Is there a relation between the dead zone of sigma delta modulator and filter order?
From the paper you link to:


  Modulators with a  higher order loop filter also exhibit a  dead-zone which can be calculated in a  similar manner. Because of the higher gain in the loop filter, the dead-zone of these modulators will be considerably smaller than the dead-zone of the first order SDM*. Very small signals (including system noise) will disturb the idle patterns of such SDMs, rendering the dead-zone undetectable in practical implementations. 


And if you had a situation where system noise didn't disturb the idle patterns that cause dead zones, you could always inject some dither that's intentionally designed to have its spectral content at high frequencies.

* SDM = sigma delta modulator, in that paper's nomenclature.