Method and apparatus for creating an open cell micro-environment for treating a substrate with an impingement spray

#The present invention relates generally to the field of cleaning or treating miniature electromechanical device surfaces with cryogenic impingement sprays. More specifically, the present invention relates to the field of environmental control for performing cryogenic spray cleaning processes. Conventional precision cleaning processes using cryogenic particle impingement sprays such as solid phase carbon dioxide require control of the atmosphere containing a treated substrate to prevent the deposition of moisture, particles and other such contaminants onto cleaned surfaces during and following cleaning treatments.

#Environmental control is required because of localized atmospheric perturbations created by the low temperatures and high velocities which are characteristic of these impingement cleaning sprays.

#For example, snow particles having a surface temperature of −100 F. and traveling through the space between the spray nozzle and substrate are continuously sublimating in transit and upon impact with a substrate surface. This rapidly lowers local ambient atmospheric temperature—causing the contaminants contained therein to condense or “rain-out” of the local atmosphere and onto treated substrate surfaces during or following spray treatments. Moreover, the cleaning spray stream exhibits lower internal pressure than the 3 surrounding atmosphere (Bernoulli Principle) and creates venturi currents adjacent to the flow of the stream. These venturi currents cause the local atmosphere surrounding the stream to collapse into the spray stream above the substrate—thus entraining and delivering a mixture of cleaning spray and atmospheric constituents to the substrate. Finally, static charge build-up and accumulation are common to cryogenic sprays due the dielectric and tribocharging characteristics. This presents two problems—potential device damage from electrostatic overstress (EOS) or discharge (ESD) events and attraction of atmospheric contaminants to treated substrates via electrostatic attractive forces.

#These and other objects and advantages of the present invention will be obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments, which are illustrated in the various figures.

#FIG. 1a is an exemplary conventional isolation technique utilizing a closed cabinet with re-circulating laminar flowing filtered air.

#FIG. 1b is an exemplary conventional isolation technique utilizing a open work bench with laminar flowing filtered air.

#Referring to FIG. 1a,an exemplary conventional isolation technique employs a fully enclosed, controlled environment work stations with a HEPA-Filtration system. In these systems, the entire cleaning system equipment and process is integrated inside the clean chamber (2), which requires careful selection and design of internal components and subassemblies so as to not create particle contamination during operation. This design isolates the equipment, process and substrates from the outside environment (4) making it suitable in any type of ambient factory environment—controlled or uncontrolled. However, this approach is the most complex and costly of all isolation techniques and only allows for batch product flow through the system. This approach is best exemplified by the commercial snow cleaning system marketed by ATS-EcoSnow Systems, Livermore, Calif.

#Referring to FIG. 1b,—an exemplary conventional isolation technique employs an open and unitized work bench with vertical or horizontal flow HEPA-Filtration. In these systems, the work station flows clean air over a clean area comprising, for example, a table-top incorporating a cleaning system, automation and subassemblies. This approach is similar to that described in FIG. 1a, except that this approach is not suitable for use within highly controlled environments such as Class 100 clean rooms. Ambient atmosphere (6) is filtered and flows over the equipment and process (8) and is discharged back into the ambient atmosphere (10). Although this approach allows for incorporating a continuous conveyor for in-line or on-line applications, it suffers from lack of overall efficiency since the clean atmosphere is continuously created and discharged into the ambient environment.

#Referring to FIG. 1c, an exemplary conventional isolation technique employs a glove box with inert gas purging. In these systems, the work cabinet is continuously purged with clean inert gas (12), wherein the substrate is placed into the cabinet (14) through some type of door and spray cleaned. This approach also suffers from loss of controlled atmosphere to the ambient atmosphere (16) and does not allow for in-line or on-line automation of the cleaning operation.