Building a plasma-enhanced atomic layer deposition system (PEALD)

     Before I could start device and circuit work, I needed to build the tool I would use to deposit my oxide layers (gate dielectric and semiconductor). I settled on building a plasma-enhanced ALD system, because it would provide highly conformal films with excellent thickness control at plastic-compatible temperatures. I designed the system based on a similar tool at Penn State, put it together from custom and commercially available components, and programmed it to run automated depositions. This is the full system:

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Above, from left to right: gas manifold in fire-proof cabinet, water baths housing bubblers with metal organic precusors; deposition chamber, manometer, vacuum pump, RF matching network; computer control, RF power supply, temperature controller.

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Deposition Chamber

This was the first time I successfully struck a plasma in my deposition chamber! Looking down at a capacitively-coupled RF argon plasma through the polycarbonate lid. 

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PEALD Cycle

This schematic shows the PEALD cycle, which provides monolayer control over layer thickness. First, metal organic precursor molecules (yellow) adsorb on the substrate surface (blue) at hydroxyl sites. Weak oxidant gas (red dots) purges excess precursor, which is pumped out through the gate valve. Once a stable pressure is achieved, the weak oxidant gas is ionized, and its byproducts oxidize the precursor, forming one layer of material. Excess byproducts are purged with more weak oxidant gas, and the cycle is repeated until the desired thickness is reached.