thanks for your reply. While searching some document in the net regarding half cell matching we found out that it is also called by the name "symmetric placement". Can you please elaborate on the same?
Also called repetition layout, this is an analog layout method sometimes used for larger symmetric cells or blocks, which guarantees excellent symmetry with regard to devices and their routing: the layout of one half of the cells will be copied (repeated, not mirrored!) close to the first half. This avoids mismatch due to the not exactly vertical impinging ion implantation.
Of course the necessary routing connections between the two halves should be accomplished as symmetrical as possible.