Cleaning and liquid contact with solids – Processes – Including application of electrical radiant or wave energy...
Reexamination Certificate
2000-06-07
2001-08-21
Coe, Philip R. (Department: 1746)
Cleaning and liquid contact with solids
Processes
Including application of electrical radiant or wave energy...
C134S033000
Reexamination Certificate
active
06276371
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to apparatuses and methods for cleaning thin discs, such as semiconductor wafers, compact discs, glass wafers and the like. More particularly, the invention relates to effective cleaning of thin disc edges.
BACKGROUND OF THE INVENTION
To manufacture a thin disc such as a semiconductor wafer, an elongated billet of semiconductor material is cut into very thin slices, about ¾ mm in thickness. The slices or wafers of semiconductor material are then lapped and polished by a process that applies an abrasive slurry to the semiconductor wafer's surfaces. A similar polishing step is performed to planarize dielectric or metal films during subsequent device processing on the semiconductor wafer.
After polishing, be it during wafer or device processing, slurry residue conventionally is cleaned from wafer surfaces via submersion in a tank of sonically energized cleaning fluid, via spraying with sonically energized cleaning or rinsing fluid, or via a scrubbing device which employs brushes made from bristles, or from a sponge-like material, etc. Although these conventional cleaning devices remove a substantial portion of the slurry residue which adheres to wafer edges, slurry particles nonetheless remain and produce defects during subsequent processing. Specifically, subsequent processing has been found to redistribute slurry residue from the wafer edges to the front of the wafer, causing defects.
A number of devices have been developed to improve wafer edge cleaning. Most of these devices are employed as a separate step following major surface cleaning or scrubbing. However, a few scrubbing devices have been developed that can simultaneously scrub both the major and edge surfaces of a wafer. One such device is shown in the side elevational view of FIG.
1
. The scrubbing device
11
of
FIG. 1
comprises a pair of PVA brushes
13
a
,
13
b
. Each brush comprises a plurality of raised nodules
15
across the surface thereof, and a plurality of valleys
17
located among the nodules
15
. The scrubber
11
also comprises a platform
19
for supporting a wafer W and a mechanism (not shown) for rotating the pair of PVA brushes
13
a
,
13
b
. The platform
19
comprises a plurality of spinning mechanisms
19
a
-
c
for spinning the wafer W. During scrubbing a fluid supply mechanism F, such as a fluid source coupled to a plurality of spray nozzles, supplies fluid to both major surfaces of the wafer, flushing dislodged particles and cleaning residue from the major surface of the wafer and rinsing brushes
13
a
and
13
b
. Preferably, the pair of PVA brushes
13
a
,
13
b
are positioned to extend beyond the edge of the wafer W, so as to facilitate cleaning the wafer's edges. This mechanism further employs a separate edge brush
21
, which is driven by a separate motor (not shown), that causes the edge brush
21
to rotate. The edge brush
21
fits over the edge of the wafer W as shown in
FIG. 1
, providing more effective wafer edge cleaning.
Although the edge brush
21
addresses the need to clean slurry residue from wafer edges, it does so at the expense of increased scrubber complexity and cost, and the requirement of frequent edge brush replacement because of excessive mechanical wear. Often, megasonic wafer cleaning within a submersion tank is preferred to scrubber type cleaning, such as when it is desirable to alter the chemistry of the cleaning solution as the PVA brushes commonly used for brush scrubbing have limited chemical compatibility (e.g., to make the wafer hydrophobic or hydrophilic). In these instances, the use of a conventional edge scrubber following megasonic cleaning significantly increases wafer cleaning time, reducing productivity, and thereby increasing the cost of each wafer unit processed.
Accordingly, the field of semiconductor wafer processing needs an improved megasonic cleaner that will simultaneously clean both the major surfaces and the edge surfaces of a wafer, and that will do so with minimal additional components so as to satisfy the ever present demand for reduced processing costs.
SUMMARY OF THE INVENTION
The present inventors have satisfied this need by repositioning and resizing conventional megasonic cleaning parts to achieve edge cleaning results previously unattainable within conventional megasonic cleaning tanks.
The present invention achieves superior edge cleaning by providing a transducer preferably equal in length to the diameter of the wafer to be cleaned. The transducer is positioned within a tank of cleaning fluid at a 180° angle from (i.e., in line with) the outer edge of a wafer supported in the tank. The wafer is supported in a rotatable manner, and is rotated during cleaning such that each portion of the wafer surface is contacted by equal amounts of sonic energy during each revolution of the wafer.
Unlike the wafer supports of conventional megasonic cleaning tanks that rotate a wafer during cleaning (described in detail with reference to FIGS.
2
and
3
), the wafer supports of the present invention are positioned outside the region of the wafer which is closest to the transducer (i.e., outside the transducer's high energy field). The wafer supports of the present invention are positioned such that approximately 25 to 50 percent of the wafer is located between the wafer supports and the transducer. Positioning 50 percent of the wafer between the wafer supports and the transducer is most preferred. However, when the present invention is configured for a vertical wafer orientation, the wafer supports are preferably positioned such that slightly less than 50 percent of the wafer is positioned between the wafer supports and the transducer to prevent the wafer from slipping through the wafer supports, and to ease tolerancing requirements.
A wafer stabilizing mechanism may be positioned along the wafer's edge to prevent wafer wobble. In order to allow the wafer to be easily lifted and lowered to and from the tank, the stabilizing mechanism is preferably positioned along the wafer's lower portion, and is as small as possible to provide stabilization while blocking minimal amounts of sonic energy from reaching the wafer. Although the stabilizing mechanism may be positioned within the transducer's high energy field, the stabilizing mechanism is offset slightly from the nadir of the wafer, and thus does not block the wafer's center from obtaining a direct line of megasonic energy during rotation.
Because the transducer preferably extends a length equal to the diameter of the wafer, and because any obstruction between the transducer and the wafer is minimal, approximately 50 percent of the wafer's edge is continually cleaned and approximately 100 percent of the transducer's energy is used for cleaning. The present invention therefore provides nearly a 50 percent edge cleaning duty cycle, and exhibits superior edge cleaning as compared to conventional systems.
Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings.
REFERENCES:
patent: 4869278 (1989-09-01), Bran
patent: 5090432 (1992-02-01), Bran
patent: 5379785 (1995-01-01), Ohmori et al.
patent: 5383484 (1995-01-01), Thomas et al.
patent: 5672212 (1997-09-01), Manos
patent: 0860860 A2 (1998-08-01), None
patent: 04049619 (1992-02-01), None
patent: 09075874 (1997-03-01), None
STEAG Electronic Systems CMP—“STEAG announces the Trident 300 Post-CMP Cleaner”.
Brown Brian J.
Fishkin Boris
Tang Jianshe
Applied Materials Inc.
Coe Philip R.
Dugan & Dugan
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