the present invention relates to a method for forming a via in a substrate which includes the flowing steps of : providing a substrate having a first surface and a second surface ; forming an accommodating groove and a plurality of pillars on the first surface of the substrate , the accommodating groove having a side wall and a bottom wall , the pillars remaining on the bottom wall of the accommodating groove ; forming a first insulating material in the accommodating groove and between the pillars ; removing the pillars so as to form a plurality of grooves in the first insulating material ; and forming a first conductive metal in the grooves . as a result , thicker insulating material can be formed in the via , and the thickness of the insulating material in the via is even .