Hans C. Pfeiffer

Recent advances in electron-beam lithography for the high-volume production of VLSI devices

Recent advances in scanning-electron-beam lithography techniques have increased the efficiency of serial exposure by several orders of magnitude over the basic SEM approach. A spectrum of shaped-beam systems which combine projection and scanning techniques has been developed for various lithographic applications. The first generation of electron-beam production systems at IBM have demonstrated the feasibility of the shaped-beam technique under manufacturing conditions. More advanced shaping techniques such as VSS and Character Projection provide the means to make a high-resolution lithography for VLSI technically and economically feasible.

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...

PREVAIL: IBM's e-beam technology for next generation lithography

PREVAIL - Projection Reduction Exposure with Variable Axis Immersion Lenses represents the high throughput e-beam projection approach to NGL which IBM is pursuing in cooperation with Nikon Corporation as alliance partner. This paper discusses the challenges and accomplishments of the PREVAIL project. 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 optical axis simultaneously with the deflected beam so that the beam effectively remains on axis. The resist images obtained with the Proof-of-Concept (POC) system demonstrate that PREVAIL effectively eliminates off- axis aberrations affecting both resolution and placement accuracy of pixels. As part of the POC system a high emittance gun has been developed to provide uniform illumination of the patterned subfield and to fill the large numerical aperture projection optics designed to significantly reduce beam blur caused by Coulomb interaction.

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.

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: Proof-of-Concept system and results

Abstract PREVAIL — Projection Reduction Exposure with Variable Axis Immersion Lenses represents the E-Beam Projection approach to Next Generation Lithography which IBM is pursuing in cooperation with Nikon as alliance partner. This paper discusses the challenges and accomplishments of the PREVAIL project. It will focus on the results obtained with a 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 - and POC has achieved its objectives.

EL5: One tool for advanced x-ray and chrome on glass mask making

The state-of-the-art for mask making continues to be driven by 1× x-ray masks. The IBM EL4+ e-beam mask writer at the Advanced Mask Facility in Burlington, Vermont, was originally designed for 0.35 μm ground rules (GRs) direct write at 50 kV, but delivered at 75 kV operation to achieve 0.25 μm GR performance for 1× mask making. Over the next 2 years, with optimization and improvements in each of the subsystems, its performance was enhanced beyond the 0.18 μm GR requirements. It is clear, however, that for 0.13 and 0.1 μm GR mask manufacturing, a new tool is required. It has also become apparent that because of the very high development and tool build costs, and small number of required x-ray mask makers, the same technology must be applicable for chrome on glass (COG) mask making. Based on the experience with EL4+, IBM is designing an EL5 tool which will provide the 0.13/0.1 μm GR performance for 1×, and easily convert to 4× COG exposure for 9 in. glass as well as 300 mm wafer direct write operation. As w...

Variable axis lens for electron beams

An electron optical focusing and deflection system for electron beam lithography has been developed which eliminates off‐axis aberrations up to the third order including transverse chromatic errors by means of a variable axis lens (VAL). Feasibility of the VAL concept has been established experimentally.