A full-field x-ray exposure system based on a 4 kW stationary palladium source emitting the 4.37 A La line has been developed and evaluated in the fabrication of silicon integrated circuits. It has been used successfully in the patterning of 1 um design rule high performance n-channel metal oxide semi-conductor (NMOS) circuits of various complexities from ring oscillators to large scale custom logic and memory devices. A shadow mask consisting of a 6µm boron nitride membrane and 0.7 pm gold-tantalum features is used to transfer patterns into a chlorine-based x-ray resist sensitive to the 4.37 A radiation. Pattern transfer to the silicon surface is faithfully reproduced through the use of a trilevel structure and anisotropic reactive ion etching. Alignment of various levels is accomplished optically through the use of a bifocal, split-field microscope at high magnification and the use of dark-field edge sensing for improved contrast. Linewidth control and registration data are presented for various NMOS circuit patterns.
E. N. Fuls, E. N. Fuls,
"X-Ray Lithography Applied To The Fabrication Of One Micrometer N-Channel Metal Oxide Semiconductor Circuits," Optical Engineering 22(2), 222199 (1 April 1983). https://doi.org/10.1117/12.7973082