We have studied the role of aluminum oxide (Al2O3) film on silver (Ag) paste contact formation at boron doped p-type silicon surface. By increasing the thickness of Al2O3 film in Al2O3/SiNx stack, the contact resistance between Ag paste and Si surface was observed to decrease to a minimum at Al2O3 film in thickness of 4 rim then increase again as the thickness increasing. Microstructure analysis via scanning electron microscopy (SEM) imaging demonstrated the number of Ag particles embedded in interfacial fits which is found to be responsible for the behavior of contact resistance. X-ray photoemission spectroscopy (XPS) data revealed out that Al2O3 incorporated into glassy phase during co-firing process. We suggested Al2O3 films affected silver paste contact formation by modifying chemical composition and properties of interfacial glassy phase.