Uday Mahajan

Effect of Particle Size of Chemical Mechanical Polishing Slurries for Enhanced Polishing with Minimal Defects

In this study the effects of oversize particle contamination in chemical mechanical polishing (CMP) slurries were investigated on the silica CMP process. The limits of light scattering technique were established in detecting coarse particles in a commercial silica CMP slurry using two different methods. The detection limits were set by observing the shift in particle size distribution curve or by the appearance of an additional peak in the particle size distribution curve of the baseline slurry when a known amount of coarser particles were added to it. Simultaneously, polishing tests were conducted by spiking the base slurry with coarser sol‐gel silica particles at the established detection limits. It was observed that the contamination of larger particles not only created surface damage but also changed the material removal rate. The mechanism of polishing in the presence of larger size particles is discussed as a function of particle size and concentration.

EFFECT OF PARTICLE SIZE DURING TUNGSTEN CHEMICAL MECHANICAL POLISHING

The size of the abrasive particles plays a critical role in controlling the polishing rate and the surface roughness during chemical mechanical polishing of interconnect materials during semiconductor processing. Earlier reports on the effect of particle size on polishing in silica show contradictory conclusions. To the best of our knowledge, a systematic study of the effect of particle size on tungsten polishing has not been published. This paper describes the controlled measurements that were conducted to determine the effect of alumina particle size during polishing of tungsten. Alumina particles of similar phase and shape with size varying from 0.1 to diam were used in these experiments. The polishing experiments showed that the local roughness of the polished surfaces was insensitive to alumina particle size. The removal rate was found to increase with decreasing particle size and increased solids loading. These results suggest that the removal rate mechanism is not a scratching type process, but may be related to the contact surface area between particles and polished surface controlling the reaction rate. ©1999 The Electrochemical Society

Effect of Slurry Ionic Salts at Dielectric Silica CMP

The effects of alkaline ionic salts on silica chemical mechanical polishing ~CMP! have been studied. Particle size, zeta potential, and stability via turbidity tests have been characterized. Particle size and size distributions have been found to increase with ionic strength for three types of alkaline ionic salts due to the decrease in the magnitude of the zeta potential of silica slurry due to the addition of alkaline ionic salts. Slurry stability measured by turbidity tests showed two regimes of slurry stability ~i.e., stable regime and unstable regime!. For the stable slurry regime, the increase in ionic strength leads to an increase in friction force and material removal rate; however, for the unstable slurry regime, the addition of ionic salts results in a decrease in the measured friction force and material removal rate. Surface root-mean-square roughness and maximum depth of surface damage (Rmax) are shown to increase with particle size and size distribution. Investigation into the effect of ionic salts on the polishing mechanism reveals both a chemical and mechanical aspect to polishing silica wafers with silica slurries containing alkaline ionic salts.

Surface interaction forces in chemical-mechanical planarization

Abstract Understanding the role of surface intra-molecular forces is critical in a variety of aspects of chemical-mechanical polishing technology. In this paper we explore some of the critical areas where this is an important parameter, such as material removal mechanisms in oxide polishing. Particular attention is given to the use of coupling single particle atomic force microscopy experiments with FTIR and TEM studies of polished oxide surfaces in studying the possible role of surface hydration effects in chemical-mechanical planarization of oxide thin films.

Effect of Particle Size During Tungsten Chemical Mechanical Polishing

Abrasive particle size plays a critical role in controlling the polishing rate and the surface roughness during chemical mechanical polishing (CMP) of interconnect materials during semiconductor processing. Earlier reports on the effect of particle size on polishing of silica show contradictory conclusions. We have conducted controlled measurements to determine the effect of alumina particle size during polishing of tungsten. Alumina particles of similar phase and shape with size varying from 0.1 μm to 10 μm diameter have been used in these experiments. The polishing experiments showed that the local roughness of the polished tungsten surfaces was insensitive to alumina particle size. The tungsten removal rate was found to increase with decreasing particle size and increased solids loading. These results suggest that the removal rate mechanism is not a scratching type process, but may be related to the contact surface area between particles and polished surface controlling the reaction rate. The concept developed in our work showing that the removal rate is controlled by the contact surface area between particles and polished surface is in agreement with the different explanations for tungsten removal.

Fundamental Studies on the Mechanisms of Oxide CMP

In this paper, results of studies on the addition of salt to a polishing slurry, in terms of its effect on slurry stability, SiO 2 polishing rate and surface roughness of the polished surface are presented. Three salts, viz. LiCl, NaCl and KCl were selected, and three concentrations were tested. Polishing rate measurements using these slurries show that adding salt leads to increased removal rate without affecting surface roughness significantly. Based on these results, we can say that the agglomerates formed by adding salt to the slurry are fairly soft and easily broken during the polishing process. In addition, turbidity and particle size measurements show that significant coagulation of the particles in the slurry occurs only at the highest salt concentration, and is fastest for LiCl and NaCl, with KCl showing the slowest coagulation. From these results, it can be concluded that the enhancement in polish rate is due to increased contact at the wafer-pad-slurry interface, and not due to formation of larger agglomerated particles in the slurry. This is because of reduced electrostatic repulsion between these three surfaces, due to the screening of their negative surface charge by the metal ions in solution, resulting in a higher wear rate.