Lithography by QED induced EUV Light Sources

YOUNGWOOD, Pa. - May 5, 2014 - PRLog -- .
Background
EUV light at 13.5 nm is planned in the next generation of computer chips. However, the production of a EUV light source is challenging Moore’s law to the point of questioning whether the goal of advancing computer technology may not be achievable. The difficulty in achieving this goal may be traced back to the requirement of classical physics that EUV light may only be produced upon ionization of atoms in dense high temperature plasmas. Because of this requirement, EUV light sources in lithography [1] have evolved to the concept of laser produced plasmas or LPP. Typically, LPP light sources use high power CO2 lasers to heat solid and gas targets, the plasma of which produces the EUV emission spectra. LPP uses solid targets of tin or lithium droplets and puffs of helium or xenon gases. Regardless, the EUV light is collected and focused by a large diameter elliptical mirror [2] and then delivered to the lithography system. Solid targets require the collector to be maintained at 400 C to evaporate debris from the collector surface that otherwise reduces its reflectivity. As the focused light projects onto the mask, it is reflected onto a series of mirrors, which reduce the size of the image prior to being focused onto a silicon wafer. See, e.g., ^http://www.cymer.com/euv_lithography/

Problem
LPP requires high temperature plasmas to create EUV light. Moreover, LPP systems are not only complex, but very expensive costing as much as $120 million. In this regard, QM differs. QM stands for quantum mechanics. Provided EM energy, say from a heater is placed under TIR confinement, EUV radiation may be created by QED at ambient temperature. EM stands for electromagnetic, and QED for quantum electrodynamics. However, the TIR confinement needs to be arranged in a lithographic configuration, and if so configured offers the promise of inexpensive EUV lithography at 13.5 nm. TIR stands for total internal reflection.

QED Configuration
QED induced EUV lithography follows the LPP light source configurations shown in the above link, except the expensive LPP Source comprising the CO2 laser and collector is replaced with the inexpensive Spherical EUV Source shown in the thumbnail. Otherwise, the QED lithography system of Illuminator and Projection Optics is the same as for LPP lithography.

Spherical EUV Source and Theory
The Spherical EUV Source comprises a low thermal expansion CerVit spherical glass lens provided on the front surface with a higher refractive index, say zinc oxide nanoscale coating. An insulated surface heater is provided on the back surface, the heat of which flows through the lens thickness into the coating. However, QM precludes any increase in the coating temperature, and instead the heat as EM energy is conserved by QED creating a steady source of EUV light. No lasers are required. In the TIR mode of the coating, the EUV wavelength λ = 2nd, where n and d are the refractive index and thickness of the coating. The Planck energy E of the QED radiation is, E = hc / λ, where h is Planck’s constant and c is the velocity of light. For zinc oxide coatings having refractive index n = 2, the QED radiation for thicknesses d < 5 nm is in the EUV having wavelengths λ < 20 nm See “QED Induced Lithography,” at http://www.nanoqed.org , 2014

Comparisons

1. Coatings LPP lithography [1] requires the silicon carbide collector [2] to be provided with a multilayer coating comprising molybdenum and silicon in order to reflect the largest amount of 13.5 nm EUV light, as otherwise the light is absorbed before ever reaching the wafer. In contrast, the glass lens in the Spherical EUV Source is provided with a zinc oxide nanoscale coating that at ambient temperature creates EUV light without absorption.

2. Power In LPP lithography, high energy CO2 lasers using 20 kW of power are required. QED lithography is far more efficient. Depending on spot size, pulsed < 5 W surface heater power is sufficient to achieve EUV fluences < 10 mJ/cm^2.

3. Debris LPP lithography requires operation at 400 C to evaporate tin and lithium debris of solid targets from the collector mirror surface in order to maintain the reflectivity and enable long component lifetimes. QED lithography operates at ambient temperature and lacking plasma avoids the need for debris control.

4. Size The large 320 mm diameter [2] of the LPP collector mirror is not required for the Spherical EUV Source of QED lithography. More study is required, but small < 100 mm spherical glass lenses are anticipated.

5. Nanostructuring The nanostructuring of materials by EUV radiation using compact desktop LPP lithography [3] may be more simply and economically performed with a hand-held < 100 mm diameter Spherical EUV Source, a variant of which is the EUV irradiation of polymer tensile specimens to simulate the effect of QED induced cross-linking on the mechanical properties of the interphase in nanocomposites. See http://www.prlog.org/12280347-cross-linking-of-polymers-i...

Conclusions

1. QED lithography may supersede its LPP counterpart, although more study is required to confirm this conclusion.

2. Nanostructuring of materials by EUV light in compact desktop LPP sources may be superseded by far simpler hand-held Spherical EUV Sources.

3. Spherical EUV Sources at 13.5 nm require coating thicknesses < 3 nm. More study is required to determine if ALD can produce uniform d < 3 nm coatings on < 100 mm diameter spherical lenses. ALD stands for atomic layer deposition.

References
[1] B. A. M. Hansson, et al., “LPP EUV Source Development for HVM,” in Emerging Lithographic Technologies X, Proc. of SPIE, Vol. 6151, 2006.
[2] N. R. Bowering, et al., “EUV Source Collector," in Emerging Lithographic Technologies X, Proc. of SPIE, Vol. 6151, 2006.
[3] H.Fiedorowicz, et al., “Nanostructured polymers by a compact laser plasma EUV source,“ in Synthesis and Photonics of Nanoscale Materials VII, edited by Jan J. Dubowski, David B. Geohegan, Frank Träger, Proc. of SPIE Vol. 7586, 75860G ·1, 2010.