Computer program product and method for determining topography

Abstract

A method of determining topography, the method comprising: obtaining a first focus value, the first focus value being derived from a computational lithography model modeling patterning of an unpatterned substrate or from measurements of a patterned layer on an unpatterned substrate; obtaining a second focus value, the second focus value being derived from measurements of a substrate having topography; and determining a value of the topography based on the first focus value and the second focus value.

Description

[0001] This application is a divisional application of the international application PCT / EP2017 / 080704, which entered the Chinese national phase on June 21, 2019, with application number 201780079785.8.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to U.S. application 62 / 438,665, filed December 23, 2016, the entire contents of which are incorporated herein by reference. Technical Field

[0004] The present invention relates to a method for determining product-induced topography by combining computational lithography modeling with on-product measurements and an apparatus for applying the method. The present invention also relates to a method and apparatus for identifying and grading hot spots. Background Art

[0005] Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In this case, a patterning device (e.g., a mask) can include or provide a device pattern (a "design layout") corresponding to a single layer of the IC, and this pattern can be transferred to a target portion (e.g., comprising one or more dies) on a substrate (e.g., a silicon wafer) that has been coated with a layer of radiation-sensitive material ("resist"), such as by irradiating the target portion with a pattern through the patterning device. Generally, a single substrate includes a plurality of adjacent target portions, and the pattern is transferred sequentially to the plurality of adjacent target portions by the lithographic apparatus, one target portion at a time. In one type of lithographic apparatus, the pattern of the entire patterning device is transferred to one target portion at a time; such an apparatus is generally referred to as a stepper. In an alternative apparatus, generally referred to as a stepper-scan apparatus, a projection beam is scanned across the patterning device in a given reference direction (the "scanning" direction) while the substrate is synchronously moved parallel or antiparallel to the reference direction. Different portions of the pattern of the patterning device are progressively transferred to one target portion. In general, since the lithographic apparatus will have a magnification factor M (typically <1), the speed F at which the substrate is moved will be a factor M of the speed at which the projection beam scans the patterning device.

[0006] Before the pattern is transferred from the pattern forming device to the substrate, the substrate may undergo various processes, such as priming, resist coating, and soft baking. After exposure, the substrate may undergo other processes, such as post-exposure baking (PEB), development, hard baking, and measurement / inspection of the transferred pattern. This series of processes serves as the basis for manufacturing a single layer of a device (e.g., an IC). The substrate may then undergo various processes, such as etching, ion implantation (doping), metallization, oxidation, chemical mechanical polishing, etc., all of which are intended to complete a single layer of the device. If several layers are required in the device, the entire process or its variations are repeated for each layer. Ultimately, a device will be present in each target portion on the substrate. Afterwards, these devices are separated from each other by techniques such as slicing or sawing, whereby a single device can be mounted on a carrier, connected to pins, etc.

[0007] Therefore, the manufacture of devices such as semiconductor devices typically involves the use of multiple fabrication processes to process a substrate (e.g., a semiconductor wafer) to form the various features and multiple layers of the device. These layers and features are typically manufactured and processed using, for example, deposition, photolithography, etching, chemical mechanical polishing, and ion implantation. Multiple devices can be made on multiple dies on a substrate, and then the devices are separated into individual devices. This device manufacturing process can be considered a patterning process. The patterning process involves performing a patterning step (such as optical and / or nanoimprint lithography) using a pattern forming device in a lithographic apparatus to transfer the pattern of the pattern forming device to a substrate, and the patterning process typically but optionally involves one or more related pattern processing steps, such as developing a resist by a developing apparatus, baking the substrate using a baking tool, etching using the pattern using an etching apparatus, and the like. Summary of the Invention

[0008] Production substrates often include pattern density-induced topography at extremely fine (submillimeter) resolution; the magnitude of this topography is typically measured in nanometers. However, this magnitude can be quite large compared to the process focus margin. Conventional level sensors within lithographic equipment are unable to measure this production substrate topography with submillimeter lateral resolution. Furthermore, the physical limitations of exposure slit size and shape make this topography extremely difficult to correct using level sensor data within the lithographic equipment focus control system.

[0009] It is therefore desirable, for example, to be able to effectively measure such topography and identify which pattern features tend to be defective due, at least in part, to the topography.

[0010] In one embodiment, a method of determining topography is provided, the method comprising: obtaining a first focus value, the first focus value being derived from a computational lithography model that models patterning of an unpatterned substrate or from measurements of a patterned layer on an unpatterned substrate; obtaining a second focus value, the second focus value being derived from measurements of a substrate having topography; and determining a value of the topography based on the first focus value and the second focus value.

[0011] In one embodiment, a method for hotspot evaluation is provided, the method comprising: obtaining process window data for each of a first hotspot and a second hotspot, the process window data comprising focus information for each of the first hotspot and the second hotspot; and evaluating the focus information of the process window data based on topography data of a substrate by a hardware computer to identify or change a critical state of the first hotspot and / or the second hotspot.

[0012] In one embodiment, a computer program product is provided, comprising a computer non-transitory readable medium having instructions recorded thereon, the instructions implementing any one of the above methods when executed by a computer. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 FIG2 is a schematic diagram of a photolithography apparatus;

[0014] Figure 2 Describing embodiments of lithographic cells or clusters;

[0015] Figure 3 The diagram corresponds to Figure 1 Block diagram of the simulation model of the subsystem in;

[0016] Figure 4A The sub-process window spanned by focus (horizontal axis) and dose (vertical axis) of the CD (CD-PW) for each of the four patterns is shown;

[0017] Figure 4B The sub-process window (represented by the dot-hatched area) spanned by focus (horizontal axis) and dose (vertical axis) of the CD (CD-OPW) of four patterns is shown;

[0018] Figure 5 The diagram shows a schematic example of a measured micron-resolution topography;

[0019] Figure 6 The figure shows a schematic topography evaluated by level sensor technology;

[0020] Figure 7 An exemplary method of topography measurement is illustrated;

[0021] Figure 81. A Poisson curve of a first hot spot and a second hot spot of a focus distribution adjusted by topography data is shown;

[0022] Figure 9 The illustration includes an exemplary scheme for identifying and / or grading the criticality of hot spots using topography; and

[0023] Figure 10 A block diagram illustrating an embodiment of a computer system that can assist in implementing any of the methods and processes disclosed herein. DETAILED DESCRIPTION

[0024] Figure 1 A lithographic apparatus LA is schematically depicted in association with which the techniques described herein may be utilized. The apparatus comprises an illumination optical system (illuminator) IL configured to condition a radiation beam B (e.g., UV radiation or DUV radiation), a patterning device support or support structure (e.g., a mask table) MT configured to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning device according to certain parameters; one or more substrate tables (e.g., wafer stages) WTa, WTb configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate according to certain parameters; and a projection optical system (e.g., a refractive, reflective, or catadioptric optical system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0025] The illumination optical system may include various types of optical components for directing, shaping or controlling radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof. In this particular case, the illumination system also includes a radiation source SO.

[0026] The patterning device support 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 patterning device support can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device. The patterning device support can be, for example, a frame or a stage, which can be fixed or movable as required. The patterning device support can ensure that the patterning device is in a desired position, for example, relative to a projection system. Any use of the terms "reticle" or "mask" herein may be considered synonymous with the more general term "patterning device."

[0027] The term "patterning device", as used herein, should be broadly interpreted as referring to any device that can be used to impart a pattern in the cross-section of the radiation beam so as to produce a pattern in a target portion of the substrate. It should be noted that, for example, if the pattern imparted to the radiation beam includes phase-shifting features or so-called assist features, this pattern may not exactly correspond to the desired pattern in the target portion of the substrate. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device (such as an integrated circuit) produced in the target portion.

[0028] The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in photolithography and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array uses a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incident radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam that is reflected by the mirror matrix.

[0029] As depicted here, the apparatus is of the transmissive type (e.g., using a transmissive patterning device). However, the apparatus can be of the reflective type (e.g., using a programmable mirror array of the type mentioned above, or using a reflective mask). The apparatus can use a patterning device of a different kind than a typical mask; examples include a programmable mirror array or an LCD matrix.

[0030] The lithographic apparatus may also be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, such as water, so as to fill the space between the projection system and the substrate. Immersion liquid may also be applied to other spaces in the lithographic apparatus, such as the space between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term "immersion" as used herein does not mean that structures such as the substrate are necessarily immersed in the liquid, but only means that the liquid is located between the projection system and the substrate during exposure.

[0031] See Figure 1, the illuminator IL receives a radiation beam from a radiation source SO (e.g., a mercury lamp or an excimer laser, an LPP (laser produced plasma) EUV source). For example, when the radiation source is an excimer laser, the radiation source and the lithographic apparatus may be separate entities. In these cases, the source is not considered to constitute part of the lithographic apparatus, and the radiation beam is transferred from the source SO to the illuminator IL by means of a beam delivery system BD comprising, for example, suitable directing mirrors and / or a beam expander. In other cases, for example, when the source is a mercury lamp, the source may be an integral part of the lithographic apparatus. The source SO and illuminator IL, together with the beam delivery system BD (where necessary), may be referred to as a radiation system.

