THE FUTURE OF OPTICAL LITHOGRAPHY

About every three years, a new DRAM generation requires a new lithogra phy system capable of imaging 3x more pixels, with a substantial impro vement in resolution. This results in a 2-5x-3x increase in the cost o f lithography lenses used for each generation and portends an increasi ng cost per square centimeter of each layer of patterned silicon. Opti cal lithography may be the least risky patterning technology through t he gigabit DRAM generation, but DOF will be a major concern, and vario us types of wave-front engineering will be needed to improve process r obustness. Steppers based on 1x, mostly reflecting optics may reduce t he escalation in cost of ownership. Such systems appear capable of mee ting the lithography requirements of the 256-Mbit DRAM and, with evolu tionary improvements, the 1-Gbit DRAM. Cost improvement is achieved wi th an incremental change in current technology and, therefore, holds m ore promise than new, more revolutionary technologies.