Provided are a semiconductor device and a method for its manufacture. In one example, the method includes forming an isolation structure having a first refraction index over a sensor embedded in a substrate. A first layer having a second refraction index that is different from the first refraction index is formed over the isolation structure. The first layer is removed from at least a portion of the isolation structure. A second layer having a third refraction index is formed over the isolation structure after the first layer is removed. The third refraction index is substantially similar to the first refraction index.