After doing Diploma and then B.Tech, can I join IIM?

Yes, you can join IIM after B.Tech. But, for this you've to pass the graduation with 50% or more and qualify the entrance exam of IIM. If you are eligible, you'll get admission.

Hello, Provided you have scored at least 50% marks in your B.Tech, you are eligible to appear for the CAT and then join an IIM (if performed well in its interviews). Good luck.

After completing graduation with 50% marks you need to qualify CAT exam with 99 percentile to get into IIMs.

Yes, you can take admission in IIMS. Eligibility criteria for admission in IIMS are graduation. At least 50% marks are to be scored in graduation.