Chemical-Mechanical Impact of Nanoparticles and pH Effect of the Slurry on the CMP of the Selective Layer Surfaces

Abstract

This paper provides a tribochemical study of the selective layer surface by chemical mechanical planarization (CMP). CMP is used to remove excess material obtained in the process of selective transfer. The paper aims at a better understanding of the planarization (polishing) and micromachining. The planarization becomes effective if the material removal rate (MRR) is optimal and the surface defects are minimal. The pH of the slurry plays a very important role in removing the selective layer by CMP, and hydrogen peroxide (H 2 O 2 ) is the most common oxidizer used in CMP slurry. The purpose of this paper is the analysis of the pH effect on the etching rate (ER) and on the behavior of selective layer polishing by a constant concentration of H 2 O 2 and the influence of nanoparticles size and concentration on selective layer surface CMP. The nanoparticle size used is 250 nm. The MRR results through CMP and ER have been shown to be influenced by the presence of oxides on the selective layer surface and have been found to vary with the slurry pH at constant H 2 O 2 concentrations. The CMP slurry plays an important role in the CMP process performance and should be monitored for optimum results and minimal surface defects. The paper analyzes the impact of chemical-mechanical, inter-nanoparticle, and pad-nanoparticle-substrate interactions on CMP performance, taking into account the state of friction at the interface, by measuring the friction force. Selective layer CMP optimization studies were required to control the chemical and mechanical interactions at the interface between the slurry and the selective layer, the slurry chemistry, the properties, and the stability of the suspended abrasive nanoparticles.

Effect of the Etching on Chemical Mechanical Planarization of the Selective Layer Surface

“…Slurry consists in its premixed form of 3.0 wt.% fumed colloidal silica particles with a median particle diameter of 250 nm, and a citric acid which is commonly used in metallic selective layer CMP slurries as a buffering or complexing agent [5,6]. H 2 O 2 was added to the premixed slurry to oxidize the selective layer (copper from the selective layer) and enhance its removal.…”

Surface Planarization of CdZnTe Wafers: Effect of Slurry Formulation and CMP Processing Parameters on Surface Planarity

“…Effect of slurry pH on rms surface roughness of CZT wafer.-The degree of oxidation by chemical species (oxidizer) in the CMP process is governed by the pH environment of the slurry. 21 Thus, acidic, neutral and alkaline pH values (2.5, 7 and 9) were used in this study to find a suitable pH environment to achieve atomically smooth CZT surfaces. It is well known that pH of the medium has significant influence on the surface charge (zeta potential) and hydrodynamic size of the dispersed silica nanoparticle which govern the stability of the dispersion.…”

Effect of Abrasive Nanoparticle Concentration on the Tribological, Thermal and Kinetic Attributes of Tungsten Chemical Mechanical Planarization

“…During CMP in general, the three-body contact between abrasive NPs, pad asperities and the wafer surface can result in NPs rolling, or sticking and slipping on the wafer surface. 20 This stick and slip results in the generation of mechanical forces which can be measured through COF. 21 When studying the tribology of CMP, stick-slip refers to a cyclic fluctuation in the magnitudes of frictional force and relative velocity between the wafer and the pad.…”

“…21 Previous work has shown that this stick-slip phenomenon creates scratches on the polished wafer surface at lower values of [NP]. 20,21 However, as [NP] increases, pitting deformations of the wafer surface occur faster than scratches, indicating that there is likely more rolling of the NPs than sticking and slipping. 20,21 This is because there is a significant reduction of the load on the individual NPs as their concentration increases.…”