Coating apparatus – Gas or vapor deposition – With treating means
Reexamination Certificate
2000-05-25
2001-06-19
Mills, Gregory (Department: 1763)
Coating apparatus
Gas or vapor deposition
With treating means
C156S345420
Reexamination Certificate
active
06247425
ABSTRACT:
BACKGROUND
The present invention relates to the field of plasma control for the processing of a workpiece, such as a semiconductor wafer, in an inductively coupled plasma reactor.
In a plasma reactor, a gaseous plasma comprising ions is formed within the reactor chamber for etching from or depositing on the workpiece. Among others, plasma parameters such as ion density within the plasma and ion flux to the workpiece control the processing rate. Adjusting the plasma parameters affects the rate and quality of processing.
A significant limiting factor in workpiece processing is uneven charge build-up on the workpiece surface. Uneven charge build-up can cause a voltage differential to build on the workpiece. If the magnitude of the differential exceeds a breakdown voltage on the workpiece, an electrostatic discharge occurs, damaging the workpiece. To prevent damage, etch rates or etch profiles must be limited.
Uneven charge build-up occurs when electrons strike the surface of the workpiece with high lateral velocity. When electrons have high lateral velocity, they are unable to adequately penetrate deep vertical holes and trenches. Ions, however, do not attain such high lateral velocity, so they can be drawn by the sheath to the bottom of the holes and trenches.
In a plasma reactor, the gaseous plasma is formed by separating electrons from atoms or molecules to create ions. Electrons and ions have equal and opposite charges. The mass of the ions, however, is much greater than the mass of the electron. So, as the electron is separated from the molecule, it flies away with a much higher thermal velocity than does the ion. The thermal velocity of the electron or v
the
is at least 100 times greater than the thermal velocity of an ion or v
thi
. Electron and ion thermal velocities are given by the equations:
v
the
=(
eT
e
/m
e
)
1/2
and;
v
thi
=(
eT
i
/m
i
)
1/2
where
e=the unsigned charge of an electron;
T
e
=temperature of the electron in volts;
T
i
=temperature of the ion in volts;
m
e
=mass of the electron; and
m
i
=mass of the ion.
The lower thermal velocity ions, having a lower lateral velocity component, can be attracted by the voltage sheath to the surface of the workpiece so that they impinge upon the surface in a generally normal or perpendicular fashion. The direction of the electrons, however, are less affected by the sheath due to their high lateral component. High velocity electrons impinge the surface of the workpiece at acute angles far less than perpendicular. This leads to uneven charge build-up.
For example, uneven charge build-up results when a deep vertical hole is etched in the workpiece surface. Ions etching the bottom surface of the hole impart a positive charge, while high temperature less directionally controlled electrons are unable to penetrate the hole. The high temperature electrons, unable to penetrate to the bottom surface of the hole, strike adjacent surfaces on the wafer and cause negative charge build-up on those surfaces. When the potential between the surfaces reaches the break down voltage of the workpiece, an electrostatic discharge occurs damaging the workpiece. Reduction of component sizes has led to the need for more extreme workpiece surface profiles. As the depth increases and breadth decreases, damage due to uneven charge build-up is even more likely to occur and more difficult to control.
One way of reducing electron velocity would be to reduce source power. Unfortunately, this would also reduce plasma density. The ability to lower electron thermal velocity to reduce uneven charge build-up without sacrificing plasma density or ion flux would not only improve processing quality, it would also improve workpiece processing time. As plasma reactors typically process thousands of workpieces, a reduction in processing time translates into a significant reduction in reactor operating time. This would not only allow demand to be met more effectively, it would reduce materials expenses and reactor maintenance costs per workpiece. Plasma and process gases are typically housed within the chamber. Exposure to the plasma and other chamber gases can cause degradation of the chamber surfaces. As a result, reactors periodically must go down for cleaning or for part replacement. Limiting exposure of reactor components to plasma and other process gases reduces maintenance costs.
It is an object of the current invention to reduce workpiece processing time. It is another object of the invention to reduce electron temperature within a plasma without substantially affecting ion density or ion flux. It is a further object of the invention to provide an inductively coupled plasma reactor that reduces workpiece damage due to uneven charge build-up. It is yet another object of the invention to reduce degradation of reactor components.
SUMMARY OF THE INVENTION
The present invention provides an apparatus and method for processing a workpiece in an inductive plasma reactor. Inductive power is applied to the reactor to generate a plasma. A magnetic field is generated within the plasma reactor having lines of force oriented perpendicular to the workpiece surface. It is a feature of the invention to control the electron temperature near the surface of the workpiece by controlling the applied magnetic field. It is a further feature to increase average ion density near the workpiece without otherwise causing damage to the workpiece due to uneven charge build-up.
The applied magnetic field can be time invariant or time variant. In both cases, processing can be optimized by adjusting the magnitude of the magnetic field to a level just below where damage due to uneven charge build-up occurs. With the time variant field, the average ion density can be adjusted with respect to average electron temperature. As such, average ion density near the workpiece can by increased without otherwise causing damage to the workpiece.
It is a further feature of the present invention to provide independently controllable conductors for generating the magnetic field and to provide an adjustable non-uniformly distributed magnetic field within the chamber. This can be used to selectively control plasma density or to selectively confine process gas species.
The foregoing and still further features and advantages of the present invention as well as a more complete understanding thereof will be made apparent from a study of the following detailed description of the invention in connection with the accompanying drawings and appended claims.
REFERENCES:
patent: 4123316 (1978-10-01), Tsuchimoto
patent: 4842683 (1989-06-01), Cheng et al.
patent: 5421891 (1995-06-01), Campell et al.
patent: 5468341 (1995-11-01), Samukawa
patent: 5556501 (1996-09-01), Collins et al.
patent: 5648701 (1997-07-01), Hooke et al.
patent: 5662819 (1997-09-01), Kadomura
patent: 5669975 (1997-09-01), Ashtiani
patent: 5824607 (1998-10-01), Trow et al.
patent: 5888414 (1999-03-01), Collins et al.
patent: 6068784 (2000-05-01), Collins et al.
patent: 6096160 (2000-08-01), Kadomura
patent: 0 489 407 (1992-10-01), None
patent: 0 633 713 (1995-11-01), None
Lee, Ho-Jun, Yang, Dong III, and Whand, Ki-Woong, “The effects of magnetic fields on a planar inductyively coupled argon plasma.”Plasma Sources Sci. Technol., vol. 5, United Kingdom, 1996, pp. 383-388.
Tynan, G.R., Bailey, A.D. III, Campbell, G.A., de Chambrier, A., Gibson, G., Hemker, D.J., Jones, K., Kuthi, A., Lee, and C., Wilcoxson, M., “Characterization of an Azimuthally Symmetric Helicon Wave High Density Plasma Source,”Trikon Technologies, Inc., Chatsworth, California, Jul. 1997.
Loewenhardt Peter
Lymberopoulos Dimitris
Yamartino John
Applied Materials Inc.
Hassanzadeh P.
Michaelson and Wallace
Mills Gregory
Wallace Robert
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