Suppression of specular reflection and resolution field stitching of mask absorbers

Abstract

A method and system for generating a mask pattern design for imaging a pattern on a substrate using a lithographic apparatus is described. These methods include identifying a region in a lithographic process between two adjacent exposure fields, and determining a location and geometry of a sub-resolution feature to be placed in a region of an absorber layer of a mask pattern design based on specified background intensity criteria. Geometric parameters such as pitches and critical dimensions (CDs) of the sub-resolution features and positional parameters such as overlay parameters and line end distances are determined to help design and locate the sub-resolution features in the absorber layer to minimize specular reflections of the absorber layer. The location parameters may also help splice images of adjacent exposure fields.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. application No. 63 / 398,929, filed on August 18, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The description herein relates to masks for photolithography processes, and more particularly to designing mask patterns. Background Art

[0004] A lithographic apparatus is a machine configured to apply a desired pattern to a substrate. For example, a lithographic apparatus can be used in the manufacture of integrated circuits (ICs). For example, a lithographic apparatus can project a pattern (also referred to as a "design layout" or "design") of a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate (e.g., a wafer). This manufacturing process may be referred to as a patterning process or a lithographic process. For example, an IC chip in a smartphone may be as small as a human thumb and may include more than 2 billion transistors. Manufacturing ICs is a complex and time-consuming process, with circuit elements in different layers and including hundreds of individual steps. Even an error in one step may cause problems with the final IC and may result in device failure. High process yields and high wafer yields may be affected by the presence of defects, especially where operator intervention is required to check for defects.

[0005] A patterning device may refer to a device that can be used to impart a patterned cross-section to an incident radiation beam corresponding to a pattern to be created in a target portion of a substrate. An example of such a patterning device is a mask. The concept of a mask is well known in lithography and includes mask types such as binary, alternating phase shift and attenuated phase shift, as well as various hybrid mask types. Depending on the pattern on the mask, placing such a mask in a radiation beam results in selective transmission (in the case of a transmission mask) or reflection (in the case of a reflective mask) of the radiation impinging on the mask. In the case of a mask, the support structure is typically a mask stage, which ensures that the mask can be maintained in the desired position in the incident radiation beam and, if necessary, it can be moved relative to the beam.

[0006] An emerging candidate for finer resolution lithography uses extreme ultraviolet (EUV) light to image patterns onto areas of a wafer. The wavelength of EUV light is in the range of about 10nm to 20nm, particularly about 13.4nm to 13.5nm. EUV lithography (EUVL) employs a reflective mask rather than a transmissive mask because such a small wavelength of EUV light is easily absorbed by the materials used in the transmissive mask.

[0007] The EUVL mask includes a reflective film (e.g., a Bragg reflector) disposed on an ultra-low expansion (ULE) substrate and an absorbing material pattern located on the reflective film. Exposure light is incident on the mask at a shallow angle (e.g., about 5 or 6 degrees) relative to the vertical direction of the mask. Some of the incident light is reflected by the reflective film, and some of the incident light is absorbed by the absorbing material, thereby generating a predefined light pattern, which is ultimately applied to an area of ​​the wafer, for example, to expose a pattern in a photoresist on the wafer.

[0008] The pattern of absorbing material and the exposed portion of the reflective film are contained in the active area (also called main pattern, pattern area, image field, etc.) of the EUVL mask. The EUVL mask also includes a border area (also called a black border area) consisting of a strip of absorbing material about 2mm-3mm wide surrounding the active area. The same EUVL mask can be used multiple times in succession to provide the same predefined light pattern on different areas (e.g., different dies) of a single wafer, and the border area is used to isolate individual patterns when they are exposed on the wafer surface. Summary of the invention

[0009] In some embodiments, a non-transitory computer readable medium having instructions is provided, which when executed by a computer causes the computer to perform a method for generating a mask pattern design for imaging a pattern on a substrate using a lithography apparatus. The method includes: identifying an area between two adjacent exposure fields in a lithography process; and determining a location and geometry of a sub-resolution feature to be placed in an area of ​​an absorption layer of the mask pattern design based on a specified background intensity criterion.

[0010] In some embodiments, a method is provided for generating a mask pattern design for imaging a pattern on a substrate using a lithography apparatus. The method includes: determining a pitch of sub-resolution features to be placed in a region of an absorption layer of the mask pattern design based on source parameters of an illumination source of the lithography apparatus; adjusting a duty cycle of the sub-resolution features to achieve a specified background intensity standard; and determining a position of the sub-resolution features in a region of the absorption layer located between two adjacent exposure fields in a lithography process.

[0011] In some embodiments, an apparatus is provided for generating a mask pattern design for imaging a pattern on a substrate using a lithography apparatus. The apparatus includes: a memory storing an instruction set; and a processor configured to execute the instruction set so that the apparatus performs a method, the method including: identifying an area between two adjacent exposure fields in a lithography process; and determining a location and geometry of a sub-resolution feature to be placed in an area of ​​an absorption layer of the mask pattern design based on a specified background intensity criterion. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a schematic diagram of a lithography projection apparatus according to an embodiment.

[0013] Figure 2 is a schematic diagram of another lithography projection apparatus according to an embodiment.

[0014] Figure 3 The flow of a photolithography process or a patterning simulation method according to an embodiment is shown.

[0015] Figure 4A Masks consistent with various embodiments are shown.

[0016] Figure 4B shows consistent with various embodiments Figure 4A The mask scatters light.

[0017] Figure 5A A mask pattern design (or portion thereof) for printing a target pattern on a wafer consistent with various embodiments is shown.

[0018] Figure 5B A sub-resolution grating (SRG) is shown consistent with various embodiments. Figure 5A Mask pattern design.

[0019] Figure 5C shows consistent with various embodiments Figure 5B The mask pattern design is exposed.

[0020] Figure 5D Shown are various embodiments consistent with Figure 5B The mask pattern is designed for the mask.

[0021] Figure 6 Various geometric and positional parameters associated with the SRG are shown consistent with various embodiments.

[0022] Figure 7 is a block diagram of a system for determining position parameters of an SRG in a mask pattern design consistent with various embodiments.

[0023] Figure 8 is a flow chart of a method for determining position parameters of an SRG in a mask pattern design consistent with various embodiments.

[0024] Fig.9A An illumination source for a lithographic apparatus consistent with various embodiments is shown.

[0025] Fig. 9B Graphs of absorber transmittance versus duty cycle of the SRG for different types of masks consistent with various embodiments are shown.

[0026] Fig. 10A Images of to-be-joined patterns and joined patterns are shown consistent with various embodiments.

[0027] Fig. 10B Graphs illustrating intensity distributions associated with a stitching pattern before and after stitching consistent with various embodiments are shown.

[0028] Fig. 10C The variation in critical dimension (CD) of the stitching pattern for various line end distances of the SRG consistent with various embodiments is shown.

[0029] Fig.11 is a flow chart of another method for determining position parameters of an SRG in a mask pattern design consistent with various embodiments.

[0030] Fig.12 The flow of a photolithography process or a patterning simulation method according to an embodiment is shown. DETAILED DESCRIPTION

[0031] In lithography, in order to print a pattern on a substrate, a pattern (also often referred to as a "design layout" or "design") of a patterning device (e.g., a mask) is projected onto a resist layer provided on a substrate (e.g., a wafer). The pattern can be projected onto one or more dies of the substrate. If the die is larger than the lithographic exposure field, multiple exposures may be required to print the pattern layer. Adjacent exposures can be stitched together ("pattern stitching") to form a layer. In the boundary area of ​​two adjacent exposures, especially for "low n" masks, the specular reflection of the mask's absorber layer increases the background intensity and reduces the imaging contrast of the area (e.g., for dense lines, the contrast loss exceeds 30%). In some embodiments, it is desirable to significantly reduce the background intensity (e.g., at least 2x to 4x) to solve the problem of pattern stitching. Additional deep ultraviolet (DUV) light from the secondary exposure may also reduce the contrast. Absorber specular reflections can be reduced in a variety of ways. For example, absorber specular reflections can be suppressed by using a three-tone mask with a black border (BB) absorber on top of the default absorber, including a grating for suppressing DUV. However, the BB boundary cannot be placed close enough to the field boundary with high precision. High transmission attenuation phase-shift masks are usually not suitable for pattern stitching.

