Patent ID: 12235224

DETAILED DESCRIPTION OF THE DISCLOSURE

Although claimed subject matter will be described in terms of certain embodiments, other embodiments, including embodiments that do not provide all of the benefits and features set forth herein, are also within the scope of this disclosure. Various structural, logical, process step, and electronic changes may be made without departing from the scope of the disclosure. Accordingly, the scope of the disclosure is defined only by reference to the appended claims.

Embodiments of the present disclosure are directed to an image-based approach enhanced with design layout to determine defects in semiconductor devices, which includes the collection of images from modulated patterns (i.e., patterns formed under different conditions). The modulated patterns may be formed deliberately on a modulated wafer used during PWQ. The modulated patterns may be used to identify where within a structure a failure or pattern variation is occurring.

The PWQ procedure performs die-to-die inspection of multiple dies or other repetitive patterns on a semiconductor wafer or other substrate, and the design pattern is lithographic using either a single die reticle, a multi-die reticle, or a mask printed by photoresist patterning performed according to the process. This procedure can select and modulate lighting operating variables. One set of possible illumination operating variables includes illumination focus, illumination exposure, overlay partial illumination coherence, illumination mode, and numerical aperture. Pattern layers recording material such as photoresist covering the test wafer substrate are exposed in the form of grid-like regions arranged in rows and columns. Each identified repeated anomaly is evaluated against a critical status. The procedure of comparing images formed with different values of lithographic operating variables makes it possible to identify single die reticles and detect design pattern defects. If the identified anomaly is in the form of a design pattern, the critical status will depend on the number of occurrences and the location of the anomaly on the design pattern.

FIG.6is an embodiment of a method100. In the method100, a reticle or a mask containing a design pattern is irradiated at101. Each of the occurrences of irradiation (e.g., light) represents a value of a member of a set of lithographic operating variables (e.g., focus and energy). The reticle or mask imparts the occurrences of irradiation design pattern information corresponding to each of the values of the member of the set. The pattern recording material of the wafer (e.g., photoresist) is patterned during the irradiating at102. The irradiating carries the design pattern information imparted by the reticle or mask. In an example with EUV for dose, modulation steps can typically be around 0.5 mJ/cm2steps and for focus 5-10 nm steps. However, this can be higher for a more robust process step with a wider process window.

A spatial pattern corresponding to the design pattern information imparted by the reticle or mask is recorded in the pattern recording material for each of the values of the member of the set at103. Each spatial pattern is recorded at a different region of the pattern recording material. This can be used to form the wafer.

A presence of a pattern anomaly associated with the pattern is determined from the recorded spatial patterns, patterning process, or patterning apparatus at104. Defects can be binned in an embodiment.

FIG.2illustrates a first embodiment of a PWQ wafer layout that can enable improved sensitivity for process window discovery. The PWQ wafer layout inFIG.2can be referred to as “hybrid” or “offset.” Two modulated conditions are used, which can reduce nuisance. Weak spots can be detected more easily because noise is reduced. In an instance, a second pass can be used to focus on what was identified in a first pass.

In the standard PWQ modulation layout, modulated dies (or fields) are compared to an unmodulated die (or field) to amplify image differences and enable these to be captured as defects. This provides the opportunity to identify failing structures, but CD variation can cause noise due to different process conditions. Rather than discovering failing pattern types where it should be easiest, in highly modulated fields, often these are missed because of the high difference in process conditions. The PWQ wafer layout inFIG.2enables comparison to varying offset modulations (between test and reference dies). This still provides the difference between failing and good structures due to changing process conditions, but reduces the impacts of noise induced by the difference in modulations of process conditions such as focus, exposure, and/or overlay. The PWQ wafer layout inFIG.2also provides a low risk of diminishing signal from failing patterns. The degree of offset is flexible and can be tuned to process capabilities. For example, there may be a two or three modulations difference between test and reference dies. The modulation offsets can also be dynamic rather than a fixed number as modulation changes from low to high value. Consequently, the layout inFIG.2can result in more accurate and often tighter process window identification than more traditional layouts.

