To understand the mechanism of noble-metal adhesion in wet processes, the behavior ol Cu adhesion to the Si surface in various chemical solutions, the shape and chemical composition of Cu contaminants adhering to Si surfaces, the surface microroughness of Si surfaces, and the influence of the type of the substrates are investigated. The results show that Cu ion deposits on the Si surface in the form of metallic particles in wet chemical processing, that Cu deposition in HF solutions causes pits to be formed on the Si surface, and that, on a patterned substrate, Cu deposits on the Si surface but not on the SiO2 surface. The experimental results imply a Cu deposition mechanism. In a dilute HF solution, the Si surface beneath the Cu particles is etched away to become SiF~ and a pit is made. Contamination with noble metals is critical. The mechanism for metal deposition may apply to noble metals in general. These metallic impurities must not be introduced into any wet chemical solution or ultrapure water when a bare Si surface is exposed.With continued advances in ultralarge scale integrated (ULSI) fabrication technology, achieving ultraclean wafer surfaces is essential. An ultraclean wafer surface is characterized as a surface which is (i) particle-free, (it) organic contamination-free, (iii) metallic contamination-free, (iv) native oxide-free, (v) completely hydrogen-terminated, and (vi) surface microroughness-free. I It is well known that the metallic contamination on the Si surface can cause fatal effects on semiconductor devices such as: increase the current leakage at the p-n junction, decrease the oxide * Electrochemical Society Active Member.

Increasing the process temperature in CO/NH3 plasma etching has been investigated to suppress an etch stop in high-density magnetic tunnel junction stack (MTJ stack) patterning with a Ta mask. In a previous study, the occurrence of an etch stop was observed when using a 100 nm space pattern; specifically, the etching depth was unchanged with the 100 nm space pattern when the etching time was increased, although when wider spaces were used, the etching depth increased proportionally. In this study, differences in the etch stop depth with 100 nm space patterns were examined by changing the electrode temperature from 120 to 300 °C. The etch stop depth became deeper as the electrode temperature was increased and it was found that a high-temperature CO/NH3 process was an effective way to prevent the etch stop effect. However, at 300 °C, the MTJ stack's thickness was observed to expand, which may induce a deterioration of the junction's magnetic properties. A scanning transmission electron microscope image and an energy dispersive x-ray spectroscopy image of the MTJ stack revealed that nitridation of the MTJ stack was the reason of its expansion in thickness. Moreover, pure N2 plasma irradiation of the MTJ stack clearly indicated that this thickness expansion occurred for an electrode temperature of over 265 °C. Finally, the results demonstrate that, for a CO/NH3 process with an electrode temperature of 250 °C, it is possible to etch a 52-nm-thick MTJ stack without either etch stop or film thickness expansion occurring.