Stacked RF excitation coil for inductive plasma processor

Details Stacked RF excitation coil for inductive plasma processor Stacked RF excitation coil for inductive plasma processor

2001-03-30

2003-03-04

Dang, Thi (Department: 1763)

Adhesive bonding and miscellaneous chemical manufacture

Differential fluid etching apparatus

With radio frequency antenna or inductive coil gas...

C118S7230IR

Reexamination Certificate

active

06527912

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to inductive plasma processors with RF plasma excitation coils and, more particularly, to such a processor with a coil including a planar winding segment that is electrically connected to a planar turn, wherein the segment is stacked vertically relative to a portion of the planar turn. Another aspect of the invention relates to a processor including a coil with a winding having a planar turn having ends that are in a first plane and connected with turns or partial turns having ends in a second plane wherein the coil is driven from RF excitation terminals that are spaced from the first and second planes and the turn ends are connected to (1) each other and/or (2) the excitation terminals by connecting structures that extend smoothly and gradually, without sharp bends, between opposite ends of the connection structure.
BACKGROUND ART
One type of processor for treating workpieces with an RF plasma in a vacuum chamber includes a coil connected to be responsive to an RF source by leads extending vertically between terminals located in a housing above the coil. The coil, which is usually planar or spherical or dome shaped, is driven by the RF source to produce electromagnetic fields that excite ionizable gas in the chamber to a plasma. The leads connecting the coil to the excitation source intersect terminals of the coil at right angles. Usually the coil is on or adjacent to a dielectric window that extends in a direction generally parallel to a planar horizontally extending surface of the processed workpiece. The excited plasma interacts with the workpiece in the chamber to etch the workpiece or to deposit material on it. The workpiece is typically a semiconductor wafer having a planar circular surface or a solid dielectric plate, e.g., a rectangular glass substrate used in flat panel displays, or a metal plate.
Ogle, U.S. Pat. No. 4,948,458 discloses a multi-turn spiral planar coil for achieving the above results. The spiral, which is generally of the Archimedes type, extends radially and circumferentially between its interior and exterior terminals connected to the RF source via an impedance matching network. Such coils produce oscillating RF fields having magnetic and electric field components that penetrate through a dielectric window to excite electrons and ions in a portion of the plasma chamber close to the window. The spatial distribution of the magnetic field in the plasma portion close to the window is a function of the sum of individual magnetic field components produced by the current at each point of the coils. The inductive component of the electric field is produced by the time varying magnetic field, while the capacitive component of the electric field is produced by the RF voltage in the coils. The inductive electric field is azimuthal while the capacitive electric field is vertical to the workpiece. The current and voltage differ at different points because of transmission line effects of the coil at the frequency of the RF source.
For spiral designs as disclosed by and based on the Ogle '458 patent, the RF currents in the spiral coil are distributed to produce a toroidal shaped electric field resulting in a toroidal plasma close to the window, which is where power is absorbed by the gas to excite the gas to a plasma. The toroidal shaped magnetic field is accompanied by a ring shaped electric field which generates a toroidal shaped plasma distribution. At low pressures, in the 1.0 to 10 mTorr range, diffusion of the plasma from the toroidal shaped region where plasma density is peaked tends to smear out plasma non-uniformity and increases plasma density in the chamber center just above the center of the workpiece. However, the diffusion alone generally can not sufficiently compensate plasma losses to the chamber walls and plasma density around the workpiece periphery can not be changed independently. At intermediate pressure ranges, in the 10 to 100 mTorr range, gas phase collisions of electrons, ions, and neutrals in the plasma further prevent substantial diffusion of the plasma charged particles from the toroidal region. As a result, there is a relatively high plasma density in a ring like region of the workpiece but low plasma densities in the center and peripheral workpiece portions.
These different operating conditions result in substantially large plasma flux (i.e., plasma density) variations between inside the toroid and outside the toroid, as well as at different azimuthal angles with respect to a center line of the chamber that is at right angles to the plane of the workpiece holder (i.e., chamber axis). These plasma flux variations result in a substantial standard deviation, i.e., in excess of six percent, of the plasma flux incident on the workpiece. The substantial standard deviation of the plasma flux incident on the workpiece has a tendency to cause non-uniform workpiece processing, i.e., different portions of the workpiece are etched to different extents and/or have different amounts of materials deposited on them.
Many arrangements directed to improving the uniformity of the plasma density incident on a workpiece have concentrated on geometric principles, usually concerning coil geometry. See, e.g., U.S. Pat. Nos. 5,304,279; 5,277,751; 5,226,967; 5,368,710; 5,800,619; 5,401,350; 5,558,722, 5,759,280, 5,795,429, 5,847,074 and 6,028,395. However, these coils have generally been designed to provide improved radial plasma flux uniformity and to a large extent have ignored azimuthal plasma flux uniformity or azimuthal symmetry.
Our commonly assigned U.S. Pat. No. 6,164,241 entitled “Multiple Coil Antenna for Inductively-Coupled Plasma Generation Systems,” discloses another coil including two concentric electrically parallel windings each having first and second terminals, which can be considered input and output terminals of each winding. Each first terminal is connected via a first series capacitor to an output terminal of a matching network driven by an RF power source. Each second terminal is connected via a second series capacitor to a common ground terminal of the matching network and RF source. Each winding can include a single winding or multiple windings that extend circumferenfially and radially in a spiral-like manner relative to a common axis of the two windings. Each winding is planar or three-dimensional (i.e., spherical or dome-shaped) or separate windings of a single winding can be stacked relative to each other to augment the amount of electromagnetic fields coupled by a particular winding to the plasma.
Holland et al, U.S. Pat. No. 6,028,395, discloses a coil including plural electrically parallel windings. Peripheral parts of the windings are stacked vertically with respect to each other and a dielectric window separating the coil from the vacuum chamber interior. The stacked coil segments are arranged so that the electromagnetic fields resulting from current flowing in parallel through the two segments is additive, to assist in maintaining relatively uniform electromagnetic fields in the chamber and a relatively uniform plasma density on the workpiece.
The parallel connections of the stacked coil portions are established by struts that extend substantially perpendicular to the two parallel, stacked coil portions. Adverse effects may occur as a result of the leads being connected perpendicular to the coil terminals. In particular, we have found that the struts and leads seem to perturb the electromagnetic fields generated by the coil and stacked coil segments particularly around the region where the leads and coil terminals are connected. In addition the struts and leads have a tendency to produce in the coil relatively large standing wave variations which usually cause a non uniform plasma to be incident on the workpiece.
It is accordingly an object of the present invention to provide a new and improved coil for a vacuum plasma processor.
An additional object of the present invention is to provide a new and improved coil for a vacuum plasma processor wherein the plas

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