The layout inFIG.2compares a modulated die or field to slightly lower offset modulated die or field. This enables sensitivity to be maintained, which can capture weak points or patterns of interest with die-to-die inspection or machine learning based approaches while reducing the noise (e.g., from CD variation) between the fields being compared. The number of nuisance events is reduced because noise is reduced. This also enables reduced test scan time and effort, reduced engineering effort for sampling and review budget, and a more accurate process window (i.e. the best sensitivity to the process window) in an empirical study comparing various modulated layouts. Two modulation steps may be used at typical modulation levels. With larger modulation steps, one modulation may be used.

The layout inFIG.2compares to a less modulated field for defect detection. Thus, the lithographic operating variables are modulated with respect to each other across a surface of the wafer. For a die-die comparison either for detection of a defect by an optical or electron beam inspector or conformation of a for an electron beam inspector or review tool, the ability to distinguish the difference of “defect” between a reference and test field may be beneficial. The reduction in modulation difference as shown in the example for focus and dose modulations. This offset modulation layout still enables the key differences to be highlighted while reducing noise. In this example, the reference condition is modulated at two steps of either focus or dose below the test condition. The test condition may show the difference between failing and good structures, such as using a transition condition, but can be other values of the operating variables. Other step sizes would be possible based on the robustness of the process. The modulation of the “reference” fields is changed as the modulation for the “test” field is changed. This can be done for focus and exposure separately as shown inFIG.2or with a combination of the two modulated together in a more complex modulation layout. Similar overlay can be modulated in the X-direction (e.g., horizontal), Y-direction perpendicular to the X-direction (e.g., vertical), or a combination of both. For example, both dose and focus modulations can applied to the same field such that the dose modulation is 0.75 mJ/cm2and a focus on −10 nm=0.75, −10.

The lithographic operating variables at a point on the wafer can both be different from the lithographic operating variables at a neighboring point on the wafer. In an instance, a more modulated value of the focus is against a less modulated value of the focus. In another instance, a more modulated value of the energy is against a less modulated value of the energy.

FIG.3illustrates a second embodiment of a PWQ wafer layout. The PWQ wafer layout ofFIG.3can be referred to as a “corner.” The layout uses process corners of modulation parameters (e.g., focus and exposure) that are compared against each other. This methodology can provide a validation of a known or expected process window or a re-confirmation of process window over time. The embodiment ofFIG.3can be used as verification of a process window. The most dissimilar (e.g., most highly modulated in different directions) modulation parameters are compared. This can help monitor a process window between wafers.

In the layout ofFIG.3, corners of an expected or estimated process window are printed. These “corner” conditions are identified as where weak points are expected to begin to appear. This may be achieved through the PWQ process or based on other learning (e.g., electrical failures). The full wafer is then modulated with the transition conditions where we transition from a region of good process window to potential failures of both focus and dose in rows to facilitate a die-die comparison by the inspector. For example, inFIG.3the process conditions are identified as this transition of a focus of +1.5 mJ/cm2to −1.5 mJ/cm2and a focus change of +0.045 nm to −0.045 nm. Conditions typically may not be symmetrical around 0 because this would depend on the centering of the process window. The high to low corners for a particular condition or combination of conditions are compared. This can provide a higher potential signal or difference between the two conditions to improve detection of a weak point or pattern of interest. This also can provide a way to monitor a process window over time or verify weak points at the boundary of the process window. The layout ofFIG.3also can provide wafer level signatures of particular weak pattern types enabling potential signal to low frequency patterns of interest. This layout can provide potential signal improvements for the verification of process windows and the ability to detect wafer level signatures.

The lithographic operating variables can be modulated such that the lithographic operating variables that are more modulated are arrayed to enable defect detection. In an instance, a region of the surface of the wafer is patterned with an expected process window, another region of the surface of the wafer is patterned with a high value of one of the lithographic operating variables, and yet another region of the wafer is patterned with a low value of the one of the lithographic operating variables. Determining a pattern anomaly can include comparing a high region to a low region for one of the lithographic operating variables. Selection of a transition region that is too large can lead to a high frequency of failures and can provide limited value. However, modulation conditions with the transition conditions can be valuable to identify other process-related or wafer-related variations that could impact the robustness of the process window such as etch uniformity across wafer or wafer flatness.

