Cleaning and liquid contact with solids – Processes – Including application of electrical radiant or wave energy...
Reexamination Certificate
2000-12-15
2002-02-12
Stinson, Frankie L. (Department: 1746)
Cleaning and liquid contact with solids
Processes
Including application of electrical radiant or wave energy...
C134S025400, C134S032000
Reexamination Certificate
active
06345630
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 substrates and the like. More particularly, the invention relates to cleaning the edges of a thin disc.
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 polyvinyl acetate (PVA) brushes, brushes made from other porous or sponge-like material, or brushes made from nylon bristles or similar materials. 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.
A conventional PVA brush scrubber disclosed in U.S. Pat. No. 5,675,856 is shown in the side elevational view of FIG.
1
. The conventional scrubber
11
, shown in
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 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.
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. However, research shows that slurry induced defects still occur, and are caused by slurry residue remaining along the edges of the wafer despite cleaning with apparatuses such as that described above. Specifically, subsequent processing has been found to redistribute slurry residue from the wafer edges to the front of the wafer, causing defects. The same is believed to be true of all major surface cleaners, and scrubbers.
For instance, another conventional technique for cleaning slurry residue and other particles from the surfaces of a semiconductor wafer employs sonic nozzles that direct jets of liquid toward a major surface of a semiconductor wafer.
FIG. 2
is a side elevational view of an exemplary sonic nozzle cleaning device
23
that includes a sonic nozzle
25
having an input port
25
a
, an output port
25
b
, and a vibrator
27
coupled to a generator
29
that drives the vibrator
27
.
In operation, a cleaning solution (e.g., deionized water or another similar cleaning solution such as NH
4
OH, KOH, TMAH, HF, citric acid or a surfactant) is supplied under pressure (e.g., 15 p.s.i.) to the input port
25
a
of the nozzle
25
. The cleaning solution travels through the nozzle
25
, passes under the vibrator
27
and travels through the output port
25
b
. As the cleaning solution leaves the output port
25
b
it strikes the major surface of an object to be cleaned (e.g., a major surface
31
a
of a semiconductor wafer
31
).
The vibrator
27
vibrates at a sonic rate (e.g., ultrasonic at a frequency in the hundreds of kHz or megasonic at a frequency in the thousands of kHz) set by the generator
29
. As the cleaning solution travels under the vibrator
27
, the vibrator
27
induces longitudinal pressure waves
33
in the cleaning solution. The longitudinal pressure-waves
33
travel to, strike and impart energy to the major surface
31
a
of the semiconductor wafer
31
approximately every 0.1 to 10 microseconds, depending on the particular frequency of the generator
29
, thereby removing slurry residue and other particles from the major surface
31
a
of the wafer
31
. The entire major surface
31
a
of the wafer
31
is cleaned by scanning the nozzle
25
across the wafer
31
while rotating the wafer
31
with a rotating mechanism
34
. Slurry residue and other particles on the edges of the wafer
31
, however, are not effectively cleaned by the jets of cleaning solution employed by this type of cleaning apparatus.
A number of devices have been developed to improve wafer edge cleaning. One such device is shown in the side elevational view of FIG.
3
. This mechanism 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. 3
, 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.
Accordingly the field of wafer cleaning requires a method and apparatus which effectively cleans both the major surfaces and the edge surfaces of a semiconductor wafer, and that does so without increased cost and complexity. In short, the semiconductor processing field needs an effective edge cleaner that satisfies the ever-present demand for reduced cost per unit wafer processed.
SUMMARY OF THE INVENTION
The present invention addresses the need for an effective edge cleaner by providing a dedicated sonic nozzle specifically positioned to clean the edge surface of a thin disc such as a semiconductor wafer. A sonic nozzle (e.g., ultrasonic, megasonic, etc.) that produces a jet of liquid (e.g., de-ionized water, NH
4
OH, KOH, TMAH, HF, citric acid or a surfactant) is positioned so that the liquid jet strikes an edge of the thin disc to be cleaned (i.e., an edge nozzle). The sonic nozzle preferably is radially spaced from the edge of the thin disc and the liquid jet preferably is directed approximately 30° to 150° from a tangent to the edge of the thin disc and approximately 135° to 225° from a major surface of the thin disc (see FIGS.
4
A-C). In this position the liquid jet impacts the edge of the thin disc, and any beveled portions thereof, with the greatest energy. Moreover the time the thin disc's edge is exposed to sonic energy (i.e., the edge cleaning duty cycle) is significantly increased, providing superior edge cleaning. When employed with a conventional major surface cleaner, rinser or scrubber (i.e., a major surface cleaning mechanism) the invention's edge nozzle may replace the fluid supply mechanisms conventionally required to rinse particles from a thin disc's major surfaces, and/or to prevent thin discs such as semiconductor wafers from drying during cleaning (as drying may leave undesirable streaks and/or particles on wafer surfaces). Thus, in its preferred embodiment, the present invention cleans thin disc edges with minimal additional parts and with minimal additional cleaning fluid. Moreover, the inventive edge nozzle lasts longer than mechanical edge scrubbers, thereby reducing or eliminating replacement and maintenance costs.
To clean the entire circumference of the thin disc, the thin disc is scanned relative to the inventive edge nozzle. That is, either the thin disc is rotated while the inventive edge nozzle remains stationary, the inventive edge nozzle is scanned around the edge of the thin disc as the thin disc remains stationary, or a combination thereof.
Because the inventiv
Brown Brian J.
Fishkin Boris
Tang Jianshe
Applied Materials Inc.
Dugan & Dugan
Stinson Frankie L.
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