Method for making mos structure with precisely controlled channel length

Claim 1

In a method for forming an MOS semiconductor structure, providing a semiconductor body formed of a material of one conductivity type, said semiconductor body having a surface, forming a mask on one surface of said semiconductor body having an opening therein, diffusing an impurity through said opening in said mask into the semiconductor body to provide a first region of opposite conductivity type and forming a first PN junction which extends to the surface and defines a continuous line that encloses an area on the surface, adding additional masking material within the opening to define a key extending into the opening, diffusing an additional impurity through the same opening in the mask to provide a second diffused region of said one conductivity type to form a source, said second diffused region forming a second PN junction extending to the surface and forming a second continuous line on the surface which encloses an area within the area enclosed by the first continuous line, the mask causing the second region to have a key portion extending into the same, said first and second PN junctions forming a channel having a precise width and including a key portion placing a layer of insulating material over the PN Junctions forming the channel, placing gate metalization formed on said layer of insulating material, placing metalization on the surface and making contact with the area within said second diffused region for forming a source contact and making contact with the key portion to short the channel to the source, and placing metalization on the surface and making contact with the region outside the first diffused region to provide a drain contact.