[0032] The illuminator IL may include an adjuster AD for adjusting the spatial intensity distribution and / or angular intensity distribution of the radiation beam. In general, at least the outer and / or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may include various other components, such as an integrator IN and a condenser CO. The illuminator can be used to condition the radiation beam to have a desired uniformity and intensity distribution in its cross-section.

[0033] The radiation beam B is incident on a patterning device (e.g. a mask) MA, which is held on a patterning device support (e.g. a mask table) MT, and is patterned by the patterning device. Having traversed the patterning device (e.g. a mask) MA, the radiation beam B passes through projection optics PS, which focuses the beam onto a target portion C of the substrate W, thereby projecting an image of the pattern onto the target portion C. With the aid of a second positioner PW and a position sensor IF (e.g. an interferometry device, a linear encoder, a 2D encoder or a capacitive sensor), the substrate table WT can be accurately 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 ) may be used to accurately position the patterning device (e.g., mask) MA relative to the path of the radiation beam B, for example, after mechanical retrieval from a mask library or during scanning.

[0034] The patterning device (e.g., mask) MA and substrate W can be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks as shown occupy dedicated target portions, the substrate alignment marks can be located in the spaces between target portions (these substrate alignment marks are called scribe line alignment marks). Similarly, in the case where more than one die is provided on the patterning device (e.g., mask) MA, the patterning device alignment marks can be located between the dies. Small alignment marks can also be included within the die among device features, in which case it is desirable to make the mark as small as possible and not require any imaging or process conditions that are different from those of adjacent features. An alignment system for detecting alignment marks is further described below.

[0035] The lithographic apparatus LA in this example is of a so-called dual-platform type having two substrate tables WTa, WTb and two stations - an exposure station and a measurement station - between which substrate tables can be exchanged. While exposing one substrate on one substrate table at the exposure station, another substrate can be loaded onto the other substrate table at the measurement station and various preparatory steps can be performed. The preparatory steps can include using a level sensor LS to draw a map of the surface control of the substrate, using an alignment sensor AS to measure the position of an alignment mark on the substrate, performing any other type of measurement or inspection, and the like. This achieves a substantial increase in the throughput of the equipment. More generally, the lithographic apparatus may be of a type having two or more stages (e.g., two or more substrate stages, substrate stages and measurement stages, two or more pattern forming device stages, and the like). In these "multi-platform" devices, a plurality of stages may be used in parallel, or preparatory steps may be performed on one or more stages while one or more other stages are used for exposure. For example, a dual-platform lithographic apparatus is described in U.S. Patent No. 5,969,441, which is incorporated herein by reference in its entirety.

[0036] Although the level sensor LS and alignment sensor AS are shown adjacent to the substrate table WTb, it will be appreciated that the level sensor LS and alignment sensor AS may additionally or alternatively be provided adjacent to the projection system PS to take measurements with respect to the substrate table WTa.

[0037] The depicted apparatus can be used in various modes including, for example, step mode or scan mode.The construction and operation of lithographic apparatus are well known to those skilled in the art and require no further description to understand embodiments of the present invention.

[0038] like Figure 2As shown in the figure, the lithography equipment LA forms part of the lithography system, which is called a lithography cell LC or lithography element or cluster. The lithography cell LC may also include equipment for performing pre-exposure and post-exposure processes on the substrate. Typically, these equipment include a spin coater SC for depositing a resist layer, a developer DE for developing the exposed resist, a chill plate CH and a bake plate BK. A substrate handler or robot RO picks up the substrate from the input / output ports I / O1, I / O2, moves the substrate between the different process equipment, and then delivers the substrate to the loading station LB of the lithography equipment. These devices, which are often collectively referred to as the coating and development system (track), are under the control of the coating and development system control unit TCU, which is itself controlled by the management control system SCS, which also controls the lithography equipment via the lithography control unit LACU. Therefore, the different equipment can be operated to maximize production volume and processing efficiency.

[0039] The pattern forming device mentioned above includes or can form one or more design layouts or patterns (hereinafter referred to as design patterns for convenience). The design pattern can be generated using a computer-aided design (CAD) program, a process often referred to as electronic design automation (EDA). Most CAD programs follow a set of predetermined design rules to generate a functional design pattern / pattern forming device. These rules are set by processing and design constraints. For example, the design rules define the spatial tolerances between circuit devices (such as gates, capacitors, etc.) or interconnects to ensure that the circuit devices or lines do not interact with each other in an undesirable manner. One or more of the design rule constraints can be referred to as a "critical dimension" (CD). The critical dimension of a circuit can be defined as the minimum width of a line or hole, or the minimum space between two lines or two holes. Therefore, the CD determines the overall size and density of the designed circuit. Of course, one of the goals in integrated circuit fabrication is to faithfully reproduce the original circuit design (via the pattern forming device) on the substrate.

[0040] Thus, in a lithographic apparatus, an illumination system provides illumination (i.e., radiation) in the form of an illumination pattern to a pattern forming device, and a projection system directs and shapes the illumination onto the substrate via an aerial image (AI) through the pattern forming device system. The illumination pattern defines the characteristics of the illumination, such as the angular or spatial intensity distribution (e.g., conventional, dipole, annular, quadrupole, etc.), the illumination sigma (σ) setting, and the like. The aerial image (AI) is the radiation intensity distribution at the substrate level. A resist layer on the substrate is exposed, and the aerial image is transferred to the resist layer as a latent image "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.

[0041] Currently, one or more parts of a patterning process can be mathematically modeled and / or simulated to implement patterning process design, control, monitoring, etc. For example, a lithography process can be simulated / modeled to analyze how an input design pattern layout is imaged by a lithography apparatus under specific conditions. Therefore, a simulation that mathematically models the imaging by the lithography apparatus will typically be performed.

[0042] Figure 3 , an exemplary flow chart for simulating lithography in a lithographic apparatus is illustrated in FIG. An illumination model 301 represents the optical properties of the illumination provided to the patterning device (including the radiation intensity distribution and / or phase distribution). A projection system model 302 represents the optical properties of the projection system (including changes to the radiation intensity distribution and / or phase distribution caused by the projection system). A design pattern model 303 represents the optical properties of a design pattern layout (including changes to the radiation intensity distribution and / or phase distribution caused by a given design pattern layout 303), which is a representation of the arrangement of features on or formed by the patterning device. An aerial image 304 can be simulated based on the design pattern model 303, the projection system model 302, and the design pattern model 303. A resist image 306 can be simulated based on the aerial image 304 using a resist model 305. Simulation of lithography can, for example, predict the profile and CD in the resist image.

[0043] More specifically, it should be noted that the illumination model 301 may represent the illumination mode and / or optical characteristics of the illumination system, including, but not limited to, numerical aperture settings, illumination sigma (σ) settings, specific illumination shapes (e.g., off-axis radiation illumination, such as toroidal, quadrupole, dipole, etc.), etc. The projection system model 302 may represent the optical characteristics of the projection system, including aberrations, distortions, one or more refractive indices, one or more physical dimensions, one or more physical scales, etc. The design pattern model 303 may represent one or more physical properties of the physical patterning device, as described, for example, in U.S. Patent No. 7,587,704, which is incorporated herein by reference in its entirety. A resist model may be used to calculate a resist image from an aerial image, an example of which may be found in U.S. Patent Application Publication No. US2009-0157360, the entire disclosure of which is incorporated herein by reference. The resist model is only related to the properties of the resist layer (e.g., the effects of chemical processes occurring during exposure, PEB, and development). The optical properties of a lithographic apparatus (e.g., the illumination mode, the properties of the patterning device, and the projection system) dictate the aerial image. Because the patterning device used in a lithographic apparatus can be varied, it may be desirable to decouple the optical properties of the patterning device from the optical properties of the rest of the lithographic apparatus, including at least the illumination system and the projection system.

[0044] Therefore, the goal of the simulation is to accurately predict, for example, edge placement, spatial image intensity slope, and / or CD, which can then be compared to the intended design. This prediction can be performed for a variety of conditions, such as various dose, focus, and so on. The intended design is typically defined as a pre-optical proximity correction (OPC) design pattern that can be provided in a standardized digital file format such as GDSII or OASIS or other file formats.

[0045] One or more portions of a design layout may be identified, which are referred to as clips, critical features, or hotspots (hereinafter referred to as hotspots for convenience). In an embodiment, a set of hotspots is extracted from the design layout, and the set represents a complex pattern in the design layout (e.g., approximately 50 to 1000 hotspots may be provided by the user, but any number of hotspots may be provided, identified, or used). These hotspots represent small portions of the design (i.e., circuits, cells, patterns, or design clips), and in particular represent small portions that require special attention and / or verification. Hotspots may be identified by experience (including hotspots provided by the user), by trial and error, or by performing full-chip simulations. In an embodiment, the imaging properties of the hotspot define the boundaries of a process window (e.g., a dose and focus process window within which the exposed features have critical dimension values within a tolerance range (e.g., ±5%, ±10) of the patterning process). The hotspot may include one or more test patterns or gauge patterns for use in its evaluation.

