TWI755453B - Method and system for qualifying a photolithographic reticle - Google Patents

Abstract

Disclosed are methods and apparatus for qualifying a photolithographic reticle. A reticle inspection tool is used to acquire a plurality of images at different imaging configurations from each of a plurality of pattern areas of a test reticle. A reticle near field is recovered for each of the pattern areas of the test reticle based on the acquired images from each pattern area of the test reticle. The recovered reticle near field is then used to determine whether the test reticle or another reticle will likely result in unstable wafer pattern or a defective wafer.

Description

Method and system for qualifying a photolithography mask

The present invention generally relates to the field of reticle inspection. More particularly, the present invention relates to pattern qualification.

In general, the semiconductor manufacturing industry involves highly complex techniques for fabricating integrated circuits using semiconductor materials, such as silicon, layered and patterned onto a substrate. Due to the large scale integration and reduced size of semiconductor devices, the fabricated devices have become increasingly sensitive to defects. That is, defects that cause malfunctions in the device become smaller and smaller. The device is fault-free until shipped to the end user or customer.

An integrated circuit is usually fabricated from a plurality of masks. First, the circuit designer provides circuit pattern data describing a particular integrated circuit (IC) design to a reticle production system or reticle writer. Circuit pattern data is typically in the form of a representative layout of the physical layers of the fabricated IC device. A representative layout includes a representative layer of each physical layer of an IC device (eg, gate oxide, polysilicon, metallization, etc.), where each representative layer consists of a patterned plurality of polygons that define a layer of a particular IC device . Mask writers use circuit pattern data to write (eg, typically an electron beam writer or laser scanner is used to expose a mask pattern) that will later be used to fabricate masks for a particular IC design.

Some photomasks or photomasks have at least transparent and opaque regions, translucent and phase-shift regions, or The absorber and reflective regions, which together define the pattern of coplanar features in an electronic device such as an integrated circuit, are in the form of an optical element. Reticles are used during photolithography to define designated areas of a semiconductor wafer for etching, ion implantation, or other fabrication processes.

After each reticle or group of reticle is fabricated, each new reticle is generally eligible for use in wafer fabrication. For example, the reticle pattern needs to be free of print defects. In addition, any wafers fabricated with the reticle need to be defect-free. Accordingly, there continues to be a need for improved reticle and wafer inspection and qualification techniques.

The following presents a simplified summary of the invention in order to provide a basic understanding of a specific embodiment of the invention. This summary is not an extensive overview of the invention, and it does not identify essential/critical elements of the invention or delineate the scope of the invention. Its sole purpose is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later.

In one embodiment, a method of qualifying a photolithography mask is disclosed. A plurality of images are acquired from each of the plurality of pattern regions of a test reticle using an imaging tool according to different illumination configurations and/or different imaging configurations. A reticle near field is recovered for each of the pattern regions of the test reticle based on the images acquired from the pattern regions of the test reticle. Next, the recovered reticle near field is used to determine whether the test reticle or another reticle would likely cause an unstable wafer pattern or a defective wafer.

In one embodiment, the reticle near field is directly analyzed to determine whether the test reticle or another reticle will likely cause an unstable wafer pattern or a defective wafer. In another aspect, the recovered reticle near field is used to detect defects in the test reticle or in a simulated wafer image simulated from the recovered reticle near field, wherein defect detection comprises: comparing different Intensity of an identical die, an adjacent die, a die and its corresponding golden die, or a die and a corresponding die from a reticle replica of the same design as the test reticle and/or phase.

In one aspect, the images are acquired at a field plane or a pupil plane. In a particular embodiment, the reticle near field is recovered without using a design database used to make the reticle. In another aspect, the acquired images include at least three reflection/transmission images acquired under different imaging conditions selected to result in the near field of a same reticle. In this aspect, the different imaging conditions include different focus settings and different pupil shapes, and the different illumination conditions include different light source intensity distributions and/or polarization settings.

In an alternative embodiment, the method includes: (i) applying a lithography model to the reticle near field of the test reticle to simulate a plurality of test wafer images; and (ii) analyzing the simulated test wafers Circle images to determine if the test reticle will likely result in an unstable or defective wafer. In this aspect, the lithography model is configured to simulate a photolithography process. In another aspect, the lithography model simulates an illumination source having a shape that differs from an illumination shape of an inspection tool used to acquire images of the test reticle or another reticle or wafer . In another aspect, the lithography model is calibrated using images generated from a design database for a calibration mask. In another example, the lithography model is calibrated using images acquired from a calibration mask. In yet another aspect, applying the lithography model to the near field of the reticle recovered for the test reticle under a plurality of different lithography process conditions, and analyzing the simulated test wafer images includes: by comparing Portions of the simulated test images associated with different process conditions and a same reticle area determine whether the test reticle will likely result in an unstable wafer under the different lithography process conditions.

In an alternative embodiment, the present invention relates to an inspection system for qualifying a photolithography mask. The system includes: a light source for generating an incident light beam; and an illumination optical module for guiding the incident light beam onto a mask. The system also includes: a collection optics module for directing an output beam from each pattern area of the reticle to at least one sensor for detecting the output beam and based on the output beam generation an image or signal. The system further includes a controller configured to perform operations similar to one or more of the method operations described above.

These and other aspects of the invention are further described below with reference to the drawings.

100: Mask near-field recovery procedure/mask recovery procedure

102: Operation

104: Operation

106: Operation

200: Model Calibration Process/Procedure

201: Masked near-field image recovered from self-calibrating mask

202: Simulated calibration mask image simulated from the design database/simulated image from the design database/simulated calibration image generated from the design database

208: Operation

210: Operation

212: Operation

214:Operation

216: Operation/Actual Results from Wafer

300: Reticle Qualification Process

302: Operation

303: Operation

322:Operation

324:Operation

326:Operation

328:Operation

330: Operation

332:Operation

334:Operation

336: Operation

400: Process

402: Operation

404: Operation

406: Operation

450: Defect Detection Program

452:Operation

454:Operation

456:Operation

500: Reticle Qualification Process/Procedure

502: Operation

522:Operation

524:Operation

526:Operation

528:Operation

530: Operation

532:Operation

534:Operation

536:Operation

600: Detection System

602: Input/input data/intensity or image data

604a: Data Distribution System

604b: Data Distribution System

606a: First block processor

606b: Block Processor

608: Switched Network

610: Inspection Control/Inspection Station

612: Block Processor and Mask Qualification System

616: Mass Storage Device

700: Lithography system

701: Numerical Aperture/Element

702: Mask plane

703: Lighting source

705: Lens

707: Lighting Optics

713: Imaging Optics

750: Detection System

751a: Illumination Optics

751b: Numerical Aperture

752: Mask plane

753a: Detection optics/collection optics/optical elements

753b: Detection Optics/Collecting Optics

754a: Sensors

754b: Sensor

760: Lighting source

773: Computer Systems

776: Beam Splitter

778: Detection Lens

M: Light Mask/Mask

W: Wafer

FIG. 1 is a flow chart illustrating a mask near-field recovery process according to an embodiment of the present invention.

2 is a flow chart illustrating a model calibration process according to a specific embodiment of the present invention.

3 illustrates a flow chart representing a reticle qualification process according to an embodiment of the present invention.

4A is a flowchart illustrating a process for determining the stability of a reticle pattern according to an exemplary application of the present invention.

4B is a flowchart illustrating a defect detection process according to another embodiment of the present invention.

5 is a flowchart illustrating a reticle qualification process applied to a recovered masked near-field image or result, according to an alternative embodiment of the present invention.

6 is a graphical representation of an exemplary detection system in which techniques of the present invention may be implemented.

7A is a simplified schematic representation of a lithography system for transferring a mask pattern from a photomask onto a wafer, according to certain embodiments.

7B provides a schematic representation of a light mask detection apparatus according to certain embodiments.

