Can I have the mothe sign something so she can't go to court later to make me pay child support. She says she doesn't want any help with the child, if I get it in writing will that help her from taking me to court later on?

In the eyes of the family court, the document would be worthless. Your only action would be a breach of contract suit. The only means for this to be done is through the courts, however even than, if she were to go on welfare, they could override the decision. If she wants nothing, than she says that to a judge. As of right now, she can wait up to 23 years to file for up to 18 years worth of child support, depending on the state.

You should consider forcing the issue. The child deserves a father, and society does not deserve to have another fatherless child thrust upon it. The battle will not be easy, but it will be worth it, if you are willing.
Single Father Rights