After the completion of your M.Sc. you can appear for the GATE (Graduation Aptitude Test in Engineering) which is conducted every year for admissions to M.Tech courses in IITs, NITs, BITS Pilani, IISc and a few other prominent institutions.

You can do M.tech in below 2 courses:

1. M.Tech in Industrial Mathematics and Scientific Computing offered by IIT MADRAS. Admissions are Via GATE MATH scores.
2. M.Tech Quality, Reliability and Operations research offered by ISI They have their own entrance exam and the eligibility is MSc with Probability and statistics as electives.

Going for M.tech after M.sc completely depends on your interest .If you are looking for career in educational institutes as a teaching profession that too particularly in engineering colleges then M.tech is necessary.
You can go for Ph.D also after M.tech degree which can add more value in your job.