Ozone, a compound consisting of three oxygen atoms, is a highly efficient cleaner. When paired with an ultraviolet light source, ozone is able to clean nearly any surface rapidly and effectively. This has been confirmed through years of testing and research.
In the 1970s, a series of experiments first began to show the efficacy of UV cleaning, and eventually, the combination of UV and ozone. An early experiment in 1972 showed that UV light, combined with a quartz filter and a mercury lamp that generated ozone, was able to successfully aid the depolymerization of photoresist polymers.
Another experiment was able to demonstrate the ability of UV and ozone to clean hydrocarbons from glass and gold surfaces. The results indicated that absorbed hydrocarbons could be removed from these surfaces after 15 hours of exposure to the UV/Ozone mixture, and that storing the surfaces underneath the cleaner would allow that cleanliness to be retained indefinitely.
Another series of tests in the late 1970s demonstrated the ability of an UV/ozone mixture to cleanse surfaces in less than a minute, under optimal conditions. Since then, use of UV/ozone has been steadily increasing in many industries.
In order to determine the optimal conditions for UV/ozone cleaning, the experimenters began by creating two UV cleaning boxes, made out of aluminum. Both boxes contained mercury lamps, which would be used to generate different wavelengths of light, serving as the variable in the experiment. Only the light that is absorbed can be of use in cleaning, so it is important to determine what wavelengths are most efficiently absorbed.
Two different wavelengths were of the most interest to the experiment- 184.9nm and 253.7nm. The lights passed through three different envelope materials (quartz, high silica glass, and glass) at each wavelength. Quartz was able to lead to the creation of both 184.9nm and 253.7nm, while the glass envelopes could not produce both. The production of both wavelengths is significant. Ozone is created at the 184.9nm level, while the presence of 253.7nm helps in the destruction of ozone. If both are present, then there is a constant creation and destruction of ozone, which in turns encourages the formation of atomic oxygen, an exceptionally strong oxidizing agent.
While ozone and UV radiation combine to be a strong cleaner, the experimenters did find that gross contamination should be removed before the process. Pre-cleaning allows for the removal of contaminants like dust, which cannot be cleaned by the ozone and UV light. Also, it prevents contaminants from forming a shield against the UV rays through excessive buildup.
By removing the major contamination with another wash process, the UV and Ozone stage will be able to strip away the more difficult to reach, smaller, particles of contamination. The experiment shows that various methods, whether they are aqueous, solvent, or a combination will be adequate.
Depending on the amount of contamination and distance from the source of the cleaning mixture, the cleaning process can be remarkably quick. To measure this, the experimenters placed one piece of material to be cleaned 5mm from the light source in the first box and in the second box placed a piece of material at 8cm. The piece located at 5mm was cleaned 10 times faster than the sample at 8cm.
With a combination of wavelengths at 184.9nm and 253.7nm through the use of a quartz filter, a small distance from the light source, and a pre-cleaning, the sample materials were cleaned in approximately 10 seconds. The materials reached a remarkably high standard of cleanliness in this method- it produced near-atomically clean surfaces, as evidenced by Auger electron spectroscopy (AES), electron spectroscopy for chemical analysis (ESCA), and ion scattering spectroscopy/secondary ion mass spectroscopy (ISS/SIMS) studies.
UV/Ozone cleaning has many applications. It can be used to clean semi-conductors, as it was in the experiment. It can also be effective in cleaning water. The cleaning combination has shown the ability to clear water of toxic contaminants like ethanol, medical waste, and pesticides. Further tests on the subject of water cleaning with UV/Ozone have shown that using the two in conjunction is more effective than using either alone.
This method of cleaning works well on many flat surfaces provided the proper setup is used. As long as the surface to be cleaned has had gross contamination removed, is properly exposed to the light, and given the optimal amount of time to be cleaned, UV/Ozone cleaning will produce a nearly completely clean surface by any measurement.
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