Fabrication of Low Resistive and Adhesive Cu Layer on Glass Substrate by Chemical Bath Deposition and Chemical Reduction

Abstract

The surface state of soda-lime glasses before and after ultrasonication pretreatments with water, acetone, ethanol, water/ethanol/NaOH solutions, and UV/O₃ treatment were estimated using atomic force microscopy（AFM）and Fourier-transformed infrared spectroscopy with attenuated total reflection mode（FT-IR-ATR）. Ultrasonication with water/ethanol/NaOH solutions and UV/O₃ treatments drastically decreased the size and number of surface contaminant particles and enhanced absorption of the isolated silanol and hydrogen-terminated silanol. The Cu（OH）₂/Cu（O,S）bilayers were prepared using chemical bath deposition（CBD）in aqueous solutions containing copper（II）nitrate hydrate, ammonium nitrate, and urea or thiourea on glass substrates treated with water/ethanol/NaOH solutions. Top metallic Cu layers were then formed chemically by simple immersion of the bilayers into a NaBH₄ aqueous solution. The sheet resistance decreased with increasing immersion time, leading to 0.68 Ω/□ sheet resistance and 3.3×10⁻⁵ Ω cm resistivity after 10 min immersion. The adhesion strength was estimated using the tape peeling off test with a tensile testing machine and adhesion tape. The Cu/Cu（OH）₂/Cu（O,S）bilayer fabricated by chemical reduction for 10 min exhibited maximum and average adhesion strengths of 13.3 N/cm and 11.0 N/cm, respectively. The adhesivity was inferred to have originated from hydrogen bonding between the oxygen ions in Cu（O,S）and -OH- in silanol of the glass substrate.