| name | cvd-coating |
| description | CVD coating — chemical vapor deposition for TiN/TiC/Al2O3, LPCVD/PECVD/HTCVD, deposition rate, film stress, step coverage, cutting tool coatings, wear resistance, ASTM B909, semiconductor and tooling applications. |
| metadata | {"priority":7,"promptSignals":{"phrases":["CVD coating","chemical vapor deposition","TiN CVD","LPCVD","PECVD","CVD film"],"minScore":3}} |
CVD Coating — Complete Skill
CVD Process Fundamentals
Chemical Vapor Deposition: gaseous precursors react/decompose at heated substrate → solid film deposits on surface
Driving force: thermodynamic (ΔG < 0 for deposition reaction); kinetic (activation energy)
General reaction:
MX_n(g) → M(s) + n/2 X₂(g) [thermal decomposition; or with reducing gas H₂]
Example: TiCl₄(g) + 2H₂(g) + ½N₂(g) → TiN(s) + 4HCl(g) [at 900–1100°C]
Sequence of steps (in order):
- Transport of reactant gases to substrate surface
- Adsorption on surface
- Surface reactions (nucleation, surface diffusion)
- Film growth / incorporation
- Desorption of by-products
- Transport of by-products away from surface
Rate-limiting step:
Mass transport limited (high T): deposition rate ∝ flow rate, low activation energy
Surface reaction limited (low T): deposition rate ∝ exp(-E_a/RT), exponential with T
CVD Variants
HTCVD (High-Temperature CVD, 700–1100°C)
Applications: TiC, TiN, TiCN, Al₂O₃ coatings on cemented carbide cutting tools
Substrate: must withstand 900–1100°C without distortion or phase change
Film stress: residual tensile stress (thermal expansion mismatch); TiC/substrate ΔCte → cracks at edges if too thick (> 10 μm)
Process parameters:
TiN: TiCl₄ partial pressure 0.5–2%; N₂ 10–50%; H₂ balance; T = 900–1050°C; P = 1 atm
TiC: TiCl₄ + CH₄ + H₂; T = 1000–1050°C
Al₂O₃ (α-phase): AlCl₃ + H₂O + H₂; T = 1000–1060°C; H₂S promoter for α-phase
Growth rates:
TiN: 0.5–2 μm/hr; TiC: 1–3 μm/hr; Al₂O₃: 0.5–2 μm/hr
Total coating thickness for cutting tools: 10–20 μm (TiC/Al₂O₃/TiN multilayer)
LPCVD (Low-Pressure CVD, 0.1–10 Torr)
Applications: Si₃N₄, poly-Si, SiO₂ in semiconductor processing
Temperature: 600–900°C
Advantages: excellent step coverage (> 95%); uniform coating in high-aspect-ratio features
Mechanism: mass transport enhanced at low P; surface reaction limited → conformal
LPCVD reactions:
SiH₄ → Si + 2H₂ (poly-Si, 620–650°C)
SiH₄ + O₂ → SiO₂ + 2H₂ (low T oxide)
3SiH₄ + 4NH₃ → Si₃N₄ + 12H₂ (600–800°C)
Film uniformity: ± 2–5% over 300 mm wafer in batch tube furnace (50–100 wafers)
PECVD (Plasma-Enhanced CVD, 200–400°C)
Applications: SiO₂, Si₃N₄ passivation layers; low-T deposition over aluminum interconnects
Plasma: RF (13.56 MHz) or pulsed DC; generates reactive species at low thermal energy
Advantages: low substrate temperature (aluminum melts at 660°C → PECVD needed); fast deposition
Disadvantages: non-stoichiometric films; more H incorporation; lower quality than LPCVD
PECVD reactions:
SiH₄ + N₂O → SiO₂ + N₂ + 2H₂ (≈ 300°C)
SiH₄ + NH₃ + N₂ → SiNₓH (300–400°C; high H content → stress and moisture uptake)
Deposition rate: 50–500 nm/min (much faster than LPCVD or HTCVD at same T)
MOCVD (Metal-Organic CVD)
Applications: III-V semiconductors (GaN, InGaAs, AlGaAs), LEDs, HEMT, solar cells
Precursors: organometallics (trimethylgallium TMGa, trimethylaluminum TMAl) + hydrides (AsH₃, PH₃, NH₃)
Temperature: 600–1100°C; group V/III ratio controls stoichiometry
