If you look at the die shots (wafer shots?), you'll notice small holes a few millimeters across spaced roughly at reticle spacing. Those are drilled holes to al

If you look at the die shots (wafer shots?), you'll notice small holes a few millimeters across spaced roughly at reticle spacing. Those are drilled holes to allow through-wafer liquid cooling. With liquid cooling not just around but through the wafer, the temperature differential is minimized.