Cross-references to related applications

This application claims the US patent application filed by Rui-fang Shi et al. on July 3, 2017 Priority to and a continuation-in-part of Application No. 15/641,150, which claims under 35 USC § 120 by Abdurrahman Sezginer et al. filed on August 5, 2016 Priority right to PCT Application No. PCT/US2016/045749, which claims prior application US Application No. 14/822,571 filed by Abdurrahman Sezginer et al. on August 10, 2015 (now U.S. Application No. 9,547,892, filed January 17, 2017). This application also claims priority to US Provisional Application No. 62/508,369, filed on May 18, 2017. The entire contents of these applications and patents are incorporated herein by reference for all purposes.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The present invention may be practiced without some or all of these specific details. In other instances, well-known process operations or device components have not been described in detail so as not to unnecessarily obscure the present invention. While the invention will be described in conjunction with specific embodiments, it will be understood that the invention is not intended to be limited to these embodiments.

Detect defects in each mask and otherwise characterize various aspects of the mask (eg, pattern stability, CD, CD uniformity) before shipping the mask to a fabrication facility, before using the mask to fabricate wafers It would be advantageous to manufacture and/or periodically requalify the mask after the mask has been used in the manufacturing process for a certain period of time.

One embodiment of the present invention includes techniques for recovering a near-field image of a reticle based on reticle images obtained from an inspection tool under a plurality of different imaging parameters. This reticle near-field image can then be used in many reticle qualification applications. In one example, the reticle near-field image can be input to a lithography model to predict a wafer image or various wafer pattern properties related to how the resulting pattern will be printed on the wafer. Next, a predicted wafer image and/or various wafer properties Can be analyzed for defect detection, reticle qualification or requalification, and/or any other suitable metrology or inspection application. The reticle near-field image itself may also be analyzed for various purposes as described further herein.

The terms "reticle,""mask," and "photomask" are used interchangeably herein and can each generally include a transparent substrate on which a layer of opaque material is formed, such as glass, borosilicate glass, Quartz or fused silica. The opaque (or substantially opaque) material may comprise any suitable material that completely or partially blocks photolithography light (eg, deep UV or extreme UV). Exemplary materials include chromium, molybdenum silicide (MoSi), tantalum silicide, tungsten silicide, opaque MoSi on glass (OMOG), and the like. A polysilicon film can also be added between the opaque layer and the transparent substrate to improve adhesion. A low reflection film can be formed over an opaque material, such as molybdenum oxide (MoO ₂ ), tungsten oxide (WO ₂ ), titanium nitride (TiO ₂ ), or chromium oxide (CrO ₂ ). In a specific example, an EUV reticle may include layers with alternating layers of different refractive indices and low absorption properties, such as molybdenum (Mo) and silicon (Si), and an absorber material, such as composed of a thin Tantalum boron nitride film capped with anti-reflection oxide).

The term reticle refers to different types of reticle including, but not limited to, a clear-field reticle, a dark-field reticle, a binary reticle, a phase shift mask (PSM), an alternating PSM , an attenuated or halftone PSM, a ternary attenuated PSM, a chromeless phase lithography PSM, and a chromeless phase lithography (CPL). A clear field mask has a transparent field or background area, and a dark field mask has an opaque field or background area. A binary reticle is a reticle with transparent or opaque patterned regions. For example, a photomask made from a transparent fused silica blank having a pattern defined by a chromium metal adsorption film can be used. Binary masks differ from phase shift masks (PSMs), one type of which can include films that only partially transmit light, and such masks can often be referred to as halftone or embedded phase shift masks Masks (EPSM) such as ArF and KrF masks. If a phase shifting material is placed on the alternating clear space of a reticle, the reticle is called an alternating PSM, an ALT PSM, or a Levenson PSM. One type of phase-shifting material applied to an arbitrary layout pattern is called an attenuated or halftone PSM, which can be fabricated by substituting a partially transmissive or "halftone" film for the opaque material. A ternary attenuated PSM system also includes a fully opaque feature, an attenuated PSM.

The next generation of lithography has introduced the use of extreme ultraviolet radiation (EUV, wavelength 13.5 nm), which is absorbed in the normal atmosphere as well as in glass. To this end, the lithographic EUV process takes place under vacuum, and an optical reflective lens/mirror is used to focus to an EUV light mask that will have reflective and absorber patterns instead of translucent and opaque patterns.

FIG. 1 is a flowchart illustrating a masked near-field recovery procedure 100 according to an embodiment of the present invention. The following mask recovery process 100 may be performed for a particular reticle or group of reticles at any suitable time in the life cycle of a reticle, as further described below in various use cases of recovered mask near-field. By way of example, a mask near-field may be recovered prior to fabricating any wafers with the mask(s), at the start of mass wafer fabrication, or during requalification of the mask(s).

First, in operation 102, at least three images of the mask are acquired according to different imaging configurations using a mask detection tool. Alternatively, two images could be used, but three images have been found to work well. Acquisition using different imaging configurations can be simultaneous or sequential. The acquired image does not have to be at the field plane. By way of example, two or more images can be acquired at the pupil plane where the diffracted intensity can be directly accessed.

Two or more images may be acquired using various suitable combinations of illumination and/or collection configurations. Generally, different imaging configurations are selected to provide images from which the masked near field can be calculated. Any suitable imaging or optical configuration can be selected so that the mask near field remains the same under different operating conditions. Examples include different focus settings, different illumination shapes (eg, different directions or patterns), different polarizations for the entire illumination pupil or different parts of the illumination pupil, different apodization settings to shade different parts of the collected beam, etc. . In one embodiment, different focus settings may be used (over focus and defocus (such as 0 focus, ±800 or ±1600 defocus, etc.)) to acquire different images. In another example, different quadrants of the illumination pupil may have different polarization settings. In another example, the imaging configuration may include high resolution images, such as transmission images with different pupil shapes and/or different focus conditions (eg, for ArF masks). In another embodiment, three or more reflected images with different pupil shapes and/or different focus conditions may be obtained (eg, for EUV masks).

A "substantially low resolution" imaging mask can be used with a relatively low NA (eg, less than 0.5). In contrast, a "substantially high-resolution image" generally refers to those in which the features printed on the reticle appear substantially as they were formed on the reticle (in the optics of the reticle inspection system used to generate the image). within the limits) of an image of a reticle. A "substantially high-resolution image" of a reticle is created by imaging the physical reticle at the plane of the reticle with a substantially high-resolution reticle inspection system (eg, with a numerical aperture (NA) greater than 0.8) produce an image. The "substantially low NA" used to generate a reticle image can be used substantially with an exposure/lithography system on the reticle side to project an image of the reticle onto a wafer to thereby characterize the reticle The NA transferred onto the wafer is the same. In a substantially low NA image (or LNI), the reticle features may have an appearance that is substantially different from the actual reticle features. For example, a reticle feature may appear to have more rounded corners in a LNI of a feature than the actual feature formed on the reticle.

In general, any suitable imaging tool can be used to mask the near-field recovery process. In certain embodiments described herein, the results of an initial recovery process can later be used for pattern stability or defect detection assessments on that same reticle or other reticle based on additional reticle images from a particular inspection tool . For consistency in these use cases, a detector of a reticle inspection system that will be used for subsequent inspection of the same or other reticle or a similarly configured reticle inspection system (eg, with The same approach and model of the reticle inspection system A different reticle inspection system system) to acquire an image of the reticle used to mask the near-field recovery. In other words, images that can be used for mask recovery can be acquired under the same optical conditions as will be used during subsequent mask inspection or qualification processes. In this way, the interaction of the reticle with the illuminating electromagnetic waves of the detection system can be measured as directly as possible.

In alternative embodiments, the tool used for mask near-field recovery may be different from a mask inspection system. For example, the imaging tool may utilize the same wavelength (eg, wavelength (193.3 nm for DUV or 13.5 nm for EUV)) as the lithography system in which the reticle will be used for wafer fabrication. In fact, any suitable electromagnetic wavelength can be used for mask near-field recovery.

Referring again to the depicted example, then, in operation 104, three or more images may be aligned with each other or each image may be aligned with a post OPC database. For example, acquired images can be aligned via spatial or frequency domain methods. Alignment adjustments may depend on the specific geometry of the imaging system used. If different images are obtained using different collection paths, some adjustment of the images can be made to compensate for differences in optical paths.

In an imaging tool, a reticle having various patterns is illuminated by electromagnetic (EM) waves incident from many directions. The incident light is diffracted from different points of the mask pattern according to different electromagnetic field phases that interfere with each other differently. The near field of a mask is the electromagnetic field at a close distance of one wavelength of the mask.