FIGS.4and5illustrate a third embodiment of a PWQ wafer layout. The PWQ wafer layout ofFIGS.4and5can be referred to as “biased.” This embodiment can use process modulation parameters such as focus, exposure, and/or overlay at transition values. Areas of a wafer are modulated to an edge of a process window. This may be achieved through the PWQ process or based on other learnings such as electrical failures. This can be used to estimate criticality (related to failure frequency) of particular weak points of interest. Field (or die) or wafer level signatures can be studied on such a layout. Proactive improvements can be determined.

The layout ofFIGS.4and5can use fixed modulations along the X-axis (e.g., inspection direction). Along the perpendicular Y-axis, the same modulations can be used or different sets of modulations can be used. The modulation level can be in the transition zone. Thus, the modulation level can be based on prior PWQ discovery studies and can be set at low levels to mid-levels. The process parameters can be pushed out of nominal conditions, but the process parameters are configured to avoid introducing massive failures. Pattern failure rates and defect signature can be analyzed, which may lead to insights for further monitoring of weak spots.

The lithographic operating variables can be modulated such that only one or multiple of the lithographic operating variables is modulated. In an instance, the one of the lithographic operating variables is modulated in a center of an aggregate process window. In another instance, the one of the lithographic operating variables is modulated on either side of a nominal condition and within a process window.

InFIGS.4and5, A and B are focus, dose, or overlay modulations. Some combination of conditions is possible. Only one of A and B is modulated. C is a control modulation, which is typically in a center of an aggregate process window (e.g., a nominal condition). A and B can be chosen to be on either side of nominal condition, but within the edge of the process window. The edge can be levels beyond which patterns start to fail consistently showing an increase in defects. Comparing die at the same modulation condition can be used to identify subtle changes in the printing of “weak points” and used to identify changes in process window over time, due to some intervention or change in the condition of a process tool or due to unexpected interactions with deliberate process changes. This can also be used to identify systematic issues affecting the process window not related to the lithography conditions that can be changed (e.g., focus, dose and/or overlay). These can include, but are not limited to, etch uniformity variation across wafer, CMP intra-die or across wafer effects or wafer shape and any changes to wafer shape caused by wafer processing.

PWQ leverages the unique ability of lithography tools to modulate lithography exposure process parameters at the reticle or mask shot level using variables like focus or exposure to determine design-lithography interactions. However, PWQ can be limited to the direct comparison of dies on a wafer that are printed with modulated focus and/or exposure parameters. The impact of other process variables associated with process steps such as etch, deposition, thermal processing, chemical-mechanical polishing (CMP), etc. cannot be directly assessed by PWQ since these variables can only be modulated at the wafer level. These other process variables can be monitored using the embodiments ofFIGS.4and5because these layouts highlight such variations across the wafer that cannot be detected with a single or small number of modulated fields.

In an example, bowing or other wafer conditions can affect measurements. The embodiment ofFIGS.4and5can compensate for center-to-edge variation across a wafer.

The PWQ layouts disclosed herein can be used with the current techniques for process window discovery and hotspot monitoring and used in existing flows with minimal amounts of customization. Further understanding of weak patterns in design can be provided. This includes stochastic effects in EUV lithography. As an example, sampling plans can be revisited and potentially simplified, tighter process windows can be obtained, and weak hotspots can be monitored or their failure rate can be studied.

The embodiments disclosed herein can enable the detection of weak points or patterns of interest with reduced noise, scan time, and engineering effort. Biased layout helps to understand weak pattern criticality and die (or field) and wafer level signatures. Monitoring of hotspots also can be enabled. The disclosed layouts can be used to replace existing PWQ layouts with the current best-known methods for process window discovery and can be used in existing manufacturing lines with minimal amounts of customization.

One embodiment of a system200is shown inFIG.7. The system200includes optical based subsystem201. In general, the optical based subsystem201is configured for generating optical based output for a specimen202by directing light to (or scanning light over) and detecting light from the specimen202. In one embodiment, the specimen202includes a wafer. The wafer may include any wafer known in the art. In another embodiment, the specimen202includes a reticle. The reticle may include any reticle known in the art.

