Double Channel Doping in Transistor Formation

A method of forming a transistor in a Static Random Access Memory (SRAM) cell, the method comprising:

• performing a first well doping on an active region;
• after the first well doping, forming a dummy gate covering a middle portion of the active region, wherein end portions of the active region on opposite sides of the middle portion of the active region are exposed;
• forming an Inter-Layer Dielectric (ILD) over the active region, wherein the ILD overlaps the end portions;
• removing the dummy gate to form a recess in the ILD;
• performing a second well doping through the recess, wherein the middle portion of the active region is doped during the second well doping;
• and
• forming a gate dielectric and a gate electrode in the recess to form the transistor, wherein the middle portion forms a channel region of the transistor.

A method comprising:

• performing a first well implantation on a first and a second semiconductor strip simultaneously, wherein the first and the second semiconductor strips are between isolation regions;
• recessing the isolation regions, wherein top portions of the first and the second semiconductor strips form a first and a second semiconductor fin, respectively;
• forming a first and a second dummy gate covering a first middle portion and a second middle portion of the first and the second semiconductor fins, respectively;
• forming an Inter-Layer Dielectric (ILD), wherein the ILD overlaps end portions of the first and the second semiconductor fins;
• removing the first and the second dummy gates to form a first recess and a second recess, respectively, in the ILD;
• forming a mask, wherein the mask covers the second middle portion of the second semiconductor fin, and wherein the first middle portion of the first semiconductor fin under an opening in the mask;
• performing a second well implantation on the first middle portion, wherein impurities of a same conductivity type are introduced by the first well doping and the second well doping;
• and
• after the second well implantation, removing the mask.