Titanium targets are central to magnetron sputtering in Vapor deposition, enabling the Preparation of thin films with tight control over thickness (±1–2%) and uniformity (≤2–3% 1σ across 200–300 mm wafers). Their high sputter yield in Ar and Ar/N2 plasmas, low impurity levels (<10–20 ppm O, C, N), and stable morphology support barrier/adhesion layers for Logic devices and interconnect stacks, as well as diffusion barriers in New storage devices. In Ti and TiN processes, deposition rates of 0.5–2.0 nm/s at power densities of 5–15 W/cm² are routine, while step coverage can be enhanced via collimation or HiPIMS for high-aspect trenches (AR 5:1–10:1). Titanium’s low resistivity in TiN (20–60 μΩ·cm) and strong adhesion to Si/SiO2/low k dielectrics reduce via resistance and electromigration risk, improving yield by 0.5–1.5% in advanced BEOL flows. For Advanced devices such as three-dimensional integration, wafer-to-wafer and die-to-wafer bonding benefit from Ti/TiN’s robust interfaces and diffusion control. With optimized target purity, cooling, and magnetic confinement, titanium targets deliver repeatable, contamination-lean films that scale from 200 mm to 300 mm production with excellent tool-to-tool matching.
1. Functional Material Requirements in IC Metallization
High-purity metal sputtering targets address diverse film functions across front-end-of-line (FEOL), middle-of-line (MOL), back-end-of-line (BEOL), and advanced assembly:
· Interconnect wiring: conductive lines in Al or Cu ecosystems
· Diffusion barriers: prevent cross-diffusion between metals and dielectrics/semiconductors
· Vias and contacts: low-resistance, stable junctions to transistor source/drain and gate
· Metal gates: stable work function, thermal endurance, and interface control
· Wetting and adhesion layers: robust interfaces for subsequent metals or solders
· Anti-oxidation and capping layers: suppress corrosion and electromigration, protect Optical stacks in some packaging contexts
1.1 Evolution of interconnects
· Early Al interconnects: Aluminum and aluminum alloys formed the primary lines; titanium served as a diffusion barrier/adhesion layer beneath Al to suppress spiking into Si and to improve line integrity.
· Post-90 nm, Cu interconnects: Copper and Cu alloys became mainstream for lower resistivity and better electromigration performance, with tantalum (Ta/TaN) replacing Ti/TiN as the dominant barrier/liner system. Even so, Ti/TiN maintained roles in underlayers, capping, and specialized integration steps (e.g., W plug liners).
1.2 Contact materials to transistors
As nodes scaled, contact silicides evolved from TiSi2 and CoSi2 toward Ni-based silicides (e.g., NiPtSi) to lower contact resistance and maintain junction integrity. Titanium remained relevant as an adhesion/wetting promoter and as part of tailored barrier stacks interfacing with these silicides.
1.3 Metal gate integration
With the introduction of high k dielectrics and metal gates at the 45 nm era, metals such as titanium and tantalum (and their nitrides) supplanted polysilicon for gate electrodes to tune effective work function and increase thermal stability. Ti/TiN layers, deposited by sputtering or reactive sputtering, became integral to gate stacks due to controllable work function, strong adhesion to high k oxides, and excellent Corrosion resistance in subsequent wet cleans.
2. R&D Landscape for High-Purity Titanium Targets in IC Manufacturing
2.1 Roles of Ti and TiN films
· Ti/TiN in Al interconnect flows:
o Ti or Ti/TiN acts as a diffusion barrier between Al lines and Si, protecting junctions from Al spiking.
o Ti serves as a base/adhesion layer, a cap, and an anti-reflective layer that improves lithographic contrast for Optical critical dimension control.
· Ti/TiN with W plugs:
o Ti is commonly used as the underlayer and adhesion layer prior to CVD W, aiding nucleation and improving plug continuity.
· TiN in Cu interconnect flows:
o PVD TiN can function as a robust hard mask or etch stop; it also serves as a protective cap layer over Ni Pt compounds and as part of barrier stacks in specific dual-damascene or via-first variants.
· Advanced packaging:
o Ti/TiN supports under-bump metallization (UBM), redistribution layers (RDL), and as a wetting layer to enhance solder joint reliability, thanks to strong adhesion and Corrosion resistance.
