Cleaning and liquid contact with solids – Processes – Including application of electrical radiant or wave energy...
Reexamination Certificate
1999-06-30
2001-08-21
Coe, Philip R. (Department: 1746)
Cleaning and liquid contact with solids
Processes
Including application of electrical radiant or wave energy...
C134S153000, C134S184000, C134S198000, C134S902000
Reexamination Certificate
active
06276370
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to sonic cleaning, such as ultrasonic or megasonic cleaning. More particularly, it relates to cleaning very small particles from semiconductor wafers.
BACKGROUND OF THE INVENTION
Ultrasonic and megasonic energy cleaners have been in use for removing particles from immersed substrates, such as semiconductor wafers. Higher frequency megasonic cleaners were implemented as it was recognized that energy for the cleaning is limited by cavitation—the generation of bubbles in low pressure regions—and by the width of a laminar flow boundary layer. The collapse of these bubbles on the wafer surface caused damage to films on the wafer. The higher frequencies permitted the use of much higher energy before cavitation was initiated. The higher frequencies also resulted in a thinner fluid boundary layer. Both these effects permitted removal of smaller particles that more strongly adhered to the wafer surface.
However, as semiconductor wafer line widths get smaller, so does the size of particle that must be removed by wafer cleans. Typically a killer defect is created by a particle having a size that is greater than half the device line width, so emerging technologies having 0.2 &mgr;m lines require that particles that are equal or greater than 0.1 &mgr;m in size be removed.
Various improvements have been proposed to improve sonic cleaners, such as providing antireflection mechanisms to avoid standing waves, as described in commonly assigned U.S. Pat. No. 5,427,622. Another technique to sweep the frequency of vibration to eliminate or reduce standing waves, resonances, cavitation and non-uniform sound fields is described in U.S. Pat. No. 5,834,871. A staggered array of megasonic transducers, each emitting a focused beam of megasonic energy, and arranged so that the emitted beams from all the transducers collectively envelop the objects to be cleaned is described in U.S. Pat. No. 5,383,484. However, these ideas have not sufficiently provided the ability to remove the 0.1 micrometer and smaller particles from the surface of wafers. Thus, a better solution for megasonic cleaning is required to address the challenges of breaking fluid boundary layers and removing the smaller particles without damaging the fine lines and other films on a wafer, and solutions are provided by the following invention.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to remove small particles from a substrate, such as a semiconductor wafer.
It is a further object of the present invention that the apparatus provides an interference signal for cleaning the wafer.
It is a further object of the present invention that the interference signal is the superposition of signals from a plurality of transducers directed at the same surface of the wafer.
It is a feature of one embodiment of the present invention to sweep the interference signal across the wafer.
It is another feature of the present invention that the interference signal provides an amplitude greater than the amplitude of either of its component signals.
It is an advantage of the present invention that sonic energy is applied uniformly across the wafer while interference minima (dead spots) are avoided.
These and other objects, features, and advantages of the invention are accomplished by an apparatus for cleaning a substrate having a first side, comprising a fluid. A first transducer and a second transducer are coupled to the fluid. The first transducer directs a first signal having a first frequency and a first phase to the first side of the substrate. The second transducer directs a second signal having a second frequency and a second phase to the first side of the substrate so as to provide an interference signal to the first side that is the superposition of the first signal and the second signal. Neither the first signal nor the second signal passes through the substrate before interfering. The interference signal is for cleaning the substrate.
In one embodiment, the interference signal is swept across the substrate, thereby providing more uniform cleaning than can be achieved with a static signal. The sweeping is accomplished electronically by altering the phase difference between the two signals. The sweeping can also be accomplished mechanically.
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Fisch Emily E.
Gale Glenn W.
Okorn-Schmidt Harald F.
Syverson William A.
Coe Philip R.
International Business Machines - Corporation
Leas James M.
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