Comparative study of thin poly-Si films grown by ion implantation and annealing with spectroscopic ellipsometry, Raman spectroscopy, and electron microscopy

Abstract

Polycrystalline silicon (poly-Si) thin films prepared by recrystallization of α-Si either with annealing or ion implantation and annealing have been studied with the optical techniques of spectroscopic ellipsometry (SE) and Raman spectroscopy (RS), as well as with transmission electron microscopy (TEM). A detailed analysis of the SE dielectric function ε(ω) with the effective-medium theory (EMT) has demonstrated the formation of a silicon oxinitride layer on the top of the poly-Si films and a rms surface roughness of about 10 Å. The experimental ε(ω) data have been also analyzed with the second-derivative technique in order to study the effect of the different ion fluencies on the films’ properties and the results are compared with those from TEM. Based on the presented experimental findings we propose the following: (a) The ion-implanted and annealed samples exhibit grain sizes several times larger than those of the only annealed samples; (b) implantation with low ion energies and concentrations induces a disordered material similar to that obtained by annealing; and (c) the mechanism that is responsible for the decrease of the lifetime of the excited carrier is mainly the scattering at the microcrystallite boundaries. Furthermore, the study of the Raman TO vibrational modes reveals the existence of compressive stress in the Si substrate and tensile stress in the poly-Si films. For the latter, results from both RS and SE suggest that the average stress amounts to 2–3 kbar. Finally, the use of a broadening-dependent dielectric function as reference instead of that of c-Si in the EMT analysis, as a consequence of the finite grain size, leads to acceptable structural characteristics similar to those obtained by electron microscopy and RS.

Optical studies of phosphorus-doped poly-Si films

“…Calculating the energy of the singlet is quite involved (10-13), but the final result is the following: Under a (001) biaxial stress, the change in the Raman shift of the singlet is Ao3=(p~J2o~o)+qexx/mo=b~, where p and q were determined in (11) resulting in b=-831 cm -t. The stress is thus X=-Aox0.217 GPa/cm l, since X=exl80 GPa. Since our grain sizes and film thicknesses are large, the position of the Raman peak is not affected by confinement (14)(15).…”

“…4 (symbols). Next, we fit the derivative in the E1 region with the simple 2-D analytical lineshape (14)(15)(16) -2500 3.1 3.2 3.3 3.4 3.5 3.6 Energy (eV) FIGURE 4. Second derivative of the dielectric function for wafer #24 in the Ej critical-point range (symbols) along with a fit to the data using analytical lineshapes (lines).…”

“…Both negative (compressive) and positive (tensile) stresses occur, in contrast to As-doped poly-Si, where the stress is always tensile. Because of different interactions between the film and the substrate (14), only data for the same film thickness should be compared. The broadenings are between 3.2 and 3.8 cm ~, indicating a very high film quality in comparison with the literature (14-16).…”

Crystallization of amorphous silicon thin films using nanoenergetic intermolecular materials with buffer layers

“…It reveals that the stress was reduced for this case compared to the laser crystallization method presenting 6.82-7.54 cm À1 of FWHMs [19]. The variation of FHWM through the different molar ratios indicates that the nano size grain and the residual stress is the origin of the peak shift, respectively [16]. The.…”

“…The crystalline fraction can be expressed by X c =(I m +I c )/(I m +I c +I a ), where I a , I m and I c indicatingindicate amorphous, intermediate state, and crystalline state, respectively [15]. In addition, by comparing the peak wave number of the transverse-optical (TO) obtained from the silicon (o) and that obtained from stress-free single-crystal bulk silicon (o c ), the stress can be estimated by following equation [16]. s(MPa)=À250(oÀo c ) (cm À1 ), where s is the in-plane stress.…”