Characteristics of very high-aspect-ratio contact hole etching

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