Plasma Chamber Capacitance Tuning for Stable Sheath Voltage
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Solution Overview
Problem
Conventional DC pulse implementations in plasma processing face challenges due to substrate charging, which reduces the voltage differential and lowers the effectiveness of ion flux at the substrate, making it difficult to maintain optimal parameter values for plasma sheath voltage without altering DC pulse frequency or duty ratios.
Innovation Solution
A plasma processing apparatus with a tunable electrical characteristic, utilizing a capacitive pre-coat layer and a tuning circuit with variable capacitance, adjusts the RC time constant to control substrate charging and maintain sheath voltage, allowing control over ion energy distribution and flux without altering DC pulse frequency or duty ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If DC pulse frequency and duty ratios are manipulated to reduce substrate charging, then substrate charging is reduced, but ion energy distribution function changes undesirably
Solution Approach 1:
The patent introduces a new parameter (capacitance of pre-coat layer) to control substrate charging without changing the DC pulse frequency or duty ratios. By adjusting the capacitance value, the RC time constant is modified to reduce charge buildup on the substrate while maintaining the desired ion energy distribution function.
Solution Approach 2:
The pre-coat layer with specific capacitance acts as an intermediary between the DC pulse generator and the substrate. It mediates the charging process by storing and releasing charge in a controlled manner, reducing substrate charging without directly altering the DC pulse parameters that control ion energy.
2Strength
If DC pulse frequency is increased to maintain sheath voltage, then sheath voltage is maintained, but substrate charging increases
Solution Approach 1:
Instead of increasing DC pulse frequency to maintain sheath voltage, the patent changes the capacitance parameter of the pre-coat layer. This allows the system to maintain sheath voltage through controlled charge storage and release, avoiding the harmful effect of increased substrate charging that would result from higher pulse frequencies.
3Quantity of substance
If DC pulse frequency and duty ratios are adjusted to control ion flux, then ion flux is controlled, but charge buildup on biased electrode increases
Solution Approach 1:
The pre-coat layer serves as a charge management intermediary that decouples ion flux control from charge buildup. By selecting appropriate capacitance values, the system can maintain desired ion flux levels while the pre-coat layer absorbs excess charge, preventing charge buildup on the biased electrode.
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
The apparatus effectively reduces substrate charging, enabling control over ion energy spread, increasing average ion energy, and enhancing high energy ion flux at the substrate, thereby improving plasma processing efficiency.
Implementation Method 1
a capacitive pre-coat layer disposed between the DC coupling element and the plasma. The capacitive pre-coat layer increases the RC time constant of the DC current path according to the DC pulse frequency
Implementation Method 2
a source power coupling element configured to generate plasma in an interior of the plasma processing chamber by coupling source power to the plasma processing chamber
Implementation Method 3
a DC pulse generator configured to generate a DC pulse train at a DC pulse frequency... the DC coupling element being configured to bias the substrate holder relative to the reference potential node using the DC pulse train
Data Source
AI summary
A method of tuning an electrical characteristic of a plasma processing chamber of a plasma processing apparatus includes determining a capacitance value from a range of capacitance values according to a direct current (DC) pulse frequency of a DC pulse train to be generated by a DC pulse generator of the plasma processing apparatus, tuning the electrical characteristic by selecting the determined capacitance value using a tuning circuit coupled between a DC coupling element and the DC pulse generator, the tuning circuit comprising a variable capacitance tunable in the range of capacitance values, and biasing the DC coupling element relative to a reference potential node by generating the DC pulse train at the DC pulse frequency using the DC pulse generator.