Effect of process parameters on surface morphology and characterization of PE-ALD SnO2 thin films for gas sensing

Tin dioxide (SnO2) thin films were deposited by plasma enhanced-atomic layer deposition (PE-ALD) on Si(1 0 0) substrate using dibutyl tin diacetate (DBTA) ((CH3CO2)2Sn[(CH2)3-CH3]2) as precursor. The process parameters were optimized as a function of substrate temperature, source temperature and purging time. It is observed that the surface phenomenon of the thin films was changed with film thickness. Atomic force microscopy (AFM) images and X-ray diffraction (XRD) pattern were used to observe the texture and crystallanity of the films. The films deposited for 100, 200 and 400 cycles were characterized by XPS to determine the chemical bonding properties. XPS results reveal that the surface dominant oxygen species for 100, 200 and 400 cycles deposited films are O2−, O− and O2−, respectively. The 200 cycles film has exhibited highest concentration of oxygen (O−) species before and after annealing. Conductivity studies revel that this film has best adsorption strength to the oxygen ions forming on the surface. The sensor with 200 cycles SnO2 thin film has shown highest sensitivity to CO gas than other films. A correlation between the characteristics of Sn3d5/2 and O1s XPS spectra before and after annealing and the electrical behavior of the SnO2 thin films is established.