Fabrication of sub-60-nm contact holes in silicon dioxide layers

We have developed a fabrication technique, comprising electron-beam writing, chemical shrinking, and silicon dioxide etching, for the fabrication of sub-60-nm contact holes. The dimensions of the contact holes after the electron-beam writing, chemical shrinkage, and plasma etching steps were 140, 93, and 53 nm, respectively. We carefully evaluated the critical process parameters, such as mixing-bake temperature, mixing-bake time, plasma etch selectivity, and the profile shapes. A higher mixing-bake temperature led to an overhang of the contact hole in the resist; the optimal mixing-bake conditions occur when heating at 110°C for 70 s. A fluorinated mixture of gases (CHF₃/CF₄=1:1) was used to etch the nano-scale contact holes in the silicon dioxide layer. The formation of side-wall polymers during the plasma etch phase contributed further to the contact hole shrinkage in addition to resist chemical shrinkage. The ratio of the hole's perimeter to its area affects the shrinkage dimensions of the etch process, especially for smaller contact holes. The pattern reduction due to side-wall polymer deposition in etch process has the inverse relationship with the diameter of contact hole.