Issue 1: Etching Defects in High Aspect Ratio Structures

Phenomenon: Sidewall scalloping, bottom bowing, and unpenetrated vias (e.g., 3D NAND 60:1 deep vias).

Root Cause: Insufficient ion directionality and difficulty in byproduct removal, leading to local over-etching.

Solutions:

• Equipment Optimization:Adopt pulsed plasma technology (e.g., Lam Research’s Flex® system), which periodically switches between etching and passivation steps to protect sidewalls.

• Process Adjustment:Introduce sidewall protection gases (e.g., C₄F₈) to form polymer passivation layers.Optimize pressure/power ratios to enhance ion directionality (e.g., low pressure with high bias).

Issue 2: Loss of Etch Uniformity Control (WIW/W2W)

Phenomenon: Etch rate variation >5% between wafer edges and centers, causing dispersion in chip performance.

Root Cause: Uneven plasma distribution, temperature gradients, and unstable gas flow fields.

Solutions:

• Real-Time Monitoring:Integrate in-situ sensors (e.g., optical emission spectroscopy, OES) to dynamically adjust process parameters.

• Hardware Design:Use multi-zone temperature-controlled electrodes (e.g., Applied Materials’ Sym3® etcher) to compensate for thermal effects across zones.

Issue 3: Insufficient Selectivity Leading to Critical Dimension (CD) Loss

Phenomenon: Unintended etching of underlying materials (e.g., oxide layer breakthrough under polysilicon gates).

Root Cause: Low selectivity of etch gases for mask/underlying materials (e.g., SiO₂/Si selectivity <20:1).

Solutions:

• Gas Chemistry Innovation:For silicon etching, use HBr/Cl₂/O₂ mixed gases to increase SiO₂/Si selectivity to 50:1.

• Mask Optimization:Replace photoresist with metal hard masks (e.g., TiN), enhancing corrosion resistance by 10x.

Issue 4: Residue and Contamination

Phenomenon: Metal fluorides (e.g., AlF₃) or carbon polymers adhering to sidewalls, causing short circuits or high resistance.

Root Cause: Hard-to-volatilize reaction byproducts and chamber memory effects.

Solutions:

• In-Situ Cleaning:Periodically clean the reaction chamber with NF₃/O₂ plasma.

• Post-Treatment:Use wet cleaning (e.g., SC-1 solution) to remove micro-residues.

Issue 5: Demand for Atomic-Scale Precision (<5nm Nodes)

Challenge: Ion damage from conventional RIE processes causes device leakage.

Solution:Adopt Atomic Layer Etching (ALE): Perform surface modification (e.g., Cl₂ adsorption) and low-energy ion stripping (e.g., Ar⁺) stepwise to achieve angstrom-level precision.