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CCP vs ICP Plasma: Key Differences Explained

Both create a plasma by ionizing gas with RF power, but they differ in how the power is delivered to the plasma. CCP applies an RF voltage between two facing electrodes, and the electric field accelerates electrons. ICP passes RF current through a coil, and the induced electric field created by the changing magnetic field accelerates electrons, so it can create a high-density plasma at low pressure. ICP has a separate bias supply on the wafer side, allowing plasma density and ion energy to be adjusted separately.

AspectCCP (capacitively coupled plasma)ICP (inductively coupled plasma)
Plasma generationAn RF voltage is applied to parallel-plate electrodes, and the electric field between them accelerates electronsRF current flows through a coil, and the induced electric field accelerates electrons
Tool structureTwo electrodes facing each other top and bottom. The wafer sits on one electrodeA coil is placed outside (above or around) a dielectric window, and a separate bias supply is connected to the wafer stage
Plasma density (typical)Moderate, about 10⁹ to 10¹⁰ cm⁻³High, about 10¹¹ to 10¹² cm⁻³
Operating pressure (typical)Often about a few Pa to a few tens of PaLow pressure, about 0.1 Pa to a few Pa
Control of density and ion energyWith a single supply, raising power changes density and self-bias together, so they are hard to control independently. Dual-frequency designs split the rolesCoil power sets density and wafer-side bias power sets ion energy, so they are easy to adjust separately
Ion energyLarge self-bias makes high ion energy easy to obtainLowering the bias delivers many ions at low energy, making damage easy to limit
Gas dissociationRelatively low. Source molecules and their fragments tend to remainHigh. The gas is well decomposed, with many radicals and ions
Etching strengthsDielectric films such as oxide and low-k films. Strong ion bombardment and fluorocarbon polymers provide selectivity. High-aspect-ratio contact holesFast, highly anisotropic etching of silicon (gates and isolation trenches), metals (such as aluminum interconnects) and compound semiconductors
Deposition applicationsParallel-plate plasma CVD (PECVD). The ratio of high- and low-frequency power adjusts film stressHigh-density plasma CVD (HDP-CVD). Ion sputtering trims the trench opening during deposition to fill narrow trenches
Equipment configurationRelatively simple: electrodes and an RF supplyNeeds a coil, a dielectric window, two supplies and more, so it is somewhat complex

Figures are typical orders of magnitude and vary by process generation and product.

When to use which

CCP (capacitively coupled plasma)
Etching dielectric films such as oxide, nitride and low-k films, including deep contact holes that need high ion energy and polymer-based selectivity. Parallel-plate plasma CVD.
ICP (inductively coupled plasma)
Fast, highly anisotropic etching of silicon and metals. When you want a high-density plasma with low ion energy to limit damage. HDP-CVD for filling narrow trenches.
Trend
Even in CCP, dual-frequency designs in which a high frequency sets density and a low frequency sets ion energy are widely used, offsetting the weakness of hard-to-separate control.

FAQ

Why can ICP control plasma density and ion energy separately?

Because the supply that powers the coil to create the plasma and the supply that biases the wafer are separate. Coil power adjusts plasma density, and wafer-side RF power adjusts self-bias and ion energy.

Why is CCP often used for oxide etching?

SiO2 has strong bonds, so etching it requires high ion energy. CCP easily produces a large self-bias, and gas dissociation is relatively low, so fluorocarbon polymers make it easy to obtain selectivity against the underlying nitride or silicon.

Are CCP and ICP used for anything besides etching?

Yes. Parallel-plate CCP is widely used in plasma CVD (PECVD) tools, and high-density plasmas such as ICP have been used in HDP-CVD, which deposits and sputters at the same time to fill narrow trenches.

Check your understanding

Which is a characteristic of inductively coupled plasma (ICP) etching equipment?

  1. AIt does not use plasma
  2. BIt generates high-density plasma with a coil, and plasma density and ion energy are easy to control separately
  3. CIt uses liquid chemicals
Show answer and explanation

Answer: B. It generates high-density plasma with a coil, and plasma density and ion energy are easy to control separately

An ICP etcher drives RF current through a coil above or around the chamber to induce an electric field that sustains a dense plasma of 10¹¹–10¹² cm⁻³, while a separate RF supply biases the wafer. Plasma density (radical and ion flux) and ion energy at the wafer can be set independently, enabling fast, highly anisotropic etching at pressures of a few Pa or less; ICP tools are widely used for silicon and metal etching.

In plasma tools such as capacitively coupled ones, what is the phenomenon called in which the wafer-side electrode naturally acquires a negative DC potential that accelerates ions toward the wafer?

  1. AThe Hall effect
  2. BThe Seebeck effect
  3. CSelf-bias
Show answer and explanation

Answer: C. Self-bias

On an RF-driven electrode, light, mobile electrons flow in more readily than ions, so a capacitively coupled electrode settles at a negative average DC potential—the self-bias, tens to hundreds of volts. This potential accelerates positive ions from the plasma nearly vertically into the wafer, enabling anisotropic etching. Changing RF power changes the self-bias and thus ion energy.

Which correctly describes reactive ion etching (RIE)?

  1. AEtching that combines chemical reactions and ion bombardment in a plasma of reactive gases
  2. BEtching by immersing the wafer in a chemical solution
  3. CGrinding the wafer surface with a polishing pad
Show answer and explanation

Answer: A. Etching that combines chemical reactions and ion bombardment in a plasma of reactive gases

Reactive ion etching (RIE) combines chemical reactions driven by radicals from a reactive-gas plasma (fluorine- or chlorine-based, etc.) with bombardment by ions accelerated in an electric field. Ions striking perpendicular to the wafer promote reactions at the feature bottom, so etching proceeds vertically with high anisotropy. Despite the name, ions do not etch alone; the synergy with radicals is the essence.

  1. What is needed to etch oxide and stop on the nitride underneath?
  2. Why has high-density plasma CVD (HDP-CVD) been used to fill narrow trenches with insulator?
  3. Which method is used to tune the stress of plasma CVD silicon nitride from compressive to tensile?

Practice Etching questions

Key terms explained

ICP (inductively coupled plasma)
A method that generates a high-density plasma with RF current in a coil. It makes it easy to control plasma density and the energy of ions reaching the wafer independently.
Self-bias
The negative DC potential that the wafer electrode naturally acquires in a capacitively coupled plasma. It accelerates positive ions toward the wafer, aiding anisotropic etching.
RIE (reactive ion etching)
Dry etching that combines reactive species in a plasma with ions accelerated by an electric field. It enables vertical, anisotropic etching.
HDP-CVD (high-density plasma CVD)
CVD using a high-density plasma that deposits while ion sputtering trims film at the trench openings. It has been used to fill narrow trenches with insulator without voids.
PECVD (plasma-enhanced CVD)
CVD that decomposes source gases with plasma to deposit films. It can deposit at lower temperatures than thermal CVD and is used for insulating films in interconnect steps and the like.

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