Review and Adjudication Information. Group: Inspection & Metrology Task Force North America 3DS-IC Committee Date: April 2, 2013 April 2, 2013

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1 Background Statement for SEMI Draft Document 5410 NEW STANDARD: GUIDE FOR METROLOGY TECHNIQUES TO BE USED IN MEASUREMENT OF GEOMETRICAL PARAMETERS OF THROUGH-SILICON VIAS (TSVs) IN 3DS-IC STRUCTURES Notice: This background statement is not part of the balloted item. It is provided solely to assist the recipient in reaching an informed decision based on the rationale of the activity that preceded the creation of this Document. Notice: Recipients of this Document are invited to submit, with their comments, notification of any relevant patented technology or copyrighted items of which they are aware and to provide supporting documentation. In this context, patented technology is defined as technology for which a patent has issued or has been applied for. In the latter case, only publicly available information on the contents of the patent application is to be provided. Background This guide will assist the user in selection and use of TSV metrology tools, as well as a protocol for performing TSV measurements of geometrical parameters of an individual TSV, or of an array of TSVs, such as pitch, top CD, top diameter, top area, depth, taper (or sidewall angle), bottom area, bottom CD, bottom diameter, and possibly others (e.g. scalloping and overall tilt). This guide will address the various metrology techniques that are currently available that enable TSV measurements used for 3DS-IC packaging. New TSV dimensions with higher aspect ratios and smaller diameters may challenge TSV metrology techniques. The guide will provide examples of measurements in TSVs at different aspect ratios, TSV measurement limits for a variety of metrology tools, the relative levels of substrate interaction, and recommendations by application. Subsequently this guide can assist producers and users of TSV metrology to develop products and conduct meaningful evaluations. New measurement techniques will likely arise and can be dealt with in future revisions of this document. This document was approved for yellow ballot in Cycle 1 of 2013 by the N.A. 3DS-IC committee on Oct. 30, The creation of this document was authorized by Committee 3DS-IC on April 3, Review and Adjudication Information Task Force Review Committee Adjudication Group: Inspection & Metrology Task Force North America 3DS-IC Committee Date: April 2, 2013 April 2, 2013 Time & Time zone: 8:00 AM to 10:00 AM, Pacific Time 3:00 PM to 5:00 PM, Pacific Time Location: SEMI Headquarters SEMI Headquarters City, State/Country: San Jose, California San Jose, California Leader(s): Victor Vartanian (SEMATECH) David Read (NIST) Yi-Shao Lai (ASE) Urmi Ray (Qualcomm) Sesh Ramaswami (Applied Materials) Richard Allen (SEMATECH) Chris Moore (Semilab) Standards Staff: Paul Trio (SEMI NA) /ptrio@semi.org Paul Trio (SEMI NA) / ptrio@semi.org

2 SEMI Draft Document 5410 NEW STANDARD: GUIDE FOR METROLOGY TECHNIQUES TO BE USED IN MEASUREMENT OF GEOMETRICAL PARAMETERS OF THROUGH-SILICON VIAS (TSVs) IN 3DS-IC STRUCTURES 1 Purpose 1.1 This guide will assist the user in selection and use of tools for performing measurements of geometrical parameters of an individual TSV (through-silicon via), or of an array of TSVs. TSVs are expected to be a critical element in future three-dimensional stacked integrated circuit (3DS-IC) packaging. Advanced TSV designs with higher aspect ratios and smaller diameters may challenge TSV metrology techniques. This guide will address the various metrology techniques that are currently available that enable TSV (through-silicon via) dimensional measurements. This guide can also assist producers and users of TSV metrology to develop products and conduct meaningful evaluations. 2 Scope 2.1 This guide focuses on the geometrical parameters of the openings (i.e., holes) in thin silicon slices, within which the conductive vias will be constructed. Additional layers on the surface of the silicon wafer, such as a hard mask, may be present; such layers may affect the performance of the metrology tools described below. 2.2 A complete TSV will typically require additional components, for example, a conductive material and insulating layers. The measurement tools described in this guide represent the present state of the art for measurements of the TSV opening. Some of them may be applicable to other TSV features that become present at a later stage of manufacture, while others may not. Figure 1 Sketch of a TSV Showing Some Geometrical Properties of Interest for TSV Metrology Page 1 Doc SEMI