[0046] The initial large set of hotspots may be provided a priori by the user based on one or more known critical feature areas in the design pattern that require special attention. Alternatively, in an embodiment, the initial large set of hotspots may be extracted from the entire design pattern using some automatic (such as machine vision) or manual algorithm that identifies one or more critical feature areas.

[0047] The simulation may involve evaluating the process window of some of the patterns in the design pattern. The process window of a pattern is the space of processing parameters that will produce a pattern within specifications. From a mathematical perspective, the process window is the region in vector space spanned by all processing parameters. In a given patterning process, the process window of a pattern is dictated by the pattern specifications and the physics involved in the patterning process.

[0048] It may be inconvenient to use the region in the vector space spanned by all process parameters as a process window. Instead of the region of the space spanned by all process parameters ("full PW"), a region of a subspace (i.e., a space spanned by fewer process parameters than all process parameters) ("sub-PW") can be used. For example, in a patterning process with many process parameters, a region of the subspace spanned by focus and dose can be used as a sub-PW.

[0049] Processing parameters are parameters of the patterning process. The patterning process can include processes both upstream and downstream of the actual photolithographic transfer of the pattern. Processing parameters can fall into multiple categories. The first category can be parameters of the lithographic apparatus or any other equipment used in the patterning process. Examples of this category include parameters of the lithographic apparatus's illumination system, projection system, substrate stage, etc. The second category can be parameters of any process performed during the patterning process. Examples of this category include focus, dose, bandwidth, exposure duration, development temperature, chemical composition used in development, etc. The third category can be parameters of the designed pattern. Examples of this category include resolution enhancement technology (RET) or optical proximity correction adjustments, such as the shape and / or location of assist features. The fourth category can be parameters of the substrate. Examples include properties of the structure underlying the resist layer, the chemical composition of the resist layer, and / or the physical dimensions of the resist layer. The fifth category can be parameters representing characteristics of temporal variations in one or more parameters of the patterning process. Examples of this category can include characteristics of high-frequency stage movement (e.g., frequency, amplitude, etc.), high-frequency laser bandwidth changes (e.g., frequency, amplitude, etc.), and / or high-frequency laser wavelength changes. These high frequency changes or movements are higher than the response time of the mechanisms used to adjust the underlying parameters (e.g., stage position, laser intensity, etc.) A sixth category may be characteristics upstream or downstream of exposure, such as post-exposure bake (PEB), development, etching, deposition, resist coating, doping, and / or packaging.

[0050] Various patterns in a design pattern can have different process windows. Examples of pattern specifications related to potential systematic defects include checking CD, necking, line pullback, line thinning, edge placement, overlap, resist top loss, resist undercut, and / or bridging. The process windows of all patterns in a design pattern, or a portion thereof, can be obtained by combining the process windows of each individual pattern (e.g., overlapping the process windows).

[0051] In an example, when a pattern specification specifies only the CD of a pattern, the process window of the pattern may be referred to as a CD process window (CD-PW). When a pattern specification specifies only the CD of a group of patterns, the overlapping process windows of the group of patterns may be referred to as a CD overlapping process window (CD-OPW). A CD-PW or CD-OPW may have sub-PWs. Figure 4A The sub-PW spanned by focus (horizontal axis) and dose (vertical axis) of the CD (CD-PW) for each of the four patterns is shown. Figure 4B The sub-PWs (represented by the dotted area) spanned by focus (horizontal axis) and dose (vertical axis) of the CD of the four patterns (CD-PW) are shown. Thus, the CD-OPW is the overlapping area of the CD-PWs of the four patterns.

[0052] As mentioned above, those process windows that define patterns that overlap the boundaries of the process windows can be considered hotspots because those patterns are likely to be defective if one or more of the process window processing parameters deviate relatively slightly from their respective process window definitions. Therefore, it is useful to focus on the hotspots by, for example, identifying them, reducing their number under consideration, and / or ranking their potential to be defects subject to process variations in the patterning process.

[0053] Now, in typical processing of a substrate, one or more overlapping layers of a device structure are formed on the substrate. Thus, in an embodiment, a first layer may be formed by patterning a resist, which is then used as a mask for etching the layer. Thereafter, one or more materials may be deposited on this first layer. For example, one or more filler materials may be provided to "fill" any remaining recesses. Subsequently, before applying another resist layer to pattern the next layer, a planarization process (e.g., chemical mechanical polishing (CMP)) may be performed to smooth the layer of substrate for application of the resist layer. Smoothing is provided so that the subsequent resist layer is desirably smooth.

[0054] However, topography can exist in layers of the substrate underlying the resist layer, regardless of whether a planarization process has been performed on those layers. Topography can be introduced by local pattern density variations across multiple layers on the substrate, even when a planarization process has been applied to one or more of those layers. Thus, the combined effects of pattern density and planarization of layers 0 to N-1 create the topography encountered during exposure of layer N.

[0055] Thus, topography may particularly induce intra-die or intra-field effects because they arise from pattern density variations at the die or field level (hereinafter, the discussion will focus on the die level, but the same considerations apply to the field level - in embodiments, a die corresponds to a portion of an object that becomes a single device. That is, in the case where the object is a semiconductor wafer, the object is cut into small pieces corresponding to the die, each die becoming, for example, a semiconductor device; while in embodiments, a field corresponds to the size or dimension of the exposure field of a lithographic apparatus used to pattern a substrate, and thus a field may include multiple dies, where, for example, a pattern forming device provides a pattern including multiple dies). This topographic effect is different from die-to-die variations across the substrate (e.g., caused by substrate warping, etc.). Furthermore, this intra-die topographic effect is highly systematic and relatively predictable, and is based on the spatial frequency of one or more functional blocks of the device design. This is because, for a particular patterning process for manufacturing a particular device on the substrate, essentially the same combination of pattern density variations occurs in each die across the substrate.

[0056] Figure 5Schematic example of sub-millimeter (typically sub-micron) resolution topography of a field (with multiple dies, in this case 30 dies) extending in the X and Y directions on a substrate is shown. Relatively systematic variations in the topography are visible. This topography can be obtained using high-resolution optical measurement tools (such as interferometry measurement equipment). However, this process is destructive because it involves specific coatings and is performed without patterning process stacks (e.g., resists, anti-reflective coatings, etc.). Therefore, the absence of patterning process stacks and the presence of coatings that are different from those in typical patterning processes make this measurement not representative of the topography in the patterning process. Therefore, typical tools used to measure topography tend to be slow, may be destructive to the substrate device pattern, and / or may not represent the topography in the typical patterning process. Therefore, this topography measurement is not particularly compatible with patterning process integration.

[0057] Figure 6 The convolution process using the pattern profile enhancement level sensor measurement is shown to evaluate the Figure 5 Schematic example of the topography of a field that is the same as the field measured by a level sensor (such as level sensor LS) in FIG. This technique involves estimating the topography by oversampling the measurement using pattern layout aware deconvolution. However, although the level sensor has good integration in the patterning process (it is fast, non-destructive, and can measure the topography in general patterning processes), this technique is relatively crude (and in comparison to Figure 5 is a less accurate estimate), and due to the physical limitations of the relatively large horizontal sensor spot fingerprint, this technique may not achieve the best resolution. Figure 6 As seen in , the level sensor will not recognize much, if any, of the topography. Consequently, a level sensor-based control system that manages focus control will not correct for much, or most, of the topography, if any, because its measurements will not show much, or most, of the topography, if any.

[0058] This micron-resolution topography can create a host of issues with focus control and process window centering. Therefore, knowledge of the topography can be important in improving pattern fidelity of hotspots and other pattern features. Furthermore, grading of patterned hotspots and post-CMP hotspot identification also require this topography information.

[0059] Therefore, it is desirable to have, for example, accurate, process-integrated, high-resolution topography measurement technology.

[0060] Thus, a novel topography measurement technique is provided herein. In one embodiment, this technique involves using a combination of data corresponding to an unpatterned substrate (e.g., CD data) and non-topography measurement data (e.g., CD data) of a substrate having topography to obtain topography. For example, in one embodiment, this technique involves determining topography using a combination of computational lithography process modeling and relatively high resolution (compared to, for example, level sensors) and relatively fast critical dimension measurements. This technique can be easily integrated into a patterning process and its control system. Thus, a process-integratable, scalable, on-demand resolution topography measurement technique is provided.

[0061] An example of a process flow for the technology is described in Figure 7 middle. Figure 7 Demonstrating the process of submicron resolution topography determination.

[0062] At 1110, the resolution of the topography determination is specified along with the location on the substrate where the topography is determined. Thus, the graph at 1110 displays, in dot format, examples of the locations where the topography is determined along with the resolution of the topography. In this case, a resolution of 0.5 mm is selected as an example, and the resolution is displayed at dot intervals. Furthermore, in this example, the location and resolution are specified for a specific die. The location and resolution are not specified for a portion of a die, a field comprising multiple dies, a region of the substrate, or the like.

