Disturbance of the topography of Cu layers deposited by magnetron sputtering as a potential technique for increasing the absorption area of photovoltaic cells

Abstract

This paper addresses the influence of the sputtering time and hence thickness of thin copper (Cu) layers on the grain size, surface morphology and electrical properties. Cu layers 54–853 nm thick were deposited at room temperature from a Cu target with a sputtering power of 2.07 W⋅cm− 2 in an argon atmosphere at a pressure of 8⋅10− 3 mbar. The structural and electrical properties were determined on the basis of four-contact probe measurements, stylus profilometry, atomic force microscopy (AFM), scanning electron microscopy (SEM) with an X-ray microanalysis (EDS) detector, and X-ray diffraction (XRD). The results of the conducted experiments show that the structure of thin copper layers can significantly change depending on the thickness and deposition process parameters. Three characteristic areas of structural changes and growth of copper crystallites/grains were distinguished. Ra and the RMS roughness linearly increase with increasing film thickness, while the crystallite size significantly changes only for copper films thicker than 600 nm. In addition, the resistivity of the Cu film is reduced to approximately 2 microohm⋅cm for films with a thickness on the order of 400 nm, and a further increase in their thickness does not have a significant effect on their resistivity. This paper also determines the bulk resistance for the Cu layers under study and estimates the reflection coefficient at the grain boundaries.