Effects of abrasive particle size and molecular weight of poly(acrylic acid) in ceria slurry on removal selectivity of S
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Hyung-Soon Park Hynix Semiconductor Inc., Icheon-si, Kyungki-do 467-701, Korea
Ungyu Paika) Division of Advanced Materials Science Engineering, Hanyang University, Seoul 133-791, Korea
Jea-Gun Parkb) Nano-SOI Process Laboratory, Hanyang University, Seoul 133-791, Korea (Received 14 August 2006; accepted 13 December 2006)
The effects of the molecular weight and concentration of poly(acrylic acid) (PAA) with different primary abrasive sizes in ceria slurry on the nitride film loss, removal rate, film surface roughness, and removal selectivity of SiO2-to-Si3N4 films were investigated by performing chemical mechanical polishing (CMP) experiments using blanket and patterned wafers. In the case of the blanket wafers, we found that for a lower PAA molecular weight, the removal selectivity of SiO2-to-Si3N4 films increased more significantly with increasing PAA concentration in slurry containing a larger primary abrasive size. For the patterned wafers, with a higher PAA molecular weight in the ceria slurry suspension, the erosion of the Si3N4 film was less, but the removed amount was also smaller, and the surface roughness became worse after CMP. These results can be qualitatively explained by the layer of PAA adsorbed on the film surface, in terms of electrostatic interaction and rheological behavior.
I. INTRODUCTION
Chemical mechanical polishing (CMP) has emerged with rapid growth as a process for device fabrication in the semiconductor manufacturing industry, and it is expected to show further rapid growth as the device design rule shrinks. Specifically, the shallow trench isolation (STI) method, which has been used in advanced sub-250nanometer integrated semiconductor device manufacturing, applies CMP to planarize gap-fill SiO2 layers deposited on the front surfaces of wafers.1,2 During the STI process, the active region where transistors are fabricated is generally covered with Si3N4 film.3 The Si3N4 film acts as a mask for protection against reactive ion etching (RIE) during the trench formation step and as a barrier that stops the polishing process immediately after complete removal of the SiO2 film. Ceria (CeO2) slurries with organic additive are widely used in STI-CMP4,5 Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/JMR.2007.0097 J. Mater. Res., Vol. 22, No. 3, Mar 2007
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because they have high removal selectivity of SiO2 with respect to Si3N4 and widen the process margin in mass production. In addition to the high removal selectivity, ceria slurries also minimize the Si3N4 film loss while maintaining a high SiO2 removal rate.6,7 To achieve these benefits, however, the STI process itself must be optimized, and the material and consumable characteristics, such as the slurry performance and the nanoscale topography of the wafer surface and polishing pad, must be thoroughly investigated.8–10 To improve the performance of high-selectivity ceria slurry in STI-CMP, it is essential to con
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