Scandium Aluminium Nitride Sputtering for Low-Defect RF Films
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Solution Overview
Problem
Existing methods for depositing additive-containing aluminium nitride films face challenges in maintaining low defect density and high electromechanical coupling coefficient, especially when the additive concentration exceeds 8 At%, which affects the quality and crystallinity of the films used in RF resonator devices.
Innovation Solution
A pulsed DC reactive sputtering method involving a two-step process where a first layer is deposited in a highly nitrogen-rich atmosphere to create a seed layer with compressive stress, followed by a second layer with a lower nitrogen content gas mixture, reducing argon incorporation and enhancing sputtering efficiency, thereby reducing crystallographic defects and improving texture and crystallinity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the amount of additive element in additive-containing aluminium nitride is increased to improve electromechanical coupling coefficient, then the electromechanical coupling coefficient increases, but crystallographic defects increase and film quality deteriorates
Solution Approach 1:
The deposition process is divided into two distinct stages: a first deposition stage using a nitrogen-rich atmosphere (87-100% nitrogen) to deposit an initial layer, and a second deposition stage using a mixed atmosphere to deposit the remaining film thickness. This segmentation allows the first stage to control nucleation and suppress defect formation, while the second stage completes the film with the desired composition, resolving the contradiction between high additive content and low defect density.
Solution Approach 2:
The invention changes the gas composition parameter during deposition - specifically, the percentage of nitrogen gas in the flowing gas mixture. By using a nitrogen-rich atmosphere (87-100% nitrogen) during the first deposition stage and then adjusting to a mixed atmosphere (nitrogen plus inert gas) for the second stage, the process optimizes both defect suppression and film quality, enabling high electromechanical coupling coefficient with acceptable defect density.
2Ease of manufacture
If conventional single-stage deposition is used, then the process is simple, but defect density is high and film texture is poor when additive concentration exceeds 8 At%
Solution Approach 1:
The deposition process is divided into two distinct stages: a first deposition stage using a nitrogen-rich atmosphere (87-100% nitrogen) to deposit an initial layer, and a second deposition stage using a mixed atmosphere to deposit the remaining film thickness. This segmentation allows the first stage to control nucleation and suppress defect formation, while the second stage completes the film with the desired composition, resolving the contradiction between high additive content and low defect density.
Solution Approach 2:
The invention changes the gas composition parameter during deposition - specifically, the percentage of nitrogen gas in the flowing gas mixture. By using a nitrogen-rich atmosphere (87-100% nitrogen) during the first deposition stage and then adjusting to a mixed atmosphere (nitrogen plus inert gas) for the second stage, the process optimizes both defect suppression and film quality, enabling high electromechanical coupling coefficient with acceptable defect density.
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 allows for higher additive element concentrations while maintaining acceptable defect density and texture, enhancing the electromechanical coupling coefficient and piezoelectric properties of the films, making them suitable for high-quality RF resonator devices.
Implementation Method 1
a first layer of the additive-containing aluminium nitride film is sputter deposited onto a substrate... by pulsed DC reactive sputtering
Implementation Method 2
The film is deposited by reactive sputtering such as pulsed DC reactive sputtering
Data Source
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AI summary
According to the present invention there is provided a method for sputter depositing an additive-containing aluminium nitride film containing an additive element selected from Sc or Y, the method comprising the steps of: depositing a first layer of the additive-containing aluminium nitride film onto a substrate disposed within a chamber by pulsed DC reactive sputtering; and depositing a second layer of the additive-containing aluminium nitride film onto the first layer by pulsed DC reactive sputtering, the second layer having the same composition as the first layer; wherein: the step of depositing the first layer comprises introducing a gas or gaseous mixture into the chamber at a flow rate (in sccm), and 87-100 % of the flow rate (in sccm) is a flow of nitrogen gas; the step of depositing the second layer comprises introducing a gaseous mixture into the chamber at a flow rate (in sccm), the gaseous mixture comprising nitrogen gas and an inert gas; and the percentage of nitrogen gas in the flow rate (in sccm) used during the step of depositing the first layer is greater than the percentage of nitrogen gas in the flow rate (in sccm) used during the step of depositing the second layer.