the substrate. The compact nature of the glass plate alignment system significantly reduces the footprint of the optical system.

Description

Technical Field

[0001] Cross - reference to related applications

[0001] This application claims the priority of U.S. Application No. 63 / 355,220, filed on June 24, 2022, which is hereby incorporated by reference in its entirety.

Background Art

[0002]

[0002] The present disclosure relates to an alignment system that can be used, for example, in a lithographic apparatus.

[0003]

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. The lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that case, a patterning device (alternatively referred to as a mask or reticle) can be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g., consisting of part of one or more dies) of a substrate (e.g., a silicon wafer) having a layer of radiation - sensitive material (resist). Generally, a single substrate includes a network of adjacent target portions that are exposed continuously. Well - known lithographic apparatuses include so - called steppers, in which each target portion is irradiated by exposing the entire pattern onto the target portion in one exposure, and so - called scanners, in which the pattern is scanned in a given direction (the "scanning" direction) by a beam while simultaneously scanning the substrate in a direction parallel or anti - parallel to this direction so that each target portion is irradiated. It is also possible to transfer the pattern from the patterning device to the substrate by printing the pattern onto the substrate. As another lithographic system, there is an interference lithographic system in which there is no patterning device, but the light beam is split into two beams and the two beams are made to interfere at the target portion of the substrate by using a reflection system. Due to this interference, lines are formed on the target portion of the substrate.

[0004]

[0004] During the lithography operation, different processing steps may require the sequential formation of different layers on a substrate. Therefore, it may be necessary to align the substrate with high precision with respect to the previously formed pattern on the substrate. In general, alignment marks, which may include diffraction gratings, are arranged on the substrate so as to be aligned and positioned with respect to a second object. A lithographic apparatus can use an alignment system to detect the position of the alignment marks and to use the alignment marks to align the substrate and guarantee accurate exposure from the mask.

[0005]

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

[0006]

[0006] Alignment can be performed using an off-axis illumination beam. An illumination beam is considered off-axis when it is not perpendicular to the substrate. This is to be compared with on-axis illumination where the center of the optical axis descends perpendicular to the substrate. Off-axis illumination helps to detect finer pitch alignment marks using an existing objective system. As a result, the process window can be increased for the consumer.

Summary of the Invention

[0007]

[0007] A novel system and method for generating an off-axis illumination beam are disclosed. Off-axis illumination using a glass plate design results in a savings of space within the optical system when compared to grid-based off-axis illumination. By using a glass plate for illumination, it is possible to generate collinear beams of different wavelengths, rather than the dispersed light spectrum in the case of grid-based illumination. The glass plate can be finely adjusted, enabling better control of the off-axis illumination beam.

[0008]

[0008] According to one embodiment, an alignment illumination system includes an illumination source, at least one pair of glass plates, a transmissive optical system including at least one reflecting mirror configured to reflect radiation received from the glass plates, and an objective system configured to focus light from the transmissive optical system onto an object to be irradiated. Each glass plate has a plurality of spot mirrors that can reflect, or partially reflect and transmit, an illumination beam from the illumination source.

[0009]

[0009] In one embodiment, the optical system reflects and diffracts an illumination beam to generate a pair of off-axis illumination beams. In one embodiment, the off-axis illumination beams in each pair are in phase with each other.

[0010]

[0010] In one embodiment, the optical path difference between the off-axis illumination beams in each pair can be controlled by tilting one glass plate in the pair relative to the other using a glass plate drive motor.

[0011]

[0011] In one embodiment, the off-axis illumination beam has a small color separation or is collinear for different wavelengths. In one embodiment, the irradiation angles of all colors of the off-axis illumination beam are the same.

[0012]

[0012] In one embodiment, the spectral components of the off-axis or on-axis illumination beam can be controlled by adding a thin film coating on the spot mirror.

[0013]

[0013] In one embodiment, the off-axis illumination beam can be polarized by adding a thin film coating on the spot mirror. In one embodiment, the off-axis illumination beam is unpolarized.

[0014]

[0014] In one embodiment, the aperture plate positioned between the glass plate and the transmissive optical system blocks unwanted radiation. In one embodiment, the aperture plate blocks the on-axis illumination beam and passes the off-axis illumination beam. In one embodiment, the aperture plate blocks the off-axis illumination beam and passes the on-axis illumination beam. In one embodiment, the aperture plate passes both the on-axis illumination beam and the off-axis illumination beam.

[0015]

[0015] In one embodiment, the plurality of spot mirrors includes a metal or a dielectric or a combination thereof.

[0016]

[0016] In one embodiment, at least one pair of glass plates includes exactly two glass plates. In one embodiment, the two glass plates generate a pair of off-axis illumination beams.

[0017]

[0017] In one embodiment, at least one pair of glass plates includes four glass plates for generating two pairs of off-axis illumination beams.

[0018]

[0018] In one embodiment, the alignment system measures the alignment of an object. To generate a pair of off-axis illumination beams, an alignment illumination system and an adjustable aperture stop can be inserted into the alignment system.

[0019]

[0019] According to one embodiment, the alignment system includes a light source, at least a pair of glass plates, an aperture stop, a transmissive optical system including at least one reflecting mirror configured to reflect the radiation received from the glass plates, an objective system configured to focus the light from the transmissive optical system toward an object to be irradiated, an object stage for holding the object, and an interferometer configured to measure marks on the object. Each glass plate has a plurality of spot mirrors that can reflect, or partially reflect and transmit, the illumination beam from the light source.

[0020]

[0020] According to one embodiment, a method for alignment using an alignment illumination system includes irradiating an illumination beam from a light source, reflecting the illumination beam from the light source using at least one pair of glass plates, reflecting the radiation received from the glass plates using a transmissive optical system including at least one reflecting mirror, and focusing the light from the transmissive optical system toward an object to be irradiated using an objective system. Each glass plate has a plurality of spot mirrors.

[0021]

[0021] According to one embodiment, a method for alignment using an alignment illumination system includes irradiating an illumination beam from a light source, reflecting, or partially reflecting and transmitting, the illumination beam from the light source using at least one pair of glass plates, filtering the radiation received from the glass plates using an aperture stop, reflecting the radiation received from the aperture stop using a transmissive optical system including at least one reflecting mirror, focusing the light from the transmissive optical system toward an object to be irradiated held by an object stage using an objective system, and measuring marks on the object using an interferometer. Each glass plate has a plurality of spot mirrors.

[0022]

[0022] Further features and advantages of the present invention will be described in detail below in conjunction with the structure and operation of various embodiments of the present invention with reference to the accompanying drawings. It should be noted that the present invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Based on the teachings contained herein, additional embodiments will be apparent to those skilled in the art.

Brief Description of the Drawings

[0023]

[0023] The accompanying drawings, which are incorporated herein and form a part of this specification, illustrate the present invention and, together with the following description, explain the principles of the present invention and serve to enable one skilled in the art to make and use the present invention.

