Edge Rings for Plasma Etchers

If you’ve ever tuned a plasma etcher for edgetocenter uniformity, you know that the wafer edge is where things get tricky. The plasma density tends to droop or spike near the periphery, the sheath curvature changes, and ions start hitting the chamber wall instead of the wafer. That’s where the edge ring comes in – it’s not just a mechanical spacer; it’s an active part of the electrical and chemical environment.

At Semixlab, we make edge rings from three material families: ultrahighpurity silicon, fully dense solid silicon carbide, and graphite with a CVD SiC coating. Each type has its own sweet spot, but all share one goal – keep the plasma confined, the particles low, and the etch rate uniform across the entire wafer surface. Our rings are used in logic, memory, power devices, MEMS, compound semiconductors, and even advanced packaging lines.

Why the Edge Ring Deserves More Attention

In a typical plasma chamber, the wafer sits on an electrostatic chuck, and the edge ring surrounds it. During etching, ions are accelerated toward the wafer – but at the edge, the electric field can warp, causing the ion angular distribution to shift. Without a welldesigned ring, you’ll see:

● Faster etching near the edge (or slower, depending on chemistry)

● Nonuniform critical dimensions across die

● More particles flaking off from unprotected chamber surfaces

● Drift in chamber impedance, which messes up your matching network

A good edge ring mitigates all that. It shapes the plasma boundary, protects the underlying chuck and liner from ion bombardment, and helps you get the same result from wafer #1 to wafer #1000.

What Sets Our Edge Rings Apart

We don’t just machine a ring and ship it. We think about how it behaves under real production conditions – highdensity plasma, alternating gases (SF₆, C₄F₈, Cl₂, BCl₃), and thermal cycles that can swing from room temperature to several hundred degrees in seconds.

● Material purity – Our silicon is > 99.999% (5N), and our SiC grades are equally controlled. Trace metal levels are kept below 1 ppm, so you don’t get unexpected contamination on highsensitivity layers.

● Plasma resistance – Solid SiC and CVDcoated parts easily withstand aggressive fluorine and chlorinebased recipes, with erosion rates that are typically an order of magnitude lower than bare quartz or alumina.

● Dimensional precision – We hold tolerances of ±0.02 mm on diameter and thickness, with flatness better than 10 µm across the ring. That ensures a snug fit in Lam, TEL, or AMAT chambers without gas leakage paths.

● Surface finish – After machining, we polish the surfaces to a mirrorlike finish (Ra < 0.4 µm) to minimise area for particle adhesion and shedding.

● Thermal shock resistance – Both solid SiC and coated graphite handle rapid temperature ramps without cracking, thanks to matched CTE and high fracture toughness.

Three Material Choices – Which One Fits Your Process?

All three are available in custom diameters, thicknesses, and inner/outer profiles – just send us your drawing.

Where You’ll Find Our Rings in the Fab

● ICP etchers (inductively coupled plasma) – both downstream and directplasma designs

● CCP etchers (capacitively coupled) – especially for dielectric layers like SiO₂ and SiN

● Deep reactive ion etching (DRIE) for TSV and MEMS

● Compound semiconductor etch – GaAs, InP, GaN – where purity and erosion control are critical

● Advanced packaging – e.g., waferlevel fanout and RDL processes that require clean, uniform plasma trimming

Manufacturing Flow – From Raw Material to Cleanroom Package

● Material selection – Incoming verification of purity, grain size (for SiC), and density.

● Preform machining – Rough turning and milling to nearnet shape.

● Precision grinding – Diamondwheel grinding to achieve final geometry and flatness.

● Polishing – Mechanical or chemicalmechanical polish to get the required surface roughness.

● CVD coating (if applicable) – For coated graphite, we deposit a 100–200 µm SiC layer with controlled stoichiometry.

● Final inspection – CMM for dimensions, profilometer for roughness, and optical microscopy for defects.

● Ultrasonic cleaning – Removes any residual particles, followed by drying in a Class 100 cleanroom.

● Vacuumsealed packaging – Doublebagged for shipment.

Quality Assurance – We Check Everything

Every batch undergoes a strict release checklist:

● Certificate of material purity (GDMS or ICPMS)

● Dimensional report with critical-to-function measurements

● Surface roughness profile

● Coating thickness and adhesion (for coated models) – we use a scratch test and SEM crosssection on representative samples

● Visual inspection under highintensity light for cracks, pits, or inclusions

● Particle count after cleaning – we use liquid particle counters to ensure < 0.1 particles/cm² > 0.1 µm

Common Questions from Our Customers

Q1: How often should I replace an edge ring?

A: It depends on your recipe and power level. In heavy fluorocarbon etching, solid SiC rings can last 3–6 months of continuous operation; silicon rings might need replacement every 1–2 months. We recommend tracking your edgerate uniformity – when you see a shift > 5%, it’s time to check the ring.

Q2: Can I use a coated graphite ring in a highdensity ICP etcher?

A: Yes, but only if the coating is fully dense and thick enough (we recommend > 150 µm). In very aggressive conditions, we’d suggest solid SiC instead – but for many 200 mm dielectric etchers, coated graphite works fine and costs less

Q3: Do you offer rings with different inner bevel angles?

A: Absolutely. The inner edge profile affects plasma sheath coupling. We can machine a straight edge, a chamfered edge, or a radiused edge – whatever your process engineer prefers.

Q4: What about electrostatic chuck compatibility?

A: Our rings are designed to sit on the chuck shoulder with a controlled gap (typically 0.2–0.5 mm) to avoid arcing. We can adjust the bottom surface flatness and backside roughness to match your chuck’s clamping requirements.

Q5: Do you provide sample rings for qualification?

A: Yes. We often supply a small batch (2–5 pieces) for ontool testing. Once you confirm performance, we scale to production quantities.

Why Fab Engineers Keep Coming Back to Semixlab

We’re not a huge catalogue supplier – we’re a specialty shop that focuses on processcritical consumables. Our team includes former etch process engineers who understand what a drift in edge rate does to your yield. We respond quickly to RFQs, offer competitive lead times (typically 2–3 weeks for standard sizes), and we don’t cut corners on cleanliness. Whether you need a oneoff prototype for a new chamber design or a steady monthly supply for a 24/7 production line, we can scale accordingly.