Increasing clock speed will require a different technology than silicon. It's not impossible to think that graphene or carbon nano tubes could allow higher clock speeds.
As you increase clock speed, temperatures approach the surface of the sun.
Besides being hard to cool, it causes chemical, delamination and other changes to the chip, eroding it.
"In 2001, Pat Gelsinger—then Intel‘s CTO—predicted that within a decade the energy density of chips would be equivalent to the surface the sun if nothing was done."
