A new optical focus system for wafer steppers, insensitive to structures on the wafer surface, is presented. It is based on the grazing‐incident beam method. In traditionally used monochromatic focus systems, interference effects in the layer stack on the wafer are a severe limitation on the accuracy. In the system presented here, this problem is overcome by using an incandescent lamp as a polychromatic light source. Due to the large spectral range of 300 nm, interference effects in the layer stack on the wafer are averaged. Calculations of the influence of these interference effects on the focus measurement show good agreement with the experimental results. An additional feature of the system is its large measurement spot, which averages effects related to locally varying reflection and topography. Moiré fringe and modulation techniques are used to enhance the signal‐to‐noise ratio. As a result the dynamic range of the system is increased to 103. The mechanical stability is considerably improved by the addition of a reference branch that measures the position of the projection lens. This enables the accurate and precise measurement of the required distance between lens and wafer. The extra optical features together with the mechanical stability yield a vertical accuracy and precision better than 100 and 20 nm, respectively. The combination of four of these focus systems within one stepper permits the measurement of the local tilt of the wafer.