Collection optics generally direct a diffraction-limited portion of the light from the reticle toward a detector (or wafer) to form an image. The detector detects the intensity, but not the phase, as a result of interference due to the near-field of the mask.

Although the far field strength is obtained in the detected signal, it may be desirable to recover the masked near field including amplitude and phase. In the illustrated embodiment, the mask near-field is restored and stored based on these acquired mask images, as shown in operation 106 . In general, multiple images (or signals) are used to recover a masked near field that includes both phase and amplitude components. can be based on the image obtained from the mask by a regression Technical determination of near-field data. For example, a quasi-Newton or conjugate gradient technique can be used to recover (regress) the intensity of a selected portion of the reticle from the acquired optical image or the intensity of the image recorded at the plane of the detector. near field. Additionally, any other suitable regression method and/or algorithm may be used to determine near-field data from one or more actual images.

Mask near-field recovery is typically achieved by solving an optimization problem that seeks to minimize the difference between the observed intensity image and the resulting image assuming the masked optical field. In particular, recovering the near-field of a reticle from its intensity image is an inverse problem or a regression problem. The near field can be iteratively recovered by minimizing a cost function (eg, energy or penalty function). The number that is minimized may be the sum of the squares of the difference between the acquired image and the intensity image calculated at the detector from the masked near field. In other words, intensity images can be computed from the final mask near-field for various sets of optical system properties, and when the mask near-field is found, these computed images will most closely match the acquired images. Various masked near-field recovery methodologies and system embodiments are further described in US Patent No. 9,478,019, issued October 25, 2016 by Abdurrahman Sezginer et al, which is incorporated herein by reference in its entirety for all purposes middle.

In situations where multiple images are acquired under various optical conditions, the recovered near-field mask m carrying phase and amplitude information can be determined by the following equation:

係描述檢測成像系統之一組特徵向量，

係成像系統之一組對應特徵值，且c _a 係0與1之間的一非負加權因數。可例如透過諸如擬牛頓或共軛梯度之方法迭代地求解上述方程式。 In Equation 1 above, I _a is the measured image for imaging condition α,

is a set of eigenvectors describing the detection imaging system,

is a set of corresponding eigenvalues for the imaging system, and c _a is a non-negative weighting factor between 0 and 1. The above equations can be solved iteratively, eg, by methods such as quasi-Newtonian or conjugate gradients.

Another example is the Gerchberg-Saxton algorithm, in which both the amplitude and phase of the object can be solved using a combination of field plane images and pupil plane diffraction orders.

In one embodiment, the near field of the mask may be determined via a Hopkins approximation based on the acquired image. In another embodiment, the regression does not include a thin mask approximation. For example, the near field of a reticle is calculated as the electromagnetic field that appears near the surface of the reticle when illuminated by a normally incident plane wave. In lithography and inspection, a reticle is illuminated by plane waves incident from many directions. When the incident direction changes, according to the Hopkins approximation, the direction of the diffraction order changes but its equal amplitude and phase approximations remain unchanged. Embodiments described herein may use the Hopkins phase approximation but do not perform the so-called thin mask or Kirchhoff approximation.

其中正則項R可併有關於近場之先前資訊或基於遮罩基板/材料之實體理解之預期。另外，用於影像差異之範數可為一l-範數(l-norm)且可基於最佳化函數之特定需求而調整。 The recovery formula can also be changed with the addition of different norms or a regular term R , which is not conducive to the oscillation in the near field, as follows:

The canonical term R may incorporate prior information about the near field or expectations based on a physical understanding of the mask substrate/material. Additionally, the norm for image disparity can be an 1-norm and can be adjusted based on the specific needs of the optimization function.

It is interesting to note that due to the wider range of incident angles of light with a higher NA and the associated interference electric field component, the interference of the masked electromagnetic field vector due to a higher NA will be larger (greater than a higher NA). low NA detection system).

The actual mask may vary with the expected design pattern due to the mask writing process. Obtaining the near-field mask from the masked image means obtaining the near-field mask from the actual physical mask rather than the design database. That is, the near field of the mask can be restored without using the design database.

Next, the masked near-field results can be used in various applications. In one embodiment, the masked near-field results may be used to predict wafer patterns using one or more models. That is, a lithographic image can be simulated using the restored mask near-field. Lithographic images can be simulated based on masked near-field images using any suitable technique. One embodiment includes computing the lithography image through a partial coherence model:

表示TCC之特徵向量(核心)；s係晶圓堆疊，其包含膜折射率；f係焦點；且z係微影平面在抗蝕劑材料中之垂直位置。方程式2之交叉轉印係數(TCC)可包含場通過微影投影儀(包含晶圓上之膜堆疊)之向量傳播。 Wherein λ _i represents the characteristic value of lithography TCC (transfer cross coefficient);

represents the eigenvector (core) of the TCC; s is the wafer stack, which includes the film refractive index; f is the focal point; and z is the vertical position of the lithography plane in the resist material. The cross transfer coefficient (TCC) of Equation 2 can include the vector propagation of the field through a lithographic projector, including the film stack on the wafer.

Before using a model to predict wafer results, the model can be calibrated to produce the most accurate results possible. The model can be calibrated using any suitable technique. Certain embodiments of the present invention provide techniques for calibrating a lithography model based on mask near-field results recovered from a calibration mask. In an alternative embodiment, the model is calibrated using a design database. For example, calibration mask images can be generated from a design database.

A calibration reticle will typically be designed to have characteristics substantially similar to the reticle(s) that are to be inspected for defect detection or to be measured for metrology purposes. For example, the calibration reticle and the test reticle are preferably formed from substantially the same material having substantially the same thickness and composition. Additionally, the same process may have been used to form both masks. The two masks may not necessarily have the same pattern printed thereon, as long as the pattern on the mask can be broken down into substantially the same segments (eg, lines of similar width, etc.). In addition, the reticle to be inspected and the reticle used to acquire the image may be the same reticle.

FIG. 2 is a flowchart illustrating a model calibration process 200 in accordance with one particular embodiment of the present invention. As shown, in operation 208, a set of initial model parameters can be used to model the photolithography process and photoresist as applied to the masked near-field image (201) recovered from a calibration mask. Alternatively, the calibration process 200 may use a simulated calibration reticle image (202) simulated from a design database. A reticle image can be generated from the database by simulating the reticle fabrication and imaging process on the design database. Any suitable model can be used to generate optical images for the features of the design database. By way of example, this simulation may include using the Sum of Coherent Systems (SOCS) or Abbe methodologies described herein. There are several software packages that can simulate the intensity image of an optical system from a known design database. An example is Dr. LiTHO developed at Fraunhofer IISB in Erlangen, Germany. In the case of simulating an image 202 from a design database, the near field can be simulated first, which can be achieved by the software packages cited above, as well as several other packages including Prolith from KLA-Tencor, HyperLith from Panoramic Technologies, etc. Finish.

The model used to generate the wafer image based on the reticle near-field image may only include the effects of the photolithography scanner, and it may also include the effects of resist, etching, CMP, or any other wafer process. An exemplary process simulation model tool is commercially available from Prolith, KLA-Tencor, Inc., Milpitas, CA. The resist and etch process can be closely or approximately modeled. In a particular embodiment, the model may be in the form of a compact resist model that includes 3D acid diffusion within a particular resist material and the configuration of the imposed boundary conditions therein, and applied to form one of the latent images A single threshold value.

It should be noted that the modeled lithography tool may have a different illumination shape or light source than the reticle inspection tool used to acquire the actual image of the reticle. In certain embodiments, a modeling lithography tool may have a light source that is the same as or similar to a reticle detector tool.

Other simulation methods such as SOCS or Abbe can be used. An algorithm commonly referred to as Summation of Coherent Systems (SOCS) attempts to convert an imaging system into a bank of linear systems whose outputs are squared, scaled, and summed. SOCS methods have been described elsewhere, including Nicolas Cobb's doctoral thesis "Fast Optical and Process Proximity Correction Algorithms for Integrated Circuit Manufacturing" (UC Berkeley, Spring 1998). The Abbe algorithm involves computing the image of the object for each point source one at a time, and then summing the intensity images together and taking into account the relative intensities of each source point.

