Northumbria Optical Coatings (NOC) manufacture thin film interference filters for use in measurement instrumentation, spectroscopy and related fields. With multiple layers of semiconductor materials deposited on quartz substrates with nano-metre precision; variability associated with process conditions, operator skill, equipment and material characteristics can all impact manufacturing yield. Such a complex process can give rise to a complex set of potential failure modes during manufacture, which can be difficult to interpret and address. Inter-layer delamination was a specific failure mode of interest, where TWI engaged with NOC to help understand some fundamental material conditions, in support of a broader study aimed at improving product quality and manufacturing yield.
TWI's nano-indentation equipment was utilised in order to measure hardness and elastic modulus of the multiple layers of semiconductor materials in cross section. The technique is based on measuring the response of the material to plunging a very fine tip into the surface layers of the material, during loading and unloading of the tip. With NOC's layer thicknesses typically less than 1 micron, no other technique exists for undertaking such evaluations.
The support gave rise to enhanced knowledge of materials and process conditions, and explored the impact of process induced hysteresis associated with material strain, and the potential of 'locking in' residual stresses. This paved the way for a more in-depth study relating to failure modes in support of improvements to quality and productivity. The investigation showed how the nano-indentation technique can be used to extract quantitative information regarding the profile of mechanical properties of thin films.
For more information on how this approach can be applied, please contact us .