Formation of Silicon Nitride Structures by Direct Electron-Beam Writing.

摘要

Localized deposits of silicon nitride, which are stable to at least 500 C, have been formed by a new technique: electron bombardment of nitrogen molecules weakly bound on a clean Si(100)-(2 X 1) surface chilled to T approximately 30 K. This process is fairly efficient; for an initial coverage of one monolayer of molecular nitrogen, we estimate the effective dissociation cross section (primary electron energy = 2000 eV) to be (0.54 - 1.2) x 10 to the 15th power sq cm. Using Auger electron spectroscopy and LEED, we have studied the growth of a silicon nitride/silicon interface rigorously free from contamination and from damage due to sputtering or ion implantation. In the Si(LVV) Auger spectrum of silicon nitride, a strong peak at 83 eV predominates; the 91-eV peak characteristic of clean Si vanishes entirely for sufficiently thick nitride films (approximately 25 - 30 A). LEED measurements, with the substrate at approximately 30 K, reveal no ordered overlayers--the pattern stays (2 X 1), but the background increases with nitridation until a fully disordered structure results. Our Auger and LEED data further indicates that the initial stage of electron-induced nitridation is the formation of a monolayer of chemisorbed nitrogen via the nucleation and lateral growth of islands. Preliminary experiments have demonstrated that local deposits of silicon dioxide may be formed by the same technique used for nitridation: electron-stimulated oxidation is more rapid with the substrates at T approximately 30 K than at room temperature. With proper outgassing of all vacuum components, particularly hot filaments, oxidation proceeds without the simultaneous growth of a surface carbon layer.