  We develop a scheme of Gor'kov Green's functions to treat impurity effects on
Caroli-de Gennes-Matricon (CdGM) mode in superconductors (SCs) by improving the
Kopnin-Kravtsov scheme with respect to the coherence factors and applicability
to various SCs. We can study the impurity effects keeping the discreteness of
the energy spectrum in contrast to the quasiclassical theory. We can thus apply
this scheme to the SCs with the small quasiclassical parameter
$k_{\mathrm{F}}\xi_{0}$ (which is the product of the Fermi wavenumber
$k_{\mathrm{F}}$ and the coherence length $\xi_{0}$ in pure SC at zero
temperature) and/or superclean regime $\Delta_{\mathrm{mini}} \tau \gg1$
($\Delta_{\mathrm{mini}}$ and $\tau$ denote, respectively, the level spacing of
the CdGM mode called minigap and the relaxation time for CdGM mode and we take
$\hbar =1$). We investigate the impurity effects as a white noise for a vortex
in an s-wave SC and two types of vortices in a chiral p-wave SC, for various
values of the quasiclassical parameters and impurity strengths (from moderately
clean regime to superclean regime), and confirm the validity of this scheme.
