Stress-Related Defects in Implanted Locos + Trench - Isolated Structures
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STRESS-RELATED DEFECTS IN IMPLANTED LOCOS + TRENCH ISOLATED STRUCTURES. Barbara Vasquez and N. David Theodore Motorola Inc., Advanced Technology Center, 2200 W. Broadway Rd., Mesa, AZ 85202 ABSTRACT Poly-buffered local-oxidation of silicon + trench-isolation (PBLT) is a technique being explored for device isolation. In an earlier study, we had reported the presence of dislocations associated with a combination of high-dose (-5E14 cm-2 ) phosphorous implants and PBLT isolation. In the present study, the behavior of extended defects present in the structures is analyzed in greater detail. The origin and behavior of the defects is modelled to explore potential mechanisms to explain the observations. Implantation induced dislocation-loops interact with stress fields associated with PBLT isolation-trenches. Some of the implant loops (in the presence of a stress field) transform to dislocation sources which then create glide dislocations in the structures. Strategies for defect engineering are discussed, including reducing implantinduced damage (lowering the implant dose) or reducing stress fields (by moving the edge of the implanted region away from the trench). Defect densities can be reduced or eliminated. INTRODUCTION Semiconductor devices are being scaled down into the submicron regime in order to meet technological demands for increased device packing-densities. Due to dimensional limitations of conventional LOCOS (local oxidation of silicon) isolation, variations on the technique are being explored for further miniaturization of devices. One such method involves poly-buffered LOCOS + trench-isolation (PBLT). The method is a combination of the two techniques mentioned. Poly-buffered LOCOS [ 1,2] is an improvement on conventional LOCOS in that it limits lateral encroachment of field oxide into active device-regions. Control of oxide encroachment makes higher integration densities possible. The second technique, deep-trench isolation provides a means to support device scaling and reduce parasitic capacitances [3,4]. The combined method involves integration of deep-trench isolation with poly-buffered LOCOS to create self-aligned shallow field-oxide elements with minimal encroachment into active regions [5]. Previous micro-probe Raman measurements of active regions surrounded by PBLT isolation provided cross-sectional stress-distributions at room temperature [6]. Compressive stresses are maximum at the center of the active area and decrease as the isolation edge is approached. The inverted 'U' shape of the stress distribution is independent of whether the measurements are made from the surface or from a cleaved cross-section. These structures had not received any implants and no dislocations were observed. In an earlier study [7], for PBLT structures in combination with high-dose [-IE15 cm- 2] phosphorus implants, dislocations were observed. The effect of fabrication-related stresses in the structures was of interest because extended defects, if formed, could degrade device performance. The present study investigates a
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