Slope control of molybdenum lines etched with reactive ion etching

Abstract

A reactive ion etching mask erosion method has been used to prepare highly sloped molybdenum lines. A computer simulation method was used to examine major factors that affect the final metal slope, such as the etch time, the etch ratio (photoresist to metal), and the original masking profile. A highly sloped metal line can be obtained with a high etch ratio. Experimentally, we have studied the following plasma parameters that control the etch ratio, which have a direct impact on the final metal slope: various gas mixtures such as CF 4 /O 2 , CF 3 Cl/O 2 , and CF 2 Cl 2 /O 2 , oxygen concentration, pressure, total gas flow rate, and self-bias voltage. A high etch ratio can be obtained with the CF 4 /O 2 plasma in the low-pressure, low-oxygen condition. A high total gas flow rate also favors the high etch ratio. Scanning electron microscopy pictures confirm that when the original photoresist profile is fixed, the final metal profile is mainly affected by the etch ratio. Auger electron spectroscopy (AES) results show fluorine was strongly bonded to the molybdenum surface. © 1990, American Vacuum Society. All rights reserved.