Localized analysis of photonic circuits with new sub-millimeter spot-size x ray diffractometer

This work reports recent improvements in structural characterization by high resolution x-ray diffraction (HRXRD) performed on multiple quantum well (MQW) heterostructures grown on InP substrates. Up to now, HRXRD profiles obtained with a standard laboratory diffractometer gives only information about structural properties averaged over broad areas due to the large incident x-ray beam provided (few millimeters down to half a millimeter). In this work, a new diffractometer , with a sub-millimeter x-ray spot, was used in the laboratory. This setup is equipped with a microfocus x-ray source achieving a sub-millimeter (50 x 100 µm2) spot size on the sample. Accurate lateral positioning of the sample (within two microns) is achieved with a laser-video microscope. We compared two set of samples: (i) one is the as-grown material, fully accessible on the complete wafer; (ii) the other one is the same set of samples after different technological processes, leading therefore to very small volume of material localized at specific places on cleaved wafers or chips. Different photonic integrated circuit (PIC) processes were tested such as buried-ridge-structure laser or laser structure bonding followed by wafer removing