A double-exposure end-point detection technique (DEEP· DET) enables precise development of lines below 1, μm. A small test area first receives a precalibrated blanket exposure. During the masking operation, features of several micrometers are printed on it. When the resist in the test area, observed by eye or under a low-power microscope, is completely cleared, the wafer is accurately developed. An efficient method of precalibration is described. The capability of a 0.01-μm accuracy is estimated analytically. An experimental demonstration of the accuracy and a scheme for automatic detection are given. Copyright © 1978 by The Institute of Electrical and Electronics Engineers, Inc.