2.2 Global capability and gaps
· Global status: Overall, domestic and international suppliers can mass-produce most IC-grade titanium target formats for 200/300 mm platforms with competitive performance in purity and dimensional control.
· Remaining gaps: There is still separation from the global frontier in long-life/high-efficiency target designs, ultra-fine grain microstructures, residual-stress control, and high-strength diffusion-bonded multi-tile targets that minimize particle risk during end-of-life.
· Purification progress:
o Because titanium is chemically active and challenging to purify, advanced flows combine molten-salt electrolysis with electron-beam (EB) refining to deliver 4N5 (99.995%) and 5N (99.999%) purity feedstock at scale.
o Further improvements are needed in 5N5 (99.9995%) routes, ingot homogeneity, and billet-to-billet consistency to match the tightest parametric controls demanded by leading-edge Logic devices and New storage devices.
3. How to Increase Sputtering Efficiency of Titanium Targets
Sputtering efficiency is a system outcome: target metallurgy, geometry, and backing meet process physics and tool architecture. Key levers include:
3.1 Purity, inclusions, and gas control
· Purity targets:
o For mainstream BEOL liners and caps, 4N–4N5 Ti typically suffices; for ultra-sensitive stacks (e.g., barrier under extreme low k dielectrics or front-end Optical stacks), 5N Ti can reduce oxygen, carbon, nitrogen, and metallic tramp impurities to the low ppm or sub ppm regime.
· Inclusion control:
o Agglomerates of TiO, TiN, or intermetallics cause arcing, particle bursts, and wafer defects. EB melting with multiple passes, inert-atmosphere handling, and high-precision deoxidation/decarburization limit inclusion size and frequency.
· Outgassing:
o Degassing schedules for targets and backing plates reduce trapped gases that destabilize plasma and shift the process window. Vacuum bake or controlled pre-sputter sequences shorten time-to-stability and improve wafer-to-wafer uniformity.
3.2 Microstructure: density and grain engineering
· High density (>99.5% theoretical) reduces “wormholes,” suppresses micro-arcing, and raises sputter yield consistency as the erosion track advances.
· Fine, equiaxed grains (e.g., 10–50 µm) with low texture anisotropy promote uniform erosion and stable secondary electron emission, improving thickness uniformity across 200–300 mm wafers.
· Hot isostatic pressing (HIP) and carefully tuned rolling/forging create uniform density; stress-relief anneals prevent microcracks that otherwise shed particles late in the target life.
3.3 Backing, bonding, and thermal management
· Diffusion-bonded or metallurgically bonded Ti to Cu (or Ti to Al for specific tools) ensures low thermal resistance and efficient heat extraction. Stable bonding curbs hot spots, which can trigger arcing and chemistry drift.
· Cooling optimization:
o Match water flow, channel design, and magnet pack gap to maintain a uniform temperature field across the racetrack. Temperature gradients worsen film composition drift in reactive sputtering (e.g., TiN).
· Tile-mosaic designs:
o For large cathodes, tight-gap multi-tile assemblies with precision shims minimize step edges that cause local plasma intensification and debris.
3.4 Reactive sputtering control for TiN
· Process stabilization:
o Implement partial-pressure feedback or optical emission control to regulate nitrogen flow and avoid “hysteresis” between metallic and poisoned target states.
· High Power Impulse Magnetron Sputtering (HiPIMS):
o HiPIMS increases ionization fraction, improving step coverage and density at modest substrate bias. This can raise conformality for high-aspect vias/trenches (AR 5:1–10:1), important for Advanced devices such as three-dimensional integration.
· Target conditioning:
o Standardize pre-sputter recipes (e.g., several minutes at production power) to clean the surface, remove adsorbates, and stabilize the racetrack before exposure to product wafers.
3.5 Particle and arc mitigation
· Edge shielding and raceway guards capture flakes from the target periphery.
· Low-defect clamping hardware, smooth shields, and clean magnet arrays reduce local field spikes.
· Real-time arc suppression electronics (fast arc detect/quench) protect the wafer and sustain plasma stability, especially in reactive modes.