[0063] The selection of resolution and / or location can be automatically selected by the system (e.g., a hardware processor running software to implement at least part of the process) or manually controlled by the user. The selection of resolution and / or location can be dictated by, for example, process efficiency (e.g., higher resolution, more processing time), the capabilities of the measurement tools described below, the needs of the user, etc. Thus, the desired resolution can vary based on the needs of the application. Additionally, the locations and their distribution can be selected so as to achieve an optimal inspection speed for the inspection device (e.g., so that multiple locations are within the same field of view of the inspection device). Alternatively, the minimum resolution can be derived from the cutoff frequency of the power spectral density of the pattern density map of the topography (which is related to the resolution).

[0064] The identified parts are processed by calculation via 1160 and measurement via 1120 and 1130 at the specifications of the resolution and part.

[0065] At 1120, a photolithographic apparatus exposes a resist layer on a substrate having a topography evaluated using a pattern. In an embodiment, the pattern is a non-device test pattern or a device pattern.

[0066] Additionally, the pattern is exposed onto the substrate at a plurality of different focus conditions (e.g., a plurality of focus values around the optimal focus). Thus, referring to 1110, the die depicted herein can be exposed at each of a plurality of focus conditions at, above, and below the optimal focus condition. For example, the exposure can be a focus exposure matrix (FEM), which is typically used to identify the optimal dose and focus (or process window) based on CD measurements of selected portions of the die by analyzing, for example, a Poisson curve. While this technique does not require dose data from the FEM exposure, focus data at a particular dose can be used in this technique to obtain the topography.

[0067] At 1130, a non-topographic parameter (e.g., CD) sensitive to focus is measured for each location for each focus condition. That is, the one or more features for which the non-topographic parameter is measured are features whose magnitude varies with changes in focus. Desirably, features with high sensitivity (e.g., within 20% of the maximum sensitivity) are selected. Computer simulations can be used to identify features with high focus sensitivity.

[0068] Thus, multiple dies exposed under different focus conditions are measured. Additionally, multiple sites within each of those dies are measured. Thus, referring back to the die in 1110, a measurement of a non-topographic parameter (e.g., CD) will be obtained for, for example, the top left site within the die for each of the multiple focus conditions. Similarly, all other sites within the die will have a collection of measurements of the non-topographic parameter (e.g., CD) at each of the multiple focus conditions. Thus, each site will have a data set of values for the non-topographic parameter (e.g., CD) for the multiple focus conditions. This data set can then be provided to the computational process at 1140, described in further detail below. Alternatively, a best focus can be determined for each site based on those measurements (e.g., the center, mean, or peak of the distribution of the data, where the center, mean, or peak corresponds to the non-topographic parameter value that is closest to the expected value of the non-topographic parameter) and provided as a data set to 1140.

[0069] In an embodiment, the metrology tool used to inspect non-topographic parameters (e.g., CD) has a resolution significantly higher than, for example, a level sensor and can perform measurements at, for example, 0.5 mm resolution. In an embodiment, the metrology is an electron beam inspection tool. In an embodiment, the measurement is performed after development of the resist. In an embodiment, the measurement is performed after etching. In an embodiment, the measurement is non-destructive (e.g., the electron beam is configured so as not to be destructive).

[0070] In embodiments, there may be one pattern type to be measured at a location, or only one pattern type to be measured at a location. Thus, each location will have one non-topography parameter value. In embodiments, there may be more than one pattern type at a location, and thus, multiple non-topography parameter measurements may be made for each location. If more than one non-topography parameter measurement is obtained for each location, then, as discussed further below, more than one topography determination may be performed for each location. This may, for example, increase accuracy. However, this may, for example, increase measurement time.

[0071] At 1150, the computational lithography model is used to obtain data for comparison with the data at 1130. In an embodiment, the data may be obtained using the computational lithography model described above. Figure 3 The simulation model described is used to obtain the pattern for the exposure at 1120 and predict the best focus at or near each of the locations for each of the one or more pattern features of the pattern for the exposure at 1120. That is, the model performs calculations based on the absence of topography and the fact that the substrate surface is completely flat. The prediction of the best focus for each location can then be output at 1140 for comparison with the data at 1130. In embodiments, the data can include data similar to that generated at 1130. For example, the above description of the best focus can be used. Figure 3 The simulation model described is used to acquire a pattern for exposure at 1120 and determine predicted CDs of one or more pattern features at each of the locations for a range of focus conditions. Thus, the computational lithography model can produce output comparable to the measurements at 1130 (e.g., a collection of CD measurements at each location for multiple focus conditions).

[0072] Additionally or alternatively, for prediction using the computational lithography model at 1150, an unpatterned substrate covered with a resist layer (i.e., a substrate without the topography being considered) may be exposed and measured in a manner similar to 1120 and 1130 to obtain a set of CD measurements at each location for a plurality of focus conditions. This data may then be supplied to 1140, or a best focus may be determined from those measurements for each location and then supplied to 1140.

[0073] Next, at 1140, the datasets from 1130 and 1150 (one dataset corresponding to each region) are processed to determine the topography at each of the regions. In embodiments, the difference between the statistical or other representative information for each dataset 1130, 1150 for a region provides a measure of the topography of that region. For example, if both datasets 1130, 1150 include best focus values, then the difference between the best focus values for a region represents a measure of the topography at that region. If both datasets 1130, 1150 include non-topography parameter values that vary with focus at the region, the center, average (e.g., mean), or peak value of the distribution of CD values that vary with focus can be determined for each dataset 1130, 1150. The difference between those focus centers, averages, or peaks (best focus) then yields a measure of the topography at that region. Of course, the best focus of one dataset 1130, 1150 can be compared against the determined focus center, average, or peak value of the other dataset 1130, 1150.

[0074] See Figure 7 1140 in the figure depicts an example plot 1160 of the distribution of CD values (on the vertical axis) as a function of focus (on the horizontal axis, where 0 is nominal focus and other values are defocus from nominal focus) for a particular location in the die 1110 and based on data from 1150 (e.g., predicted data or measured data from an unpatterned substrate). Additionally, the center, average, or peak value of focus (best focus) is depicted at 1165. Similarly, an example plot 1170 of the distribution of CD values as a function of focus for a particular location in the die 1110 and based on data from 1130 (e.g., measured data from a substrate having topography) is depicted in the same graph. Additionally, the center, average, or peak value of focus (best focus) is depicted at 1175. Based on this data, the topography at a location can be calculated as the difference between the center, average, or peak value 1175 and the center, average, or peak value 1165. In embodiments, depending on where a nominal plane extending through the topography is defined, the sign of the difference may indicate whether the topography is a protrusion or a depression relative to the plane. This analysis may then be repeated for each of the locations at 1140 to obtain the topography of the region of the substrate, as schematically depicted at 1190. Of course, no curves need be generated, and are presented merely for visualization of the method. Furthermore, point 1165 and / or point 1175 may represent the respective best focus provided from 1150 or 1130. Furthermore, while the data may be discontinuous, data between the data points may be obtained through interpolation, extrapolation, fitting, and the like.

[0075] The topography measured with this technique can be supplemented with the larger range of topography resolved by one or more lithographic apparatus metrology systems. For example, the topography measured with this technique can be varied over portions for which the lithographic apparatus can generate relatively accurate topography data.

[0076] Furthermore, the topography measured using this technique can be supplemented with substrate-specific topography data obtained by one or more lithography apparatus metrology systems. Thus, a more customized topography can be generated for a specific substrate based on topography data from one or more lithography apparatus metrology systems measuring the specific substrate. Thus, for example, in embodiments, a "just-in-time" topography can be generated by combining topography from this technique with topography modified by data from a level sensor of a lithography apparatus measuring the specific substrate to obtain a specific topography for a substrate or a specific location on the substrate.

[0077] The topography measured using this technique can be used to calibrate another topography determination technique. For example, the other technique can be a model generated from a pattern perimeter density map (i.e., pattern density information of structures in the current and all underlying layers), which can provide an estimate of the topography. Thus, the topography measured using the techniques described herein can provide a calibration for the model.

[0078] The topography determined using the techniques described in this invention can be used as feedback or feed-forward data for controlling equipment in a patterning process (eg, a lithographic apparatus) to achieve, for example, layout / process window aware control.

[0079] The topography determined using the techniques described herein can be used for computational hotspot identification and / or improved grading of hotspot criticality or criticality; embodiments of topography-aware hotspot identification and grading are described below. Thus, this technique can be used in combination with systematic, topography-assisted, patterned hotspot detection and / or grading methods induced by the product.

[0080] The topography determined using the techniques described in this invention can be used to identify overlay issues induced by pattern geometry. For example, defocus induced by local microtopography can introduce a sidewall angle in one layer that is different from the sidewall angles in other layers. The etching process can then react differently to this different sidewall angle in one layer than in another layer, causing a shift in CD from one layer to another and, therefore, causing overlay concerns. Therefore, understanding this microtopography can help control such overlay issues.

