Method for physically unclonable function through gate height tuning

A method for physically unclonable function through gate height tuning, comprising:

• providing a semiconductor substrate;
• forming a high-k dielectric layer and a dummy silicon layer on said semiconductor substrate;
• completely removing said dummy silicon layer, so that an original position of said dummy silicon layer is emptied to form recesses;
• forming a work function layer and a metal filling layer on said high-k dielectric layer in said recesses;
• performing a chemical mechanical planarization process to partially remove said metal filling layer and said work function layer, thereby remaining said metal filling layer and said work function layer form metal gates in said recesses and make heights of said metal gates lower than a critical gate height, wherein said critical gate height is set at a level higher than a bottom surface of said metal filling layer and depends on required gate work function;
• and
• using said metal gates to manufacture programmed I/O pairs in an internal bias generator, wherein a local threshold voltage mismatching of said programmed I/O pairs becomes larger since said heights of said metal gates are lower than said critical gate height, so as to achieve random code generation in physically unclonable function.