Apparatus for single disc ultrasonic cleaning

Details Apparatus for single disc ultrasonic cleaning Apparatus for single disc ultrasonic cleaning

2001-01-10

2003-09-16

Gulakowski, Randy (Department: 1746)

Cleaning and liquid contact with solids

Apparatus

With movable means to cause fluid motion

C134S902000

Reexamination Certificate

active

06619305

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to apparatus and methods for treating workpieces with ultrasonic energy. More specifically, the present invention relates to apparatus and methods for performing ultrasonic cleaning of workpieces having a pair of opposed, planar surfaces, for example, disc-shaped workpieces. The invention has particular utility in the manufacture of disc-shaped magnetic and magneto-optic (“MO”) recording media and semiconductor devices employing semiconductor wafer substrates.
BACKGROUND OF THE INVENTION
The ever-increasing areal recording densities of magnetic and MO recording media, as in the form of discs, results in continued reduction in the sizes of critical defects formed during the manufacturing process, which necessitate removal of particles having sizes (i.e., diameters) below about 0.5 &mgr;m. According to conventional practices utilizing ultrasonic and/or megasonic techniques for treating, e.g., cleaning, desmutting, etc., of such disc-shaped workpieces as are utilized as layer deposition substrates in the manufacture of various types of magnetic and MO recording media, as well as semiconductor integrated circuit (IC) devices processed from a single semiconductor wafer substrates, a plurality of discs are simultaneously processed in an ultrasonic tank in batches. Conventional ultrasonic apparatus for performing such batch cleaning operations typically comprise a stainless steel tank or vessel with several ultrasonic transducers attached to the bottom thereof. The ultrasonic transducers are driven by generators so as to vibrate at ultrasonic frequencies (~20-500 kHz) that create pressure waves in the cleaning liquid contained within the tank or vessel, which pressure waves in turn remove contaminants, particulate matter, etc., from the workpiece surfaces by different mechanisms. A simplified, schematic top plan view of a typical bottom-mounted transducer ultrasonic cleaning apparatus
10
comprising a rectangularly-shaped stainless steel tank
1
having a plurality of vertically oriented workpieces
2
, e.g., discs, each having opposed, planar surfaces
2
a
and
2
b
, is shown in FIG.
1
. The major advantage of the conventional batch method is that typically ca. 100-150 workpieces can be processed in about 300-360 sec.
However, such batch processing techniques utilizing bottom-mounted transducer ultrasonic cleaning apparatus as illustrated in
FIG. 1
incur several disadvantages and drawbacks, including:
(1) the intensity of the ultrasonic (i.e., acoustic) energy field that a surface of a particular workpiece experiences is different for each disc, primarily as a result of the geometric arrangement of the discs and significant variation in the acoustic energy across the bottom of the tank or vessel, for example, arising from the formation of standing (or stationary) acoustic waves rather than progressive (or traveling) waves. For example,
FIG. 2
illustrates the large variation in transmitted acoustic energy (measured in terms of power density, watts/unit area) across the bottom surface of a conventional ultrasonic apparatus employing a plurality of bottom-mounted ultrasonic transducers; and
(2) the relatively large tanks or vessels of conventional batch-type ultrasonic treatment apparatus contain a considerable amount of cleaning liquid or bath, which liquid bath is, on average, utilized for a very long interval, typically about 10-12 hours, before being replaced with fresh cleaning solution. However, as the workpieces (e.g., discs) are processed in the tank, particulate matter and other contaminants, such as soluble and/or insoluble materials, are removed from the workpiece surfaces and become suspended and/or dissolved in the cleaning solution, thereby increasing the likelihood of particle redeposition, damage to the workpiece surfaces arising from the mechanical abrading action exerted thereon by the suspended particles, and a general reduction in effectiveness of the cleaning/removal properties of the cleaning bath or solution due to exhaustion of the active ingredients or components thereof, e.g., surfactants, detergents, etc. As a consequence, in order to extend the effectiveness of the cleaning solution, the latter is typically recirculated through a filter, which filter has a further disadvantage of incurring contaminant loading necessitating periodic cleaning and/or replacement of the filter material or cartridge.
SUMMARY OF THE INVENTION
Accordingly, there exists a clear need for improved apparatus and methodology for performing simple, reliable, rapid, and cost-effective ultrasonic treatment of workpieces, e.g., disc-shaped workpieces used as deposition substrates in the manufacture of magnetic and/or MO recording media and semiconductor wafer substrates utilized in the fabrication of semiconductor IC devices, which apparatus and methodology avoids the drawbacks and disadvantages associated with use of the conventional, batch-type, bottom transducer-mounted ultrasonic devices, and provides, inter alia, single-disc ultrasonic processing where each disc is subjected to the same amount/intensity of acoustic energy providing equal removal forces; relatively small tank or vessel sizes facilitating rapid and frequent cleaning bath replacement, filtering, or replenishment; elimination of “dead spaces” of very low acoustic power within the tank or vessel due to reduction or elimination of disadvantageous stationary wave formation and enhanced formation of progressive waves; obtainment of production economies resulting from lower cost and maintenance of a bank of relatively small ultrasonic tanks operating in parallel, vis-à-vis a single large tank; and smaller impact on product throughput than which results upon malfunction of a single large tank.
The present invention, wherein the reflection and transmission characteristics of ultrasonic waves supplied to a liquid contained in a relatively small chamber or tank via a sidewall-mounted transducer and simultaneously applied to the opposing surfaces of a single planar workpiece, e.g., a disc-shaped workpiece such as a deposition surface of a substrate for a magnetic or MO recording medium or a semiconductor wafer, are manipulated to locally increase the acoustic power density and/or formation of progressive waves, effectively addresses and solves the above-stated need for improved methodology and instrumentalities for performing ultrasonic treatment of planar-surfaced workpieces. Further, the methodology and apparatus provided by the instant invention can be implemented in a cost-effective manner utilizing readily available materials and components, and the methodology and apparatus afforded by the present invention enjoy diverse utility in the manufacture of numerous types of manufacturing processes in addition to those specifically enumerated.
An advantage of the present invention is an improved apparatus for treating surfaces of a single workpiece with ultrasonic energy.
Another advantage of the present invention is an improved apparatus for treating a single workpiece having a pair of opposed, planar surfaces with ultrasonic energy.
Yet another advantage of the present invention is an improved method for treating surfaces of a single workpiece with ultrasonic energy.
Still another advantage of the present invention is an improved method for treating a single workpiece having a pair of opposed, planar surfaces with ultrasonic energy.
Additional advantages and other features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to one aspect of the present invention, the foregoing and other advantages are obtained in part by an apparatus for treating surfaces of a single workpiece with ultrasonic energy, comprising:
(a) a chamber defining an interior space

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