Semiconductor CNC processing essentials

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  What semiconductor CNC processing covers
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  Which materials hold up in a fab
• 3
  Process choices: 3-axis, 5-axis and grinding
• 4
  Particle control and surface cleanliness
• 5
  When CNC is the wrong answer
• 6
  Matching the process to the part

The name covers everything mechanical that touches a fab or a chip assembly line, minus the wafer itself. Chamber bodies, gas delivery manifolds, showerhead plates, electrostatic chuck bases, end effectors, load-port frames, test sockets, heat sinks and probe card holders all start as a block of metal or ceramic that has to be cut to shape.

Semiconductor CNC processing is not one operation. A manifold needs leak-tight sealing faces. A chuck base needs flatness across the full face. An end effector needs mass low enough that the robot arm does not oscillate. Each of those pushes the machine setup in a different direction.

The reason tolerances run to microns is rarely the drawing dimension. It is the stack. A showerhead sits above a wafer at a fixed gap; if the plate bows 20 μm, gas flow across the wafer changes, and film thickness follows. Flatness and surface finish carry more weight than a small diameter tolerance.

GreatLight has run these parts since 2011 from three wholly-owned plants, 7,600 m² of floor space and 150 technicians. The work is a small share of total output, but it is the part of the shop where inspection paperwork matters most.

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  Machined, not grownEverything here is a mechanical part, not a wafer or a deposited layer.
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  Function drives the specFlatness, finish and cleanliness usually outrank a tight OD.
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  Small lots are normalPrototype and low-volume builds dominate this segment.

Aluminum is the default for chamber hardware and structural frames. 6061-T6 and 6082 machine cleanly, take anodizing well and keep their shape. 7075 is used where stiffness per kilogram matters, such as robot arms and end effectors, but it is harder to anodize to a uniform color.

Stainless covers the wet side. 316L and 17-4PH (SUS630) resist process gas corrosion and clean up without rust bloom. 304 is fine for frames and brackets that never see plasma. Note that stainless galls during tapping, so thread forming and generous lubrication matter more than on aluminum.

Ceramics and refractory metals are the hard cases. Alumina and silicon carbide give the dielectric strength and thermal stability a chamber needs, but they are ground with diamond, not milled with carbide. Inconel and titanium appear in high-temperature and plasma-facing hardware. They work-harden, so shallow passes and constant coolant are the rule.

Beryllium copper and C101 copper handle heat spreading and RF conduction. They are gummy, they burr, and they need sharp tooling. Copper parts also need a clean, oxide-free surface before any plating or bonding step.

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  Anodize before assemblyMasked sealing faces keep flatness after the coating builds up.
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  Know the cleaning pathUltrasonic, DI rinse and bake change which finish you can use.
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  Mixed-material stacksAluminum frames with stainless inserts need press-fit tolerances checked early.

Flat plates with through-holes and a few pockets belong on a 3-axis mill. Showerhead plates, backing plates and mounting flanges fall here. Setup is simple, the part sits on one face, and flatness is controlled by how the plate is clamped and by a light final pass rather than by machine motion.

Parts with compound angles, deep side pockets or features on five faces need simultaneous 5-axis. GreatLight runs 16 simultaneous 5-axis machining centers with travels of 750 × 1,150 × 550 mm, 600 × 600 × 600 mm, 500 × 500 × 450 mm and 500 × 310 × 200 mm, plus a Ø400 mm rotary table. One setup removes the re-fixturing error that stacks up across three operations.

Turning and mill-turn handle round geometry: gas nozzles, feedthrough bodies, shaft adapters and collar parts. 16 mill-turn centers let a single program cut the OD, the bore and the cross-ports without losing concentricity between them.

When flatness goes below about 10 μm or finish below Ra 0.4 μm, grinding takes over from milling. Surface grinding and cylindrical grinding remove the residual stress layer that a milling pass leaves behind. That stress is what makes a thin plate bow after it is unclamped, even though it measured flat on the machine.

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  Rough, stress-relieve, finishThin plates benefit from a stress-relief cycle between roughing and finishing.
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  Clamp lightHeavy clamping distorts a plate before the cutter ever touches it.
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  Probe on the machineIn-process probing catches drift before a batch is finished.

A part that measures perfectly can still fail in the fab. Loose burrs, trapped polishing compound and machining oil residue all become particle sources once the part is inside a chamber or a clean enclosure. Particle control is a machining requirement, not a cleaning afterthought.

The practical controls start at the drawing review. Avoid blind tapped holes that trap chips. Specify edge breaks on every external edge unless the edge is a sealing surface. Where a sealing surface exists, specify the flatness and the surface finish together, because a rough face will not hold a metal seal no matter how flat it is.

In the shop, deburring is done by hand for critical edges and by tumbling or bead blasting for the rest. Bead blasting leaves media that must be fully removed, so parts that will see vacuum usually go to ultrasonic cleaning with a DI rinse and a nitrogen dry.

Inspection then has to match. GreatLight inspects 100% of parts before shipment, with raw material checks, in-process monitoring and a final inspection, and reports are available on request. For semiconductor work the finish and flatness numbers on that report are usually the ones the customer needs first.

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  No blind holesThrough-holes or vented pockets are easier to clean and to verify.
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  Edge breaks on everythingA 0.2–0.4 mm break removes the burr line that sheds particles.
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  Match cleaning to finishBead blasting and a vacuum-facing surface are a poor combination.

CNC is not always the right route. If the part is a large, simple enclosure made in the hundreds, sheet metal fabrication or die casting will cost less per unit and hold adequate tolerance. If it is a complex organic shape with no critical faces, 3D printing may be enough for a fit check.

There is also a size and geometry limit. GreatLight machines up to 4,000 mm maximum processing size, with a 4,000 × 400 × 150 mm travel envelope for long parts. Anything beyond that envelope is not a machining problem we can solve by trying harder.

Deep, narrow internal channels are the other boundary. A curved cooling channel inside a chuck base cannot be cut by a rotating tool. That geometry belongs to additive manufacturing, sometimes followed by CNC finishing on the mating faces.

The honest test is this: list the features that carry the function. If they are faces, bores, slots and holes, CNC is competitive. If they are internal volumes or free-form shells, it usually is not.

Where CNC does win is when the part is needed fast and the design is still moving. No tooling, no mold, no minimum order quantity. One prototype or a 10,000-part run, both from the same program.

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  Simple and numerousCasting or sheet metal beats machining on unit cost.
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  Internal channelsAdditive, then machine the sealing faces.
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  Design still changingMachining absorbs revisions without new tooling.