Ni Silicide Morphology On Small Features
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C4.4.1
Ni Silicide Morphology On Small Features Oxana Chamirian (1), Anne Lauwers, Jorge A. Kittl (2), Mark Van Dal (3), Muriel De Potter, Christa Vrancken, Richard Lindsay and Karen Maex (1) IMEC, Kapeldreef 75, 3001 Leuven, Belgium 1. E.E. Department, K.U.-Leuven 2. Affiliate researcher at IMEC from Texas Instruments 3. Philips Research Leuven
ABCTRACT
Silicidation of small features of various geometries and sizes using Ni-silicide was studied. Effects of dopants, surface preparation and silicidation parameters on silicide morphology were investigated. It was found that Ni silicide thickness and quality of the silicide/silicon interface (presence of NiSi2 pyramids) are dependent on the area dimensions and geometry. NiSi formed on narrow lines is thicker compared to wide areas. We found that pyramids of epitaxial NiSi2 protruding into the Si substrate are formed during the silicidation of undoped, boron-doped and BF2-doped active areas. The presence of pyramids was not observed on As-doped silicon. Rough interface due to the pyramids could be the reason for a more pronounced linewidth dependence of leakage current in the case of p+/n diodes. A higher density of pyramids was found on narrow lines (below 0.2µm) and particularly islands structures. No pyramids were found when a Ge preamorphisation implant was used.
INTRODUCTION
Nowadays, Ni silicide is replacing CoSi2 as a contact material for source/drain areas and poly-Si gates. NiSi offers a number of advantages for the sub-100 nm technology nodes, such as a low resistivity, low formation temperature and no adverse linewidth effect [1]. However, implementation of NiSi imposes some problems related mostly to the low thermal stability of NiSi and to the excessive silicidation of narrow areas [2]. When Ni reacts with Si, usually the Nirich phases are formed first, then Ni-monosilicide is formed, and finally the monosilicide is converted into disilicide if the temperature is high enough [3]. As Ni is the dominant diffusion species and a continuous supply of Ni is available from Ni on surrounding areas, NiSi formed on narrow lines is significantly thicker compared to NiSi formed on wider areas [4]. Moreover, in some cases [5,6] epitaxial NiSi2 has been observed to grow first, at quite low temperatures, forming characteristically shaped pyramids (faceted along (111) planes) protruding into the Si substrate. As the interface roughness can worsen junction leakage, formation of pyramids is undesirable and should be avoided. In this work, a study of NiSi formation on small features is presented and factors influencing the growth of Ni-disilicide pyramids are considered.
C4.4.2
EXPERIMENTAL
8” (100) Si wafers were used. Active areas of various shapes (long lines and islands) and varied dimensions (0.15-0.75 µm) were defined by Shallow Trench Isolation (STI). Junctions were formed by Boron (2e15 cm-2 or 6e15 cm-2, 2 keV ), Arsenic (4e15 cm-2, 20 keV), or BF2 (2e15 cm-2, 15 keV) implantation and spike anneal at 1050°C. Undoped substrates were also used. For some wafers
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