Magnification inferred curvature for real-time curvature monitoring

Abstract

The in situ and real-time measurement of curvature changes of optically reflecting surfaces is a key element to better control bottom-up fabrication processes in the semiconductor industry, but also to follow or adjust mirror deformations during fabrication and use for space or optics industries. Despite progresses made in the last two decades thanks to laser deflectometry-based techniques, the community lacks an instrument, easy to use, robust to tough environments and easily compatible with a large range of fabrication processes. We describe here a new method, called magnification inferred curvature (MIC), based on the determination of the magnification factor of the virtual image size of a known object created by a reflecting curved surface (the substrate) acting as a spherical mirror. The optical formalism, design, and proof of concept are presented. The precision, accuracy, and advantages of the MIC method are illustrated from selected examples taken from real-time growth monitoring and compared with state-of-the-art laser deflectometry-based instruments.

Growth of BiSb on GaAs (001) and (111)A surfaces: A joint experimental and theoretical study

“…The two growth modes are further confirmed by in situ strain measurements 37 during growth on the two GaAs surfaces, that present totally different behaviors on both substrates.…”

Structural and Electrical Characterizations of BiSb Topological Insulator Layers Epitaxially Integrated on GaAs

“…Once a critical density is achieved, for sample thicknesses above 30 nm, the grains develop, become larger, and coalesce, leading to the formation of a continuous layer (Figure c–f). To define a critical thickness, corresponding to the grain coalescence, an in situ optical monitoring of the wafer curvature was carried out on the 90 nm thick sample . This measurement records the accumulated stress during the BiSb growth (see Figure S9).…”

“…To define a critical thickness, corresponding to the grain coalescence, an in situ optical monitoring of the wafer curvature was carried out on the 90 nm thick sample. 28 This measurement records the accumulated stress during the BiSb growth (see Figure S9). At the beginning of the BiSb growth, a compressive stress appears on the wafer corresponding to the grain nucleation.…”

Integration of the Rhombohedral BiSb(0001) Topological Insulator on a Cubic GaAs(001) Substrate

“…Finally, Bi and Sb are evaporated simultaneously, and the Bi 0.9 Sb 0.1 layer is grown for 50 min, which corresponds to 200 nm. Thanks to an in situ optical monitoring of the wafer curvature, 27 the stress of the system is probed during the growth, as reported in Figure 1c. When Bi and Sb shutters are opened, the stress accumulates for 70 s before reaching a step.…”