New avenues for residual stress analysis in ultrathin atomic layer deposited free-standing membranes through release of micro-cantilevers

• Published in: Heliyon Vol. 10; no. 4; p. e26420
• Main Authors: Burgmann, S., Lid, M.J., Johnsen, H.J.D., Vedvik, N.P., Haugen, B., Provine, J., van Helvoort, A.T.J., Torgersen, J.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 29-02-2024; Elsevier
• Subjects: ALD; FIB; Residual stress; Strain analysis; Ultrathin membranes; ALD; Strain analysis; Ultrathin membranes; FIB; Residual stress
• DOI: 10.1016/j.heliyon.2024.e26420
• EISSN: 2405-8440

The fabrication of thinnest, yet undeformed membrane structures with nanometer resolution is a prerequisite for a variety of Microelectromechanical systems (MEMS). However, functionally relevant thin films are susceptible to growth-generated stress. To tune the performance and reach large aspect ratios, knowledge of the intrinsic material properties is indispensable. Here, we present a new method for stress evaluation through releasing defined micro-cantilever segments by focused ion beam (FIB) milling from a predefined free-standing membrane structure. Thereby, the cantilever segment is allowed to equilibrate to a stress-released state through measurable strain in the form of a resulting radius of curvature. This radius can be back-calculated to the residual stress state. The method was tested on a 20 nm and 50 nm thick tunnel-like ALD ▪ membrane structure, revealing a significant amount of residual stress with 866 MPa and 6104 MPa, respectively. Complementary finite element analysis to estimate the stress distribution in the structure showed a 97% and 90% agreement in out-of-plane deflection for the 20 nm and 50 nm membranes, respectively. This work reveals the possibilities of releasing entire membrane segments from thin film membranes with a significant amount of residual stress and to use the resulting bending behavior for evaluating stress and strain by measuring their deformation.
•A FIB milling procedure allowing the release of defined micro-cantilevers from free-standing membrane-based microstructures.•Through the release of the micro-cantilever, an ultrathin ALD ▪ membrane's residual stress releases to measurable strain.•Minimally invasive milling parameters allowing the release of micro-cantilevers without perturbing the initial stress state.•Evaluated residual stress of 866 MPa and 6104 MPa for a 20 nm and a 50 nm thick ▪ membrane structure, respectively.•Composite FEM model maps membrane stress distribution, aligning well with out-of-plane deflection.