Xiaokai Hu

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.

Measurement and simulation of thermoelectric efficiency for single leg.

Thermoelectric efficiency measurements were carried out on n-type bismuth telluride legs with the hot-side temperature at 100 and 150°C. The electric power and heat flow were measured individually. Water coolant was utilized to maintain the cold-side temperature and to measure heat flow out of the cold side. Leg length and vacuum pressure were studied in terms of temperature difference across the leg, open-circuit voltage, internal resistance, and heat flow. Finite-element simulation on thermoelectric generation was performed in COMSOL Multiphysics, by inputting two-side temperatures and thermoelectric material properties. The open-circuit voltage and resistance were in good agreement between the measurement and simulation. Much larger heat flows were found in measurements, since they were comprised of conductive, convective, and radiative contributions. Parasitic heat flow was measured in the absence of bismuth telluride leg, and the conductive heat flow was then available. Finally, the maximum thermoelectric efficiency was derived in accordance with the electric power and the conductive heat flow.

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.

Preparation of Silica Abrasives from Water Glass and Application in Silicon Wafer Polishing

Chemical mechanical polishing technique is more frequently adopted for planarization in integrated circuit fabrication. The silica abrasives in colloidal state are fabricated with the sodium silicate solution as raw materials through the polymerization reaction among silicic acid molecules. By continuous injection of silicic acid into the preexisting silica solution, the diameter of silica nanoparticles increases. The different sized silica nanoparticles are imaged by scanning electron microscopy, and the dried silica are characterized by X-ray diffraction and thermal analysis. The polishing test on silicon wafer with as-fabricated silica abrasives shows that the surface flatness reaches 1.1 nm roughness, however, micro scratches are still present in the surface.