Figure 1

[0024] It is a schematic diagram of an alignment system using a grid-based illumination structure.

Figure 2A

[0025] It is a schematic diagram of a reflective lithography apparatus according to an embodiment of the present disclosure.

Figure 2B

[0026] It is a schematic diagram of a transmissive lithography apparatus according to an embodiment of the present disclosure.

Figure 2C

[0027] It is a more detailed schematic diagram of a reflective lithography apparatus according to an embodiment of the present disclosure.

Figure 3A

[0028] It is a schematic diagram of a lithographic cell according to an embodiment of the present disclosure.

Figure 3B

[0029] It is a schematic diagram of an inspection system according to an embodiment of the present disclosure.

Figure 3C

[0030] It is a schematic diagram of a metrology technique according to an embodiment of the present disclosure.

Figure 3D

[0031] It is a schematic diagram of the relationship between the radiation illumination spot of an inspection system and a metrology target according to an embodiment of the present disclosure.

Figure 4

[0032] Schematic diagram of an alignment system according to an embodiment of the present disclosure.

Figure 5

[0033] Schematic diagram of an optical system of an alignment system having a pair of off-axis illumination beams according to an embodiment of the present disclosure.

Figure 6

[0034] Top view of an optical system of an alignment system having two pairs of off-axis illumination beams according to an embodiment of the present disclosure.

Figure 7

[0035] Side view of an optical system of an alignment system having two pairs of off-axis illumination beams according to an embodiment of the present disclosure.

Figure 8

[0036] View of an optical system of an alignment system having two pairs of off-axis illumination beams according to an embodiment of the present disclosure rotated.

DETAILED DESCRIPTION OF THE INVENTION

[0024]

[0037] FIG. 1 shows an alignment system 100 that generates off-axis illumination beams using a grating structure 109. The alignment system 100 includes an illumination system 112, a grating structure 109, a lens 110, a mirror 111, an objective system 117, a stage 122 movable along a direction 124, an image rotation interferometer 126, a detector 128, and a signal analyzer 130. The illumination system 112 generates a radiation beam 113 that impinges on the grating structure 109. The grating of the grating structure 109 diffracts the radiation beam 113 into wide-angle rays. Next, the lens 110 focuses the radiation beam 113 onto the mirror 111. The mirror 111 can be configured to direct the radiation beam 113 onto the substrate 120 to irradiate the alignment mark 118.

[0025]

[0038] The radiation beam 113 then reflects from the alignment mark 118 to become a diffracted radiation beam 119, and the diffracted radiation beam 119 is directed along the alignment axis 121 towards the image rotation interferometer 127. Thereafter, in order to detect the position of the substrate 120, the signal 127 is passed to the detector 128. The signal analyzer 130 then receives the signal 129 to determine the position of the stage 122 and correlates the position of the stage 122 with the position of the center of symmetry of the alignment mark.

[0026]

[0039] The problem with this grating structure alignment system is that the grating structure diffracts the radiation beam into a wide-angle beam, so that the radiation beam occupies a significant amount of space. In order to maintain all the beams containing colored light at different angles, an enormous volume of the volume dedicated to light transmission is required. As a result, the grating alignment system is cumbersome and difficult to handle.

[0027]

[0040] In contrast to the system shown in FIG. 1, this alignment system uses a glass plate to generate an off-axis illumination beam. As few as two beams can be used, which is far fewer than in the case of a grating. By reducing the amount of the beam from the wide-angle beam used in grating alignment to just two beams of the glass plate alignment, a lot of space within the optical system can be saved. As a result, the footprint of the optical system can be greatly reduced. Further advantages of using a glass plate for alignment include that, in contrast to the dispersed optical spectrum in the case of grating alignment, all wavelengths are collinear. The glass plate can be finely adjusted, enabling better control of the off-axis illumination beam. Another advantage of off-axis alignment using a glass plate is efficiency. While the required number of off-axis illumination beams are generated, grating-based illumination generally has additional diffraction orders that must be blocked or removed from the system.

[0028]

[0041] However, before describing such embodiments in more detail, it is beneficial to present an exemplary environment in which embodiments of the present invention can be implemented.

[0029] Exemplary reflective and transmissive lithography systems

[0042] FIGS. 2A and 2B are schematic views of a lithography apparatus 200 and a lithography apparatus 200' in which embodiments of the present disclosure can be implemented. The lithography apparatus 200 and the lithography apparatus 200' each include an illumination system (illuminator) IL for conditioning 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, a reticle, or a dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA, and a substrate table (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. The lithography apparatus 200 and the lithography apparatus 200' also include a projection system PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., including one or more dies) of the substrate W. In the lithography apparatus 200, the patterning device MA and the projection system PS are reflective. In the lithography apparatus 200', the patterning device MA and the projection system PS are transmissive.

[0030]

[0043] The illumination system IL may include various optical components, such as refractive optical components, reflective optical components, refractive-reflective optical components, magneto-optical components, electro-magnetic optical components, electro-static optical components, or other types of optical components, or combinations thereof, for guiding, shaping, or controlling the radiation beam B.

[0031]

[0044] The support structure MT holds the patterning device MA in a manner that depends on, for example, the orientation of the patterning device MA with respect to a reference frame, the design of at least one of the lithographic apparatuses 200 and 200’, and other conditions such as whether the patterning device MA is held in a vacuum environment. The support structure MT may use mechanical clamping, vacuum clamping, electrostatic clamping, or other clamping techniques for holding 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, for example, that the patterning device MA is in the desired position with respect to the projection system PS.

[0032]

[0045] The term “patterning device” MA should be interpreted broadly as referring to any device that can be used to impart a pattern to a cross-section of the radiation beam B in order to create a pattern in a target portion C of the substrate W. The pattern imparted to the radiation beam B may correspond to a particular functional layer in a device that is created in the target portion C to form an integrated circuit.

[0033]

[0046] The patterning device MA may be transmissive (such as the lithographic apparatus 200’ in Fig. 2B) or reflective (such as the lithographic apparatus 200 in Fig. 2A). 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 masks, Levenson-type phase-shift masks, half-tone type phase-shift masks, and various hybrid-type masks. An example of a programmable mirror array uses a matrix array of small mirrors, each of which can be individually tilted so as to reflect an incident radiation beam in a plurality of different directions. The tilted mirrors impart a pattern to the radiation beam reflected by the matrix of small mirrors.

[0034]

[0047] The term "projection system" PS can include any type of projection system, including refractive optical systems, reflective optical systems, catadioptric optical systems, magneto-optical systems, electro-magnetic optical systems, and electro-static optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or other factors such as the use of an immersion liquid or a vacuum on the substrate W. A vacuum environment can be used for EUV or electron beam radiation because other gases absorb excessive radiation or electrons. Thus, with the help of vacuum walls and vacuum pumps, a vacuum environment can be provided throughout the beam path.

