Comprehensive guide to AlTi alloys for sputter cathode applications
- Christos Pernagidis
- May 12
- 3 min read
AlTi alloys are a critical material for high-performance sputtering targets in PVD applications.
This article provides a detailed overview of their phase behavior, manufacturing processes, and purity requirements—key factors that determine coating consistency, target lifetime, and process stability in demanding industrial environments.
What are AlTi alloys and why are they used in PVD?
Aluminum-Titanium (AlTi) alloys are widely used in Physical Vapor Deposition (PVD) processes due to their ability to form hard, corrosion-resistant thin films. These coatings are essential for applications in:
Semiconductors
Optics
Decorative and functional surfaces
Cutting tools
Aerospace components
AlTi-based sputter targets enable precise control over film composition and properties, making them ideal for magnetron sputtering and ion plating systems.
AlTi phase diagram: the foundation of alloy design
The AlTi phase diagram is essential for understanding the thermodynamic behavior of these binary alloys. It identifies key intermetallic compounds and phase transformations that directly impact the performance and structure of sputter targets.
Key intermetallic phases:
Al₃Ti: Predominant in Al-rich compositions; tetragonal structure.
AlTi: Found near equiatomic compositions; Ni₃Sn-type structure (hP8, P6₃/mmc).
AlTi₃: Appears in Ti-rich compositions; hexagonal structure.
Important phase transformations:
Peritectic reactions (e.g., L + β ↔ AlTi at ~1480°C)
Order-disorder transformations
Eutectic and eutectoid transitions
These transformations guide alloy selection to balance sputtering behavior and film properties.
Homogeneity and solid solubility:
Aluminum’s solubility in Ti (α-phase): ~10 wt%
Titanium’s solubility in Al: <0.1 wt%
Stoichiometric AlTi: 50:50 at%, with a broad homogeneity range (0.467–0.62)
Controversial regions:
Phase behavior in the 55–77 at.% Al and 900–1450°C range remains debated, highlighting the need for precise control and validation in alloy processing.
Manufacturing AlTi sputter targets: from raw material to final product
The manufacturing of AlTi alloys for sputter cathodes must meet strict requirements for purity, homogeneity, and structural stability.
Common compositions:
67:33, 50:50, 70:30 at.% Al:Ti
Purity levels: 99.6% to 99.9%
Key production techniques:
1. Hot Isostatic Pressing (HIP)
Uniform microstructure
Fine grain size
Optimized for magnetron sputtering systems
2. Vacuum ARC Melting (VAR Melting)
High-purity casting under vacuum
Low contamination risk
Purity and Process Control in AlTi Targets
Why Purity Matters:
Impurities like oxygen, carbon, or iron cause arcing, poor adhesion, or non-uniform films.
Semiconductor-grade targets require impurity levels in the ppb range.
Common Testing Methods:
X-Ray Fluorescence (XRF): Elemental composition
Inductively Coupled Plasma (ICP): Trace metals
Glow Discharge Mass Spectrometry (GDMS): Ultra-sensitive impurity detection
Key Process Controls:
Raw material selection: 3N or higher aluminum and at least titanium grade 2 sponge
Cleanroom conditions for melting and casting in VAR
Continuous monitoring of melt conditions and vacuum levels
Ultrasonic inspections for bonding and microstructural integrity
Sputtering Behavior and Target Poisoning:
In reactive sputtering (e.g., with oxygen or nitrogen), surface compounds like Al₂O₃ or TiN can form, reducing yield.
The AlTi phase diagram is essential to optimize reactive gas flow rates and avoid hysteresis or arcing.
Plasma conditions (argon pressure, power density) must be tailored to each phase’s sputtering rate.
Summary Table: Critical Parameters in AlTi Sputter Target Production
Aspect | Description | Impact |
Purity | 99.8% or better to avoid O, C, Fe contaminants | Ensures sputtering stability and film quality |
Grain Size | Refined to <100 µm through HIP or forging of VAR quality (expansive!) | Promotes uniform erosion and thin film consistency |
Reactive Gases | Oxygen or nitrogen can form insulating compounds on the target | Reduces sputtering efficiency; phase control required |
Burn-In Process | Stabilizes preferential sputtering of Al or Ti during startup | Reaches steady-state composition faster |
Vacuum Processing | Prevents oxidation during melting, casting, and bonding | Maintains purity and mechanical integrity |
Conclusion: AlTi alloys as high-performance sputtering materials
AlTi alloys are a core material class for high-quality sputter cathodes used in PVD systems. A deep understanding of the AlTi phase diagram, combined with advanced manufacturing techniques and strict purity control, enables consistent and reliable coating processes across a range of industries.
By tailoring alloy compositions and processing strategies, manufacturers can meet the growing demands for precision coatings in electronics, optics, tools, and decorative surfaces. Despite ongoing debates in certain phase regions, proper engineering and testing ensure that AlTi targets deliver optimal performance under real-world PVD conditions.
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