Defect-Characterization in Implanted Locos + Trench-Isolated Structures
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DEFECT-CHARACTERIZATION IN IMPLANTED LOCOS + TRENCH-ISOLATED STRUCTURES N. David Theodore, Barbara Vasquez and Peter Fejes Motorola Inc., Advanced Technology Center, 2200 W. Broadway Rd., Mesa, AZ 85202
ABSTRACT As device dimensions decrease in silicon integrated-circuits, conventional LOCOS (local-oxidation of silicon) isolation becomes inadequate to meet dimensional demands. Variations on LOCOS are therefore being explored for further miniaturization of devices. One such variation involves poly-buffered LOCOS + trench-isolation (PBLT). In this structures were characterized using TEM. Wright-etched cross-section SEM showed etch-pits associated with a combination of high-dose (> 5E14 cm-2 ) implants and PBLT isolation. TEM characterization showed that dislocations were
study, PBLT micrographs phosphorous formed in the
structures for a combination of high-dose (IEl5 cm- 2) phosphorous implants (followed by an anneal) and PBLT isolation. Structures exposed to lower-dose (1E14 cm-2) implants showed no defects and neither did 1E15 implanted structures prior to annealing. The results are modelled in terms of the stress configurations present in the structures, and in terms of dislocation-sources resulting from implantation-related dislocation-loops. The dislocation-sources operate in the presence of stresses associated with the isolation-trenches. Glide-loops form, which then grow in response to stresses in the structures and dislocations result on glide planes.
INTRODUCTION As silicon devices are scaled down in dimension, circuit densities increase and new techniques of device-isolation need to be developed. The commonly used isolation-technique, LOCOS (LOCal-Oxidation of Silicon), is subject to dimensional limitation due to lateral encroachment of oxide. This limitation has led to interest in techniques that are variations on conventional LOCOS. Poly-buffered LOCOS [1,21 for instance is a means of limiting lateral encroachment of field-oxide into the active device-region. Control of the oxide-encroachment reduces device-sizes and makes greater packing densities possible. Another technique, deeptrench isolation provides a means to support device scaling [3,4]. In this work deep-trench isolation is integrated with poly-buffered LOCOS to create self-aligned shallow field-oxide elements with minimal encroachment into active regions [5]. An understanding of the behavior of the materials and structures being used and their interactions under different processing conditions is necessary for the use of these technologies. The effect of fabrication-related
Mat. Res. Soc. Symp. Proc. Vol. 239. ©1992 Materials Research Society
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stresses in the structures is of interest because extended-defects, if formed, could electrically degrade devices. The interaction between trench + poly-buffered LOCOS -isolated (PBL+T) structures and a phosphorous-implant was evaluated in this study. Figure 1 shows a schematic of the structures being investigated. A phosphorus implant [1E14-1E15 cm-21 is used to form a deep Optional Collector-I
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