AFM analysis of HF Vapor Cleaned SiO 2 Surfaces
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R.J. Carter%, E.J. Bergman"*, D.R. Lee'**, J. Owyang"*, and R.J. Nemanich÷' "Department of Materials Science and Engineering and 'Department of Physics, North Carolina State University, Raleigh, NC 27695-8202; Semitool, West Reserve Dr., Kalispell, MT 59901; ***LSI Logic,655 3115 Alfred St., MS J-202, Santa Clara, CA 95054; Abstract Si(100) surfaces were cleaned using HF/IPA vapor chemistries at ambient pressure and temperature with nitrogen as the carrier gas. Three distinct cases for oxide removal were studied: vapor etching of native oxides, RCA chemical oxides, and thermal oxides. Atomic Force Microscopy (AFM) was used to characterize the surface morphology after the HF vapor etching process. The AFM indicated exaggerated peaks in random places on the surface, These peaks were identified as residue remaining after the vapor etching process. The average lateral width of the peaks were - 50 nm. The average height of the peaks for native and chemical oxide etched surfaces was relatively the same, approximately 8 nm. The average height of the peaks after thermal oxide removal was significantly smaller, approximately 1-2 nm. Peak density for native oxide etched surfaces was significantly greater than chemical or thermal oxide etched surfaces. We suggest that impurities in the oxide contribute to residue formation on the surface. Introduction As device geometries shrink, the move towards vapor and gas phase cleaning becomes more critical. HF vapor cleaning has shown distinct advantages over conventional aqueous cleaning, such as: cleaning high aspect ratios, reduced contamination, improved process uniformity, clustertool integration, and reduced chemical consumption [1,2]. The use of HF/H 20 vapor has shown good thermal to deposited oxide etch selectivity [3-5]. However, H20 as the solvent for HF has been shown to result in surfaces with high particle counts [6]. Water is a byproduct of the vapor etching reaction and it is the least volatile species of the reaction. It has been speculated that particles in the form of Si(OH), will result and remain on the wafer surface if the water by-product is not volatilized [7,8]. A drying agent, such as alcohol (IPA, Methanol, or Ethanol), may be employed to volatilize the by-product [7,8]. The employment of alcohols has resulted in reduced particle contamination, increased wafer uniformity, and increased device yield [91. In this study vapor etching for surface oxide removal will be investigated for three distinct surfaces: a native oxide, an RCA chemical oxide, and a thermal oxide. After the vapor etching process, AFM analysis will be done to characterize the surface morphology. Based upon results it was found that, while particle contamination was controlled, vapor etching still resulted in surface residue. Particle counters currently do not have the capability to detect this surface residue, 481
Mat. Res. Soc. Symp. Proc. Vol. 477 0 1997 Materials Research Society
because residue size is much smaller than that of detectable particles. residue has been indicat
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