A method of generating a high-level vacuum comprises evacuating a chamber having a substantially-pure gas therein to a medium-level vacuum, and freezing the residual gas to generate the high-level vacuum within the chamber. Impurities, such as atmospheric air, may be purged from the chamber by evacuating the chamber to a medium level vacuum (e.g., around 10.sup.-2 Torr) and subsequently filling the chamber with the gas. This purging process may be repeated multiple times to decrease the level of impurities in the gas filling the chamber. The substantially-pure gas may have an impurity-level of less than approximately 100 PPM and may comprise carbon-dioxide, although the scope of the invention is not limited in this respect. The medium level vacuum may range between approximately 1.times.10.sup.-2 Torr and 5.times.10.sup.-2 Torr allowing the use of a roughing pump, and the high-level vacuum may range between approximately 1.times.10.sup.-5 and 1.times.10.sup.-8 Torr.