Volume 7, Number 2 March/April Chemo-Mechanical Polishing (CMP) Research at CREOL Dr. Kathleen Richardson, University of Central Florida

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1 Volume 7, Number 2 March/April 1999 Chemo-Mechanical Polishing (CMP) Research at CREOL Dr. Kathleen Richardson, University of Central Florida Like the optical industry, the semiconductor industry has a need to rapidly and consistently produce high quality plano surfaces. While the end product is different from an optic, the process issues related to planarizing (plano grinding and polishing) the alternating conductive and insulating multi-layers that make-up an integrated circuit chip (IC), are of interest to optics manufacturers. Planarization issues include: high removal rates, good plano figure accuracy, and high surface quality. Simplistically, IC devices are produced by stacking multiple layers of conductive circuit grids, one on top of the other. Each individual conductive layer must be isolated from the conductive layer immediately above and below itself, by depositing an insulating layer called an interlayer dielectric (ILD). The ILD material is usually SiO 2, which is not only a good insulator, but one that is easily ground flat. (a) Without With Figure 1. Cross sections of similar multilevel IC devices processed without (a) and with (b) CMP. (b) Figure 1 depicts a typical multilayer IC structure cross-section. When the ILD material is deposited upon a wire grid layer, it conforms to the wires' non-uniform surface topography, as can be seen in Figure 1a. So that each of the conductive layers will be accurately registered to the layer above and below it, the ILD material must be planarized (flattened) in order to provide a smooth, flat base. In Figure 1b, the multilevel circuit has been planarized between levels, providing each layer with a suitable base. CMP consumables used in the process are manufactured by a variety of companies and are routinely tailored to either metal or oxide polishing processes. The chemo in CMP refers to the chemical interaction between the medium to be polished and the slurry, and can be either in the form of a high (oxide) or low (metal) ph slurry. The suspensions currently used usually contain an added oxidizer for metal polishes (promoting the postulated oxidation, passivation, and removal mechanism for metals), however slurry chemistry, composition, and lifetime remains closely guarded information. The abrasives currently used in the suspensions are either alumina, silica or ceria-based. continued on page 2 Inside: CLEO /QELS Job Postings...5 COM Summer School...6 OptiPro PX New APOMA Members.7 OSLO...7 Industry Calendar...8 Copyright University of Rochester CENTER FOR OPTICS MANUFACTURING 1

2 continued from page 1 Our laboratory has examined various aspects of CMP slurry behavior including assessment of slurry stability and aggregation behavior using traditional electrochemical techniques (zeta potential and sedimentation) and we have compared these data to de-stabilization as predicted by multiple light scattering techniques [1-6]. Figure 2 illustrates the change in an Enhanced Backscattered (EBS) signal on dense (e.g. undiluted) alumina slurry in its fresh (time = 0) and aged (time = 13 days) state. The broadening of the cone, and the slight shift up of the baseline, indicates a change in the mean free path between scattering events, representative of a change in either particle size or suspension density. Upon destabilization, the signal to noise of the EBS measurement increases and the ability to obtain quantitative information from the peak characteristics is significantly reduced. We are developing optical, non-destructive tests which can be used as candidate online monitoring tools in an effort to monitor slurry behavior and successfully predict slurry lifetime endpoints. 0.9 t=0 t=13 days Normalized intensity Figure 2. EBS cone of fresh and aged alumina Angle slurries. (mrad) The change in cone shape indicates a change in the scattering path length associated with the slurry s aging behavior. 2 IC1000 layer (thickness ~ 1.37 mm) Bonding epoxy layer (thickness ~ 300 µm) SubaIV layer (thickness ~ 1.24 mm) IC1000/SubaIV SEM Cross Section 40x Figure 3. SEM micrograph of IC1000/SubaIV cross-section. Note the difference in morphology of the top and bottom layers of the pad material which possess dramatically different chemical and mechanical properties characteristic to the pad stack. These pad Pads used to support the silicon wafer during polishing (now up to 8 in diameter) are primarily polyurethane based, but may be made up of various forms of bulk, foam or felt-like microstructures. Just as in conventional optical fabrication, the pad serves to suspend the slurry abrasive while in contact with the wafer workpiece, while at the same time providing a rigid base upon which the chemical action of the slurry can be activated. Figure 3 illustrates an SEM cross section of a two pad composite (IC1000/ SubaIV). We are currently investigating tests which will predict pad performance prior to extensive wafer cycling. By furthering our understanding of what chemical and mechanical properties most affect the wafer quality metrics of interest, it is expected that pad lifetime can be enhanced and ultimate polished wafer quality can be improved. continued on page 3

