Single photon emitters (SPEs) in solid are a building block of quantum applications, such as quantum computing and information technologies. Silicon carbide (SiC) is regarded as a promising host of SPEs due to its wide bandgap and mature process technologies. In addition to SPEs in bulk SiC, such as V_Si and V_SiV_C, those at SiO_2/SiC interfaces are also attractive because of their bright luminescence. However, having control over the density and the optical properties of the interface emitters is challenging. In a previous study, we reported a method to form spatially well-isolated SPEs at the SiO_2/SiC interface by post-oxidation CO_2 anneal. In this study, we further investigated the impact of CO_2 anneal on the emitter density and compared it with Ar anneal.