AlScN Plasma Etching Chemistry for Underlayer Selectivity
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Solution Overview
Problem
The etching of AlScN films with high scandium content faces challenges such as reduced etch rate, decreased selectivity to masks and metal underlayers, leading to issues like shallower sidewall angles and increased underlayer loss, which impair device performance.
Innovation Solution
A plasma etching method using specific gas ratios and plasma conditions, including BCl3, H2, and an inert diluent gas, with controlled ratios and power settings, to enhance selectivity to metal underlayers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high scandium content is used in AlScN film to improve piezoelectric properties, then piezoelectric performance is improved, but etch rate decreases and selectivity to metal underlayers deteriorates
Solution Approach 1:
The patent changes the chemical composition parameters of the etching plasma by introducing BCl3 gas in combination with H2 and inert diluent gas at specific flow rate ratios. This chemical parameter change enables effective etching of high-Sc content AlScN films by altering the etching mechanism to one that is less sensitive to Sc content, thereby resolving the contradiction between maintaining high piezoelectric performance and achieving sufficient etch rate
Solution Approach 2:
The patent uses BCl3 as an intermediary chemical species that mediates the etching process. The BCl3 introduces boron-containing reactive species that facilitate the etching of AlScN films with high scandium content, acting as a bridge between the plasma environment and the resistant AlScN material, thus improving etch rate without compromising the underlying metal layer selectivity
2Reliability
If high scandium content is used in AlScN film, then piezoelectric properties are enhanced, but selectivity to masks deteriorates leading to shallower sidewall angles
Solution Approach 1:
The patent modifies the plasma chemistry parameters by using BCl3 combined with H2 and inert diluent gas at controlled ratios. This changes the etching mechanism from a physical/sputtering-dominated process to a chemical reaction-dominated process, which maintains anisotropic etching and steep sidewall angles even in high-Sc content films, thereby preserving manufacturing precision while enabling high piezoelectric performance
3Productivity
If etch rate is increased by adjusting platen bias or Cl2 flow, then AlScN etch rate improves, but underlayer loss increases
Solution Approach 1:
The patent introduces BCl3 as an intermediary that selectively reacts with AlScN film while being less reactive with metal underlayers. The specific gas ratio formulation creates a plasma chemistry that preferentially etches the AlScN film through boron-chlorine-aluminum-scandium reactions, while the H2 component helps protect the metal underlayer by reducing metal-chlorine reactions, thus achieving high etch rate with minimal underlayer loss
Solution Approach 2:
The patent creates locally different chemical environments at the AlScN film interface versus the metal underlayer interface by controlling the BCl3:H2:inert diluent gas ratios. This local quality differentiation ensures that the etching chemistry is aggressive toward AlScN (high etch rate) while being gentle toward metal underlayers (low underlayer loss), resolving the contradiction between productivity and material loss
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
Improves the selectivity of AlScN etching to metal underlayers, maintaining sidewall profiles and reducing underlayer loss, thus enhancing device performance.
Implementation Method 1
establishing a plasma within the chamber to plasma etch the additive-containing aluminium nitride film
Implementation Method 2
the etch becomes increasingly physical
Implementation Method 3
standard chlorine (Cl2)/argon (Ar) based chemistries
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
An apparatus and method are disclosed for plasma etching an additive-containing aluminium nitride film containing an additive element selected from scandium (Sc), yttrium (Y) or erbium (Er). The method comprises the steps of: placing a workpiece upon a substrate support within a plasma chamber, the workpiece comprising a substrate having a metal film disposed thereon, an additive-containing aluminium nitride film deposited on the metal film and a mask disposed upon the additive-containing aluminium nitride film which defines at least one trench; introducing BCl3 gas into the chamber with a BCl3 flow rate in sccm; introducing H2 gas into the chamber with a H2 flow rate in sccm; introducing an inert diluent gas into the chamber with an inert diluent gas flow rate in sccm; and establishing a plasma within the chamber to plasma etch the additive-containing aluminium nitride film exposed within the trench; wherein a ratio of the inert diluent gas flow rate to the BCl3 flow rate is in the range 1:3 to 1:11 and a ratio of the BCl3 flow rate to the H2 flow rate is in the range 11:1 to 2:1.