3 continued from page 2 The lifetime of these consumables is extremely important in that their cost (and potential use/quality degradation) is small in the context of the overall device cost. Usually CMP consumables are used and discarded, and to date limited efforts to recycle materials have been made. Current research at UCF examining pad wear mechanisms and lifetime is ongoing. Figure 4 shows the variation in absorbance of aqueous solutions of varying ph. We have shown that pad uptake, and retention following redry, can be related to the reversible and irreversible components of chemical and mechanical properties of the polyurethane structure. We are currently extending that model based on tests with organic solvents which preferentially attack key components of the isocyanate-polyol pad structure [7,8]. By verifying the change in physical properties as a result of measurable chemical changes to the pad microstructure, we can predict what species in the metal or oxide polishing environment should be most dominant in pad war and eventual breakdown. This is extremely important in that it has been shown that at the high ph s where oxide polishing is usually performed, measured defect densities scale with increasing ph. A potential form of a yield-decreasing defect is shown in Figure 5. The defect shown is most likely a piece of shredded pad, shown by EDS to be composed of C, H and N; key components of the polyurethane material are shown on a wafer polished at high ph. Percent Absorbance (%) Polytex Supreme Polytex Supreme (embossed) SubaIV IC1000/SubaIV IC1000/Foam IC solution ph Figure 4. ph dependence of relative moisture absorbance for various pad types. Figure 5. SEM image of IC defect after an oxide polish using Klebesol 1501 (ph 10.4). continued on page 4 3

4 continued from page 3 Considerable effort and resources have been put towards the polishing of wafers during the IC fabrication process. Using a combination of optical metrology, material science and device engineering know-how, improvements that will have long lasting impacts on our understanding of the science of these materials, as well as the pricetags of the resulting devices, will continue to be realized. For more information, please contact Dr. Kathleen Richardson at UCF/CREOL (phone ; fax ; kcr@mail.creol.ucf.edu). References: 1) Chemical and structural characterization of metal oxide slurries, M. Lauwidjaja, K. Chamma, K. Richardson and A. Dogariu, Ceramic Transactions, Advances in the Fusion and Processing of Glass II, 82 American Ceramic Society, , (1998). 2) Chemical and structural characterization of alumina slurries, M. Lauwidjaja, G. Popescu, L. Denney, K. Richardson and A. Dogariu, Proceedings of the 193rd Meeting of the Electrochemical Society; submitted for publication, J. Electrochemical Society (May 1998). 3) Aging effect in CMP slurries probed by multiple light scattering, M. Lauwidjaja, G. Popescu, L. Denney, K. Richardson and A. Dogariu, Proceedings of the 193rd Meeting of the Electrochemical Society; submitted for publication, J. Electrochemical Society (May 1998). 4) Aggregate formation in metal CMP slurries, D.C. Tamboli, V. Desai, A. Dogariu, K.B. Sundaram, Y. Obeng and A. Maury, Proceedings of the 193rd Meeting of the Electrochemical Society (1998). 5) Polarization asymmetry in photon backscattering from highly absorbant random media, A. Dogariu, M. Dogariu, K. A. Richardson, S.D. Jacobs, and G.D. Boreman, Applied Optics 36, 31, (1997). 6) Characterization of the stability of aluminum oxide slurries for optical polishing, M. Lauwidjaja, M.S. thesis in Industrial Chemistry, University of Central Florida (1998). 7) Mechanistic aspects of the relationship between CMP consumables and polishing characteristics, Y. Obeng, K.M. Forsthoefel, K.A. Richardson and R.H. Burton, Proceedings 127th Electrochemical Society (May 1998). 8) Mechanistic aspects of the relationship between CMP consumables and polishing characteristics, I. Li, K.M. Forsthoefel, K.A. Richardson, and Y.S. Obeng, submitted to Thin Solid Films, (1999). CLEO /QELS 99 Conference on Lasers and Electro-Optics Quantum Electronics and Laser Science Conferences Baltimore Convention Center (Baltimore, MD), May 23-28, 1999 Technical Exhibit, May 25-27, 1999 Discover the latest information on lasers and electro-optics. Registration Deadline: April 15, 1999 Housing Deadline: April 23, For more information contact: OSA Customer Service Phone: (202) ; (800) Fax: (202) cust.serv@osa.org Visit our website at:

