Power segmented electrode

Details Power segmented electrode Power segmented electrode

2000-02-03

2001-05-29

Paschall, Mark (Department: 3742)

Electric heating

Metal heating

By arc

C219S121410, C219S121520, C156S345420, C118S7230IR, C204S298340

Reexamination Certificate

active

06239403

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to an electrode for generating a plasma and/or local plasma density control in a plasma reaction chamber. The electrode can be incorporated in an upper electrode and/or incorporated in a substrate support such as a chucking device for holding a substrate such as a semiconductor wafer, flat panel display, etc., during processing thereof in a plasma gas environment.
BACKGROUND OF THE INVENTION
Equipment for processing semiconductor wafers in a plasma gas environment typically couple radio frequency (RF) power from the plasma gas to the wafer to effect surface treatment of the wafer (e.g., etching, deposition, etc). For instance, U.S. Pat. No. 4,617,079 discloses a parallel plate arrangement wherein a wafer is supported on a lower electrode, RF power from a low frequency generator passes through a low frequency network, RF power from a high frequency generator is combined with the low frequency RF power in a high frequency matching and combining network, and the combined signals are applied across upper and lower electrodes. In this arrangement, the high frequency matching and combining circuit can include a high frequency trap (capacitor and inductor in parallel) tuned to the frequency of the high frequency source for preventing signals generated by the high frequency source from being fed back to the low frequency source but allowing signals generated by the low frequency source to pass therethrough without being attenuated.
U.S. Pat. No. 4,948,458 discloses a parallel plate arrangement wherein the upper electrode is in the form of an electrically conductive coil located outside the plasma reaction chamber and by inducing an RF current in the coil a magnetic field is produced in a planar region parallel to the plane of the coil. The coil is driven by an RF generator which supplies power to a matching circuit having a primary coil and a secondary loop. A variable capacitor in series with the secondary loop adjusts the circuit resonant frequency with the frequency output of the RF generator and impedance matching maximizes efficiency of power transfer to the planar coil. An additional capacitor in the primary circuit cancels part of the inductive reactance of the coil in the circuit.
When processing semiconductor wafers in plasma gas environments, it is desired to uniformly process the entire surface of the wafer. For example, U.S. Pat. No. 4,615,755 discloses a plasma etching technique wherein uniformity of the wafer temperature is achieved by He backcooling of a wafer supported on a bowed electrode. By bowing the wafer away from the lower electrode with the cooling helium, cooling performance of the wafer is sacrificed in order to achieve etch uniformity. However, variations in the thickness of the wafer results in sub-standard control of the wafer bowing and thereby reduces the etch uniformity.
In plasma etching processes which use electrostatic (ESC) wafer clamping systems, the wafer cannot be bowed away from the surface of the electrode to control etch rate uniformity. Accordingly, other techniques are necessary for controlling the uniformity of the wafer surface treatment in plasma processing which are applied to ESC wafer clamping systems.
SUMMARY OF THE INVENTION
The invention provides a power segmented electrode for providing uniform processing of a substrate in a plasma reaction chamber. The power segmented electrode includes first and second electrodes and a capacitive network. The power segmented electrode is attachable to the plasma reaction chamber such that the first electrode is distributed across a first zone of the plasma reaction chamber and the second electrode is distributed across a second zone of the of the plasma reaction chamber. The capacitive network controls distribution of radio frequency power in the first and second zones such that plasma coupled to a substrate supported in the plasma reaction chamber provides uniform processing across the substrate. In a preferred embodiment, the substrate comprises a semiconductor wafer and the power segmented electrode is incorporated in an electrostatic chuck located in a plasma reaction etching chamber.
The power segmented electrode can be embodied in various ways. For instance, the first electrode can be separated from the second electrode by a gap filled with dielectric material to form an interelectrode capacitor of the capacitive network. In a preferred embodiment, the first electrode surrounds the second electrode and is separated from the second electrode by a gap filled with dielectric material, the gap forming an interelectrode capacitor of the capacitive network. In this case, the first and second capacitors can form part of the capacitive network and radio frequency power from a power source can pass sequentially through the first capacitor, through the first electrode, through the second capacitor, through the second electrode, and to an electrical ground.
According to another embodiment, the first and second electrodes form part of a concentric electrode arrangement comprising a plurality of spaced apart annular electrodese, the electrodes being electrically connected to a radio frequency power source through variable capacitors forming part of the capacitive network and radio frequency power from the power source sequentially passing through each of the variable capacitors and to a respective one of the electrodes. In this case, current sensing mechanisms can be provided for automatically adjusting capacitance of a respective one of the variable capacitors such that adjustment signals emitted therefrom compensate for deviations from uniformity of processing of the substrate in an annular zone of the substrate facing a respective one of the annular electrodes. The capacitive network can comprise first and second capacitors, the first capacitor being connected to the first electrode and the second capacitor being connected to the second electrode, the first and second capacitors being electrically connected in parallel to a radio frequency power source. The power segmented electrode can include a third electrode, the first electrode surrounding the second electrode and the second electrode surrounding the third electrode, each of the electrodes being electrically connected to a radio frequency power source, radio frequency power from the power source passing sequentially through a power splitter and to a respective one of the electrodes. Alternatively, the first electrode can surround only part of the second electrode. The first and second electrodes can be incorporated in an electrostatic chuck and the electrodes can be electrically connected to direct current biasing sources which allow the chuck to electrostatically clamp a substrate on the chuck. The radio frequency power can be supplied in phase or out of phase to the first and second electrodes. Also, a passive network can be used for supplying power and DC bias to the first and second electrodes.
According to another aspect of the invention, the power segmented electrode can include a sine wave generator for generating a numerically sequenced sine wave, a biasing unit for generating a DC offset value, a summation unit for summing the numerically sequenced sine wave and the DC offset value, a digital/analog converter for converting the signal output from the summation unit to an analog summation signal, a low pass filter for filtering predetermined low frequency portions of the analog summation signal, and a power amplifier for amplifying the analog summation signal filtered by the low pass filter and driving the first and second electrodes with the amplified signal. In this case, the first electrode completely surrounds the second electrode and the capacitive network supplies more power to the second electrode than to the first electrode. The first electrode can surround the second electrode and power is supplied to the first and second electrodes by sequentially passing through the first electrode, an interelectrode capacitor formed by a dielectric material disposed in a gap between the first and

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