Radical-enhanced atomic layer deposition of silver thin films using phosphine-adducted silver carboxylates

Metallic silver films are deposited by radical-enhanced atomic layer deposition (REALD) using (2,2-dimethylpropionato)silver(I)triethylphosphine and hydrogen radicals. The silver precursor used is synthesized in-house, and characterized using CHN elemental analysis, infrared (IR) spectroscopy, nuclear magnetic resonance (NMR), mass spectrometry (MS), and then mogravimetric analysis/single differential thermal analysis (TGA/SDTA). The crystal structure of Ag(O2C'Bu)(PEt3) is also solved. Trimeric units are revealed as the building blocks. The hydrogen radicals are produced by dissociating molecular hydrogen with a microwave plasma discharge. The evaporation temperature of the silver precursor is 125 degrees C, and the film deposition temperature is 140 degrees C. The deposition is successful on glass and silicon, and the films are conformal. The saturated growth rate is 0.12 nm per cycle, with a 3 s silver precursor pulse and 5 s hydrogen radical pulse time. The overall cycle time is 14 s. The films are polycrystalline and are visually mirror-like. The films contain 10 at.-% oxygen, 4.0 at.-% phosphorous, 1.0 at.-% carbon, and 5.0 at.-% hydrogen as impurities. Nevertheless, the films exhibit low resistivity, only 6 mu Omega cm for a 40 nm thick film.