When the precursors leave the chamber during Atomic Layer Deposition (ALD) they can condense and clog exhaust lines. The heated trap is designed to reduce organometallic precursors to the metal and an organic gas which passes easily through the exhaust system. Another issue with ALD precursors is they can condense on the exhaust line and when the reactive precursor is present the same reaction that occurs on the substrate surface occurs on the exhaust lines. In the case of the metal-organic precursors the nitride or oxide films can be quite hard to remove.
Atomic layer deposition is being used more because of the increasing demands of thin film and device engineering, structures and sizes. The precursors used in ALD are not transformed in the deposition process as they would in a plasma or thermal deposition process. In addition with the Heated Trap other process gases can be dissociated like trimethylaluminum (TMA) used for CVD deposition. The Heated Trap provides significant advantages in cost and yield for the chamber exhaust process.
The heated trap works best the closer to the chamber. This ideal installation right after the turbo pump reduces the number of heaters needed when the trap is farther away from the pump exit. If the pumping system can accommodate an few extra liters of inert gas, the combination of the Virtual Wall and the heated trap will provide increased uptime and reduced maintenance time. If heaters are required, MKS has heaters that can run as high as 250°C if the line before the trap needs to be heated instead of another solution.
The heated trap can run at temperatures up to 450°C and the gas temperature leaving the trap will increase the pressure locally and a recommended distance of at least 1 meter to allow for gas cooling is recommended before the gas reaches the pump.