I faced the back EMF problem from the 3 phase induction motor. whenever EMF is generated our ATMEGA8L micro controller is get interrupted please suggest me to overcome this problem.
Use 1N4007 Diode across the relay coil.
Since Atmega 8(any MCU) cant drive relay directly u need to use ULN2003 or simple transistor to drive the relay. In this way you are isolating the MCU from motor driver also.
you can use PC817 opto isolator to drive a BD140 transistor, and drive a relay with that BD140. dont forget to add 1N4148 across relay`s coil.
use different power supply trace to power your relay and mega8 micro. add a decoupling capacitor near the power supply pin of atmega8 controller. don`t leave unused port pin of atmega floating, make it output...