Determination of copper contamination from various sources in an RFIC wafer fab using VPD -TXRF methodology

The expansion of radio frequency (RF) applications has given a tremendous push to an increment of circuit density which is can be pack more electronic components on a chip and thereby provide higher performance. However as integrated circuits become denser as well as feature size become smaller, the conventional metallization aluminium (Al) has it limitations. But then the use of copper (Cu) is increasingly attractive because they have higher electromigration resistance and demonstrate a lower resistivity than Al. Due to the superior properties of Cu, a chip made by Cu may need only half as many metal layers as one made with Al, providing considerable reduction in manufacturing cost. Since Cu has many advantages and offer a cost saving, manufacturers prefer to have a shared line together with Al. However, despite all the advantages, Cu also has some drawbacks because it is a deep level dopant on silicon and cause large generation of electron and holes in depletion layers. So, results in large leakage and degraded reliability. These imply that prevention of Cu contamination is important in a fabrication. Hence, appropriate methodology is required to prevent it seeing as current method of Cu contamination detection highlighting on a wafer surface only. This paper presents a new method, VPD-TXRF, which can be use to detect a Cu contamination that come from many sources in a wafer fab. This method was definite by gauge repeatability and reproducibility (GR&R) study and correlation with current method; Inductive Couple Plasma Mass Spectrometer (ICPMS). A positive result validated this method as a novel method to evaluate the level of Cu that come from many sources in a wafer fab.