Characterization methods for silicon photodiode and silicon sub-surface properties

This thesis considers the characterization of silicon photodiode and the applications of silicon photodiodes in precision metrology, and some aspects of the silicon material characterizations. Such material characterizations are required in the process of semiconductor device manufacturing, one example of which is the silicon photodiode manufacturing. The motivation for the research on radiometry reported in this thesis has been the development of optical metrology at the Helsinki University of Technology (HUT). Most of the applications for this research are found in the UV-metrology. Importance of the UV-metrology arises from the environmental importance of accurate gauging of optical power at these wavelengths. This thesis describes the derivation and experimental verification of simple mathematical models, based on Fresnel equations. These models have allowed significant reductions in the uncertainties of spectrophotometric and radiometric measurements, especially in the UV wavelengths. These measurements are carried out using silicon photodiode-based detection systems. The reductions achieved in the measurement uncertainties have been utilized in the detector-based realizations of optical quantities maintained as national standards at HUT. The structure and operating principle of silicon photodiodes brings up the process of manufacturing of these devices, and the material characterizations required during this process. Novel methods in machining of silicon wafers for semiconductor industry pose new challenges for these characterizations. One such challenge is the need to characterize sub-surface damage in silicon wafers, induced by abrasive machining. The measurement of the sub-surface damage in silicon was the goal set for the work on materials characterization reported here. Various potential solutions to this requirement have been studied in this thesis, some of which are based on the spectrophotometric research carried out at HUT. Complete solution to this requirement has not been found. This thesis compares a number of promising methods and combines their respective advantages in order to create a more comprehensive understanding on the subject under study.reviewe

MOVPE growth of GaN on patterned 6-inch Si wafer

We demonstrate that thicker layers can be achieved in gallium nitride (GaN) epitaxy by using a patterned silicon (Si) substrate compared to a planar Si substrate. GaN films were grown by metalorganic vapour-phase epitaxy on 6-inch Si (111) substrates patterned with arrays of squares with various corner shapes, height and lateral dimensions. Stress spatial distributions in the GaN pattern units were mapped out using confocal Raman spectroscopy. It was found that the corner shapes have an effect on the uniformity of the stress distribution. Patterns with round corners were found to have more uniform stress distribution than those with sharp corners. The largest crack-free square size for a 1.5 μm thick GaN film is 500 × 500 μm2.Peer reviewe