A New Experimental Setup to Measure the Through Thickness Relaxed Stress Profile of Ultra-thin Films

Thin films are used to obtain high performance and reliability in a large number of technologies including optical communications, microelectronics and wear-resistant coatings. Knowledge about the residual stress is crucial because it can limit the performance and lifetime. Residual stresses already start developing during deposition and growth of the thin films and will further change due to short and long term relaxation effects.

Numerical models have been developed to calculate these residual stress as a function of the thickness for single layers. Due to the complex origin of the residual stress the models in literature depend on many parameters making accurate determination of these parameters challenging. When a multi-layer stack is deposited, the layers start to interact with each other significantly affecting the residual stress. There are no models available to accurately describe these changes in residual stress due to this interaction.

Therefore, a new experimental setup is needed to measure the through thickness relaxed stress profile of a multi-layered stack with a resolution in thickness of 1 nm and resolution of stress in a layer of 10 nm of 10 MPa, also in case of a multilayer stack.

In the new setup, the stress will be measured with an inhouse developed high accuracy stress sensor that will measure the average stress in the multilayer stack. To obtain the stress as function of thickness, the multilayer stack will slowly be etched and from the change in average residual stress, the residual stress in the removed layer can be assessed. At the same time the change in thickness must be monitored.

Therefore, the through thickness stress measurement setup consists of three components; a stress sensor to measure in-situ the average residual stress, a setup able to uniformly remove the material, and a device capable of measuring how much material has been removed. Each of these components will be individually discussed and compared with their alternatives.