Structure and chemistry of silicon surfaces after pre- and backsputtering, studied with Auger spectroscopy, ellipsometry, and RHEED

Abstract

Presputtering and backsputtering are cleaning processes usually performed prior to the sputter deposition of thin films. The effectiveness of these cleaning procedures was investigated with ellipsometry, RHEED, and Auger spectroscopy, using silicon substrates. Presputtering produced no deposits or disturbed surface layer, and the major surface contaminants were C and O totalling ∼ 3 monolayers which adsorbed during air exposure, prior to presputtering. Backsputtering produced an amorphous Si substrate surface, contaminated with Ar, C, and W, totalling ≳ 3 monolayers. Ar (2–20 at% in the first 5 atom layers of the surface) was incorporated from the sputtering gas, and C (5–50%) and W (15–70%), were sputtered from the substrate support plate and redeposited on the substrate. W films deposited on Si substrates after backsputtering contained ≲ 1 Å of silicon oxide layer at the W-Si interface; this result was obtained by following the chemical depth profile of various elements by using simultaneous Ar ion-milling and Auger spectroscopy. The detection limit of this technique for an SiO 2 interface layer was < 1 Å.