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Liquid-target laser-plasma source for X-ray lithography
MICROELECTRONIC ENGINEERING ELSEVIER
Mieroeleetroaic Engineering 35 (1997) 535-536
LIQUID-TARGET LASER-PLASMA SOURCE FOR X-RAY LITHOGRAPHY L. Malmqvist*, A. L. Bogdanov t, L. Montelius t and H. M. Hertz" Department of Physics, Lund Institute of Technology, P.O. Box 118, S-221 00 Lund, Sweden 'Division of Atomic Physics tDivision of Solid State Physics We describe a compact and practically debris-free laser-plasma x-ray source suitable for proximity lithography. The source is based on a microscopic fluorocarbon continuous liquid jet droplet target, generating highbrightness ~=1.2-1.7 nm x-ray emission with -5% conversion efficiency. This target type has the advantages of producing only negligible amounts of debris, and being regenerative, thereby allowing high-repetition-rate uninterrupted operation. The source is combined with an Au/SiNx x-ray mask to demonstrate lithography of sub100 nm structures in SAL-601 chemically enhanced resist.
1. INTRODUCTION Laser plasmas are attractive sources for proximity x-ray lithography due to their high brightness and comparatively low cost [1]. However, conventional laser-plasma target systems, e.g., bulk metals or thin film tape targets, limit the applicability of these sources. The limitations primarily concern repetition rate, operating time, target cost and debris emission. In this paper we present table-top nm lithography using a chemically enhanced negative resist exposed by a droplet-target laser plasma x-ray source [2,3]. The source practically eliminates the debris problem and allows long periods of uninterrupted operation.
~5%, corresponding to ~2xlO 12 ph./sr..puise [3]. For suppression of the longer wavelength radiation from carbon ions, a freestanding metal filter of 1 ~tm aluminium and 100 nm copper is used, resulting in an x-ray transmission of about 40% through the filter and the mask (cf. below).
2. EXPERIMENTS
In the experimental arrangement [3], ~ 1 0 6 liquid droplet targets per second are produced by forcing liquid fluorocarbon through a -1 MHz piezoelectrically vibrated nozzle into a vacuum chamber. The resulting ~15 ~tm liquid droplets are hit by 10 Hz, 70 mJ, ~,=532 nm, 70-100 ps laser pulses focused to approximately 12 ~tm. The dominant emission lines from the plasma are F IV at ~,=1.495 nm and F VIII at k=1.681 nm and Z,=1.446 nm. The x-ray conversion efficiency into the wavelength region below ~,=1.7 nm has been determined to
Fig. 1 Electron micrograph of resist pattern in SAL-601 produced by x-ray lithography.
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L. Malmqvist et al. / Microelectronic Engineering 35 (1997) 535-536
The debris emission has been measured to 70 pg/(sr.pulse), which is several orders of magnitude less than for conventional target systems. This is important since damage to masks and other fragile components can be avoided. The x-ray mask is manufactured by ion milling of a 200 nm thick gold layer on a 250 nm thick silicon nitride membrane [4]. The resist mask for the ion milling was prepared by e-beam lithography with 50 keV electrons to minimize proximity effects. The x-ray mask is pressed onto a wafer coated with 0.6 p.m of an acid-catalyzed novolak-based negative E-beam resist (SAL-601 ER7) [5], using a 13 [am polyimide spacer. The distance between the plasma and the wafer was 40 mm. In Fig. 1 a typical lithography result is presented, showing sub-100 nm structures with high-aspect ratios.
REFERENCES
1. J. R. Maldonado, in Applications of Laser Plasma Radiation II, edited by M. C. Richardson and G. A. Kyrala, Proc. SPIE 2523, 2 (1995). 2. L. Rymell, and H. M. Hertz, Opt. Commun. 103, 105 (1993). 3. L. Malmqvist, L. Rymell and H. M. Hertz, Appl. Phys. Lett. 68, 2627 (1996). 4. L. Malmqvist, A. L. Bogdanov, L. Montelius and H. M. Hertz "Nanometer table-top proximity x-ray lithography with liquid-target laser-plasma source", submitted to J. Vac. Sci. Technol. B. 5. M. L. Schattenburg, K. Early, Y. C. Ku, W. Chu, M. I. Shepard, S. C. The, H. I. Smith, D. W. Peters, R. D. Frankel, D. R. Kelly, and J. P. Drumheller, J. Vac. Sci. Technol. B8, 1604 (1990).
