SPECTRO-ELLIPSOMETRIC INVESTIGATIONS OF POLYCRYSTALLINE SILICON SURFACE-ROUGHNESS

Polycrystalline silicon (polysilicon) became to be an important materi al, with wide spread application in microsystems, sensors and actuator s technologies. The most important parameters which can influence sign ificantly the devices properties surface roughness and grain size. Rou ghness can be characterised by an average height of irregularities and it is a relative quantity depending by the ratio of the length scale of the ''mountains and valleys'' to the wavelength of light. Spectro-e llipsometry is a sensitive, rapid, nondestructive and noninvasive tech nique which used different wavelength, for complex refractive index ev aluations of the investigated sample, Spectro-ellipsometry has been de monstrated to operate in air, vacuum and liquids very well. There are many steps during fabrication process, in which the spectro-ellipsomet ry could be involved [1]: epitaxy [2] (nucleation and solidification, film thickness, index), cleaning (surface quality), oxidation (film th ickness and index), ion-implantation [3] (film thickness and damage). On the other hand, spectro-ellipsometry is a precision optical techniq ue and requires careful alignment and calibration in order to obtain a ccurate measurements. Newly developed scanning probe microscopes are e merging as a powerful tool for imaging microscopic topography. The mos t important members of this scanning probe technique are:(i) Scanning Tunnelling Microscope (STM) based on the quantum mechanical tunnelling effect and (ii)Scanning Force Microscope or Atomic Force Microscope ( SFM or AFM) for which the principle is based on the force between tip and sample atoms. The purpose of this paper is an attempt to demonstra te that using spectro-ellipsometry on surface roughness investigation of polysilicon has been possible. In order to support these results th e same samples were analysed with AFM.