Nano-roughness Measurement of Semiconductor Substrates by Using Light Scattering Properties

The roughness of semiconductor substrate is an important issue in growing the isotropic layers by liquid phase epitaxial (LPE) procedure. After the preparation process (grinding and polishing), the roughness of substrate is measured by equipments like stylus profilemeters or scanning probe microscope (SPM). These equipments are costly and their tip may even cause mechanical damage on surface. In this paper, we propose an effective, non-destructive, non-contact and easy optical method to measure root mean square (RMS) roughness (Rq) in nanometer scale.Total integrated scattering (TIS) and angle-resolved scattering (ARS) are methods that are most often used for measuring the surface roughness by light scattering [1]. In both of the two methods, a coherent laser beam with wavelength λ, is incident on a rough surface at angle θ , which is scattered in hemisphere. In TIS, for a surface with Gaussian distributed height, the ratio of the specular reflectance (Is) to the total scattering (Io) (including Is), is related to RMS roughness (Rq) as [1]: 22)/4exp()/cos4exp(λπλθπqqosRRIITIS≅== (1)On the other hand, ARS deals with angular distribution of laser light around the specular scattering direction. ARS have a direct relation with power spectral density (PSD) of surface height [1, 2]. However, the relation is more complicated and the experimental data are often used to obtain a mathematical formula