At Cu/low-K interconnection based BEOL etch technology with double patterning scheme, metal hard mask (MHM) etch process is the key step to define final physical structure of Cu line. Gap fill and reliability performance are highly related with MHM pattern CD and profile. During double patterning-based MHM etch process, tri-layers (including organic and inorganic nonmetallic materials) and HM film (e.g. TiN metalloid material) etch processes are involved. Precondition, by-product and etch stop layers are different for each etch flow in double patterning-based MHM open process, which could easily induce final CD variation in first wafer and both trench patterns. First wafer effect with large CD variation in MHM etch process could induce interconnection fail and poor WAT/RE property. In this paper, we investigate double patterning-based MHM etch performance with different etch flow and wafer-less auto clean (WAC)/season process from the viewpoints of CD variation control. Variation control method and mechanism for double patterning-based MHM etch process are also addressed.