The flatness of membranes for micromachining applications is extremely important. Any deformation is a sign of internal stress that makes the structure susceptible to mechanical damage therefore unsuitable for any practical application. In microwave applications, surface protrusions act as harmful radiating elements. There is therefore a demand for the characterisation of the flatness and surface morphology of such structures. Usual methods are scanning electron microscopy, surface stylus profilometry, atomic force microscopy and various optical methods. One of the potential optical methods is the so-called Makyoh (or magic-mirror) topography, which has proved to be a powerful topographic method for the characterisation of the morphology of mirror-.like surfaces, such as semiconductor wafers and layer structures. In Makyoh topography, the local irregularities of the sample surface act as concave or convex mirrors therefore a collimated light beam impinging on the surface produces an image on a screen that, in a certain extent, reflects the sample morphology. Makyoh topography is advantageous for the studies of membrane structures for the following reasons: (i) Makyoh is contactless, which is important for the delicate structures, (ii) It gives instantaneous results, (iii) The set-up is simple and inexpensive, (iv) The resulting ‘raw’ image is visually informative. However, the quantitative interpretation of Makyoh images is not straightforward. This work firs describes a comprehensive geometrical optical model of the Makyoh image formation mechanism with an aim to provide a basis both for the in-depth quantitative analysis as well as for the quick, qualitative or semi-quantitative visual interpretation of the images. Methods for the measurement of overall curvature and the reconstruction of the surface profile from the observed images are described. One-dimensional simulations of the images of a hillock (or depression) and a periodic (sinusoidal) surface are presented as well. Then, the construction of our Makyoh-topography set-up is detailed. Then, the study of the deformations of dielectric membranes and structures is reported. It is shown that Makyoh is suitable to detect and quantify the deformations of the whole wafer, the individual membranes as well as the substrate areas adjacent to the membranes. For small membranes and strongly patterned structures, the imaging is limited by diffraction effects. However, qualitative study is possible. The results are interpreted qualitatively within the framework of continuum mechanics
The application of Makyoh (magic-mirror) topography for the study of deformations in dielectric membrane structures
Giacomozzi, Flavio;
2000-01-01
Abstract
The flatness of membranes for micromachining applications is extremely important. Any deformation is a sign of internal stress that makes the structure susceptible to mechanical damage therefore unsuitable for any practical application. In microwave applications, surface protrusions act as harmful radiating elements. There is therefore a demand for the characterisation of the flatness and surface morphology of such structures. Usual methods are scanning electron microscopy, surface stylus profilometry, atomic force microscopy and various optical methods. One of the potential optical methods is the so-called Makyoh (or magic-mirror) topography, which has proved to be a powerful topographic method for the characterisation of the morphology of mirror-.like surfaces, such as semiconductor wafers and layer structures. In Makyoh topography, the local irregularities of the sample surface act as concave or convex mirrors therefore a collimated light beam impinging on the surface produces an image on a screen that, in a certain extent, reflects the sample morphology. Makyoh topography is advantageous for the studies of membrane structures for the following reasons: (i) Makyoh is contactless, which is important for the delicate structures, (ii) It gives instantaneous results, (iii) The set-up is simple and inexpensive, (iv) The resulting ‘raw’ image is visually informative. However, the quantitative interpretation of Makyoh images is not straightforward. This work firs describes a comprehensive geometrical optical model of the Makyoh image formation mechanism with an aim to provide a basis both for the in-depth quantitative analysis as well as for the quick, qualitative or semi-quantitative visual interpretation of the images. Methods for the measurement of overall curvature and the reconstruction of the surface profile from the observed images are described. One-dimensional simulations of the images of a hillock (or depression) and a periodic (sinusoidal) surface are presented as well. Then, the construction of our Makyoh-topography set-up is detailed. Then, the study of the deformations of dielectric membranes and structures is reported. It is shown that Makyoh is suitable to detect and quantify the deformations of the whole wafer, the individual membranes as well as the substrate areas adjacent to the membranes. For small membranes and strongly patterned structures, the imaging is limited by diffraction effects. However, qualitative study is possible. The results are interpreted qualitatively within the framework of continuum mechanicsI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
