An Effect of Dopants on Contact Electromigration
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EUNGSOO KIM, KYUNGWON CHO, HYUNGWOO JANG AND SOONKWON LIM Microprocess Development Team, Semiconductor R&D Center, Samsung Electronics Co., Buchun, Kyunggi-Do, Korea
ABSTRACT Recently, device reliability has been an important issue since the design rule is scaled down and complicated processing is involved. To improve the reliability, many problems should be solved. One of the problems in interconnection failure is short or open circuits at interconnection lines. Contact or via hole failure has been ignored while the metal line failure has been strongly studied by many researchers. In this study, electromigration (EM) phenomena at the submicron size of contact hole are presented with respect to the type of dopants, boron and arsenic, implanted by high dose. In both cases, the failure mode at the contact hole, the values of the activation energy and the mean-time-tofailure (MTTF) are much different. For example the value of MTTF in boron is lower than that in As. The contact failure by EM is analyzed by SEM micrographs, FIB micrographs, EM measurement. One of the interesting results is void formation at the interface between implanted surface and silicon dioxide film, which is located between contact holes. This fact indicates that the interface migration of Si is much faster than the self-diffusion of Si because the current path is mainly formed along the interface.
INTRODUCTION In the view of metal reliability, a lot of researches [1-3] for electromigration have been done, which are mainly concerned on the metal line. Also, the effect of adding impurities such as Si and Cu to Al has been well reported.[4,5] Since the design rule becomes scaled down, the width of metal line is decreased. In turn, the contact hole is gradually smaller and so the step coverage becomes poor. Therefore, the study of EM at contact hole or via hole is recently carried out, but the EM at the contact hole (called 'contact EM') is not a well-studied phenomenon. There are a few papers on the contact failure mechanism.[5-8] According to previous reports done by others[5-7], the failure mechanism is the accumulation and depletion of Al atoms at the ends of negative and positive sides, respectively. However, Gargini et al.[8] claim that the aluminum is undergoing two competing migration mechanisms. At the leading edge of the contact the aluminum is driven into the pit formed by the silicon migration. Concurrently, the electron wind pushes the aluminum away from the pit and edges of the contact.[8] Thus the contact EM is still under debate and no one has reported on dopant-dependent EM failure. In this study, we concentrate on the dopant effect with respect to contact EM, depending on the electrical type of dopants. We investigate the difference of the EM-induced failure between N+ resistor and P+ resistor, which are the MTTF and activation energy differences in both types of resistors. It seems that the major reason for the activation energy difference is the charge difference. In addition, we observe the void formation at the open window of
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