[0032] According to the present disclosure, the absorber of the mask is patterned with a sub-resolution feature, such as a sub-resolution grating (SRG), which scatters light outside the projection system (e.g., outside the pupil of the illumination source), thereby reducing absorber reflection in the BB region. By configuring the duty cycle (e.g., CD to pitch ratio) of the SRG to a specified value, first-order intensity light is scattered outside the pupil of the illumination source, and zero-order intensity light is suppressed or eliminated, thereby reducing the background intensity of the boundary area of ​​two adjacent exposures, and pattern stitching is achieved. At the specified duty cycle, destructive interference is generated between the zero-order contributions of the absorption layer and the non-absorption layer of the mask, which cancel or suppress each other, thereby reducing the intensity. In some embodiments, the geometry of the SRG can be determined based on the source parameters of the illumination source, and the position of the SRG in the absorption layer of the mask can be determined based on the parameters that contribute to the CD variation of the target pattern to be stitched on the stitching line ("stitching pattern"). The SRG can be incorporated into the mask pattern design, and the mask can be manufactured using the mask pattern design for lithography to print the target pattern on the substrate.

[0033] Figure 1 A lithographic apparatus according to one or more embodiments is schematically depicted. The apparatus comprises:

[0034] - an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or DUV radiation);

[0035] a first object holder or support structure (e.g., mask table) MT configured to hold a patterning device (e.g., mask) MA and connected to a first positioner PM configured to accurately position the patterning device according to certain parameters;

[0036] a second object holder, such as a substrate holder or substrate table (e.g. wafer stage) WT, which is configured to hold a substrate (e.g. resist-coated wafer) W and is connected to a second positioner PW configured to accurately position the substrate according to certain parameters; and

[0037] - a projection system (eg, a refractive projection lens system) PS configured to project the pattern imparted to the radiation beam B by the patterning device MA onto a target portion C of the substrate W (eg, comprising one or more dies).

[0038] The illumination system may include various types of optical elements, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical elements, or any combination thereof, for directing, shaping or controlling the radiation.

[0039] The support structure holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as, for example, whether the patterning device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure can be, for example, a frame or a stage, which can be fixed or movable as required. The support structure can ensure that the patterning device is in a desired position, for example, relative to a projection system. The terms "reticle" or "mask" used herein can be considered synonymous with the more general term "patterning device".

[0040] The term "patterning device" as used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section so as to create a pattern in a target portion of the substrate. It should be noted that the pattern applied to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Typically, the pattern applied to the radiation beam will correspond to a specific functional layer in a device (such as an integrated circuit) created in the target portion.

[0041] Patterning devices may be transmissive or reflective. Examples of patterning devices include 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. One example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incoming radiation beam into different directions. The tilted mirrors impart a pattern in the radiation beam that is reflected by the matrix of mirrors.

[0042] The term "projection system" as used herein should be broadly interpreted as including any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, depending on the exposure radiation used, or other factors such as the use of immersion liquid or the use of a vacuum. Any use of the term "projection lens" herein may be considered a synonym for the more general term "projection system".

[0043] As shown, the device is of the transmissive type (eg, using a transmissive mask). Alternatively, the device may be of the reflective type (eg, using a programmable mirror array of the type described above, or using a reflective mask).

[0044] The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and / or two or more support structures). In such a "multi-stage" machine, the additional tables / support structures may be used in parallel, or preparatory steps may be performed on one or more tables / support structures while exposure is being carried out using one or more other tables / support structures.

[0045] refer to Figure 1 , the illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In this case, the source is not considered to be part of the lithographic apparatus, and the radiation beam is transferred from the source SO to the illuminator IL with the help of a beam delivery system BD comprising, for example, suitable guide mirrors and / or a beam expander. In other cases, the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, and the beam delivery system BD if required, may together be referred to as a radiation system.

[0046] The illuminator IL may include an adjuster AD configured to adjust the angular intensity distribution of the radiation beam. Typically, at least the outer and / or inner radial extent of the intensity distribution in a pupil plane of the illuminator (commonly referred to as outer σ and inner σ, respectively) may be adjusted. Furthermore, the illuminator IL may include various other components, such as an integrator IN and a converger CO. The illuminator may be used to adjust the radiation beam so that it has a desired uniformity and intensity distribution in a cross section.

[0047] The radiation beam B is incident on a patterning device (e.g. a mask) MA, which is held on a support structure (e.g. a reticle stage) MT, and is patterned by the patterning device. After passing through the patterning device MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of a second positioner PW and a position sensor IF (e.g. an interferometer, a linear encoder or a capacitive sensor), the substrate table WT can be precisely moved, for example, in order to position a different target portion C in the path of the radiation beam B. Similarly, a first positioner PM and a further position sensor ( Figure 1 The support structure MT may be used to accurately position the patterning device MA relative to the path of the radiation beam B, for example after mechanical retrieval from a mask library, or during scanning. Typically, movement of the support structure MT may be achieved 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 achieved 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 support structure MT may be connected to the short-stroke actuator only, or it may be fixed. The patterning device MA and the substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks shown occupy dedicated target portions, they may be located in the space between target portions (these are called scribe lane alignment marks). Similarly, where more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies.

[0048] The described device can be used in at least one of the following modes:

[0049] 1. In stepping mode, the support structure MT and the substrate table WT remain substantially stationary,

[0050] The entire pattern imparted to the radiation beam is projected onto the target portion C at one time (ie,

[0051] Single static exposure). The substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure.

[0052] 2. In scan mode, the support structure MT and substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The speed and direction of the substrate table WT relative to the support structure MT may be determined by the (de)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width of the target portion in a single dynamic exposure (in the non-scanning direction), while the length of the scanning movement determines the height of the target portion (in the scanning direction).

[0053] 3. In another mode, the support structure MT is kept substantially stationary so as to hold the programmable patterning device, and the substrate table WT is moved or scanned whilst a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, a pulsed radiation source is typically employed, and the programmable patterning device is updated as required after each movement of the substrate table WT or between successive radiation pulses during a scan. This mode of operation may be readily applied to maskless lithography utilising a programmable patterning device, such as a programmable mirror array of the type described above.

[0054] Combinations and / or variations on the above described modes of use, or entirely different modes of use, may also be employed.

[0055] Figure 2 is a schematic diagram of another lithographic projection apparatus (LPA) according to an embodiment. The LPA may include a source collector module SO, an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. EUV radiation), a support structure MT, a substrate table WT and a projection system PS.

[0056] The support structure (e.g., patterning device stage) MT may be configured to support a patterning device (e.g., mask or reticle) MA and connected to a first positioner PM configured to accurately position the patterning device;

[0057] A substrate table (eg, wafer stage) WT may be configured to hold a substrate (eg, a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate.

[0058] The projection system (eg, a reflective projection system) PS may be configured to project the pattern imparted to the radiation beam B by the patterning device MA onto a target portion C of the substrate W (eg, comprising one or more dies).

[0059] As shown, the LPA can be reflective (e.g., using a reflective patterning device). It should be noted that since most materials are absorptive in the EUV wavelength range, the patterning device can have a multilayer reflector, such as a multilayer stack including molybdenum and silicon. In one example, the multilayer stack reflector has 40 layers of paired molybdenum and silicon, each layer being a quarter wavelength thick. X-ray lithography can produce smaller wavelengths. Since most materials are absorptive at EUV and x-ray wavelengths, a thin piece of patterned absorbing material on the patterning device topography (e.g., a TaN absorber on top of a multilayer reflector) defines where features will be printed (positive resist) or not (negative resist).

[0060] The illuminator IL may receive a beam of extreme ultraviolet radiation from a source collector module SO. Methods for generating EUV radiation include, but are not limited to, converting a material into a plasma state having at least one element, such as xenon, lithium, or tin, with one or more emission lines in the EUV range. In one such method, commonly referred to as laser produced plasma ("LPP"), a plasma may be generated by irradiating a fuel, such as a droplet, stream, or cluster of a material having a line emitting element, with a laser beam. The source collector module SO may be part of an EUV radiation system that includes a laser ( Figure 2 The resulting plasma emits output radiation, such as EUV radiation, which is collected using a radiation collector disposed in the source collector module. The laser and source collector module may be separate entities, such as when a CO2 laser is used to provide the laser beam for fuel excitation.

[0061] In this case, the laser may not be considered as part of the lithographic apparatus, and the radiation beam may be delivered from the laser to the source collector module with the aid of a beam delivery system comprising, for example, suitable guide mirrors and / or a beam expander. In other cases, the source may be an integral part of the source collector module, such as when the source is a discharge produced plasma EUV generator, often referred to as a DPP source.

[0062] The illuminator IL may include an adjuster for adjusting the angular intensity distribution of the radiation beam. Typically, at least the outer and / or inner radial extent of the intensity distribution in a pupil plane of the illuminator (commonly referred to as outer σ and inner σ, respectively) may be adjusted. Furthermore, the illuminator IL may include various other components, such as a facet field and pupil mirror devices. The illuminator may be used to adjust the radiation beam so that it has a desired uniformity and intensity distribution in a cross section.

