Dual-Lower Electrode Plasma Processing for Density Uniformity
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Solution Overview
Problem
Conventional capacitively coupled plasma processing apparatuses face nonuniformity in plasma density and etching accuracy due to high-frequency power distribution issues when using dual frequencies, leading to trade-offs between plasma uniformity and anisotropic etching uniformity.
Innovation Solution
The apparatus vertically divides the lower electrode into two parts, applying a first high frequency power of a lower frequency to the upper electrode and a second high frequency power of a higher frequency to the lower electrode, with the lower electrode having a recess filled with a dielectric material and a high-resistivity material to optimize electric field intensity distributions for plasma generation and ion attraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a high frequency power of a high frequency (40 MHz or greater) is applied to a single lower electrode, then plasma generation efficiency is improved, but plasma density becomes nonuniform in the radial direction due to skin effect
Solution Approach 1:
The lower electrode is divided into a first lower electrode and a second lower electrode that are electrically isolated from each other. The first lower electrode receives high frequency power for plasma generation, while the second lower electrode receives high frequency power for ion attraction. This segmentation allows independent optimization of each electrode's function, resolving the contradiction between plasma generation efficiency and plasma density uniformity.
Solution Approach 2:
The first lower electrode is provided with a recess filled with dielectric material at its central portion, creating local impedance variation. This local quality modification adjusts the electric field distribution specifically at the central region, compensating for the nonuniform plasma density caused by skin effect while maintaining high plasma generation efficiency.
2Adaptability or versatility
If dual high frequency powers are applied to a single lower electrode, then plasma density and anisotropic etching selectivity can be optimized, but electric field intensity distribution becomes nonuniform leading to trade-offs between plasma uniformity and anisotropic etching uniformity
Solution Approach 1:
By dividing the lower electrode into two electrically isolated electrodes, each can be independently controlled with different high frequency powers. The first lower electrode optimizes plasma density while the second lower electrode optimizes ion attraction for anisotropic etching, eliminating the trade-off that occurs when both functions are combined in a single electrode.
Solution Approach 2:
The recess filled with dielectric material in the first lower electrode creates localized impedance modification that adjusts electric field intensity distribution. This ensures uniform electric field across the electrode surface, which directly improves anisotropic etching uniformity while maintaining the ability to independently control plasma density through dual frequency application.
3Manufacturing precision
If a high-resistance member is disposed at the central portion of the electrode, then electric field distribution is improved, but power consumption increases due to Joule heat
Solution Approach 1:
Instead of using a high-resistance member that dissipates energy as Joule heat, a dielectric material is used as an intermediary substance in the recess. The dielectric material modifies the electric field distribution through its permittivity properties without causing significant resistive losses, thus improving electric field uniformity while avoiding the energy loss associated with high-resistance members.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration allows for independent control of electric field intensities, improving the efficiency and accuracy of plasma processing by ensuring uniform plasma density and anisotropic etching across the substrate.
Implementation Method 1
forming flowerpot-shaped or tapered recesses on a main surface of an electrode to which a high frequency power is applied and burying a dielectric material in the recesses
Implementation Method 2
a high frequency power is applied to either one of the upper and the lower electrode. Electrons are accelerated by an electric field formed by the high frequency power to collide with a processing gas. As a result of ionization by the collision between the electrons and the processing gas, a plasma is generated
Implementation Method 3
a high frequency power applied from a high frequency power supply to a rear surface or a backside surface of an electrode via a power supply rod is made to propagate to an electrode main surface (which faces a plasma) by a skin effect, whereby a high frequency current is made to flow on the electrode main surface from an edge portion toward a central portion thereof
Data Source
AI summary
In a plasma processing apparatus including a vacuum-evacuable processing chamber, a first lower electrode for supporting a substrate to be processed thereon is disposed in the processing chamber and an upper electrode is disposed above the first lower electrode to face the first lower electrode. Further, a second lower electrode is disposed under the first lower electrode while being electrically isolated from the first lower electrode. A processing gas supply unit supplies a processing gas into a space between the upper electrode and the first lower electrode. A first high frequency power supply unit applies a first high frequency power of a first frequency to the first lower electrode, and a second high frequency power supply unit applies a second high frequency power of a second frequency higher than the first frequency to the second lower electrode.