[0035]

[0048] The lithographic apparatus 200 and / or the lithographic apparatus 200' may be of a type having two or more (dual stage in the case of two) substrate supports WT (and / or two or more mask tables). In such a "multi-stage" machine, additional substrate tables WT may be used in parallel, or preparation steps may be performed on one or more tables while one or more other substrate tables WT are being used for exposure. In some situations, the additional table may not be a substrate table WT.

[0036]

[0049] Referring to FIGS. 2A and 2B, the illuminator IL receives a radiation beam from the radiation source SO. For example, if the source SO is an excimer laser, the source SO and the lithographic apparatuses 200, 200' may be separate physical entities. In such a case, the source SO is not considered to form part of the lithographic apparatus 200 or 200', and the radiation beam B is sent from the source SO to the illuminator IL with the help of a beam delivery system BD (in FIG. 2B) including, for example, suitable guiding mirrors and / or a beam expander. In other cases (for example, if the source SO is a mercury lamp), the source SO can also be made an integral part of the lithographic apparatuses 200, 200'. The source SO and the illuminator IL can be called a radiation system together with the beam delivery system BD if necessary.

[0037]

[0050] The illuminator IL can include an adjuster AD (in FIG. 2B) that adjusts the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radius ranges (usually referred to as “σ-outer” and “σ-inner” respectively) of the intensity distribution within the pupil plane of the illuminator can be adjusted. Additionally, the illuminator IL can include various other components (in FIG. 2B) such as an integrator IN and a condenser CO. By using the illuminator IL to adjust the radiation beam B, a desired uniformity and intensity distribution can be imparted to the cross-section of the radiation beam B.

[0038]

[0051] Referring to FIG. 2A, the radiation beam B is incident on a patterning device (e.g., a mask) MA held on a support structure (e.g., a mask table) MT and is patterned by the patterning device MA. In the lithographic apparatus 200, the radiation beam B is reflected from the patterning device (e.g., a mask) MA. After being reflected from the patterning device (e.g., a mask) MA, the radiation beam B passes through the projection system PS, which focuses the radiation beam B onto a target portion C of the substrate W. With the aid of a second positioner PW and a position sensor IF2 (e.g., an interferometer device, a linear encoder, or a capacitance sensor), the substrate table WT can be accurately moved (e.g., to position different target portions C within 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., a mask) MA with respect to the path of the radiation beam B. The patterning device (e.g., a mask) MA and the substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0039]

[0052] Referring to FIG. 2B, the radiation beam B is incident on a patterning device (e.g., mask MA) held on a support structure (e.g., mask table MT) and is patterned by the patterning device. After passing through the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto the target portion C of the substrate W. The projection system has a pupil PPU conjugate to the pupil IPU of the illumination system. The various parts of the radiation originate from the intensity distribution in the pupil IPU of the illumination system, cross the mask pattern without being affected by diffraction in the mask pattern, and create an image of the intensity distribution in the pupil IPU of the illumination system.

[0040]

[0053] With the aid of the second positioner PW and the position sensor IF (e.g., an interferometer device, a linear encoder, or a capacitance sensor), the substrate table WT can be accurately moved (e.g., to position different target portions C within the path of the radiation beam B). Similarly, the first positioner PM and another position sensor (not shown in FIG. 2B) can be used to accurately position the mask MA with respect to the path of the radiation beam B (e.g., after mechanically retrieving it from a mask library or during scanning).

[0041]

[0054] Generally, the movement of the mask table MT can be achieved with the help of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning) that form part of the first positioner PM. Similarly, the movement of the substrate table WT can be achieved using a long-stroke module and a short-stroke module that form part of the second positioner PW. In the case of a stepper (in contrast to a scanner), the mask table MT may be connected only to the short-stroke actuator or may be fixed. The mask MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. The (exemplary) substrate alignment marks occupy dedicated target portions, but the substrate alignment marks can also be placed within the space between the target portions (known as scribe line alignment marks). Similarly, in a situation where one or more dies are provided on the mask MA, the mask alignment marks may be placed between the dies.

[0042]

[0055] The mask table MT and the patterning device MA may be within a vacuum chamber, and a vacuum in-chamber robot IVR can be used to move patterning devices such as masks in and out of the vacuum chamber. Alternatively, when the mask table MT and the patterning device MA are outside the vacuum chamber, an out-of-vacuum robot can be used for various transport operations, similar to the vacuum in-chamber robot IVR. Both the in-vacuum and out-of-vacuum robots need to be calibrated for the smooth movement of any payload (e.g., a mask) to a fixed kinematic mount of the relay station.

[0043]

[0056] The lithographic apparatuses 200 and 200’ can be used in at least one of the following modes.

[0044]

[0057] 1. In the step mode, while keeping the support structure (e.g., mask table) MT and the substrate table WT basically stationary, the entire pattern imparted to the radiation beam B is projected onto the target portion C at once (i.e., single static exposure). Then, the substrate table WT can be shifted in the X and / or Y directions, thereby enabling another target portion C to be exposed.

[0045]

[0058] 2. In the scan mode, while synchronously scanning the support structure (e.g., mask table) MT and the substrate table WT, the pattern imparted to the radiation beam B is projected onto the target portion C (i.e., single dynamic exposure). The speed and direction of the substrate table WT relative to the support structure (e.g., mask table) MT can be determined by the (reduction) magnification and image inversion characteristics of the projection system PS.

[0046]

[0059] 3. In another mode, while keeping the support structure (e.g., mask table) MT basically stationary and moving or scanning the substrate table WT while holding the programmable patterning device, the pattern imparted to the radiation beam B is projected onto the target portion C. A pulsed radiation source SO can be used, and further, the programmable patterning device is updated as needed after each movement of the substrate table WT or between consecutive radiation pulses during scanning. This operating mode can be easily applied to maskless lithography using a programmable patterning device such as a programmable mirror array.

[0047]

[0060] Combinations and / or variations of the above usage modes, or completely different usage modes, can also be used.

[0048]

[0061] In some embodiments, the lithographic apparatus 200 includes an extreme ultraviolet (EUV) source configured to generate a beam of EUV radiation for EUV lithography. Generally, the EUV radiation source is configured within a radiation system, and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV source.

[0049]

[0062] FIG. 2C shows the lithographic apparatus 200 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 the closed structure 220 of the source collector apparatus SO. An EUV emission plasma 210 can be formed by a discharge generating plasma source. The EUV radiation can be generated by a gas or vapor (such as Xe gas, Li vapor, or Sn vapor) in which a high-temperature plasma 210 is generated to emit radiation within the EUV region of the electromagnetic spectrum. The high-temperature plasma 210 is generated, for example, by causing at least an incompletely ionized plasma by means of a discharge. For efficient radiation generation, for example, Xe, Li, Sn vapor with a partial pressure of 10 Pa or any other suitable gas or vapor may be required. In one embodiment, an excited tin (Sn) plasma is supplied to generate EUV radiation.

