Glass substrate cleaning using a low energy ion source

Characterisation of hard disk substrates before and after heating using X-ray photoelectron spectroscopy (XPS) has shown that organic surface contamination cannot be removed totally by only using a standard heating process. First, studies of an ion source with ion energies of up to 350 eV have given strong evidence that this method is a suitable candidate to achieve a better surface cleaning. The work described here concentrates on the investigation of the carbon etch rates for this source operated with Ar, O2 and Ar/O2 mixture gas and on the ion bombardment-induced topographical surface modifications of the glass substrate. The used DC glow discharge-based multi cell ion source was adapted to a hard disk production sputter system. The power vs. voltage characteristics of this source were measured for the different discharge gases. Carbon films have been prepared on glass-substrates using a magnetron sputtering source. Carbon etch rates were measured using optical density change of the thin carbon films which has shown to be a linear function of the film thickness in the investigated range. The carbon etching rate increases almost linearly with discharge power. A higher oxygen gas flow also leads to a linear increase in etching rate. Using different O2 percentages in the discharge gas shows that more oxygen causes a significant enhancement of the carbon etch rate. For all discharge parameters etch rates have been measured as a function of the position on the disk substrate. Etching-induced topographical surface modifications have been investigated using atomic force microscopy (AFM). Etching of the glass substrate leads to a reduction of the mean roughness of the surface. This is similar to the etch modifications on NiP-plated Al substrates which are also used for hard disk production.