Laser beam homogenization (schematically).
Square hole (crater) made by rectangular homogenized beam of KrF laser in the SiON layer: (a) Optical micrograph of crater’s contour for pulses (top view). Notice the flat bottom surface without any structure. The rectangular color frames around the crater are the interference stripes on slightly tilted crater’s walls (in the optical microscope). (b) Corresponding profile of the crater made by pulses. (c) Optical micrograph of crater’s contour for (top view). Notice a dark filamentary structures (rolls) of the RBC convection formed at the SiON/Si interface. (d) Corresponding profile of the crater made by pulses.
Diagram of the crater’s depth, , vs the number of pulses, . Notice that the depth increases with every pulse in highly absorptive ceramic SiON layer, up to about , when the SiON/Si interface is reached. For , the crater’s depth increases only slightly due to much larger coefficient of reflectivity and reduced absorption of the Si surface. (Great number of pulses larger than few hundred is needed to reach larger depth in silicon).
SEM micrograph of the surface of the ablated crater obtained after irradiation by 30 pulses.
Domains of Marangoni regular and chaotic roll structures. (a) SEM micrograph of the regular domain. (b) Fourier spectrum of regular domain in Fig. 6(a). (c) SEM micrograph of the chaotic domain. (d) Fourier spectrum of chaotic domain in Fig. 6(c).
Comparative view of the micrographs showing domain with evolution of dislocation defect in the roll structure and numerical simulation based on the SH [Eq. (2)]. The evolution of dislocation defects is induced by the Eckhaus instability in the original roll structure. (a) SEM micrograph showing a series of dislocation defects in the roll structure. (b) Numerical simulation showing a series of dislocation defects corresponding to a. (c) SEM micrograph showing detail of the dislocation with appearance of the wavy perturbation in its surrounding. (d) Numerical simulation showing dislocation [corresponding to (c)]. (e) SEM micrograph showing a dense roll structure formed after decrease of the period caused by a number of dislocations in the original roll structure. (f) Numerical simulation of the defect structure from corresponding to e.
Chaotic region of rolls with abrupt change of the roll direction. (a) SEM micrograph of chaotic region of rolls. (b) Numerical simulation of the chaotic roll organization.
The surface section profile for the regular stripes: (a) after 20 and (b) after 50 laser pulses. (c) The period of rolls (measured at the micrograph) decreases with increasing number of laser pulses.
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