5 Job Postings Melles Griot Photonics Components Millikan Avenue Irvine, CA Attn: Sherry Ramirez Fax: Title: Optical Engineer Description: Will support technical/sales inquires, product training, new product development, and trade shows. A thorough understanding of optics, opto-mechanical hardware, instruments, and lasers is required. Experience: BS in Optical Engineering and 3-5 years of photonics industry work experience. Melles Griot Optics 55 Science Parkway Rochester, NY Attn: Deborah Gsellmeier Fax: Title: Marketing Manager Description: Responsibilities include all aspects of marketing for the Rochester Division. Demonstrated ability to effectively sell and market division s product lines is required, as well as excellent communication skills, strong technical writing skills, project management of promotion/development of product, and the ability to understand technical concepts of optical product lines. Experience: BS in Physics, Optics or EE required. Minimum of five years experience in the optics/optical products marketplace. The MicroDisplay Corporation 3055 Research Drive San Pablo, CA Attn: Madelyn Homick Fax: mhomick@microdisplay.com Title: Director of Optics and Materials Description: Coordinate OM R&D and manage OM group efforts on projects. Must have high level knowledge of optics and the effects/ interactions of optics with LCD systems. Design application-specific optical systems; develop innovative optical systems that optimize displays and/or customer product; manage work schedules and direction of OM group; order and maintain equipment; attend seminars/ conferences, attend group/project meetings; maintain lab, projects, documentation. Experience: MS/PhD in Optics/Liquid Crystal Technology; 5+ years experience in Optics/LC product development. Experience with stateof-the-art display technology a plus. Title: Liquid Crystal Manufacturing Technologist Description: Guide and assist in the manufacturing of LCDs within MicroDisplay's pilot manufacturing facility. Research existing and future LC material and associated applications/technologies leading to development/manufacture of microdisplays. Improve the performance of existing displays; interface with other design groups. Identify and develop manufacturing process leading to successful assembly of microdisplays; identify and resolve LC material-related display issues; plan/execute approved projects to improve the performance and as- sembly of microdisplays; assist in benchmarking and testing/ character-iztion of displays. Experience: Experience with characterization/process of liquid crystal materials in a commercial environment; knowledge of semiconductor and flat panel display equipment. Experience in high volume manufacturing of liquid crystal displays, and/or of electronic components or assemblies, is a must. Title: Senior Research Engineer - Optics Description: Definition of optical specification for products and demonstration prototypes for microdisplays. Work with product de-velopment group in the design and engineering of products and demonstration prototypes; interface with research scientists, marketing, and management to develop MicroDisplay technology into consumer products. Provide optical assistance to other groups on request. Experience: MS/PhD in Physics, with a specialization in optics. 3+ years of experience in research/product development with microoptics. Plummer Precision Optics 601 Montgomery Avenue Pennsburg, PA Attn: Human Resources Department Fax: Title: Optical Manufacturing Engineer Description: To be involved in the design, implementation and improvement of processes used to fabricate high precision customer optics. Experience: Qualified candidates should have a BS degree in Optical Engineering or Physics; 2+ years experience in manufacturing is preferred. Experience in the following areas is desirable: optics and optical assembly manufacturing; interferometric and prototype testing; computer aided design; process/procedure documentation. Raytheon Missile Systems Co. TU, Building 840, MS East Hermans Road Tucson, AZ Attn: Frank Degel Fax: fcdegel@mail.hac.com Title: Master Optician Description: Lead activities in its Optical Element Fabrication Lab; read/interpret engineering blueprints; develop processes and methodize fabrication of prototype and low volume precision optical components; fabricate optical components (lenses, mirrors, windows, domes, prisms) ranging in size from 0.1 to 8 inches; fabricate components having unique geometries (tilted and off-axis components, unique mounting features, etc.); fabricate optical components from a wide variety of optical materials including glasses, metals, and crystalline IR materials. Applicant will be responsible for leading the day-to-day activities in the lab, for maintaining inventory of consumables, and managing the lab s workload. Experience: Expertise in precision machining (NC equipment and diamond point turning is desirable, but not essential). 5

