Cleaning and liquid contact with solids – Apparatus – With non-impelling fluid deflector or baffle other than...
Reexamination Certificate
1999-04-27
2001-04-03
Stinson, Frankie L. (Department: 1746)
Cleaning and liquid contact with solids
Apparatus
With non-impelling fluid deflector or baffle other than...
C134S184000, C134S902000, C211S041180
Reexamination Certificate
active
06209555
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to substrate holders, and more particularly to a substrate cassette for optimizing megasonic cleaning of substrates supported therein.
In the production and manufacture of electrical components, it is a recognized necessity to be able to clean, etch or otherwise process substrates to an extremely high degree of cleanliness and uniformity. Various cleaning, etching, or stripping processes may be applied to the substrates a number of times in conjunction with the manufacturing steps to remove particulates, predeposited layers or strip resist, and the like.
One cleaning process that is often employed involves ultrasonic cleansing; that is, the application of high amplitude ultrasonic energy to the substrates in a liquid bath. More specifically, the ultrasonic energy is generally, but not limited to, the range of 0.60-1.00 MHz, and the process is termed megasonic cleaning. The liquid bath may comprise deionized water, standard cleaning solvents, dilute HF, sulfuric, phosphoric, organic strip, or the like. The amplitude and the length of time of application of the sonic energy are generally well known in the prior art.
Substrates are typically processed in batches, and likewise are generally cleaned in batches. For example, it is known in the prior art to support 20-50 substrates in a holder immersed in a megasonic bath for cleaning purposes. The holder (hereinafter, substrate cassette) maintain the substrates in a parallel array in regular spacing. It is known that megasonic energy is highly directional, and typically tends to impinge on the substrates in the cassette in an uneven manner. That is, the structural components of the substrate cassette comprise obstacles that block direct line-of-sight application of the sonic energy to some portions of some of the substrates, thereby reducing the effectiveness of the megasonic cleaning, etching, or stripping process and ultimately leading to a reduction in yield of those substrates.
One approach to overcoming this problem involves rotation of the substrates in the megasonic bath to expose all surface areas to sonic energy in a more uniform manner. Ironically, this tactic requires a cassette that is larger and more intricate than the stationary substrate cassettes, thereby blocking more of the megasonic energy. Moreover, the edge supports of the rotating substrates create friction and abrasion of the substrate edge surfaces, increasing the possibility of damage to the substrates as they are being cleaned or otherwise processed.
It is also possible to physically move the megasonic transducers in an attempt to eliminate the shadowed areas of the substrates in the cassette. This approach also leads to similar drawbacks and complexities that are not amenable to mass production and reliable results.
SUMMARY OF THE INVENTION
The present invention generally comprises a substrate cassette that is designed to support a plurality of substrates during megasonic cleaning, etching, or stripping. A salient aspect of the cassette is that it couples the megasonic energy from the cleaning or processing bath into the substrates supported in the cassette, thereby eliminating sonic-shadowed areas of the substrates and maximizing the cleaning, etching, or stripping performance of the megasonic bath.
The substrate cassette includes a pair of end panels spaced apart longitudinally, and a plurality of longitudinal supports extending between the end panels. The supports include a pair of side rails extending longitudinally along opposed sides of the cassette, and at least one bottom support extending between lower portions of the end panels. The supports are each provided with a plurality of shallow channels extending laterally therein and spaced regularly therealong, each channel disposed to receive an edge portion of a substrate. The channels of all the longitudinal supports are disposed in serial registration, so that a plurality of substrates may be supported in parallel, spaced apart fashion generally perpendicular to the longitudinal axis of the cassette.
The longitudinal supports and channels of the substrate cassette are all formed of plate components that are dimensioned to transmit the maximum mount of the megasonic energy projected into the cleaning, etching, or stripping bath, so that the components do not cause sonic-shadowing of the substrates supported in the cassette. In particular, the side rails and bottom supports are formed of narrow plates having a thickness equal typically to one wavelength of the ultrasonic energy in the material that comprises the side rails and bottom supports. Alternatively, the thickness dimension may be comprised from an integer multiple (i.e., 1, 2, 3, etc.) or an even fractional (i.e., ½, ¼, etc.) number of wavelengths. In addition, the channels of the bottom supports are dimensioned in this particular example to have a depth equal to one-half wavelength of the ultrasound energy. For example, if the side rails and bottom supports are formed of quartz plates, and the megasonic frequency is 0.95 MHz, the plate thickness is approximately 0.238 inches (6.05 mm), and the channels are 0.119 inches (3.02 mm) deep. The wavelength matching dimensions of the structural components couples the sound energy into the quartz to a maximum extent, and it is transmitted through the quartz to the liquid bath as well as into the substrates supported by the structural components. Thus sonic-shadows are eliminated, and the megasonic cleaning, etching, or stripping effect is more uniform across the surfaces of the substrates.
In addition, the narrow plate components may be tilted slightly so that their upper and lower surfaces are not horizontal. This arrangement permits any bubbles that are formed by the megasonic energy in the liquid to slide off the lower surfaces and rise to the surface of the bath, thereby eliminating the detrimental acoustic effects of the bubbles with respect to the megasonic energy transmission performance.
REFERENCES:
patent: 3610613 (1971-10-01), Worden
patent: 5593505 (1997-01-01), Erk et al.
patent: 5715851 (1998-02-01), Jung et al.
patent: 5908042 (1999-06-01), Fukunaga et al.
patent: 6098643 (2000-08-01), Miranda
patent: 5-13400 (1993-01-01), None
patent: 5-47738 (1993-02-01), None
Harris Zimmerman
Imtec Acculine, Inc.
Stinson Frankie L.
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