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| In ], '''immersion lithography''' is a variant technique that interposes a liquid medium between the optics and the wafer surface, replacing the usual air gap. With the 193 ] wavelength, the typical liquid used is ultra-pure, degassed water. Immersion lithography increases the effective depth-of-focus for a given ] and permits the use of optics with numerical apertures above 1.0, thus raising the maximum resolution potential of extant wavelength technologies. | In ], '''immersion lithography''' is a variant technique that interposes a liquid medium between the optics and the wafer surface, replacing the usual air gap. With the 193 ] wavelength, the typical liquid used is ultra-pure, degassed water. Immersion lithography increases the effective depth-of-focus for a given ] and permits the use of optics with numerical apertures above 1.0, thus raising the maximum resolution potential of extant wavelength technologies. | ||
| As of 2005, it is expected that immersion lithography at the 193 nm wavelength will be used in 2009 to print 45 nm lines and spaces . Following its aggressive introduction, it is speculated that technology enhancements will be used to prolong the use of the technology to smaller features. | As of 2005, it is expected that immersion lithography at the 193 nm wavelength will be used in 2009 to print 45 nm lines and spaces . Following its aggressive introduction, it is speculated that technology enhancements will be used to prolong the use of the technology to smaller features. | ||
| Such enhancements include the use of higher ] materials in the final lens, immersion fluid, and ]. Each of these materials puts a limit on the largest angle that the light makes with the image plane. | Such enhancements include the use of higher ] materials in the final lens, immersion fluid, and ]. Each of these materials puts a limit on the largest angle that the light makes with the image plane. | ||
| Numerical aperture cannot be increased indefinitely, as features on the ] approach subwavelength sizes. Subwavelength features no longer obey the laws of classical imaging optics but need to be rigorously analyzed using electromagnetic theory (see for example, ). | Numerical aperture cannot be increased indefinitely, as features on the ] approach subwavelength sizes. Subwavelength features no longer obey the laws of classical imaging optics but need to be rigorously analyzed using electromagnetic theory (see for example, ). | ||
| Once the maximum numerical aperture is reached, the only way immersion lithography can print denser features would be to split a dense layer into two looser layers . | Once the maximum numerical aperture is reached, the only way immersion lithography can print denser features would be to split a dense layer into two looser layers . | ||
Revision as of 10:17, 26 November 2005
In photolithography, immersion lithography is a variant technique that interposes a liquid medium between the optics and the wafer surface, replacing the usual air gap. With the 193 nm wavelength, the typical liquid used is ultra-pure, degassed water. Immersion lithography increases the effective depth-of-focus for a given numerical aperture and permits the use of optics with numerical apertures above 1.0, thus raising the maximum resolution potential of extant wavelength technologies.
As of 2005, it is expected that immersion lithography at the 193 nm wavelength will be used in 2009 to print 45 nm lines and spaces . Following its aggressive introduction, it is speculated that technology enhancements will be used to prolong the use of the technology to smaller features.
Such enhancements include the use of higher refractive index materials in the final lens, immersion fluid, and photoresist. Each of these materials puts a limit on the largest angle that the light makes with the image plane.
Numerical aperture cannot be increased indefinitely, as features on the photomask approach subwavelength sizes. Subwavelength features no longer obey the laws of classical imaging optics but need to be rigorously analyzed using electromagnetic theory (see for example, ).
Once the maximum numerical aperture is reached, the only way immersion lithography can print denser features would be to split a dense layer into two looser layers .
References:
1. M. LaPedus, "Litho race," EE Times, October 21, 2005.
2. C-W Chang et. al., Laser Physics Letters 2, pp. 351-355 (2005).
3. G. Vandenberghe, "How Optical Lithography Prints a 32 nm Node 6T-SRAM Cell," Semiconductor International, June 1, 2005.
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