Critical dimension control on I-line steppers

As chip dimensions decrease, I-line steppers can still provide very good performance for uncritical layers at low cost and high throughput. However, while older technologies are relatively insensitive to tool and process variations, process control of advanced technologies on I-line becomes critical. In this paper, we will concentrate on critical dimension variations of I-line lithography and provide some examples. The topics considered here primarily cover variations in CD range and CD mean that can be detected in SPC charts. We also discuss the benefits and drawbacks of measurements performed in the kerf rather than in the chip, in relation with the above CD control investigation. Finally we discuss how sampling should be effectively related to the process stability (Cpk values).