Defects Introduced by Plasma Processing of Silicon
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DEFECTS INTRODUCED BY PLASMA PROCESSING OF SILICON J. L. BENTON AT&T Bell Laboratories, Murray Hill, New Jersey 07974
ABSTRACT The electrical and optical properties of defects introduced by Reactive Ion Etching (RIE) in the near surface region of Si after dry etching with various gases and plasma conditions is studied with spreading Resistance (SR), photoluminescence (PL), and capacitance-voltage profiling (CV). Plasma etching in chlorine and fluorine based gases produce donors at the surface in both ntype and p-type, Czochralski and float-zone silicon. Isochronal annealing reveals the presence of two distinct regions of dopant compensation. The surface damage region is confined to 1000A and survives heat treatment at 400'C, while the defect reaction region extends _Ž1 jim in depth and recovers by 250 0 C. A comprehensive picture of the interstitial defect reactions in RIE silicon is completed. The interstitial defects, Ci and Bi, created in the ion damaged near surface region, undergo recombination enhanced diffusion caused by the presence of ultraviolet light in the plasma, resulting in the long range diffusion into the Si bulk. Subsequently, the interstitial atoms are trapped by the background impurities forming the defect pairs, Ci Oi, C, Ci, or. Bi Oi, which are observed experimentally. The depth of the diffusion-limited trapping and the probability of forming specific pairs depends on the relative concentrations of the reactants, oxygen, carbon or boron, present in the bulk material.
INTRODUCTION Reactive ion etching (RIE) and plasma assisted processing steps are becoming increasingly important in silicon device manufacturing. As design rules decrease to submicron dimensions and junction depths are limited to hundreds of Angstroms, the anisotropic nature of RIE becomes critical. RIE is typically used for pattern transfer, oxide definition and trench isolation. The process, however, introduces extended damage and point defects into the silicon surface. Characterizing these defects, understanding their effect on the optical and electrical properties of the resulting devices, and optimizing the processing parameters emerges as an important area of research for the microelectronics industry. A comprehensive picture of the defects introduced by plasma processing has emerged and is summarized in this paper. Chemical interaction of the reacting ions with the substrate, displacement damage caused by energetic particles, and electromagnetic energy in the form of ultraviolet light in the reactor combine to produce defects in the expos~d silicon. There are two distinct regions of damage, a surface damage region extending 1000A from the surface and a point defect reaction region which can extend to depths >ljtm. [1] [21 131Realization of the existence of these two distinct regions resolves the apparent contradictions in the observed types of plasma induced damage and the variations in reported defect penetration depths. Extended defects are created in the near surface region by RIE. Previous work has characterized thes
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