[0081] Thus, this technique provides a new topography determination technique that involves using a combination of data corresponding to an unpatterned substrate (e.g., CD data) and non-topography measurement data (e.g., CD data) of a substrate having topography to obtain topography. In embodiments, the technique involves combining computational lithography modeling with non-topography parameter measurements to obtain topography. Additionally, this technique can be easily integrated into patterning processes and their control systems. Furthermore, in embodiments, this technique is relatively fast and can produce accurate, relatively high-resolution topography determinations without the need for non-destructive measurements.

[0082] As mentioned above, computational lithography models can be used to identify and evaluate hotspots. For example, a user can provide pattern features suspected of being faulty, and the model can then detect whether those pattern features are likely to be defective during or after the patterning process based on, for example, process window analysis and patterning process variation considerations. Similarly, the model can evaluate all or many of the features in a pattern layout and detect whether any pattern feature is likely to be defective during or after the patterning process based on, for example, process window analysis.

[0083] Thus, computational hotspot detection can identify pattern features that are process window (depth of focus / exposure latitude) limiting and potential defects (hotspots). However, computational hotspot detection can identify a large number of hotspots (e.g., millions per full wafer). This presents a significant challenge (if not impossibility) for monitoring and controlling these hotspots in high-volume manufacturing. Therefore, a smaller subset of hotspots (e.g., a few hundred or fewer) is typically identified as the most critical hotspots. This typically involves ranking the hotspots so that the most critical hotspots are identified at the end of the ranking.

[0084] There are different methods that can be used to evaluate the criticality of hot spots and rank them according to their criticality level. For example, hot spots on multiple process window PW boundary points (boundary parameters such as the leftmost of best focus, the rightmost of best focus, the highest exposure dose, and the lowest exposure dose) are ranked based on the minimum overlapping process windows.

[0085] While these methods rank hotspots by considering their aerial image properties, they may fail to identify the most critical hotspot or hotspots that are actually on the substrate. This can occur, for example, when the substrate has a topography (e.g., a product-induced topography that is typically systematic across the die and substrate). In that case, the overlap process window (or available process window) is affected not only by the depth of focus and best focus difference per hotspot, but also by the topography of each hotspot.

[0086] Therefore, methods are desired to identify and / or classify the criticality of hot spot features on a product substrate, for example, where topographical differences exist between the features.

[0087] Thus, techniques are provided for identifying and / or ranking the most critical or more critical hotspots based on the aerial image properties of the hotspots and the topography of the substrate in which the pattern corresponding to the hotspots is generated. Specifically, methods are disclosed that include modeled or measured intra-die or intra-field topography for hotspot identification and / or ranking. Thus, in embodiments, a patterned hotspot identification and / or ranking method is provided that is aided by systematic topography induced by a product.

[0088] As mentioned above, conventional hotspot identification and ranking methods may not account for shifts (eg, systematic shifts) in focus distribution due to topography. Therefore, methods are provided that factor topography into hotspot identification and / or ranking.

[0089] Figure 8 Example Poisson curves are shown for two example pattern features (in this case, hotspots), where the curves depict their critical dimensions (on the left vertical axis) as a function of defocus (on the horizontal axis). A first curve 1300 is for a first feature 1305, and a second curve 1310 is for a second, different feature 1315. Further specified is a CD threshold 1320 that defines the lower limit of acceptable CD for the first and second features. Of course, more than just one threshold is required; for example, each pattern feature can have its own respective threshold. For convenience, only one threshold is shown here.

[0090] Two additional thresholds are also shown that define the outer limits or outside extents of the focus range of these features when within the CD thresholds. Thus, threshold 1330 specifies where curve 1300 of the first feature intersects threshold 1320, and threshold 1340 specifies where curve 1310 intersects threshold 1320. Thus, the region between thresholds 1330 and 1340 and beyond threshold 1320 generally provides a process window for detecting hotspots. Any defocus outside these outer limits will, with a high probability, result in defects in both the first and second features.

[0091] Now, Figure 8Further shown are a focus profile 1350 (in the form of a histogram) of a first feature 1305 across the substrate adjusted for the topography associated with the first feature, and a focus profile 1360 (in the form of a histogram) of a second feature 1315 across the substrate adjusted for the topography of the second feature. As will be appreciated, there will not be uniform focus across the substrate. Therefore, a focus profile that describes the variation in focus across the substrate can be used. For example, when exposing a particular feature across the substrate, the focus profile can effectively provide a count of the number of times each of a plurality of focus values occurs for the particular feature. Thus, the particular focus profile used can be, for example, a focus profile known from past executions of the patterning process under consideration, a different patterning process, etc. Additionally, it can be specific to a particular combination of equipment and / or process steps. For example, it can be a normal (Gaussian) distribution.

[0092] Additionally or alternatively, the actual focus distribution obtained from the substrate (with tolerance for variations) may be used or used to further fine-tune the grading.The actual focus distribution on the substrate may not necessarily be Gaussian, especially if there are systematic fingerprints that skew the distribution.

[0093] To obtain an actual focus profile, for example during the exposure process of a particular feature, a level sensor can measure the height of the substrate in the area including the particular feature and thus give a focus value, i.e., whether it is in focus, positively defocused, or negatively defocused. However, the measurement resolution of the level sensor is significantly lower than the topography described above (e.g., hundreds of microns compared to micron or sub-micron topography). Furthermore, while the level control system will adjust to bring the substrate into optimal focus as much as possible, it will be understood that not all areas of the exposure field will generally be placed into optimal focus—while some portions are in optimal focus, other portions will be out of focus.

[0094] Thus, these measurements may be obtained for multiple areas (e.g., all areas on a substrate) where a particular feature is exposed, including multiple areas within a die where the particular feature is repeated within the die. Thus, for example, if a feature only appears once in a die and there are 100 dies across the substrate, then 100 focus values may be obtained for the particular feature, and thus a distribution may be obtained, such as Figure 8 In an embodiment, pattern features are measured in the same number of locations across the substrate so that there is no sampling bias.

[0095] The focus profile therefore gives a measure of the extent of defocus that a particular feature will likely experience across the substrate due to various factors such as levelling errors, warping of the substrate table, process induced deformations of the substrate and so on.

[0096] In this case, the focus distributions 1350 and 1360 are approximately normal distributions. However, they need not be normal distributions. While the extreme values of the distribution will generally indicate the probability of failure, the extreme values of the distribution are significantly large because the patterning process will generally be designed to ensure that the center portion of the distribution causes features to be exposed correctly and in the desired manner without defects.

[0097] With these focus distributions, the focus distributions are then adjusted by using the modeled or measured topography of the particular feature. In effect, the topography causes the distribution to shift to the left or right. In effect, in an embodiment, a first feature 1305 is positioned below a plane extending through the topography (e.g., the middle of the topography) (e.g., greater than 10 nanometers and up to 15 nm, lower), while a second feature 1315 is positioned above the plane (e.g., at a protrusion) (e.g., greater than 5 nanometers and less than 10 nanometers, higher). Thus, the topography of the first feature 1305 causes its focus distribution to shift in one direction, while the topography of the second feature 1315 causes its focus distribution to shift in the opposite direction. The respective first feature focus distributions and the second feature focus distributions are shifted as a result of their respective topography in Figure 8 Illustrated in FIG. 1 are focus profiles 1350 and 1360 .

[0098] Through evaluation Figure 8 Without considering the focus distributions 1350 and 1360, it can be seen that on the positive defocus side of the process window, the curve 1300 of the first feature 1305 drops below the CD threshold 1320 at a lower absolute value of defocus than the curve 1310 of the second feature 1315, and thus the first feature 1305 is considered to be more restrictive on the positive defocus side than the second feature 1315 (which would have a CD greater than the CD threshold at the defocus at which the first feature 1305 drops below the CD threshold). Therefore, the first feature 1305 can be considered to be critical on the positive defocus side of the process window. Similarly, on the negative defocus side of the process window, the curve 1310 of the second feature 1315 falls below the CD threshold 1320 at a lower absolute defocus value than the curve 1300 of the first feature 1305, and thus the second feature 1315 is considered to be more restrictive on the negative defocus side than the first feature 1305 (which would have a CD greater than the CD threshold at a defocus at which the second feature 1315 falls below the CD threshold). Therefore, the second feature 1315 can be considered to be critical on the negative defocus side of the process window. For convenience, the results are tabulated in Table 1 below:

[0099] Table 1

[0100]

[0101] Thus, in embodiments, patterning process design, control, modification, etc. may be performed based on such ranking for each of first feature 1305 and second feature 1315. That is, both first feature 1305 and second feature 1315 may be highly ranked.

[0102] However, as mentioned above, in embodiments, topography is considered when identifying whether a pattern feature is a critical hotspot and / or when grading pattern features according to their criticality as hotspots. For example, systematic topographical differences between pattern features may result in a change in the identification and / or grading of critical hotspots compared to the identification and / or grading discussed above.

