Surface Chemical Reactions Stimulated by Low Energy Electron Bombardment
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SURFACE CHEMICAL REACTIONS STIMULATED BY LOW ENERGY ELECTRON BOMBARDMENT R.R. KUNZ AlD T.M. MAYER Department of Chemistry, Carolina 27514
University of North
Carolina,
Chapel
Hill,
North
ABSTRACT A low energy, broad beam electron source was used to induce chemical reactions on surfaces. Electron beam energies were selected to maximize the emission of secondary electrons, for the purpose of determining if these low contributed to the overall reaction. Room temperature energy electrons silicon oxidation showed maximum terminal oxide thickness (35 1) at the primary electron energy that produced the maximum secondary electron flux (300 eV). XPS showed these films to be mostly sub-oxide in nature. Similar results were obtained in analogous experiments using tetraethoxysilane to deposit SiO and using iron pentacarbonyl to deposit Fe. By increasing the incident angle of the electron beam to 70 degrees from the normal, the deposition yields of SiO2 and Fe increased by 45% and 30%, respectively. This again was thought to be a result of secondary electron contributions, as the secondary yield increased by a factor of two upon tilting the beam.
INTRODUCTION The use of electron beams for the processing of materials has received to needs in prima- ly due in recent years, attention increasing microstructure fabrication. Electron bombardment on a solid surface can result in the heating, ionization, electronic excitation, or decomposition of in the presence of the appropriate When performed an irradiated area. reactants, chemical processes such as resist decomposition, film deposition, and etching can occur. Work devoted to the investigation of such chemical alterations induced by electrons is quite extensive; some examples include fabrication of 8 nm features in silicon [1], selective deposition of W from WF6 [2], formation of submicron oxide strips on Al [31, a host of work investigating chemical changes induced during Auger analysis [4-6], electron assisted etching of silicon using XeF 2 [7-9] and SF 6 [10], nitridation [11,12] and oxidation [9,12,13] of silicon, and deposition of Al and Cr using condensed organometallics [14]. The electron accelerating voltages used in these studies have ranged from 100 keV [1] to as low as 10 eV [13], with the majority of work done between I and 15 keV [2-8,10). This may be a result of experimental simplicity, as most sources operate in this energy range, or a result of applications of such work to Auger analysis. Fewer studies discuss of low energy ionization probabilities the increased dissociation and electrons. Electron-molecule interactions that lead to decomposition or reaction occur most efficiently when the electron's energy lies near the cross-section Two such processes are electron impact maxima for the given process. impact attachment. Electron electron and dissociative dissociation dissociation occurs when an electron collides with a molecule or atom, parent molecule. the excitation and dissociation of the resulting in Dissociative electron attachment is a resonant process
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