[0050]

[0063] The radiation emitted by the high-temperature plasma 210 is passed from the source chamber 211 into the collector chamber 212 through an optional gas barrier or contaminant trap 230 (sometimes also referred to as a contaminant barrier or foil trap) positioned within or behind the opening of the source chamber 211. The contaminant trap 230 may include a channel structure. The contaminant trap 230 may also include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 230 further shown herein includes at least a channel structure well-known in the art.

[0051]

[0064] The collector chamber 212 may include a radiation collector CO, which may be a so-called grazing incidence type collector. The radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation traversing the radiation collector CO can be reflected by the grating spectral filter 240 and focused on the virtual light source point IF. The virtual light source point IF is generally called an intermediate focus, and the source collector device is arranged such that the intermediate focus IF is positioned at or near the aperture 219 of the closed structure 220. The virtual light source point IF is an image of the radiation emitting plasma 210. The grating spectral filter 240 is used particularly for suppressing infrared (IR) radiation.

[0052]

[0065] Next, the radiation traverses the illumination system IL, which can include a facet field mirror device 222 and a facet pupil mirror device 224 arranged to provide a desired angular distribution of the radiation beam 221 and a desired radiation intensity uniformity in the patterning device MA. When the radiation beam 221 is reflected by the patterning device MA held by the support structure MT, a patterned beam 226 is formed, and the patterned beam 226 is imaged onto the substrate W held by the wafer stage or substrate table WT via the reflection elements 228, 229 by the projection system PS.

[0053]

[0066] Generally, there may be more elements in the illumination optical unit IL and the projection system PS than shown in the figure. The grating spectral filter 240 can be optionally present depending on the type of lithographic apparatus. Further, there may be more mirrors than shown in the figure. For example, the projection system PS may have 1 to 6 additional reflection elements compared to those shown in FIG. 2.

[0054]

[0067] As shown in FIG. 2, the collector optical system CO is shown as a nested collector including grazing incidence reflectors 253, 254, and 255 as merely an example of a collector (or a collector mirror). The grazing incidence reflectors 253, 254, and 255 are axially symmetrically arranged around the optical axis O, and this type of collector optical system CO is preferably used in combination with a discharge generating plasma source, often called a DPP source.

[0055] Exemplary lithographic cell

[0068] FIG. 3A shows a lithographic cell 300, often also called a litho cell or a cluster. The lithographic apparatus 200 or 200' may form part of the lithographic cell 300. The lithographic cell 300 may also include apparatus for performing pre- and post-exposure processes on a substrate. Conventionally, these include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a cooling plate CH, and a bake plate BK. A substrate handler or robot RO picks up substrates from the input / output ports I / O1, I / O2, moves them between different processing apparatuses, and then delivers them to the loading bay LB of the lithographic apparatus. These devices, often collectively called a track, are under the control of a track control unit TCU, which itself is controlled by a monitoring control system SCS that also controls the lithographic apparatus via a lithographic control unit LACU. In this way, different apparatuses can be operated to maximize throughput and processing efficiency.

[0056] Embodiment of an alignment system

[0069] To enable alignment, one or more targets are provided, particularly on a substrate. Typically, the targets are specially designed and may include a periodic structure. For example, the target on the substrate can include one or more 1D periodic structures (such as geometric features like a grating), and the 1D periodic structure is printed such that after development, the periodic structure features are formed from solid resist lines. As another example, the target can include one or more 2D periodic structures (such as a grating), and the 2D periodic structure is printed such that after development, one or more periodic structures are formed from solid resist pillars or vias in the resist. Alternatively, the bars, pillars or vias may be etched into the substrate (e.g., within one or more layers on the substrate).

[0057]

[0070] Figure 3B shows an exemplary alignment system 10 that can be used to detect alignment and overlay and / or perform other metrology operations. The alignment system 10 includes a radiation source or illumination source 2 that projects or irradiates radiation onto a substrate W (which may typically include metrology marks). The re-directed radiation is passed to sensors such as a spectrometer 4 that measures the spectrum (intensity as a function of wavelength) of specularly reflected radiation and / or diffracted radiation, as shown, for example, in the left graph of Figure 3C, and / or other sensors. The sensors can generate an alignment signal that conveys alignment data indicative of the characteristics of the reflected radiation. From this data, a structure or profile that gives rise to the detected spectrum can be reconstructed by one or more processors PRO (a generalized example is shown in Figure 3C) or by other operations.

[0058]

[0071] Similar to the lithographic apparatuses 200 and 200' of FIGS. 2A and 2B, one or more substrate tables may be provided to hold the substrate W during the measurement operation. The one or more substrate tables may have a shape similar to or the same as the substrate table WT of FIGS. 2A and 2B. In an example where the inspection system 10 is integrated with the lithographic apparatus, it is even possible to use the same substrate table for the one or more substrate tables. A coarse positioner and a fine positioner may be provided and configured to accurately position the substrate relative to the measurement optical system. For example, various sensors and actuators are provided to obtain the position of the target portion of interest of the structure (e.g., a metrology mark) and move it under the objective lens. Typically, many measurements are made on the target portion of the structure at various locations across the entire substrate W. The substrate support can be moved in the X and Y directions to acquire different targets, and can also be moved in the Z direction to acquire the desired location of the target relative to the focus of the optical system. For example, even if in practice the optical system remains substantially stationary (typically in the X and Y directions, but optionally also in the Z direction) and only the substrate moves, it is preferably described in terms of the objective lens being moved to various locations relative to the substrate for convenience. If the relative position of the substrate and the optical system is correct, whether in the real world one of them is moving, or both are moving, or a part of the optical system is moving (e.g., in the Z and / or tilt directions) while the rest of the optical system remains stationary and the substrate is moving (e.g., in the X and Y directions, but optionally also in the Z and / or tilt directions) is not, in principle, important.

[0059]

[0072] In the case of a typical alignment measurement, the target (portion) 30 on the substrate W may be a 1D grating printed such that after development, bars are formed from solid resist lines (which may be covered by a deposited layer, for example) and / or other materials. Alternatively, the target 30 may be a 2D grating printed such that after development, the grating is formed from solid resist pillars and / or other features within the resist.

[0060]

[0073] Bars, pillars, vias, and / or other features can be etched into or on a substrate (e.g., in one or more layers on the substrate), deposited on the substrate, covered by a deposited layer, and / or can have other characteristics. A target (portion) 30 (e.g., a bar, pillar, via, etc.) is sensitive to changes in processing in a patterning process (e.g., optical aberrations in a lithographic projection system such as a projection system, changes in focus, changes in dose amount, etc.), and as a result, process variations appear as variations in the target 30. Thus, measurement data from the target 30 can be used to determine adjustments to one or more of the manufacturing processes and / or as a basis for making actual adjustments.

