There is no need for a deposit but in general you pay small amount for ads advertising in legit companies.
First you say that you have to pay 100 dollars in order to register the account and start earning money via viewing ads, and now you say that you don't have to deposit anything, so which one is it then?
Anyway, it is an obvious scam, most likely some sort of pyramid scheme hidden behind "earning money by viewing ads" bullshit.
I mean if I want to advertise an ad in YouTube and someone watch the video I pay small amount in cents.