Liquid purification or separation – Processes – Including controlling process in response to a sensed condition
Reexamination Certificate
1998-12-03
2001-07-31
Walker, W. L. (Department: 1723)
Liquid purification or separation
Processes
Including controlling process in response to a sensed condition
C210S745000, C210S805000, C210S096100, C210S138000, C210S143000, C210S196000, C210S340000, C210S341000, C134S902000
Reexamination Certificate
active
06267894
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of rapid filtration of a chemical bath having particles therein of greatly varying sizes.
2. Brief Description of the Prior Art
Chemical baths, particularly such baths used in the fabrication of semiconductor devices, become contaminated with particles that may enter the bath from the semiconductor wafer introduced into the bath, from the chemical processing of the wafer, from the ambient and from countless other sources. Such contaminants can vary in size from very small to very large. It is necessary to remove these contaminants from the bath with increased requirement for removal of the very small particles as the geometry of the semiconductor devices is diminished.
Contaminant removal involves recirculation of the bath fluids through filters prior to reintroduction of the bath fluids back into the bath. The normal convention for recirculating and filtering a solution is to input the filtered solution into the tank bottom at the center of the tank and allow the solution being used in the tank to overflow over the tank top and into a wier with the overflow then being extracted from the bottom of the wier. In order to insure removal of the smaller particles, a small pore filter has been used which was capable of removing the smaller particles of interest. A problem with the use of such small pore filters is that the flow of fluid in the recirculation path is limited, thereby preventing rapid removal of all particles and particularly the larger particles. When larger pore sized filters have been used in place of the small pore filters, in situ particle monitors (ISPMs) have revealed a lower total particle count than when the smaller pore sized filter is used. This effect results from the fact that the bath fluid makes more passes through the filter and, presumably, the large particles trapped in the filter provide some filtering action also. However, this method still fails to remove a sufficient amount of the small particles for many types of devices and this problem will be exacerbated with the further diminution of device geometries. It is therefore apparent that a solution to the problem of particle removal is required wherein small particles can be removed in adequate amounts while filtration proceeds at a rapid rate.
BRIEF DESCRIPTION OF THE INVENTION
The above problem of filtration is minimized in accordance with the present invention.
Briefly, there is provided a dual path into the recirculation line, one path with large pore filtration having pores from about 0.2 to about 2.0 micrometers and the other path with small pore filtration having pores from about 0.001 to about 0.2 micrometers. It should be understood that the pore sizes of the filters will depend upon the requirements of the operation being conducted, it merely being necessary that the large pore filter be sufficiently large to trap a reasonable amount of the large particulate material and pass through the small particulate material with the small pores being generally from about 20 to about 80 percent of the size of the large pores. Programmability between the two paths is provided such that either or both paths can be used at any time. The programmability can be based upon any predetermined criterion, such as, for example, whether or not the bath is in use, the particle count in the recirculation line as determined by, for example, an ISPM, etc.
A first preferred embodiment of the filtration system in accordance with the present invention includes a single pump embodiment wherein effluent from a chemical bath is passed along two parallel paths, one path containing a filter with large pores and the other path containing a filter with small pores. The output of both filters is pumped back to the bath by a single pump. One or more controllable valves are provided in each path to control the flow to each of the filters whereby either filter, both filters or no filter can be in use at any time. The valves are under control of an external source such as, for example, an ISPM which can be in the recirculation path upstream or downstream of the filters or both.
A second preferred embodiment of the filtration system in accordance with the present invention includes a dual pump embodiment wherein effluent from a chemical bath is passed along two paths, one path containing a filter with large pores and the other path containing a filter with small pores. The output of each filter is separately pumped back to the bath. One or more controllable valves are provided in each path to control the flow to each of the filters whereby either filter, both filters or no filter can be in use at any time. The valves are under control of an external source such as, for example, one or more ISPMs which can be in the recirculation path upstream or downstream of the filters or in both locations.
The present invention provides flexibility in filtration to meet specific process requirements. Filtration is programmable to permit different filtration for product as against an empty bath, as a function of process time or dependence upon bath conditions as determined by ISPM. Also, often filtration is required before commencement of a fabrication process even when all or part of the bath has not previously been used since the addition of new materials into the bath can also introduce unwanted particles.
It should be understood that the filters used in accordance with the present invention can be any type of filter or filter-like material such as, for example, those that remove ionic, metallic, organic, bacterial, biologic or other specific contaminants in the stream.
REFERENCES:
patent: 2979160 (1961-04-01), Haas
patent: 4568438 (1986-02-01), Lauke
patent: 4659450 (1987-04-01), Lauke
patent: 5262047 (1993-11-01), Benskin et al.
patent: 5647386 (1997-07-01), Kaiser
Doshi Vikram N.
Drumm James M.
Guldi Richard L.
Brady III Wade James
Sorkin David
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
Valetti Mark A.
LandOfFree
Method for efficient filtration of chemical baths does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for efficient filtration of chemical baths, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for efficient filtration of chemical baths will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2566109