Electric heating – Metal heating – By arc
Reexamination Certificate
2001-05-15
2002-12-10
Paschall, Mark (Department: 3742)
Electric heating
Metal heating
By arc
C219S121570, C219S123000, C219S121590
Reexamination Certificate
active
06492613
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to a system and method for using an atmospheric plasma in the processing of substrates and particularly to the fabrication of semiconductor devices. More specifically this invention relates to a method and system to regulate the position of a plasma jet used to produce an intense hot gas stream employed in the manufacture of semiconductor devices such as Miniature Electro-Mechanical Systems (MEMS).
BACKGROUND OF THE INVENTION
An atmospheric arc-type plasma referred to as a plasma jet may be used for processing substrates used in the manufacture of semiconductor devices. An atmospheric, plasma jet generation system has previously been described; see the International patent WO9746056, by Siniaguine, entitled “Apparatus for generating and deflecting a plasma jet.” This atmospheric plasma provides a means for generating an intense, hot gas stream that subsequently can be used for processing a substrate. Processing of the substrate may include: etching by reactive species generated in the hot gas stream; deposition resulting from species introduced into the gas stream; and thermal processing of the substrate by the heat flux carried to the substrate by the hot gas stream. An etching application for polymer removal, has previously been disclosed in the prior International patent pending application no. PCT/US00/27113 by Bollinger and Tokmouline and which is entitled: “Atmospheric process and system for controlled, rapid removal of polymers from high depth to width aspect ratio holes.” The application of very rapid thermal processing has been disclosed in International patent pending Application No. PCT/US00/41492 by Bollinger and Tokmouline “Method for rapid thermal processing of substrates.”
This atmospheric plasma as used in these prior international patent applications is shown in FIG.
1
and is also described in the aforementioned patent applications by Bollinger and Tokmouline. In such system, an arc-type electrical discharge or plasma jet
20
is generated between two electrode subassemblies, an anode
22
and a cathode
24
. The geometric configuration of the generated plasma jet
20
is such that it creates a vertex
25
where an intense hot gas stream
26
is produced that is directed toward a substrate or wafer
28
that is to be processed by the stream
26
. The substrate
28
is held in a substrate holder
30
that is moved through the hot gas stream. Control and repeatability of the hot gas stream
26
is critical for highly controlled, repeatable treatment of the substrate.
Arc-type plasmas by their nature involve electrical current flow and are well known for unstable behavior. Stabilization using this type of plasma generation system is accomplished in the prior art as illustrated in
FIG. 2
by an optical sensing of the plasma jet position at P with optical sensors such as a CCD camera. These generate an image into a computer, which produces a feedback signal, not shown, to a steering magnetic field M. The magnetic field M is intended to correct for a sensed deviation in the plasma jet path position as shown from the solid line at
20
to the dashed line at
20
′. In the prior art the adjustment possible with a single magnetic field does not lend itself for compensating for both a positional and angular alignment of the jet at the vertex
25
. Hence, the repeatability of a process as measured by uniformity of treatment by gas stream
26
, U%, has been limited to approximately 5%.
%
U
=100×(max. treatment−min. treatment)/(ave. treatment) (1)
Where “treatment” refers to a measured process result depending on the application, such as etch depth in an etch application or diffusion depth of a doping impurity in a thermal processing application. For some applications, such as for stripping photoresist from a wafer in which the etch selectivity to the layer underlying the photoresist is practically infinite, this process repeatability is sufficient. For other applications, such as for very rapid thermal processing as described in the above referenced in patent application PCT/US00/41492, thermal treatment to better than 1% is needed.
Prior literature has described the concept of optically sensing the plasma jet position from its light emission and feeding back the sensed position to magnetic fields applied to the plasma jet over a single localized area to stabilize and to re-adjust the plasma jet position. Localized magnetic fields applied to a localized area of the plasma jet have been described in open literature and patent disclosures. A three magnetic pole geometry is described in the International patent WO9212610 by Pavlovich et al “Device for plasma-arc processing of material.” Four magnetic pole configurations are described in the Russian patent RU2059344 by Siniaguine “Plasma current generating device;” in the International patent WO9746056 by Siniaguine “Apparatus for generating and deflecting a plasma jet;” and WO9831038 by Siniaguine “Plasma generation and plasma processing of materials.” In these configurations, the position of each leg of the plasma jet is sensed at one location and a steering magnetic field is applied at one location.
The magnetic fields are generated by electromagnets. Changing the electrical current to the coils in the magnetic circuits varies the applied magnetic field strength. Response time to a sensed change in the path position to magnetically correcting the path position can be fast. Feed back loops with response time near 1 msec have been demonstrated. However, these magnetic field configurations are limited in their capability to precisely control the plasma jet position with consequent limitation in control of the treatment of the substrate.
The prior art of sensing the plasma jet path position at a single point and feed-back control to the magnetic field applied to one localized position cannot precisely control the plasma jet position and direction in the vertex region where the hot gas stream is generated. The difficulty arises from variations in the direction of the plasma jet path as it emerges from the electrode assemblies
22
and
24
. Particularly for the cathode assembly
24
, the path direction of the emerging plasma jet varies from one position to another within a cone concurrent with the longitudinal axis of the electrode assembly. It is believed this variation in the path direction originates from a variation in the position of the electron emission spot on the emitting surface within the electrode assembly.
The prior art optically senses the position of each leg
21
.
1
(PJ
1
) and
21
.
2
(PJ
2
) of the plasma jet
20
and to feed-back any deviation from a pre-set position to a localized magnetic field whose strength and direction may be varied to bring the plasma jet position back to the pre-set position at the optical sensing point. Optical sensing of the path position at a given location is conveniently done by using two optical sensors, S
1
and S
2
, at different positions that are aligned to pick-up the emitted light from that given location on the plasma jet path. The optical signal is fed from each sensor position to a photo-sensitive array such as contained by a CCD camera. The electrical current output from the pixels in the photo-sensitive array along with the geometry of the positioning of two optical sensors, which view the plasma jet position, can then be used to determine the position of the plasma jet at the given, sensed location.
Magnetic field configurations using three and four magnetic poles, referenced above, apply a localized magnetic field that can be varied in intensity and direction in the two directions perpendicular to the plasma jet path direction. The current in the plasma jet then responds to a force by the applied magnetic field according to the well-known relation:
dF=I
(
d/×B)
(2)
where: dF is the force that results from an applied magnetic field, B, on the current element of length d/ (i.e., plasma jet element of length d/) through which a current, i is flowing
Bollinger Lynn David
Tokmouline Iskander
Jetek, Inc.
Paschall Mark
St. Onge Steward Johnston & Reens LLC
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