A Scratch Intersection Model of Material Removal During Chemical Mechanical Planarization (CMP)

Abstract

A scratch intersection based material removal mechanism for CMP processes is proposed in this paper. The experimentally observed deformation pattern by SEM and the trends of the measured force profiles (Che et al., 2003) reveal that, for an isolated shallow scratch, the material is mainly plowed side-way along the track of the abrasive particle with no net material removal. However, it is observed that material is detached close to the intersection zone of two scratches. Motivated by this observation, it is speculated that the deformation mechanism changes from ploughing mode to shear-segmentation mode as the abrasive particle approaches the intersection of two scratches under small indentation depth for ductile metals. The proposed mechanistic material removal rate (MRR) model yields Preston constant similar to those observed experimentally for CMP processes. The proposed model also reveals that the nature of the slurry-pad interaction mechanism, and its associated force partitioning mechanism, is important for determining the variation of MRR with particle size and concentration. It is observed that under relatively soft pads, small particles and low particle concentration, the pad undergoes local deformation, yielding an increased MRR with increasing particle size and concentration. At the other extreme, the intact walls of the surface cells and the connecting cell walls between the surface pores deform globally, resembling a beam or a plate, and a decreasing trend in MRR is observed with increasing particle size and concentration. The predicted MRR trends are compared to existing experimental observations. KeywordsChemical mechanical planarization (CMP), Ductile metals, Isolate shallow scratch, Material removal rate (MRR), force measurement, particle size analysis, scanning electron microscopy

Material Removal Mechanism during Copper Chemical Mechanical Planarization Based on Nano-Scale Material Behavior

“…Che et al asserted that the material dislodged by a scratching event is removed only when it is involved in another scratching event based on the experimental observations of material removal by micro-scale scratches. 2 However, this modeling approach has shown clear limitation in predicting the MRR trend when the influence of chemical additives is considered. Nano-or micro-indentation experiments have been employed to estimate the hardness of copper during CMP exposed to various chemical environments.…”

“…This dislodged material is then removed by chemical additives in the slurry 4 or by another abrasion. 2 Some researchers have also argued that material is cut from the surface by sliding abrasive particles, with detached material becoming debris. 1 Regardless of whether the dislodged material becomes debris or piles up, plastic deformation of copper has generally been assumed.…”

“…It also suggests that the material removed during copper CMP is not limited to the weak and soft surface layer as postulated previously. 2,[15][16][17] Note that the evaluated corrosion rates might have underestimated the total oxidation rate of copper if hydrogen peroxide acted via a Fenton-type mechanism that yielded hydroxyl radicals, which are strong oxidizers. This is because the oxidation through this mechanism is not measured electrochemically.…”

“…[1][2][3][4][5][6] Material was considered to be removed by abrasion by abrasive particles that are trapped between a wafer and pad asperities while sliding on the surface being polished. The chemical additives in the slurry were considered to react with the surface of a wafer to soften the material 2,3,[6][7][8] or dissolve physically dislodged material.…”

“…[1][2][3][4][5][6] Material was considered to be removed by abrasion by abrasive particles that are trapped between a wafer and pad asperities while sliding on the surface being polished. The chemical additives in the slurry were considered to react with the surface of a wafer to soften the material 2,3,[6][7][8] or dissolve physically dislodged material. 4 In contrast, Kaufmann et al proposed a synergistic model for metal CMP that attributes material removal during CMP of metals to the cyclic removal of the passive layer on the surface of a metal through mechanical abrasion by abrasives and pad asperities, and subsequent active oxidative dissolution of the metal from the resulting exposed regions, until the passive layer has been regenerated.…”