Papers by Author: Francesco Pipia

Abstract: The use of various H₂O₂ based chemistries for TiW etch was studied on single wafer and wet bench tools. The focus of the investigation was put on the different behaviors of these chemicals on blanket and patterned wafers. The results of the etch rate tests showed much higher values on the wafers where copper was exposed, leading to the hypothesis that the etch rate on TiW should be driven by the catalysis effect of the transition metal on the H₂O₂ decomposition reaction. Additional optical inspections, ToF SIMS, SEM and TEM analyses were carried out to confirm this hypothesis and find the best conditions in terms of morphology for RDL applications. Finally, the collected data were also used to evaluate the process cycle time and cost of ownership.

Abstract: The defectivity of a batch process for polymer removal in AlCu BEOL technology has been investigated, reasearching the defectivity source and studying the composition of the defects. Different solutions for the minimization of this defectivity have been found, working on the positioning of the wafers or additional cleanings. The complete eradication of the defectivity has also been demonstrated performing the process on a single wafer tool.

Abstract: Three different cases of wet polymer removal in presence of AlCu are described: namely a) oxide passivation opening, b) vias etch and c) pad patterning. The occurrence of pitting at such levels is analyzed and linked to halogens presence. Moving from these results, a proposal to limit such kind of defects is given, focusing on a trimmed DIW rinsing step and on a possible AlCu passivation through a plasma ashing process.

Abstract: In damascene architecture, widely used both in flash memories and in DRAM as interconnect scheme since 90 nm node, copper surface is exposed after via etch. A deep understanding of the effect of different wet cleanings on Cu surface is therefore mandatory, not only to ensure an efficient post etch polymer removal, but also to provide a better surface termination, capable to minimize Cu oxidation kinetic and to reduce the growth of Cu-rich precipitates which may negatively effect contact resistance. In this work we have analyzed the Cu surface after processing with several cleaning chemistries -often present in BEOL cleaning processes- using XPS (X-ray Photoelectron Spectroscopy) and ToF-SIMS (Time of Flight – Secondary Ion Mass Spectroscopy), fast and powerful techniques widely used in Cu surface characterization [1]. In addition, the evolution of the surface with storage time has been monitored using the same techniques, in order to better understand the effect of the different cleaning chemistries. XPS has been proven to be very sensitive to monitor Cu oxidation, while ToF-SIMS has been used to reveal organic species adsorbed on the surface.

Abstract: Tungsten is a metal widely used for interconnections. As a consequence of more stringent requirements in terms of aspect ratio deriving from device shrinking, the filling of W plugs is becoming more and more critical and new deposition techniques need to be employed to properly fill contacts and trenches. For example ALD nucleation layers need to be coupled to CVD deposition. Since physical-chemical properties of W are heavily influenced by deposition techniques, the effect of wet cleanings on different kind of W needs to be fully understood in order to avoid any kind of W corrosion or recession during wet cleaning with W exposed. In this paper the effect of several chemicals commonly used in BEOL wet cleanings for polymer removal, has been investigated on W films deriving from both CVD and ALD deposition techniques.