Fill formula series using VBA

Hello Experts,
I want to fill this formula series

=MID(Table_Query_from_table22[[#This Row],[file]],C2,D2-C2)

say from row2 till row20 for a column.
But the above formula is only valid for row2. What I want is for row3 the formula should change to

=MID(Table_Query_from_table22[[#This Row],[file]],C3,D3-C3)

and so on for other rows.....

I tried the following code in VBA

For iRow = 2 To lRowCount
arg11 = "C" & iRow
arg22 = "D" & iRow & "-C" & iRow

Cells(iRow, "A").Formula = "=MID(Table_Query_from_perforce3023[[#This Row],[file]], arg11, arg22)"

Next iRow

but it inserts value in row as

=MID(Table_Query_from_table22[[#This Row],[file]], arg11, arg22)

.

Please help me here...

Thanks in advance

Regards,
Shrujan