SYNTHESIS AND CHARA TERISATION OF N1-BASED MULTILAYER NANOCOATING FOR ELECTRONIC APPLICATION

Abstract

Electroless nickel thin film was deposited on the single crystal silicon wafers (n/n++), phosphorous doped, (100) oriented, and single side polished. The pH was varied between the ranges 4 -10. The temperature was also varied in the range of 60 - 90°C. The film quality was judged by visual inspection. The electroless nickel -coating was highly adherent and uniform in n side, but the coating was not adherent on the n++ side. Scanning electron microscope micrograph images show: , that there are no microscopic pores on the n++ side, so that mechanical anchoring of the pores by the film is not possible. The good quality films were subjected to further characterization by advanced techniques like AFM, XRD and I-V, before and after annealing at two different temperatures of 500°C and 900°C for half-an-hour in flowing argon atmosphere. For comparison, nickel was also coated on silicon by sputtering. This film was subjected to the same characterization techniques like electroless coated silicon; in addition the results after annealing the sputtered films at 500°C, for 30 minutes were also compared. This study shows that electroless nickel deposition process with a suitable post annealing process is marked by the superior adhesion values with better ohmic contacts which are desired for ultimate device applications. In the as-deposited state they show superior ohmic characteristics compared to the structurally superior sputtered Ni films. The deposition at lower pH value results superior quality films. The choice of annealing temperature is to be guided by the film application. In the case of electroless deposition a metal-semiconductor type contact is formed, while in a sputtered film it is of metal-insulating-semiconductor type. The distortion of the interface by either the hydrogen evolved, or the diffusion of phosphorous into silicon during/after the electroless deposition process has a favorable effect in realizing Qhmic contact. In films deposited at higher pH values (9.46) the presence of new reflections in the XRD plots is observed on annealing at 900°C. Further investigations are required to find the reasons underlying superior ohmic contacts to silicon by electroless deposition as compared to sputtering and the origin of new reflections in XRD for 9.46 pH deposited films.