[0061]

[0074] For example, measurement data from the target 30 can indicate the overlay of layers of a semiconductor device. Measurement data from the target 30 can be used to determine one or more semiconductor device manufacturing process parameters based on the overlay and to determine adjustments to a semiconductor device manufacturing apparatus based on the one or more determined semiconductor device manufacturing process parameters. In some embodiments, this can include, for example, adjustments to stage position, or can include determining adjustments to mark design, metrology target design, semiconductor device design, radiation intensity, radiation angle of incidence, radiation wavelength, pupil size and / or shape, resist material, and / or other process parameters.

[0062]

[0075] Figure 3D shows a plan view of a typical target (e.g., a metrology mark) 30, along with the extent of a typical radiation illumination spot S in the system of FIG. 5. Typically, in order to obtain a diffraction spectrum free from interference from the surrounding structure, the target 30 is, in one embodiment, a periodic structure (e.g., a grating) that is larger than the width (e.g., diameter) of the illumination spot S. The width of the spot S may be smaller than the width and length of the target. In other words, the target is "underfilled" by the illumination, and the diffraction signal contains substantially no signal from product features or the like outside the target itself. The illumination arrangement may be configured to provide illumination of uniform intensity, for example, across the rear focal plane of the objective system. Alternatively, the illumination can be restricted in the on-axis or off-axis direction, for example, by including an aperture in the illumination path.

[0063]

[0076] FIG. 4 shows a schematic cross-sectional view of an alignment system 400 that can be implemented as part of or in combination with a lithographic apparatus 200 or 200' and / or other lithographic apparatus according to one embodiment. In an example of this embodiment, the alignment system 400 can be configured to align a substrate (e.g., a semiconductor wafer, such as the substrate W described above) with respect to a patterning device (e.g., the patterning device MA described above). The alignment system 400 can further be configured to detect the position 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 the lithographic apparatus 100 or 100'. Such alignment of the substrate can ensure accurate exposure of one or more patterns on the substrate.

[0064]

[0077] According to one embodiment, the alignment system 400 includes a light source 412, an optical system 414, an objective system 417, an image rotation interferometer 426, a detector 428, and a signal analyzer 430. The light source 412 can be configured to provide an electromagnetic narrow-band radiation beam 413 having a first polarization state such as a linearly polarized state. In one example, the narrow-band radiation beam 413 can be within a wavelength spectrum of about 500 nm to about 900 nm. In another example, the narrow-band radiation beam 413 includes a discrete narrow passband within a wavelength spectrum of about 500 nm to about 900 nm. In yet another example, the radiation beam 413 can be monochromatic light provided by a monochromatic light source such as a laser light source of the light source 412. It is also possible to use a multi-color light source such as an LED as the light source 412 to provide a multi-color radiation beam 413.

[0065]

[0078] The optical system 414 can be configured to receive the radiation beam 413. In one example of this embodiment, the optical system can further be configured to direct the radiation beam 413 onto the substrate 420, as shown in FIG. 4. The optical system 414 can include a transmissive optical system including at least one reflective mirror configured to direct the radiation beam 413 toward an alignment mark 418 positioned on the substrate 420. The optical system 414 can also include an optical system that generates additional illumination beams that are split or replicated from the radiation beam 413 and directs them toward the alignment mark 418.

[0066]

[0079] The substrate 420 can be provided on a stage 422 movable along the direction 424. The radiation beam 413 can be configured to irradiate an alignment mark 418 positioned on the substrate 420. In one example of this embodiment, the alignment mark 418 can be coated with a radiation-sensitive film. In another example, the alignment mark 418 can have 180° symmetry. That is, when the alignment mark 418 is rotated 180° about a symmetry axis perpendicular to the plane of the alignment mark 418, the rotated alignment mark 418 can be substantially identical to the non-rotated alignment mark 418.

[0067]

[0080] As shown in FIG. 4, according to one embodiment, the objective system 418 can be configured to direct the diffracted radiation beam 419 towards the image rotation interferometer 426. The objective system 417 can include any suitable number of optical elements suitable for directing the diffracted radiation beam 419. In one exemplary embodiment, the diffracted radiation beam 419 can be at least a portion of the radiation beam 413 diffracted from the alignment mark 418. In FIG. 4, the diffracted radiation beam 419 is shown as passing outside the optical system 414, but it should be noted that the present disclosure is not limited thereto. The optical system 414 can substantially transmit the diffracted radiation beam 419 and pass the diffracted radiation beam 419 through without substantially changing the characteristics of the diffracted radiation beam 419. Further, although the objective system 417 is shown as directing the radiation beam 419 towards the image rotation interferometer 426, it should be noted that the present disclosure is not limited thereto. Other optical arrangements may be used to obtain similar results in detecting the diffraction signal from the alignment mark 418.

[0068]

[0081] In some embodiments, the image rotation interferometer 426 can include any suitable set of optical elements (e.g., a combination of prisms configured to form two images of the alignment mark 418 based on the received diffracted radiation beam 419). It should be understood that although it is not necessary to form a high-quality image, the features of the alignment mark 418 must be resolved. The image rotation interferometer 426 can further be configured to rotate one of the two images by 180° with respect to the other of the two images and recombine the rotated image and the non-rotated image using the interferometer.

[0069]

[0082] Detector 428 may be configured to receive the recombined image and detect interference as a result of the recombined image when the alignment axis 421 of the alignment system 400 passes through the center of symmetry (not shown) of the alignment mark 418. Such interference may be due to, according to an exemplary embodiment, the alignment mark 418 being 180° symmetric and the recombined images causing constructive or destructive interference. Based on the detected interference, detector 428 may be further configured to determine the position of the center of symmetry of alignment mark 418 and thus detect the position of substrate 420. According to one example, alignment axis 421 may be aligned with an optical beam that is perpendicular to substrate 420 and passes through the center of the image rotation interferometer 426.

[0070]

[0083] In some embodiments, signal analyzer 430 may be configured to receive a signal 429 that includes information about the determined center of symmetry. Signal analyzer 430 may be further configured to determine the position of stage 422 and relate the position of stage 422 to the position of the center of symmetry of alignment mark 418. Thus, based on stage 422, the position of alignment mark 418 and thus the position of substrate 420 can be accurately known. Alternatively, signal analyzer 430 may determine the position of alignment system 400 or any other reference element, such that the center of symmetry of alignment mark 418 can be accurately known based on alignment system 400 or any other reference element.

[0071] Embodiments of the optical system

[0084] FIG. 5 shows a schematic cross-sectional view of an optical system 514 according to one embodiment. Optical system 514 may represent an exemplary embodiment of optical system 414 shown in FIG. 4. Illumination beam 513 may be similar to radiation beam 413 described above with reference to FIG. 4. Since illumination beam 513 travels along optical axis 410, it is on-axis.

