Semiconductor Etching Process

Semiconductor etching process is one of the core steps in wafer fabrication. It selectively removes thinfilm materials from silicon wafers following photolithography, transferring circuit patterns from photoresist onto wafer surfaces. Without precise etching, tiny transistors, vias and interconnect structures inside semiconductor chips cannot be formed. Semiconductor etching is divided into two major technical categories: dry etching and wet etching. Each has unique characteristics and occupies different positions in chip manufacturing workflows.

Basic Workflow Position in Semiconductor Manufacturing

The etching step comes right after photolithography. The complete sequence is: wafer cleaning → thinfilm deposition → photoresist coating → UV exposure & development (photolithography) → etching process → photoresist stripping → inspection. Photoresist acts as a protective mask. Exposed areas without photoresist protection will be removed by etching, while masked regions retain the original film material. This transfers microcircuit patterns onto silicon, silicon dioxide, silicon nitride or metal layers on the wafer.

Dry Etching (Plasma Etching)

Dry etching, also called plasma etching, uses highenergy ionized gas plasma to achieve material removal inside a vacuum chamber. It is the dominant etching technology for modern advancednode semiconductor production. According to material removal mechanism, dry etching can be classified into physical etching, chemical etching, and reactive ion etching (RIE), which combines both physical bombardment and chemical reaction.

Key Features of Dry Etching

1. High anisotropy: Etching proceeds mainly in vertical direction. Lateral sideundercut is extremely low. It can create steep, nearvertical sidewalls for ultrasmall nanometerscale patterns. This capability is irreplaceable for making deep vias, highaspectratio trenches and fine transistor structures.

2. Good pattern fidelity: Precisely replicates ultrafine patterns defined by photolithography, suitable for advanced process nodes down to several nanometers.

3. Vacuum environment requirement: Processes run inside sealed vacuum equipment, gas composition, radiofrequency power, pressure and temperature are tightly controlled.

4. Higher equipment investment: Dry etching tools are complex and expensive capital equipment in fabs.

Typical Dry Etching Applications

l Etching polysilicon for transistor gates

l Highaspectratio via hole etching for interconnection

l Silicon nitride and silicon dioxide dielectric layer etching

l Metal layer etching for circuit interconnects

l Deep silicon trench etching for MEMS and power semiconductors

Wet Chemical Etching for Semiconductors

Semiconductor wet etching adopts liquidphase chemical etchant to dissolve exposed wafer thinfilm materials. It happens in chemical bath tanks at controlled temperature. Wet etching belongs to isotropic etching: chemical reactions take place in all directions equally, leading to obvious lateral undercut beneath the photoresist mask.

Key Features of Semiconductor Wet Etching

1. Isotropic performance: Same etching rate on vertical and horizontal directions, producing rounded side profiles. Not suitable for nanoscale ultrafine patterns.

2. High selectivity: Can achieve extremely high selectivity ratio between target film and underlying layer. Etchant removes target material rapidly while barely attacking substrate or mask layer.

3. Lower cost: Simple tanktype equipment, widely used for oldernode chips, cleaning and material stripping processes.

4. Batch processing: Multiple wafers can be processed together inside chemical baths.

Typical Wet Etching Applications

l Removal of sacrificial layers

l Silicon dioxide layer etching for certain power devices

l Wafer cleaning, residue stripping and surface treatment

l MEMS device manufacturing with larger feature sizes

l Less used for advanced logic chip pattern transfer

Critical Performance Indicators for Semiconductor Etching

1. Etch rate: Material thickness removed per unit time, needs stable and repeatable across the whole wafer and batchtobatch.

2. Selectivity: Etching rate ratio between target material and mask / underlying substrate. High selectivity prevents overetch damage to underlying structures or photoresist mask.

3. Anisotropy vs Isotropy: Anisotropic for vertical steep sidewalls; isotropic brings rounded profiles with lateral undercut.

4. Uniformity: Etch result consistency across entire wafer surface. Poor uniformity causes partial circuit failure.

5. Profile control: Sidewall angle, surface roughness, residuefree after etching completion.

6. Minimal microdamage: Reduce plasmainduced damage for sensitive gate oxide layers.

Dry Etching VS Wet Etching in Semiconductor Industry

Dry plasma etching dominates advancednode chip manufacturing because of anisotropic vertical profile capability for nanometer circuits. Wet etching retains important roles in special thinfilm removal, cleaning, stripping, power semiconductor and MEMS production. Many semiconductor manufacturing workflows combine both technologies. Dry etching forms precision micropatterns; wet etching performs selective layer removal and wafer cleaning.

Difference Between Semiconductor Wafer Etching and Industrial Metal Chemical Etching

Semiconductor etching targets siliconbased wafers for microchip circuits under ultraclean fab environments, pursuing nanometerlevel precision. Industrial metal photochemical etching processes stainless steel, nickel, copper and other metal sheets for mechanical, energy and medical components, usually at micrometer dimensional tolerance level. Although both adopt “etching” concept, equipment, cleanliness requirement, mask material and production purposes are totally different.

Conclusion

Semiconductor etching process is the core patterntransfer technology after photolithography. Dry plasma etching provides anisotropic nanoscale pattern capability for advanced chips. Wet chemical etching delivers highselectivity material removal for cleaning, stripping and specialpurpose devices. Balancing etch rate, selectivity, uniformity and sidewall profile directly determines wafer yield and chip performance. As semiconductor process nodes keep shrinking, etching equipment and process parameter tuning become increasingly critical for modern wafer fabrication.