Vacuum plasma processor having coil with minimum magnetic field in its center
First Claim
1. A vacuum plasma processor for treating a workpiece in a vacuum chamber comprising a sealed window transparent to electromagnetic energy, a coil having plural arcuate turns for exciting gas in the processor to a plasma state in response to r.f. energization of the coil, the turns of the coil being arranged so the coil extends radially outward from an interior turn to an exterior turn, the coil being located outside the processor and positioned to couple energy to plasma in the chamber through the window, the coil being surrounded by a shield which tends to cause magnetic flux coupled from peripheral portions of the coil to the gas to be less than magnetic flux coupled from interior portions of the coil to the gas, the coil being arranged so magnetic flux derived from a center portion of an area circumscribed by the coil is less than the magnetic flux derived from all other areas circumscribed by the coil so plasma flux across the workpiece is substantially the same.
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Accused Products
Abstract
A substantially planar coil of a vacuum plasma processor has plural turns for exciting gas in the processor to a plasma state in response to r.f. coil energization. The coil is located outside the processor and surrounded by a shield tending to cause magnetic flux coupled from peripheral portions of the coil to the gas to be less than magnetic flux coupled from interior portions of the coil to the gas. The coil is arranged so magnetic flux derived from a center portion of an area circumscribed by the coil is less than the magnetic flux derived from all other areas circumscribed by the coil. The magnetic flux is such that the density of the plasma in the processor on a processed substrate is relatively uniform even though the coil exhibits transmission line properties so there are substantial peak-to-peak current variations along the length of the coil.
116 Citations
41 Claims
- 1. A vacuum plasma processor for treating a workpiece in a vacuum chamber comprising a sealed window transparent to electromagnetic energy, a coil having plural arcuate turns for exciting gas in the processor to a plasma state in response to r.f. energization of the coil, the turns of the coil being arranged so the coil extends radially outward from an interior turn to an exterior turn, the coil being located outside the processor and positioned to couple energy to plasma in the chamber through the window, the coil being surrounded by a shield which tends to cause magnetic flux coupled from peripheral portions of the coil to the gas to be less than magnetic flux coupled from interior portions of the coil to the gas, the coil being arranged so magnetic flux derived from a center portion of an area circumscribed by the coil is less than the magnetic flux derived from all other areas circumscribed by the coil so plasma flux across the workpiece is substantially the same.
- 23. Apparatus for treating a workpiece with a plasma comprising a vacuum chamber in which the plasma is formed and the workpiece is adapted to be located, the vacuum chamber being at a pressure of at least 35 milliTorr while the workpiece is being treated, the chamber having a sealed window transparent to electromagnetic energy, a substantially planar coil positioned outside the chamber for coupling a magnetic field through the window, the coil being responsive to an r.f. source so an r.f. magnetic field is derived from the coil being excited by the r.f. source, the field being coupled through the window to excite the plasma, the coil being surrounded by a metal shield so some energy from the coil is coupled to the shield instead of being coupled through the window to excite the plasma and there is a tendency for a substantial decrease in energy from the coil as coupled to a peripheral region of the chamber approximately aligned with the shield relative to the energy coupled from the coil to a region of the chamber approximately aligned with the center of the window, the coil having a geometry and position relative to the plasma and workpiece to cause the plasma to have an approximately uniform density across a surface of the workpiece exposed to the plasma.
- 25. A vacuum plasma processor for treating a workpiece in a vacuum chamber comprising a coil having plural arcuate turns for exciting gas in the processor to a plasma state in response to r.f. energization of the coil, the turns of the coil being arranged so the coil extends radially outward from an interior turn to an exterior turn, the coil including plural electrically parallel windings driven in parallel by r.f. current from a source of the r.f. energization, each winding including plural arcuate portions on diametrically opposite sides of a center point of the area, each of the arcuate portions being removed from the area center point, the windings being arranged and connected to the r.f. source so instantaneous r.f. current flows in the same direction in spatially adjacent portions of the different parallel windings.
- 33. A vacuum plasma processor for treating a workpiece in a vacuum chamber comprising a coil having plural turns for exciting gas in the processor to a plasma state in response to r.f. energization of the coil, the turns of the coil being arranged so the coil extends radially outward from an interior turn to an exterior turn, the coil having sufficient length for the frequency of the r.f. excitation to have transmission line type effects so that at least one current maximum and minimum exist in the coil at different locations along the coil length, the coil being positioned and arranged so the magnetic fluxes from at least some pairs of adjacent turns are additive and the different locations are adjacent each other, the coil being arranged to have a lower electromagnetic field coupling coefficient to the plasma at a region of maximum peak-to-peak current than at a region of minimum peak-to-peak current.
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40. A vacuum plasma processor for treating a workpiece in a vacuum chamber comprising a coil having plural arcuate turns for exciting gas in the processor to a plasma state in response to r.f. energization of the coil, the turns of the coil being arranged so the coil extends radially outward from an interior turn to an exterior turn, the coil including plural electrically parallel windings driven in parallel by r.f. current from a source of the r.f. energization, each winding including plural arcuate portions on diametrically opposite sides of a center point of the area, each of the arcuate portions being removed from the area center point, the windings being arranged and connected to the r.f. source so the parallel windings are surrounded by a further winding connected in series to the parallel windings so the sum of the currents flowing in the parallel windings flows in the further winding.
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41. A vacuum plasma processor for treating a workpiece in a vacuum chamber comprising a coil having plural substantially coaxial turns spaced by different radii from a common center part of the coil, reactively coupled to the gas for exciting gas in the processor to a plasma state in response to r.f. energization of the coil, the turns of the coil being arranged so the coil extends radially outward from an interior turn to an exterior turn, the plural portions having adjacent ends lying along different radii from the common center point, characterized by each pair of the adjacent ends of the different turns being connected to each other by a substantially straight lead that extends radially with respect to the common center point and circumferentially with respect to the substantially coaxial turns.
Specification