Effects of the polymer residues on via contact resistance after reactive ion etching

Abstract

The effects of CF4 addition to O2 reactive ion etching (RIE) of a polyetherimide (Ultem®) surface and resultant via contact resistance were investigated using scanning electron microscopy (SEM), x-ray electron spectroscopy (XPS), and cross bridge Kelvin resistor (CBKR). In pure O2 RIE, the SEM micrograph showed that the originally smooth Ultem surface became rough and the rough features coarsened with increasing RIE time, resulting in residual particles on the metal pads. However, in the case of O2+CF4 RIE, the Ultem surface remained smooth throughout the etching process, and residue free metal pads were obtained. The XPS experiments identified that the origin of the Ultem surface roughening was organo-Si compound, which is easily converted to silicon oxide during O2 RIE. In contrast, the atomic fluorine in O2+CF4 RIE process etched out the silicon and the silicon oxide, resulting in smooth film surface and residue free metal pads. The metal to metal via contact resistance was measured by CBKR, and the pattern fabricated by O2+CF4 RIE showed lower contact resistance than those by O2 RIE. These results are discussed in the criterion of contact area and contact conformality differences.