Hallo Ramesh,

did you solve the problem?

Mhm. This ICL7660 might not be a good way to produce negative supply voltage. It's generating so much noise, that preventing offset in the microvolt range is a bit difficult.

If you are not happy with OP177 you could also use chooper-chips like LTC1052 and ICL7650. These provide you with 0.7µV offset voltage, 1.5pA input bias current, 0.01µV/°C offset voltage drift and 100nV/SQRT(month) long term drift (all typicals at 25°C).

But I have the feeling, that not the operational amplifier is the problem, but the arrangement of the whole circuitry. So, it would be of very high benefit, if you could publish the schematic here, and possibly the layout of PCB.

Keep in mind: The more information we get from you, the more we can help!!!

Good luck,
Kai