Herbert Buschbeck

Large-field ion optics for projection and proximity printing and for maskless lithography (ML2)

Recent studies carried out with Infineon Technologies have shown the utility of Ion Projection Lithography (IPL) for the manufacturing of integrated circuits. In cooperation with IBM Storage Technology Division the patterning of magnetic films by resist-less Ion Projection Direct Structuring (IPDS) has been demonstrated. With masked ion beam proximity techniques unique capabilities for lithography on non-planar (curved) surfaces are outlined. Designs are presented for a masked ion beam proximity lithography (MIBPL) exposure tool with sub - 20 nm resolution capability within 88 mmo exposure fields. The possibility of extremely high reduction ratios (200:1) for high-volume ion projection mask-less lithography (IP-ML2) is discussed.

Ion projection lithography below 70 nm: tool performance and resist process

Abstract Ion projection lithography (IPL) uses electrostatic ion-optics for reduction printing of stencil mask patterns to wafer substrates. The IPL process development tool (PDT) prints field sizes of 12.5 mm×12.5 mm (wafer) at a demagnification factor of 4. First printing results demonstrating different aspects such as resolution, linearity, exposure schemes with stencil masks and image stabilization are available. As an integral part of IPL a resist process suitable for 50 nm minimum feature size has been established using the IMS 1:1 ion beam proximity exposure tool. This resist process has been transferred successfully to the PDT. Compared to previous experiments, sensitivity and contrast have been determined for a larger number of resist materials and with higher precision. Improved resist patterns, better CD linearity and higher stability with respect to pattern collapse have been achieved by optimizing the process parameters. For a Shipley resist, system input parameters for simulations have been determined. Results for the quantum efficiency obtained by Szmanda’s titration method will be presented.

Large-field particle beam optics for projection and proximity printing and for maskless lithography

Recent studies have shown the utility of ion projection lithography (IPL) for the manufacturing of integrated circuits. In addition, ion projection direct structuring (IPDS) can be used for resistless, noncontact modification of materials. In cooperation with IBM Storage Technology Division, ion projection patterning of magnetic media layers has been demonstrated. With masked ion beam proximity techniques, unique capabilities for lithography on nonplanar (curved) surfaces are outlined. Designs are presented for a masked ion beam proximity lithography (MIBL) and masked ion beam direct structuring (MIBS) tool with sub-20-nm resolution capability within 88-mm□ exposure fields. The possibility of extremely high reduction ratios (200:1) for high-volume projection maskless lithography (projection-ML2) is discussed. In the case of projection-ML2 there are advantages of using electrons instead of ions. Including gray scaling, an improved concept for a ⩽50-nm projection-ML2 system is presented with the potential to meet a throughput of 20 wafers per hour (300 mm).

Experimental results of the stochastic Coulomb interaction in ion projection lithography

Throughput and resolution are connected in ion and electron projection lithography (IPL and EPL) because of the space charge and Coulomb interaction between the particles in the beam. Due to the lack of experimental data it was not possible to estimate this effect accurately. Therefore an experiment setup has been developed which has the most significant parameters close to planned IPL exposure tools. These parameters are the linear particle density and the crossover shape and size. The stochastic Coulomb interaction blur, depending on the total beam current, has been measured in about 100 settings of the beam current, beam energy, and crossover shape. The results show that the stochastic Coulomb interaction blur scales to the power of 0.587±0.101 (1σ) of the linear particle density in a system with a uniform crossover of 400 μm. To decrease the current density in crossover IPL systems can have an aberrated crossover. In case of this type of crossover of 670 μm the current dependency is 0.820±0.072 (1σ). ...

Projection maskless lithography

Recent studies have shown the feasibility of Projection Mask-Less Lithography (PML2) for small and medium volume device production (2-5 WPH) for the 45nm technology node. This PML2 tool concept comprises a combined electrostatic-magnetic electron optical column with 200x de-magnification factor. Instead of a mask there is a programmable aperture plate enabling dynamic beam structuring. Wafer exposure is done stripe-by-stripe with a scanning 300mm wafer stage. Detailed calculations of the PML2 optical column (2-step demagnification) including Monte-Carlo simulations of Coulomb interactions are presented. The extendibility of PML2 technology for the 32nm node will be discussed.

Fabrication of open stencil masks with asymmetric void ratio for the ion projection lithography space charge experiment

For the ion projection lithography space charge experiment [P.W.H. de Jager et al., J. Vac. Sci. Technol. B 17, 3098 (1999)] a suitable stencil test mask has been realized and used. This article addresses the stress engineering and fabrication process of this specific test mask with openings in the range of some few 100 nm up to some 100 μm. This large difference in stencil pattern dimensions causes reactive ion etching (RIE) lag (dependence of the etch rate on feature size and pattern density) during the fabrication process and considerable stress variations across the membrane field. The solution to these problems was by (i) implementing novel doping technologies to create variable thickness areas on the membrane serving as reinforcement and stress relief structures, and (ii) adjusting the design to feature sizes and pattern densities to the same order of magnitude for the e-beam lithography and RIE processing steps. The etching of the openings through the 3 μm thick Si membrane was done by inductively ...

Masked ion beam lithography and direct structuring on curved surfaces

We have previously demonstrated (Proc. SPIE Vol. 4688, 595, 2002; JM3 Vol. 2, Nr. 1, 34, 2003) a depth of focus of several millimeters in masked ion beam lithography (MIBL). This work illustrates the use of this capability to pattern concave and convex spherical substrates 25 mm in diameter and 5.5 mm deep. Features as small as 175nm were printed across a convex substrate with 75 keV He+ ions where the mask-to-wafer gap varied from 1 mm on the center to 6.5 mm on the edge. We also demonstrate, for the first time, the fabrication of 800 nm features in a 4 nm thick Cr coating by masked ion beam direct structuring (MIBS), where 45 keV Argon ions sputter the film through a stencil mask. We demonstrate electronic adjustment of the radial beam profile of the incident ion beam to compensate for the continuously changing angle between the beam and the spherical substrate, thus achieving constant exposure dose (for MIBL) or sputtering rate (for MIBS) a 50 × 50 mm2 field.

Comparison of experimental and Monte Carlo results of stochastic Coulomb interaction in projection beam lithography

Coulomb interaction limits the beam current for a required resolution but it can be influenced by the layout of the optical system. Therefore it is necessary to obtain design information for future charged particle lithography tools. Monte Carlo simulations are an important tool in this design. Two of these programs, COUTRAC and BOERSCH, are compared with experimental data of an Ion Projection Lithography (IPL) set-up. The results of COUTRAC are in agreement with the measurements to within 19% in case of a uniform cross-over. With an aberrated cross-over the difference increases to 126 % near the axis since the experiment showed no increase of Coulomb interaction over the inner quarter of the exposure field while both Monte Carlo models show a monotone increase to the axis.