Since your glass substrate is not conductive, you need metal sputtering over your sample and connecting it to the SEM holder by carbon tape.

I agree with Morteza answer, but you can also use thermally-etched become  conductive material

It *may* be possible without sputtering, with very low voltages (ca. 0.5 kV), and very small working distance (ca. 1 mm), especially if you have an 'in-lens' detector rather than the common SE detector. We can image insulating polymer samples under these conditions.

Good luck!

Thank you for all your response. It is really helpful.