Electric heating – Metal heating – By arc
Reexamination Certificate
2000-02-10
2002-05-14
Paschall, Mark (Department: 3742)
Electric heating
Metal heating
By arc
C219S121540, C219S121430, C219S121590, C156S345420, C315S111510
Reexamination Certificate
active
06388226
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the field of generating activated gas containing ions, free radicals, atoms and molecules and to apparatus for and methods of processing materials with activated gas.
BACKGROUND OF THE INVENTION
Plasma discharges can be used to excite gases to produce activated gases containing ions, free radicals, atoms and molecules. Activated gases are used for numerous industrial and scientific applications including processing solid materials such as semiconductor wafers, powders, and other gases. The parameters of the plasma and the conditions of the exposure of the plasma to the material being processed vary widely depending on the application.
For example, some applications require the use of ions with low kinetic energy (i.e. a few electron volts) because the material being processed is sensitive to damage. Other applications, such as anisotropic etching or planarized dielectric deposition, require the use of ions with high kinetic energy. Still other applications, such as reactive ion beam etching, require precise control of the ion energy.
Some applications require shielding the material being processed from the plasma because the material is sensitive to damage caused by ions or because the process has high selectivity requirements. Other applications require direct exposure of the material being processed to a high density plasma. One such application is generating ion-activated chemical reactions. Other such applications include etching of and depositing material into high aspect ratio structures.
For some applications, activated gases need to be generated at or near the surfaces to be treated, because of the high reactivity and short lifetime of the gases. One example is atomic fluorine, which can be used to clean chemical vapor deposition (CVD) chambers for deposition of thin films onto substrate surfaces. CVD chambers need to be routinely cleaned, in order to remove the deposits that build up on the surfaces of chamber parts other than the substrate surfaces. Whereas wet cleaning of the chambers is labor intensive and hazardous to the workers, cleaning the chamber with atomic fluorine generated by a plasma source allows the deposits to be removed without opening the chamber to atmosphere, improving tool productivity and working conditions. Typical source gases for atomic fluorine include perfluorocompounds (PFCs) such as NF
3
, CF
4
, CHF
3
, C
2
F
6
, and C
4
F
8
. A high dissociation rate of the PFCs is important to reduce their emission to the environment and to improve process throughput. Another example is photoresist removal in microelectronics fabrication. After pattern generation, photoresist is removed by exposing the wafer surface to atomic oxygen generated by a plasma source. Atomic oxygen reacts rapidly and selectively with photoresist, allowing the process to be conducted in a vacuum and at relatively low temperature.
Plasmas can be generated in various ways including DC discharge, radio frequency (RF) discharge, and microwave discharge. DC discharges are achieved by applying a potential between two electrodes in a gas. RF discharges are achieved either by electrostatically or inductively coupling energy from a power supply into a plasma. Parallel plates are typically used for electrostatically coupling energy into a plasma. Induction coils are typically used for inducing current into the plasma. Microwave discharges are achieved by directly coupling microwave energy through a microwave-passing window into a discharge chamber containing a gas. Microwave discharges are advantageous because they can be used to support a wide range of discharge conditions, including highly ionized electron cyclotron resonant (ECR) plasmas.
RF discharges and DC discharges inherently produce high energy ions and, therefore, are often used to generate plasmas for applications where the material being processed is in direct contact with the plasma. Microwave discharges produce dense, low ion energy plasmas and, therefore, are often used to produce streams of activated gas for “downstream” processing. Microwave discharges are also useful for applications where it is desirable to generate ions at low energy and then accelerate the ions to the process surface with an applied potential.
However, microwave and inductively coupled plasma sources require expensive and complex power delivery systems. These plasma sources require precision RF or microwave power generators and complex matching networks to match the impedance of the generator to the plasma source. In addition, precision instrumentation is usually required to ascertain and control the actual power reaching the plasma.
RF inductively coupled plasmas are particularly useful for generating large area plasmas for such applications as semiconductor wafer processing. However, prior art RF inductively coupled plasmas are not purely inductive because the drive currents are only weakly coupled to the plasma. Consequently, RF inductively coupled plasmas are inefficient and require the use of high voltages on the drive coils. The high voltages produce high electrostatic fields that cause high energy ion bombardment of reactor surfaces. The ion bombardment deteriorates the reactor and can contaminate the process chamber and the material being processed. The ion bombardment can also cause damage to the material being processed.
Faraday shields have been used in inductively coupled plasma sources to contain the high electrostatic fields. However, because of the relatively weak coupling of the drive coil currents to the plasma, large eddy currents form in the shields resulting in substantial power dissipation. The cost, complexity, and reduced power efficiency make the use of Faraday shields unattractive.
Plasma sources can also be used to remove harmful gases from gas streams. Concern over global warming has driven semiconductor and other manufacturing industries to reduce their emission of PFCs. Conventional methods of abating environmental pollutants typically utilize thermal techniques which break down pollutant molecules by burning the gases at a high temperature. Due to the thermal stability of many of the PFCs, however, the thermal techniques are not very effective, and can be very expensive.
SUMMARY OF THE INVENTION
The invention relates to an apparatus for generating excited gases containing ions, free radicals, atoms and molecules, and for abating hazardous compounds.
In one embodiment, the invention provides an improved toroidal low-field plasma source with an ignition control circuit that allows plasma ignition within a wider range of gas conditions than are permitted generally by prior art plasma sources. In another embodiment, the invention improves the power efficiency of a toroidal low-field plasma source by automatically adjusting the power delivered to the plasma based on the load to the power supply. In another embodiment, the invention improves the dissociation and abatement efficiencies of a toroidal low-field plasma source by providing a gas mixing device.
In one embodiment, the invention provides a method for operating a plasma source over a wider pressure range than generally allowed by prior art plasma sources. In another embodiment, the invention provides a method for increasing the output of atomic species from a plasma source. In another embodiment, the invention provides a method for increasing the plasma etch rate of organic materials.
In another embodiment, the invention provides an apparatus and method for efficiently removing PFCs and other hazardous gaseous compounds from effluent gas streams, by converting the hazardous compounds into scrubbable products.
Accordingly, the present invention features an apparatus for dissociating gases into a plasma that includes a plasma chamber. In one embodiment, the apparatus includes a process chamber that is coupled to the plasma chamber and positioned to receive reactive gas generated by a plasma in the plasma chamber.
The apparatus also includes a transformer having a primary winding and having a magnetic core surr
Chen Xing
Georgelis Eric
Holber William M.
Smith Donald K.
Applied Science and Technology Inc.
Paschall Mark
Testa Hurwitz & Thibeault LLP
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