Effect of Ion Bombardment on the Dopant Diffusion During Reactive Ion Etching (RIE) of Dielectric Films Deposited on Sil
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EFFECT OF ION BOMBARDMENT ON THE DOPANT DIFFUSION DURING REACTIVE ION ETCHING (RIE) OF DIELECTRIC FILMS DEPOSITED ON SILICON
K. SHENAI, N. LEWIS, C. A. SMITH, and B. J. General Electric Corporate Research and Schenectady, NY 12301
BALIGA Development
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ABSTRACT We report on the results obtained from a study conducted to understand the effect of reactive ion etching (RIE) of oxide films on the dopant diffusion in ion-implanted silicon. Thermally grown oxide films on silicon were plasma etched in a CHF 3 /CO 2 plasma. The residual silicon surface damage created during plasma etching was removed by employing a low ion-bombardment, two-step surface plasma cleaning process. The samples with oxide films etched in a wet chemical etchant provided the control for evaluating the effect of the RIE process. The samples were implanted with boron and boron was activated under various conditions to form p-n junctions to obtain a range of boron doping profiles and junction depths. +Some boron doped samples were implanted with arsenic to form a heavily doped n region at the silicon surface. The resulting doping profiles were analysed using spreading resistance profiling (SRP), four-point probe measurements, and secondary ion-mass spectrometry (SIMS) to understand the activation, diffusion, and precipitation of various dopants. Detailed transmission electron microscopy (TEM) analysis was used to study the microstructural effects. It was observed that plasma etching of the oxide films prior to the formation of boron diffused surface regions in silicon resulted in significant changes in boron diffusion. For low boron implant doses, plasma etched silicon surfaces resulted in retarded boron diffusion. For high boron implant doses, plasma etched silicon surfaces lead to enhanced boron diffusion.
INTRODUCTION
Submicron VLSI technologies demand low thermal budgets (product of dopant diffusivity and diffusion time) to facilitate the formation of shallow junctions (1-3]. Various techniques to form heavily doped shallow source/drain junctions have been proposed in the literature [4-6]. It has been pointed out that the characteristics of the surface damage and surface point defects play an important role in determining the properties of shallow junctions in silicon [7]. There is, however, limited experimental data and understanding pertaining to the formation of deep-diffused junctions in silicon [8]. The diffusion of dopants at extremely high temperatures in excess of II00°C is usually required to form phosphorus and boron doped deep junctions used in silicon VLSI and smart power applications [9-12]. Predeposition as well as ion-implantation of impurities have been used to form deep diffused junctions in silicon. The microstructural properties of surface damage and defects generated during the incorporation of dopants by these two techniques may not be similar.
Present Address: Department of Electrical and Computer Carolina State University, Raleigh, NC 27695-7911
Mat. Res. Soc. Symp. Proc. Vol. 128. '1989 Materials
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