Growth rate: 1–10 μm/hr; precise layer control (nm precision) via rapid gas switching
Film Properties
Stress in CVD Films
Intrinsic stress (growth stress):
σ_int = E_f / (1-ν_f) × (a_f - a_s) / a_s [depends on lattice mismatch; can be tensile or compressive]
Thermal stress (on cooling):
σ_thermal = E_f × (α_s - α_f) × ΔT / (1 - ν_f)
ΔT = T_deposition - T_room [negative → cooling → thermal stress]
Total stress: σ_total = σ_int + σ_thermal
Compressive σ → film tends to buckle/blister; tensile σ → film tends to crack
Wafer bow measurement: Stoney's equation → σ from radius of curvature R
σ = E_s t_s² / (6(1-ν_s) R t_f) [t_s = substrate thickness; t_f = film thickness]
Adhesion
Scratch test adhesion (ASTM C1624): critical load L_c [N] to cause film delamination
CVD TiN on carbide: L_c = 80–120 N (excellent)
PVD TiN: L_c = 30–60 N (good); CVD generally better adhesion (chemical bonding)
Pull-off test (ASTM D4541): for thicker coatings (thermal spray, etc.)
Hardness and Tribological Properties
| Coating | Hardness [GPa] | Friction vs. steel | Wear rate k [mm³/N·m] |
|---|
| TiN | 20–28 | 0.4–0.6 | 1×10⁻⁶ |
| TiCN | 28–35 | 0.2–0.4 | 5×10⁻⁷ |
| TiC | 30–38 | 0.3–0.5 | 3×10⁻⁷ |
| Al₂O₃ (α) | 20–25 | 0.5–0.7 | 2×10⁻⁶ (but oxidation resistant) |
| DLC (a-C:H) | 20–40 | 0.05–0.15 | 1×10⁻⁸ |
| SiC | 25–35 | 0.3–0.5 | 2×10⁻⁷ |
Step Coverage
Aspect ratio: H/W of feature (trench/via); higher AR → harder to coat bottom
Step coverage = t_bottom / t_top:
HTCVD (mass-transport-limited): 50–80% step coverage (poor for high AR)
LPCVD (reaction-limited): 90–100% conformal (excellent step coverage)
PECVD: 50–80% (directional plasma component reduces conformality)
ALD (Atomic Layer Deposition): 100% conformal to any AR; 0.1–1 nm/cycle (very slow)
Uses self-limiting surface reactions; alternative to CVD for ultra-thin conformal coatings
Cutting Tool Coatings (Industry Application)
Standard multilayer coating sequence:
TiC (inner) → TiCN → Al₂O₃ → TiN (outer, gold color, wear indicator)
Total: 10–18 μm; deposited by HTCVD at 1000–1050°C
Post-coating treatment:
Edge prep: micro-hone (10–30 μm ER) to remove "feather edge" after coating
Blasting/polishing: smooth outer TiN → lower friction, better chip flow
Cutting speed capabilities (coated vs. uncoated carbide):
Coated: 200–400 m/min (steel); 800–2000 m/min (aluminum)
Uncoated: 100–200 m/min (steel)
Standards
| Standard | Scope |
|---|
| ASTM B909 | CVD coatings for cutting tools |
| ASTM C1624 | Scratch adhesion test |
| ISO 28199 | Evaluation of automotive coating properties |
| SEMI M16 | Specifications for CVD equipment for semiconductors |
| VDI 3824 | Quality assurance of PVD and CVD coatings |
| ISO 9241 | Hardness measurement of thin hard coatings |
Output
Provide: CVD variant (HTCVD/LPCVD/PECVD/MOCVD), coating material and chemistry, deposition temperature [°C] and pressure [Torr], precursor gases and partial pressures, deposition rate [nm/min or μm/hr], film thickness [μm], film hardness [GPa], residual stress σ [MPa] (tensile/compressive), step coverage [%] at given AR, adhesion L_c [N] by scratch test, friction coefficient μ and wear rate k [mm³/N·m], substrate material and thermal mismatch ΔCte, post-deposition treatment, application performance metric (tool life improvement [%] or electrical property), and applicable standard (ASTM B909, ISO 28199).
