Dear Jitendra Singh,
Your sequence of taking action is rather strange.
First, you have suggests to issue a Show Cause Notice. SCN is issued normally when, you are about the take a decision about the final punishment. In your post it seems that as if a SCN is just a caution letter issued to delinquent employee.
Second, you have suggested to give him a Warning Letter if the employee is found sleeping for the second time. Here you need to call for his explanation for the reason of this repetition and if necessary issue him a Warning Letter, if necessary.
Thirdly, you suggested to Terminate him by knowing the reasons of his repeatedly going to sleep.
However, as a last resort, if he is found habitual of sleeping during working hours, he should got medically checked up, A SCN be issued to him to know the cause of the reoccurring incidences followed by an inquiry and followed by a very reasoned decision towards the punishment to be given or not and if to be punished the quantum of punishment or suggest the remedial measures to avoid occurrence of such incidents.
Termination alone is not the solution.