In the embodiment of the system200shown inFIG.7, optical based subsystem201includes an illumination subsystem configured to direct light to specimen202. The illumination subsystem includes at least one light source. For example, as shown inFIG.7, the illumination subsystem includes light source203. In one embodiment, the illumination subsystem is configured to direct the light to the specimen202at one or more angles of incidence, which may include one or more oblique angles and/or one or more normal angles. For example, as shown inFIG.7, light from light source203is directed through optical element204and then lens205to specimen202at an oblique angle of incidence. The oblique angle of incidence may include any suitable oblique angle of incidence, which may vary depending on, for instance, characteristics of the specimen202.

The optical based subsystem201may be configured to direct the light to the specimen202at different angles of incidence at different times. For example, the optical based subsystem201may be configured to alter one or more characteristics of one or more elements of the illumination subsystem such that the light can be directed to the specimen202at an angle of incidence that is different than that shown inFIG.7. In one such example, the optical based subsystem201may be configured to move light source203, optical element204, and lens205such that the light is directed to the specimen202at a different oblique angle of incidence or a normal (or near normal) angle of incidence.

In some instances, the optical based subsystem201may be configured to direct light to the specimen202at more than one angle of incidence at the same time. For example, the illumination subsystem may include more than one illumination channel, one of the illumination channels may include light source203, optical element204, and lens205as shown inFIG.7and another of the illumination channels (not shown) may include similar elements, which may be configured differently or the same, or may include at least a light source and possibly one or more other components such as those described further herein. If such light is directed to the specimen at the same time as the other light, one or more characteristics (e.g., wavelength, polarization, etc.) of the light directed to the specimen202at different angles of incidence may be different such that light resulting from illumination of the specimen202at the different angles of incidence can be discriminated from each other at the detector(s).

In another instance, the illumination subsystem may include only one light source (e.g., light source203shown inFIG.7) and light from the light source may be separated into different optical paths (e.g., based on wavelength, polarization, etc.) by one or more optical elements (not shown) of the illumination subsystem. Light in each of the different optical paths may then be directed to the specimen202. Multiple illumination channels may be configured to direct light to the specimen202at the same time or at different times (e.g., when different illumination channels are used to sequentially illuminate the specimen). In another instance, the same illumination channel may be configured to direct light to the specimen202with different characteristics at different times. For example, in some instances, optical element204may be configured as a spectral filter and the properties of the spectral filter can be changed in a variety of different ways (e.g., by swapping out the spectral filter) such that different wavelengths of light can be directed to the specimen202at different times. The illumination subsystem may have any other suitable configuration known in the art for directing the light having different or the same characteristics to the specimen202at different or the same angles of incidence sequentially or simultaneously.

In one embodiment, light source203may include a broad band plasma (BBP) source. In this manner, the light generated by the light source203and directed to the specimen202may include broad band light. However, the light source may include any other suitable light source such as a laser. The laser may include any suitable laser known in the art and may be configured to generate light at any suitable wavelength or wavelengths known in the art. In addition, the laser may be configured to generate light that is monochromatic or nearly-monochromatic. In this manner, the laser may be a narrowband laser. The light source203may also include a polychromatic light source that generates light at multiple discrete wavelengths or wavebands.

Light from optical element204may be focused onto specimen202by lens205. Although lens205is shown inFIG.7as a single refractive optical element, it is to be understood that, in practice, lens205may include a number of refractive and/or reflective optical elements that in combination focus the light from the optical element to the specimen. The illumination subsystem shown inFIG.7and described herein may include any other suitable optical elements (not shown). Examples of such optical elements include, but are not limited to, polarizing component(s), spectral filter(s), spatial filter(s), reflective optical element(s), apodizer(s), beam splitter(s) (such as beam splitter213), aperture(s), and the like, which may include any such suitable optical elements known in the art. In addition, the optical based subsystem201may be configured to alter one or more of the elements of the illumination subsystem based on the type of illumination to be used for generating the optical based output.

The optical based subsystem201may also include a scanning subsystem configured to cause the light to be scanned over the specimen202. For example, the optical based subsystem201may include stage206on which specimen202is disposed during optical based output generation. The scanning subsystem may include any suitable mechanical and/or robotic assembly (that includes stage206) that can be configured to move the specimen202such that the light can be scanned over the specimen202. In addition, or alternatively, the optical based subsystem201may be configured such that one or more optical elements of the optical based subsystem201perform some scanning of the light over the specimen202. The light may be scanned over the specimen202in any suitable fashion such as in a serpentine-like path or in a spiral path.

