Throughput is probably the most important factor in choosing a stepper, given that resolution capabilities are equal. Cost of Ownership or cost per tool is important but as you can see from your numbers, the ASMLF is almost twice the throughput of the Nikon system. Therefore, even if the ASMLF cost twice as much as the Nikon, it is close to a wash with the exception of the R7M costs, service contracts, and of course, valuable floorspace utilized.
However, throughput is also a bogus number in certain respects. Some of these numbers might be quoted in terms of "blind stepping" which is just a blanket step/scan/expose with no layer to layer alignment for the very first photo layer. At subsequent litho steps the systems may have to do either a global or site by site alignment of one layer to another. This alignment time (registering one layer to another) dramatically affects throughput. In addition to this, the filed size capable of being exposed will affect throughput of the system. So when you calculate throughput of the system, I like to consider the throughput per given field size or area exposed. Again, if the Nikon Stepper had twice the field size as the ASMLF, the systems are equally matched. Finally, the step and scan portion of the process must also be quantified.
It has been my experience that comparing Data Specification sheets from one vendor to another does not give a real accurate assessment since each vendor can "massage" the numbers relative to how they report or list certain equipment parameters.
The rule of thumb has historically been that the lithography exposure tools usually are the gate to manufacturing capacity for any given fab. Therefore, within reason, the number of wafers starts per unit time per fab is directed gated by the throughput of the steppers. Anything that can be done to increase the throughput of these systems could usually translate itself into more wafer starts for the facility. This scenario is possibly being challenged today by CMP. It seems that CMP tooling takes up a great deal of space and has very low throughput relative to other processing tools. Therefore, we may be seeing CMP tools replacing the steppers as the capacity limiting tools or process.
Andrew |
