AFM Investigations of Chemical-Mechanical Processes on Silicon(100) Surfaces
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AFM Investigations of Chemical-Mechanical Processes on Silicon(100) Surfaces Ruiji Imoto1, Forrest Stevens1, Steven Langford1, and Tom Dickinson2 1 Washington State University, Pullman, WA, 99164 2 Washington State University, Washington State University, 2814 Physical Sciences, Pullman, WA, 99164-2814 Abstract Atomic force microscopy (AFM) was used to examine chemical-mechanical processes on Si (100) surfaces. Places where the underlying silicon was exposed etched in basic solution, producing structures 100 nm or less in size. Etching occurs only in the presence of combined mechanical and chemical effects. By performing AFM in basic solution, the entire etching process could be observed directly. High-force scans were used to remove oxide and initiate etching in selected locations, followed by low-force scans which imaged the etching process. Although roughness initially increased during etching, the final surfaces were smooth. The etching was measured for different applied loads, numbers of scans, concentrations of the etching solution, and time. The oxide layer was extremely sensitive to applied stress, and even very light scanning caused the oxide layer to dissolve more rapidly. Once the oxide layer was removed, chemical etching proceeded with or without AFM scanning, but if AFM scanning was continued additional material was removed, probably by a tribochemical mechanism on pure Si. *Corresponding author: email address: [email protected] Introduction Selective processing of silicon is important for semiconductor device production, microelectrical mechanical systems, and nanotechnology. The use of combinations of chemical and mechanical stimuli, for example during chemical mechanical planarization (CMP), is frequently used to remove material. Using an atomic force microscope (AFM) with a fluid cell, we are able to examine many of the details of combined chemical and mechanical stimuli on a nanometer size scale. The tip of the AFM can be used to apply both normal and lateral forces (by translation of the tip along the surface) and also to provide images of the topographical changes in the surface following such stimuli. In this report, we are interested in examining the specific consequences of combined AFM raster scanning over a square of a few hundred nanometers dimension on a Si (100) surface in the presence of a known etchant, NaOH/water solution. These mechanistic studies are relevant to understanding both CMP of Si and also the use of nanometer scale mechanical systems to generate structures. Chemical etching is a common method for creating silicon structures where etch-resistant masks are used to control the location of etching. An alternative is to use the tip of an AFM to “write” nano-scale regions on the surface that become preferred etch regions. The AFM itself can be used either at low contact force to image a surface without disturbing it, or at high contact force to wear or modify a surface. The purpose of this paper is to examine in more detail the consequences of combined chemical mechanical
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