Hi Alok, everyone

Etching glass can be a problem.  SF6 will etch silica or quartz, but most
glasses contain other oxides that are not so readily removed by fluorine
chemistry.  A few years ago, we did some work with Balzers (who make lots of
different types of glass) using CF3Cl, but this is not a very popular gas
now (being a CFC!).  If you want to etch most basic types of glass
(soda-lime, borosilicates, barosilicates etc.) then you need some chlorine
containing gases in with the fluorine based gases.  If you have a loadlocked
system, you can use Cl2, but I would not recommend this in an open load
system.
Often, it is useful to have some carbon present (i.e. use CHF3 or CF4) as
this will react with the oxygen and help to expose the other species on the
surface.  Also, CO2 is a bit more environmentally friendly (and does not
smell as bad) than SO2.

Regards,

Martin