Hi Ramesh,
Scaling down means reducing the sizes of a transistor. Since if the size of a transistor is reduced , the no of transistors in a IC will be more.
Scaling follws the pace with which MOORE has described.
Below are the few process with problem and solution:
Process Problem Solution
180nm Conductors become too resistive Replace alum. with copper
130nm Features smaller than light wavelength Computational lithography*
90nm Limitations on active current Strained silicon
45nm Gate leakage limits scaling Hi-K metal gate
22nm Loss of channel control Tri-gate transistor
There are lot of articles in the internet on the same , you can explore.