[0072]

[0085] In an example of this embodiment, the optical system 413 may include a pair of glass plates 550, an aperture plate 552, and a transmissive optical system 553. Each of the glass plates 550 has a plurality of spot mirrors 560 for reflecting and refracting the illumination beam 513. As a result, the illumination beam 513 is incident on the glass plate 550 to generate a pair of illumination beams 515. The illumination beams 515 are off-axis. There is an aperture plate 552 downstream of the glass plate 550, and the aperture plate 552 selectively blocks unwanted radiation. FIG. 5 shows a case where the on-axis illumination beam 513 and the off-axis illumination beam 515 are maintained. There is a transmissive optical system 553 downstream of the aperture plate 552. The transmissive optical system 553 includes a plurality of reflection mirrors 563. Each reflection mirror 563 is associated with an illumination beam. The reflection mirrors 563 reflect the on-axis illumination beam 513 and the off-axis illumination beam 515 toward the objective system 417. The objective system 417 may be configured to focus the illumination beams 513 and 515 onto the substrate 420. The illumination beams 513 and 515 converge on the alignment marks 418 of the substrate 420 shown in FIG. 4.

[0073]

[0086] FIGS. 6 to 8 show a schematic cross-sectional view of an optical system 614 according to an embodiment. FIG. 6 is a top view, FIG. 7 is a side view, and FIG. 8 is a view of the optical system 614 rotated. The optical system 614 may represent an exemplary embodiment of the optical system 414 shown in FIG. 4. The illumination beam 613 may be similar to the radiation beam 413 described above with reference to FIG. 4. Since the illumination beam 613 travels along the optical axis 610, it is on-axis.

[0074]

[0087] In one example of the present embodiment, the optical system 614 may include a pair 650 of first glass plates, a pair 651 of second glass plates, an aperture plate 652, and a transmissive optical system 653. Each of the glass plates 650 and 651 has a plurality of spot mirrors 660 and 661 for reflecting and refracting the radiation beam 613, respectively. As a result, the illumination beam 613 is incident on the pair 650 of first glass plates to generate a pair 615 of first illumination beams, as clearly shown in FIGS. 6 and 8. FIG. 7 shows only the first illumination beam 615 because the second beam 615 is below the first beam 615 in this figure and is covered by the first beam 615 (the first beam 615 also covers the illumination beam 613). Further, as clearly shown in FIGS. 7 and 8, the illumination beam 613 then is incident on the pair 651 of second glass plates to generate a pair 616 of second illumination beams. Similarly to the above, FIG. 6 shows only the first illumination beam 616. The illumination beams 615 and 616 are off-axis illumination beams. Downstream of the glass plates 650 and 651, there is an aperture plate 652, and the aperture plate 652 selectively blocks unwanted radiation. FIGS. 6 to 8 show the case where the off-axis illumination beam 613 and the off-axis illumination beams 615 and 616 are maintained. Downstream of the aperture plate 625, there is a transmissive optical system 653. The transmissive optical system 653 includes a plurality of reflection mirrors 663. Each reflection mirror 663 is associated with the illumination beam. The reflection mirrors 663 reflect the on-axis illumination beam 613 and the off-axis illumination beams 615 and 616 toward the objective system 417, as shown in FIGS. 7 and 8. The objective system 417 may be configured to focus the illumination beams 613, 615, and 616 onto the substrate 420, as shown in FIGS. 7 and 8. The illumination beams 613, 615, and 616 converge on the alignment mark 418 of the substrate 420 shown in FIG. 4.

[0075]

[0088] The above-described embodiment has either one pair or two pairs of off-axis illumination beams, but the system is not so limited. It is also possible to generate two or more pairs of off-axis illumination beams.

[0076]

[0089] The glass plates 550, 650, and 651 are each a pair of glass plates. Each pair of the glass plates 550, 650, and 651 receives the illumination beams 513 and 613 and generates a pair of off-axis illumination beams 515, 615, and 616, respectively. To generate additional pairs of off-axis illumination beams, additional pairs of glass plates can be inserted into the optical path. Further, one glass plate in each pair can be finely tilted with respect to the other to vary the characteristics of the off-axis illumination beams. The glass plates can be tilted using a glass plate drive motor (not shown). As a result, the optical path difference, light quantity, and power between the pairs of beams can be controlled.

[0077]

[0090] The plurality of spot mirrors 560, 660, and 661 are partial reflection spot mirrors or total reflection spot mirrors. A partial reflection spot mirror diffracts a part of the radiation beam while reflecting the rest of the beam. On the other hand, a total reflection spot mirror reflects the entire beam. Each spot mirror is a discrete reflective coating area on the glass plate. The reflective coating includes a metal, a dielectric, or a combination thereof.

[0078]

[0091] The aperture plates 552 and 652 are positioned between the glass plates 550, 650, and 651 and the transmissive optical systems 553 and 653. The aperture plates 552 and 652 block unwanted radiation while allowing a specific illumination beam to pass through and reach the alignment mark 418. The aperture plates 552 and 652 can be moved into and out of the path of the illumination beam using an aperture plate drive motor (not shown). In a first configuration, the aperture plates 552 and 652 block the on-axis illumination beams 513 and 613 and allow the off-axis illumination beams 515, 615, and 616 to pass through. In a second configuration, the aperture plates 552 and 652 block the off-axis illumination beams 515, 615, and 616 and allow the on-axis illumination beams 513 and 613 to pass through. In a third configuration, the aperture plates 552 and 652 allow both the on-axis illumination beams 513 and 613 and the off-axis illumination beams 515, 615, and 616 to pass through.

[0079]

[0092] The transmissive optical systems 553 and 653 include a plurality of reflective mirrors 563. The reflective mirror 653 can be a total reflection type. The number of mirrors in the transmissive optical system is equal to the number of illumination beams. The transmissive optical systems 553 and 653 reflect each of the beams toward the objective system 417.

[0080]

[0093] Further details of the pair of off-axis illumination beams are described below. The pair of off-axis illumination beams 515, 615, and 616 are in phase with each other and have a coincident optical path. Further, the optical path differences between the beams 515, 615, and 616 in each pair can be finely adjusted by tilting one of the glass plates 550, 650, and 651 with respect to the other glass plate in the pair. Additionally, the off-axis illumination beams may be polarized or non-polarized. This can be achieved by adding a thin film coating on the spot mirrors 560, 660, and 661. Alternatively, a polarizer (not shown) in the optical path can change the off-axis illumination beam to either polarized or non-polarized. Since the off-axis illumination beams are generated by glass plates (rather than a grating structure), the off-axis illumination beams can have a small color separation, or be completely colorless, or be collinear for different wavelengths. In other words, the off-axis illumination beams are all the same color and do not have a color spectrum as in the case of a grating structure. As a result, the irradiation angles of all colors of the off-axis illumination beams are the same. Further, the spectral components of the off-axis illumination beams can be controlled by adding a film coating. The film coating changes the power intensity of the off-axis illumination beams.

[0081]

[0094] In some embodiments, the optical systems 514 and 614 can be inserted into an existing alignment system similar to the alignment system 400 of FIG. 4. As a result, the optical systems 514 and 614 are backward compatible and can be used to upgrade an existing alignment system.