[0103] See Figure 8 In embodiments, identification and / or classification of critical hotspots can be accomplished by, for example, taking into account the topography of the substrate using an adjusted focus profile. For example, considering the positive defocus side, it can be seen that the focus profile 1350 of the first feature 1305 is almost entirely within the process window of curve 1300 (i.e., every value of the focus profile 1350 at the positive defocus side will result in a CD value on curve 1300 that is greater than the CD threshold 1320). In contrast, however, it can be seen that the focus profile 1360 of the second feature 1315 is not entirely within the process window of curve 1310. That is, there are many focus profiles 1360 at the positive defocus side that will result in CD values on curve 1310 that are less than the CD threshold 1320. These are generally given in region 1390. Therefore, the second feature 1315 should be considered critical at the positive defocus side. However, recall that the second feature 1315 was considered less critical at the positive defocus side. Thus, given this analysis, the second feature 1315 can be identified as being critical at the positive defocus side and / or its classification can be adjusted accordingly. Similarly, the first feature 1305 can be identified as being less critical at the positive defocus side and / or its classification can be adjusted accordingly.

[0104] Therefore, considering the topography, the second feature 1315 is more likely to be a defect (a positive defocus defect) because the focus distribution at the location of the second feature 1315 on the substrate (e.g., across the entire substrate) substantially overlaps with the process window boundary. Therefore, the second feature 1315 can be considered to be more critical when considering the topography data.

[0105] Considering the negative defocus side, it can be seen that the focus profile 1350 of the first feature 1305 is almost entirely within the process window of the curve 1300 (i.e., every value of the focus profile 1350 at the negative defocus side will result in a CD value on the curve 1300 that is greater than the CD threshold 1320). Similarly, it can be seen that the focus profile 1360 of the second feature 1315 is almost entirely within the process window of the curve 1310 (i.e., every value of the focus profile 1360 at the negative defocus side will result in a CD value on the curve 1310 that is greater than the CD threshold 1320). Therefore, in this case, the first feature 1305 and the second feature 1310 can be considered relatively equally critical or neutral. However, recalling earlier, the first feature 1305 was considered less critical at the negative defocus side, while the second feature 1315 was considered critical at the negative defocus side. Therefore, the second feature 1315 can be identified as being equally critical or neutral at the negative defocus side, and / or its classification can be adjusted accordingly. Similarly, the first feature 1305 may be identified as being equally critical or neutral at the negative defocus side, and / or its grading may be adjusted accordingly.

[0106] For convenience, the results of this analysis are tabulated in Table 2 below:

[0107] Table 2

[0108]

[0109] Interestingly, even though first feature 1305 may be relatively lower than a plane extending through the topography compared to second feature 1315 being higher than a plane extending through the topography, second feature 1315 may still be identified and / or classified as critical or more critical.

[0110] Appropriate thresholds or functions may be applied to determine the degree of overlap between the focus distribution and the process window. For example, there may be a limit that at least 0.5%, 1%, 2%, or 5% of the focus distribution must be outside the applicable process window to result in identification of a critical state of a hotspot and / or a change in classification. In embodiments, there may be a relative consideration of overlap or non-overlap, such as the ratio of overlap (or non-overlap) of a first feature's focus distribution relative to its process window to the ratio of overlap (or non-overlap) of a second feature's focus distribution relative to its process window. For example, the relative amount of occurrence outside of each process window (between features) may be evaluated.

[0111] like Figure 8As shown in , there may be a search range for determining whether a pattern feature should be identified as a critical or less critical hotspot and / or whether the hotspot classification should be adjusted. For example, search range 1370 can be used to evaluate such identification and / or classification adjustment for the negative defocus side. Since the second feature 1315 will be considered critical on the negative defocus side regardless of topography, if the focus distribution of the first feature 1305 is present in search range 1370, at least the criticality and / or classification of the second feature 1315 will be adjusted. Similarly, search range 1380 can be used to evaluate such identification and / or classification adjustment on the positive defocus side. Since the first feature 1305 will be considered critical on the positive defocus side regardless of topography, if the focus distribution of the second feature 1315 is present in search range 1380, at least the criticality and / or classification of the first feature 1305 will be adjusted.

[0112] Although the topography data is described as being added / subtracted from the focus distribution data, it can be added / subtracted from the simulated process window curve data. Also, although the discussion has described analysis with respect to curves and graphs, the described techniques can be performed solely on the data without necessarily generating curves, graphs, etc.

[0113] Figure 9 The diagram includes an exemplary scheme for topography in hotspot identification or classification. At 1601, the process identifies and / or classifies hotspots as described above based on topography data. The process 1601 obtains information about a focus distribution at 1602. At 1602, the focus distribution can be measured as described above, or the focus distribution can be a normal (e.g., Gaussian) distribution. The distribution can be similar to focus distributions 1350 and 1360. The process 1601 further obtains process window results for multiple pattern features (hotspots) based on computational modeling of the patterning process. At 1601, simulations can be performed to obtain results similar to curves 1300 and 1310. The process 1601 obtains information about topography associated with the pattern features considered at 1604 and / or 1605. At 1604, the topography information can be a modeled topography, which can be obtained by performing calculations using a model to derive a topography that at least considers the pattern features. At 1605, the topography information may be a measured topography that takes into account at least the features of the pattern, which may be obtained by using the above-described Figures 5 to 7 The process 1601 is then based on the measurement of the interferometer, SEM or modeling assisted measurement techniques described above. Figure 8 The described process results in the identification and / or ranking (e.g., re-ranking) of the criticality of hot spots. These identified / ranked hot spots are then more reflective of the patterning process and can enable more accurate hot spot criticality determination, which then leads to better patterning process design, control, modification, etc. and, therefore, better patterning process results.

[0114] Thus, in embodiments, modeled or measured intra-die or intra-field topography is used to identify or rank critical hotspots, which can result in better identification and / or grading results than conventional techniques. For example, the present techniques can provide a way to account for the effects of planarization (e.g., chemical mechanical polishing) on hotspots. Thus, topography-assisted hotspot identification / grading can more accurately identify more restrictive or most restrictive hotspots, thereby potentially reducing verification / monitoring metrology time.

[0115] In an embodiment, a method of determining topography is provided, the method comprising: obtaining a first focus value derived from a computational lithography model that models patterning of an unpatterned substrate or derived from measurements of a patterned layer on an unpatterned substrate; obtaining a second focus value derived from measurements of a substrate having topography; and determining a value of the topography based on the first focus value and the second focus value.

[0116] In an embodiment, the determining comprises a difference between a first focus value and a second focus value. In an embodiment, the first value and the second value correspond to best focus values. In an embodiment, obtaining the second value comprises performing a measurement of a non-topography parameter for each of a plurality of focus values. In an embodiment, the non-topography parameter comprises a critical dimension. In an embodiment, the second focus value is derived from measurements of a substrate having a topography by electron beam inspection equipment. In an embodiment, the first focus value is derived from a computational lithography model that models patterning of an unpatterned substrate. In an embodiment, the first focus value is derived from measurements of a patterned layer on an unpatterned substrate. In an embodiment, all concavities and convexities of the topography are submicron-scale. In an embodiment, the first focus value, the second focus value, and the determined value of the topography are obtained at a plurality of locations across the substrate, and the plurality of values of the topography are combined to form a map of the topography. In an embodiment, the method further comprises selecting, by a user, a resolution of the locations and / or a positional arrangement of the locations on the substrate.

[0117] In an embodiment, a method for hotspot evaluation is provided, the method comprising: obtaining process window data for each of a first hotspot and a second hotspot, the process window data comprising focusing information for each of the first hotspot and the second hotspot; and evaluating the focusing information of the process window data based on the morphology data of the substrate by a hardware computer to identify or change the critical state of the first hotspot and / or the second hotspot.

[0118] In an embodiment, the evaluation comprises evaluating the focus information against a focus distribution across the substrate, and wherein the topography data is used to shift the focus distribution or the focus information. In an embodiment, the focus distribution is obtained based on measurements of a plurality of fields or dies positioned across the substrate. In an embodiment, the evaluation comprises a relative consideration of the overlap or non-overlap of the focus distribution with the focus information of a first hotspot and the overlap or non-overlap of the focus distribution with the focus information of a second hotspot. In an embodiment, the evaluation comprises adjusting the grading of the criticality of the first hotspot relative to the criticality of the second hotspot. In an embodiment, the process window data is obtained by computational lithography modeling. In an embodiment, the focus information at the negative defocus extremes or the positive defocus extremes of the process window data is evaluated to identify or change the criticality of the first hotspot and / or the second hotspot. In an embodiment, the topography is submicron or nanometer scale.

[0119] As will be appreciated by those skilled in the art, the present application may be implemented as a system, method, or computer program product. Thus, aspects of the present application may take the form of a complete hardware embodiment, a complete software embodiment (including firmware, resident software, microcode, etc.), or a combination of software and hardware embodiments, all of which may be generally referred to herein as a "circuit," "module," or "system." Furthermore, aspects of the present application may take the form of a computer program product implemented in any one or more computer-readable media having a computer-usable program code implemented thereon.