[0063] A radiation beam B may be incident on a patterning device (e.g., mask) MA, which is held on a support structure (e.g., patterning device table) MT, and patterned by the patterning device. After reflection from the patterning device (e.g., 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. With the aid of a second positioner PW and a position sensor PS2 (e.g., an interferometer, a linear encoder, or a capacitive sensor), the substrate table WT may be precisely moved, for example, in order to position different target portions C in the path of the radiation beam B. Similarly, a first positioner PM and a further position sensor PS1 may be used to precisely position the patterning device (e.g., mask) MA relative to the path of the radiation beam B. The patterning device (e.g., mask) MA and the substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2.

[0064] The depicted device LPA can be used in at least one of the following modes, namely a stepping mode, a scanning mode and a stationary mode.

[0065] In step mode, the support structure (e.g., patterning device table) MT and the substrate table WT remain substantially stationary, and an entire pattern imparted to the radiation beam is projected at once onto a target portion C (i.e., a single static exposure). The substrate table WT is then moved in the X and / or Y direction so that a different target portion C can be exposed.

[0066] In scan mode, the support structure (e.g. patterning device table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The speed and direction of the substrate table WT relative to the support structure (e.g. patterning device table) MT may be determined by the (de)magnification and image reversal characteristics of the projection system PS.

[0067] In stationary mode, the support structure (e.g., patterning device table) MT remains substantially stationary to hold the programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, a pulsed radiation source is typically employed, and the programmable pattern generating device is updated as required after each movement of the substrate table WT or between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography utilizing a programmable patterning device such as a programmable mirror array of the type described above.

[0068] Figure 3 An example flow chart for the modeling and / or simulation portion of a patterning process is shown in . As will be appreciated, the models may represent different patterning processes, and need not include all of the models described below. The source model 300 represents the optical characteristics of the illumination of the patterning device (including the radiation intensity distribution, bandwidth, and / or phase distribution). The source model 300 may represent the optical characteristics of the illumination, including but not limited to the numerical aperture setting, the illumination sigma (σ) setting, and any specific illumination shape (e.g., off-axis radiation shapes such as toroidal, quadrupole, dipole, etc.), where σ (or sigma) is the outer radial extent of the illuminator.

[0069] The projection optics model 310 represents the optical properties of the projection optics (including changes in the radiation intensity distribution and / or phase distribution caused by the projection optics). The projection optics model 310 can represent the optical properties of the projection optics, including aberrations, distortions, one or more refractive indices, one or more physical sizes, one or more physical dimensions, etc.

[0070] The patterning device / design layout model module 320 captures how design features are laid out in the pattern of the patterning device and may include a representation of detailed physical properties of the patterning device, for example, as described in U.S. Pat. No. 7,587,704, the entire contents of which are incorporated herein by reference. In one embodiment, the patterning device / design layout model module 320 represents the optical properties (including changes in radiation intensity distribution and / or phase distribution caused by a given design layout) of a design layout (e.g., a device design layout corresponding to features of an integrated circuit, memory, electronic device, etc.), which is a representation of the arrangement of features on or formed by the patterning device. Since the patterning device used in the lithographic projection apparatus can change, it is desirable to separate the optical properties of the patterning device from the optical properties of the rest of the lithographic projection apparatus (including at least the illumination and projection optics). The goal of the simulation is typically to accurately predict edge locations and CDs, which are then compared to the device design. The device design is typically defined as a pre-OPC patterning device layout and will be provided in a standardized digital file format, such as GDSII or OASIS.

[0071] An aerial image 330 can be simulated from the source model 300, the projection optics model 310, and the patterning device / design layout model module 320. The aerial image (AI) is the radiation intensity distribution at the substrate level. The optical characteristics of the lithography projection apparatus (e.g., the characteristics of the illumination, patterning device, and projection optics) determine the aerial image.

[0072] The resist layer on the substrate is exposed by the aerial image, and the aerial image is transferred to the resist layer as a potential "resist image" (RI) therein. The resist image (RI) can be defined as the spatial distribution of the solubility of the resist in the resist layer. The resist image 350 can be simulated from the aerial image 330 using a resist model 340. The resist model can be used to calculate the resist image based on the aerial image, an example of which can be found in U.S. Patent Application Publication No. US2009-0157360, the entire contents of which are incorporated herein by reference. The resist model typically describes the effects of chemical processes occurring during resist exposure, post-exposure baking (PEB), and development to predict, for example, the profile of the resist features formed on the substrate, so it is typically only related to these characteristics of the resist layer (e.g., the effects of chemical processes occurring during exposure, post-exposure baking, and development). In one embodiment, the optical properties of the resist layer (e.g., refractive index, film thickness, propagation, and polarization effects) can be captured as part of the projection optical model 310.

[0073] Therefore, in general, the link between the optics and the resist model is the simulated spatial image intensity within the resist layer, which is caused by the radiation projected onto the substrate, refraction at the resist interface and multiple reflections in the resist film stack. The radiation intensity distribution (spatial image intensity) is converted into a latent "resist image" by absorption of the incident energy, which is further modified by diffusion processes and various loading effects. Efficient simulation methods that are fast enough for full-chip applications approximate the true three-dimensional intensity distribution in the resist stack by a two-dimensional spatial (and resist) image.

[0074] In one embodiment, the resist image may be used as input to the post-pattern transfer process model module 360. The post-pattern transfer process model module 360 ​​defines the performance of one or more post-resist development processes (eg, etching, developing, etc.).

[0075] For example, a simulation of a patterning process can predict profiles, CD, edge locations (e.g., edge location errors), etc. in the resist and / or etch images. Thus, the purpose of the simulation is to accurately predict, for example, edge locations and / or spatial image intensity slopes and / or CD, etc. of a printed pattern. These values ​​can be compared to an intended design, for example, to correct the patterning process, identify locations where defects are predicted to occur, etc. The intended design is typically defined as a pre-OPC design layout, which can be provided in a standardized digital file format, such as GDSII or OASIS or other file formats.

[0076] Thus, the model formula describes most, if not all, of the known physical and chemical properties of the entire process, and each model parameter ideally corresponds to a different physical or chemical effect. Thus, the model formula sets an upper limit to how well the model can be used to simulate the entire manufacturing process.

[0077] Figure 4A A mask consistent with various embodiments is shown. In some embodiments, mask 400 can be an EUV mask. Mask 400 can include a reflective layer 430, which includes a multilayer reflective film arranged on a substrate 435. Substrate 435 can be composed of, for example, ultra-low expansion titanium silicate glass, but within the scope of the present invention, any suitable material can be used. Reflective layer 430 can include a multilayer material with alternating refractive indices for providing resonant reflectivity when the period of the layer is approximately half the wavelength of the radiation used in the imaging system. In some embodiments, reflective layer 430 can include alternating layers of molybdenum (Mo) and silicon (Si). Reflective layer 430 can include any suitable number of Si and Mo layers, such as about 30 to 80 pairs of Mo / Si layers.

[0078] In some embodiments, the mask 400 includes a buffer layer 425 composed of ruthenium (Ru), but other materials such as tantalum nitride (TaN), silicon dioxide (SiO2), carbon (C), and mixtures of these materials may also be used. The buffer layer 425 may be formed on the top layer of the reflective layer 430. Figure 4A As shown, the absorption layer 420 is disposed on the buffer layer 425, wherein the material used for the absorption layer 420 absorbs radiation at a wavelength used in the imaging system and can be selectively etched. The absorption layer 420 can be composed of any suitable material or composition, such as nickel (Ni), cobalt nickel alloy (CoNi), tantalum (Ta), tantalum nitride (TaN) or tantalum boron nitride (TaBN).

[0079] In some embodiments, mask 400 includes an active region 405 in which a pattern corresponding to a target pattern to be printed on a substrate can be generated. Active region 405 can be surrounded by border region 410 (or black border region 410), which is also made of an absorbing material. Active region 405 is the region of mask 400 in which absorbing layer 420 can be patterned using conventional semiconductor processing techniques, such as masking and selectively etching the material of absorbing layer 420 to expose reflective layer 430. The pattern created in absorbing layer 420 at active region 405 can define the pattern provided to a lithography apparatus such as a photolithography apparatus. Figure 2 The pattern of light at the die position on the substrate in the lithographic apparatus LPA of FIG. 4 is a lithographic apparatus of FIG. 400 . Thus, any desired pattern can be provided in the active area 405. The border region 410 includes a relatively wide strip 420 of the absorption layer surrounding the active area 405, which can also be referred to as a black border. In some embodiments, the black border can also be patterned as an additional layer on top of the absorption layer 420.

[0080] Figure 4B shows consistent with various embodiments Figure 4A The mask 400 scatters light.

