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IC Steppers and Scanners—Immersion Lithography Technology—Boosting Performance of ICs that Support the Digital Society

1. Development of ICs makes our lives more convenient


IC chips are used in various kinds of equipment.

Mobile phones, personal computers and CPU-based electrical appliances are widely used in today's digital society. ICs (Integrated Circuit), which serve as the brains of these devices, are indispensable for all sorts of electrical products. It's amazing to know that tiny ICs only a few square millimeters in size are essential to keeping rooms at comfortable temperatures, cooking delicious rice and taking digital photos.

As ICs develop, the devices that incorporate them improve. ICs can make mobile computers, mobile phones, music players and similar devices smaller yet more multifunctional. To make this happen, however, the widths of lines that form IC circuit patterns must be ever thinner. Theoretically, reducing a line width (process rule) by half enables four times more circuitry to be integrated into the same space, and, at the same time, quadruples processing speed.

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2. Overcoming a barrier in the conventional manufacturing process

The optical path of an IC stepper and scanner
IC steppers and scanners print complicated circuit patterns onto wafers using a high-performance projection lens.

Today's ICs are manufactured with IC steppers and scanners. It is not incorrect to say that IC steppers and scanners resemble photographic enlargers. In photography, small images on film are enlarged and printed onto photographic paper, whereas in IC manufacturing, images of immensely complicated circuit patterns drawn on large reticles (masks) are reduced using high performance lenses (optical system) and printed onto silicon discs called wafers.


The line width of IC circuit patterns has fallen from 1 micrometer to 45 nanometers in 20 years, an almost 20-fold reduction.

Improvements in the optics of IC steppers and scanners (use of a larger diameter), introduction of a shorter light source wavelength and the development of materials have resulted in higher integration of ICs. However, for a long time the IC manufacturing process, which uses light to print circuit patterns, was hindered by the limitations of the refractive index of air, which made it impossible to create patterns at a precision finer than a certain process level.

The technology that solved this problem was Immersion Lithography Technology, incorporated into Nikon's IC steppers and scanners.

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3. Nikon puts high precision immersion lithography technology to practical use


Principle of Immersion Lithography

Immersion lithography is a technology used to fill the space between the projection lens and the wafer with purified water (refractive index 1.44*1)—a medium with a refractive index higher than air (refractive index 1.00). This method achieves greater precision by using the liquid as if it were a lens. This has enabled IC manufacturing at a precision less than 45 nm (1 nm=1/1,000,000 millimeter), greatly surpassing conventional limitations. Specifically, this allows as many as 1,800 lines to be drawn within a space the width of a human hair.

  • *1 Refractive index 1.44: refractive index with the exposure wavelength

Nikon's immersion lithography technology can be incorporated into IC steppers and scanners without any major changes to its principle and basic structure. This technology can therefore quickly respond to the demands of a rapidly developing IC industry. IC steppers and scanners utilizing immersion lithography technology are used in advanced flash memory*2 and other leading-edge device mass production lines, and will soon be applied to the production of DRAM*3 and personal computer CPU. ICs that have achieved high integration through immersion lithography will continue to be used in a wide variety of IT devices and electrical appliances, providing greater comfort and convenience to our lives. Last but not least, higher integration and miniaturization of ICs lessen power consumption, leading to a reduced burden on the global environment.

  • *2 Flash memory: a memory chip that can retain information without requiring electricity until the information is rewritten. Flash memory is used in digital camera and music player memory cards.
  • *3 DRAM: a memory chip that is temporarily used to process digital information. For mobile phones and personal computers to run faster, DRAMs must have greater storage capacity and run ever faster.