Dislocation Locking by Intrinsic Point Defects in Silicon
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Dislocation Locking by Intrinsic Point Defects in Silicon Igor V. Peidous, Konstantin V. Loiko, Dale A. Simpson, Tony La, and William R. Frensley1 R&D Department, Dallas Semiconductor Corporation, Dallas, TX 1 Department of Electrical Engineering, University of Texas at Dallas, Richardson, TX ABSTRACT Dislocation pileups with abnormally weak inter-dislocation repulsion have been observed in locally oxidized silicon structures. To verify if this could be attributed to elastic interaction of dislocations with intrinsic point defects, distributions of self-interstitials in dislocation stress fields have been studied using theoretical calculations and computer simulations. According to the obtained results, self-interstitials can form atmospheres about dislocations causing dislocation stress reduction and therefore screening of dislocations from interaction with external stresses. This may represent an additional mechanism of dislocation locking in silicon alternative to oxygen pinning. INTRODUCTION Dislocation locking in silicon was intensively studied in the 70’s and was clearly demonstrated to be dependent on oxygen concentration [1, 2]. Since then, most observations of dislocation locking in silicon are traditionally attributed to their interaction with oxygen atoms and precipitates [3, 4]. Advances in silicon materials science during the past two decades have revealed an important role of Si-interstitials in defect evolution [5]. Si-interstitials are highly mobile and readily available at very high concentrations during silicon processing in device manufacturing. Being the centers of dilatation, they must interact elastically with dislocations and may cause more or less significant dislocation pinning [6]. In the present work, an estimate of dislocation locking efficiency by self-interstitials is made based on analytical calculations and computer modeling. EXPERIMENTAL DETAILS AND CALCULATION MODELS Dislocations were intentionally introduced in CZ (100) 150 mm silicon wafers by local oxidation. The wafers were p-type 6-9 Ohm·cm boron-doped with an oxygen concentration of 25-26 ppm (ASTM F1619). A 200 nm film of LPCVD silicon nitride was deposited and patterned using conventional lithography and plasma etch to obtain long nitride strips oriented along directions on the wafer surface. Dislocation pileups were generated at the edges of the nitride film during oxidation carried out at 1100°C. After the removal of nitride and locally grown oxide films in phosphoric and hydrofluoric acids, wafers were cleaved along directions perpendicular to the nitride strips. Silicon defects were delineated using preferential etching in Wright solution. Finally, dislocation distributions were studied on the wafer crosssections using optical microscopy. Point defect interaction with dislocations was estimated in 2-dimensional approximation of plain strains as described in detail earlier [7]. Dislocations were assumed not to act as a source or sink for point defects. Self-interstitial atoms were modeled as elastic balls. The deviation o
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