[0081] Projection beam 450 is projected by an illumination source onto mask 400 and is reflected to form a patterned projection beam or zero-order reflection 455 that enters a projection system (eg, Figure 2 423). The energy incident on the mask 400 causes zero-order, first-order, or higher-order reflections (e.g., depending on the type of illumination source). For example, for light from a dipole illumination source, zero-order and first-order reflections can be generated. For a projection beam 450 incident on the reflective layer 430 (e.g., at region 422), the mask 400 causes a zero-order reflection 455 and first-order reflections 456 and 457. Most of the energy in the projection beam 450 incident on an absorption region in the mask pattern (such as absorption region 423) is absorbed. However, some of the energy is reflected. For example, the absorption layer 420 causes a zero-order reflection 465 (specular reflection) and first-order reflections 466 and 467. Such specular reflections can degrade the imaging of the pattern at the substrate, for example, by increasing the background intensity or contrast loss at the boundary region 410, which can hinder pattern stitching.

[0082] In some embodiments, specular reflection of the absorption layer 420 may be reduced by incorporating sub-resolution features, such as sub-resolution gratings (SRGs), in the mask pattern design. Figure 5AMask pattern designs (or portions thereof) for printing a target pattern on a wafer consistent with various embodiments are shown. A first mask pattern design 550 shows a black border region 410 and a pattern 525 corresponding to the target pattern to be printed at a target location on a substrate. A second mask pattern design 551 also shows a black border region 410 and a pattern 526 corresponding to the target pattern to be printed at a target location on a substrate. In some embodiments, the two mask pattern designs are considered symmetrical and can be printed on the same die on a substrate as adjacent exposures. In some embodiments, the two mask pattern designs can be printed on two separate masks.

[0083] Figure 5B A schematic diagram of a circuit having an SRG consistent with various embodiments is shown. Figure 5A . The first mask pattern design 560 includes an SRG 510 placed between the black border region 410 and the pattern 525, and the second mask pattern design 561 includes an SRG 510 placed between the black border region 410 and the pattern 526, which is a pattern to be printed on the substrate. The dotted line indicates a stitching line or stitching area 530, on which two adjacent exposures of the mask pattern designs 560 and 561 must be stitched. That is, the stitching area 530 can be an area close to a stitching pattern, which is a pattern to be stitched before printing on the substrate. For example, the stitching area 530 can be close to the line patterns 525 and 526 to be stitched before printing on the substrate. By placing the SRG 510 near the stitching area 530, the absorber transmittance or specular reflection from the absorber layer 420 near the black border region 410 is significantly minimized (e.g., from 15% or 25% to 0.7% or 0.3%). This results in a significant reduction in intensity near stitching region 530, which enables stitching of patterns in adjacent exposures. In some embodiments, an image of the pattern, such as an aerial image (eg, aerial images of patterns 525 and 526), ​​may be used to characterize the exposure.

[0084] Figure 5B The SRG 510 depicted in FIG. 5 is a horizontal grating. However, the SRG 510 may also be in other configurations. For example, the SRG 510 may be a vertical grating or a contact hole.

[0085] Figure 5C shows consistent with various embodiments Figure 5B 560. First image 570 corresponds to the exposure of a portion of first mask pattern design 560, and second image 571 corresponds to the exposure of a portion of second mask pattern design 561. Note that the intensity in regions 572 and 573 near stitching region 530 is minimized. In some embodiments, images 570 and 571 may be aerial images.

[0086] Figure 5D Shown are various embodiments consistent with Figure 5B In some embodiments, the mask 500 may be similar to Figure 4A 4, but mask 500 includes SRG 510 patterned in absorption layer 420. In some embodiments, SRG 510 is patterned in region 505 close to a stitching pattern between adjacent exposure fields, which in the mask pattern design is generally between black border region 410 and active region 405. In some embodiments, the width of black border region 410 can be reduced to incorporate SRG 510 into the mask pattern design.

[0087] Figure 6 Various geometric and positional parameters associated with the SRG are shown consistent with various embodiments. In some embodiments, the mask pattern design 660 corresponds to Figure 5B A portion of mask pattern design 560, mask pattern design 661 corresponds to Figure 5B 561. In some embodiments, the SRG 510 is associated with various geometric parameters. For example, the geometric parameters may include a critical dimension (CD) 605 and a pitch 610 of the SRG 510. The geometric parameters may also include a duty cycle, which may indicate a ratio of the CD 605 to the pitch 610. The position parameters may include an overlay parameter 615, which indicates an amount of overlap of two patterns in the Y direction, and a line end distance 620, which indicates a distance between the SRG 510 and the line end of the pattern 525 to be spliced. The pattern 525 is associated with a CD 625.

[0088] As described above, by placing the SRGs in the mask pattern design, specular reflections from the absorbing layers can be minimized. This reduction in specular reflections can be achieved when the design or geometry and location of the SRGs in the mask pattern design are appropriate. For example, by configuring the duty cycle of the SRGs 510 to a specified value, scattering of first-order intensity light outside the pupil of the illumination source is maximized, while zero-order intensity light is suppressed or eliminated. At the specified duty cycle, a phase shift and amplitude balance of approximately 180 degrees is achieved between the zero-order contribution or reflection of the absorbing layer 420 and the non-absorbing layer (e.g., the reflective layer 430) of the mask 500, which suppresses or eliminates the zero-order contribution by destructive interference. By obtaining appropriate values ​​for the overlay parameter 615 and the line end distance 620 to place the SRG 510 near the stitching area 530 (e.g., between the black border region 410 and the stitching pattern 525 and between the black border region 410 and the stitching pattern 526), ​​the variation of the CD 625 of the stitching pattern (e.g., the combination of pattern 525 and pattern 526) can be minimized. Figure 7-Figure 11 Additional details regarding the geometry and location of the SRG are described.

[0089] Figure 7 is a block diagram of a system 700 for determining position parameters of SRGs in a mask pattern design, consistent with various embodiments. Figure 8 8 is a flow chart of a method 800 for determining position parameters of an SRG in a mask pattern design consistent with various embodiments. At process P810, the SRG assembly 725 may obtain source parameters 702 of an illumination source. In some embodiments, the source parameters 702 may include a numerical aperture (NA), a wavelength (λ), a partial coherence factor (σ), or a wavelength of the illumination source (e.g., Figure 2 The SRG component 725 may obtain the source parameters 702 in various ways (eg, via user input).

[0090] At step P820, SRG assembly 725 determines the pitch of the SRGs to be placed in the region of the absorption layer of mask pattern design 550. In some embodiments, the pitch (e.g., pitch 610 of SRG 510) is the distance between gratings in the SRG. In some embodiments, the pitch is the minimum pitch required to scatter or remove all first order intensity light from the pupil of the illumination source. The pitch can be determined based on one or more source parameters of the illumination source, as described below with reference to at least Fig.9A described. Fig.9A An illumination source for a lithographic apparatus consistent with various embodiments is shown. Fig.9AThe illumination source depicted in is a dipole source with a pupil 905 defined by a circular sigma. For each point in the pupil 905, the maximum Δσ (delta sigma) required to scatter all first-order light outside the pupil 905 is determined. For example, for a first point 902, the maximum Δσ along a horizontal grating (such as SRG 510) along a direction 910 is determined. In another example, for the first point 902, the maximum Δσ along a vertical grating along a direction 915 is determined. Similarly, for a second point 904, the maximum Δσ along a horizontal grating along a direction 912 is determined, or the maximum Δσ along a vertical grating along a direction 917 is determined. Such maximum Δσ values ​​can be determined for all points in the pupil 905.

[0091] In some embodiments, the minimum pitch can then be determined using the following equation:

[0092] P min =λ / NA / max(Δσ) Equation (1)

[0093] For example, if the maximum value (Δσ) is 1.5, the NA of the EUV scanner is 0.33, and λ is 13.5, then the minimum pitch required on the wafer is about 27 nm so as not to have any first order intensity within the pupil 905. For a 4x magnification system, the minimum pitch of the SRG on the mask is about 109 nm (27*4). Therefore, the pitch 610 of the SRG 510 is determined based on the source parameters 702. It should be understood that the present disclosure can be used for scanners with other NA values, such as high NA and ultra NA. Referring to the method 800, at process P830, the SRG assembly 725 adjusts the duty cycle of the SRG by changing the CD of the SRG until the specified background intensity criteria are met. For example, the duty cycle can be adjusted by changing the CD 605 of the SRG 510 from a CD value equal to the pitch (e.g., obtained using Equation 1) to a CD value equal to zero, and the change in reflection or transmission of the absorber layer 420 can be monitored. Fig. 9BA graph of absorber transmittance versus duty cycle of the SRG for different types of masks consistent with various embodiments is shown. In some embodiments, the x-axis represents the duty cycle of the SRG and the y-axis represents the absorber transmittance. Graph 930 indicates the absorber transmittance versus duty cycle for various types of masks. The duty cycle at which the absorber transmittance is minimum (e.g., the background intensity is minimum) is determined to be the duty cycle of the SRG 510 at which the specular reflection of the absorption layer 420 is minimum. That is, at a determined duty cycle, the first-order diffraction of light is scattered outside the pupil 905, and the zero-order diffraction from the absorption layer 420 and the non-absorption layer balances each other in amplitude and anti-phase, causing them to be canceled or suppressed due to destructive interference, thereby reducing the intensity at the stitching area 530. Note that for most masks, the absorber transmittance is determined to be the lowest (e.g., approximately 0.275) at the duty cycle 925. After the duty cycle is determined, the value of CD 605 at the determined duty cycle 925 is the CD 605 of SRG 510. For example, if the duty cycle is 0.275, the CD of the SRG at the wafer may be about 8 nm so as not to have any first order intensity within pupil 905. For a 4x magnification system, the CD 605 of the SRG on the mask is about 32 nm (8*4). Therefore, the pitch of SRG 510 is determined based on the source parameters.

