Kazuo Ushida

The Way To One-Half Micrometer Photolithography

To investigate the way to achieve 0.5 µm photolithography, experiments have been performed with a high-numerical-aperture lens, with multilayer and contrast-enhancement-layer resist processes, and with an excimer laser deep-UV stepper. The 0.6 N.A. lens is for the g-line and has a 5 mm x 5 mm field size. Single-layer resist exposures show good profiles at 0.6 µm line/space (L/S), with no effects from highly oblique illumination, and a depth of focus of 1.25 µm. Multilayer resists using spin-on-glass and contrast-enhancement layers improve the resolution to 0.375 µm with a large N.A. lens and to 0.5 µm with an i-line lens of N.A. = 0.35. Because the large numerical aperture alone cannot reach 0.5 µm and because a large field, large N.A. lens is difficult to manufacture, an i-line lens with moderate N.A. and large field appears to be a better approach. As a more advanced experiment, a KrF excimer laser stepper with an achromatic quartz/fluorite lens of N.A. = 0.37 shows no effect of speckle and has produced a 0.35 µm L/S in PMMA for a k of 0.5. The resolution with MP2400 photoresist is only 0.4 µm because of deep-UV absorption. This shows the need for more work on practical deep-UV photoresists.

The Optical Stepper With A High Numerical Aperture I-Line Lens And A Field-By-Field Leveling System

A high N.A. i-line lens and a field-by-field leveling system have been developed. Resolution of the lens is better than 0.65 μm. The leveling system has achieved ±0.3 uμ/field on an experimental basis.

Excimer Laser Stepper For Submicron Lithography

To investigate the way to half micron photolithography, experiments have been performed with a high numerical aperture lens, with multilayer and contrast enhancement layer resist processes, and with an excimer laser deep UV exposure system. The 0.6 N.A. lens is for the g-line and has a 5 mm by 5 mm field size. Single layer resist exposures show good profiles at 0.6 μm line/space with no effect of highly oblique illumination, and a depth of focus of 1.25 μm. Multilayer resists using spin-on-glass and contrast enhancement layers improve the resolution to 0.375 μm with the large N.A. lens. This lens, which proves the practicality of achieving better resolution through larger N.A. and improved resist, has been made available as a first generation small field half micron stepper. As a more advanced experiment, a KrF excimer laser stepper with an achromatic quartz/fluorite lens of N.A. = 0.37 shows no effect of speckle and has produced 0.35 μm L/S in PMMA which proves the usefulness of achieving higher resolution through shorter wavelength. The resolution with MP2400 photoresist is only 0.4 μm because of the high deep UV absorption, and points out the need for more work on practical deep UV resists. In addition, much more work remains on alignment, lasers, and illuminators to make possible a production excimer stepper.

Future Lithography Challenges

For the past 25 years, the resolution and productivity of lithography exposure tools have continuously improved. The latest exposure tools have adopted immersion technology with ArF excimer lasers for the production of half pitch (HP) 55 nm to 45 nm patterns and beyond. For HP 32 nm, EUVL is the main candidate. The author reports the status of development of EUV tools and future lithography challenges.

Image quality of higher NA I-line projection lens

These days much attention is being paid to the potential of i-line lithography. We have manufactured a high numer ical aperture ( N. A. ) i-lme lens in order to study this potential. The lens specification is as follows magnification : 1/10 N. A. : 0. 65 field size : 5X5min. In this paper we first compare the difference between the image quality of g-line and i-line optics with the same resolution and then we present the results of our experiment with the new i-line lens which shows the considerable P055 ibil ity of sub-half micron 1 ithography with an i-l me optical stepper. 1.

New Projection Lenses For Optical Stepper

Optical step and repeat systems are now considered to be the major exposure equipment for the production of VLSI devices. Because of their high resolution and overlay accuracy, they are being used extensively to produce high density MOS memories, but are expected to be used increasingly in the production of custom LSI and discrete ICs, as well as highly integrated future MOS memories with submicron design rules. Projection lenses for optical steppers are required to have a wide exposure field and high resolution. This, however, is a design dichotomy which is difficult to achieve simultaneously. One possibility is to have a wide exposure field lens, but with a moderate resolution, and another is to have a high resolution lens, but with a narrow exposure field. Recently several projection lenses have been developed at Nikon. One has an extremely wide exposure field in order to achieve a high throughput, and another has an extremely high resolution, but a smaller exposure field. In this paper, the performance and special features of these lenses will be discussed. Special emphasis will be placed on the performance of the high resolution lens for submicron lithography, and SEM resist profiles produced by these lenses will be shown.