A method to design a high performance robust tracking controller to track step references for uncertain continuous MIMO plant is presented. A non-linear sliding surface is proposed by which the damping ratio of closed loop system is increased as output approaches setpoint. Stability with the proposed non-linear surface is proved. A new control law is designed to guarantee the existence of sliding mode around the proposed non-linear surface. Position controller of stepper is designed using the proposed algorithm and corresponding simulation results are presented to show the effectiveness of the proposed scheme.