CHARACTERISTICS OF VERY HIGH-ASPECT-RATIO CONTACT HOLE ETCHING

An ultrahigh-aspect-ratio, 0.06-mu m-diameter, 2-mu m-deep contact hol e pattern of SiO2 was successfully fabricated using a poly-Si mask and a magnetically enhanced reactive-ion-etching (RIE) system in a mixtur e of CHF3/CO gas. In this dimensional area, processing for vertical pr ofiles is extremely difficult, and problems in the form of bowing at t he sidewalls of the holes can occur. Furthermore, it is possible that ion flux and energy are significantly reduced when ions pass through t he poly-Si mask, rather than through the SiO2 hole. The bowing is asso ciated with bending of the incident ion trajectories, where the first stage of the trajectory change occurs at the mask, and subsequent mult iple scattering of ions at the sidewall of the hole can occur. Other f actors include sidewall protection by redeposited Si sputtered from th e poly-Si mask and/or the deposited fluorocarbon polymers, and the eff ects of ion energy and flux bombarding these deposited materials.