Effect of the exposure of underlying dielectric (borophosphosilicate glass) films to a humid air ambient on crystallographic orientation in Al-Si-Cu/Ti/TiN/Ti layered films has been investigated as a function of the boron content and exposure time of the dielectric films. The Al(111) orientation in the layered films was found to improve drastically with increasing boron content and exposure time of the dielectric films. The full width at half maximum value of the rocking curve for an Al(111) x-ray diffraction peak reached 0.63 degrees, which is the lowest value ever reported for an Al-alloy film on Ti and/or TiN underlayers. It was also found that the Al-Si-Cu surface became smoother and the average grain size increased as the Al(111) orientation improved. The improved Al(111) orientation was attributed to the improved Ti(002) orientation of the bottom Ti film. The cause of the improved Ti(002) orientation was then investigated. As a result, it was confirmed that the Ti(002) orientation improved with increasing surface concentration of the water absorbed in the dielectric films. Further, it was demonstrated that interconnects fabricated from the improved layered film had excellent electromigration resistance.