Yup, I agree with Mike, those are the best ways of sterilizing tree branches IMO. If you do choose to microwave be very careful, it works very well but it gets incredibly hot VERY fast. My microwave had a branch 3" thick smoking in 1.5 minutes!
It's good to give it a good scrub before baking/micro, but make sure not to use bleach, hot water is good enough. The branch will absorb anything you use so it's best to avoid any chemicals/detergents