Method of making FET utilizing shadow masking and diffusion from a doped oxide

摘要

A novel self-align type method of making an FET with a very short gate length and a good high frequency characteristic, and a low noise characteristic, the method comprising the steps of: forming on a silicon epitaxial layer (13) of n-type conductivity a doped oxide film (14) containing boron as an impurity to give p-type conductivity, forming a mask (15a, 16a) containing Si3N4 film and having a width larger than that of a gate region (19) to be formed on said n-type epitaxial layer (13), etching said doped oxide film (14) by utilizing said mask (15a, 16a) as an etching mask to expose surface of said silicon crystal layer (13) in a manner that sides of the part of said doped oxide film (14) covered by said mask (15, 16a) are side-etched by a predetermined width, ion-implanting an impurity of said first conductivity type into said n-type epitaxial layer (13) by utilizing said mask as implanting mask, and carrying out a heat treating thereby diffusing said second conductivity type impurity from said doped oxide film (14) retained only under said mask into said n-type epitaxial layer (13) to form said gate region (19) and driving said ion-implanted first conductivity type impurity into said silicon crystal layer (13) to form a source region (17) and a drain region (18).