Spectroscopic Ellipsometry and Interference Reflectometry Measurements of CVD Silicon Grown on Oxidized Silicon
- PDF / 390,673 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 104 Downloads / 181 Views
SPECTROSCOPIC ELLIPSOMETRY AND INTERFERENCE REFLECTOMETRY MEASUREMENTS OF CVD SILICON GROWN ON OXIDIZED SILICON G. E. JELLISON, JR.,* M. KEEFER,** AND L. THORNQUIST** *Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 "**PrometrixCorp., Santa Clara, CA 95054 ABSTRACT Several samples of thin-film silicon grown on oxidized Si, both oxidized and unoxidized, have been examined using spectroscopic ellipsometry (SE) and constant angle reflection interference spectroscopy (CARIS). The SE data was fit to 5- or 6- layer models of the sample nearsurface region, using the optical functions of thin-film silicon determined from a previous work. Reasonable fits were obtained from samples containing amorphous Si (a-Si) or large-grain polycrystalline Si (p-Si), but fits to samples containing small-grain, undoped p-Si were poor unless a 8-15 nm surface roughness layer is included. Furthermore, the optical functions of p-Si:ud are not consistent from sample to sample. The optical functions determined from SE measurements were then used to interpret CARIS measurements, extracting the thicknesses of the films, which are then compared with the thicknesses obtained from SE. INTRODUCTION Polycrystalline Si (p-Si) and amorphous Si (a-Si) grown by CVD on oxidized Si are important starting materials for many integrated circuit applications. At present, optical techniques play a central role in characterizing these structures, but the interpretation of optical data requires either a detailed knowledge of the optical functions of thin-film Si, or a technique to simulate these optical functions. For p-Si, this problem is compounded because the optical properties depend considerably on growth conditions. One technique which has received much attention during the last few years is spectroscopic ellipsometry (SE) [1-10], where the complex Fresncl reflection coefficient ratio is measured p = rp / rs = tan V eiA.
(1)
The quantity rp (rs) is the Fresnel reflection ratio for light polarized parallel (perpendicular) to the plane of incidence and the angles Wand A are the traditional ellipsometry parameters. Often, the ellipsometric data is represented by the pseudodielectric function, which is given by = +i = sin 2 0{l+[(1-p)/(1+p)]
2
tan2 0},
(2)
where 0 is the angle of incidence; is calculated assuming that the sample consists of a single material with no overlayer, and corresponds to the actual dielectric function (a= el + ie2) of the sample when the sample surface has no overlayer. Constant angle reflection interference spectroscopy (CARIS) measures the reflected intensity of light from a sample surface, where R= 0.5 (rsrs* + rprp* )112.
(3)
The CARIS technique utilizes a white-light source (UV and visible). Figure 1 shows and for small-grain, undoped p-Si (p-Si:ud) grown on oxidized Si, determined from SE. 10 In the non-interference part of the spectrum (E>3 eV), the light does not penetrate the p-Si:ud film, and so is representative of the real optical functions of p-Si:ud, modified only by the surface overlayer. B
Data Loading...