[0120] Any combination of one or more computer-readable media may be utilized. A computer-readable medium may be a computer-readable signal medium or a computer-readable storage medium. A computer-readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, device, component, or any suitable combination of the foregoing. More specific examples (non-exhaustive list) of computer-readable media would include the following storage media: an electrical connector with one or more wires, a portable computer floppy disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CDROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer-readable storage medium may be any tangible medium that can contain or store a program for use by or in conjunction with an instruction execution system, device, or device.

[0121] A computer-readable signal medium may include a propagated data signal having computer-readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including but not limited to electromagnetic, optical, or any suitable combination thereof. A computer-readable signal medium may be any computer-readable medium that is not a computer-readable storage medium and that can communicate, propagate, or transport a program for use by or in conjunction with an instruction execution system, apparatus, or device.

[0122] Computer code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, radio frequency (RF), etc., or any suitable combination thereof.

[0123] Computer program code for carrying out operations of aspects of the present application may be written in any combination of one or more programming languages including languages such as Java. TM 、Smalltalk TM , C++ or its similar languages, and conventional procedural programming languages such as "C" or similar programming languages. The program code may be executed entirely on the user's computer, partially on the user's computer, as a separate software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the latter case, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0124] The computer program instructions may also be loaded onto a computer, other programmable data processing device, or other apparatus, so that a series of operational steps are performed on the computer, other programmable device, or other apparatus to produce a computer-implemented process, so that the instructions executed on the computer, other programmable device, or other apparatus provide a process for implementing the functions / actions specified in a box or multiple boxes of the flowchart and / or block diagram.

[0125] As mentioned above, it should be understood that the exemplary embodiments may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment containing both hardware and software elements. In an exemplary embodiment, the mechanisms of the illustrated embodiments may be implemented in software or program code, including but not limited to firmware, resident software, microcode, etc.

[0126] A data processing system suitable for storing and / or executing program code will include at least one processor coupled directly or indirectly to a storage element via a system bus. The storage element may include local memory used during actual execution of the program code, bulk storage, and cache memories that provide temporary storage of at least some program code in order to reduce the number of times the code must be retrieved from bulk storage during execution.

[0127] Input / output or I / O devices (including but not limited to keyboards, displays, pointing devices, etc.) can be coupled to the system either directly or through intervening I / O controllers. Network adapters may also be coupled to the system to enable the data processing system to be coupled to other data processing systems or remote printers or storage devices through intervening private or public networks. Modems, cable modem and Ethernet cards are just a few of the currently available types of network adapters.

[0128] The description of the present application has been presented for the purpose of illustration and description, and this description is not intended to be exhaustive or to limit the invention to the disclosed form. Many modifications and variations will be apparent to those skilled in the art. Embodiments are selected and described to best explain the principles of the present invention, practical applications, and to enable other persons skilled in the art to understand the present invention for various embodiments with various modifications suitable for the intended specific use.

[0129] Figure 10 A block diagram of an embodiment of a computer system 1700 that can assist in implementing any of the methods and processes disclosed herein is shown. The computer system 1700 includes a bus 1702 or other communication mechanism for communicating information, and a processor 1704 (or multiple processors 1704 and 1705) coupled to the bus 1702 for processing information. The computer system 1700 also includes a main memory 1706, such as a random access memory (RAM) or other dynamic storage device, coupled to the bus 1702 for storing information and instructions to be executed by the processor 1704. The main memory 1706 can also be used to store temporary variables or other intermediate information during the execution of instructions to be executed by the processor 1704. The computer system 1700 also includes a read-only memory (ROM) 1708 or other static storage device coupled to the bus 1702 for storing static information and instructions for the processor 1704. A storage device 1710, such as a magnetic disk or optical disk, is provided and coupled to the bus 1702 for storing information and instructions.

[0130] The computer system 1700 may be coupled via bus 1702 to a display 1712, such as a cathode ray tube (CRT) or a flat panel display or a touch panel display, for displaying information to a computer user. An input device 1714, including alphanumeric and other keys, is coupled to bus 1702 for communicating information and command selections to processor 1704. Another type of user input device is a cursor controller 1716 (such as a mouse, trackball, or cursor direction keys) for communicating direction information and command selections to processor 1704 and for controlling cursor movement on display 1712. Such input devices typically have 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.

[0131] According to one embodiment, portions of the processes described herein may be performed by computer system 1700 in response to processor 104 executing one or more sequences of one or more instructions contained in main memory 1706. Such instructions may be read into main memory 1706 from another computer-readable medium (such as storage device 1710). Execution of the sequences of instructions contained in main memory 1706 causes processor 1704 to perform the process steps described herein. One or more processors in a multi-processing arrangement may also be used to execute the sequences of instructions contained in main memory 1706. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions. Thus, the description herein is not limited to any specific combination of hardware circuitry and software.

[0132] As used herein, the term "computer-readable medium" refers to any medium that participates in providing instructions to processor 1704 for execution. Such media can take many forms, including but not limited to non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as storage device 1710. Volatile media include dynamic memory, such as main memory 1706. Transmission media include coaxial cables, copper wire, and optical fibers, including the wires that comprise bus 1702. 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 tape, any other magnetic media, CD-ROMs, DVDs, any other optical media, punch cards, paper tape, any other physical media with a pattern of holes, RAM, PROMs and EPROMs, FLASH-EPROMs, any other memory chips or cartridges, carrier waves as described below, or any other medium from which a computer can read.

[0133] Various forms of computer-readable media may be involved in transmitting one or more sequences of one or more instructions to processor 1704 for execution. For example, the instructions may initially be carried on a disk of a remote computer. The remote computer may load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to computer system 1700 may receive the data over the telephone line and convert the data into an infrared signal using an infrared transmitter. An infrared detector coupled to bus 1702 may receive the data carried in the infrared signal and place the data on bus 1702. Bus 1702 transmits the data to main memory 1706, from which processor 1704 retrieves and executes the instructions. The instructions received by main memory 1706 may optionally be stored on storage device 1710 before or after execution by processor 1704.

[0134] The computer system 1700 may also include a communication interface 1718 coupled to the bus 1702. The communication interface 1718 provides bidirectional data communication coupled to a network link 1720 connected to a local network 1722. For example, the communication interface 1718 may be an integrated services digital network (ISDN) card or a modem for providing a data communication connection with a corresponding type of telephone line. As another example, the communication interface 1718 may be a local area network (LAN) card for providing a data communication connection with a compatible LAN. A wireless link may also be implemented. In any such embodiment, the communication interface 1718 sends and receives electrical, electromagnetic, or optical signals that carry digital data streams representing various types of information.

[0135] The network link 1020 typically provides data communication to other data devices through one or more networks. For example, the network link 1720 can provide a connection to a host computer 1724 or to data equipment operated by an Internet Service Provider (ISP) 1726 through a local network 1722. The ISP 1726, in turn, provides data communication services through the global packet data communication network now commonly referred to as the "Internet" 1728. Both the local network 1722 and the Internet 1728 use electrical, electromagnetic, or optical signals that carry digital data streams. The signals through the various networks and the signals on the network link 1720 and through the communication interface 1718, which carry the digital data to and from the computer system 1700, are exemplary forms of carrier waves transporting the information.

[0136] Computer system 1700 can send messages and receive data, including program code, through the network, network link 1720, and communication interface 1718. In the Internet example, server 1730 can transmit the requested code for an application program through Internet 1728, ISP 1726, local network 1722, and communication interface 1718. For example, one such downloaded application can provide the methods described herein, or portions thereof. The received code can be executed by processor 1704 as it is received and / or stored in storage device 1710 or other non-volatile storage for later execution. In this manner, computer system 1700 can obtain application code in the form of a carrier wave.

[0137] The embodiments may be further described using the following aspects:

[0138] 1. A method for determining a topography, the method comprising:

[0139] obtaining a first focus value derived from a computational lithography model modeling patterning of an unpatterned substrate or derived from a measurement of a patterned layer on an unpatterned substrate;

[0140] obtaining a second focus value, the second focus value being derived from a measurement of a substrate having a topography; and

[0141] A value of the topography is determined based on the first focus value and the second focus value.

[0142] 2. The method of clause 1, wherein the determining comprises a difference between the first focus value and the second focus value.

[0143] 3. The method of clause 2, wherein the first value and the second value correspond to best focus values.

[0144] 4. The method of any one of clauses 1 to 3, wherein obtaining the second value comprises performing a measurement of a non-topographic parameter for each of a plurality of focus values.

[0145] 5. The method of clause 4, wherein the non-topographical parameter comprises a critical dimension.

[0146] 6. The method of any one of clauses 1 to 5, wherein the second focus value is derived from a measurement of the substrate having the topography by electron beam inspection equipment.

[0147] 7. The method of any one of clauses 1 to 6, wherein the first focus value is derived from a computational lithography model that models patterning of an unpatterned substrate.

[0148] 8. The method of any one of clauses 1 to 6, wherein the first focus value is derived from a measurement of a patterned layer on an unpatterned substrate.

[0149] 9. The method of any one of aspects 1 to 8, wherein all valleys and peaks of the topography are on a submicron scale.