[0094] Thus, as described above, the SRG assembly 725 captures the geometric parameters 714 of the SRG 510 (eg, the pitch 610 and the CD 605 ).

[0095] At process P840, stitching component 750 determines the location of the SRG in the region of the absorber layer of the mask pattern design between two adjacent exposure fields in the lithography process. Figure 5B As described above, the stitching area 530 is an area on the absorption layer 420 of the mask pattern design 560, and two adjacent exposures of the mask pattern designs 560 and 561 can be stitched on this area. That is, the stitching area 530 can be an area close to the stitching pattern, and the stitching pattern is the pattern in the two adjacent exposures to be stitched before printing on the substrate. For example, the stitching area 530 can be close to the line patterns 525 and 526 to be stitched before printing on the substrate. In the mask (for example, Figure 5D 4. On a mask 500 of FIG. 4, SRG 510 may be patterned in a region 505 between the black boundary region 410 and the active region 405. The region 505 close to the stitching pattern between adjacent exposure fields corresponds to a stitching region 530. By placing the SRG 510 near the stitching region 530, specular reflection from the absorption layer 420 near the black boundary region 410 is significantly minimized.

[0096] In some embodiments, determining the position of the SRG includes at least one of determining an overlap between stitching patterns in adjacent exposure fields, or determining a line end distance indicating a distance between the SRG and an end of a line of the stitching pattern. Fig. 10A Images of patterns to be stitched and images of stitched patterns consistent with various embodiments are shown. The first image 570 shows the intensity distribution of a portion of the pattern 525 along the X direction 1006 and the Y direction 1007 of the pattern, and the second image 571 shows the intensity distribution of a portion of the pattern 526 along the X direction 1006 and the Y direction 1007 of the pattern. In some embodiments, the value of Y is "0" at the stitching area 530, the Y value above the stitching area 530 is positive, and the Y value below the stitching area 550 is negative. Therefore, for the first image 570, the intensity value in the negative Y direction is greater than the intensity value in the positive Y direction. For the second image 571, since the second image 571 is symmetrical about Y=0 (e.g., the stitching area 530), the intensity value in the positive Y direction is greater than the intensity value in the negative Y direction. The stitched image 1050 shows the intensity distribution of the stitched pattern (e.g., stitching a portion of the pattern 525 with a portion of the pattern 526 along the stitching area 530) along the X direction 1006 and the Y direction 1007.

[0097] Fig. 10B Graphs of intensity distributions associated with a stitched pattern before and after stitching consistent with various embodiments are shown. A first graph 1005 shows an intensity distribution associated with a portion of pattern 525 (e.g., which needs to be stitched with a portion of pattern 526) along the Y direction 1007 of pattern 525. In some embodiments, the first graph 1005 corresponds to a first image 570 of pattern 525. A second graph 1010 shows an intensity distribution associated with a stitched pattern (e.g., a portion of pattern 525 that is stitched with a portion of pattern 526) along the Y direction 1007 of the stitched pattern. In some embodiments, the second graph 1010 corresponds to a stitched image 1050. The x-axis of the first graph 1005 and the second graph 1010 corresponds to the Y direction 1007 of the pattern and varies from -Y to +Y, where line 1015 corresponds to Y=0 on the x-axis, which is the stitching zone 530 where the stitching is performed. The y-axis of the first graph 1005 and the second graph 1010 depicts the spatial image intensity of the corresponding pattern.

[0098] In the first graph 1005, a first line 1021 indicates an intensity profile associated with a pattern 525 without SRG 510. The first line 1021 indicates an intensity cross section through the peak intensity (top) of the line-space pattern 525 without SRG 510, and has a significant background intensity in the region after the end of the pattern. The second line 1020 indicates an intensity cross section through the peak intensity (top) of the line-space pattern 525 including SRG 510. The background intensity is now suppressed. The third line 1031 indicates an intensity cross section through the valley intensity (bottom) of the line-space pattern 525 not including SRG 510. The fourth line 1030 indicates an intensity cross section through the valley intensity (bottom) of the line-space pattern 525 including SRG 510. The suppressed intensity from SRG 510 preserves the contrast (peaks and valleys) of the pattern across the stitching area 530 when the intensities of these patterns are added with the mirrored pattern from the secondary exposure. Without the SRG 510, the background intensity is doubled and the contrast is significantly reduced.

[0099] In the second graph 1010, a first line 1041 indicates a drop in intensity of patterns 525 and 526 near line 1015, which represents Y=0 (e.g., stitching region 530). A second line 1042 indicates a drop in intensity of a combined pattern with 3.0 nm overlap. As can be seen from the images 570 and 571 of the patterns, the intensity decreases near the stitching region 530, which may indicate that the designed gap / overlap between patterns 525 and 526 and the pattern may be adjusted to reduce the intensity deviation across the stitching region 530. Therefore, patterns 525 and 526 must overlap precisely to minimize the CD error within the stitching region 530.

[0100] The stitching component 750 can minimize the overlay error by determining an overlay parameter (e.g., an overlay parameter 615) that indicates the amount of overlap between the two patterns in the Y direction. In some embodiments, the overlay parameter 615 can be determined by moving the image in the Y direction toward the stitching area by a specified value until the intensity along the Y direction is substantially consistent (e.g., the change in intensity along the Y direction is less than or at least less than a specified threshold), as shown in the third line 1040 and the fourth line 1043. The distance the image is moved to obtain the minimum intensity change in the Y direction is the value of the overlay parameter 615.

[0101] The stitching component 750 also determines a line end distance (eg, line end distance 620) that indicates the distance between the SRG and the end of the line of the pattern to be stitched 525. In some embodiments, the line end distance contributes to the CD variation of the stitched pattern. Fig. 10CThe variation of CD in the stitching pattern for different line end distances of the SRG consistent with various embodiments is shown. The x-axis of the third graph 1055 corresponds to the Y direction 1007 of the stitching pattern and varies from -Y to +Y, and the line 1060 corresponds to Y=0 on the x-axis, which is the stitching zone 530 where the stitching is performed. The y-axis of the third graph 1055 depicts the CD 625 of the stitching pattern. For various line end distances of the SRG, each line indicates the variation of the CD 625 of the stitching pattern along the Y direction 1007. For example, the first line 1065 indicates the variation of the CD 625 of the stitching pattern along the Y direction for a first value of the line end distance 620 of the SRG 510. In another example, the second line 1070 indicates the variation of the CD 625 of the stitching pattern along the Y direction for a second value of the line end distance 620 of the SRG 510. The stitching component 750 can identify the line end distance value at which the variation of the CD of the stitching pattern is the smallest. For example, the stitching component 750 can determine that the CD variation of the stitching pattern of the second line 1070 is the smallest, and can obtain the line end distance value associated with the second line 1070 as the line end distance 620 .

[0102] At process P850, the stitching component 750 can output position parameters 724 (eg, overlay parameters 615 and line end distance 620).

[0103] In some embodiments, the geometric parameters 714 and the position parameters 724 can be used to generate a mask pattern design having an SRG (e.g., SRG 510) to print a target pattern on a target location (e.g., one or more dies) of a substrate. A mask can be manufactured using the mask pattern design and printed on a lithography apparatus (e.g., Figure 2 The invention is used in a lithography apparatus) to print a target pattern on a substrate by a photolithography process.

