Chalcopyrite $CuInSe_2$ (CIS) thin films were prepared without Se- / S-containing gas by co-sputtering using $CuSe_2$ and $InSe_2$ selenide-targets and rapid thermal annealing. The grain size increased to a maximum of 54.68 nm with a predominant (112) plane. The tetragonal distortion parameter ${eta}$ decreased and the inter-planar spacing $d_{(112)}$ increased in the RTA-treated CIS thin films annealed at a $400^{circ}C$, which indicates better crystal quality. The increased carrier concentration of RTA-treated p-type CIS thin films led to a decrease in resistivity due to an increase in Cu composition at annealing temperatures ${geq}350^{circ}C$. The optical band gap energy ($E_g$) of CIS thin films decreased to 1.127 eV in RTA-treated CIS thin films annealed at $400^{circ}C$ due to the improved crystallinity, elevated carrier concentration and decreased In composition.