3 2.3 This guide will assist the user in selection and use of TSV metrology tools, as well as a protocol for performing TSV measurements of geometrical parameters of an individual TSV, or of an array of TSVs, such as pitch, top CD, top diameter, top area, depth, taper (or sidewall angle), bottom area, bottom CD, bottom diameter, and possibly others (e.g. scalloping and overall tilt). Figure 1shows some of these. 2.4 This guide will provide examples of measurements of TSVs at different sizes and aspect ratios, TSV measurement using a variety of metrology tools, the relative levels of substrate interaction, and recommendations by application. It targets the particular set of geometrical parameters defined in SEMI 3D1. It focuses on the various measurement principles available, rather than on particular instruments. 2.5 The examples given have been provided by qualified industry colleagues, and are believed to be representative of instrument performance that can be routinely achieved. Substantial efforts have been made to obtain performance data that are representative of the marketplace in However, this guide is not an exhaustive survey of the state of the art of TSV geometrical metrology. 2.6 The TSV measurements described in this guide extend over TSV diameters from a few micrometers up to tens and even hundreds of micrometers, and TSV depths in the range of 10 to 200 µm. 2.7 Company names, brand names, and trademarks of individual instruments are not included in this guide. NOTICE: SEMI Standards and Safety Guidelines do not purport to address all safety issues associated with their use. It is the responsibility of the users of the Documents to establish appropriate safety and health practices, and determine the applicability of regulatory or other limitations prior to use. 3 Limitations 3.1 The content of this guide is limited to examples of TSV measurement methods gathered from the published technical literature and contributed by the participating organizations. No independent verification of the performance of the metrology approaches or tools described here has been conducted. 3.2 While this guide provides guidance on the capability and conditions of use for available techniques, it does not provide the level of detail typically available in test methods. 3.3 This guide does not contain guidance as to whether any particular technique should be applied in any particular case or any particular stage of process development or production. The strategy for applying TSV metrology must be selected by each individual investigator or company, based on their particular manufacturing process sequence and the purpose of the measurements made. 3.4 The examples of TSV measurements presented in this guide should not be construed as indications of the limits of applicability of the corresponding measurement techniques or instruments. The examples were made available by contributors from data that were available at a particular moment in time, mid These measurement techniques, and the commercial products at which they are targeted, are evolving rapidly. 4 Referenced Standards and Documents 4.1 SEMI Standards and Safety Guidelines SEMI 3D1 Terminology For Through Silicon Via Metrology SEMI M59 Terminology for Silicon Technology SEMI MF1530 Test Method for Measuring Flatness, Thickness, and Total Thickness Variation on Silicon Wafers by Automated Non-Contact Scanning NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions. 5 Terminology 5.1 General terms, acronyms, abbreviations and symbols associated with silicon technology and used in this standard are listed and defined in SEMI M The important geometrical parameters of TSV s are defined in SEMI 3D1. Page 2 Doc SEMI