[0104] Fig.11 1 is a flow chart of another method 1100 for determining position parameters of an SRG in a mask pattern design consistent with various embodiments. In process P1110, the SRG component 725 identifies an area between two adjacent exposure fields in a lithography process to locate the SRG. In some embodiments, the area between the two adjacent exposure fields may be referred to as a stitching area (e.g., stitching area 530). As described above with at least reference to Figure 5B As described above, the stitching area 530 is an area on the absorption layer 420 of the mask pattern design 560, and two adjacent exposures of the mask pattern designs 560 and 561 can be stitched on this area. That is, the stitching area 530 can be an area close to the stitching pattern (for example, these patterns are patterns in two adjacent exposures to be stitched before printing on the substrate). For example, the stitching area 530 can be close to the line patterns 525 and 526 to be stitched before printing on the substrate. In the mask (for example, Figure 5D4. On a mask 500 of FIG. 4, SRG 510 may be patterned in a region 505 between the black boundary region 410 and the active region 405. The region 505 close to the stitching pattern between adjacent exposure fields may correspond to a stitching area 530. By placing the SRG 510 near the stitching area 530, specular reflection from the absorption layer 420 near the black boundary region 410 is significantly minimized.

[0105] At process P1120, the SRG assembly 725 or the stitching assembly 750 can determine the location and geometry of the SRG to be placed in the region of the absorbing layer of the mask pattern design based on the specified background intensity criteria. For example, as described at least with reference to processes P820 and P830 of method 800 above, the SRG assembly 725 can determine the geometric parameters 714 of the SRG 510, such as the CD 605 or the pitch 610 of the SRG 510. In some embodiments, by determining an appropriate duty cycle (e.g., CD to pitch ratio) for the SRG 510, the specular reflection of the absorbing layer 420 can be minimized. In some embodiments, at an appropriate duty cycle, the first order diffraction is scattered outside the pupil of the illumination source, and the zero order diffraction from the absorbing layer 420 and the non-absorbing layer balances each other in amplitude and anti-phase, causing them to be canceled or suppressed due to destructive interference, thereby reducing the intensity and minimizing the contrast loss at the stitching area 530.

[0106] In another example, as described at least with reference to process P840 of method 800 above, stitching component 750 can determine position parameters 724 of SRG 510, such as overlay parameters 615 or line end distance 620 of SRG 510, which can be used to determine the position of SRG 520 in the mask pattern design. In some embodiments, overlay parameters 615 indicating a distance that an image of a pattern must move in the Y direction can be used to minimize overlay errors between two adjacent exposures (e.g., which can result in incorrect alignment between stitched patterns). In some embodiments, line end distance 620 indicating a distance between SRG 510 and the end of a line of a stitched pattern can be used to minimize variations in CD 625 of the stitched pattern.

[0107] While the above paragraphs describe minimizing specular reflections from absorber layers by placing SRGs in the mask pattern design, using such SRGs during the optical proximity correction (OPC) process can provide the added benefit of reducing mirror / lens heating effects.

[0108] Furthermore, while the above paragraphs describe minimizing specular reflections from the absorber layer by placing SRGs in the mask pattern design, there are other ways to minimize specular reflections. For example, by varying the absorber layer thickness (e.g., a three-tone mask), possibly in combination with SRGs, an inversion of the zero-order contributions of the absorber and non-absorber layers can also be achieved to minimize specular reflections. In another example, a high density material such as Ni / Ta can be deposited on the black border. In another example, SRGs can be used in the collector mirror or G mirror to suppress DUV. In another example, dual gratings in the absorber layer can be used to achieve DUV suppression.

[0109] Fig.12 1 is a block diagram illustrating a computer system 100 that can help implement the systems and methods disclosed herein. The computer system 100 includes a bus 102 or other communication mechanism for communicating information, and a processor 104 (or multiple processors 104 and 105) coupled to the bus 102 to process information. The computer system 100 also includes a main memory 106, such as a random access memory (RAM) or other dynamic storage device, coupled to the bus 102, which stores information and instructions to be executed by the processor 104. The main memory 106 can also be used to store temporary variables or other intermediate information during the execution of instructions to be executed by the processor 104. The computer system 100 also includes a read-only memory (ROM) 108 or other static storage device coupled to the bus 102, which stores static information and instructions for the processor 104. A storage device 110, such as a magnetic disk or optical disk, is provided and coupled to the bus 102 to store information and instructions.

[0110] The computer system 100 may be coupled to a display 112, such as a cathode ray tube (CRT) or a flat panel or touch panel display, via the bus 102 to display information to a computer user. An input device 114, including alphanumeric and other keys, is coupled to the bus 102 to communicate information and command selections to the processor 104. Another type of user input device is a cursor control 116, such as a mouse, trackball, or cursor direction keys, which is used to communicate direction information and command selections to the processor 104 and to control cursor movement on the display 112. The input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), which allows the device to specify a position in a plane. A touch panel (screen) display may also be used as an input device.

[0111] According to one embodiment, portions of the optimization process may be performed by computer system 100 in response to processor 104 executing one or more sequences of one or more instructions contained in main memory 106. Such instructions may be read into main memory 106 from another computer-readable medium such as storage device 110. Execution of the sequence of instructions contained in main memory 106 causes processor 104 to perform the processing steps described herein. One or more processors in a multi-processing arrangement may also be employed to execute the sequence of instructions contained in main memory 106. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions. Therefore, the description herein is not limited to any specific combination of hardware circuitry and software.

[0112] The term "computer-readable medium" as used herein refers to any medium that participates in providing instructions to the processor 104 for execution. Such media can take a variety of forms, including but not limited to non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as storage device 110. Volatile media include dynamic memory, such as main memory 106. Transmission media include coaxial cables, copper wires, and optical fibers, including wires that constitute bus 102. Transmission media can also take the form of sound waves or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media include, for example, floppy disks, flexible disks, hard disks, magnetic tapes, any other magnetic media, CD-ROMs, DVDs, any other optical media, punch cards, paper tapes, any other physical media with hole patterns, RAM, PROMs and EPROMs, FLASH-EPROMs, any other storage chips or boxes, carrier waves described below, or any other media that a computer can read.

[0113] Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to processor 104 for execution. For example, the instructions may initially be stored on a disk of a remote computer. The remote computer may load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to computer system 100 may receive the data on the telephone line and use an infrared transmitter to convert the data to an infrared signal. An infrared detector coupled to bus 102 may receive the data carried in the infrared signal and place the data on bus 102. Bus 102 transfers the data to main memory 106, from which processor 104 retrieves and executes the instructions. The instructions received by main memory 106 may optionally be stored on storage device 110 before or after execution by processor 104.

[0114] The computer system 100 also preferably includes a communication interface 118 coupled to the bus 102. The communication interface 118 provides a bidirectional data communication coupling with a network link 120 connected to a local network 122. For example, the communication interface 118 can be an integrated services digital network (ISDN) card or a modem for providing a data communication connection to a corresponding type of telephone line. As another example, the communication interface 118 can be a local area network (LAN) card for providing a data communication connection to a compatible LAN. A wireless link can also be implemented. In any such implementation, the communication interface 118 sends and receives electrical, electromagnetic or optical signals carrying digital data streams representing various types of information.

[0115] The network link 120 typically provides data communication to other data devices through one or more networks. For example, the network link 120 may provide a connection to a host computer 124 or to data equipment operated by an Internet Service Provider (ISP) 126 through a local network 122. The ISP 126 in turn provides data communication services through a global packet data communication network, now commonly referred to as the "Internet" 128. Both the local network 122 and the Internet 128 use electrical, electromagnetic, or optical signals that carry digital data streams. The signals through the various networks, as well as the signals on the network link 120 and the signals through the communication interface 118, are example forms of carrier waves that transport the information, and these signals carry the digital data to and from the computer system 100.

[0116] The computer system 100 can send messages and receive data, including program code, through the network(s), network link 120, and communication interface 118. In the Internet example, server 130 can send the requested code for an application program through Internet 128, ISP 126, local area network 122, and communication interface 118. For example, one such downloaded application can provide illumination optimization of an embodiment. The received code can be executed by processor 104 as it is received, and / or stored in storage device 110 or other non-volatile storage for later execution. In this manner, computer system 100 can obtain application code in the form of a carrier wave.

[0117] Embodiments of the present disclosure may be further described by the following clauses.

[0118] 1. A non-transitory computer readable medium having instructions which, when executed by a computer, cause the computer to perform a method for generating a mask pattern design for imaging a pattern on a substrate using a lithographic apparatus, the method comprising:

[0119] Identify the area between two adjacent exposure fields in a photolithography process; and

[0120] The locations and geometries of sub-resolution features to be placed in the region of the absorbing layer of the mask pattern design are determined based on specified background intensity criteria.

[0121] 2. The computer-readable medium of clause 1, wherein identifying the region comprises identifying the region on the mask pattern design based on a region proximate to a stitching pattern between the two adjacent exposure fields.

[0122] 3. The computer-readable medium of clause 2, wherein the tiled pattern is a subset of a target pattern to be printed on a substrate.

