I just used a regular un-notarized copy

If an interview is not required, a regular copy is enough.

In the interview letter, original birth certificate is required for every interviewee. But in my interview, the officer did not asked it at all, nor did she ask for anything from myself. The only thing she asked for was an employment verification letter my company lawyer brought.

I might be wrong though. I don't think it hurts to give a notarized copy.