Rigidbody question (19500)

Hi I'm making a Top-Down space game and i have an enemy spaceship. I added a Rigidbody to the spaceship because it was going through walls. I froze all the rotations and froze the position on the x-axis, but when i shoot it it moves backward, How do i stop it from moving backward so when i shoot it it stays still?

  rigidbody.isKinematic = true;

  rigidbody.freezeRotation = true;