Abstract：Residual foreground contamination in cosmic microwave background (CMB) maps, such as the residual contamination from thermal Sunyaev-Zeldovich (SZ) effect in the direction of galaxy clusters, can bias the cross-correlation measurements between CMB and large-scale structure optical surveys. It is thus essential to quantify those residuals and, if possible, to null out SZ cluster residuals in CMB maps. In this talk, I will introduce our recent work of quantifying for the first time the amount of SZ cluster contamination in the released Planck 2015 CMB maps through (i) the stacking of CMB maps in the direction of the clusters, and (ii) the computation of cross-correlation power spectra between CMB maps and the SDSS-IV large-scale structure data.  Our cross-power spectrum analysis yields an overall 54 sigma detection of SZ cluster residuals in the Planck CMB maps, corresponding to a ~44% left-over of the tSZ residuals. We also provide an alternative SZ-free CMB map using the 2D-ILC component separation method. I will also discuss the impact of the SZ residuals in CMB maps on the measurement of the ISW effect.