Junji Sugamoto

Influence of annealing ambient on oxygen out-diffusion in Czochralski silicon

The out-diffusion of oxygen in Czochralski grown silicon (100) wafers annealed at high temperature under a hydrogen or an argon ambient has been investigated by secondary ion mass spectrometry (SIMS). The wafers were annealed with three successive process: loading of wafers into furnace at 850 °C then ramping up, annealing at 1200 °C for 1 h, and ramping down from 1200 to 850 °C. It was found that oxygen diffusivities obtained from the above two kinds of samples showed almost the same values. Also, no difference in the oxygen concentration of the subsurface region in Si was observed between the above two kinds of samples within SIMS detection limit of 2×1016 atoms/cm3. The result indicates that there is no significant difference in oxygen diffusivity between the two annealing ambients of hydrogen and argon gases.

Analysis of wafer flatness for CD control in photolithography

Wafer-induced focus error is investigated for analysis of our focus budget in photolithography. Using a newly developed wafer monitor, NIWF-300 (Nikon Corp.), we directly measure surface flatness of the wafer placed on wafer holder with vacuum chuck. Single site polished Si wafers were evaluated with NIWF-300 and a conventional flatness monitor. We also investigated the effect of wafer holder using a ring-shape wafer support and a pin-shape wafer support. As a result, we found wafer shape measured in a freestanding condition does not represent surface flatness of the wafer on a holder. The holder has an impact on the wafer surface. The increase of adsorption ratio between wafer and holder improves the surface flatness.

Determination of Surface Impurities on a Gallium Arsenide Wafer by Inductively Coupled Plasma Mass Spectrometry

The surface impurities on a GaAs wafer were determined by inductively coupled plasma mass spectrometry to clarify the diffusion behavior which affected the layer construction. The sample was etched by hydrofluoric acid in a PTFE vessel at room temperature. Depth analysis of the wafer was performed by repeated etching as impurities were thought to exist near the wafer surface. Copper was difficult to dissolve by hydrofluoric acid due to an ionization tendency compared to the hydrogen ion. The method used in this study was demonstrated to be effective for determining surface impurities on a GaAs wafer for an impurity level of 1011 atoms/cm2 and for analyzing depth profiles from the surface.