Engineering

First of all, congratulations to get good marks in your 12th. Taking admission in NIT or IIIT is dream of many students in India. To get admission in NIT or IIIT, you need to appear for JEE Mains exam conducted by NTA every year. Every year 7-8lakh students appear to give this exam
There are 31 NIT and 25 iiit in india in which there are approximately 25,000 Sets for B.Tech in all NIT and approximately 5000 seats for B.Tech in all iiit. As you got 89 percentile in JEE Mains score, to get admission in NIT or IIIT bassd on your this score, it depends on that from which category you belong like general, OBC, SC, ST, PwD
If you are from general category, then you will not get any NIT and iiit
But if you are from SC or ST or PwD category, then you will surely get any NIT or iiit with best B.Tech branch as per your choice.

In today's time, almost every student wants to pursue B.Tech CSE from best college whether it is a government college or university or private college or university, almost every top private college whose annual fees is around 1.5lakh gives same the highest package around 40lakh and average package around 5-6lakh
It depends on you, that how you perform during your academics in college, if you are a good programmer, and have done internships in different companies then you will get best placement offer during oncampus placement approximately 40lakh
As per your query, to get minimum package of 20lpa, you should take admission in high fees private colleges, in which top companies recruit students, same companies which also recruit from IIT and NIT like GOOGLE, MICROSOFT, ORACLE, IBM, ACCENTURE, DXC. Here are that some college :-
BITS PILANI
VIT VELORE
THAPAR INSTITUTE OF TECHNOLOGY PATIALA
LOVELY PROFESSIONAL UNIVERSITY
AMITY SCHOOL OF ENGINEERING AND TECHNOLOGY
PSG COLLEGE OF TECHNOLOGY
ICT MUMBAI
These colleges have best placement offers with maximum upto 1 crores.