The present invention relates to a method for forming a via in a substrate which includes the flowing steps of: (a) providing a substrate having a first surface and a second surface; (b) 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; (c) forming a first insulating material in the accommodating groove and between the pillars; (d) removing the pillars so as to form a plurality of grooves in the first insulating material; and (e) 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.