Influence of the electrokinetic behaviors of abrasive ceria particles and the deposited plasma-enhanced tetraethylorthos
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Takeo Katoh and Jea-Gun Park Nano Silicon on Insulator (SOI) Process Laboratory, Hanyang University, Seoul 133-791, Korea (Received 13 January 2003; accepted 17 June 2003)
The effects of the electrokinetic behavior of abrasive ceria particles suspended in an aqueous medium and the deposited plasma-enhanced tetraethylorthosilicate (PETEOS) and chemical vapor deposition (CVD) Si3N4 films on chemical mechanical planarization (CMP) for shallow trench isolation were investigated. The colloidal characteristics of ceria slurries, such as their stability and surface potential, in acidic, neutral, and alkaline suspensions were examined to determine the correlation between the colloidal properties of ceria slurry and CMP performance. The surface potentials of the ceria particles and the PETEOS and CVD Si3N4 films in an aqueous suspending medium were dependent on the pH of the suspending medium. The differences in surface charges of ceria particles and the PETEOS and CVD Si3N4 films have a profound effect on the removal rate and oxide-to-nitride selectivity of CMP performance.
I. INTRODUCTION
One of the most important applications of chemical mechanical planarization (CMP) is in shallow trench isolation (STI) on silicon substrates.1–5 STI replaced local oxidation of silicon for isolation formation when the feature size is smaller than 0.35 m.6 A wide range of global planarization is required to attain a sufficient depth of focus with the process margin of exposure equipment for the fine patterns of process technology. CMP consists of a chemical effect from the nanoceramic particulate slurry and a physical effect from the pressed pad and abrasive particulates.7 Among the many abrasives used in CMP polishing slurry, ceria, which is used mainly in optical lens polishing, is being increasingly used for STI.8–10 Compared with other abrasive slurries, ceria slurry has a good selectivity in polishing rates between the SiO2 and Si3N4 chemical vapor deposition (CVD) films.11 STI CMP processes with conventional
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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 18, No. 9, Sep 2003
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oxide slurries (e.g., silica and alumina slurry) require an additional process, a reactive ion etching (RIE) etchback preplanarization step, to precisely control the CMP process. This is primarily due to the low removal rate selectivity of conventional slurries between the SiO2 and Si3N4 CVD films (i.e., 4:1 at most).12 For the STI CMP process, high oxide-to-nitride selectivity is very important to ensure that the polishing process stops at the Si3N4 CVD film surface. The oxide-to-nitride selectivity can affect CMP-induced defects, such as erosion or dishing, and can also be important for endpoint detection. STI CMP performance depends on several processes such as deposited nitride thickness, trench depth, thickness and type of deposited trench-fill oxide, removal rate consistency, the physicochemical nature of CeO2 particles, organic additives, and susp
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