R. Ditchfield

Surface diffusion of In on Si(111): Evidence for surface ionization effects

Second harmonic microscopy has been used to quantify the surface diffusion of In on Si(111). At temperatures near 50% of the bulk melting temperature and in the coverage range 0<θ<0.7, the activation energy Ediff and pre‐exponential factor D0 lie at 42±0.5 kcal/mol and 3×103±0.3 cm2/s, respectively. These parameters, which are quite large, are explained semiquantitatively by reference to an adatom–vacancy model recently developed for related systems. The present work, when compared with the results of these other systems, offers significant evidence for the effects of adatom–vacancy ionization.

Rapid Thermal Processing: Fixing Problems with the Concept of Thermal Budget

The rapid complexification of integrated circuits poses increasing challenges for the associated manufacturing technologies. Until now, kinetic effects in rapid thermal processing have been assessed using the concept of thermal budget, with the idea that thermal budget minimization should minimize dopant diffusion and interface degradation. This work highlights shortcomings with that principle. Experiments directly comparing the rate of Si chemical vapor deposition with that of dopant diffusion show how thermal budget minimization can actually worsen diffusion problems rather than mitigate them. The authors present a straightforward framework for improving the results through comparison of activation energies of the desired and undesired phenomena. This framework explains all the experimental results and provides strong kinetic arguments for continued development of rapid isothermal processing and small batch fast ramp methods.

Adsorption of Chlorine on TiSi2: Application to Etching and Deposition of Silicide Films

The interaction of Cl 2 with polycrystalline TiSi 2 has been investigated by temperature programmed desorption to better understand the role of adsorbed chlorine in the etching of TiSi 2 films and in the chemical vapor deposition of TiSi 2 from TiCl 4 and SiH 4 . Five different desorption states were observed in response to Cl 2 adsorption over a wide exposure range, including the products TiCl 4 , SiCl 4 , and SiCl 2 . The sticking probability for Cl 2 and the desorption kinetics for the products were incorporated into a quantitative model for TiSi 2 etching. The predicted etch rates matched closely those measured in an etching reactor operated under typical processing conditions. Etch rates of 200 A/s were obtained at 600 K with p Cl2 of 5 x 10 -4 Torr. These rates are an order of magnitude higher than those obtained using plasma-based systems, while the Cl 2 pressure is at least an order of magnitude lower. Coadsorption studies with SiH 4 were performed to examine the inhibition effects of surface chlorine during silicide CVD and the role of surface titanium in adsorbate bonding.

Problems with The Concept of Thermal Budget: Experimental Demonstrations

Up to now, kinetic effects in rapid thermal processing (RTP) have been assessed using the concept of thermal budget, with the idea that thermal budget minimization should minimize dopant diffusion and interface degradation. This work highlights shortcomings with that principle. Experiments comparing directly the rate of Si chemical vapor deposition with that of dopant diffusion show how thermal budget minimization can actually worsen diffusion problems rather than mitigate them. We present a straightforward framework for improving the results through comparison of activation energies of the desired and undesired phenomena. This framework explains the experimental results and provides strong kinetic arguments for continued development of rapid isothermal processing and small batch fast ramp methods.

General Kinetic Rules for Rapid Thermal Processing

Up to now, kinetic effects in rapid thermal processing (RTP) have been assessed qualitatively and rather vaguely through the concept of thermal budget. The authors discuss the shortcomings associated with thermal budget and present an alternate conceptual framework that explicitly treats selectivity between desired and undesired physical phenomena. This framework is quite simple and is intended for rapidly assessing the qualitative effects of various heating programs. From a purely kinetic perspective, selecting the best program involves only comparing the activation energies for the desired and undesired rate phenomena. They cite examples where application of the thermal budget approach gives incorrect guidance for minimizing the undesired process. Such deficiencies are rectified by the framework presented here.