Role of surface chemistry in improving performances of electronic devices

Abstract

Surface science and chemistry have been researched in many different disciplines. In this dissertation, the role of surface chemistry in improving performances of electronic devices are discussed. Three different perspectives: optical, reliability, and etching performance in targeted applications are investigated. ☐ In the first topic, Ta2O5 moth-eye structures as broadband antireflection coatings (ARCs) in dual junction solar cells on Si substrates are reported. Wafer-scale sub-wavelength structures are directly patterned on the top of tandem cells by using deep UV photolithography and plasma etching. These processes give moth-eye structures with an aspect ratio of 1.2, which results in excellent antireflection properties with an average reflectance of 7% over the entire 400-1100nm range. Further optimizations of moth-eye and traditional double layer antireflection coatings (DLARCs) on the device using the finite-difference time-domain (FDTD) method are performed. Optimized moth-eye structures outperform optimized traditional DLARCs with reflection as low as 2.2% from 400-1100nm. ☐ In the second topic, the mixed flowing gas (MFG) test is used to study accelerated Ag and Cu corrosion behavior in highly corrosive environments. Synergistic effects between Cl2 and H2S on Ag corrosion rate in the MFG chamber are presented. Effects of relative humidity (RH), RH cycling, NO2 concentration and temperature on Ag corrosion are also investigated using a combination of analytical techniques such as weight gain, cathodic reduction, and SEM/EDX. Cu coupons are used with Ag coupons for direct comparison and reference to chamber corrosivity. The Ag corrosion mechanism is proposed, which enables the establishment of new MFG test conditions to simulate Ag corrosion in more aggressive environments. ☐ In the third topic, thermal atomic layer etching using sequential reactions of Cl2 and Hexafluoroacetylacetone (Hfac) is proposed to etch Fe and Co. Self-limiting behavior of both Cl2 and Hfac steps at 170°C is first found and a range of etching temperatures from 140°C to 185°C is investigated. The etching rates of Fe and Co can be achieved as low as 0.3nm/cycle and 0.2nm/cycle respectively at 140°C. Atomic force microscopy (AFM) is also used to compare surface morphology of the pristine and etched Co samples. This work provides the patterning solution for achieving high- density magnetic random access memory (MRAM) devices.