what is different between the actual width and original W?

[020170]

in mosfet, there is an effect which called "width modulation".

in layout process, the actual width of source is smaller than original width.

because of the oxide encroachment.

please explain to me in detail that how to proceed the oxide encroachment process.

i don't understand why did the oxide is encroached which caused width modulation.

another Question : in many CMOS processes, what order is the oxide ncroachment ?

 

[wwfieee]

Re: what is different between the actual width and original

i can't tell much about enroachment, but the reason why the actual width is less than the design width is because the implantation of the n/p drain and source diffuses outward. some of it gets under the gate in the process. this lowers the width of the gate. another thing is that some process specifically introduce a small overlap under the gate to prevent 'hot electron' effect. this is lighter doped compared to the drain/source.