[0082]

[0095] Embodiments can be further described using the following clauses. 1. An illumination source, and at least one pair of glass plates, each glass plate having a plurality of spot mirrors capable of reflecting, or partially reflecting and transmitting, an illumination beam from the illumination source. A transmissive optical system comprising at least one reflective mirror configured to reflect radiation received from a glass plate, An objective system configured to focus light from the transmissive optical system onto an object to be irradiated, An alignment illumination system comprising the above. 2. The alignment illumination system according to clause 1, wherein the glass plate reflects and refracts an illumination beam to generate a pair of off-axis illumination beams. 3. The alignment illumination system according to clause 2, wherein the off-axis illumination beams in each pair are in phase with each other. 4. The alignment illumination system according to clause 2, wherein the optical path difference between the off-axis illumination beams in each pair can be controlled by tilting one glass plate in the pair with respect to the other using a glass plate drive motor. 5. The alignment illumination system according to clause 2, wherein the off-axis illumination beams have a small color separation or are collinear for different wavelengths. 6. The alignment illumination system according to clause 2, wherein the irradiation angles of all colors of the off-axis illumination beams are the same. 7. The alignment illumination system according to clause 2, wherein the spectral components of the off-axis illumination beams or the on-axis illumination beams can be controlled by adding a thin film coating on a spot mirror. 8. The alignment illumination system according to clause 2, wherein the off-axis illumination beams are polarized by adding a thin film coating on a spot mirror. 9. The alignment illumination system according to clause 2, wherein the off-axis illumination beams are unpolarized. 10. The alignment illumination system according to clause 1, wherein an aperture plate positioned between the glass plate and the transmissive optical system blocks unwanted radiation. 11. The alignment illumination system according to clause 10, wherein the aperture plate blocks the on-axis illumination beam and allows the off-axis illumination beam to pass through. 12. The aperture plate is the alignment illumination system according to clause 10, which blocks off-axis illumination beams and allows on-axis illumination beams to pass through. 13. The aperture plate is the alignment illumination system according to clause 10, which allows on-axis illumination beams and off-axis illumination beams to pass through. 14. The plurality of spot mirrors are the alignment illumination system according to clause 1, including metal or dielectric or a combination thereof. 15. The at least one pair of glass plates are the alignment illumination system according to clause 1, including exactly two glass plates. 16. The two glass plates are the alignment illumination system according to clause 15, which generates a pair of off-axis illumination beams. 17. The at least one pair of glass plates are the alignment illumination system according to clause 1, including four glass plates for generating two pairs of off-axis illumination beams. 18. An alignment system for measuring the alignment of an object, wherein the alignment illumination system of clause 1 and an adjustable aperture stop can be inserted into the alignment system to generate a pair of off-axis illumination beams. 19. A light source, At least one pair of glass plates, each glass plate having a plurality of spot mirrors capable of reflecting, or partially reflecting and transmitting, the illumination beam from the light source, An aperture stop, A transmissive optical system including at least one reflecting mirror configured to reflect the radiation received from the glass plate, An objective system configured to focus the light from the transmissive optical system onto the object to be irradiated, An object stage for holding the object to be irradiated, An interferometer configured to measure the marks on the object, Comprising an alignment system. 20. A method for alignment using an alignment illumination system, Irradiating an illumination beam from an illumination source, Using at least one pair of glass plates to reflect, or partially reflect and transmit, an illumination beam from an illumination source, each glass plate having a plurality of spot mirrors, Using a transmissive optical system comprising at least one reflective mirror to reflect the radiation received from the glass plate, Using an objective system to focus the light from the transmissive optical system onto an object to be irradiated, A method comprising. 21. The method according to clause 20, wherein the glass plate reflects and refracts the illumination beam to generate a pair of off-axis illumination beams. 22. The method according to clause 21, wherein the off-axis illumination beams in each pair are in the same phase with each other. 23. The method according to clause 21, wherein the optical path difference of the off-axis illumination beams in each pair can be controlled by tilting one of the glass plates in the pair with respect to the other using a glass plate drive motor. 24. The method according to clause 21, wherein the off-axis illumination beams have small color separation or are collinear for different wavelengths. 25. The method according to clause 21, wherein the irradiation angles of all colors of the off-axis illumination beams are the same. 26. The method according to clause 21, wherein the spectral components of the off-axis illumination beams or the on-axis illumination beams can be controlled by adding a thin film coating on the spot mirror. 27. The method according to clause 21, wherein the off-axis illumination beams are polarized by adding a thin film coating on the spot mirror. 28. The method according to clause 21, wherein the off-axis illumination beams are unpolarized. 29. The method according to clause 20, wherein an aperture plate positioned between the glass plate and the transmissive optical system blocks unwanted radiation. 30. The method according to clause 29, wherein the aperture plate blocks the on-axis illumination beam and allows the off-axis illumination beam to pass through. 31. The method according to clause 29, wherein the aperture plate blocks off-axis illumination beams and allows on-axis illumination beams to pass through. 32. The method according to clause 29, wherein the aperture plate allows on-axis illumination beams and off-axis illumination beams to pass through. 33. The method according to clause 20, wherein the plurality of spot mirrors includes metal or dielectric or a combination thereof. 34. The method according to clause 20, wherein the at least one pair of glass plates includes exactly two glass plates. 35. The method according to clause 34, wherein the two glass plates generate a pair of off-axis illumination beams. 36. The method according to clause 20, wherein the at least one pair of glass plates includes four glass plates for generating two pairs of off-axis illumination beams. 37. A method for measuring the alignment of an object using an alignment system, wherein the alignment illumination system and an adjustable aperture stop according to clause 20 can be inserted into the alignment system to generate a pair of off-axis illumination beams. 38. A method for alignment using an alignment illumination system, irradiating an illumination beam from an illumination source, using at least one pair of glass plates to reflect, or partially reflect and transmit, the illumination beam from the illumination source, each glass plate having a plurality of spot mirrors, using an aperture stop to filter the radiation received from the glass plates, using a transmissive optical system having at least one reflecting mirror to reflect the radiation received from the aperture stop, using an objective system to focus the light from the transmissive optical system onto an object to be illuminated held by an object stage, using an interferometer to measure a mark on the object, comprising the method.

[0083]

[0096] This specification discloses one or more embodiments incorporating features of the present invention. The disclosed embodiments merely illustrate the present invention. The scope of the present invention is not limited to the disclosed embodiments. The present invention is defined by the claims appended hereto.

[0084]

[0097] The described embodiments and references in this specification to "an embodiment", "one embodiment", "an exemplary embodiment", etc., indicate that the described embodiments may include a particular feature, structure, or property, but not all embodiments necessarily include such particular feature, structure, or property. Also, such language does not necessarily refer to the same embodiment. Further, when a particular feature, structure, or property is described in connection with one embodiment, it will be understood by those skilled in the art that such feature, structure, or property can be associated with other embodiments, whether or not explicitly stated.