The optical based subsystem201further includes one or more detection channels. At least one of the one or more detection channels includes a detector configured to detect light from the specimen202due to illumination of the specimen202by the subsystem and to generate output responsive to the detected light. For example, the optical based subsystem201shown inFIG.7includes two detection channels, one formed by collector207, element208, and detector209and another formed by collector210, element211, and detector212. As shown inFIG.7, the two detection channels are configured to collect and detect light at different angles of collection. In some instances, both detection channels are configured to detect scattered light, and the detection channels are configured to detect light that is scattered at different angles from the specimen202. However, one or more of the detection channels may be configured to detect another type of light from the specimen202(e.g., reflected light).

As further shown inFIG.7, both detection channels are shown positioned in the plane of the paper and the illumination subsystem is also shown positioned in the plane of the paper. Therefore, in this embodiment, both detection channels are positioned in (e.g., centered in) the plane of incidence. However, one or more of the detection channels may be positioned out of the plane of incidence. For example, the detection channel formed by collector210, element211, and detector212may be configured to collect and detect light that is scattered out of the plane of incidence. Therefore, such a detection channel may be commonly referred to as a “side” channel, and such a side channel may be centered in a plane that is substantially perpendicular to the plane of incidence.

AlthoughFIG.7shows an embodiment of the optical based subsystem201that includes two detection channels, the optical based subsystem201may include a different number of detection channels (e.g., only one detection channel or two or more detection channels). In one such instance, the detection channel formed by collector210, element211, and detector212may form one side channel as described above, and the optical based subsystem201may include an additional detection channel (not shown) formed as another side channel that is positioned on the opposite side of the plane of incidence. Therefore, the optical based subsystem201may include the detection channel that includes collector207, element208, and detector209and that is centered in the plane of incidence and configured to collect and detect light at scattering angle(s) that are at or close to normal to the specimen202surface. This detection channel may therefore be commonly referred to as a “top” channel, and the optical based subsystem201may also include two or more side channels configured as described above. As such, the optical based subsystem201may include at least three channels (i.e., one top channel and two side channels), and each of the at least three channels has its own collector, each of which is configured to collect light at different scattering angles than each of the other collectors.

As described further above, each of the detection channels included in the optical based subsystem201may be configured to detect scattered light. Therefore, the optical based subsystem201shown inFIG.7may be configured for dark field (DF) output generation for specimens202. However, the optical based subsystem201may also or alternatively include detection channel(s) that are configured for bright field (BF) output generation for specimens202. In other words, the optical based subsystem201may include at least one detection channel that is configured to detect light specularly reflected from the specimen202. Therefore, the optical based subsystems201described herein may be configured for only DF, only BF, or both DF and BF imaging. Although each of the collectors are shown inFIG.7as single refractive optical elements, it is to be understood that each of the collectors may include one or more refractive optical die(s) and/or one or more reflective optical element(s).

The one or more detection channels may include any suitable detectors known in the art. For example, the detectors may include photo-multiplier tubes (PMTs), charge coupled devices (CCDs), time delay integration (TDI) cameras, and any other suitable detectors known in the art. The detectors may also include non-imaging detectors or imaging detectors. In this manner, if the detectors are non-imaging detectors, each of the detectors may be configured to detect certain characteristics of the scattered light such as intensity but may not be configured to detect such characteristics as a function of position within the imaging plane. As such, the output that is generated by each of the detectors included in each of the detection channels of the optical based subsystem may be signals or data, but not image signals or image data. In such instances, a processor such as processor214may be configured to generate images of the specimen202from the non-imaging output of the detectors. However, in other instances, the detectors may be configured as imaging detectors that are configured to generate imaging signals or image data. Therefore, the optical based subsystem may be configured to generate optical images or other optical based output described herein in a number of ways.

It is noted thatFIG.7is provided herein to generally illustrate a configuration of an optical based subsystem201that may be included in the system embodiments described herein or that may generate optical based output that is used by the system embodiments described herein. The optical based subsystem201configuration described herein may be altered to optimize the performance of the optical based subsystem201as is normally performed when designing a commercial output acquisition system. In addition, the systems described herein may be implemented using an existing system (e.g., by adding functionality described herein to an existing system). For some such systems, the methods described herein may be provided as optional functionality of the system (e.g., in addition to other functionality of the system). Alternatively, the system described herein may be designed as a completely new system.

