Evaluation of Inhibitors for ECMP of Copper Using Electrochemical Quartz Crystal Microbalance (EQCM) Technique
- PDF / 217,952 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 31 Downloads / 190 Views
0914-F12-09
Evaluation of Inhibitors for ECMP of Copper Using Electrochemical Quartz Crystal Microbalance (EQCM) Technique Ashok Muthukumaran, Viral Lowalekar, and Srini Raghavan Materials Science and Engineering, The University of Arizona, 4715 E Ft Lowell Rd, Tucson, Arizona, 85712 Abstract Chemical formulations for the electrochemical mechanical planarization (ECMP) of copper must contain constituents that are stable at anodic potentials. A key component of the formulation is a corrosion inhibitor, which is required to protect low lying areas while higher areas are selectively removed. Organic compounds, which adsorb on copper at low overpotentials and form a film by oxidation at higher overpotentials, may be particularly useful for ECMP. The objective of this work is to evaluate the effect of two inhibitors on copper dissolution in oxalic acid based systems using an electrochemical quartz crystal microbalance (EQCM) technique. By recording current as well as mass changes during the application of potential to electrodeposited copper films, the extent and mechanism of inhibition of sulfhydryl based acid (SBA) inhibitor has been explored. Introduction Electrochemical mechanical polishing is a recent development in the chemical mechanical planarization technology. In a copper ECMP process, copper film on wafer is polarized anodically by an applied voltage while a pad makes mechanical contact with the copper surface [1]. The applied pressure is very low (< 0.3 psi) to ensure that the metal film does not delaminate from the underlying low-k film. Low applied pressure also minimizes dishing that is common in conventional CMP processes [2]. Due to enhancement of chemical factors, the particulate content of the slurries can be significantly reduced. ECMP allows modification of the polish recipe based on the thickness profile of the incoming wafer. The applied charge is controlled by an independent electro-chemical zone system such that the charge at different portions of the wafer can be varied [3]. Liu et al [4] have reported excellent planarization efficiency with high removal rate (9000 Å/min) in areas containing features over a broad size range of 0.18 to 100 um. In ECMP, the low-lying areas of the film that are not contacted by the pad are protected by a passive layer while the higher features are removed through a combination of electrochemical and mechanical factors [5]. Oxalic acid based slurry systems containing an inhibitor have been tested for CMP of copper [6]. Oxalic acid (C2H2O4) complexes copper ions and the formation constant of 1:1 complex is reported to be 6.23 [7]. Benzotriazole (BTA) is a well known inhibitor for copper. Previous work [8] has shown that the effectiveness of BTA to protect copper decreases with applied anodic over potential. An inhibitor which can be oxidized to a film forming compound at anodic potentials would be ideal for ECMP. One such inhibitor is sulfhydryl based acid (SBA). The objective of this work was to evaluate a novel film forming inhibitor containing sufhydryl groups fo
Data Loading...
