Effect of the End of Range Loop Layer Depth on the Evolution of {311} Defects
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ABSTRACT The interactions between end of range dislocation loops and {311 } defects as a function of their proximity was studied. The dislocation loops were introduced at 2600 A by a dual I x 10 15 cm 2 , 30 keV and a 1 x 1015 cm 2 , 120 keV Si' implantation into Silicon followed by a anneal at 850 'C for 30 minutes. The depth of the loop layer from the surface was varied from 2600 A to 1800 A and 1000 A by polishing off the Si surface using a chemical-mechanical polishing (CMP) technique. A post-CMP I x 1014 cm 2 , 40 keV Si' implantation was used to create point defects at the projected range of 580 A. The wafers were annealed at 700, 800 and 900 'C and plan-view transmission electron microscopy (TEM) study was performed. It was found that the number of interstitials in {3111 defects decreased as the projected range damage was brought closer to the loop layer, while the number of rectangular elongated defects (REDs) increased. Experimental investigation showed that REDs are formed at the end-of-range. It is concluded that the interstitials introduced at the projected range are trapped at the end-of-range dislocations. The REDs are formed due to the interactions between the interstitials and the pre-existing loops. INTRODUCTION Continued scaling to the 100 nm CMOS device technology generation has created many challenges in front-end processes [1]. One of the key challenges is the production of shallow junctions. The junction depth is controlled by dopant diffusion, which is a function of the concentration of native point defects during the high temperature anneal step [2]. Transient enhanced diffusion (TED) of the implanted dopant during annealing occurs due to the implant damage, which evolves into a supersaturation of excess interstitials [3]. The interstitials precipitate on {311} planes as a single monlayer of hexagonal Si giving rise to rod-like defects known as {311 } defects running along < 110> directions [4]. Extended defects such as end-of-range (EOR) dislocation loops, which are clusters of point defects, are inevitably formed at the amorphous/crystalline interface after a high dose amorphizing implant due to the existence of a supersaturation of interstitials in the region [5]. These EOR dislocation loops affect the dopant distribution by capturing or releasing point defects during a subsequent thermal cycle. Because these 61 Mat. Res. Soc. Symp. Proc. Vol. 532 ©1998 Materials Research Society
processes are critical to the overall device performance requirements, a greater level of fundamental knowledge about the evolution of extended defects and their interactions with point defects is necessary. Dislocation loops behave like traps because of dangling bonds at their periphery and the associated strain fields. They nucleate and grow by the emission and capture of Si interstitials atoms. It has been shown that these loops maintain a high supersaturation of free interstitials during their dissolution which induces a strong increase in dopant diffusivity [6]. It has also been shown that EOR dislocation
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