Crack Formation during Electrodeposition and Post-deposition Aging of Thin Film Coatings - 4th Quarterly Report
Prof. Stanko R. Brankovic*
University of Houston
Houston, Texas, USA
Editor’s Note: This NASF-AESF Foundation research project report covers the fourth quarter of project work (October-December 2016) on this AESF Foundation Research project at the University of Houston. Access information to past project reports referred to in this paper is listed at the end of this report. A printable PDF version of this report is available by clicking HERE.
- Stanko R. Brankovic, PI, Electrical and Computer Engineering and Chemical and Biomolecular Engineering, University of Houston,
- Kamyar Ahmadi, PhD Student, Material Science Program, University of Houston,
- Nikhil Chaudhuri, PhD Student, Material Science Program, University of Houston.
The objective of the proposed work is to study fundamental and practical aspects of crack formation in electrodeposited thin films. The aim is to identify and quantify the key parameters of the electrodeposition process affecting the crack formation in thin films. This study should enable development of an effective strategy generally applicable in practice whenever electrodeposition process for crack-free films is demanded.
The activities in this period were focused on studies of stress evolution in chromium thin films, ~8 microns in thickness deposited on 1 micron of copper on 100 nm NiCr seed (Cu/NiCr seed), during aging at room temperature in air and during annealing at 250°C in air. The chromium films were deposited from Cr+3-containing electrolytes (EXDBA 1411 Bath at pH 5). In parallel to the in situ stress measurements, complementary impedance measurements of chromium thin films during relaxation in air at room temperature and during annealing at 250°C have been performed for the same temperature range and ramping rate.
In situ stress measurements
Room temperature relaxation of chromium films deposited from EXDBA 1411 Bath at pH 5, on Cu/NiCr seed
The one issue that had to be addressed from our previous report (3rd Quarterly Report) was the complete comparability among the samples for air and annealing studies. In that report, the air relaxation experiment was performed on the samples that were deposited on copper seed, which is much more conductive than Cu/NiCr (rest of the samples) but with poorer adhesion. Therefore, small changes in the copper seed conduction/delamination during the aging process could be the reason for the large impedance change during air aging that we observed. For this reason, a set of new in situ stress and impedance measurements was performed on chromium films deposited on 1 micron Cu/20 nm NiCr (Cu/NiCr) seed during air aging, representing the same situation as in our annealing studies at 250°C; fast ramping rate, (see previous report). The resulting in situ stress data are shown in Fig. 1(a), for chromium films of ~8 micron thickness. A comparison between the data obtained on chromium films deposited on copper seed (previous report) and chromium films on Cu/NiCr seed (this report) is shown in Fig. 1(b).