RIE vs ICP-RIE vs ALE: Plasma Etching Methods Compared
All three are dry etching methods that use a plasma, but they differ in how the plasma is generated and how material is removed. Capacitively coupled (CCP) RIE applies RF power to parallel-plate electrodes; it is simple, but plasma density and ion energy are hard to set independently. ICP-RIE generates a high-density plasma with a coil and sets the ion energy with a separate power supply on the wafer side, so it etches fast with limited damage. ALE alternates surface modification and removal, taking off only an atomic-layer amount per cycle; it is slow, but gives extremely precise depth control.
| Aspect | Capacitively coupled RIE (CCP) | ICP-RIE | ALE (atomic layer etching) |
|---|---|---|---|
| Plasma generation | RF power is applied between parallel-plate electrodes, typically at 13.56 MHz. Many tools use two frequencies | RF current flows through a coil outside a dielectric window, and the induced electric field accelerates electrons. A separate bias supply is connected on the wafer side | No fixed method. It is usually done in an etch tool such as an ICP type, switching gas supply and bias step by step (plasma ALE) |
| Typical pressure | About a few Pa to a few tens of Pa | Low pressure, about 0.1 Pa to a few Pa | Set for each step: gas is adsorbed in the modification step, and ions are applied in the removal step |
| Plasma density | Lower (about 10⁹ to 10¹⁰ cm⁻³) | High (about 10¹¹ to 10¹² cm⁻³) | Depends on the tool. What matters more than density is that each step stops in a self-limiting way |
| Ion energy control | A single power sets both density and self-bias, so they are hard to control separately. Dual frequency partly decouples them | Coil source power sets the density and wafer-side bias power sets the ion energy, almost independently | The ion energy in the removal step is set within a narrow window (typically a few tens of eV) that removes only the modified layer without sputtering the underlying material |
| Etch rate | Moderate (about tens to hundreds of nm/min depending on conditions) | Fast (about hundreds of nm/min to several µm/min for silicon) | Very slow: about 0.1 to 0.5 nm per cycle, and gas switching and purging take time |
| Directionality | Anisotropy comes from ion bombardment and sidewall protection | At low pressure, ions arrive almost vertically, which favors high-aspect-ratio anisotropic etching | Plasma ALE is directional and can etch only the bottom surface. Thermal ALE is isotropic |
| Damage | Ion energy tends to be high, so damage to the underlying layer and charging are more likely | Lowering the bias reduces damage while keeping the etch rate | Lowest. Ions have low energy, and the surface stays smooth |
| Depth control | Set by time and endpoint detection. Stopping within a few nm is difficult | Set by time and endpoint detection. Conditions are switched near the underlying layer to raise selectivity | Set by the number of cycles. It can stop at the atomic-layer level, with little difference between dense and sparse patterns |
| Throughput | High | High | Low. Used only for the critical final part of a process |
| Typical uses | Etching oxide and nitride films with fluorocarbon gases, and patterning dielectrics such as contact holes | Silicon and polysilicon gates, STI, metal interconnects, compound semiconductors, deep MEMS etching (Bosch process) | Steps that must stop within a few nm, such as around GAA nanosheets and gates, patterning extremely thin films, low-damage recesses |
Figures are typical orders of magnitude and vary by process generation and product.