Atomic force microscopy study of the role of molecular weight of poly(acrylic acid) in chemical mechanical planarization
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Jea-Gun Park Nano-SOI Process Laboratory, Hanyang University, Seoul 133-791, Korea
Wolfgang M. Sigmund Department of Materials Science and Engineering, University of Florida, Gainesville, Florida, 32611-6400 (Received 21 August 2005; accepted 31 October 2005)
The influence of the molecular weight of poly(acrylic acid) (PAA) on chemical mechanical planarization (CMP) for shallow trench isolation (STI) was investigated. The adsorption behaviors of PAA as a function of molecular weight on deposited plasma-enhanced tetraethylorthosilicate and chemical vapor deposition Si3N4 films were analyzed by the force measurement using atomic force microscopy (AFM). The AFM results revealed that the affinity of PAA with the nitride film is higher than the affinity with the oxide film, and thus a denser adsorption layer on the nitride film is formed with higher molecular weight of PAA, which leads to higher selectivity in STI CMP. Additionally, to determine the correlation between the dispersion stability of the CeO2 resulting from the presence of PAA with different molecular weight and CMP performance, the colloidal properties of the slurry as a function of the molecular weight of PAA were examined.
I. INTRODUCTION
Shallow trench isolation (STI) is one of the most important applications of chemical mechanical polishing (CMP) technologies and has replaced the local oxidation of silicon (LOCOS) method in the ultralarge scale integration (ULSI) process.1–4 The most important advantage of STI CMP is to significantly reduce the area required to isolate transistors, enhancing the device density. STI CMP also offers a high degree of planarity, which is necessary to meet stringent photolithography requirements. The selectivity of the removal rate between the oxide and nitride layers is a critical factor in the STI CMP process because it can determine the STI process margin. To meet this demand, the CeO2 slurry is being widely used for STI CMP because CeO2 slurry offers a higher oxide-to-nitride selectivity, minimizing nitride loss while maintaining a high oxide removal rate compared to that of the conventional SiO2 slurry.5,6 High oxide-to-nitride selectivity can be obtained by considering both the physical properties of the abrasive particles
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0054 J. Mater. Res., Vol. 21, No. 2, Feb 2006
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and the chemical contribution of the organic additives in the slurry.7 Generally, it is accepted that the physical properties of the abrasive particles mainly affect mechanical removal of the wafer surface.7–11 However, a modulation of the slurry chemistry by the presence of organic additives in the slurry also plays an important role in determining the selectivity. In previous works,8,11,12 the role of the organic additives in the CeO2 slurry for STI CMP performance and the resulting interactions between the abrasive and the deposited films were investigated. The addition of the sufficient polymer
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