Silicon controlled rectifier and method for making the same

A silicon controlled rectifier, comprising:

• a P-type substrate (80);
• a first N-type well (60) disposed in the P-type substrate (80), wherein the first N-type well (60) comprises a first P-type heavily doped region (20) and a first N-type heavily doped region (28) in an upper portion of the first N-type well (60), wherein the first P-type heavily doped region (20) and the first N-type heavily doped region (28) form a first electrode of the silicon controlled rectifier;
• and a first shallow trench isolation disposed between the first P-type heavily doped region (20) and the first N-type heavily doped region (28);
• a second N-type well (62) located in the P-type substrate (80), wherein the second N-type well (62) comprises a second P-type heavily doped region (22) and a second N-type heavily doped region (26) in an upper portion of the second N-type well, wherein the second P-type heavily doped region (22) and the second N-type heavily doped region (26) form a second electrode of the silicon controlled rectifier;
• and a second shallow trench isolation disposed between the second P-type heavily doped region (22) and the second N-type heavily doped region (26);
• and
• a P-type well (70) disposed adjacent to each of the first N-type well (60) and the second N-type well (62) in the P-type substrate (80), so that PN junctions are formed at interfaces between the P-type well (70) and the first N-type well (60) and the second N-type well (62) respectively;
• wherein an upper portion of the P-type well (70) comprises a third P-type heavily doped region (24);
• wherein the first P-type heavily doped region (20) and the first N-type heavily doped region (28) of the first electrode are in mirror symmetry with the second P-type heavily doped region (22) and the second N-type heavily doped region (26) of the second electrode with respect to the third P-type heavily doped region (24);
• wherein the first N-type heavily doped region (28) and the second N-type heavily doped region (26) are disposed at closer positions to the third P-type heavily doped region (24) than the first P-type heavily doped region (20) and the second P-type heavily doped region (22) to the third P-type heavily doped region (24) respectively, and wherein the first P-type heavily doped region (20) and the second P-type heavily doped region (22) are disposed at farther sides of the first and the second shallow trench isolations from the third P-type heavily doped region (24);
• and
• wherein a first active region of the first N-type well (60) is disposed between the third P-type heavily doped region (24) and the first N-type heavily doped region (28), and a second active region of the second N-type well (62) is disposed between the third P-type heavily doped region (24) and the second N-type heavily doped region (26).