Key Chemical Components in Metal CMP Slurries

Abstract

Chemical-mechanical planarization (CMP) slurries can be classified into two general categories according to their applications: metal CMP slurry and nonmetal CMP slurry. Two most important metals incorporated into IC chip manufacturing via CMP are W and Cu. Depending upon integration schemes, a metal CMP slurry may or may not carry out the function of removing the film(s) immediately below the overburden metal such as cap, adhesion, and barrier layers. For tungsten CMP, a single-step slurry is typically used to remove both excess tungsten and its barrier/adhesion layer. For copper CMP, after the removal of copper, a subsequent barrier removal step is often required. This chapter reviews the basic requirements for the key components found in common metal slurries.It is generally understood that a metal CMP slurry chemically modifies the surface to be polished and yields a softer and porous complex layer, which is then removed by mechanical force in the process. Although these metals may differ in their physical and chemical properties, the underlying principle for the design of slurries is the same. A production-worthy metal CMP slurry must address several issues, such as material removal rate (MRR), within-wafer nonuniformity (WIWNU), step height reduction efficiency, dishing/erosion, minimum ILD loss, corrosion, scratching, slurry residue, and other surface defects. Typical metal CMP slurry may contain an oxidant, a chelating agent, abrasive particles, a surfactant, and other additives. These components must work in concert to produce adequate material removal rate, high planarization efficiency, and Microelectronic Applications of Chemical Mechanical Planarization, Edited by Yuzhuo Li

Chemical Mechanical Planarization of Tungsten with Hard Abrasives

“…This trend followed the indentation mechanism, which predicts higher MRR with larger particle size. 16 By contrast, an earlier study of W CMP by Bielmann et al 17 revealed an opposite trend, which was also observed by Lu et al 18 in Cu/Ta CMP. However, both articles focused on CMP slurries with larger particle sizes and higher abrasive contents than the present slurry formulation.…”

Recycling a slurry for reuse in chemical mechanical planarization of tungsten wafer: Effect of chemical adjustments and comparison between static and dynamic experiments

“…It is a major drawback, especially in the case of W-CMP slurry, for which the chemical composition plays a major role in the chemical and mechanical polishing. As reviewed by several authors, the chemical composition of W-CMP slurry is a determining factor in obtaining uniform and non-defective polishing [5,24,25]. Moreover, in our case, recycling slurry has to be directly operational and all the settings related to the polishing process have to stay unchanged.…”

“…It was shown that the reduction of particles agglomeration prevents the formation of defects [44]. Moreover, surfactants are used as dissolution inhibitors of the metal surface in chemical mechanical polishing [5,44]. In the case of tungsten CMP, this kind of inhibitor is not particularly required because of the low corrosive potential of tungsten [30], but could help to decrease the excess of dissolution mechanism for tungsten slurry recycling [46,47].…”

“…Slurries usually consist of an abrasive material such as silica, alumina or ceria and an aqueous medium that facilitates the suspension of the abrasive particles [5,6]. In the case of tungsten polishing (W-CMP), the aqueous medium contains a strong oxidizer (hydrogen peroxide) and an iron catalyst such as ferric nitrate [7].…”

CMP Method and Practice

“…From the Pourbaix diagram shown [25] in Figure 7.14, copper forms the oxides Cu 2 O and CuO, depending on the process conditions. From the Pourbaix diagram shown [25] in Figure 7.14, copper forms the oxides Cu 2 O and CuO, depending on the process conditions.…”