4 5.3 Other Abbreviations and Acronyms IR infrared SEM scanning electron microscopy TSOM through-focus scanning optical microscopy 5.4 Other Definitions destructive operations that prevent a wafer from being processed through the subsequent bonding, thinning, edge-bevel trimming, and thermal processes in 3D integration. Some methods and instruments for measuring the geometrical parameters of TSVs require destructive specimen preparation techniques etch any process used to remove silicon in a controlled fashion to create the TSV opening image-based as applied to TSVs, a metrology technique in which TSV dimensions are extracted from an image of the TSV. The image is obtained by some type of microscopy or tomography, and the dimensions are then measured from point to point in the image non-destructive operations that allow a wafer to be processed through the subsequent bonding, thinning, edge-bevel trimming, and thermal processes in 3D integration specimen preparation operations needed to prepare a wafer for examination by use of a metrology tool, or to extract a portion of a wafer and prepare it for examination. 6 Considerations in Making Dimensional Measurements on TSVs 6.1 Image-based dimensional measurements A typical route to performing image-based dimensional measurements of TSVs consists of two steps: a) Acquire a digital image of the TSV; and b) Analyze the image. It hardly needs to be stated that in the 21st century both of these steps are carried out with the aid of digital computers of some sort. The capability of acquiring digital images is offered by multiple vendors for all of the measurement tools listed above. Basic interactive tools for the analysis of digital images are widely available, in some cases free, for example ImageJ 1. Several images of TSVs have been published in the open technical literature; SEM images are particularly popular 2,3. Examples are shown below. 6.2 Challenges to accurate and consistent extraction of dimensional parameters The metrology issues in SEM imaging and image analysis have been discussed at length in a technical article 4 on SEM as a technique for dimensional metrology. These usually come down to identifying the exact pixel or fraction of a pixel that corresponds to the edge of a feature to be measured. Best practices in image analysis are beyond the scope of this guide; however, proper reporting of TSV dimensions would clearly appear to be incomplete, and hence of limited use, without documentation of the methodologies used for both imaging and image analysis. 6.3 Substrate interactions Additional layers on the surface of the silicon wafer, such as a hard mask, may be present on a wafer that contains TSVs to be measured; such layers may affect the performance of the metrology tools described in this guide. These layers are typically visible and distinguishable from silicon in SEM, optical, and x-ray microscopy techniques. Therefore, they can be accounted for in the analysis of the image and the extraction of the TSV dimensions. However, the transmittance and reflectance of these layers may be different from that of silicon, and therefore may affect spectral reflectometry measurements, which are discussed below. The models used to extract TSV dimensions from spectral reflectometry data may need to account for layers of material present on top of the silicon. This may require more effort in the modeling, and more care in the measurements to be sure that the surface layers are properly accounted for. 1 Rasband, W.S., ImageJ, U. S. National Institutes of Health, Bethesda, Maryland, USA, Kamto, A., Liu, Y., Schaper, L., and Burkett, S.L., Reliability study of through-silicon via (TSV) copper filled interconnects, Thin Solid Films 518 (2009): pp Ham, Y.H., Kim, D.P., Park, K.S., Jeong, Y.S., Yun, H. J., Baek, K. H., Kwon, K. H., Lee, K. and Do, L. M., Dual etch processes of via and metal paste filling for through silicon via process, Thin Solid Films 519 (2011): pp Postek, M. T., Critical Issues in Scanning Electron-Microscope Metrology, Journal of Research of the National Institute of Standards and Technology 99 (1994): pp Page 3 Doc SEMI

