Weird Thermal Reliefs in Eagle PCB
You need to change the width of your ground polygon. The polygons are actually made up of many wires drawn to make a continuous surface. If you zoom in on a polygon that is drawn in a non-solid pattern (like an inner layer on a 4 or greater layer board) you can see what I mean.

When you draw the polygon you can choose the size of the wires used, just the same as when drawing wires. You can also change it after the fact using change->width, if I remember correctly.

You probably want to make the width no greater than the width of your IC pads.