High resolution studies of crystalline damage induced by lapping and single-point diamond machining of Si(100)
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High resolution studies of crystalline damage induced by lapping and single-point diamond machining of Si(100) R. R. Kunz, H. R. Clark, P. M. Nitishin, and M. Rothschild Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, Massachusetts 02173-9108
B. S. Ahern Rome Air Development Center, Hanscom Air Force Base, Massachusetts 07131-5000 (Received 19 July 1995; accepted 15 January 1996)
Si(100) wafers were prepared by both diamond turning and standard lapping and polishing techniques. For single-point diamond machining, characterization of subsurface damage resulting from ductile-regime machining identified a plastic-yield zone consisting of slip planes and dislocation networks extending 1 to 3 mm deep despite surface root-mean-square roughness values as low as 5 nm. For conventional lapping and polishing using alumina grit, a transition from brittle to ductile yield was observed for grit sizes less than 300 nm. Subsurface damage depth correlated to surface roughness in a more straightforward manner than for the diamond point machining. Completely damage-free material removal was obtained only when a chemical component to the polishing was present.
I. INTRODUCTION
II. EXPERIMENTAL
Mechanical and chemical-mechanical forming of single-crystal silicon has become technologically important for a number of applications. Silicon wafer lapping and polishing for optical and electronic applications, as well as machining of three-dimensional structures for advanced optical applications such as for asphere production or binary optics, are leading edge technologies. Many aspects of this technology have matured to a high level. Recent advances in machining silicon using single-point diamond lathes have identified a regime where material removal is ductile, rather than brittle, and the resultant material has been observed to have less damage as determined by surface roughness.1 However, detailed crystallographic characterization of the extent and nature of subsurface damage that is generated by these processes has not been reported. In fact, “subsurface damage” has been almost exclusively defined in terms of relatively gross morphological changes, such as microfractures or microcracks. In this study we have focused on the nature and extent of much more subtle damage, such as localized defects in the atomic arrangement of single crystals. We report on the evaluation of such subsurface crystalline damage that occurs upon machining, polishing, and lapping of Si(100) and its correlation to surface roughness. High resolution transmission electron microscopy was used in combination with atomic force microscopy (AFM), optical profilometry, x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM).
A. Single-point diamond machining
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http://journals.cambridge.org
J. Mater. Res., Vol. 11, No. 5, May 1996
Downloaded: 15 Mar 2015
A standard commercially available single-point diamond machining (SPDM) tool was used to machine the Si(100) surfaces i
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