Werner Stickel

Projection reduction exposure with variable axis immersion lenses: Next generation lithography

Projection reduction exposure with variable axis immersion lenses (PREVAIL) represents the high throughput e-beam projection approach to NGL, which IBM is pursuing in cooperation with Nikon as alliance partner; another e-beam projection approach is SCALPEL pursued by Lucent Technologies. This article discusses the challenges and accomplishments of the PREVAIL project. It will focus on the results obtained with the proof of concept (POC) system. This system was developed to demonstrate key technical building blocks required for high throughput, high resolution e-beam step, and scan projection lithography. The supreme challenge facing all e-beam lithography approaches has been and still is throughput. Since the throughput of e-beam projection systems is severely limited by the available optical field size, the key to success is the ability to overcome this limitation. The PREVAIL technique overcomes field-limiting off-axis aberrations through the use of variable axis lenses, which electronically shift the o...

EL‐4, a new generation electron‐beam lithography system

The new generation electron‐beam lithography system EL‐4 is described, designed for direct wafer exposure as well as optical reticle and x‐ray mask making. The new architecture features control through workstations and local area network communication between these and the microprocessor‐controlled subsystems. The system has on‐line error checking and diagnostics. Wafers up to 200 mm diam are handled individually with a Standard Mechanical InterFace‐compatible, fully robotic system, and are electrostatically chucked to the stage. Reticles are clamped to the stage with double‐sided e/s chucks, ring‐bonded membrane masks are kinematically held in a carrier chucked to the stage. The reticle/mask maker has an internal temperature control system in addition to the clean‐room climate control for the entire mechanical hardware. The electron optics accommodate triangle as well as rectangle spot formation, and for direct write application a throughput‐enhancing third level in the deflection hierarchy. High resolut...

Optimization of variable axis immersion lens for resolution and normal landing

This paper describes a variable axis immersion lens system capable of better than 0.1‐μm resolution at 25 A/cm2 over a 10‐mm2 deflection field with perpendicular landing for both electrostatic (high speed) and magnetic deflections. Computer predictions of spot acuity and landing angles are compared to actual measurements for various degrees of field compensation accuracy.

Recent advances with the variable axis immersion lens

The novel variable axis immersion lens (VAIL) magnetic focusing and deflection system has been shown to produce excellent images over large fields. A practical lithography tool, however, requires high throughput (writing speed) which the magnetic deflection alone cannot provide. This paper describes the incorporation of a unique high‐speed electrostatic deflection system in VAIL which maintains perpendicular landing everywhere on the target. In order to keep the beam at optimum focus when the target height or spot size is changing, a high‐speed focus coil was developed which does not produce any positional errors when excited.

Electron optical image correction subsystem in electron beam projection lithography

To obtain ultimate image fidelity in the PREVAIL electron beam projection lithography system (EB stepper) [Pfeiffer et al., J. Vac. Sci. Technol. B 17, 2840 (1999)], precise dynamic corrections [Zhu et al., Proc. SPIE 2522, 66 (1995)] of an exposed reticle subfield image on the wafer are required. The electron beam column for the EB stepper covers a large deflection area by a curvilinear variable axis lens (CVAL) [Stickel and Langner, J. Vac. Sci. Technol. B 17, 2847 (1999)] type deflection with high current, and very large 0.25 mm square beam. Because of these features together with tighter specifications for electron optics in below 70 nm node, aberrations which can be negligible in prior art electron beam lithography systems, can no longer be ignored. Therefore the electron optical image correction subsystem in the EB stepper is required to precisely correct the increased numbers of possible measurable aberrations caused by deflection as well as by space charge effects. In this article, a systematic ov...

PREVAIL Alpha system: Status and design considerations

An overview is given of the PREVAIL Alpha system program, a joint project of IBM and Nikon to develop a production-level electron project lithography system. The Alpha system program is based on the successful completion of an initial feasibility phase conducted by the IBM/Nikon alliance team and on the PREVAIL proof of concept results reported at EIPBN 1999. The electron beam column and associated electronics and software are under development at IBM’s Semiconductor R&D Center in East Fishkill, New York, while the high speed, high precision stages for both reticle and wafer as well as the overall systems architecture are being developed at Nikon’s facilities. A key architectural objective is the combination of leading edge stepper technology with state-of-the-art PREVAIL electron optics. The design of the electron optics is based on carefully balancing geometric aberrations and Coulomb interactions for optimum resolution at the required high beam current. Cornerstones of the design are the high emittance...

PREVAIL: Operation of the electron optics proof-of-concept system

A proof-of-concept (POC) system was built to prove the electron optics concept of PREVAIL as a viable technology for next generation lithography (NGL), and is described elsewhere (H. C. Pfeiffer et al., J. Vac. Sci. Technology B, these proceedings; W. Stickel et al. ibid., these proceedings). The primary objective of the PREVAIL POC system is the embodiment of the curvilinear variable-axis lens (CVAL) optics which provides superior performance in terms of minimum geometric aberrations over unusually large deflection distances off the system axis (see Stickel et al.). Another major benefit of the CVAL is the minimization of the Coulomb interaction blur, since this approach permits the reduction of the column length to the smallest practical dimensions. The implementation of the PREVAIL CVAL requires a much higher degree of complexity than that of probe-forming systems, even of those which incorporate variable-axis immersion lenses [M. A. Sturans et al., J. Vac. Sci. Technol. B 8, 1682 (1990)] in the projec...

PREVAIL-EPL alpha tool: Early results

The IBM/Nikon alliance is developing an EPL stepper alpha tool based on the PREVAIL technology. This article provides a status report on the alliance activity with particular focus on the electron optical subsystem developed at IBM. We have previously described design features of the PREVAIL Alpha system. The state-of-the-art e-beam lithography concepts have since been reduced to practice and turned into functional building blocks of a production level lithography tool. The electron optical subsystem has been designed, built, assembled, and tested at IBM’s Semiconductor Research and Development Center (SRDC) in East Fishkill, NY. After demonstrating subsystem functionality, the column, an interim mechanical system and all associated control electronics hardware and software have been shipped during January 2001 to Nikon’s facility in Kumagaya, Japan, for integration into the Nikon commercial e-beam stepper Alpha tool. Postshipment activity has been directed primarily toward demonstrating subfield stitchin...

PREVAIL - Evolution and properties of large area reduction projection electron optics

The large area reduction projection optics with beam scanning of the PREVAIL proof-of-concept system is described as the result of an evolution of a variable axis lens doublet system from one with a straight to one with a curvilinear axis, driven by the need to contain image blur caused by Coulomb interactions, and to maintain symmetry of the resulting optics.

PREVAIL: Dynamic correction of aberrations

The curvilinear variable axis lens concept for the PREVAIL proof-of-concept (POC) system, and its practical implementation have been described in a previous publication [H. C. Pfeiffer et al., J. Vac. Sci. Technol. B 6, 2844 (1999)]. The objective of this article is to show experimental results regarding the dynamic compensation of the deflection-dependent focus and astigmatism aberration control in the projected subfield. The POC system contains a plurality of dynamic correction elements in the imaging section between reticle and wafer. Using a pair of properly positioned stigmators, we have demonstrated nearly independent control of feature astigmatism (image quality) and subfield distortion (shape astigmatism). In this article, we will describe a technique that was used to control the subfield distortion. In addition, using three dynamic focus coils, and an inverted sensitivity matrix approach, we have also demonstrated independent control of the subfield magnification, rotation, and axial focus.