Scallop Reduction in Bosch Process Using a Small Chamber and Rapid Gas Switching Rate

We have developed an inductively-coupled plasma-reactive ion etching system (ICP-RIE) in a human-size machine of minimal fab for processing a half-inch wafer. The etching system has performed a Bosch etching process with a short switching cycle in a tiny chamber with a volume of 1/4ℓ. For the tiny chamber, a plasma density generated by typical radio frequency of 13.56 MHz is too low according to the small space of the chamber. Thus, a higher frequency of 100 MHz is employed for a high density plasma operation although the power consumed is only ~40W. The Si etching rate of the Bosch process is ~2.5µm/min. Moreover, owing to a fast residence time of ~0.2 second, deposition gas (C4F8) and etching gas (SF6) are exchanged rapidly, which makes a Bosch cycle time of only 2 seconds. The resultant etching sidewall of Si structure becomes a scallop-less straight wall.