The processor214may be coupled to the components of the system200in any suitable manner (e.g., via one or more transmission media, which may include wired and/or wireless transmission media) such that the processor214can receive output. The processor214may be configured to perform a number of functions using the output. The system200can receive instructions or other information from the processor214. The processor214and/or the electronic data storage unit215optionally may be in electronic communication with a wafer inspection tool, a wafer metrology tool, or a wafer review tool (not illustrated) to receive additional information or send instructions. For example, the processor214and/or the electronic data storage unit215can be in electronic communication with a scanning electron microscope.

The processor214, other system(s), or other subsystem(s) described herein may be part of various systems, including a personal computer system, image computer, mainframe computer system, workstation, network appliance, interne appliance, or other device. The subsystem(s) or system(s) may also include any suitable processor known in the art, such as a parallel processor. In addition, the subsystem(s) or system(s) may include a platform with high-speed processing and software, either as a standalone or a networked tool.

The processor214and electronic data storage unit215may be disposed in or otherwise part of the system200or another device. In an example, the processor214and electronic data storage unit215may be part of a standalone control unit or in a centralized quality control unit. Multiple processors214or electronic data storage units215may be used.

The processor214may be implemented in practice by any combination of hardware, software, and firmware. Also, its functions as described herein may be performed by one unit, or divided up among different components, each of which may be implemented in turn by any combination of hardware, software and firmware. Program code or instructions for the processor214to implement various methods and functions may be stored in readable storage media, such as a memory in the electronic data storage unit215or other memory.

If the system200includes more than one processor214, then the different subsystems may be coupled to each other such that images, data, information, instructions, etc. can be sent between the subsystems. For example, one subsystem may be coupled to additional subsystem(s) by any suitable transmission media, which may include any suitable wired and/or wireless transmission media known in the art. Two or more of such subsystems may also be effectively coupled by a shared computer-readable storage medium (not shown).

The processor214may be configured to perform a number of functions using the output of the system200or other output. For instance, the processor214may be configured to send the output to an electronic data storage unit215or another storage medium. The processor214may be configured according to any of the embodiments described herein. The processor214also may be configured to perform other functions or additional steps using the output of the system200or using images or data from other sources.

In an instance, the processor214is in communication with the system200. The processor214is configured to determine from the recorded spatial patterns a presence of a pattern anomaly associated with the pattern, patterning process, or patterning apparatus. In an instance, the specimen202was irradiated with a value of a member of a set of lithographic operating variables (e.g., focus and energy). The specimen202can include any of the PWQ layouts disclosed herein. The processor214can be configured to make determinations of pattern anomalies of any of the PWQ layouts disclosed herein.

An additional embodiment relates to a non-transitory computer-readable medium storing program instructions executable on a controller for performing a computer-implemented method for determining from the recorded spatial patterns a presence of a pattern anomaly associated with the pattern, patterning process, or patterning apparatus, as disclosed herein. In particular, as shown inFIG.7, electronic data storage unit215or other storage medium may contain non-transitory computer-readable medium that includes program instructions executable on the processor214. The computer-implemented method may include any step(s) of any method(s) described herein, including method100.

The program instructions may be implemented in any of various ways, including procedure-based techniques, component-based techniques, and/or object-oriented techniques, among others. For example, the program instructions may be implemented using ActiveX controls, C++ objects, JavaBeans, Microsoft Foundation Classes (MFC), Streaming SIMD Extension (SSE), or other technologies or methodologies, as desired.

Another embodiment relates to the wafer, mask, reticle, or other specimen that is used to determine from the recorded spatial patterns a presence of a pattern anomaly associated with the pattern, patterning process, or patterning apparatus, as disclosed herein. The specimen can be used with any step(s) of any method(s) described herein, including method100. The specimen can include the patterns shown inFIGS.2-5.

Although the present disclosure has been described with respect to one or more particular embodiments, it will be understood that other embodiments of the present disclosure may be made without departing from the scope of the present disclosure. Hence, the present disclosure is deemed limited only by the appended claims and the reasonable interpretation thereof.