PECVD Physics and Chemistry
Plasma-Enhanced Chemical Vapor Deposition uses RF power to generate a plasma that dissociates precursor gases, enabling low-temperature deposition through ion-assisted reactions.
RF Power Coupling
η_coupling = P_plasma / P_RF = f(frequency, pressure, geometry)
Typical efficiency: 60-80% at 13.56 MHz
Plasma Density
n_e = n_e0 × (P_RF / P_0)^α × (p / p_0)^β
where α ≈ 0.5-0.7, β ≈ 0.3-0.5
n_e: electron density (cm⁻³), P_RF: RF power (W), p: pressure (mTorr)
Electron Temperature
T_e = T_e0 × (E/p)^γ
E: electric field (V/cm), p: pressure (Torr)
Typical values: 2-5 eV in capacitive discharges
Gas Phase Chemistry - Silane Dissociation
SiH₄ + e⁻ → SiH₃* + H* + e⁻ (electron impact dissociation)
SiH₃* + SiH₄ → Si₂H₆ + H* (radical reactions)
Dissociation fraction: α = k_diss × n_e × τ_residence
Ethylene Dissociation
C₂H₄ + e⁻ → C₂H₃* + H* + e⁻
C₂H₃* + surface → film growth
Controls carbon incorporation in SiC films
Ion Bombardment
Φ_ion = 0.25 × n_i × v̄_thermal × exp(-V_bias / T_e)
E_ion = e × V_sheath = e × (kT_e/e) × ln(0.61 × (M_i/m_e)^0.5)
Φ_ion: ion flux (cm⁻²s⁻¹), E_ion: ion energy (eV)
Film Composition
[Si]/[C] ratio = f(P_SiH₄/P_C₂H₄, E_ion, T_substrate)
Higher ion energy → more carbon incorporation
Lower pressure → higher dissociation fraction
Deposition Rate
R_dep = k × (Φ_radical × S_radical + Φ_ion × S_ion)
S: sticking coefficient (0.1-0.8 for radicals, ~1 for ions)
Typical rates: 50-500 Å/min depending on power/pressure