cvd-coating

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):

1. Transport of reactant gases to substrate surface
2. Adsorption on surface
3. Surface reactions (nucleation, surface diffusion)
4. Film growth / incorporation
5. Desorption of by-products
6. 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).