Fabrication limits of electron beam lithography and of UV, X-ray and ion-beam lithographies

The paper discusses and compares the lithography methods being developed for the fabrication of future generations of silicon integrated circuits. The smallest features in today's circuits are about 0.3 mu m in size and this will be reduced to 0.1 mu m within the next ten years. The methods discussed include optical (ultraviolet light) projection, which is used predominantly at present, projection printing at wavelengths between the X-ray and ultraviolet regions, X-ray proximity printing, and scanning and projection with electrons and ions. There are severe problems to be overcome with all of the methods before they can satisfy future needs. The difficulties are not just connected with obtaining adequate resolution. The more challenging requirements are those associated with the elimination of distortion in the highly complex trillion pixel images and of achieving an exposure rate of about one per second with a system of acceptable cost, that is less than about $10M. The various approaches for correcting distortion and obtaining adequate throughput are described, as are the factors limiting resolution. Finally, the ultimate capabilities of electron beam methods for fabricating structures and devices with dimensions down to 1 nm are described.