SCRs with checker board layouts
An Electro-Static Discharge (ESD) protection circuit includes a plurality of groups of p-type heavily doped semiconductor strips (p+ strips) and a plurality of groups of n-type heavily doped semiconductor strips (n+ strips) forming an array having a plurality of rows and columns. In each of the rows and the columns, the plurality of groups of p+ strips and the plurality of groups of n+ strips are allocated in an alternating layout. The ESD protection circuit further includes a plurality of gate stacks, each including a first edge aligned to an edge of a group in the plurality of groups of p+ strips, and a second edge aligned to an edge of a group in the plurality of groups of n+ strips.
1. An Electro-Static Discharge (ESD) protection circuit comprising:
a plurality of groups of p-type heavily doped semiconductor strips (p+ strips);
a plurality of groups of n-type heavily doped semiconductor strips (n+ strips), wherein the plurality of groups of p+ strips and the plurality of groups of n+ strips form an array having a plurality of rows and columns, and wherein in each of the rows and the columns, the plurality of groups of p+ strips and the plurality of groups of n+ strips are allocated in an alternating layout;
a plurality of gate stacks, each comprising:
a first edge aligned to an edge of a group in the plurality of groups of p+ strips; and
a second edge aligned to an edge of a group in the plurality of groups of n+ strips; and
a conductor electrically connecting a first one of the plurality of groups of p+ strips to a second one of the plurality of groups of n+ strips, wherein the first one and the second one are in a same semiconductor strip column.
2. The ESD protection circuit of claim 1 further comprising:
an input/output pad;
a Vss node; and
a plurality of conductors comprising the conductor, wherein each of the plurality of conductors electrically connects one of the plurality of groups of p+ strips in a semiconductor strip column to one of the plurality of groups of n+ strips in the semiconductor strip column.
3. The ESD protection circuit of claim 2 comprising a plurality of diodes forming a diode string, wherein each of the plurality of diodes comprises one of the group in the plurality of groups of p+ strips as an anode and one of the group in the plurality of groups of n+ strips as a cathode, and wherein the plurality of diodes are serially connected between the input/output pad and the Vss node.
4. The ESD protection circuit of claim 3 , wherein the cathode of each of the diodes in the diode string is between the Vss node and the anode of the each of the diodes in the diode string.
5. The ESD protection circuit of claim 3 , wherein the plurality of diodes comprises two diodes.
6. The ESD protection circuit of claim 5 , wherein the plurality of diodes comprises fourth diodes.
7. The ESD protection circuit of claim 1 , wherein the array comprises at least four columns and at least two rows.
8. An Electro Static Discharge (ESD) protection circuit comprising:
a semiconductor substrate of a first conductivity type;
a first well region and a second well region of a second conductivity type opposite to the first conductivity type, wherein the first well region and the second well region are separated from each other by a portion of the semiconductor substrate;
a first semiconductor strip extending in a row direction and overlapping and contacting the first well region, wherein the first semiconductor strip comprises:
a first heavily doped portion of the first conductivity type;
a second heavily doped portion of the second conductivity type; and
a third portion of the second conductivity type connecting the first portion to the second portion;
a first gate stack overlapping the third portion of the first semiconductor strip; and
a second semiconductor strip extending in the row direction and overlapping and contacting the second well region, wherein the second semiconductor strip comprises:
a fourth heavily doped portion of the first conductivity type;
a fifth heavily doped portion of the second conductivity type; and
a sixth portion of the second conductivity type connecting the fourth portion to the fifth portion, wherein the first and the fifth portions are in a same first column, and wherein the second and the fourth portions are in a same second column;
a second gate stack overlapping the sixth portion of the second semiconductor strip; and
a first conductor electrically connecting the second portion to the fourth portion, wherein the first and the second gate stacks and the first and the second semiconductor strips are comprised in a first Silicon-Controlled Rectifier (SCR)/diode-string unit.
9. The ESD protection circuit of claim 8 further comprising:
an input/output pad electrically connected to the first heavily doped portion; and
a Vss node electrically connected to the fifth heavily doped portion.
10. The ESD protection circuit of claim 8 further comprising:
a second SCR/diode-string unit having a structure identical to the first SCR/diode-string; and
a second conductor electrically connecting the fifth portion of the first SCR/diode-string unit to the first portion of the second SCR/diode-string unit.
11. The ESD protection circuit of claim 8 further comprising:
a second SCR/diode-string unit having a structure identical to, and connected to in parallel with, the first SCR/diode-string, wherein the first semiconductor strip of the first SCR/diode-string unit and the first semiconductor strip of the second SCR/diode-string unit are portions of a same straight and continuous semiconductor strip.
12. The ESD protection circuit of claim 8 , wherein the first conductivity type is p-type, and the second conductivity type is n-type.
13. The ESD protection circuit of claim 8 :
wherein the first semiconductor strip further comprises:
a seventh heavily doped portion of the first conductivity type;
an eighth heavily doped portion of the first conductivity type; and
a ninth portion of the first conductivity type connecting the seventh portion to the eighth portion;
wherein the second semiconductor strip further comprises:
a tenth heavily doped portion of the second conductivity type;
an eleventh heavily doped portion of the second conductivity type; and
a twelfth portion of the second conductivity type connecting the tenth portion to the eleventh portion, and wherein the ESD protection circuit further comprises:
a third gate stack over the ninth portion of the first semiconductor strip; and
a fourth gate stack over the twelfth portion of the second semiconductor strip, wherein the seventh and the twelfth portions are in a same third column, and wherein the eighth and the tenth portions are in a same fourth column.
14. The ESD protection circuit of claim 8 further comprising shallow trench isolation regions, and wherein the first and the second semiconductor strips comprise first portions extending between the shallow trench isolation regions, and second portions over top surfaces of the shallow trench isolation regions.
15. An Electro-Static Discharge (ESD) protection circuit comprising:
a p-type semiconductor substrate;
a diode string comprising a first, a second, a third, and a fourth diode, wherein the first, the second, the third, and the fourth diodes are aligned sequentially in a column, and wherein each of the first, the second, the third, and the fourth diodes comprises:
a p+ semiconductor strip as an anode;
an n-type semiconductor strip and a n+ semiconductor strip as a cathode, wherein the anodes and the cathodes of the first, the second, the third, and the fourth diodes form an array, and wherein in each of rows and columns of the array, the anodes and the cathodes are allocated in an alternating layout; and
a gate electrode overlapping the n-type semiconductor strip; and
four n-well regions, each overlapped by and in contact with one of the first, the second, the third, and the fourth diodes, wherein the four n-well regions are separated from each other by portions of the p-type semiconductor substrate.
16. The ESD protection circuit of claim 15 further comprising an input/output pad and a Vss node, wherein the first, the second, the third, and the fourth diodes are serially coupled between the input/output pad and the Vss node.
17. The ESD protection circuit of claim 16 further comprising an additional diode string having an identical structure as the diode string, wherein the additional diode string is connected in parallel with the diode string.
18. The ESD protection circuit of claim 15 , wherein the first, the second, the third, and the fourth diodes are biased in a same direction.
19. The ESD protection circuit of claim 15 , wherein the diode string comprises eight serially connected diodes.
20. The ESD protection circuit of claim 15 further comprising:
a first conductor connecting the cathode of the first diode to the anode of the second diode;
a second conductor connecting the cathode of the second diode to the anode of the third diode; and
a third conductor connecting the cathode of the third diode to the anode of the fourth diode.