Method using megasonic energy in liquefied gases

Claim 1

A process for removing undesired sub-micrometer particulates from a surface of a substrate comprising the steps of: (a) placing said substrate containing said undesired particulates having a size of 1.0 micrometer or less in a cleaning chamber provided with (1) means for supporting said substrate in said cleaning chamber, (2) megasonic energy-producing transducer means attached to said means for supporting said substrate and oriented so as to emit megasonic energy parallel to said surface of said substrate, and (3) means for deflecting said megasonic energy so as to prevent said megasonic energy from destructively interfering with itself; (b) introducing into said cleaning chamber a fluid selected from the group consisting of (1) a liquefied gas, (2) a mixture of liquefied gases, and (3) a liquefied gas containing less than 50 vol/vol percent of a liquid modifier, said liquid modifier added to increase solubility properties of said gas, said fluid formed by applying a pressure of about 600 to 3,000 pounds per square inch (42.2 to 210.9 Kg/cm 2 ) at a temperature of up to about 50° C. thereto, and contacting said substrate containing said undesired particulates with said fluid at a temperature below the critical temperature of said gas, said gas selected from the group consisting of carbon dioxide, nitrogen, nitrous oxide, sulfur hexafluoride, and xenon and mixtures thereof; and (c) exposing said fluid in said cleaning chamber to said megasonic energy transducer means emitting a frequency ranging from about 110 to 2,000 Kilohertz to generate a series of pressure waves applied parallel to said surface for a period of time sufficient to thereby remove said undesired sub-micrometer particulates from said substrate.