  We present a new method to introduce rotationally invariant terms in
staggered fermions which is based on an $SO(2D)$ Clifford algebra formulation,
where $D$ means the number of space-time dimensions. We have four candidates
for improved mass terms that can split the degenerate mass of staggered
fermions. Among them, we analyze three types of combinations and find only one
case that can identify with the light single Dirac mode.
