Hidden Architecture: PECM's Role in Safer, Smarter Semiconductor Design & Toxic Gas Containment
- Kirk Abolafia
- Nov 4
- 6 min read
How Voxel's ability to machine non-line-of-sight, internal features in critical gas delivery infrastructure can benefit semiconductor design, prevent equipment outages, and minimize danger to human operators.
To learn about other ways PECM can enable new developments in semiconductor manufacturing, read out recent article on direct-to-chip-cooling.
Contact us with any questions, suggestions, or ideas on your next project.
Among the world’s most advanced and lucrative manufacturing sectors—semiconductors—relies on seemingly invisible architecture, including hidden, non-line-of-sight, internal features, finishes and geometries that dictate equipment lifespan, resistance to temperature and corrosion, and operator safety. These challenges are further magnified by the industry’s reliance on highly toxic and corrosive gases inherent to the manufacturing process which, if leaked even on a microscopic level, can cause significant damage to equipment, the semiconductors themselves, and even human health.
In this article, we’ll discuss how non-line-of-sight machinability and internal finishing is becoming increasingly critical for handling toxic gases in semiconductor manufacturing and beyond, and how PECM’s ability to machine and finish complex internal features can be utilized in-parallel with AM-enabled designs in the semiconductor manufacturing space and other key parts like heat exchangers to enable safer and more efficient internal designs.
As semiconductors are essentially comprised of dozens of ultra-thin layers of metals and dielectrics, manufacturers sometimes use chemical vapor deposition (CVD) to coat surfaces with certain materials, including metals, using high-temperature gases. A good example is Tungsten Hexafluoride: when this toxic gas is utilized in semiconductor manufacturing, it produces both a “good” reaction as a pure tungsten film layer on the chip, as well as a “bad” reaction of HF (hydrogen fluoride) gas by hydrolyzing in moisture; HF is a significantly corrosive and toxic gas to both organic and inorganic materials.
Other toxic gases are used to etch microscopic patterns onto silicon within the fabrication process to create the web of microscopic circuits needed for the actual computational power of chips. Aggressive gases such as chlorine, bromine, or hydrogen fluoride-based gases are considered some of the best “atomic scalpels” for creating these deeply complex patterns, capable of atomic-level material removal without damaging any underlying layers.
Additionally, manufacturers may rely on other fluoride-based gases (such as NF3 and ClF3) to self-clean specific chambers that accrue residue buildup over time. Fluorine is especially useful at eating away built-up film on the inside of chamber walls that can then be flushed out without damaging the part.
However, even the smallest leakage of these gases can cause significant problems. Leaks measured in standard cubic centimeters per second (std cm³/s) identified to be dangerous in this industry are in the realm of 10⁻⁹–10⁻¹¹ std cm³/s, or a billionth of a cubic centimeter of gas per second: loosely equivalent to the volume of a single grain of salt leaking every 8 hours.
Manufacturers are heavily incentivized to regulate and control the flow of these gases, as even tiny leakage during the manufacturing process can result in three consequences:
The most negligibly, microscopically small leaks can quietly dismantle multi-million dollar equipment for semiconductor manufacturing. HF can easily attack and corrode sensors, seals, electronics, and more, resulting in tens, or even hundreds of thousands of dollars in replacement costs, as a result of extremely small surface defects inside of equipment causing a leak, especially consequential for the high-demand environment of semiconductor fabrication.
The complexity of semiconductor fabrication makes it extremely sensitive: gas leaks can introduce cross-contamination that can create non-uniform film thicknesses, incomplete etching, introduce debris on wafers, and more. Features and tolerances are on the nanometer-scale, so the very tiniest impurities can render a chip unusable.
Even trace amounts of these gases can cause damage or death in humans: HF gas, a byproduct of the tungsten hexafluoride reaction, is strong enough to dissolve the calcium in bones and ClF3 is so flammable it can easily ignite organic material and clothing. Furthermore, many of these gases are entirely odorless and colorless, adding to their lethality.
