hi,
after completing diploma you can opt for b.tech course since you have desire to higher education..see robotics is a new emerging technology and students from any engineering stream may learn it. I suggest you to go for electronics and communication engineering since major architecture of robotics includes electronics , also you can get exposure to computer hardware programming languages. you need to appear in lateral entry exam to get admission in btech courses like jelet, upsee lateral, odisha lateral entry exam.