Electrochemical Analysis of Surface Oxide Layers of Various Copper Films in Microelectronics

Copper is a commonly used conductor and metallization materials. However, surface copper oxide layers which readily form during fabrication and assembly processes will increase electrical/thermal resistance, and even cause reliability problems. The dominating factors include the constituent phases of surface oxide layer, as well as the thickness ratio of CuO/Cu2O. The most common way to analyze surface oxide layer are XPS (X-ray photoelectron spectroscopy) and TEM (Transmission electron microscopy) techniques. However, sophisticated instruments are required and sample preparation is time-consuming. Efficient and accurate on-line or at-line measurement is very crucial. In this study, the analysis of oxidized layer of electroplated, and cold-rolled copper surface by means of coulometric reduction method was developed. Various microelectronic assembly processes were simulated to obtain copper surface with different oxidation conditions, including molding, curing, reflowing, and high temperature aging were also performed. Experimental results demonstrate that coulometric reduction can precisely detect the oxide phase and their thickness regardless of the sample conditions.