The Order of DEM Creating Steps

Hello All.
I created dem from sentinel-1B image. Here is my steps and result.

  1. S1 TOPS Coregistration
  2. Creating Interferogram
  3. Debursting
  4. Goldenstein Phase Filtering
  5. Multilooking
  6. Exporting to Snaphu, unwrapping and importing back
  7. Phase to Elevation
  8. Range-Doppler Terrain Correction
  9. Fill DEM hole

Finally, Q
My final DEM imported into QGIS. But here is some problem of elevation limit (-32768).

  1. how i can remove minus value?
  2. Why it is showing me different height value on DEMs from ALOS and Sentinel? Which one is correct?