Mieroeleetroaic Engineering 35 (1997) 535-536
LIQUID-TARGET LASER-PLASMA SOURCE FOR X-RAY LITHOGRAPHY L. Malmqvist*, A. L. Bogdanov t, L. Montelius t and H. M. Hertz" Department of Physics, Lund Institute of Technology, P.O. Box 118, S-221 00 Lund, Sweden 'Division of Atomic Physics tDivision of Solid State Physics We describe a compact and practically debris-free laser-plasma x-ray source suitable for proximity lithography. The source is based on a microscopic fluorocarbon continuous liquid jet droplet target, generating highbrightness ~=1.2-1.7 nm x-ray emission with -5% conversion efficiency. This target type has the advantages of producing only negligible amounts of debris, and being regenerative, thereby allowing high-repetition-rate uninterrupted operation. The source is combined with an Au/SiNx x-ray mask to demonstrate lithography of sub100 nm structures in SAL-601 chemically enhanced resist.
1. INTRODUCTION Laser plasmas are attractive sources for proximity x-ray lithography due to their high brightness and comparatively low cost [1]. However, conventional laser-plasma target systems, e.g., bulk metals or thin film tape targets, limit the applicability of these sources. The limitations primarily concern repetition rate, operating time, target cost and debris emission. In this paper we present table-top nm lithography using a chemically enhanced negative resist exposed by a droplet-target laser plasma x-ray source [2,3]. The source practically eliminates the debris problem and allows long periods of uninterrupted operation.
~5%, corresponding to ~2xlO 12 ph./sr..puise [3]. For suppression of the longer wavelength radiation from carbon ions, a freestanding metal filter of 1 ~tm aluminium and 100 nm copper is used, resulting in an x-ray transmission of about 40% through the filter and the mask (cf. below).
2. EXPERIMENTS
In the experimental arrangement [3], ~ 1 0 6 liquid droplet targets per second are produced by forcing liquid fluorocarbon through a -1 MHz piezoelectrically vibrated nozzle into a vacuum chamber. The resulting ~15 ~tm liquid droplets are hit by 10 Hz, 70 mJ, ~,=532 nm, 70-100 ps laser pulses focused to approximately 12 ~tm. The dominant emission lines from the plasma are F IV at ~,=1.495 nm and F VIII at k=1.681 nm and Z,=1.446 nm. The x-ray conversion efficiency into the wavelength region below ~,=1.7 nm has been determined to
Fig. 1 Electron micrograph of resist pattern in SAL-601 produced by x-ray lithography.
536
L. Malmqvist et al. / Microelectronic Engineering 35 (1997) 535-536
The debris emission has been measured to 70 pg/(sr.pulse), which is several orders of magnitude less than for conventional target systems. This is important since damage to masks and other fragile components can be avoided. The x-ray mask is manufactured by ion milling of a 200 nm thick gold layer on a 250 nm thick silicon nitride membrane [4]. The resist mask for the ion milling was prepared by e-beam lithography with 50 keV electrons to minimize proximity effects. The x-ray mask is pressed onto a wafer coated with 0.6 p.m of an acid-catalyzed novolak-based negative E-beam resist (SAL-601 ER7) [5], using a 13 [am polyimide spacer. The distance between the plasma and the wafer was 40 mm. In Fig. 1 a typical lithography result is presented, showing sub-100 nm structures with high-aspect ratios.
REFERENCES
1. J. R. Maldonado, in Applications of Laser Plasma Radiation II, edited by M. C. Richardson and G. A. Kyrala, Proc. SPIE 2523, 2 (1995). 2. L. Rymell, and H. M. Hertz, Opt. Commun. 103, 105 (1993). 3. L. Malmqvist, L. Rymell and H. M. Hertz, Appl. Phys. Lett. 68, 2627 (1996). 4. L. Malmqvist, A. L. Bogdanov, L. Montelius and H. M. Hertz "Nanometer table-top proximity x-ray lithography with liquid-target laser-plasma source", submitted to J. Vac. Sci. Technol. B. 5. M. L. Schattenburg, K. Early, Y. C. Ku, W. Chu, M. I. Shepard, S. C. The, H. I. Smith, D. W. Peters, R. D. Frankel, D. R. Kelly, and J. P. Drumheller, J. Vac. Sci. Technol. B8, 1604 (1990).