The Effect of Thermal Annealing on Cobalt Film Properties and Grain Structure
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.257
The Effect of Thermal Annealing on Cobalt Film Properties and Grain Structure Natalia V. Doubina, Tighe A. Spurlin, Edward C. Opocensky, and Jonathan D. Reid Lam Research Corporation, Tualatin, OR 97062, U.S.A
ABSTRACT
The grain structure of electrodeposited Cobalt is important to device electrical and reliability performance. This paper describes thermal annealing studies performed on electroplated blanket and pattern Cobalt wafers. A systematic study of Co film properties and effect of various anneal parameters such as temperature, time, hydrogen pressure and thermal cycling was completed. Co film resistivity, purity, grain structure, phase composition and orientation as well as in-feature grain size have been characterized by various analytical methods such as XRD, STEM, SIMS and EBSD. It was observed that electroplated cobalt films with resistivity approaching bulk Cobalt value can be obtained by annealing in the temperature range of 300°C - 350°C which is favorable for hcp Co phase formation.
INTRODUCTION As interconnect dimensions continue to decrease, the extendibility of conventional copper damascene processing becomes increasingly problematic, in terms of yield and reliability. Decreasing line dimensions result in higher line current densities which can cause void formation and reduce reliability [1]. Decreasing dimensions also leads to greater RC delay and IR drop due to the exponential increase in resistivity with decreasing line cross section [2,3]. The space occupied by the barrier becomes more important with smaller sized features and a new alternative that allows for thinning of the barrier and avoiding the PVD seed overhang is required. An attractive candidate to address copper extendibility issues for interconnects is cobalt metal which has a much 1
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shorter mean free path than copper thus resulting in superior scalability of resistivity to smaller line dimensions due to reduced scattering at material interfaces and grain boundaries [4]. Cobalt may require less barrier increasing the relative amount of metal within the line. Based on melting points, cobalt filled features are expected to have improved electromigration performance over copper [5]. Similar benefits are also achieved for filling middle of line contacts (MOL) with cobalt [6]. Contact resistance in traditional tungsten-based contacts is becoming more significant as interconnect sizes scale down. Using Cobalt as the alternative metal enables improved contact resistance by thinning of the barrier and elimination of seams formed during tungsten metal chemical vapor deposition process [7]. An electrochemical cobalt deposition process has been developed that utilizes a single suppressive additive to achieve bottom up cobalt depos
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