Sentinel-1 SLC Subset

I want to finish interferogam by Snap,because my study area is very little in a swath ,I dont want to process the whole swath ,how can I subset the area in swath.
I think the subset workflow is as follow:deburst->merge->subset->coregistration
am I right?

Please start with TOPS Split and reduce the number of bursts in the swath (also only select VV polarization).

You find detailled instructions on interferogram generation (including reducing the size) in this tutorial: Displacement mapping with Sentinel-1 IW data