5 7 Measurement Techniques 7.1 Scanning electron microscopy Cross-section SEM is an image-based metrology technique that has been used to measure TSV dimensions from their beginning. 5 The sub-micrometer resolution (<10 nm) of a cross-sectional SEM micrograph is typically much better than that required for relatively large features like 1 to 5 micrometer diameter TSVs. Dimensional metrology in the SEM down to the nanometer level is available. 4,6 This level of precision is easily sufficient to meet the needs of present-day TSV metrology. Specimen preparation is required to allow cross-sectional geometrical measurements on TSVs. Examples of two different procedures are described below: cleavage, and focused-ion-beam (FIB) milling. Both of these techniques are destructive, although FIB milling can be done in such a manner as to affect only a very small portion of the wafer surface at the TSV of interest. An issue that may arise is the selection, creation, and verification of a suitable cross-section plane. The exact location of the surface plane of the cross-section influences the dimensions measured on the imaged surface. Despite these limitations, cross-section SEM is the tool usually used in verification of other, less direct methods of obtaining TSV dimensions. 7.2 Optical microscopy The precision of dimensional measurements by optical microscopy in the focal plane is in the range of tenths of a micrometer. Similar levels of precision for selected features can be obtained in the out-ofplane direction (z-direction) by use of instruments with a calibrated focus distance. An elaboration of optical microscopy that is being researched is through-focus scanning optical microscopy (TSOM). TSOM utilizes a set of images acquired at different focus settings, that is, at different settings of the distance between the specimen and the objective lens. 7 By analyzing this series of images, the TSOM procedure provides improved lateral and vertical measurement resolution, relative to conventional optical microscopy, enabling measurement of in-plane dimensions and line widths as well as out-of-plane dimensions such as via depths with measurement resolution into the nanoscale. TSOM operates by comparing a TSOM image set either against a library of images, to find a best match, or against another TSOM image set. The library can consist of simulated or actual images. TSOM does not produce enhanced-resolution images; it applies comparative analysis to extract hidden information from conventional optical images. 7.3 Infrared microscopy and reflectometry Because silicon is partially transparent to infrared light, IR microscopy can be used as an image-based technique in a non-destructive procedure. The longer wavelength of infrared light, compared to the visible, and other issues associated with imaging through the partially transparent silicon, cause the resolution of this method to be typically below that of a conventional optical microscope. However, the ability to image through silicon may be a decisive advantage, and technical advances have been proposed. 8 Measurement of reflectometry over a wide band of wavelengths of light, combined with detailed interpretation of the collected signal as a function of wavelength by various techniques, forms the basis for several commerciallyavailable tools aimed at non-destructive, rapid inspection of wafers in the production setting. 7.4 Interferometry Some of the measurement techniques to be introduced below utilize interferometry. Interferometry refers to measurements that rely on the interference of light; optical interference occurs for light of all wavelengths, including, in the present context, optical and IR. A beam of light has several properties that can affect an interferometric measurement; here we give a simplified description that considers only the wavelength, and assume that other properties, such as spectral purity, polarization, coherence length, and velocity of light in the transmission medium present, are controlled as needed. In interferometry, the optical beam from a light source is caused to impinge on a material or structure that splits the beam, reflecting or refracting part of the beam, but not all of it. The two parts of the original optical beam are then redirected along separate paths toward a single detector, which may be an optical intensity measuring device or a camera. The basis of the measurement operation is that the effective length of the optical path traveled by the reflected or refracted part of the beam is different from the length of the path traveled by the undisturbed part. Because of the wavelike nature of light, the physical recombination of the two parts of the beam at the detector can be additive or subtractive, depending on the difference in the two 5 Swinnen, B., Ruythooren, W., De Moor, P., Bogaerts, L., Carbonell, L., De Munck, K., Eyckens, B., Stoukatch, S., Tezcan, D.S., Tokei, Z., Vaes, J., Van Aelst, J., and Beyne, E., "3D integration by Cu-Cu thermo-compression bonding of extremely thinned bulk-si die containing 10 µm pitch through-si vias," in Electron Devices Meeting, IEDM '06. (2006): pp Larrabee, R.D. and Postek, M.T., Precision, Accuracy, Uncertainty and Traceability and their Application to Submicrometer Dimensional Metrology, Solid-State Electronics 36 (1993): pp Attota, R., "TSOM Method for Nanoelectronics Dimensional Metrology," in Frontiers of Characterization and Metrology for Nanoelectronics: , D. G. Seiler, A. C. Diebold, R. McDonald, A. Chabli and E. M. Secula, Eds., ( Amer Inst Physics, 2011). 8 Delacretaz, Y. and Depeursinge, C., "Digital holographic microscopy for silicon microsystems metrology," in Silicon Photonics and Photonic Integrated Circuits 7719, G. C. Righini, Ed., (SPIE-Int Soc Optical Engineering, Bellingham, 2010): art M. Page 4 Doc SEMI

