Electric heating – Inductive heating – With power supply system
Reexamination Certificate
2000-01-24
2002-05-21
Leung, Philip H. (Department: 3742)
Electric heating
Inductive heating
With power supply system
C219S664000, C219S121540, C323S299000, C363S074000
Reexamination Certificate
active
06392210
ABSTRACT:
BACKGROUND
This invention relates to improved methods and apparatus for controlling input power requirements for delivering radio frequency (RF) power for process operations. RF power is extensively used in a wide variety of applications for carrying out process operations. Exemplary of such process operations is RF induction heating. RF induction heating involves coupling RF power to a material that absorbs the RF power and converts the RF power into heat. In other words, the currents induced in material by the RF power are converted into heat because of the electrical resistance of the material that absorbs the RF power. In this manner, the RF power can be used to heat an object without having physical contact between the power source and the object. This type of heating can be used wherein the object is the material that absorbs the RF power and is heated directly by the RF power. Alternatively, the object may be in contact with or near a second material that absorbs RF power; the second material absorbs the RF power and creates the heat; the heat is then transferred to the workpiece by conduction, convection, or radiation.
In another example of RF heating, the RF power can be coupled to a gas to produce a thermal plasma. Free electrons in the thermal plasma absorb the RF power and are raised to high energy levels. These energetic free electrons interact with other gas phase species to produce a high temperature mixture that can transfer their thermal energy to other gases, liquids, or solids.
The thermal plasmas mentioned above can be used to promote chemical reactions. Chemical reactions can be promoted because of the high temperatures of the thermal plasma. Alternatively, thermal plasmas are able to promote chemical reactions because of the ability of the energetic electrons to break chemical bonds and allow chemical reactions to occur that would proceed with difficulty under non-plasma conditions.
The manufacture of optical fiber preforms is an example of the use of thermal plasmas generated using RF power. The RF thermal plasma provides the energy for driving the chemical reactions in gas mixtures of silicon compounds, oxygen, and dopants. The chemical reactions cause deposition of doped silica layers.
Another example involving RF power thermal plasmas is the operation of high-pressure gas lasers. In gas laser operation the important characteristic of the RF plasma is the light emission that occurs because of the plasma. The thermal energy that is produced is generally not considered important to the operation of the laser.
In other applications, RF power is used to produce non-thermal plasmas, also referred to as non-equilibrium plasmas. The manufacture of semiconductor devices is one area in which non-thermal plasmas are extensively used. The non-thermal plasmas are used for etch processes wherein the non-thermal plasmas are used to generate reactive species in a gas to accelerate reactions between the species and a solid surface. The etch process can be a general removal of components on the surface as in a cleaning process or the selective removal of material from certain areas on the surface through use of a masking material that has been previously patterned. Non-thermal plasmas are used to promote deposition reactions wherein gas phase species are caused to react to form a solid product that deposits on surfaces. During the manufacture of semiconductor devices, etch processes involving RF plasmas and deposition processes involving RF plasmas are used repeatedly during the fabrication process. One of the main benefits of using the non-thermal plasma is the ability of the non-thermal plasma to stimulate chemical reactions that would otherwise require temperatures that are too high for use in the fabrication of semiconductor devices.
RF power non-thermal plasmas are also used as cleaning processes in manufacture of semiconductor devices. The non-thermal plasmas are commonly used to strip photoresist materials from semiconductor wafers as part of post etch wafer clean procedures. The photoresist material serves as a mask material during etch processes used in patterning the surface of the devices. Resist material is stripped from the surface of the wafers by creating a non-thermal plasma in a gas containing oxidizing species such as oxygen and possibly halogen species that are capable of reacting with and volatilizing the resist material. In some applications, the non-thermal plasma is maintained at a position upstream of the wafer. Reactive species generated in the non-thermal plasma flow downstream and react with the wafer surface for the stripping process.
Another cleaning process that uses non-thermal plasmas is the cleaning of reaction chambers used in manufacturing semiconductor devices. Sometimes, the reaction chambers used in plasma etch processes experience a buildup of deposits from the etch process. These deposits must be removed as part of the reactor maintenance process. Also, the reactors that are used in deposition processes for semiconductor device fabrication undergo a buildup of deposits on the reactor walls; the wall deposit must be removed as part of reactor maintenance. Non-thermal plasmas generated using RF power and gases containing species that are reactive with the deposits have been used to volatilize and remove the deposits built up on the walls of etch reactors and deposition reactors.
RF power plasmas have also been used for decomposition of chemical compounds that are hazardous or otherwise undesirable. Some of the compounds are highly refractory in nature and are difficult to decompose. Examples of compounds that have been decomposed or abated with plasmas include chlorofluorocarbons (CFC) and perfluorocompounds (PFC).
The applications given above where RF power is used as part of a process makeup only a small fraction of the applications for RF power. There are numerous additional processing applications for RF power. However, the methods and apparatus typically used to deliver RF power have deficiencies and may be inefficient for use in existing applications. Some of the deficiencies are common for multiple applications. The existing deficiencies in the prior methods and apparatus for RF power delivery may limit the use of RF power for possible new applications.
One frequently encountered problem with standard RF power delivery systems is that the equipment is typically designed for use at only one set of optimized input power conditions. Specifically, the required input current and input voltage only have a small range of values for operation of the RF power delivery system. The narrow operating conditions for input power in terms of current and voltage presents a problem for the typical AC power source lines available in homes, offices, and factories around the world. To accommodate the input power requirements for standard RF power delivery systems, three phase AC power sources are typically required to assure having adequate current and voltage for the power input to the RF power delivery system. Providing three phase AC power sources may require additional wiring if the three phase AC lines are not already available. Consequently, the use of some RF power delivery systems can be hindered by the unavailability of three phase AC electric power. Furthermore, the variation in the standard current and voltage for AC power lines used in different countries can also hinder the use of RF power delivery systems. To overcome these problems, the old-style RF power delivery systems have been required to have special power converters to accommodate the current and voltage sources available in each country.
Based on the variety of possible applications for RF power delivery as described above, there are numerous situations in which it would be advantageous to have an RF power delivery system capable of operating over a wide range of input current and voltage. There is a need for improved RF power delivery methods and apparatus that require a minimum or no special wiring to access the electric power source. In addition, there is a need for RF
Camus Curtis C.
Jewett Russell F.
Leung Philip H.
Williams Larry
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