Inputs to the model and its modeling parameters include a set of process conditions applied to a recovered near-field mask. That is, the model is configured to simulate different sets of process conditions on the reconstructed near-field mask (or simulated mask image). Each set of process conditions generally corresponds to a set of wafer process parameters that characterize or partially characterize a wafer process for forming a wafer pattern from a mask. For example, a particular focus and exposure setting can be input to the model. Other adjustable model parameters can also include one or more of the following parameters: a projection lens wavefront parameter, an apodization parameter, a chromatic aberration focus error parameter, a vibration parameter, a resist profile index, a resist float Slag metrics, top loss metrics, etc. Using this model with different sets of process conditions can result in a set of simulated wafer or resist pattern images formed from the reconstructed near-field masks under different processing conditions, and these simulated wafer images can be used for pattern stability and Defect detection evaluation, as further described herein.

In operation 216, a calibration reticle may also be used to fabricate a calibration wafer from which the actual image was obtained. In one example, a critical dimension (CD) scanning electron microscope (SEM) is used to acquire the actual image. Other imaging tools can be utilized, but a high resolution tool is preferred.

In general, a calibration wafer will contain any number of known structures, which can vary widely. The structure may be in the form of a generally periodic grating. Each grating may be periodic in one direction (X or Y) (eg, as a one-line spatial grating), or it may be periodic in both directions (X and Y) (eg, as a raster space raster). An example of a grid space grating may include an array of lines in the Y direction, where each line is segmented in the X direction. Another grid space instance is an array of point structures. That is, each structure may take the form of a line space grating, a grid space grating, a checkerboard pattern structure, or the like. Structural design characteristics may each include line width (width at a particular height), line space width, line length, shape, sidewall angle, height, pitch, grating orientation, top profile (degree of top rounding or T-top) ), bottom profile (footing), etc. Calibration wafers may contain structures with different combinations of these characteristic properties. As should be appreciated, different structural properties (such as not same width, spacing, shape, pitch, etc.) exhibit different responses to focus points, and therefore the calibration mask preferably includes different structures with different characteristics.

In a particular embodiment, the calibration wafer may take the form of a "design of experiment (DOE)" wafer with different measurement points subjected to different processing conditions. In a more general embodiment, process parameter variations are organized in a pattern on the surface of a semiconductor wafer (referred to as a DOE wafer). In this way, the measurement points correspond to different locations on the wafer surface with different associated process parameter values. In one example, the DOE pattern is a focus/exposure matrix (FEM) pattern. Typically, a DOE wafer exhibiting an FEM pattern includes a grid pattern of measurement points. In one grid direction (eg, the x-direction), the exposure dose varies while the depth of focus remains constant. In the orthogonal grid direction (eg, the y-direction), the depth of focus varies while the exposure dose remains constant. In this way, the measurement data collected from the FEM wafer includes data that correlates with known changes in focus and dose process parameters.

FEM measurement points are generally positioned across the focal exposure matrix wafer. In fact, there may generally be one or more measurement points per field. Each field may be formed using one of the different combinations of focus and exposure combinations (or may just focus or exposure). For example, a first field can be generated using a first combination, and a second field can be generated using a second combination different from the first combination. Multiple combinations can be created using varying focus and varying exposure, varying focus-constant exposure, constant focus-varying exposure, and the like.

The number of measurement points can also vary. The number of points per field is typically low on production wafers because real estate on production wafers is extremely precious. Furthermore, fewer measurements are performed on a production wafer than on a focus-exposed matrix wafer due to time constraints in production. In one embodiment, a single point is measured per field. In another embodiment, multiple points are measured per field.

In most FEM cases, measurement point structures are formed from the same designed pattern using different processing parameters. However, it should be noted that different focus exposure matrices may have different structures. For example, a first matrix can be implemented using a first raster type, and a second matrix can be implemented using a second raster type that is different from the first raster type.

In an alternate embodiment, a simulated calibration image (202) generated from a design database for a calibration mask may be used as input to the model. That is, the model can be calibrated without recovering the near field from a physical calibration mask. Instead, the lithography image is simulated by simulating the (non-recovery) near field from a self-designed database and applying a lithography imaging model to the simulated near field to achieve lithography results comparable to the actual results from the wafer (216) .

In general, optical signal data associated with known variations of any set of process parameters, structural parameters, or both can be envisaged. Regardless of the form, the calibration wafer structure can be printed in a variety of different wafer layers. In particular, standard lithography processes (eg, projecting a circuit image through a reticle and onto a photoresist-coated silicon wafer) are generally used to print the printed structures on a photoresist in the layer. The wafer may be one of the calibration wafers with a material layer corresponding to the material typically present on the product wafer at this step in the testing process. The printed structures can be printed on top of other structures in the underlying layers. A calibration wafer can be a production wafer that has the potential to produce a working device. The calibration wafer may be a simple wafer used only for the calibration model. The calibration wafer can be the same wafer used to calibrate the OPC design model. More than one calibration wafer can be used to calibrate the lithography model. When using multiple calibration wafers, the same or different calibration masks can be used. Different calibration masks can have patterns of different sizes to generate a wider range of image data.

The process parameters used to form the calibration structures are generally configured to keep the characteristics of the pattern within desired specifications. For example, calibration structures can be printed on a calibration wafer as part of a calibration process, or the like can be printed on a production wafer during production. At the time of production, the calibration structure is Often printed in scribe lines between device areas (eg, dies that define ICs) disposed on a production wafer. The measurement point may be a dedicated calibration structure disposed around the device structure, or the like may be part of the device structure (eg, a periodic part). As should be appreciated, using a portion of the device structure can be more difficult, but tends to be more accurate because it is part of the device structure. In another embodiment, the alignment structures may be printed across an entire alignment wafer.

Referring again to FIG. 2, in operation 210, the corresponding modeling results and calibration results (eg, images) may be compared. Next, in operation 212, it may be determined whether model parameters are to be adjusted. If model parameters are to be adjusted, the model parameters are adjusted in operation 214 and the process 200 repeats operation 208 to model the lithography process (and resist) using the adjusted parameters. Model parameters may be adjusted until a quantification of the difference between the model image and the calibration image has reached a minimum value that is also below a predefined threshold value. The minimized amount may be the sum of the squares of the differences between the acquired calibration image and the simulated image. The output of this process 200 is a lithography/resist model and its final model parameters. This set of model parameters overcomes the technical hurdles associated with masking process modeling and masking 3D diffraction calculations by exploiting the nature of the near-field of masks.

The simulated wafer pattern based on the recovered mask near-field results can be used for many mask inspection, metrology and/or qualification purposes. In one embodiment, a reticle qualification is performed by evaluating whether the recovered mask near field will likely cause wafer pattern defects under a series of simulated wafer fabrication conditions. For defect detection, the printability of a reticle defect on the wafer is important, and the printability of reticle defects is directly dependent on the reticle near field and lithography systems.

After obtaining a final calibrated lithography/resist/etch model for a particular process (regardless of how the model was obtained), the model can be used to generate accurate images from a mask prior to wafer fabrication using the mask Wafer plane resist images (eg, after development or etching) or used to requalify the mask. These resist images will allow us to Spot and exposure settings or other lithography parameters to evaluate wafer images of any inspection pattern. Since this evaluation process can occur prior to wafer fabrication, qualification and defect detection cycles can be significantly shortened. Simulated wafer images also enable the isolation of different patterning problem sources by comparing simulated wafer images after lithography, after resist pattern application, and after etching.

FIG. 3 illustrates a flow chart representing a reticle qualification process 300 in accordance with an embodiment of the present invention. In operation 302, a mask near-field image is recovered, eg, for a particular reticle based on images acquired from the particular reticle. This operation may include the masked near-field recovery operation of FIG. 1 . After a masked near-field is obtained, in operation 303 the final model parameters for the recovered masked near-field can also be used to model the lithography process (and resist). For example, use the final model to simulate the wafer image using a masked near-field image.

Next, in operation 322, the simulated wafer pattern may be evaluated to determine pattern stability and/or locate defects. It can generally be determined whether the corresponding reticle will likely cause an unstable or defective wafer pattern. In one embodiment, a model is applied to mask near-field images or results using a plurality of different process conditions, such as focus and dose, to evaluate mask design stability under varying process conditions.

