Patent ID: 7696054

Claim:
A method of designing a transistor, comprising: specifying a standard transistor including a first active region which is defined by a first device isolation layer, a first gate line which crosses over the first active region and includes a first lateral bottom length overlapping the first active region, a first lower-concentration impurity-doped region which is located in the first active region, and a first higher-concentration impurity-doped region which is apart from both the first device isolation layer and the gate line and located in the first active region; and counting a first sum of first lengths of the first lower-concentration impurity-doped region overlapping with a first straight line which is parallel to the first gate line and crossing over both the first lower-concentration impurity-doped region and the first higher-concentration impurity-doped region; specifying a simulation transistor comprising a second active region which is defined by a second device isolation layer, a second gate line which crosses over the second active region and comprises a second lateral bottom length overlapping the second active region, a second lower-concentration impurity-doped region which is located in the second active region, and a second higher-concentration impurity-doped region which is apart from both the second device isolation layer and the second gate line and located in the second active region; and counting a first ratio of the first lateral bottom length to the second lateral bottom length, wherein the specifying of the simulation transistor comprises adjusting at least one out of the second lateral bottom length and second lengths of the second lower-concentration impurity-doped region overlapping with a second straight line which is parallel to the second gate line and crossing over both the second lower-concentration impurity-doped region and the second higher-concentration impurity-doped region, such that a second ratio of the first sum to a second sum of the second lengths of the second lower-concentration impurity-doped region is equal to the first ratio.