The implant layer defines the regions were the silicon is doped with impurities to form an n-type or p-type silicon . This implantation is necessary for the formation of source/drain regions , poly Si gates and bulk ties. The implant layer have higher importance when it intersects with the active area region (region with thin oxide) . because this intersection only defines the n+ or p+ regions which is used to create transistors and bulk ties . If the implant layer exists in a place where there is no thin oxide , the doping will be light and can not be used in S/D regions or ohmic bulk ties.