[0123] 4. The computer-readable medium of clause 1, wherein identifying the region comprises identifying a region between a black border and a stitching pattern on the absorbent layer.

[0124] 5. The computer-readable medium of clause 1, wherein determining the location comprises:

[0125] The sub-resolution features are positioned relative to a stitching pattern to minimize variations in a critical dimension of the stitching pattern in a resulting stitched image of the two adjacent exposure fields.

[0126] 6. The computer-readable medium of clause 5, wherein determining the location comprises determining a distance between a stitching pattern and the sub-resolution feature.

[0127] 7. The computer-readable medium of clause 1, wherein determining the geometric shape comprises determining a duty cycle of the sub-resolution features.

[0128] 8. The computer-readable medium of clause 7, wherein determining the duty cycle comprises determining at least one of a critical dimension or a pitch of the sub-resolution features.

[0129] 9. The computer-readable medium of clause 7, wherein determining the duty cycle comprises varying the duty cycle to reduce zero-order diffraction from a region of the absorbing layer.

[0130] 10. The computer-readable medium of clause 7, wherein determining the duty cycle comprises varying the duty cycle to maximize first order intensity light to be scattered outside of a pupil of an illumination source of a lithographic apparatus.

[0131] 11. A computer-readable medium according to clause 7, wherein determining the duty cycle includes: changing the duty cycle to change the phase and amplitude of radiation from the absorbing layer and the non-absorbing layer on the mask to reduce zero-order diffraction from both the absorbing layer and the non-absorbing layer.

[0132] 12. The computer-readable medium of clause 7, wherein determining the duty cycle comprises:

[0133] determining, based on an illumination source of a lithographic apparatus, a minimum pitch of the sub-resolution features for removing first order intensity light from a pupil of the illumination source; and

[0134] Based on the minimum pitch, a critical dimension of the sub-resolution feature at which reflection from the absorbing layer is minimized is determined.

[0135] 13. The computer-readable medium of clause 12, wherein determining the minimum pitch comprises:

[0136] The minimum pitch is determined based on at least one of a numerical aperture, a wavelength, or a partial coherence factor of the illumination source.

[0137] 14. The computer-readable medium of clause 12, wherein determining the critical dimension comprises:

[0138] The critical dimension is changed from a value equal to the minimum pitch to zero to determine the duty cycle at which the zero-order intensity light at the substrate is minimum.

[0139] 15. The computer-readable medium of clause 1, wherein the sub-resolution features comprise at least one of horizontal grating or vertical grating.

[0140] 16. The computer-readable medium of clause 1, further comprising:

[0141] An overlay between mosaic patterns of images of adjacent exposure fields is determined to reduce variations in critical dimensions of the mosaic patterns printed on the substrate.

[0142] 17. The computer-readable medium of clause 1, further comprising:

[0143] A mask pattern is generated based on the sub-resolution features, the mask pattern comprising a pattern corresponding to a target design layout to be printed on the substrate.

[0144] 18. The computer-readable medium of clause 17, further comprising:

[0145] A patterning step is performed using the mask pattern to print the pattern on the substrate via the photolithography process.

[0146] 19. The computer-readable medium of clause 1, wherein the lithography process is an extreme ultraviolet (EUV) lithography process.

[0147] 20. A computer-implemented method for generating a mask pattern design for imaging a pattern on a substrate using a lithographic apparatus, the method comprising:

[0148] determining a pitch of sub-resolution features to be placed in the region of the absorber layer of the mask pattern design based on source parameters of an illumination source of the lithographic apparatus;

[0149] adjusting a duty cycle of the sub-resolution feature to achieve a specified background intensity criterion; and

[0150] A location of the sub-resolution feature in the region of the absorber layer between two adjacent exposure fields is determined during a photolithography process.

[0151] 21. The method of clause 20, wherein determining the pitch comprises:

[0152] Based on the source parameters, a minimum pitch of the sub-resolution features for removing first order intensity light from a pupil of the illumination source is determined.

[0153] 22. The method of clause 20, wherein the source parameters include at least one of: a numerical aperture, a wavelength, or a partial coherence factor of the illumination source.

[0154] 23. The method of clause 20, wherein adjusting the duty cycle comprises:

[0155] The critical dimension of the sub-resolution feature is varied to determine the duty cycle at which zeroth order diffraction from the region of the absorber layer is minimized.

[0156] 24. The method of clause 20, wherein adjusting the duty cycle comprises varying the duty cycle to maximize first order intensity light to be scattered outside a pupil of the illumination source.

[0157] 25. The method of clause 20, wherein adjusting the duty cycle comprises changing the duty cycle to change the phase and amplitude of radiation from the absorbing and non-absorbing layers on a mask to reduce zero-order diffraction from both the absorbing and non-absorbing layers.

[0158] 26. The method of clause 20, wherein the region comprises a region proximate a stitching pattern between the two adjacent exposure fields.

[0159] 27. The method of clause 26, wherein the tiled pattern is a subset of a target pattern to be printed on a substrate.

[0160] 28. The method of clause 20, wherein the region comprises an area between a black border and a stitching pattern on the absorbent layer.

[0161] 29. The method of clause 20, wherein determining the location comprises:

[0162] The sub-resolution features are positioned relative to a stitching pattern to minimize variations in a critical dimension of the stitching pattern in a resulting stitched image of the two adjacent exposure fields.

[0163] 30. The method of clause 29, wherein determining the location comprises determining a distance between a stitching pattern and the sub-resolution feature.

[0164] 31. The method of clause 20, wherein the sub-resolution features comprise at least one of a horizontal grating or a vertical grating.

[0165] 32. The method according to clause 20, further comprising:

[0166] An overlay between mosaic patterns of images of adjacent exposure fields is determined to reduce variations in critical dimensions of the mosaic patterns printed on the substrate.

[0167] 33. The method according to clause 20, further comprising:

[0168] A mask pattern is generated based on the sub-resolution features, the mask pattern comprising a pattern corresponding to a target design layout to be printed on the substrate.

[0169] 34. The method according to clause 33, further comprising:

[0170] A patterning step is performed using the mask pattern to print the pattern on the substrate via the photolithography process.

[0171] 35. An apparatus for generating a mask pattern design for imaging a pattern on a substrate using a lithographic apparatus, the apparatus comprising:

[0172] a memory storing an instruction set; and

[0173] A processor is configured to execute the instruction set so that the apparatus performs a method, the method comprising:

[0174] Identify the area between two adjacent exposure fields in a photolithography process; and

[0175] The locations and geometries of sub-resolution features to be placed in the region of the absorbing layer of the mask pattern design are determined based on specified background intensity criteria.

[0176] While the concepts disclosed herein may be used for imaging on substrates such as silicon wafers, it should be understood that the disclosed concepts may be used with any type of lithography imaging system, such as systems for imaging on substrates other than silicon wafers.

[0177] As used herein, the terms "perform optimization" and "optimization" refer to or indicate adjusting a patterning device (e.g., a lithography apparatus), a patterning process, etc., so that the result and / or process has more desirable characteristics, such as higher projection accuracy of the designed pattern on the substrate, a larger process window, etc. Therefore, as used herein, the terms "perform optimization" and "optimization" refer to or indicate a process that identifies one or more values ​​of one or more parameters, and the identified one or more values ​​provide an improvement in at least one related metric, such as a local optimum, compared to an initial set of one or more values ​​of the one or more parameters. "Optimal value" and other related terms should be interpreted accordingly. In one embodiment, the optimization steps can be applied iteratively to provide further improvements in one or more metrics.

[0178] Aspects of the present invention may be implemented in any convenient form. For example, an embodiment may be implemented by one or more appropriate computer programs, which may be carried on an appropriate carrier medium, which may be a tangible carrier medium (e.g., a disk) or an intangible carrier medium (e.g., a communication signal). Embodiments of the present invention may be implemented using a suitable device, which may specifically take the form of a programmable computer running a computer program, which is arranged to implement the methods described herein. Therefore, embodiments of the present disclosure may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present disclosure may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include a read-only memory (ROM); a random access memory (RAM); a disk storage medium; an optical storage medium; a flash memory device; an electrical, optical, acoustic, or other form of propagation signal (e.g., a carrier wave, an infrared signal, a digital signal, etc.), etc. In addition, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be understood that such descriptions are merely for convenience and that such actions are actually caused by computing devices, processors, controllers or other devices executing firmware, software, routines, instructions or the like.

[0179] In the block diagrams, the components shown are depicted as discrete functional blocks, but embodiments are not limited to systems in which the functionality described herein is organized as shown. The functionality provided by each component may be provided by software or hardware modules organized differently than currently depicted, for example, such software or hardware may be mixed, connected, replicated, decomposed, distributed (e.g., within a data center or geographically), or otherwise organized differently. The functionality described herein may be provided by one or more processors of one or more computers executing code stored on a tangible, non-transitory machine-readable medium. In some cases, a third-party content delivery network may host some or all of the information delivered over the network, in which case, to the extent that information (e.g., content) is supplied or otherwise provided, the information may be provided by sending instructions to retrieve the information from the content delivery network.

