A Highly Reliable Al Line with Controlled Texture and Grain Boundaries
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M. HASUNUMA, H. TOYODA, T. KAWANOUE, S. ITO, H.KANEKO, AND M. MIYAUCHI Toshiba Corp., Research and Development center, Materials and Devices Lab. 1, Komukai Toshiba-cho, Saiwaiku, Kawasaki, 210, Japan
ABSTRACT In order to clarify the relationship between Al line reliability and film microstructure, especially grain boundary structure and crystal texture, we have tested three kinds of highly textured Al lines, namely, single-crystal Al line, quasi-single-crystal Al line and hypertextured Al line, and two kinds of conventional Al lines deposited on TiN/Ti and on SiO2. Consequently, the empirical relation between the electromigration (EM) lifetime of Al line r and the (Ill1) full width at half maximum (FWHM) value (c is described by r - (0-2 [1]. This improvement of Al line reliability results from as following reasons; firstly, homogeneous microstructure and high activation energy of 1.28eV for the single-crystal Al line (w=0.1 8 '); secondly, sub-grain boundaries which consisted of dislocation arrays found in the quasi-single-crystal Al line (w--0. 26 ') has turned out to be no more effective mass transport paths because dislocation lines are perpendicular to the direction of electron wind. Although there exist plural grain boundary diffusion paths in the newly developed hypertextured Al line (U)=0.50) formed by using an amorphous Ta-Al underlayer I 11, the vacancy flux along the line has been suppressed to the same order of magnitude of single crystal line. It has been clarified that the decrease of FWHM value has promoted the formation of sub-grain boundaries and low-angle boundaries with detailed orientation analysis of individual grains in the hypertextured film. The longer EM lifetime for the hypertextured Al line is considered to be due to the small grain boundary diffusivities for these stable grain boundaries, and this diffusivity reduction resulted in the suppression of void/hillock pair in the Al lines. These results have confirmed that controlling texture and/or grain boundary itself is a promising approach to develop reliable Al lines which withstand higher current densities required in future ULSIs.
INTRODUCTION An open circuit failure of Al line induced by electromigration (EM) and/or thermal stress has become more serious reliability problem brought about by current density increase and line width shrinkage in accordance with the progressive miniaturization of ULSIs. To improve the endurance of metal lines against EM, many efforts have been focused on seeking new alloying elements, such as Al-Si-Ti 121, Al-Cu-Ti [31, Al-Pd-Si [41 and Al-Sc 151 alloys, or on employing a layered-structure with TiW and TiN/Ti underlying barrier metals 16,71. From the Al film microstructural standpoint of view, to facilitate the bamboo alternation by abnormal grain growth 181 or rapid thermal annealing [91, and (111) texture improvement has stimulated the basic research to understand the role of grain boundaries. Although the recent researches have revealed that (I 1l) texture improvement makes the EM lifetime longer [1
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