6 effective path lengths relative to the wavelength of the light. If the paths differ by a full wavelength, or a multiple thereof, the interference is constructive, while if the path difference has a value different from an even multiple of a wavelength, interference occurs. For well-conditioned signals, this interference can be completely destructive, resulting in a null signal. The sensitivity of interferometric measurements results from the change from constructive to destructive interference produced by an effective path length change of only one half of the wavelength of light. The strategy for designing an interferometric measurement is to define the relationship between the quantity to be measured and an accessible effective optical path length. Interferometry is useful in a variety of applications because a variety of physical effects can cause changes in the effective optical path length, which includes the physical length, the velocity of light along the path, and the effect of any reflective or refractive elements that are present in the path. NOTE 1: The X-ray microscope works by detecting transmitted X-rays after they pass through a material. The x-ray microscopy technique as practically applied to date is image-based and destructive. Most commercially available lab-based X-ray microscopes are founded on the principle of point projection, wherein the incident X-ray source is transmitted through the sample and onto a detector. The achievable resolution depends on the X-ray source spot size, the detector resolution, and the geometrical arrangement. As the distance between the source and object becomes shorter, the magnification of the image increases, but with image blur in the detector plane. Therefore, a high resolution detector is required. Generally, resolution as high as ~100 nm can be achieved. For better resolution (50 nm), an improved X-ray optical system is implemented using diffraction instead of refraction to focus the X-rays. However, the improved optical system will limit the rotating area (required for tomography), requiring sample preparation to fit, and high precision measurements may require long imaging times. The published technical literature to date contains some examples of the use of x-ray microscopy to detect voids in the copper fill of TSVs, but no examples of measurements of the TSV properties listed in Examples of Dimensional Metrology of TSVs by Use of SEM 8.1 Specimen preparation for measurements on TSVs by use of SEM This section describes two methods of specimen preparation for examination and measurement of TSVs by SEM: cleavage, and focused-ion-beam (FIB) milling Cleavage Wafers of certain crystallographic orientations, particularly (100), can be fractured, or cleaved, to obtain a cross-section of the wafer. If the cleavage plane intersects a TSV, the exposed TSV cross-section can be observed by SEM. Cleavage is a destructive technique. An offset array of TSVs can be used to facilitate obtaining a cleave at the TSV center for SEM metrology (SEM bar). These features can be built into the die and located by naked eye for cleaving, resulting in some usable TSVs being visible. Depth and profile measurements are easily obtained on unfilled TSVs. By use of a commercially-available micro-cleaver, the cleave line can be more accurately placed (reported placement accuracy to within 300 nm of a feature of interest in the product literature). The micro-cleaver used in this example was equipped with a high magnification camera to precisely locate and position the cleaving mechanism. An individual TSV could then become the targeted feature of interest, and the cleave could be positioned close to the center of that particular TSV. A micro-cleaver is also useful when die layouts do not have sufficient area to include an offset array of TSVs for SEM metrology (SEM bar) FIB-milling Sub-surface SEM imaging is possible on whole 300 mm wafers, without cleaving, when an inline dual beam FIB-SEM is utilized. 9 The cross-sectioning is done by a gallium beam ion-mill (liquid metal ion source) to excavate wells on the wafer surface, in order to expose a cross-section of one or more TSVs. Although the wafer does not need to be cleaved before FIB milling, the wells used to reveal the TSV are considered destructive and prevent the wafer from being processed through the subsequent bonding, thinning, edge-bevel trimming, and thermal processes in 3D integration. Furthermore, the milled wells may weaken the wafer and create cracks or breaks when the wafer is subjected to the forces associated with subsequent processing. The FIB method does not allow an exactly vertical (90 ) observation of the TSV cross section. Dimensional metrology under non-vertical examination conditions may require trigonometric calculations to extract the desired quantities. An example of a SEM image of a TSV with metallization, from a cross section prepared by FIB milling, is shown in Figure 2. 9 Krause, M., Altmann, F., Schmidt, C., Petzold, M., Malta, D., and Temple, D., "Characterization and Failure Analysis of TSV Interconnects: From Non-destructive Defect Localization to Material Analysis with Nanometer Resolution," in Electronic Components and Technology Conference (ECTC) 2011, pp: Page 5 Doc SEMI

7 Figure 2 SEM Image of TSVs with Metallization, from a Cross section Prepared by FIB Milling 8.2 Examples of measurements of TSV dimensions on SEM images Example images from contributing organizations and the technical literature, demonstrating measurements of dimensions of TSVs and similar structures in cross-sectional SEM images, are shown in Figures 3-5. Figure 3, from a contributing organization, illustrates research-style manual annotation of the image to obtain dimensions by use of an image analysis software package. Note the dimension on the figure. The TSV depth is approximately 50 µm. Figure 4, from a contributing organization, shows a TSV-like excavation in a silicon wafer, imaged as a SEM cross-section, annotated with measurements of the depth and diameters at several intermediate depths. Figure 5 shows an image of a TSV made by laser drilling. 10. The topography of the sidewall is different from that of TSVs made by other etch processes. 10 Tang, C. W., Young, H. T., and Li, K. M., Innovative through-silicon-via formation approach for wafer-level packaging applications, Journal of Micromechanics and Microengineering 22 (2012). Page 6 Doc SEMI

8 Figure 3 TSV Openings Imaged in a SEM Cross-Section, Showing a Measurement of the Approximate TSV Depth Figure 4 TSV-like Excavation in a Silicon Wafer, Imaged in a SEM Cross-Section, Showing Measurements of the Depth and the Diameter at Several Intermediate Depths Page 7 Doc SEMI

