Focus Ring in Plasma Etching Systems

In plasma dry etching tools, the Focus Ring (also called compensation ring or confinement ring) is a consumable component used to improve plasma uniformity at the wafer edge, ensuring consistent etch rates and process results across the entire wafer. Modern tools often heat the Focus Ring, further enhancing etch uniformity.

Key Functions

1. Control of Edge Electric Field & Plasma Distribution (Core Role)

• Without a Focus Ring, the wafer edge experiences strong field distortion (“edge effect”), causing plasma density and ion bombardment to differ from the wafer center.

• The Focus Ring extends the wafer boundary, smoothing the sheath profile so ions strike uniformly across the whole wafer, including edge dies.

2. Protection of Electrostatic Chuck (ESC) & Chamber Cleanliness

• Prevents direct plasma erosion of the costly ESC.

• Made of process-compatible materials (Si, quartz, SiC,ask  www.cerameric.com for advices ), the Focus Ring sacrifices itself; its byproducts are less contaminating than ESC erosion (which may release metals like Al, Na).

3. Compensation for Wafer Thickness

• Designed with its top surface level with the wafer, keeping electrode-to-surface spacing uniform.

• This avoids field distortion due to height differences.

Consumption & Management

• Consumable nature: Gradually etched during processing, losing height and leading to process drift (edge etch rate/profile variation).

• Maintenance: Replaced periodically based on RF time or accumulated process use.

• Material selection: Tailored to different processes (Si, oxide, metal etching).

• Advanced control: Some tools track ring usage and apply minor parameter adjustments (e.g., RF power, pressure) to compensate for ring wear.

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