In transitioning from 300mm to 450mm wafer processing, the surface area of each wafer approximately doubles and so the mass of direct materials used in deposition and etch chambers can be expected to increase accordingly. Consequently, the cost to deliver and abate process chemicals will likewise double…unless we re-examine how our process tools are integrated into our fab facilities. The abatement of toxic effluent gases from deposition and etch chambers is an ongoing challenge for fabs, and there are different “optimal” solutions depending on whether we take a unit-process or a total-fab perspective.
From a unit-process perspective, perhaps that held by a manufacturing process engineer responsible for sustaining a particular cluster tool on the fab floor, the effluent management may not even be within their consideration. The performance evaluation of a fab process engineer or engineering manager may be based strictly on the availability of a given cluster-tool, with no consideration for the efficiency of effluent abatement from that cluster-tool. Consequently, the costs for De-Ionized Water (DIW), for energy, for wet-precipitation, and for bases to neutralize acidic-waste are hidden from the process people.
For example, a clean step for an etch chamber may use 300 sccm of Cl2 flowing in 40 slm of N2, and a wet-scrubber with 99.5% efficiency will let pass 375 ppm Cl2. This level of Cl2 in the exhaust ducting will cause corrosion over time, resulting in fab downtime and cost to replace ductwork. However, all of this is typically hidden from the engineering team responsible for the etch chamber. A dry-scrubber can reduce Cl2 levels to <1 ppm.
Dry-scrubber technologies such as those provided by CS Clean Systems provide toxic effluent abatement at significantly lower overall costs to the fab. Dry-scrubber systems capture and convert gases to solids using chemical principles of adsorbtion and absorption and reaction with granular material packed into a column, thereby avoiding the need to burn the effluent stream to create toxic ash. We should note that no single technology can abate all of the different effluents from all of the different modern semiconductor process chambers, and PerFluoroCarbon (PFC) species typically need some manner of high temperature abatement such as gas-fueled or plasma combustion.
Dry-scrubbing technology allows for spontaneous, passive, room-temperature abatement of toxic effluents in high-volume manufacturing (HVM) lines, with no need for feed-forward quick-start active sub-systems. The result is more dependable and more efficient abatement, with all of the costs clearly disclosed. With conservation of energy and cost reduction more relevant then ever, let’s step back and take a rational look at the possibilities of how we set up our fab at this point, and not just do more of the same.
Author: Joe Guerin
Head of Sales and Marketing – CS Clean Systems AG, Ismaning, Germany