[0180] Unless expressly stated otherwise, it will be apparent from the discussion that discussions in this specification using terms such as "processing," "computing," "calculating," "determining," etc. refer to actions or processes of a specific device, such as a special purpose computer or similar special purpose electronic processing / computing device.

[0181] The reader should understand that this application describes several inventions. These inventions are not separated into multiple independent patent applications, but are grouped into one document because their related subject matter helps save costs during the application process. But the unique advantages and aspects of these inventions should not be conflated. In some cases, embodiments solve all the deficiencies described herein, but it should be understood that the present invention is independently useful, and some embodiments only solve a subset of these problems, or provide other unmentioned benefits that are clear to those skilled in the art who read this disclosure. Due to cost constraints, some of the inventions disclosed herein are not currently claimed for protection, and claims may be made in later applications, such as continued applications or by amending existing claims. Similarly, due to space limitations, neither the abstract nor the content of the invention section of this document should be regarded as a comprehensive list containing all such inventions or all aspects of such inventions.

[0182] It should be understood that the specification and drawings are not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.

[0183] In view of this description, modifications and alternative embodiments of various aspects of the present invention will be clear to those skilled in the art. Therefore, this description and the accompanying drawings are to be interpreted as illustrative only and are used to teach those skilled in the art the general manner of implementing the present invention. It should be understood that the forms of the present invention shown and described herein are to be regarded as examples of embodiments. Elements and materials may be substituted for those shown and described herein, parts and processes may be reversed or omitted, certain features may be used independently, and embodiments or features of embodiments may be combined, all of which are clear to those skilled in the art. Changes may be made to the elements described herein without departing from the spirit and scope of the present invention as described in the following claims. The headings used herein are for organizational purposes only and are not intended to limit the scope of the description.

[0184] The word "may" used in this application is used in a permissive sense (i.e., it is possible), not in a mandatory sense (i.e., it must). The words "include", "comprises", and "have" are meant to include but are not limited to. The singular forms "one", "an", and "said" used in this application include plural references unless the content clearly states otherwise. Thus, for example, although other terms and phrases such as "one or more" are used for one or more elements, references to "one" elements or "an" elements include combinations of two or more elements. As used herein, unless otherwise specifically stated, the term "or" includes all possible combinations unless not feasible. For example, if a component is specified to include A or B, then, unless otherwise specifically stated or not feasible, the component may include A, or B, or A and B. As a second example, if a component is specified to include A, B, or C, then, unless otherwise specifically stated or not feasible, the component may include A, or B, or C, or A and B, or A and C, or B and C, or A and B and C.

[0185] Terms describing conditional relationships (e.g., "in response to X, Y," "at X, Y," "if X, Y," "when X, Y," etc.) include causal relationships where the preposition is a necessary causal condition, the preposition is a sufficient causal condition, or the preposition is a contributing causal condition to the result, for example, "state X occurs when condition Y is obtained" is a general term for "X only occurs when Y" and "X occurs when Y and Z." Such conditional relationships are not limited to results that occur immediately after the preposition is obtained, as some results may be delayed, and in the conditional statement, the preposition is related to its result, such as the preposition is related to the likelihood of the result occurring. Unless otherwise specified, a statement that maps multiple features or functions to multiple objects (e.g., one or more processors that perform steps A, B, C, and D) includes all of these features or functions mapped to all of these objects, as well as features or functions that are mapped to subsets of features or functions (e.g., all processors, each processor performs steps AD, and processor 1 performs step A, processor 2 performs step B and part of step C, and processor 3 performs part of step C and step D). Furthermore, unless otherwise stated, a statement that a value or action is "based on" another condition or value includes both the case where the condition or value is the only factor and the case where the condition or value is one of multiple factors. Unless otherwise stated, a statement that "each" instance of a set has a certain property should not be read to exclude the case where some of the same or similar members of the larger set do not have the property, i.e., each does not necessarily mean every one. References to selections from a range include the endpoints of the range.

[0186] In the above description, any process, description or block in the flowchart should be understood to represent a code module, segment or portion, which includes one or more executable instructions for implementing specific logical functions or steps in the process, and alternative implementations are included in the scope of the exemplary embodiments of the present development, in which the functions may be performed in an order different from that shown or discussed, including substantially concurrently or in reverse order, depending on the functions involved, as understood by those skilled in the art.

[0187] To the extent that certain U.S. patents, U.S. patent applications, or other materials (e.g., articles) have been incorporated by reference, the text of such U.S. patents, U.S. patent applications, and other materials is incorporated by reference only to the extent that there is no conflict between such materials and the statements and drawings described herein. If such a conflict arises, any such conflicting text in the incorporated by reference U.S. patents, U.S. patent applications, and other materials is not incorporated by reference herein.

[0188] Although certain embodiments have been described, these embodiments are presented only as examples and are not intended to limit the scope of the present disclosure. In fact, the new methods, devices, and systems described herein may be embodied in a variety of other forms; moreover, various omissions, substitutions, and changes in the form of the methods, devices, and systems described herein may be made without departing from the spirit of the present disclosure. The accompanying claims and their equivalents are intended to cover forms or modifications that fall within the scope and spirit of the present disclosure.

Claims

1. A non-transitory computer readable medium having instructions which, when executed by a computer, cause the computer to perform a method for generating a mask pattern design for imaging a pattern on a substrate using a lithographic apparatus, the method comprising: Identify the area between two adjacent exposure fields in the photolithography process; as well as Based on specified background intensity criteria, the locations and geometries of sub-resolution features to be placed in the region of the absorbing layer of the mask pattern design are determined.

2. The computer-readable medium of claim 1 , wherein identifying the region comprises: An area is identified on the mask pattern design based on an area proximate to a stitching pattern between the two adjacent exposure fields, wherein the stitching pattern is a subset of a target pattern to be printed on a substrate.

3. The computer-readable medium of claim 1 , wherein identifying the region comprises: Identify the area between the black border and the stitching pattern on the absorbent layer.

4. The computer-readable medium of claim 1 , wherein determining the location comprises: The sub-resolution features are positioned relative to a stitching pattern to minimize variations in a critical dimension of the stitching pattern in a resulting stitched image of the two adjacent exposure fields.

5. The computer-readable medium of claim 4, wherein determining the location comprises: A distance between the stitching pattern and the sub-resolution feature is determined.

6. The computer-readable medium of claim 1 , wherein determining the geometric shape comprises: A duty cycle of the sub-resolution feature is determined, and wherein determining the duty cycle includes determining at least one of a critical dimension or a pitch of the sub-resolution feature.

7. The computer-readable medium of claim 6, wherein determining the duty cycle comprises: The duty cycle is varied to reduce zero order diffraction from regions of the absorbing layer.

8. The computer-readable medium of claim 6, wherein determining the duty cycle comprises: The duty cycle is varied to maximize the first order intensity light to be scattered outside the pupil of an illumination source of the lithographic apparatus.

9. The computer-readable medium of claim 6, wherein determining the duty cycle comprises: The duty cycle is varied to change the phase and amplitude of radiation from the absorbing and non-absorbing layers on the mask to reduce zero-order diffraction from both the absorbing and non-absorbing layers.

10. The computer-readable medium of claim 6, wherein determining the duty cycle comprises: determining, based on an illumination source of a lithographic apparatus, a minimum pitch of the sub-resolution features for removing first order intensity light from a pupil of the illumination source; as well as Based on the minimum pitch, a critical dimension of the sub-resolution feature at which reflection from the absorbing layer is minimized is determined.

11. The computer-readable medium of claim 10, wherein determining the minimum pitch comprises: The minimum pitch is determined based on at least one of a numerical aperture, a wavelength, or a partial coherence factor of the illumination source.

12. The computer readable medium of claim 10, wherein determining the critical dimension comprises: The critical dimension is changed from a value equal to the minimum pitch to zero to determine the duty cycle at which the zero-order intensity light at the substrate is minimum.

13. The computer-readable medium of claim 1, wherein the sub-resolution features include at least one of horizontal grating or vertical grating.

14. The computer-readable medium of claim 1, further comprising: An overlay between mosaic patterns of images of adjacent exposure fields is determined to reduce variations in critical dimensions of the mosaic patterns printed on the substrate.

15. The computer readable medium of claim 1, wherein the sub-resolution features include at least one of horizontal gratings or vertical gratings, and wherein the lithography process is an extreme ultraviolet (EUV) lithography process.

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