Tapered Photoresist for a Doping Profile
Original Publication Date: 1983-Nov-01
Included in the Prior Art Database: 2005-Feb-07
A method is provided to achieve in a semiconductor structure a graded dopant profile by using a tapered photoresist pattern which is obtained by exposing the resist with broad-band mid UV (254-313 nm). This method takes advantage of the tapered resist profile during ion-implantation, thus creating a graded impurity profile that reduces the electric field at the junction edge, particularly in shallow junctions. For example, in the figure shown above, a desired dopant profile at the drain is established with a low concentration edge separated from a high concentration edge by 0.5 to 0.6 mm. This is accomplished by forming an SiO2 layer of about 300 ˜ on a silicon wafer for use as a screen oxide during the implantation of a highly doped drain region. An equivalent SiO2 layer of about 570 ˜ remains over the lightly doped region.