Semiconductor device and method of manufacturing the semiconductor device
A MISFET has a threshold voltage that is not undesirably increased due to channel narrowing of the MISFET, and the MISFET is reduced in size and increased in withstand voltage. An anti-inversion p-type channel stopper region provided below an element isolation trench has an end that projects toward a channel region below a gate oxide film, and terminates short of the channel region. That is, the end is offset from the end of the channel region (the end of the element isolation trench). This suppresses diffusion in a lateral direction (channel region direction) of an impurity in the p-type channel stopper region, and thus suppresses a decrease in carrier concentration at the end of the channel region. As a result, a local increase in threshold voltage is suppressed.
1. A method of manufacturing a semiconductor device, the method comprising the steps of:
(a) providing a semiconductor substrate of a first conduction type;
(b) forming a low-concentration source region and a low-concentration drain region of a second conduction type in a main surface portion of the semiconductor substrate by ion-implanting an impurity into the semiconductor substrate with a first photoresist film as a mask;
(c) forming a channel stopper region of a first conduction type in the main surface portion of the semiconductor substrate by ion-implanting an impurity into the semiconductor substrate with a second photoresist film as a mask;
(d) after the step (b) and the step (c), forming element isolation regions in the main surface portion of the semiconductor substrate;
(e) forming a gate insulating film in a surface portion of an active region of the semiconductor substrate, the active region being partitioned by the element isolation regions;
(f) forming a gate electrode over the gate insulating film; and
(g) ion-implanting an impurity into a part of the low-concentration regions with a third photoresist film as a mask, thereby forming a high-concentration region of the second conduction type in the part of the low-concentration regions, the high-concentration region having an impurity concentration higher than the low-concentration regions,
wherein the low-concentration source region faces the low-concentration drain region in a length direction of the gate electrode, and
wherein, in a width direction of the gate electrode perpendicular to the length direction of the gate electrode, an end of the channel stopper region facing toward the center of the gate electrode in the width direction is offset from an end of the element isolation region facing toward the center of the gate electrode in the width direction.
2. The method according to claim 1 , wherein an offset between the end of the element isolation region and the end of the channel stopper region is 0.5 to 0.7 μm.