Plasma Etching RF-DC Pulse Timing for Mask Selectivity
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Solution Overview
Problem
Conventional plasma processing techniques face challenges in improving the selectivity ratio of masks during etching, particularly in next-generation etching target film structures with reduced pitch and CD size, while maintaining the opening characteristics of concave portions.
Innovation Solution
A plasma processing apparatus that controls RF power and DC pulse voltage with a delay period, where RF power is supplied at varying levels and DC pulse voltage is maintained in an OFF-state during a portion of the cycle, allowing for improved selectivity ratio without damaging the bottom of concave portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If continuous RF power and DC voltage are applied during etching, then etching efficiency is improved, but mask damage and poor selectivity ratio occur
Solution Approach 1:
The patent applies periodic pulsed DC voltage with RF power, where the DC voltage is applied in pulses during the first sub-period and stopped during the second sub-period. This periodic action allows ion bombardment to occur only during specific time windows when plasma density is optimized, improving etching efficiency while preventing continuous mask damage that occurs with constant DC voltage application.
Solution Approach 2:
The patent applies a delay period at the beginning of the first sub-period before applying DC voltage. This preliminary action allows plasma to be generated first, ensuring sufficient electron density and reactive species are present before ion bombardment begins, thereby improving etching efficiency while controlling mask damage through optimized timing sequences.
2Productivity
If higher ion bombardment is applied to improve etching rate, then productivity increases, but mask selectivity ratio deteriorates
Solution Approach 1:
The patent uses periodic pulsed DC voltage where the duty cycle and pulse width are optimized to deliver sufficient ion bombardment for high etching rates during the first sub-period, then stops ion bombardment during the second sub-period to allow mask protection and plasma relaxation, thereby achieving high productivity while maintaining excellent mask selectivity ratio.
Solution Approach 2:
The patent dynamically adjusts the timing and duration of DC voltage application relative to the RF power cycle. By optimizing the delay period, pulse width, and duty cycle, the system dynamically controls ion flux to match plasma density variations, achieving optimal balance between etching rate and mask selectivity ratio for next-generation etching target film structures.
3Speed
If DC voltage is applied immediately with RF power, then etching starts faster, but electron density optimization is compromised
Solution Approach 1:
The patent implements a delay period at the start of the first sub-period where RF power is applied before DC voltage. This preliminary action generates plasma and builds up electron density first, ensuring sufficient reactive species are available when ion bombardment begins, thereby optimizing both etching start speed and electron density for high-quality etching of next-generation structures.
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 solution enhances the selectivity ratio of masks and maintains the verticality of etching target film structures by controlling the timing of RF and DC power, reducing ion collisions and optimizing electron density, thereby improving etching efficiency and mask protection.
Implementation Method 1
radio-frequency power is supplied, and then, a negative direct current (DC) voltage is applied to a lower electrode of a substrate support, to etch a substrate by positive ions from a plasma
Implementation Method 2
the amount of electrostatic charges on the substrate is reduced by the negative ions, thereby improving etching efficiency
Implementation Method 3
positive ions from a plasma... negative ions are supplied to the substrate
Data Source
AI summary
A plasma processing apparatus includes a plasma processing chamber; a substrate support disposed within the plasma processing chamber and including a lower electrode; an upper electrode disposed above the substrate support; and an RF power supply configured to supply an RF signal to the upper electrode or the lower electrode, the RF signal having a first power level during a first sub-period in a repetition period and a second power level during a second sub-period in the repetition period; and a DC power supply configured to supply a DC signal to the lower electrode. The DC signal has an OFF-state during a delay period in the first sub-period, has a sequence of a plurality of DC pulses during the first sub-period excluding the delay period, and has an OFF-state during the second sub-period, the delay period being within a range of 2% to 7% of the repetition period.