3.6 Metrology-driven feedback
· Close the loop using:
o In-situ rate monitors and endpoint Optical emission signals
o Ex-situ four-point probe, XRR, XRD, SIMS for composition/thickness
o Particle monitors (wafer scanners) to track end-of-life and schedule target swaps
· Statistical process control (SPC) on sheet resistance Rs, film stress, and uniformity (≤2–3% 1σ) helps standardize recipes across multiple chambers and fabs.
4. Efficiency Benchmarks in Production Context
While tool, recipe, and wafer size determine absolute numbers, mature lines commonly see:
· Deposition rates:
o Ti: ~0.5–2.0 nm/s at 5–15 W/cm² DC magnetron power with Ar; higher with optimized target-cathode designs.
o TiN (reactive): ~0.2–1.0 nm/s depending on N2 partial pressure and regime (transition vs. poisoned).
· Uniformity:
o ≤2–3% 1σ across 200/300 mm wafers with proper magnet shimming and pedestal rotation.
· Electrical/structural:
o TiN resistivity: ~20–60 µΩ·cm, tunable via N content and substrate bias; dense films with low hydrogen uptake improve electromigration margins in BEOL.
· Adhesion and barrier function:
o Ti/TiN stacks provide low contact resistance to Si/SiO2 and robust diffusion blocking against Al, Cu, and W, supporting yield improvements particularly in MOL/BEOL vias.
5. Reliability, Corrosion Resistance, and Clean Integration
· Chemical robustness:
o Ti/TiN layers resist common cleans and mild plasma exposures; Ti’s Corrosion resistance is advantageous in wet steps and packaging environments. This stability helps preserve work function in gate stacks and maintain contact integrity.
· Interface engineering:
o Proper wetting/adhesion underlayers reduce via resistance variability and prevent delamination under thermal cycling.
· Cleanroom compatibility:
o Low-particle targets, controlled surface roughness, and inert handling protect Optical lithography fidelity by limiting stray reflectance and defectivity near critical features.
6. Supply and Standardization
Target Specifications:
Rotating, planar, single-piece, and multi-piece targets are standard configurations for 200/300 mm targets from major original equipment manufacturers (OEMs); their flatness and hole shape are held to strictly controlled mechanical tolerances.
Advances in Purification Processes:
Molten salt electrolysis combined with electron beam refining technology has enabled the domestic production of 4N5-5N and 5N5 titanium raw materials. Contact us for details.
Frequently Asked Questions and Answers
Q1: What purity levels are required for titanium targets used in high-precision integrated circuit (IC) manufacturing to ensure minimal impurity contamination and meet strict device performance standards?
A1: For mainstream BEOL barrier/adhesion applications, 4N–4N5 (99.99–99.995%) purity is typically sufficient. For the most sensitive FEOL/MOL interfaces, Optical anti-reflective layers, or ultra-low-defect BEOL caps, 5N (99.999%) is preferred to minimize O, C, N, and metallic tramp elements to low-ppm or sub-ppm levels. Leading-edge logic or New storage devices targeting the tightest leakage and reliability windows may specify 5N or higher, with strict lot-to-lot homogeneity and certified impurity budgets.
Q2: How does the density and grain uniformity of titanium targets affect the sputtering rate and thin-film thickness control in high-precision integrated device fabrication processes?
A2: High relative density (>99.5% theoretical) and fine, uniform grains stabilize sputter yield across the racetrack, reducing arcing and particle generation. Uniform microstructure delivers consistent secondary electron emission and erosion behavior, improving within-wafer uniformity (often ≤2–3% 1σ) and wafer-to-wafer repeatability. Coarse or porous regions can create hot spots and rate drift, degrading thickness control and film properties.
Q3: What specific surface treatment or manufacturing techniques are critical for titanium targets to achieve consistent deposition results in high-precision integrated systems, such as advanced semiconductor or microelectromechanical systems (MEMS)?
A3: Multi-pass electron-beam melting for impurity reduction; HIP densification; controlled rolling/forging plus stress-relief anneals for fine grains; precision diffusion bonding to high-thermal-conductivity backplates; vacuum bake or pre-sputter conditioning to reduce outgassing; and edge/chamfer finishing to prevent flaking are all critical. In reactive TiN, closed-loop nitrogen partial-pressure control and fast arc-suppression electronics further ensure stable, repeatable deposition suitable for MEMS and advanced semiconductor device requirements.