9 Figure 5 SEM Image of a Laser-Drilled TSV 10 NOTE: Published with Permission from the Journal of Micromechanics and Microengineering, IOP Publishing 9 Examples of Dimensional Metrology of TSVs by Use of Non-Destructive Techniques 9.1 Optical techniques A wide variety of techniques that employ light, especially infrared light, are in use or under development for TSV metrology. Some examples provided by participating companies are shown below. These techniques are generally quite sophisticated, and differ in the wavelengths of light used, the direction from which the TSVs are illuminated, the manner of directing light toward the TSVs to be measured, and the methods of collecting and interpreting the signal. NOTE 2: Details of the specific tools and example data presented here are beyond the scope of this guide Examples of optical techniques that measure an individual TSV Two examples of optical techniques that can measure dimensions of an individual TSV are presented Top down optical technique The reflected beams collected in an interferometry technique from the top side of a single TSV are illustrated in Figure 6. The intensity of the reflection from the bottom of the TSV is clearly an important parameter in this type of a measurement. Figure 7 shows example results for four TSVs with depths of about 49 µm. Figure 6 Reflected Beams from the Top Wafer Surface and the Bottom of the TSV are Collected in an Interferometry Technique for Depth Measurement Page 8 Doc SEMI

10 View of the wafer surface TSV depth measurement # TSV depth measurement #2 TSV depth measurement # Figure 7 Example of Repeated Measurements of Depths of a Set of Four TSVs Back surface interferometry A method that avoids the need for transmission of light through the narrow bore of a TSV was reported in the literature 11. This method scans an infrared beam across an individual TSV from the back surface of the wafer, and extracts its depth from an interferometric signal that gives the distance from the back side of the wafer to the bottom of the TSV, when the beam falls upon the bottom of the TSV, and the full thickness of the wafer, when the beam falls outside the TSV. This technique has the advantage that the measurement is independent of the aspect ratio of the TSV. The optical setup is shown in Figure 8. An implementation of this method was reported 11 to be capable of measuring both individual TSVs and of averaging over an array of them. For TSVs with diameter smaller than the spot size of the infrared light, which was about 5 µm for this example, the minimum TSV depth that could be measured with this implementation was limited to about 5 µm. The 3σ repeatability of TSV depths in this example was reported at approximately 0.07 to 0.2 % for TSVs with depths from 13.9 µm to 31.8 µm. An example of a map of TSV depths across a wafer showed deeper TSVs in the center and shallower ones toward the wafer edge, as illustrated in Figure Teh, W. H., Marx, D., Grant, D., and Dudley, R., Backside Infrared Interferometric Patterned Wafer Thickness Sensing for Through-Silicon- Via (TSV) Etch Metrology, IEEE Transactions on Semiconductor Manufacturing 23, (2010): p Page 9 Doc SEMI

11 Microscope Locates TSV Wafer with TSV Infrared Sensor Measures TSV Depth Figure 8 Optical Setup for Back Surface Infrared Interferometry Page 10 Doc SEMI

12 Figure 9 Example of TSV Depth Distribution Across a Wafer, Produced by Back Surface Infrared Interferometry Use of spectral reflectometry to measure an array of TSVs Spectral reflectometry technniques are similar in concept to scatterometry, where a signal that contains information from arrays of features, TSVs in this case, is collected and analyzed. Illumination at one or a few wavelengths may be used, or a broader-band light input may be employed. A basic setup is indicated schematically in Figure 10. Key features are that the light may follow a variety of paths to reach the detector, including paths that cross through the silicon for wavelengths for which silicon is partially transparent, and that multiple components of the signal over a broad band of wavelengths may be collected and interpreted, as indicated in Figure 11. NOTE 3: The received optical signal may contain information of various types. TSV metrology tools that have been described publicly so far differ in their use of the various components of the signal. Page 11 Doc SEMI

13 Figure 10 Schematic of Basic Setup for Optical Measurements of TSV Dimensions by Spectral Reflectometry Figure 11 Optical Signal Collected by the Apparatus Shown in Figure 10 Page 12 Doc SEMI

