Electric lamp and discharge devices: systems – Discharge device load with fluent material supply to the... – Plasma generating
Reexamination Certificate
2000-01-24
2001-09-18
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Discharge device load with fluent material supply to the...
Plasma generating
C315S111210, C315S111410, C219S121140, C156S345420
Reexamination Certificate
active
06291938
ABSTRACT:
BACKGROUND
This invention relates to improved methods and apparatus for igniting and sustaining inductively coupled plasmas produced from radio frequency (RF) power for process operations.
RF plasma is extensively used in a wide variety of applications for carrying out process operations. For example, thermal plasmas can be used to promote chemical reactions 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.
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. 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 non-thermal plasmas are also used in 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. 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 semiconductor manufacturing.
RF 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).
One frequently encountered problem with standard inductively coupled RF plasma systems is the difficulty of igniting and sustaining the plasma. Plasma ignition is unreliable because coupling an ignition voltage high enough to generate the energetic species needed to produce the plasma is difficult. The voltage required to generate the energetic species is frequently referred to as the breakdown voltage. The breakdown voltage for a gas depends upon a variety of factors. Two major factors are the pressure of the gas and the electronic properties of the gas such as the electronegativity of the gas and its plasma products. The absolute value of the magnitude of the breakdown voltage undergoes a minimum with respect to the pressure of the gas. Specifically, the magnitude of the breakdown voltage increases for plasma ignition at pressures higher or lower than the pressures at which the minimum breakdown voltage occurs. Consequently, igniting plasmas at very low pressures and at high pressures is difficult. The electronegativity of the gas affects the magnitude of the breakdown voltage so that the gas with higher electronegativity requires higher breakdown voltages at every pressure.
Unfortunately for standard inductively coupled plasma technology, the absence of strong electric fields and the absence of strong capacitive coupling make it difficult to overcome the plasma ignition problems resulting from gas pressure and gas electronegativity. At pressures that are too high or too low or for gases with high electronegativities, the required breakdown voltage may equal or exceed the capacity of the RF power source, making plasma ignition unreliable. As a result, it may be necessary to make several attempts to ignite the plasma, greatly reducing the productivity and efficiency of the plasma process. The unreliable plasma ignition can waste valuable process gases, can increase pollution problems, and can ruin valuable product
In addition to the problem of igniting the plasma, there is also the problem of poor plasma stability. After the plasma has been ignited it is possible for the plasma to go out, i.e. become extinguished, because of changes in RF power delivery conditions. For instance, the plasma can go out while performing a process and cause the same unfortunate results that occur for unreliable plasma ignition.
Clearly, there are numerous applications requiring reliable and efficient methods and apparatus for igniting and sustaining inductively coupled RF plasmas. Unfortunately, typical methods and apparatus for old-style inductively coupled RF plasma systems have characteristics that are undesirable for some applications. There is a need for methods and apparatus for igniting and sustaining inductively coupled RF plasmas that are simple to use, operate automatically, and provide high reliability.
SUMMARY
This invention seeks to provide methods and apparatus that can overcome deficiencies in known RF power inductively coupled plasma technology. One aspect of the present invention includes methods and apparatus for igniting and sustaining an inductively coupled RF powered plasma. The methods and apparatus make it easier to ignite and sustain the RF plasma and can provide greater reliability and greater stability than is typical for standard RF plasma technology. The apparatus has features built in that automatically facilitate igniting and sustaining the plasma. The methods and apparatus are simple to use, operate automatically, and provide high reliability.
In one embodiment, the apparatus comprises a load such as a plasma chamber capable of receiving gases for generating a plasma, an RF power source, and an RF power antenna such as a RF power induction coil. The RF power induction coil is positioned near the plasma chamber so the induction coil can couple RF power to the plasma. The resonant section is connected with the RF power source to receive RF power from the RF power source. At least one non-resonant section is electrically attached to a location on the resonant section. Application of a substantially steady-state magnitude of RF power to the resonant section of the RF coil produces a high current in the resonant section in the absence of the plasma. In addition, the at least one nonresonant section maintains high voltages that produce an enhanced electric field in the plasma chamber. The enhanced electric field in the plasma chamber facilitates igniting the plasma. After the plasma has been ignited, the plasma is sustained by inductive coupling of the RF power to the plasma. Inductive coupling of RF power to the plasma causes the current in the resonant section to decrease. The decrease in the current in the resonant section causes the voltages in the at least one nonresonant sections to decrease and maintain lower voltages. Consequently, after the plasma is ignited, the plasma is sustained by inductive coupling of RF power from the resonant section, and the nonresonant sections do not contribute significant amounts of power to the plasma.
A further embodiment of the present invention includes a control system responsive to the presence or absence of the plasma when RF power is applied to the resonant section of the coil. The control system sends a signal to the RF power source if the plasma is absent while RF power is been applied to the resonant section. The signal commands the RF power source to provide an output RF power pulse to the resonant section. The magnitude of the output RF power pulse is substantially greater, preferably at least five percent greater, than the steady state output RF power. More preferably, the magn
Camus Curtis C.
Jewett Russell F.
Litmas, Inc.
Vu Jimmy
Williams Larry
Wong Don
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