Zefang Zhang

Two-Step Chemical Mechanical Polishing of Sapphire Substrate

Chemical mechanical polishing CMP , as a widely used planarization technology, requires high removal rate and low surfaceroughness generally. However, it is difficult to meet these requirements in a single-step polishing process. To get an ultrasmoothsurface of the sapphire substrate, we investigated a two-step CMP of the sapphire substrate using ultrafine -alumina-based slurryand nanoscale silica-based slurry. Also, in situ coefficient of friction COF measurements were conducted. The results show thatduring the first-step polishing in the alumina-based slurry, the COF decreases with polishing time first and then tends to be aconstant; a relatively high material removal rate was reached, and the root-mean-square rms roughness value of the polishedsurface can be decreased from 968.9–21.98 A. In the second-step CMP, the nanoscale silica slurry was adopted; the COF increasedin the first minute of polishing and then became stable too, and the rms roughness of the sapphire substrate surfaces can be furtherreduced to 6.83 A by using the optimized process parameters. In addition, the CMP mechanism of sapphire using the above twoslurries was deduced and documented preliminarily.© 2010 The Electrochemical Society. DOI: 10.1149/1.3410116 All rights reserved.Manuscript submitted July 20, 2009; revised manuscript received March 27, 2010. Published May 3, 2010.

Particle size and surfactant effects on chemical mechanical polishing of glass using silica-based slurry

This study explores the effect of particle size and surfactant on the chemical mechanical polishing (CMP) of glass using colloidal silica-based slurry. It was found that the material removal rate strongly depends on the particle size and the types of surfactants and that the rms roughness was independent of particle size and correlated to surfactants. On the basis of polishing results, it was concluded that the main polishing mechanism was changed from indentation mechanism to surface-area mechanism, with the variation of particle size. In addition, the molecular structure, charge type, and lubricating effect of the surfactants play an important role in the dispersion of abrasive particles and in the CMP performance.

Influence of pH and abrasive concentration on polishing rate of amorphous Ge2Sb2Te5 film in chemical mechanical polishing

This study explores the effect of pH and abrasive concentration on the chemical mechanical polishing (CMP) of blank amorphous Ge2Sb2Te5 (GST) film using the colloidal silica-based slurry. It was found that material removal rate (MRR) strongly depends on the pH and abrasive concentration. When using only pH adjusted de-ionized water, the MRR decreases as the pH was raised or lowered toward neutral, which indicates that chemical effects dominate in the polishing rates. However, electrostatic interactions between the abrasive particles and the surface of GST control the polishing rate with the variation in pH when the silica-based slurry was used. In addition, MRR was proportional to abrasive concentration and MRR per abrasive particle was calculated to explain the effect of abrasive concentration on GST CMP. With the variation of abrasive concentration, MRR is strongly correlated with coefficient of friction.

Chemical Mechanical Polishing of Ge2Sb2Te5 Using Abrasive-Free Solutions of Iron Trichloride

Chemical mechanical polishing (CMP) of amorphous Ge2Sb2Te5 (GST) is studied using aqueous solutions of iron trichloride (FeCl3) as possible abrasive-free slurries. The polishing performance of abrasive-free solutions is compared with abrasive-containing (3wt% colloidal silica) slurry in terms of polishing rate and surface quality. The experimental results indicate that the abrasive-free solutions have a higher polishing rate and better surface quality. In order to further investigate the polishing mechanism, post-CMP GST films using the abrasive-free solutions and abrasive-containing slurry are characterized by x-ray photoelectron spectroscopy. Finally, it is verified that the abrasive-free solutions have no influence on the electrical property of the post-CMP GST films through the resistivity test.

A nano-scale mirror-like surface of Ti?6Al?4V attained by chemical mechanical polishing*

Metal Ti and its alloys have been widely utilized in the fields of aviation, medical science, and micro-electro-mechanical systems, for its excellent specific strength, resistance to corrosion, and biological compatibility. As the application of Ti moves to the micro or nano scale, however, traditional methods of planarization have shown their short slabs. Thus, we introduce the method of chemical mechanical polishing (CMP) to provide a new way for the nano-scale planarization method of Ti alloys. We obtain a mirror-like surface, whose flatness is of nano-scale, via the CMP method. We test the basic mechanical behavior of Ti?6Al?4V (Ti64) in the CMP process, and optimize the composition of CMP slurry. Furthermore, the possible reactions that may take place in the CMP process have been studied by electrochemical methods combined with x-ray photoelectron spectroscopy (XPS). An equivalent circuit has been built to interpret the dynamic of oxidation. Finally, a model has been established to explain the synergy of chemical and mechanical effects in the CMP of Ti?6Al?4V.

Synthesis of Spherical-like Ceria Particle with PVP as Assistant Agent and Its CMP Performance on Shallow Trench Isolation

Chemical Mechanical Polishing (CMP) has become a widely accepted global panarization technology. Abrasive is one of the key elements during CMP process. Du to its high selectivity, ceria particle is often used as abrasive in shallow trench isolation (STI) CMP slurries. But its irregular shape and agglomeration is not acceptable. In the present work, the spherical-like ceria nano-particles were successfully synthesized by homogeneous precipitation of ammonium cerium nitrate and urea, with Polyvinylpyrrolidone (PVP) as assistant agent. The precipitated ceria particles were characterized by means of XRD, FTIR, SEM and EDS as well as Zeta potential test. The results indicated that these nano-particles had a good dispersibility in water media without addition of any extra dispersing agent. Then, the CMP performance of these nano-particles on STI was investigated. The results indicated that they exhibited high removal selectivity (10.8:1) between silicon dioxide and silicon nitride without any additives.