| 摘要 |
In the production of semiconductor devices an image of a circuit pattern is projected onto a semiconductor wafer. In order to achieve precise focus a focusing apparatus is provided in which air jets (68) are located immediately adjacent the exposure area. Back pressure of the air jets (68) in sensed by sensors (70) to determine the distance of the optical unit (10) of the photo-exposure system from the surface of the semiconductor wafer (14) being exposed. The average back-pressure is utilized to control movement of the optical system (10). A map of the surface aberration of the wafer (14) may be obtained by measuring the position of the camera at each die site after focusing has been achieved. |
