X-ray photoelectron spectroscopy study of low-temperature molybdenum oxidation process J. Appl. Phys. 85, 8415 (1999); 10.1063/1.370690 X-ray photoelectron spectroscopy and x-ray diffraction study of the thermal oxide on gallium nitrideThe authors present the application of synchrotron Bragg diffraction, x-ray reflectance ͑XRR͒, and x-ray photoelectron spectroscopy ͑XPS͒ to study silicon loss in the low temperature plasma oxidation of silicon-on-insulator ͑SOI͒ wafers. The Laue oscillations of the Si͑004͒ Bragg peak provide a direct measure of the number of lattice planes that are consumed in the silicon device layer during processing, while the Fourier transform of the XRR data provides a model-independent determination of the increase in the combined thickness of the silicon and surface oxide. XPS measurements provide complementary information concerning changes in thickness, chemical composition, and the bonding of the surface oxide. These methods were applied to samples processed in an oxidizing plasma system at temperatures below 250°C. The authors find that 2.7Ϯ 1 Å of silicon, corresponding to two lattice planes, is consumed while the combined thickness increases by 2.7Ϯ 0.8 Å, corresponding to a net increase in the oxide thickness of 5.4Ϯ 1.3 Å. Thus, the ratio of oxide growth to silicon loss is about 2.0Ϯ 0.9, somewhat lower than the bulk ratio of 2.2, but within experimental error. The XPS measurements show the increase to be 5.5 Å. Additionally, XPS shows clearly the consumption of silicon to form Si 2 O and SiO 2 and the net oxidation of Si 2 O 3 to SiO 2 .
The authors describe a plasma ashing system where a stationary jet of hot, activated gases removes photoresist from a scanning wafer. The jet is created by a reactant stream flowing through a 2.45GHz surface wave discharge in a 6mm quartz tube. For O2∕N2 plasmas in the medium pressure range from 20to100Torr, a luminous plasma jet emerges from the end of the discharge tube that transports both heat and reactive species to the wafer. A single scan results in a Gaussian track profile with a standard deviation of 7mm for the source-to-substrate distance of 9mm. A simple model of the ashing process, which assumes a thermally activated ash rate and Gaussian distributions for both power density and reactant flux, unifies the dependence of effective ash rate on the substrate temperature and scan speed at a constant power. The best fit activation energy at 2.5kW is 0.23eV, about half of the value found in conventional downstream ashing, implying that diffusion plays a significant role in limiting the ash rate. The peak thermal power density in a 2.5kW jet at 80Torr is 160W∕cm2, resulting in an effective instantaneous ash rate of 2.5mm∕min for a scan speed of 70cm∕s and 200°C chuck temperature. This implies that the time to clear a 1.2μm thick resist coating from a 300mm wafer is 18s.
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