4A is a flowchart illustrating a process 400 for determining wafer pattern stability according to an exemplary application of the present invention. First, in operation 402, each test image may be aligned with its corresponding reference image, also generated by the model under different sets of process conditions. Different test images and reference images are calculated by the model under different processing conditions/parameters.

In operation 404, the pairs of aligned images may be compared to each other to obtain one or more wafer pattern differences. Next, in operation 406, a threshold value may be associated with each wafer pattern difference. Wafer pattern variance and its associated thresholds can be used together to characterize pattern stability. That is, the amount of deviation (pattern variance) of a particular pattern under different simulated process conditions and whether this deviation crosses an associated threshold together characterize the pattern stability. The process window of a manufacturing process specifies an expectation or definition The amount of process variation at which the resulting pattern is evaluated to ensure that it will remain stable or within some specified variation tolerance (eg, a threshold value).

Different thresholds for evaluating pattern stability can be assigned to different regions of the reticle and thereby corresponding to the wafer pattern. The thresholds may all be the same or different based on various factors such as pattern design background, pattern MEEF (or mask error enhancement factor as further described below) level, or sensitivity of device performance to wafer pattern variations, etc. For example, we can choose a tighter threshold for the pattern in a dense region than in a semi-dense region of the reticle.

Optionally, a set of initial hot spots or pattern weakness areas can be identified in both the reference mask pattern and the test mask pattern. For example, a designer may provide a list of design hotspot coordinates that are critical to device functionality. For example, areas defined as hotspots may be assigned a detection threshold, while non-hotspot areas may be assigned a higher threshold (for defect detection). This difference can be used to optimize detection resources.

This pattern stability assessment can be used to facilitate reticle qualification, thereby overcoming many of the challenges in this field. As the density and complexity of integrated circuits (ICs) continue to increase, detecting photolithography mask patterns has become increasingly challenging. Each new generation of ICs has denser and more complex patterns that currently reach and exceed the optical limits of lithography systems. To overcome these optical limitations, various resolution enhancement techniques (RET) have been introduced, such as optical proximity correction (OPC). For example, OPC helps overcome some diffraction limitations by modifying the photomask pattern so that the resulting printed pattern corresponds to the original desired pattern. Such modifications may include perturbations to the size and edges of the primary IC features (ie, printable features). Other modifications involve adding serifs to pattern corners and/or providing nearby sub-resolution assist features (SRAFs), which are not expected to result in printed features and are therefore referred to as non-printable features. These non-printable features are expected to cancel out pattern disturbances that would otherwise occur during the printing process. However, OPC makes the mask pattern even more complex and often very different from the resulting wafer image. also, OPC defects generally do not translate into printable defects. The increased complexity of the photomask pattern and the fact that all pattern elements are not expected to directly affect the printed pattern make the task of detecting meaningful pattern defects for the photomask far more difficult. As the semiconductor industry moves toward even smaller features, leading-edge manufacturers are beginning to use even more exotic OPCs, such as inverse lithography (ILT), which result in highly complex patterns on masks. Therefore, it is highly desirable to know the mask write fidelity and its wafer print quality before the wafer is physically fabricated.

One measure of the importance of a defect is its MEEF or mask error enhancement factor. This factor correlates the size of the defect in the mask plane to the magnitude that it will affect the printed image. High MEEF defects have a high impact on the printed pattern; low MEEF defects have less or no impact on the printed pattern. An undersized primary pattern feature in a dense fine line portion of a pattern is an example of a defect with high MEEF, where a small mask plane size error can cause one of the printed patterns to collapse completely. An isolated small pinhole is one example of a defect with a low MEEF, where the defect itself is too small to print and far enough from the nearest main pattern edge to not affect how the edge is printed. Examples such as these show that the MEEF of a defect is a slightly more complex function of the defect type and the pattern background in which the defect is located.

In addition to higher MEEF mask defects causing more significant wafer defects, certain design patterns and corresponding mask patterns may also be more robust to process variations than other designs and mask patterns. When the fabrication process begins to deviate from optimal process conditions, certain mask patterns can lead to more pronounced wafer pattern disturbances and defects.

FIG. 4B is a flowchart illustrating a defect detection process 450 according to another embodiment of the present invention. In operation 452, each modeled test wafer image may be aligned with its corresponding reference image. In one embodiment, a die-to-die or cell-to-cell alignment can be accomplished. In another embodiment, the modeled test wafer image is aligned with a reference image generated from the corresponding post OPC design. For example, a post-OPC design is processed to simulate the reticle fabrication process for this design. For example, corners are rounded. In general, a reference image can be derived from the same die as a test image at an earlier time, from an adjacent same die, or generated from a design database. In a particular example, the reference image is obtained from one of the "gold" die that is certified defect-free (eg, immediately after the reticle is fabricated and qualified). The golden reticle image obtained from the reticle when the reticle is known to be defect free can be stored and used later to compute the golden reticle near field image and wafer image as needed. Alternatively, the near-field image of the gold mask can be stored for access without recomputing the near-field for future inspections.

In operation 454, each pair of aligned test images and reference images are compared to locate reticle defects based on an associated threshold value. Any suitable mechanism may be used to associate threshold values with particular reticle regions, as described further above. Any suitable metric for the test image and the reference image can be compared. For example, the profile of the test and reference wafer images can be compared as a measure of edge placement error (EPE).

Next, in operation 456, the corresponding simulated wafer defect area may be compared with its corresponding reference pre-OPC area for each reticle defect. That is, the simulated wafer pattern is evaluated to determine whether a reticle defect causes a wafer defect that varies with the expected design.

Referring again to FIG. 3, in operation 324, it may then be determined whether the design is defective based on the simulated reticle image. In one embodiment, it is determined whether the design pattern results in unacceptable wafer pattern variation under a specified range (or process window) of process conditions. Determine if there is a significant difference due to process variability. If the difference between wafer patterns of different treatments is above a corresponding threshold value, the wafer patterns may be considered defective. These system defects are called hot spots. It can also be determined whether any difference between a simulated wafer pattern from the reticle and its corresponding pre-OPC pattern is above a predefined threshold. If the design is determined to be defective, in operation 332 the design may be modified.

Once the design of a reticle is verified, the reticle may still contain hot spots that should be monitored. The following operations are described as being performed on a mask that has at least some of the identified hot spots. Of course, if the mask does not contain any identified hotspots, the following operations of Figure 3 can be skipped, and the masking is used without performing hotspot monitoring during fabrication and detection.

In the depicted example, if the design is not considered to be defective, then in operation 326 it may be determined whether any hot spots can be monitored. If it is determined that the hot spot can be monitored, in operation 334 the hot spot can be monitored during the wafer process. For example, hot spot patterns can be monitored during wafer fabrication to determine if the process has gone out of specification and has caused the corresponding wafer pattern to have critical parameters that change to unacceptable values. One implementation may involve setting a relatively high MEEF level to detect reticle and/or wafer patterns corresponding to hot spots. As conditions move further away from nominal process conditions, the CD or EPE can become large and compromise the integrity of the wafer process.

Hotspot patterns can only be identified when a test mask pattern changes by a predefined amount, regardless of how the change is compared to the original intended design (eg, pre-OPC data). In other words, a significant change in the physical mask pattern under different process conditions may indicate a problem with the intended design pattern. The difference between the corresponding modeled image portions represents the difference in the effect of process conditions on the designed pattern and the fabricated mask. Differences associated with a particular design pattern are often referred to as "design hotspots" or simply "hotspots" and represent weaknesses in the design with respect to specific process conditions that have been checked (and possibly also with respect to fabricated masks). Examples of the kinds of differences that can be found between modeled images of different process conditions are CD (critical dimension) or EPE (edge placement error).

In another embodiment, if the model is applied to a post-OPC design database, the resulting wafer pattern may correspond to the pattern the designer intended to print on the wafer. Optionally, the results of applying the model to the post-OPC database can be used with the modeled image to improve hotspot detection. For example, one of the models in the post-OPC database only takes into account design effects, and thus can be used to separate wafer process pairs The effect of the design and the effect of the wafer process on the fabricated mask. The modeled pattern from the near field of the mask can be compared to the modeled wafer image from the corresponding post OPC pattern. For example, when a set of modeled wafer patterns for different process changes matches the corresponding modeled OPC wafer patterns for the same process change, the source of the change in the wafer pattern (or resist pattern) attributable to the process change can be determined From a redesigned or monitored design pattern, not from a defect in the mask pattern. However, if the on-wafer changes due to process changes from the post-OPC database are different from the on-wafer changes due to the same process changes from the restored mask (or mask near field), then this The isohotspot is considered to originate from one of the repairable or monitored hotspots from the actual mask.

