Bi-Modal Plasma Etching for High Aspect Ratio Features
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Solution Overview
Problem
High aspect ratio (HAR) etching in semiconductor fabrication faces challenges such as a trade-off between etch rate and etching selectivity, with increasing bias voltage leading to rapid loss of mask material and reduced ion energy reaching the etch front, causing inefficiencies in plasma etching processes.
Innovation Solution
A method involving a bi-modal process gas composition that switches between etching-dominant and deposition-dominant states by varying the radiofrequency power applied, using the same process gas composition to achieve etching and deposition, respectively, while controlling bias voltage to maintain etching selectivity and prevent mask material loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high bias voltage is applied to increase etch rate, then etching speed improves, but mask material is rapidly lost and etching selectivity deteriorates
Solution Approach 1:
The patent applies periodic pulsing of the plasma process, alternating between high-power etching pulses and low-power deposition pulses. During etching pulses, mask material is removed along with target material, but during subsequent deposition pulses, the mask is repaired by depositing material back onto it. This periodic alternation allows net etching to proceed while maintaining mask integrity and selectivity throughout the process.
Solution Approach 2:
The patent intentionally allows mask material to be discarded (etched away) during high-power pulses, then recovers it during low-power deposition pulses by depositing material back onto the mask surface. This cyclical discarding and recovering of mask material enables sustained high etch rates while preserving the mask for the duration of the overall process.
2Productivity
If high bias voltage is applied to improve ion energy at the etch front, then etching efficiency increases, but ion energy is depleted before reaching deep features
Solution Approach 1:
The patent uses periodic pulsing between high-power and low-power states. During high-power etching pulses, ions are accelerated to high energies to efficiently remove material at the etch front. During low-power deposition pulses, the reduced ion energy allows ions to penetrate deeper into high aspect ratio features without being completely depleted, enabling progressive etching of deep structures over multiple pulse cycles.
Solution Approach 2:
The patent performs preliminary etching actions during high-power pulses to clear material from the etch front, then follows with low-power pulses that allow ion energy to penetrate deeper into the feature. This preliminary high-energy action followed by deeper penetration action enables efficient etching of both the opening and deep portions of high aspect ratio structures.
3Adaptability or versatility
If multiple process gas compositions are used to achieve both etching and deposition, then process flexibility improves, but system complexity increases
Solution Approach 1:
The patent employs a single process gas composition that can operate in multiple modes depending on the applied power level. At high power, the same gas composition produces etching-dominant plasma, while at low power it produces deposition-dominant plasma. This multi-functionality of a single gas system eliminates the need for multiple gas delivery systems, valves, and control mechanisms, thereby reducing system complexity while maintaining process flexibility.
Solution Approach 2:
The patent changes the operating parameters (specifically RF power level and bias voltage) of a single process gas composition to achieve different plasma chemistry states. By adjusting these parameters between high and low values in a pulsing sequence, the same gas composition transitions between etching and deposition modes, providing process flexibility without requiring multiple gas compositions or complex gas switching infrastructure.
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 approach enhances etching selectivity and throughput by allowing fast switching between etching and deposition states, maintaining mask material integrity and improving etch rates in high aspect ratio features without requiring multiple gas compositions, thus addressing the limitations of conventional plasma etching techniques.
Implementation Method 1
a first radiofrequency power is applied to the bi-modal process gas composition within the plasma generation region to generate a plasma in exposure to the substrate. The plasma generated through application of the first radiofrequency power causes etching-dominant effects on the substrate
Implementation Method 2
a second radiofrequency power is applied to the bi-modal process gas composition within the plasma generation region to generate the plasma in exposure to the substrate. The plasma generated through application of the second radiofrequency power causes deposition-dominant effects on the substrate
Implementation Method 3
bias voltage applied to attract charged constituents of the plasma toward the substrate
Data Source
AI summary
A substrate is disposed on a substrate holder within a process module. The substrate includes a mask material overlying a target material with at least one portion of the target material exposed through an opening in the mask material. A bi-modal process gas composition is supplied to a plasma generation region overlying the substrate. For a first period of time, a first radiofrequency power is applied to the bi-modal process gas composition to generate a plasma to cause etching-dominant effects on the substrate. For a second period of time, after completion of the first period of time, a second radiofrequency power is applied to the bi-modal process gas composition to generate the plasma to cause deposition-dominant effects on the substrate. The first and second radiofrequency powers are applied in an alternating and successive manner for an overall period of time to remove a required amount of exposed target material.