[0150] 10. A method as described in any one of aspects 1 to aspect 9, wherein the first focus value, the second focus value and the determined value of the topography are obtained at multiple locations across the substrate, and the multiple values of the topography are combined to form a map of the topography.

[0151] 11. The method according to clause 10 further comprises selecting, by a user, the resolution of the parts and / or the positional arrangement of the parts on the substrate.

[0152] 12. A method for hotspot assessment, the method comprising:

[0153] obtaining process window data for each of a first hotspot and a second hotspot, the process window data including focus information for each of the first hotspot and the second hotspot; and

[0154] Focus information of the process window data is evaluated by a hardware computer based on topography data of the substrate to identify or change a critical state of the first hot spot and / or the second hot spot.

[0155] 13. The method of clause 12, wherein the evaluating comprises evaluating the focus information for a focus distribution across the substrate, and wherein the topography data is used to shift the focus distribution or the focus information.

[0156] 14. A method as described in clause 13, wherein the focus distribution is obtained from measurements of a plurality of fields or dies positioned across the substrate.

[0157] 15. A method as described in aspect 13 or aspect 14, wherein the evaluation includes a relative consideration between the overlap or non-overlap of the focus distribution with the focus information of the first hotspot and the overlap or non-overlap of the focus distribution with the focus information of the second hotspot.

[0158] 16. The method of any one of clauses 12 to 15, wherein the evaluating comprises adjusting a ranking of the criticality of the first hotspot relative to the criticality of the second hotspot.

[0159] 17. The method of any one of clauses 12 to 16, wherein the process window data is obtained by computational lithography modeling.

[0160] 18. The method of any one of clauses 12 to 17, wherein the focus information at the negative defocus extreme or the positive defocus extreme of the process window data is evaluated to identify or change a critical state of the first hotspot and / or the second hotspot.

[0161] 19. The method of any one of aspects 12 to 19, wherein the topography is submicron or nanometer scale.

[0162] 20. A computer program product comprising a computer non-transitory readable medium having instructions recorded thereon, the instructions implementing the method of any one of aspects 1 to 19 when executed by a computer.

[0163] Although specific reference may be made to the manufacture of ICs in the present invention, it should be clearly understood that the description of the present invention has many other possible applications. For example, it can be used in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid crystal display panels, thin film magnetic heads, etc. Those skilled in the art will understand that in the context of such alternative applications, any term "reticle," "wafer," or "die" used herein may be considered interchangeable with the more general term "mask," "substrate," or "target portion," respectively.

[0164] In this document, the terms "radiation" and "beam" are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., having a wavelength of 365 nm, 248 nm, 193 nm, 157 nm or 126 nm) and extreme ultraviolet radiation (EUV, e.g., having a wavelength in the range of about 5-100 nm).

[0165] As used herein, the terms "optimize" and "optimize" refer to or mean adjusting a pattern forming device (e.g., a lithographic device), a pattern forming process or a patterning process, etc., so that the result and / or process has more desired characteristics, such as higher accuracy of the projection of the design pattern on the substrate, a larger process window, etc. Therefore, as used herein, the terms "optimize" and "optimize" refer to or mean the process of identifying one or more values for one or more parameters that provide an improvement in at least one relevant metric compared to an initial set of one or more values for the one or more parameters, such as a local optimum. "Optimal" and other related terms should be interpreted accordingly. In an embodiment, the optimization step can be applied iteratively to provide further improvement in one or more metrics.

[0166] 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 lithographic imaging system, such as those used for imaging on substrates other than silicon wafers.

[0167] The above description is intended to be illustrative rather than restrictive. Accordingly, those skilled in the art will appreciate that modifications may be made to the described invention without departing from the scope of the claims set forth below.

Claims

1. A computer program product comprising a non-transitory computer-readable medium having instructions therein, the instructions being configured, when executed by a computer system, to cause the computer system to at least: obtaining a first value of focus or a first value related to focus, the first value being derived from a computational lithography model modeling patterning of an unpatterned substrate or from measurements of a patterned layer on an unpatterned substrate; obtaining a second value of focus or a second value related to focus, the second value being derived from a measurement of a substrate having a topography; and A value of the topography is determined based on the first value and the second value.

2. The computer program product of claim 1, wherein: The second value is derived from a measurement made by an inspection or metrology device of the substrate having the topography.

3. The computer program product of claim 1 , wherein the instructions are further configured to cause the computer system to select a plurality of locations across the substrate for measurement by an inspection or metrology device in order to optimize an inspection or measurement speed of the inspection or metrology device.

4. The computer program product of claim 1, wherein: The instructions are further configured to cause the computer system to identify an overlay error based on the value of the topography.

5. The computer program product of claim 1 , wherein: The instructions are further configured to cause the computer system to feed forward or feedback the value of the topography to an apparatus for controlling or configuring a patterning process for providing a pattern on a substrate using the apparatus.

6. The computer program product of claim 1, wherein: The first value, the second value, and the determined value of the topography are obtained at a plurality of locations across the substrate, and the plurality of values of the topography are combined to form a map of the topography.

7. The computer program product of claim 1, wherein: Determination of the value of the topography includes a difference between the first value and the second value.

8. The computer program product of claim 1, wherein obtaining the second value comprises performing a measurement of a non-topographic parameter for each of a plurality of focus values.

9. The computer program product of claim 1, wherein the first value is a focus value and / or the second value is a focus value.

10. A computer program product comprising a non-transitory computer-readable medium having instructions therein, the instructions, when executed by a computer system, being configured to cause the computer system to at least: obtaining a first value of a focus-sensitive parameter, the first value derived from modeling using a computational lithography model or from measurement of a patterned layer on an unpatterned substrate; obtaining a second value of a focus-sensitive parameter, the second value being derived from a measurement of a substrate having a topography; and A value of the topography is determined based on the first value and the second value.

11. The computer program product of claim 10, wherein the second value is derived from a measurement by electron beam inspection equipment of the substrate having the topography.

12. The computer program product of claim 10, wherein the instructions are further configured to cause the computer system to select a plurality of locations across the substrate for measurement by an inspection or metrology device in order to optimize an inspection or measurement speed of the inspection or metrology device.

13. The computer program product of claim 10, wherein the instructions are further configured to cause the computer system to identify an overlay error based on the value of the topography.

14. The computer program product of claim 10, wherein the instructions are further configured to cause the computer system to feed forward or feedback the value of the topography to an apparatus for controlling or configuring a patterning process for providing a pattern on a substrate using the apparatus.

15. The computer program product of claim 10, wherein the first value, the second value, and the determined value of the topography are obtained at multiple locations across the substrate, and the multiple values of the topography are combined to form a map of the topography.

16. The computer program product of claim 10, wherein: Determination of the value of the topography includes a difference between the first value and the second value.

17. The computer program product of claim 10, wherein: The obtaining of the second value includes performing a measurement of a non-topographic parameter for each of a plurality of focus values.

18. A method for determining a shape, the method comprising: obtaining a first value of focus or a first value related to focus, the first value being derived from a computational lithography model modeling patterning of an unpatterned substrate or from measurements of a patterned layer on an unpatterned substrate; obtaining a second value of focus or a second value related to focus, the second value being derived from a measurement of a substrate having a topography; and The value of the topography is determined by a hardware computer according to the first value and the second value. The method of claim 18 , wherein the first value is a focus value and / or the second value is a focus value.

20. The method of claim 18, wherein the first value is a value of a focus-sensitive parameter and / or the second value is a value of a focus-sensitive parameter.

21. A computer program product comprising a non-transitory computer-readable medium having instructions therein, the instructions, when executed by a computer system, being configured to cause the computer system to at least: obtaining process window data for each of a first feature and a second feature, the process window data comprising focus information for each of the first feature and the second feature; and evaluating focus information of the process window data against a focus distribution across the substrate, wherein the focus distribution represents a distribution of the number of occurrences of each of a plurality of focus values across the substrate, and using topography data of the substrate to shift the focus distribution or focus information to identify the first feature and / or the second feature as a critical hotspot, or to change the criticality of the first feature and / or the second feature as a hotspot.

22. The computer program product of claim 21, wherein the focusing distribution is obtained from measurements of a plurality of fields across a substrate or a die positioned across a substrate.

23. A computer program product as described in claim 21, wherein the instructions configured to cause the computer system to evaluate the focus information are further configured to cause the computer system to perform the evaluation by relative consideration between the overlap or non-overlap of the focus information of the first feature with the focus distribution and the overlap or non-overlap of the focus information of the second feature with the focus distribution.

24. A computer program product as described in claim 21, wherein the instructions configured to cause the computer system to evaluate the focus information are also configured to cause the computer system to adjust the classification of the critical state of the first feature as a hotspot relative to the classification of the critical state of the second feature as a hotspot.

25. A computer program product as described in claim 21, wherein the focus information at the negative defocus limit or the positive defocus limit of the process window data is evaluated to identify the first feature and / or the second feature as a critical hotspot, or is evaluated to change the critical state of the first feature and / or the second feature to a hotspot.

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