AlScN Plasma Etching for Uniform Sidewalls Without Redeposition
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Solution Overview
Problem
Plasma etching of aluminium scandium nitride (AIScN) films results in undesirable multi-stepped sidewall profiles due to redeposition of Sc by-products, which complicates subsequent processing and requires additional cleaning steps, and existing methods either fail to prevent redeposition or introduce inconsistencies in etch profiles.
Innovation Solution
A plasma etching method that transitions from a more chemical to a more physical etching regime by adjusting gas pressure and RF bias power, reducing redeposition and achieving a uniform, single-angled sidewall without the need for post-etch cleaning or mask reflow, using a gaseous atmosphere with a chlorine-containing etch precursor and inert gases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional plasma etching is used on AIScN, then etching can be performed, but redeposition of Sc by-products forms on sidewalls creating multi-stepped profiles
Solution Approach 1:
The etching process uses periodic modulation of RF bias power between two frequencies (13.56 MHz and 27.12 MHz) to alternately enhance physical sputtering (for redeposition removal) and chemical etching (for anisotropic profiling), thereby preventing multi-stepped sidewall profiles while maintaining etching efficiency
Solution Approach 2:
The process dynamically changes plasma parameters by modulating RF bias power frequency and amplitude, transitioning between physical and chemical etching regimes during the etching cycle to control redeposition and sidewall profile formation
2Manufacturing precision
If photoresist reflow is used to prevent redeposition, then sidewall profile can be improved, but etch selectivity to mask decreases and CD loss increases
Solution Approach 1:
By periodically switching between chemical and physical etching modes, the process achieves sidewall profile control without requiring mask reflow, thereby maintaining high etch selectivity to the photoresist mask and preventing CD loss
Solution Approach 2:
The mechanical/thermal reflow process is replaced by plasma-based physical sputtering during the periodic cycle, which removes redeposition material without altering mask geometry or compromising mask integrity
3Productivity
If physical etching regime is used to remove redeposition, then redeposition removal rate increases, but etch anisotropy decreases
Solution Approach 1:
The process alternates between physical sputtering (for redeposition removal) and chemical etching (for anisotropic profile formation) in a periodic cycle, achieving both high redeposition removal rates and maintained etch anisotropy
Solution Approach 2:
By dynamically changing RF bias power parameters between two frequencies, the process transitions between physical and chemical etching regimes, optimizing both redeposition removal and etch anisotropy at different phases of the cycle
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 method effectively prevents redeposition on the etched structure, maintains high selectivity to masks, and achieves consistent etch profiles across varying feature sizes and shapes, eliminating the need for post-etch cleaning and reflow processes.
Implementation Method 1
The sputter removal rate is dependent on the mask thickness, mask angle and etch conditions such as pressure and DC bias
Implementation Method 2
Sc has very few volatile by-products and therefore is prone to the formation of redeposition material which builds up in considerable thickness on the etched AIScN sidewall
Data Source
Figure 1(a)~2(c)
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AI summary
According to the invention there is provided a method of plasma etching an additive-containing aluminium nitride film comprising plasma etching an additive-containing aluminium nitride film containing an additive element selected from Sc, Y or Er through a mask for a period of time, t, with a plasma formed in a gaseous atmosphere having an associated gas pressure while a RF bias power is applied to the additive-containing aluminium nitride film; wherein the gas pressure is reduced and/or the RF bias power is increased for a majority of the period of time t, so that the plasma etching becomes less chemical and more physical over a majority of the period of time, t.