The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Advanced CMP Processes for Special Substrates and for Device Manufacturing in MEMS Applications

Martin Kulawski

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Electrical and Communications Engineering, Helsinki University of Technology, for public examination and debate in the large Seminar room at VTT Micronova (Espoo, Finland) on the 20th of October, 2006, at 12 o'clock noon.

Overview in PDF format (ISBN 951-38-6856-7)   [5339 KB]
VTT Publications 611, ISSN 1455-0849

Dissertation is also available in print (ISBN 951-38-6855-9)
Copyright © 2006 VTT Technical Research Centre of Finland
VTT Publications 611, ISSN 1235-0621
VTT-PUBS-611
TKK-DISS-2196

Abstract

The present work reports on studies and process developments to utilize the chemical mechanical planarization (CMP) technology in the field of micro electrical mechanical systems (MEMS). Approaches have been undertaken to enable the manufacturing of thick film SOI (silicon-on-insulator) substrates with a high degree of flatness as well as utilizing CMP for the formation of several novel MEMS devices.

Thick film SOI wafers are of high interest in MEMS manufacturing as they offer obvious benefits as a starting material or foundation for more complex structures. Precise control of the SOI layer thickness as well as the removal uniformity is of critical importance to fully utilize the benefits of this technology. By combining fixed abrasive (FA) pads for polishing and novel grinding techniques it is shown that major improvements can be achieved over the standard manufacturing sequence. Analysis of the material removal rate (MRR) dependency on several process parameters is made. Together with the FA pad vendor a suitable consumable set for SOI is generated, which shows long term stability in the generated process. A comparison with standard methods is undertaken to prove the surface and crystalline quality of the resulting substrate material is equivalent. Analysis is done to understand the microscopic mechanism of removal.

The CMP process is applied to several MEMS structures to smooth deposited oxide films and to enable direct wafer bonding (DWB) at low temperatures. This allows the design of bonded multiple stack layers including heat sensitive materials such as metals.

FA CMP is applied to large pattern MEMS for total planarization but also for smoothing of the surface of single protruding structures while minimizing edge rounding and preserving the original intended pattern shape. With dedicated CMP steps thick film polysilicon smoothing is demonstrated enabling DWB. The chemo-mechanical particularities of the FA pad are investigated in detail.

This thesis consists of an overview and of the following 6 publications:

  1. M. Kulawski, K. Henttinen, I. Suni, F. Weimar, J. Mäkinen; A novel CMP Process on Fixed Abrasive pads for the Manufacturing of highly planar thick film SOI Substrates; Materials Research Society Symposium Proceedings 767, (2003), pp. 133-139. © 2003 Materials Research Society. By permission.
  2. M. Kulawski, H. Luoto, K. Henttinen, I. Suni, F. Weimar, J. Mäkinen; Advances in the CMP Process on Fixed Abrasive Pads for the Polishing of SOI-Substrates with High Degree of Flatness; Materials Research Society Symposium Proceedings 816, (2004), pp. 191-196. © 2004 Materials Research Society. By permission.
  3. M. Kulawski, H. Luoto, K. Henttinen, T. Suni, F. Weimar, J. Mäkinen; Integration of CMP Fixed Abrasive polishing into the Manufacturing of Thick film SOI Substrates; Materials Research Society Symposium Proceedings 867, (2005), pp. 111-116. © 2005 Materials Research Society. By permission.
  4. M. Kulawski, H. Luoto, K. Henttinen, T. Suni, F. Weimar, J. Mäkinen; Polishing of Bulk Micro-Machined Substrates by Fixed Abrasive Pads for Smoothing and Planarization of MEMS Structures; Proceedings of the 2005 IEEE/SEMI Advanced Semiconductor Manufacturing Conference (ASMC 2005), Munich, Germany, 11-12 April 2005, pp. 5-10. © 2005 IEEE. By permission.
  5. J. Molarius, M. Kulawski, T. Pensala, M. Ylilammi; New Approach to Improve the Piezoelectric Quality of ZnO Resonator Devices by Chemomechanical Polishing; The Nano-Micro Interface: Bringing the Micro and Nano Worlds Together; Ed. H.-J. Fecht, M. Werner; Wiley-VCH Weinheim 2004; pp. 181-193; ISBN: 3-527-30978-0. © 2004 Wiley-VCH Verlag. By permission.
  6. H. Luoto, T. Suni, M. Kulawski, K. Henttinen, H. Kattelus; Low-temperature bonding of thick-film polysilicon for MEMS; Journal of Microsystems Technology, Vol. 12, No. 5, pp. 401-405, (2006). © 2006 Springer Science+Business Media. By permission.

Keywords: CMP, micro electro mechanical systems, polishing, fixed abrasive, MEMS, SOI, silicon-on-insulator, direct wafer bonding, DWB, low temperature bonding, FA

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© 2006 Helsinki University of Technology

Last update 2011-05-26