Containing these gases require a challenging combination of unique materials, superfinished internal surface quality, and complex geometries. For instance, manufacturers often opt for materials with high crystallinity, corrosion-resistance, and thermal stability, such as nickel superalloys, to survive both corrosive gases and high temperature-flux. Internal surface quality requirements of these gas containers can go down to 0.13-0.25µm (5-10µin) Ra, and the infrastructure of this equipment is akin to a complex spiderweb of valves, regulators, delivery lines and etch chambers. Consider gas delivery manifolds that regulate, mix, and route gases. These parts can be a complex, branched network of 1-6mm diameter tubes of temperature and corrosion-resistant alloys, or perhaps “showerhead” components (gas diffusers) involving a complex, tight array of thousands of microholes (sometimes down to 50µm (2 thou) wide, meant to ensure even gas flow across the testing wafer.
The key difficulty of these components is less about the exotic materials and moreso the geometric and surface-quality challenges. Rough internal surfaces (even sub-micrometer) can prove dangerous by trapping moisture and reactive residues in small, localized areas, thereby creating uneven sealing pressure and eventually, microcracks. Furthermore, the non-line-of-sight features requiring these superfinishes are sometimes within deep intersecting bores or cross-drilled channels inside a labyrinth of passages (meant to prevent backflow and particle traps), making it especially challenging for engineers to access.
Additive manufacturing is playing a helpful role in “consolidating” geometries by allowing entire multi-chamber gas management systems to be printed as a single metal part, including heat-transfer jackets wrapped around gas paths or internal conformal flow channels. However, this is also exacerbating the issue of non-line-of-sight geometries, as printed parts may lack the inherent tolerances and surface roughness needed to contain these gases and postprocessing these internal geometries creates significant manufacturing bottlenecks, especially at-scale.
Voxel is developing in-situ, internal machining and finishing capabilities for complex metal additive components via pulsed electrochemical machining (PECM), well-suited to the acute tolerances required for semiconductor manufacturing to contain toxic gases. Unlike conventional processes reliant on line-of-sight access, PECM is capable of uniformly (or selectively) removing material along internal surfaces without any mechanical contact or line-of-sight.
Akin to the atomic-level precision semiconductor fabricators choose these gases for, PECM also acutely removes workpiece material at the atomic level to produce extreme surface quality: down to .005-0.4µm (0.2-16µin) Ra on a variety of tough materials like nickel superalloys, and in unique geometries, all at scale.
PECM has been shown to be able to access serpentine gas channels for in-situ internal finishing (pictured) and may also be capable of machining lattice cores and multi-branch manifolds in gas chambers for semiconductor manufacturing where no conventional tools can fit.
PECM’s reliance on electrochemistry and its usage of electrolytic fluids also prevent any thermal reaction, thereby limiting residual stress, microcracks, surface deformities, or tool wear, ensuring no cross-contamination or disruptions to gas flow in these devices, while ensuring surfaces are sealed, preventing leaks of corrosive gases.
PECM also ensures repeatable accuracy with its minimal tool wear and multi-tooled cathode capabilities, especially useful for producing the tight-tolerance, high-feature-count microhole arrays found in showerheads and other gas delivery devices.
Adjacent to the complex web of gas flow infrastructure within semiconductor manufacturing architecture are heat exchanger features, a common application for PECM’s key capabilities. Dense networks of thin-walled, microchannel features allow precise temperature control across reactors, wafer chucks and gas delivery assemblies in semiconductor manufacturing. While PECM’s strengths are found in its ability to create dense networks of thin-walled microchannels for critical heat exchangers (for more information on these features, read this article) its other applicability for heat exchanger geometries lies in its ability to machine and finish internal geometries of channels in-parallel.
In short, thermal efficiency is heavily reliant on both the density and architecture of the channels, and of the material/surface quality of these internal features, as rough surfaces can amplify pressure drops and turbulence, trapping bubbles or residues that can ultimately reduce heat transfer capabilities. Fortunately, PECM is adept at both refining these thin-walled features and internally finishing them, sometimes able to produce dozens or hundreds of features in-parallel using a special in-situ PECM process.
This is especially useful as additively-manufactured heat exchangers are increasingly used for their ability to enable more complex geometries. Often, the internal porosity is both insufficient for heat transfer and exceedingly difficult-to-reach.
Beyond semiconductor thermal management, PECM’s ability to machine and finish difficult-to-reach internal features reaches to a variety of high-performance domains, including aerospace cooling channels, medical implants, and potentially RF/power electronic equipment for the defense industry. PECM’s non-line-of-sight precision is a boon for enabling designers to optimize geometries, utilize additive manufacturing in more scenarios, and scale complex-geometry parts requiring internal surface finishing.
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