Wet Etching Process

Wet etching operates through an intuitive mechanism: the wafer is immersed in specific chemical solutions (acids, alkalis, or buffers) that react with exposed materials to dissolve them.

Key Characteristics:

1. Isotropic Nature: The most distinctive feature. Chemical solutions attack all exposed surfaces indiscriminately, leading to undercutting and rounded edges, making it unsuitable for fine patterns (<3μm).

2. High Selectivity: Easily find reagents that aggressively etch target materials while sparing others (e.g., photoresist or underlying layers).

3. Cost-Effective: Simple tank-based systems enable batch processing with low operational costs.

Typical Applications:

1. Wafer cleaning and surface preparation

2. Bulk film removal (e.g., sacrificial layers)

3. Legacy semiconductor processes with larger feature sizes

Dry Etching Process

Dry etching is an advanced plasma-based technique performed in vacuum chambers using reactive gases (e.g., CF₄, Cl₂) ionized by RF power.

Mechanism:

1. Physical Sputtering: Ions bombard the wafer vertically, ejecting material atoms.

2. Chemical Reaction: Reactive radicals form volatile byproducts removed by vacuum.

Key Advantages:

1. Anisotropic Control: Enables vertical etching with minimal lateral undercut, achieving nanometer-scale precision (e.g., 89°±0.5° sidewall angles).

2. Parameter Flexibility: Adjusts power, pressure, and gas ratios to fine-tune etch profiles.

3. Material Versatility: Processes all materials, including III-V compounds and metals.

Dominant Applications:

• Nanoscale circuitry (transistors, interconnects)

• High-aspect-ratio structures (3D NAND, MEMS)

Conclusion

The dichotomy lies in isotropy vs. anisotropy. Wet etching retains niche uses for selective bulk removal, while dry etching underpins modern microelectronics due to its precision and controllability. Leading fabs employ both technologies in complementary steps.