Bath Additive and Current Density Effects on Copper Electroplating Fill of Cu Damascene Structures
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ABSTRACT Copper electroplating has become the leading technology for gap fill of damascene structures on advanced interconnects. A key to developing a robust electroplating process that produces deposits free of voids and seams is understanding the role of the additive components, i.e., levelers, brighteners and wetting agents, and their relative diffusion/adsorption characteristics. Additionally, obtaining insight about the cathodic current/potential relationship is critical for maximizing the effectiveness of the additive components. Our results indicate that bath additive composition and the plating parameters (plating pulse frequency, and current density) play critical roles in the outcome of the Cu fill. SEM cross sectional analysis of timed partial electroplating fill studies show two types of fill, 1) conformal and 2) bottom-up. Conformal fill of features smaller than 0.25 pm with an aspect ratio (AR) of 4.0 tends to form seam voids in the center of the structure. These seam voids can lead to early electromigration failures. On the other hand, bottom-up fill leads to a void free Cu deposit within the feature. INTRODUCTION Copper electroplating technology is being implemented as the metalization scheme for advanced chip designs [1]. The introduction of this technology for chip manufacturing presents new challenges as the feature size decreases [2], which requires a fundamental understanding of the electroplating fill mechanism, modification and control of the process chemistry in order to produce void free fill and build reliability into the process. Historically the use of additives to develop the required electroplated film properties has been steeped in art and the science was left to the chemical suppliers. For this technology to be successfully integrated into semiconductor manufacturing it is incumbent for us as end users to become intimately familiar with the science of additives and plating chemistry to the extent that we can accelerate the development of commercial solutions. Suppressing and leveling agents block the copper deposition process by creating a surface film, which inhibits deposition [3-11]. The preferential adsorption of leveling agents on flat fields creates a concentration gradient (additive flux) of the organic additives from the trench/via opening to the bottom. Due to this gradient, the deposition rate of copper is reduced at the trench/via openings and enhanced in the recessed areas, resulting in deposit leveling. The fill evolution of a trench or via can be dramatically altered by varying the additive composition, cathodic pulse frequency, and current density of the electroplating process. This paper presents data on plating process parameters and bath chemistry for void free copper fill of damascene structures. Process optimization focused on development of a bottom-up fill technique using proprietary and non-proprietary additives. 399 Mat. Res. Soc. Symp. Proc. Vol. 564 ©1999 Materials Research Society
EXPERIMENTAL Patterned wafers were metallized using a commercially availabl
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