Metal Oxide Thin Film Characterization for New Generation Chemical Mechanical Planarization Development
Authors: Basim G. Bahar , Karagoz Ayse 
Published: February 2020

This study targeted to create a basis for the new generation semiconductor industry that deals with atomic scale devices and also expected to be utilized in many other fields such as advanced coatings, interfacial adhesion, biological systems i.e. corrosion prevention and enhanced biocompatibility of bio-implants and nano/bio interfaces. We focused on the accomplishments on the microelectronics applications of the CMP process as it is used for the current and future semiconductor applications, such as metal CMP applications of the tungsten T-gate transistors, high speed shallow trench isolation transistors with germanium and furthermore isolating thin films for advanced microelectronics applications such as encapsulation of the PZT arrays of the ferroelectric memory applications.  The second part focused on the applications of the CMP induced metal oxide thin films on biomaterials and conventional metals such as steel that is used for heating elements and aluminum that is being used for airplane bodies to improve the corrosion resistance.

First of all, a fundamental understanding on the growth of nano-scale protective oxide thin films was studied to determine the effect of oxidizer type and proper oxidation time on the changes in surface properties of the thin films. The preliminary model was developed on the very well established tungsten, which is being utilized as a gate dielectric for the novel T-gate transistors currently. Thin film analyses were conducted through advanced characterization techniques and also compared to the theoretical calculations for the modeling simulations. Atomic Force Microscope (AFM) was used to measure the surface roughness of the samples conditioned in the oxidizer environment before and after the CMP was conducted.  The affect of surface roughness on wettability of the surfaces studied through contact angle measurements on the treated tungsten films. Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance FTIR/ATR technique in combination with the X-Ray Reflectivity (XRR) was utilized to determine the thicknesses of the oxidized nano films on the tungsten wafers.  The results were evaluated through the comparison of the Pilling-Bedworth ratios of the oxidized nano films to determine the ability of the created oxide films as a self-protective oxide [1].  Furthermore, a new modeling approach was introduced to CMP process optimization by means of topographic evaluation of the metal oxide thin films.  Cahn Hilliard Equation (CHE) was utilized as an alternative to classical nucleation theory in terms of analyzing the topographic nature of the protective metal oxide nano films and modeling their growth, which was observed to affect the CMP performance. It was concluded that the material removal rate mechanisms and the consequent planarization performance depend on the nature of nucleation of the metal oxide films, which is tailored by the oxidizer concentration.

The basic knowledge defined on the chemically modified thin films were also expanded to the germanium CMP applications. Particularly, formation and selective removal of chemically modified germanium/silica thin films in the presence of cationic and anionic surfactants were evaluated through AFM wear tests as well as CMP and surface wettability responses. It was determined that while the self-assembled surfactant structures help improve slurry stability, they may retard the material removal rates by inhibiting the particle surface interactions. The results of this study have shown that in the presence of hydrogen peroxide in the slurry, removal rates were mainly affected by the oxidizers surface activity resulting in the formation of germanium oxide film. However, surface quality and the selectivity of the Ge/SiO2 systems were tuned through adjusting the concentration of the oxidizer and surfactant type/chain length in the system to optimize the planarization performance [2].

References

Karagoz, A., Craciun, V., Basim, G.B., “Characterization of Nano-Scale Protective Oxide Films_ Application on Metal Chemical Mechanical Planarization”. ECS Journal of Solid State Science and Technology, 4 (2) P1- P8 (2015)

Karagoz, A., and Basim, G.B. “Controlling Germanium CMP Selectivity through Slurry Mediation by Surface Active Agents”, ECS Journal of Solid State Science and Technology, CMP Special Issue, 4 (11) P5097-P5104 (2015).