Additive Manufacturing of Microlenses on Quartz Substrates using Laser-induced Chemical Vapor Deposition (LCVD)

Kurzfassung

The aim of this thesis is to investigate the manufacture of microlenses by Laserinduced Chemical Vapor Deposition (LCVD). A silicone-containing precursor (silicone oil) is to be converted into a microlens made of SiO2 on a quartz substrate by means of laser radiation with a wavelength of 355 nm and a fluence of 4 to 8 J/cm2. The precursor should be fed from the gas phase by heating and the microlens should have the shape of a Gaussian distribution. Various process parameters such as the temperature of the test chamber, viscosity of the precursor, fluence of laser or duration of exposure are to be varied and the resulting microlenses are examined using White Light Interference Microscopy (WLIM), Differential Interference Microscopy (DIC) and Scanning Electron Microscopy (SEM). At the same time, the growth process is observed in-situ by measuring the energy in front of and behind the test chamber and the resulting transmission gives information about it. With the highly viscous precursor, no solid deposits could be generated, which is why a low-viscosity precursor was preferred in subsequent tests. Good test results were made with the low-viscosity oil of 5 cSt, a low processtemperature of 30 °C and a fluence of 5 J/cm2. Microlenses made of SiO2 (EDXanalysis) were detected with a height of 70 nm after a laser exposure of 90 minutes and after 3 hours with 250 nm. By using higher fluence of 6 J/cm2 to a maximum of 7.1 J/cm2, the growing slowed down again. In comparison, the height after the laser exposure of 90 minutes is just 37 nm and after 180 minutes 113 nm respectively 104 nm and 290 nm. With some lower fluence of 4.5 J/cm2 the oil condensed again on the surface. Best test results were observed when the fluence was set up to 5.5 J/cm2 because the growing process was faster. Microlenses grow up to 212 nm after 90 minutes of laser exposure and 420 nm if it took 180 minutes. It can thus be concluded that there is an ideal fluence and ambient temperature for manufacturing microlenses.