A modified Gaudi structure for the optimisation of the focus of wafer steppers

The performance of the Gaudi structure has been examined and its sensitivity to dimensional variation is demonstrated. It has been shown that the effect of variation in resistivity and etch can be minimised by grouping the structures close together. This procedure has been used to optimise the focus setting using the Gaudi structure. A modified Gaudi test structure that is more sensitive to dimensional changes is also proposed. It consists of a single layer of polysilicon, the resistance of which is modulated by changes in resolution. Its sensitivity is maximised as the resolution approaches perfection making it ideally suited to optimising the setup of wafer steppers for small geometry processes.< >