CO2 snow cleaning technology has demonstrated the ability to clean a variety of contamination types in a non damaging, environmentally friendly manner. CO2 snow cleaning methods have been used to clean both particles and light organics and currently can be found in a variety of high tech industries to include, semiconductor (Si and GaAs), flat panel display, disk head and media manufacturing, and fiber optics. This paper offers an introduction to basic CO2 properties and cleaning methods in general and photomask cleaning in particular. Focus will be placed on the CO2 snow cleaning method to include: the snow making process, process parameters, process issues, contaminant types, CO2 sources and specification, and safety. A new CO2 snow system to clean current and next generation photomask substrates has been developed and is currently being tested. Machine specifics, process parameters, process issues, and cleaning data, will be discussed in detail.