When removing unwanted objects in an image, selecting the area to be removed and then choosing Edit > Fill with the Contents set to Content Aware, can magically fill in areas using surrounding information. However, in some images, Photoshop may select and fill with areas that you wish it wouldn’t. In order to tell Photoshop to ignore certain areas of an image, add a layer mask and paint in the mask to hide the areas that you don’t want Photoshop to use as a fill source (in other words, if you can’t see the information, then neither can the Content Aware Fill technology). When finished, discard the layer mask without applying.
Note: make sure to run the Content Aware Fill on the Layer, not the Layer Mask.