Simulated wafer image variance can also be analyzed to determine wafer CD uniformity (CDU) metrics across die or over time (when reticle changes occur during exposure in the manufacturing process). For example, if the resolution is high enough, the CD of each object of each image can be measured by analyzing and measuring the distance between the object edges. Alternatively, the intensity difference between the reference image and the test image can be calibrated and converted to CD variation, as described in US Patent Application Serial No. 14/664,565, filed March 20, 2015 by Carl E. Hess et al. and by Rui-fang Shi et al. are further described in US Patent Application Serial No. 14/390,834, filed October 6, 2014, which is incorporated herein by reference in its entirety for all purposes.

In operation 328, it may also be determined whether the reticle should be repaired. It can be determined that the expected wafer pattern variation exceeds the specification of the process window expected to be used during the lithography process. In certain cases, the reticle may contain a defect that is repaired in operation 336 . Next, the reticle can be requalified. Otherwise, in operation 330, the reticle may be discarded if it cannot be repaired. Next, a new reticle can be fabricated and requalified.

In addition to or instead of using a recovered masked near-field image to simulate a wafer image during a qualification process image, a reticle near-field image or result can also be evaluated directly during a reticle qualification process. 5 is a flowchart illustrating a reticle qualification process 500 applied to a recovered masked near-field image or result, according to an alternative embodiment of the present invention. First, in operation 502, mask near-field results are recovered from a reticle. The near-field image of the mask can be recovered for a particular reticle based on images acquired from that particular reticle. This operation can be practiced similarly to the masked near-field recovery operation of FIG. 1 . Additionally, some of the operations of FIG. 5 may be implemented in a manner similar to the operations of FIG. 3, but for the restored reticle near-field image, including the intensity and/or phase components of this image.

As shown, then, in operation 522, the mask near-field results may be evaluated to characterize and/or locate defects. In general, it can be determined whether the corresponding reticle is defective or has a hot spot that needs to be monitored. More specifically, some of the techniques described herein for evaluating simulated wafer images can be implemented on masked near-field images. During a defect detection process, the test mask near-field image can be compared to the reference mask near-field image for any suitable metric. For example, intensities and/or phases can be compared. Different defect types will have different effects on intensity and/or phase values. These differences can be judged as true defects that would likely result in a defective wafer or identify repairable or monitorable hot spot patterns or areas (as opposed to non-intrusive defects).

For example, next, in operation 524, it may be determined whether the design is defective. If the design is determined to be defective, in operation 532 the design may be modified. For example, it can be determined whether any difference between a reticle near field image and its corresponding post OPC based near field is above a predefined threshold for detecting defects. Process 500 may continue to determine whether to monitor wafer hot spots, repair the reticle, or redesign the reticle, as described above. If the design is not considered to be defective, it may be determined in operation 526 whether any hot spots can be monitored. For example, any intensity and/or phase difference between a test reticle near-field image and a reference reticle near-field image can be determined to be close to an associated threshold value.

For example, if it is determined that a hot spot can be monitored, then in operation 534 thermal monitoring can be performed during the wafer process point. For example, hot spot patterns can be monitored during wafer fabrication to determine if the process has gone out of specification and has caused the corresponding wafer pattern to have critical parameters that change to unacceptable values. One implementation may involve setting a relatively high sensitivity level to detect reticle and/or wafer patterns corresponding to hot spots. As conditions move further away from nominal process conditions, CD errors or EPE can become large and compromise the integrity of the wafer process.

In operation 528, it may also be determined whether the reticle is to be repaired. In certain cases, the reticle may contain a defect that is repaired in operation 536 . Next, the reticle can be requalified. Otherwise, in operation 530, the reticle may be discarded if it cannot be repaired. Next, a new reticle can be fabricated and requalified.

Certain techniques of the present invention provide mask pattern qualification and early detection of weak patterns or hot spots on the physical mask prior to commencing wafer fabrication. In addition to providing the near field of the reticle based on the reticle image recovery, the effects of the wafer process (including many settings of focus and exposure, and the effects of wafer resist, etching, CMP and any other wafer process) can also be considered. How a full range affects wafer patterning. No prior knowledge of the mask is required since only the mask image is used to restore the near field of the mask and no mask design data is used. Since the mask pattern is roughly 4 times larger than the wafer pattern, a more precise location of the pattern relative to the design database can be determined. The above techniques can also be extended to any suitable type of mask, such as pattern qualification of EUV masks.

The techniques of this disclosure may be implemented in any suitable combination of hardware and/or software. FIG. 6 is a graphical representation of an exemplary detection system 600 in which techniques of the present invention may be implemented. Detection system 600 may receive input 602 from a high NA detection tool or a low NA detector emulating a scanner (not shown). The detection system may also include: a data distribution system (eg, 604a and 604b) for distributing the received input 602; an intensity signal (or patch) processing system (eg, a patch processor and mask) Qualification system (eg, 612)) for masking near field and wafer recovery replication, process modeling, etc.; a network (eg, switched network 608) that allows communication between inspection system components; an optional mass storage device 616; and one or more inspection control and/or inspection stations (eg, 610) for viewing mask near-field intensities and phases (values, images or differences), reticle/wafer images, identified hot spots, CD, CDU maps, process parameters, etc. Each processor of detection system 600 may typically include one or more microprocessor ICs and may also include interface and/or memory ICs, and may additionally be coupled to one or more common and/or global memory devices .

The detector or data acquisition system (not shown) used to generate the input data 602 may take the form of any suitable instrument for obtaining an intensity signal or image of a reticle (eg, as further described herein). For example, a low NA detector may construct an optical image or generate intensity values for a portion of the reticle based on a portion of the detected light reflected, transmitted, or otherwise directed to one or more light sensors. The low NA detector can then output intensity values or images.

Low NA detection tools are operable to detect and collect reflected and/or transmitted light as an incident beam scans across blocks of a reticle. As described above, the incident beam may be scanned across a reticle scan strip, each comprising a plurality of blocks. Light is collected in response to this incident beam from points or sub-regions of each block.

The low NA detection tool is generally operable to convert this detected light into a detected signal corresponding to an intensity value. The detected signal may take the form of an electromagnetic waveform having amplitude values corresponding to different intensity values at different locations of the reticle. The detected signal can also take the form of a simple list of intensity values and associated reticle point coordinates. The detected signal can also take the form of an image with different intensity values corresponding to different locations or scan points on the reticle. The two or more images of the reticle can be generated after all positions of the reticle are scanned and converted into detected signals, or two or more images can be generated when each reticle portion is scanned with the final two or more images. Portions of one or more images to complete the reticle after scanning the entire reticle.

The detected signal may also take the form of an aerial image. That is, an aerial imaging technique can be used to simulate the optical effects of a photolithography system to produce an aerial image of the photoresist pattern exposed on the wafer. In general, the optics of a photolithography tool are modeled to generate an aerial image based on detected signals from the reticle. The aerial image corresponds to the pattern produced by light propagating through the photolithography optics and reticle onto the photoresist layer of a wafer. In addition, the photoresist exposure process for a particular type of photoresist material can also be simulated.

Incident or detected light may travel through any suitable spatial aperture to produce any incident or detected light profile at any suitable angle of incidence. For example, programmable illumination or detection apertures can be utilized to generate a specific beam profile, such as dipole, quadrupole, quasar, ring, etc. In a particular example, light source mask optimization (SMO) or any pixelated lighting technique may be implemented. Incident light may also travel through a linear polarizer to linearly polarize all or a portion of the illumination pupil in one or more polarizations. The detected light can travel through the apodization element to block specific regions of the collected beam.

Intensity or image data 602 may be received via network 608 by a data distribution system. A data distribution system may be associated with one or more memory devices, such as RAM buffers, for holding at least a portion of the received data 602 . Preferably, the total memory is large enough to hold an entire sample of one of the data. For example, one gigabyte of memory works well for a sample of 1 million by 1000 pixels or points.

