Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-08-27
2001-02-13
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S337000, C310S364000
Reexamination Certificate
active
06188162
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to transducers used in transmitting acoustic energy, and more particularly to megasonic transducers attached to an energy transmitting means using indium.
2. Background Information
It is well-known that sound waves in the frequency range of 0.4 to 2.0 megahertz (MHz) can be transmitted into liquids and used to clean particulate matter from damage sensitive substrates. Since this frequency range is predominantly in the megahertz range, the cleaning process is commonly referred to as megasonic cleaning. Among the items that can be cleaned with this process are semiconductor wafers in various stages of the semiconductor device manufacturing process, disk drive media, flat panel displays and other sensitive substrates.
Megasonic acoustic energy is generally created by exciting a crystal with radio frequency AC voltage radiation. The acoustical energy generated by the crystal is passed through an energy transmitting member and into the cleaning fluid. Frequently, the energy transmitting member is a wall of the vessel that holds the cleaning fluid. The crystal and its related components are referred to as a megasonic transducer. For example, U.S. Pat. No. 5,355,048, discloses a megasonic transducer comprised of a piezoelectric crystal attached to a quartz window by several attachment layers. The megasonic transducer operates at approximately 850 KHz. Similarly, U.S. Pat. No. 4,804,007 discloses energy transmitting members in a megasonic transducer comprised of quartz, sapphire, boron nitride, stainless steel and tantalum.
A problem with megasonic transducers of the prior art is that the acoustic power that can be generated by the megasonic transducer in the cleaning solution is limited to about 10 watts per cm
2
of active piezoelectric surface without supplying additional cooling to the transducer. For this reason, most megasonic power sources have their output limited, require liquid or forced air cooling or are designed for a fixed output to the piezoelectric transducer or transducers. Typically, fixed output systems are limited to powers of 7-8 watts/cm
2
. This limits the amount of energy that can be transmitted to the cleaning solution. If more power is applied to the transducer, the crystal can heat up to the point where it becomes less effective at transmitting energy into the cleaning solution. This is caused either by nearing the maximum operating temperature of the crystal or, more often, by reaching the failure temperature of the material used to attach the crystal to the energy transmitting means.
Another problem with prior art cleaning systems that utilize megasonic transducers, is that there is no practical way of replacing a defective transducer once the transducer has been attached to the cleaning system. This means that users have to incur large expenses to replace defective transducers, for example by purchasing a whole new cleaning vessel.
BRIEF SUMMARY OF THE INVENTION
Briefly, the present invention is a megasonic transducer comprised of a piezoelectric crystal attached to an energy transmitting means by a layer of indium. The energy transmitting means transmits acoustic energy generated by the piezoelectric crystal into a cleaning solution. Because indium is very efficient at transmitting acoustic energy from the piezoelectric crystal to the energy transmitting means, more acoustic energy is delivered into the cleaning solution. This efficient transfer of acoustic energy allows higher power densities to be applied to the piezoelectric crystal, thereby decreasing the time needed for a cleaning cycle.
In order to complete the attachment of the energy transmitting means to the piezoelectric crystal using indium, a number of additional materials must be used. Specifically, the megasonic transducer comprises an energy transmitting member and a piezoelectric crystal having a front surface that faces the energy transmitting member and a back surface that faces away from the energy transmitting member. An attachment layer comprised of indium is positioned between the energy transmitting member and the piezoelectric crystal for attaching the piezoelectric crystal to the energy transmitting member, with the attachment layer having a first surface facing the energy transmitting member and a second surface facing the piezoelectric crystal.
A first metal layer is positioned between the first surface of the attachment layer and the energy transmitting member. A second metal layer is positioned between the second surface of the attachment layer and the piezoelectric crystal. A first blocking means for preventing the energy transmitting means from forming an alloy with the first metal layer is positioned between the first metal layer and the energy transmitting member. A third metal layer is positioned in contact with the back surface of the piezoelectric crystal. A fourth metal layer deposited on the front surface of the piezoelectric crystal, and a second blocking layer positioned between the attachment layer and the fourth metal layer.
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Budd Mark O.
Pagel Donald J.
Product Systems Incorporated
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