Plasma Etching Additive-AlN Films with BCl3 and Cl2
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Solution Overview
Problem
The etching of additive-containing aluminium nitride films, such as AlScN, with high scandium content faces challenges in achieving steep sidewall profiles and high selectivity to masks and underlayers due to decreased etch rates and increased defectivity, which impairs the performance of piezoelectric devices like BAW devices.
Innovation Solution
A plasma etching method using a boron trichloride to chlorine gas flow rate ratio of 1:1 or greater, with optional argon addition, and a two-stage etching process with adjusted power and pressure, to enhance etch rates and selectivity, particularly by promoting boron-nitrogen polymer formation and increasing the sputter component of the etch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If standard chlorine/argon based chemistries are used to etch additive-containing aluminium nitride films, then the etch rate decreases with increasing scandium content, but the sidewall profile becomes shallower and mask selectivity is reduced
Solution Approach 1:
The patent changes the chemical composition parameters of the etching gas from standard chlorine/argon to a boron trichloride-based chemistry with specific ratios (BCl3:Cl2 ≥ 1:1). This parameter change enables simultaneous achievement of high etch rates and steep sidewall profiles in high Sc content AIScN films, resolving the contradiction between etch rate and sidewall angle control.
Solution Approach 2:
The patent uses a composite gas chemistry system combining boron trichloride and chlorine in specific ratios, creating a synergistic etching environment. The BCl3 provides boron-nitrogen polymer formation for sidewall protection and enhanced etch rate, while Cl2 contributes to the etching chemistry, together resolving the trade-off between etch rate and profile control.
2Reliability
If the scandium content in aluminium nitride is increased to improve piezoelectric properties, then the etch rate decreases and underlayer selectivity is reduced, but the piezoelectric performance improves
Solution Approach 1:
The patent applies parameter changes in the etching chemistry (introducing BCl3 with Cl2 in ratios ≥ 1:1) that enable high etch rates even in high Sc content films. This allows the use of high Sc content for improved piezoelectric performance without suffering from reduced productivity, as the new chemistry maintains high etch rates across all Sc compositions.
3Device complexity
If conventional etching methods are used, then the process is simpler, but the selectivity to masks and underlayers is reduced and underlayer loss increases
Solution Approach 1:
The patent introduces specific gas composition parameters (BCl3:Cl2 ratio ≥ 1:1) that inherently provide enhanced selectivity to masks and underlayers through boron-nitrogen polymer formation. This chemical mechanism automatically protects underlying layers without requiring additional process steps, maintaining simplicity while improving manufacturing precision.
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 achieves steeper sidewall profiles and increased selectivity to masks and underlayers, reducing underlayer loss and improving the performance of piezoelectric devices by optimizing the etch rate and selectivity of additive-containing aluminium nitride films.
Implementation Method 1
promoting boron-nitrogen polymer formation
Implementation Method 2
increasing the sputter component of the etch
Data Source
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AI summary
A method of plasma etching an additive-containing aluminium nitride film is disclosed, the additive-containing aluminium nitride film containing an additive element selected from scandium, yttrium or erbium. The method comprises placing a workpiece upon a platen within a plasma chamber, the workpiece comprising a substrate having an additive-containing aluminium nitride film deposited thereon and a mask disposed upon the additive-containing aluminium nitride film, which defines at least one trench. The method further comprises introducing a first etching gas into the chamber with a first flow rate, introducing a second etching gas into the chamber with a second flow rate, and establishing a plasma within the chamber to etch the additive-containing aluminium nitride film exposed within the trench. The first etching gas comprises boron trichloride and the second etching gas comprises chlorine, and a ratio of the first flow rate to the second flow rate is greater than or equal to 1:1.