I. Core Mechanism of Dry Etching and the Role of Showerhead
Dry etching achieves high-precision pattern transfer through chemical reactions (chemical etching) between reactive gases in plasma and thin-film materials or through high-energy ion bombardment (physical etching). The Showerhead (gas distribution plate), a critical component, ensures uniform injection of process gases into the reaction chamber via its evenly distributed micro-hole structure, preventing local concentration variations. This enhances etching rate uniformity (within ±3%) and sidewall verticality (>85°), serving as the cornerstone for stable oxide (Oxide) and nitride (Nitride) thin-film etching processes.
II. Gas System for Oxide (SiO₂) Etching
1. Base Fluorocarbon Gases
o CF₄: A fundamental etching gas that dissociates to produce F radicals (·F), reacting with SiO₂ to form SiF₄↑ + O₂↑. The etching rate is approximately 1000–2000 Å/min, but sidewall roughness is relatively high (Ra > 5 nm).
o CHF₃: Introduces ·CF₂ radicals to deposit a fluorocarbon polymer layer on sidewalls, suppressing lateral etching. A CF₄/CHF₃ gas mixture (3:1 ratio) improves the anisotropy ratio from 1:1 to 5:1, optimizing sidewall verticality to 88°.
o C₄F₈: Dissociates into ·CF₂ at high temperatures (>150°C), forming a dense polymer film that reduces the etching rate of monocrystalline silicon (Si) by over 20-fold, achieving a SiO₂/Si selectivity ratio exceeding 20:1 for shallow trench isolation (STI) processes.
o SF₆: Generates a high density of F atoms (concentration up to 10¹⁵ cm⁻³), three times that of CF₄, suitable for deep trench etching (trench depth > 1 μm) with an etching rate of 800 Å/min and sidewall verticality better than 88°.
2. Auxiliary Gas Optimization
o O₂: Reacts with fluorocarbon gases to produce COF₂ and F atoms, increasing active F concentration and boosting the etching rate by 30%–50%. However, excessive O₂ (>15%) oxidizes sidewall polymers, reducing anisotropy.
o Ar: Ar⁺ ions (energy: 100–500 eV) bombard the surface, breaking through passivation layers and enhancing directionality. Adding 30%–50% Ar improves the anisotropy ratio from 3:1 to 8:1, but excessive Ar (>60%) causes silicon substrate damage (surface roughness increases by 2–3 nm).
o Typical Formulation: For STI processes, CF₄ (60%)/CHF₃ (20%)/C₄F₈ (10%) + O₂ (8%) + Ar (35%) are uniformly injected via the Showerhead, achieving high-precision etching with a trench depth of 500 nm and sidewall tilt angle < 85°.
III. Gas System for Nitride (Si₃N₄) Etching
1. Core Gases and Selectivity Control
o Traditional Fluorocarbon Gases (CF₄, CHF₃): Exhibit low selectivity for Si₃N₄ etching (SiO₂ loss rate reaches 90% of Si₃N₄), leading to hard mask failure.
o H₂: A key additive that reacts with F atoms to form HF↑, reducing active F concentration and suppressing SiO₂ etching. Adding 10% H₂ increases the Si₃N₄/SiO₂ selectivity ratio from 1:1 to 12:1 while diluting plasma to minimize polymer residue and optimize surface roughness (Ra decreases from 3 nm to 1.2 nm).
o Cl₂: Reacts with Si₃N₄ to form volatile SiCl₄↑ + 2N₂↑ but requires H₂ (15%–20% Cl₂, 12%–15% H₂) to balance etching rate and selectivity.
o SF₆: Leverages its high F density advantage, combined with CHF₃ for deep trench etching with an etching rate of 800 Å/min and sidewall verticality better than 88°.
2. Auxiliary Gas Optimization
o N₂: Dilutes plasma to reduce polymer deposition, lowering residue density from 10¹¹ cm⁻² to 10⁹ cm⁻².
o Ar: Physically bombards Si-N bonds to promote etching reactions.
o Typical Formulation: For sidewall spacer etching, CHF₃ (40%)/SF₆ (30%) + H₂ (12%) + N₂ (25%) + Ar (20%) are precisely controlled via the Showerhead, achieving high selectivity (Si₃N₄/SiO₂ > 10:1) and low residue (<10⁹ cm⁻²).
IV. Synergistic Optimization of Gas Systems by Showerhead
1. Micro-Hole Structure and Gas Mixing Efficiency: The micro-hole diameter (0.1–0.5 mm) and density (100–500 holes/cm²) of the Showerhead directly impact gas mixing uniformity. For example, a laser-drilled Showerhead can control CF₄/O₂ gas concentration fluctuations within ±2%, significantly improving etching rate repeatability.
2. Temperature Control and Polymer Deposition: The Showerhead surface temperature (typically maintained at 50–100°C) regulates chamber temperature through heat conduction, suppressing excessive fluorocarbon polymer deposition on sidewalls and avoiding etching stagnation caused by the "micro-mask effect."
3. Process Compatibility Expansion: For advanced processes (e.g., 3D NAND, FinFET), the Showerhead must support multi-zone independent temperature control (≥4 zones) to accommodate diverse gas combinations (e.g., C₄F₈/O₂/Ar for high-aspect-ratio etching, CHF₃/SF₆/H₂ for nitride selective etching).
AMTD provides high-precision Showerhead (gas distribution plate/spray head/faceplate) services for core semiconductor equipment components, including Showerheads, Face Plates, Blocker Plates, Top Plates, Shields, Liners, Pumping Rings, and Edge Rings. These products are widely used in semiconductor and display panel industries, offering exceptional performance and high market recognition.
Sources:
1. In-Depth Analysis of Dry Etching Technology (EEWorld)
2. Comprehensive Guide to Semiconductor Dry Etching Process Gas Selection (WeChat Public Platform · Tencent)
3. Impact of Showerhead Design on Dry Etching Uniformity (Semiconductor International Journal, 2023)
