The Formation of Water Marks on Both Hydrophilic and Hydrophobic Wafers
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Mat. Res. Soc. Symp. Proc. Vol. 477 01997 Materials Research Society
EXPERIMENTAL 1) Materials In the experiments, 100 mm (100) silicon wafers (10-100 Q.cm resistivities), with and without thermally grown oxide coatings (6000A), were used. Teflon and perfluoro decanoic acid organic thin film were also prepared. High purity DI water (18 MQ.cm) from a Millipore Milli Q-four bowl system was used. Electronic grade H2SO4(98%) and H2 0 2(30%) reagents were used to make Piranha etch solutions with electronic grade 0.5 % HF solutions. High purity 02 and N 2 were also used for the experiments. PSL microspheres of 0.026 and 0.104 pm in diameter were purchased from Duke Scientific Co. as an aqueous dispersion containing 1.0 x 1015 and 1.6 x 1013 particles/ml, respectively. 2) Procedures Wafers were cut with a diamond saw into 13mm x 19mm size samples. Bare wafers were cleaned in Piranha solutions followed by 0.5% HF solutions and then rinsed in DI water. Oxide coated wafers were etched in 0.5% HF for 1 min and then rinsed in DI water to obtain a fresh hydrophilic surface. The samples were subsequently dried using dry nitrogen gas. The thermal evaporation was used for the deposition of perfluoro decanoic acid thin films on oxide coated silicon. To measure the contact angle of surfaces, a static contact angle analyzer (KRIUSS,G10) was applied. A 10 jt of DI water was placed on substrates using a micro-pipet. A vacuum oven was used for the water mark experiments to control the drying atmospheres and temperatures. Under vacuum N2 and 02 were allowed to flow into the oven during the experiment to obtain the desired atmosphere. An optical microscope was used for the observation and measurements of water marks. An Auger Electron Spectroscopy ( PERKIN-ELMER, o - 670) was used for the chemical analysis of water marks. All experiments were done under a laminar flow hood of a class 100 quality. RESULTS AND DISCUSSION Wettability of substrates used for the experiments was measured by a static contact angle analyzer. Teflon surface showed the highest contact angle of 1150. Contact angles on organic film and HF etched silicon surfaces were 70' and 660, respectively. Oxide coated wafers and piranha cleaned wafers showed contact angles of 10' and 36'.
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Figure 1. The changes of initial water droplets size and drying time as a function of wettability of substrates. 514
The dry time and the initial size of water droplets were measured as a function of wettability of surfaces at different atmospheres as shown in Figure 1. The initial size of 10 0 of water droplets decreased from 12 to 3 mm as the contact angle of surfaces increased from 50 to 1150. A slight longer dry time of droplet was observed in N 2. Figure 2 shows the change in size of water marks dried as a function of surface wettability in both nitrogen and oxygen atmospheres. The formation of wat
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