[0085]

[0098] Although this text specifically refers to the use of a lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as in the manufacture of 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 such 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 referred to herein can be processed, before or after exposure, for example, by a track (a tool typically used to apply a layer of resist to the substrate and develop the exposed resist), a metrology tool, and / or an inspection tool. Appropriately, the disclosure herein can be applied to the above-mentioned and other substrate processing tools. Further, since a substrate can be processed multiple times, for example, to produce a multilayer IC, the term "substrate" as used herein can also refer to a substrate that already includes multiple processed layers.

[0086]

[0099] Although the above has specifically referred to the use of embodiments of the present invention in the field of optical lithography, it will be understood that the present invention can also be used in other applications, such as imprint lithography, depending on the context, and is not limited to optical lithography. In imprint lithography, the topography within the patterning device defines the pattern to be created on the substrate. The topography of the patterning device is imprinted into the resist layer supplied to the substrate, and the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. The patterning device is removed from the resist, and a pattern remains inside the resist when it is cured.

[0087]

[0100] It should be understood that the language or terminology in this specification is for the purpose of explanation and not limitation, and thus the terms or language in this specification should be interpreted by those skilled in the art from the perspective of the teachings in this specification.

[0088]

[0101] In the embodiments described in this specification, the terms "lens" and "lens element" can refer to any one or combination of various types of optical components, including refractive optical components, reflective optical components, magneto-optical components, electro-optical components, and electro-static optical components, as long as the context permits.

[0089]

[0102] Furthermore, as used herein, the terms "radiation" and "radiation beam" encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength λ of 365, 248, 193, 157, or 126 nm), extreme ultraviolet (EUV or soft X-ray) radiation (having a wavelength in the range of 5 - 20 nm, such as 13.5 nm), or hard X-rays operating below 5 nm, as well as particle beams such as ion beams or electron beams. Generally, radiation having a wavelength of about 400 - about 700 nm is considered visible radiation, and radiation having a wavelength of about 780 - 3000 nm (or more) is considered IR radiation. UV refers to radiation having a wavelength of about 100 - 400 nm. In lithography, the term "UV" also applies to wavelengths that can be generated by a mercury discharge lamp, G-line 436 nm, H-line 405 nm, and / or I-line 365 nm. Vacuum UV or VUV (i.e., UV absorbed by gas) refers to radiation having a wavelength of about 100 - 200 nm. Deep UV (DUV) generally refers to radiation in the range of 126 nm - 428 nm, and in one embodiment, an excimer laser can generate DUV radiation used within a lithography apparatus. It should be understood that radiation having a wavelength in the range of, for example, 5 - 20 nm relates to radiation in a specific wavelength band where at least a part thereof is in the range of 5 - 20 nm.

[0090]

[0103] As used herein, the term "substrate" generally represents a material onto which subsequent material layers are added. In embodiments, the substrate itself may be patterned, and the materials added thereon may or may not be patterned.

[0091]

[0104] As used herein, the term "in substantial contact" generally refers to elements or structures that are physically in contact with each other, typically with only a small gap resulting from misalignment tolerances. It should be understood that the relative spatial descriptions of one or more specific features, structures, or characteristics used herein (such as "vertically aligned", "substantial contact", etc.) are for illustrative purposes only, and that the actual implementation of the structures described herein may include misalignment tolerances without departing from the spirit and scope of the present disclosure.

[0092]

[0105] As used herein, the term "optically coupled" generally refers to one coupled element being configured to directly or indirectly impart light to another coupled element.

[0093]

[0106] As used herein, the term "optical material" generally refers to a material that enables light or light energy to propagate internally or through it.

[0094]

[0107] Although specific embodiments of the invention are described above, it will be understood that the invention may be practiced in other ways than those described. The description is not intended to limit the invention.

[0095]

[0108] It should be understood that for interpreting the claims, the section "Detailed Description of the Invention" rather than the sections "Summary of the Invention" and "Abstract" is intended to be used. The sections "Summary of the Invention" and "Abstract" can describe one or more exemplary embodiments as envisioned by the inventor, but cannot describe all exemplary embodiments and are thus not intended to limit the present invention and the appended claims in any sense.

[0096]

[0109] The present invention has been described above using functional building blocks that illustrate specific functions and their implementation forms. In this specification, the boundaries of these functional building blocks are arbitrarily defined for convenience of explanation. Alternative boundaries can also be defined as long as the specific functions and their relationships are appropriately implemented.

[0097]

[0110] The above description of specific embodiments fully discloses the general nature of the present invention, so that by applying the knowledge within the technical field, various applications can be easily modified and / or adapted to such specific embodiments without undue experimentation and without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and scope of equivalents of the disclosed embodiments based on the teachings and advice presented in this specification.

[0098]

[0111] 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 by the following claims and their equivalents.

Claims

1. A light source, At least one pair of glass plates, each glass plate having a plurality of spot mirrors capable of reflecting, or partially reflecting and transmitting, an illumination beam from the light source, A transmissive optical system comprising at least one reflecting mirror configured to reflect the radiation received from the glass plate, An objective system configured to focus the light from the transmissive optical system onto an object to be irradiated, An alignment illumination system comprising the above.

2. The alignment illumination system according to claim 1, wherein the glass plate reflects and diffracts the illumination beam to generate a pair of off-axis illumination beams.

3. The alignment illumination system according to claim 2, wherein the off-axis illumination beams in each pair are in the same phase with each other.

4. The alignment illumination system according to claim 2, wherein the optical path difference of the off-axis illumination beams in each pair can be controlled by tilting one of the glass plates in the pair with respect to the other using a glass plate drive motor.

5. The alignment illumination system according to claim 2, wherein the off-axis illumination beam has a small chromatic separation or is collinear for different wavelengths.

6. The alignment illumination system according to claim 2, wherein the irradiation angles of all colors of the off-axis illumination beam are the same.

7. The alignment illumination system according to claim 2, wherein the spectral components of the off-axis illumination beam or the on-axis illumination beam can be controlled by adding a thin film coating on the spot mirror.

8. The alignment illumination system according to claim 2, wherein the off-axis illumination beam is polarized by adding a thin film coating on the spot mirror.

9. The alignment illumination system according to claim 2, wherein the off-axis illumination beam is unpolarized.

10. The alignment illumination system according to claim 1, wherein an aperture plate positioned between the glass plate and the transmissive optical system blocks unwanted radiation.

11. The alignment illumination system according to claim 10, wherein the aperture plate blocks the on-axis illumination beam and allows the off-axis illumination beam to pass through.

12. The alignment illumination system according to claim 10, wherein the aperture plate blocks off-axis illumination beams and allows on-axis illumination beams to pass through. **Claim 13** The alignment illumination system according to claim 10, wherein the aperture plate allows on-axis illumination beams and off-axis illumination beams to pass through. **Claim 14** The alignment illumination system according to claim 1, wherein the plurality of spot mirrors includes metal or dielectric or a combination thereof. **Claim 15** The alignment illumination system according to claim 1, wherein the at least one pair of glass plates includes exactly two glass plates.

Images