Data distribution systems (eg, 604a and 604b) may also control the distribution of portions of received input data 602 to processors (eg, 606a and 606b). For example, the data distribution system may send a first block of data to a first block handler 606a and may send a second block of data to block handler 606b. Multiple sets of data from multiple blocks can also be sent to each block processor.

The block processor may receive intensity values or an image corresponding to at least a portion or block of the reticle. The block processors may also each be coupled to one or more memory devices (such as providing local memory bulk functions, such as a DRAM device that holds portions of the received data) (not shown) or integrated with the one or more memory devices. Preferably, the memory is large enough to hold data corresponding to a block of the reticle. For example, 8 megabytes of memory works well for intensity values or an image corresponding to a block of 512 by 1024 pixels. Alternatively, block processors can share memory.

Each set of input data 602 may correspond to a scanband of the reticle. One or more sets of data may be stored in the memory of the data distribution system. The memory can be controlled by one or more processors within the data distribution system, and the memory can be divided into partitions. For example, the data distribution system may receive data corresponding to a portion of a scanband into a first memory partition (not shown), and the data distribution system may receive another data corresponding to another scanband into a first memory partition (not shown) two memory partitions (not shown). Preferably, each of the memory partitions of the data distribution system holds only the portion of the data to be delivered to a processor associated with that memory partition. For example, the first memory partition of the data distribution system may hold the first data and deliver the first data to the block processor 606a, and the second memory partition may hold the second data and deliver the second data to the zone Block handler 606b.

The data distribution system may define and distribute sets of data for the data based on any suitable parameters for the data. For example, data can be defined and allocated based on the corresponding locations of blocks on the reticle. In one embodiment, each swath is associated with a range of row positions corresponding to the horizontal positions of pixels within the swath. For example, lines 0 through 256 of the swath may correspond to a first block, and the pixels within these lines will include the first image or first set of intensity values that are sent to one or more block processors. Likewise, rows 257-512 of the swath may correspond to a second block, and the pixels in these rows will include the second image or second set of intensity values that are sent to the different block processor(s).

The inspection apparatus may be adapted to inspect semiconductor devices or wafers with optical masks and EUV masks or masks. An example of a suitable inspection tool is a Teron ^™ operating at 193 nm or a TeraScan ^™ DUV reticle inspection tool available from KLA-Tencor of Milpitas, CA. Other types of samples that can be detected or imaged using the detection apparatus of the present invention include any surface, such as a flat panel display.

A detection tool can include: at least one light source for generating an incident beam; illumination optics for directing the incident beam onto a sample; collection optics for directing emission from the sample in response to the incident beam an output beam; a sensor for detecting the output beam and generating an image or signal of the output beam; and a controller/processor for controlling the components of the inspection tool and facilitating mask near-field generation and analytical techniques, as described further herein.

In the following exemplary detection systems, the incident light beam may be in any suitable form of coherent light. Additionally, any suitable lens configuration may be used to direct the incident beam towards the sample and the output beam from the sample towards a detector. The output beam can be reflected or scattered from the sample or transmitted through the sample. For EUV mask inspection, the output beam is usually reflected from the sample. Likewise, any suitable detector type or any suitable number of detection elements may be used to receive the output beam and provide an image or a signal based on characteristics (eg, intensity) of the received output beam.

A generalized photolithography tool will be described first, but an EUV photolithography tool will typically only have reflective optics. 7A is a simplified schematic representation of a typical lithography system 700 that can be used to transfer a mask pattern from a photomask M onto a wafer W, according to certain embodiments. Examples of such systems include scanners and steppers, more specifically the TWINSCAN NXT: 1970Ci stepper and scan system available from ASML of Veldhoven, Netherlands. In general, an illumination source 703 directs a light beam through an illumination optics 707 (eg, lens 705 ) to a light mask M positioned in a mask plane 702 . The illumination lens 705 has a numerical aperture 701 at the plane 702 . The value of numerical aperture 701 affects which defects on the photomask are lithographically significant and which are not lithographically significant defects. of the light beam traveling through the light shield M A portion forms a patterned optical signal that is directed through imaging optics 713 and onto a wafer W for initial pattern transfer. In a reflective system (not shown), the illumination beam is reflected from certain parts of the mask M (and thus absorbed by other parts of the mask M) and forms one of the reflective imaging optics directed through a wafer W patterned signal.

The inspection tool may utilize similar components or be configured similarly to the photolithography tools described above, eg, LNI capabilities. However, the inspection tool may alternatively or additionally be configured to generate high resolution images. 7B provides a schematic representation of an exemplary detection system 750 having illumination optics 751a and including an imaging lens with a relatively large numerical aperture 751b at a reticle plane 752, according to certain embodiments. For example, the numerical aperture 751b at the reticle plane 752 of the inspection system may be much larger than the numerical aperture 701 at the reticle plane 702 of the lithography system 700, which will result in discrepancies between the test inspection image and the actual printed image.

The detection techniques described herein can be implemented on various specially configured detection systems, such as the detection system schematically depicted in Figure 7B. The depicted system 750 includes an illumination source 760 that generates a light beam directed through illumination optics 751a onto a light mask M in the mask plane 752 . Examples of light sources include co-tuned laser light sources (eg, deep UV or gas laser generators), a filtered lamp, LED light sources, and the like. In certain embodiments, a light source generally provides high pulse repetition rate, low noise, high power, stability, reliability, and scalability. It should be noted that while an EUV scanner operates at a wavelength of 13.5 nm, an inspection tool for an EUV reticle need not operate at the same wavelength (although it can). In one example, the light source is a 193 nm laser.

Illumination optics 751a can include a beam steering device for precise beam positioning and a beam conditioning device that can provide light level control, speckle noise reduction, and high beam uniformity. The beam steering and/or beam conditioning device may be a physical device separate from, for example, a laser. lighting The optics 751a may also include optics for controlling polarization, focus, magnification, illumination intensity distribution, and the like.

As explained above, detection system 750 may have a numerical aperture 751b at reticle plane 752 that may be equal to or greater than a reticle plane numerical aperture of a corresponding lithography system (eg, element 701 in Figure 7A). The light mask M to be inspected is placed on a mask stage at the mask plane 752 and exposed to the light source.

The depicted detection system 750 may include detection optics 753a and 753b, which may also include microscope magnification optics designed to provide, for example, 60X to 200X magnification or greater for enhanced detection device. Collection optics 753a and 753b may comprise any suitable optics for conditioning the output light/beam. For example, collection optics 753a and 753b may include optics for controlling focus, pupil shape, polarization analyzer settings, and the like.

In a transmissive mode, the patterned image from mask M can be directed through a set of optical elements 753a that project the patterned image onto a sensor 754a. In a reflection mode, collection elements (eg, beam splitter 776 and detection lens 778) direct and capture reflected light from mask M onto sensor 754b. Although two sensors are shown, a single sensor can be used to detect reflected and transmitted light during different scans of the same reticle area. Suitable sensors include charge coupled devices (CCDs), CCD arrays, time delay integration (TDI) sensors, TDI sensor arrays, photomultiplier tubes (PMTs), and other sensors.

The rows of illumination optics can be moved relative to the mask stage and/or the stage moved relative to a detector or camera by any suitable mechanism to scan blocks of the mask. For example, a motor mechanism can be used to move the stage. For example, the motor mechanism may be formed by a screw drive and stepper motor, a linear drive with feedback position, or a belt actuator and stepper motor. System 700 may utilize one or more motor mechanisms to move any of the system components relative to the illumination or collection optical path.

The signals captured by each sensor (eg, 754a and/or 754b) may be processed by a computer system 773 or, more generally, by one or more signal processing devices, which may each An analog-to-digital converter configured to convert analog signals from each sensor to digital signals for processing is included. Computer system 773 typically has one or more processors coupled to input/output ports and one or more memories via a suitable bus or other communication mechanism.

Computer system 773 may also include one or more input devices (eg, a keyboard, mouse, joystick) to provide user input, such as changing focus and other detection recipe parameters. Computer system 773 may also be connected to the stage to control, for example, a sample position (eg, focus and scan), and to other inspection system components to control other inspection parameters and configuration of these inspection system components.

