Metal Stack Templates for ScAlN Film Growth
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Solution Overview
Problem
The challenge is to develop a metal stack template that promotes the growth of high crystal quality ScxAl1-xN (x=0-0.44) in the desired c-axis direction for ScAlN films, while being compatible with standard CMOS processing to integrate piezoelectric devices directly with CMOS circuitry, as existing templates like Pt are not post-CMOS compatible and lead to secondary grain formation.
Innovation Solution
A single-, double-, or triple-layer metal stack template is used, comprising metals like Ti, AlCu, and TiN, with specific orientations and lattice parameters, deposited using an ionized metal plasma process to achieve a highly textured, c-axis oriented ScAlN film, suppressing secondary grain formation and ensuring compatibility with CMOS processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If Pt template layer is used to promote c-axis growth of ScAlN, then crystal orientation is improved, but secondary grain formation increases and CMOS compatibility is lost
Solution Approach 1:
The patent changes the material parameters of the template layer from Pt to CMOS-compatible metals (Ti, Al, Cu) with specific crystallographic orientations. By selecting metals with appropriate lattice parameters and orientations ({002} for hexagonal, {111} for cubic), the patent achieves c-axis growth promotion while avoiding secondary grain formation, thus resolving the contradiction between crystal orientation quality and harmful secondary grains
Solution Approach 2:
The patent employs composite metal stack templates consisting of multiple layers (e.g., Ti/AlCu, Ti/TiN/AlCu) where each layer serves a specific function. The combination of different metals with complementary properties enables both excellent c-axis orientation promotion and suppression of secondary grains, while maintaining CMOS compatibility throughout the stack structure
2Manufacturing precision
If Pt template layer is used to promote c-axis growth of ScAlN, then crystal orientation is improved, but CMOS compatibility is lost
Solution Approach 1:
The patent fundamentally changes the material selection parameters from non-CMOS-compatible Pt to CMOS-compatible metals (Ti, Al, Cu) while maintaining the desired crystallographic orientation properties. This parameter change enables integration with standard CMOS processing flows, solving the adaptability issue while preserving crystal orientation quality through careful selection of metal orientations and lattice structures
Solution Approach 2:
The patent uses standard CMOS-compatible metals that are already present in or compatible with CMOS fabrication processes, replacing the expensive and incompatible Pt. These metals can be deposited using existing CMOS-compatible deposition equipment and processes, making the template layer disposable and integrable without requiring additional specialized processing steps
3Reliability
If Sc content is increased to enhance piezoelectric constant, then piezoelectric performance is improved, but crystal structure stability deteriorates
Solution Approach 1:
The patent applies preliminary templating action before ScAlN deposition to establish a stable crystal structure foundation. The metal template layer with specific orientation promotes and guides the formation of stable wurtzite structure even at high Sc content, preventing premature transition to rocksalt structure and enabling higher piezoelectric performance without compromising structural stability
Solution Approach 2:
The patent changes the deposition parameters and template characteristics to stabilize the wurtzite crystal structure at high Sc content. By using templates with specific lattice parameters and orientations, the patent extends the stable wurtzite phase to higher Sc concentrations than normally achievable, thereby enhancing piezoelectric performance while maintaining structural stability
4Ease of manufacture
If standard sputtering process is used to deposit template, then manufacturing simplicity is maintained, but template texture quality deteriorates
Solution Approach 1:
The patent modifies the sputtering process parameters (applying ionized metal plasma) to enhance template texture quality while keeping the overall manufacturing approach compatible with standard processes. The ionized plasma provides additional energy and directionality to the deposited atoms, promoting better crystallographic orientation and texture without requiring complete process redesign
Solution Approach 2:
The patent replaces standard physical sputtering with ionized metal plasma deposition, which uses plasma physics mechanisms to enhance the deposition process. The ionized state of metal atoms in the plasma provides improved directional control and energy, resulting in superior template texture quality while maintaining compatibility with vacuum deposition equipment
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
The proposed metal stack templates significantly improve the crystal quality and orientation of ScAlN films, reducing secondary grain formation and enabling high piezoelectric response, while being compatible with post-CMOS processing, thus facilitating the integration of ScAlN-based piezoelectric devices with CMOS circuitry.
Implementation Method 1
at least a portion of the metal stack formed by an ionized metal plasma (IMP) process
Implementation Method 2
deposited using an ionized metal plasma process
Implementation Method 3
a highly textured, c-axis oriented ScAlN film
Data Source
AI summary
A metal stack for templating the growth of AlN and ScAlN films is disclosed. The metal stack comprises one, two, or three layers of metal, each of which is compatible with CMOS post-processing. The metal stack provides a template that promotes the growth of highly textured c-axis {002} AlN and ScAlN films. The metal stacks include one or more metal layers with each metal layer having either a hexagonal {002} orientation or a cubic {111} orientation. If the metal stack includes two or more metal layers, the layers can alternate between hexagonal {002} and cubic {111} orientations. The use of ScAlN results in a higher piezoelectric constant compared to that of AlN for ScAlN alloys up to approximately 44% Sc. The disclosed metal stacks resulted in ScAlN films having XRD FWHM values of less than approximately 1.1° while significantly reducing the formation of secondary grains in the ScAlN films.