Self defence is just that. The defence of your self, till you are no longer in danger. Under the law you are only allowed to use as much force as is deamed nessary to stop or subdue your attacker, not kill them.
That may be the way the law is in Ontario, Canada, in the USA it depend upon where you are. Generally speaking in the USA deadly force is only allowed in response to a deadly attack. It also depends upon if he's in your house or not, in Washington State if an intruder is in your house you can shoot him on sight. This goes back to English Common Law which states a man's home is his castle. This was tested severely a few years back when a 14 year old broke into a man's house. As the youth was in the process of fleeing out a window the home owner shot the youth in the buttocks with a shotgun, no charges were filed as he had not exited the house, if he had been in the front, side or backyard the owner would have been charged.