The evolution of semiconductor technologies into sub-10 nm nodes and 3D architectures like high-bandwidth memory (HBM), even small static potentials can result in critical device failures. The effectiveness of DC ionization compared to AC systems, especially for protecting advanced packaging structures such as micro-bumps and TSVs. As semiconductor processes scale down and packaging grows more complex, controlling ESD during wet cleaning and drying becomes essential. These steps are necessary for surface preparation but often induce electrostatic charge via fluid shear, triboelectric interaction, or coupling effects. Devices with ultrathin dielectrics and dense interconnects are particularly sensitive—failures can occur at voltages under 10 V.
Surface Charging Mechanisms
- Electro kinetic Charging: Spinning deionized water separates ions, generating surface potentials of hundreds of volts.
- Triboelectric Charging: Wet interaction with polymers (e.g., PTFE, PFA) can induce ±15 kV in low humidity.
- Capacitive Coupling: Nearby charged surfaces create localized potential gradients during spin-dry.
| Event | Observed Voltage | Vulnerable Structures |
|---|---|---|
| Spin-dry acceleration | 300–5,000 V | Sub-2 nm gate oxides (fail >30 V) |
| High-pressure spray | 500–10,000 V | TSVs, micro-bumps (<100 V) |
| CDM discharge | 30–100 V | HBM stacks, fine-pitch interconnects |
| Sub-10 V ESD events | <10 V | Advanced nodes, thin dielectrics, TSVs, micro-bumps |
Mitigation Strategies
- Grounding & Materials: Ground all tools (<1 Ω); use static-dissipative materials.
- Chemistry: Use ionic rinses (e.g., NH4OH) to neutralize charge.
- Ionization: Deploy ionizers 20–40 cm above process areas; maintain ±5 V ion balance.
- Monitoring: Use charge plate monitors; set alarms at ±50 V; inspect via SEM/AFM.
DC Ionization in HBM Process HBM structures (TSVs, micro-bumps) are highly ESD-sensitive. DC ionization offers:
- Tight ion balance (±1–5 V)
- Low EMI, stable field (no AC polarity switching)
- Continuous coverage during grinding, bonding, and testing
| Feature | AC Ionizers | DC Ionizers |
|---|---|---|
| Ion Balance | ±10–50 V | ±1–5 V |
| EMI Risk | High | Low |
| Neutralization Speed | ~2–5 s | <1 s |
| Output Mechanism | Single emitter | Dual emitter, continuous |
| Field Stability | Fluctuating | Steady |
ESD during wet processes poses a growing risk for advanced semiconductor nodes. DC ionization—along with robust grounding, material changes, and inline monitoring—has emerged as a key strategy for protecting sub-10 nm structures. As leading foundries adopt these practices, ESD resilience becomes integral to process success and product reliability.
