Semiconductor memory device and method of manufacturing the same
View Patent ↗A contact connected to a word line is formed on a gate electrode of an access transistor of an SRAM cell. The contact passes through an element isolation insulating film to reach an SOI layer. A body region of a driver transistor and that of the access transistor are electrically connected with each other through the SOI layer located under the element isolation insulating film. Therefore, the access transistor is in a DTMOS structure having the gate electrode connected with the body region through the contact, which in turn is also electrically connected to the body region of the driver transistor. Thus, operations can be stabilized while suppressing increase of an area for forming the SRAM cell.
1. A semiconductor memory device comprising an SRAM (static random access memory) cell, said SRAM cell including:
an access MOS (metal oxide semiconductor) transistor;
a driver MOS transistor; and
a contact connecting a word line and a gate electrode of said access MOS transistor with each other, wherein
said contact is connected both to a body region of said access MOS transistor and to a body region of said driver MOS transistor.
2. The semiconductor memory device according to claim 1 further comprising a resistor, wherein
said resistor is interposed between the body region connected to said word line through said contact and said word line, the body region being at least either of said access MOS transistor or of said driver MOS transistor.
3. The semiconductor memory device according to claim 1 ,
wherein said contact has a surface provided with barrier metal.
4. The semiconductor memory device according to claim 1 , wherein said contact includes polysilicon.
5. The semiconductor memory device according to claim 1 , wherein
a resistance between the body region connected to said word line through said contact and said word line ranges between 1 kΩ and 100 MΩ, the body region being at least either of said access MOS transistor or of said driver MOS transistor.
6. The semiconductor memory device according to claim 1 comprising a diode having a cathode connected to the side of said word line, wherein
said diode is interposed between the body region connected to said word line through said contact and said word line, the body region being at least either of said access MOS transistor or of said driver MOS transistor.
7. The semiconductor memory device according to claim 6 , wherein
said contact has a surface provided with barrier metal.
8. The semiconductor memory device according to claim 6 , wherein
said contact includes polysilicon.
9. The semiconductor memory device according to claim 6 , wherein
when said diode is reverse biased, a resistance between the body region connected to said word line through said contact and said word line ranges between 1 kΩ and 100 MΩ, the body region being at least either of said access MOS transistor or of said driver MOS transistor.
10. The semiconductor memory device according to claim 1 , wherein
said access MOS transistor and said driver MOS transistor are formed in a first active region defined in a first well region of a first conductivity type formed in a semiconductor layer, said access MOS transistor and said driver MOS transistor each including said body region of said first conductivity type and source/drain regions of a second conductivity type,
said first active region is defined by an element isolation insulating film selectively formed in the upper surface part of said first well region, and
the body region is joined to said first well region under said element isolation insulating film to be connected to said contact, the body region being at least either of said access MOS transistor or of said driver MOS transistor.
11. The semiconductor memory device according to claim 10 , wherein
said contact passes through said element isolation insulating film to be connected to said first well region located under said element isolation insulating film.
12. The semiconductor memory device according to claim 11 , wherein
a portion of said first well region connected to said contact is formed with a region having an impurity concentration different from that of the remaining portion of said first well region.
13. The semiconductor memory device according to claim 11 , wherein
said first well region and said contact forms a Schottky junction.
14. The semiconductor memory device according to claim 11 , wherein
said contact has a surface provided with barrier metal, and
a portion of said first well region connected to said contact and said barrier metal are reacted to form a silicide layer.
15. The semiconductor memory device according to claim 11 , wherein
said first well region under said element isolation insulating film is of P-type, and
said contact includes N-type polysilicon.
16. The semiconductor memory device according to claim 10 , wherein.
said SRAM cell further includes a second active region of said first conductivity type defined by said element isolation insulating film in said first well region,
said second active region is joined to said first well region located under said element isolation insulating film, and
said contact is connected to said second active region.
17. The semiconductor memory device according to claim 16 , wherein
said second active region has an impurity concentration different from that of said first well region.
18. The semiconductor memory device according to claim 16 , wherein
said second active region and said contact forms a Schottky junction.
19. The semiconductor memory device according to claim 16 , wherein
said contact has a surface provided with barrier metal, and
a portion of said second active region connected to said contact and said barrier metal are reacted to form a silicide layer.
20. The semiconductor memory device according to claim 16 , wherein
said second well region is of P-type, and
said contact includes N-type polysilicon.
21. The semiconductor memory device according to claim 10 , wherein
said semiconductor layer is formed on an insulating layer,
said SRAM cell further includes a load MOS transistor formed in a second well region of said second conductivity type formed in said semiconductor layer, and
said element isolation insulating film between said access MOS transistor and said driver MOS transistor and said load MOS transistor reaches said insulating layer.
22. The semiconductor memory device according to claim 10 , comprising a plurality of said SRAM cells connected to the same bit line and arranged along the extensional direction of said bit line, wherein
said semiconductor layer is formed on an insulating layer, and
said element isolation insulating film located between said plurality of SRAM cells reaches said insulating layer in said first well region.
23. The semiconductor memory device according to claim 10 , having no well potential fixing cell independent of said SRAM cell for fixing said first well region of said SRAM cell to a prescribed potential.
24. The semiconductor memory device according to claim 1 , wherein
said SRAM cell further includes a load MOS transistor,
at least upper surface parts of a drain region of said driver MOS transistor and a drain region of said load MOS transistor are connected with each other and an integral silicide layer is formed on said upper surface parts of said drain region of said driver MOS transistor and said drain region of said load MOS transistor.