Computer system 773 can be configured (eg, with programmed instructions) to provide a user interface (eg, a computer screen) to display mask near-field intensity and phase (value, image, or difference), mask/crystal Circle image, identified hot spots, CD, CDU map, process parameters, etc. Computer system 773 may be configured to analyze reflected and/or transmitted detected and/or analog signals or images, intensity, phase, and/or other characteristics of the recovered reticle near-field results, and the like. Computer system 773 can be configured (eg, with programmed instructions) to provide a user interface (eg, on a computer screen) to display the resulting intensity and/or phase values, images, and other detection characteristics. In particular embodiments, computer system 773 is configured to implement the detection techniques detailed above.

Because such information and program instructions may be implemented on a specially configured computer system, such a system includes program instructions/computer code storable on a computer-readable medium for performing the various operations described herein . Examples of machine-readable media include, but are not limited to: magnetic media, such as hard disks, floppy disks, and magnetic tapes; optical media, such as CD-ROM optical disks; magneto-optical media, such as optical disks; and those specially configured to store and execute program instructions hardware devices such as read only memory (ROM) and random access memory (RAM). Examples of program instructions include Such as both machine code generated by a compiler and files containing higher-level code that can be executed by a computer using an interpreter.

7B shows an example in which an illumination beam is directed towards the sample surface at a substantially normal angle relative to the surface being inspected. In other embodiments, an illumination beam may be directed at an oblique angle, which allows for separation of the illumination beam and the reflected beam. In these embodiments, an attenuator may be positioned in the reflected beam path to attenuate a zero-order component of the reflected beam before it reaches a detector. Additionally, an imaging aperture can be positioned in the reflected beam path to shift the phase of the zero-order component of the reflected beam.

It should be noted that the above description and drawings should not be construed as limiting the particular components of the system and that the system may be embodied in many other forms. For example, it is contemplated that inspection or metrology tools may have any suitable features from any number of known imaging or metrology tools configured to detect defects and/or resolve critical aspects of features of a reticle or wafer. For example, an inspection or metrology tool can be adapted for bright-field imaging microscopy, dark-field imaging microscopy, all-sky imaging microscopy, phase contrast microscopy, polarized light contrast microscopy, and coherent detection microscopy technique. It is also contemplated that single-image and multi-image methods can be used to capture images of the target. Such methods include, for example, single grasp, double grasp, single grasp coherent probing microscopy (CPM), and double grasp CPM methods. Non-imaging optical methods, such as scatterometry, are also expected to form part of detection or metrology equipment.

Although the foregoing invention has been described in considerable detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications can be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing the process, system and apparatus of the present invention. Accordingly, the present examples are to be regarded as illustrative and non-limiting, and the invention is not to be limited to the details given herein.

300: Reticle Qualification Process

302: Operation

303: Operation

322:Operation

324:Operation

326:Operation

328:Operation

330: Operation

332:Operation

334:Operation

336: Operation

Claims (26)

A method of qualifying a photolithography reticle, the method comprising: using an imaging tool to acquire a plurality of images from each of a plurality of pattern areas of a test reticle with different illumination configurations and/or different imaging configurations ; recover a reticle near field for each of the pattern areas of the test reticle based on the images obtained from the pattern areas of the test reticle; and use the recovered reticle near field to determine the test light Whether the mask or another reticle will likely result in an unstable wafer pattern or a defective wafer. The method of claim 1, wherein the reticle near field is directly analyzed to determine whether the test reticle or another reticle would likely result in an unstable wafer pattern or a defective wafer. The method of claim 1, wherein the plurality of images are acquired at a field or pupil plane. The method of claim 1, wherein the recovered reticle near field is used to detect defects in the test reticle or in simulated wafer images simulated from the recovered reticle near field, wherein defect detection comprises : Compare the intensity of an identical die at different times, an adjacent die, a die with its corresponding gold die, or a die with a corresponding die from a reticle replica of the same design as the test reticle and / or phase. The method of claim 1, wherein the reticle near field is recovered without using a design database used to make the test reticle. The method of claim 1, wherein the acquired images comprise at least three reflection images acquired under different imaging conditions selected to result in a same reticle near field, and wherein the different imaging conditions comprise different focus settings, Different pupil shapes and/or polarization analyzer settings, where different lighting conditions include different light source intensity distributions and/or polarization settings. The method of claim 1, wherein the acquired images comprise at least three transmission images acquired under different imaging conditions selected to result in a near field of the same reticle, and wherein the different imaging conditions comprise different focus settings, Different pupil shapes or polarization analyzer settings, wherein the different lighting conditions include different light source intensity distributions and/or polarization settings. The method of claim 1, further comprising: applying a lithography model to the reticle near field of the test reticle to simulate a plurality of test wafer images, and analyzing the simulated test wafer images to determine the test Whether the reticle will likely result in an unstable or defective wafer where the lithography model is configured to simulate a photolithography process. 8. The method of claim 8, wherein the lithography model simulates an illumination source having a different illumination shape than an illumination shape of an inspection tool used to acquire an image of the test reticle or another reticle or wafer shape. The method of claim 8, wherein the application is generated from a design database for a calibration reticle to calibrate the lithography model. The method of claim 8, wherein the lithography model is calibrated using images obtained from a calibration mask. The method of claim 8, wherein the lithography model comprises a compact resist model. The method of claim 8, wherein the lithography model is applied to the near field of the reticle recovered for the test reticle under a plurality of different lithography process conditions, and wherein analyzing the simulated test wafer images comprises: using Whether the test reticle will likely result in an unstable wafer under the different lithography process conditions is determined by comparing portions of the simulated test images associated with different process conditions and a same reticle area. An imaging system for qualifying a photolithography mask, the system comprising: a light source for generating an incident beam; an illumination optical module for guiding the incident beam onto a photomask a collection optics module for directing an output beam from each pattern area of the reticle to at least one sensor; at least one sensor for detecting the output beam and based on the output beam generating an image or signal; and a controller configured to: cause a plurality of images to be acquired from each of a plurality of pattern areas of a test reticle according to different illumination configurations and/or different imaging configurations ; recover a reticle near field for each of the pattern areas of the test reticle based on the images acquired from the pattern areas of the test reticle; and use the recovered reticle near field to determine the test reticle Or whether another reticle will likely result in an unstable wafer pattern or a defective wafer. The system of claim 14, wherein the reticle near field is directly analyzed to determine whether the test reticle or another reticle would likely cause an unstable wafer pattern or a defective wafer. The system of claim 14, wherein the plurality of images are acquired at a field or pupil plane. The system of claim 14, wherein the recovered reticle near field is used to detect defects in the test reticle or in simulated wafer images simulated from the recovered reticle near field, wherein defect detection comprises : Compare the intensity of an identical die at different times, an adjacent die, a die with its corresponding gold die, or a die with a corresponding die from a reticle replica of the same design as the test reticle and / or phase. The system of claim 14, wherein the reticle near field is recovered without using a design database used to make the test reticle. The system of claim 14, wherein the acquired images comprise at least three reflection images acquired under different imaging conditions selected to result in a same reticle near-field, and wherein the different imaging conditions comprise different focus settings and Different pupil shapes. The system of claim 14, wherein the acquired images comprise at least three transmission images acquired under different imaging conditions selected to result in a same reticle near field, and wherein the different imaging conditions comprise different focus settings and Different pupil shapes. The system of claim 14, wherein the controller is further configured to: apply a lithography model to the reticle near field of the test reticle to simulate a plurality of test wafer images, and analyze the simulated test wafers A circular image is used to determine whether the test reticle will likely result in an unstable or defective wafer, wherein the lithography model is configured to simulate a photolithography process. The system of claim 21, wherein the lithography model simulates an illumination source having a different illumination shape than an illumination shape of an inspection system used to acquire images of the test reticle or another reticle or wafer shape. The system of claim 21, wherein the lithography model is calibrated using images generated from a design database for a calibration mask. The system of claim 21, wherein the lithography model is calibrated using images obtained from a calibration reticle. The system of claim 21, wherein the lithography model comprises a compact resist model. The system of claim 21, wherein the lithography mold is subjected to a plurality of different lithography process conditions The model is applied to the reticle near field recovered for the test reticle, and wherein analyzing the simulated test wafer images includes: by comparing the simulated test images associated with different process conditions and a same reticle area In part, it is determined whether the test reticle will likely result in an unstable wafer under the different lithography process conditions.

Images