Difference between IW1 and IW2

Hi everyone.
I require a little help, I am working on an S1 SLC product to generate a deformation map, for that purpose I need to unwrap the interferogram but when I open the interferogram torun the dialog ‘‘Spatial Subset from View’’ I can not find my area of interest on that Swath mode which is IW1.
When I merge the subswath I can find my area of interest as it lies in Subswath IW2 but I can not unwrap it as it is terrain corrected.
Now my question is can I generate an Interferogram by Selecting IW2 subswath and or it is mandatory to generate interferogram using IW1?

You can select any sub-swath (blue circle) and bursts (red circle) in the TOPS Split operator

Also, processing is much faster when you only select VV polarization


Thank You So much