14 Model Based Infrared Reflectometry (MBIR) A report from the literature 12 shows a specific application of this optical technique, which uses mid-infrared and near-infrared light (wavelengths 0.9 to 20 µm) to measure the depth and critical dimensions of arrays of high aspect ratio 3D structures in silicon. The technique works by directing a beam of light of a variable wavelength upon an array of TSVs, collecting the signal at each wavelength, and analyzing the resultant data using an optical model. Use of an effective medium approximation allows rapid evaluation of the relevant parameters. Figure 12 shows the reported correlation between reference values of TSV dimensions measured using the destructive cross-section SEM (x-sem) technique and values measured using MBIR. Figure 13 shows the distribution of TSV dimensions over a 300 mm wafer. These measurements reveal a concentric etch profile with deeper vias toward the edge of the wafer. The vias are consistently tapered throughout the wafer, with smaller CD at the bottom compared to the top. The TSVs in this example were square with a pitch of 6 µm and a top diameter of 4 µm. Because this is an array technique, where the received signal corresponds to several TSVs, the small TSV pitch was advantageous for the measurements shown here. Figure 12 Comparison between TSV Dimensions as Measured by Cross-section SEM (x-sem) and by MBIR Figure 13 Distribution of TSV Dimensions over the Surface of a 300-mm Diameter Wafer 12 Le Cunff, D., Hoglund, L.J., and Laurent, N., "In-line Metrology of High Aspect Ratio Structures with MBIR Technique," in Advanced Semiconductor Manufacturing Conference 2011, (2011): pp Page 13 Doc SEMI

15 Dark field reflectometry A different application of the spectral reflectometry technique was contributed by a participating company. In this example reflected light over a broadband spectrum is collected in a dark-field optical configuration in which light reflected from the wafer surface is blocked, while light from within the TSV is collected. This technique provides information about the profile of the TSV. The measured spectrum is compared against a pre-built library of spectra, calculated for different TSV parameters. Figure 14 illustrates an application of this technique. Figure 15 shows the comparison of the optical results to cross-section SEM measurements. Figure 14 Schematic of the interpretation of spectral data to provide values of TSV side wall angle (SWA) Figure 15 Comparison between TSV SWA Measured by cross-section SEM and by Dark Field Reflectometry Page 14 Doc SEMI

16 10 Example of an Optical Technique in the Research Stage 10.1 Use of through-focus scanning optical microscopy (TSOM) in dimensional metrology This example was contributed by a participating laboratory 7 The premise of this approach is that the use of conventional optical microscopy components, as opposed to infrared reflectometry, may provide a cost-effective approach to TSV metrology, especially for process control. In the example presented, dimensional differences among three TSVs from three die are evaluated by comparing the TSVs, pairwise, by use of differential TSOM images. The comparison can be evaluated numerically, and can also be displayed graphically. Figure 16 shows experimental data for TSVs with a nominal diameter of 1 µm. The bar graphics above the image plots indicate which two TSVs are being compared in each plot; the values of the parameter MD indicate the overall magnitude of the dimensional differences between the TSVs being compared; and the colors indicate the spatial distribution of dimensional differences between each pair of TSVs. The similarity of the two differential images on the right indicates a similar pattern of dimensional differences between the TSVs compared. The MD value of the image at the right is the highest, indicating the largest magnitude dimensional difference, while the lowest MD value of the left image indicates the smallest difference. If a library of differential TSOM images corresponding to known dimensional mismatch were available, the actual dimensional mismatch corresponding to these image patterns could be evaluated. Figure 16 Differential TSOM Plots Representing the Pairwise Differences between TSOM Images of Three TSVs in Three Different Dies NOTICE: Semiconductor Equipment and Materials International (SEMI) makes no warranties or representations as to the suitability of the Standards and Safety Guidelines set forth herein for any particular application. The determination of the suitability of the Standard or Safety Guideline is solely the responsibility of the user. Users are cautioned to refer to manufacturer s instructions, product labels, product data sheets, and other relevant literature, respecting any materials or equipment mentioned herein. Standards and Safety Guidelines are subject to change without notice. By publication of this Standard or Safety Guideline, SEMI takes no position respecting the validity of any patent rights or copyrights asserted in connection with any items mentioned in this Standard or Safety Guideline. Users of this Standard or Safety Guideline are expressly advised that determination of any such patent rights or copyrights, and the risk of infringement of such rights are entirely their own responsibility. Page 15 Doc SEMI