In this work, we address the optimization of vertical backhaul framework where multiple aerial base station (ABS) are deployed to conFigure the intermediate backhaul links for terrestrial base stations (TBS) in wireless networks. Here, we focus on maximizing the downlink network throughput in mixed RF/FSO backhaul networks by optimizing resource allocation and placement. Specifically, the ABS-TBS association, transmit power, and positions of ABSs are alternately and iteratively optimized. To solve the corresponding mixed-integer non-convex optimization problem, we propose an efficient iterative algorithm by applying the block coordinate descent method and successive convex optimization techniques. Although we obtain suboptimal solutions due to the non-convexity of the problems, simulation results indicate that the proposed scheme demonstrates the significant network throughput gain compared with the conventional scheme.