6 New Machines, Tools and Processes for Modern Optics Manufacturing (with Labs) COM s annual summer school, New Machines, Tools and Processes for Modern Optics Manufacturing, will be offered from June 21-24, 1999 in Rochester, New York. The course is organized into 21 talks and tutorials providing an overview of emerging technologies that will shape the way optics are manufactured into the next century. Guest speakers join the Center for Optics Manufacturing/University of Rochester professors and engineers to present the most recent manufacturing technology advances in deterministic processing and flexible automation for producing spherical, aspheric, and conformal optics. The program is very interactive, providing two full afternoons of laboratory work on computer integrated manufacturing of aspheres, programming a CNC machine for complex shapes, on-machine probes, magnetorheological finishing, and modern optics metrology. The cost for the 4 day course is $1,000; more information may be obtained by contacting Gayle Thompson at the Institute of Optics (phone , fax , GAYLE@OPTICS.ROCHESTER.EDU). A full course listing will be mailed to all APOMA members in early April 99. Nanotech TM 150AG Asphere Grinder by Moore Nanotechnology Systems, LLC Nanotech TM 500FG Conformal Grinder by Moore Nanotechnology Systems, LLC Q22 Magnetorheological Finishing (MRF) Machine by QED Technologies, LLC We welcome your submissions! Fax or your news and job postings to Michele Richard at COM fax: MRIC_COM@LLE.ROCHESTER.EDU Stop by and visit COM on the web! 6

7 OptiPro Systems Introduces PX 150 SPHERICAL POLISHER CNC Polishing of lenses up to 150 mm diameter. For use with the SX/DSX series of generators. Completely adjustable cycle parameters. Welcome New APOMA Members! HOLOTEK 205 Summit Point Drive Henrietta, NY Rep: John Hart Phone: Fax: M Company 3M Center Building St. Paul, MN Rep: Mark Schwabel Phone: Fax: For information contact Charles Klinger at OptiPro Systems, Inc. (phone , Check out the APOMA website! How to Use OSLO April 5-6, 1999 Rochester, New York Presented by Sinclair Optics at the Center for Optics Manufacturing Warren Smith s Modern Lens Design April 7-9, 1999 Rochester, New York Presented by Warren Smith and Sinclair Optics at the Center for Optics Manufacturing How to Use OSLO is an intensive two-day course that covers the use of OSLO in detail. It is suitable both as an introductory course for new users, and as a refresher course for current users who want to use the new features in the program most effectively. The course includes lectures, demonstrations, and laboratory sessions. You and a partner will use OSLO SIX to get hands-on experience by setting up and solving a contemporary design problem, as well as following the demonstrations presented during lectures. After completing the course, you ll be ready to use the program on your own or attend our more advanced course on Modern Lens Design. For detailed information, please contact: Sinclair Optics, Inc. Telephone , Fax sales@sinopt.com Now matter what software you use, you still need to know something about lens design to design a good lens. This course fills that need. Taught by Warren J. Smith, one of the world s leading lens designers, Modern Lens Design emphasizes useful, practical approaches to real-world lens evaluation and design. The course includes lectures and computer laboratory sessions that show you how to design standard lenses. In the laboratories you will use the OSLO SIX optical design program. It will be assumed that you know the material from the How to Use OSLO course, as well as basic first-order optics. For detailed information, please contact: Sinclair Optics, Inc. Telephone , Fax sales@sinopt.com 7

8 1999 Industry Events Representatives from COM will be attending the following optics industry events. Stop and see us at: AeroSense 99, Orlando, FL April 5-9, 1999 CLEO/QELS 99, Baltimore, MD May 23-28, 1999 COM Summer School 99, Rochester, NY June 21-24, 1999 SPIE Annual Meeting 99, Denver, CO July 18-23, 1999 NEWSLETTER MAILING LIST UPDATE Please let us know of any address corrections, additions, or deletions by completing this form. Mail or fax to Michele Richard at the Center, fax Name: Title: Company: Address: City, State, Zip: Phone: Fax: 8 CENTER FOR OPTICS MANUFACTURING University of Rochester 240 East River Road Rochester, NY