Torbjörn Sandström

RET for optical maskless lithography

Due to the ever-increasing mask cost, Optical Maskless Lithography provides an attractive alternative to mask-based lithography, especially for low-volume runs. In order to offer a seamless mix-and-match solution with mask-based scanners, or a complete transfer from mask-based to maskless lithography, the imaging performance of a maskless tool must at least match the performance of a regular scanner. This paper reports results from simulations showing very good agreement with a mask-based scanner at the 65 nm design node, including semi-isolated lines of 50 nm (AttPSM), 45 nm (CPL), and 35 nm (phase edge). Due to a new enhanced rasterization, the results show minor or no influence at all from the pixel grid. The results also indicate that a maskless tool can use the same OPC model as a mask-based scanner, including phase-shifting.

Phase-shifting optical maskless lithography enabling asics at the 65 and 45 NM nodes

An architecture for SLM-based mask writing and optical maskless lithography has been described in previous articles. This work reports on phase-shifting capabilities of different SLMs in light of rasterization and image stability. The tilting mirror SLM proven in the Micronic Sigma7300 mask writer has in other papers been presented as comparable to an attenuated phase-shift reticle. This article will feature the novel tilting phase-step mirror SLM. which has phase shifting capabilities enabling it to emulate hard phase-shift reticles. For a straight-forward rasterization architecture where individual pixels are determined by local pattern data it is required that the complex amplitude created by a mirror is confined to the real axis. This is the case for both the normal tilting mirror and the tilting phase-step mirror. For other micro-mirror designs this might not be true and in the case of the piston-mirror SLM this requirement leads to the demand that two or several mirrors work collectively, loosing degrees of freedom and resolution. The tilting phase-step mirror SLM provides a new rule-set for lithography: no penalty for phase shifting or aggressive OPC, seamless pattern decompositions, choice of optimal tones for each pattern, etc. This gives performance and flexibility not possible before.

New laser pattern generator for DUV using a spatial light modulator

Fraunhofer Institute for Microelectronic Circuits and Systems,Dresden GermanyAbstractA new breed of pattern generators for photomasks using spatial light modulator (SLM) technology with manyarchitectural similarities to that of a modern stepper is under development. The SLM, having an array of individuallyaddressed micromirrors, is illuminated by an excimer DUV laser pulse and imaged onto the surface of a photomask. A stagemoves the photomask to a new position and the SLM is reloaded with a new portion of the pattern, followed by a newexposure. The complete pattern is stitched together at a high rate. Analog modulation of each pixel provides an address gridsatisfying the requirements of the industry roadmap without speed penalty. The new SLM technology has the resolution torival that of e-beam pattern generators, yet provides the productivity of laser patterning due to the massive parallel exposurestrategy. 2001 Elsevier Science B.V. All rights reserved.Keywords: Pattern generator; Photomask; DUV; SLM; Micromirror

High-speed one-dimensional spatial light modulator for Laser Direct Imaging and other patterning applications

Fraunhofer IPMS has developed a one-dimensional high-speed spatial light modulator in cooperation with Micronic Mydata AB. This SLM is the core element of the Swedish company’s new LDI 5sp series of Laser-Direct-Imaging systems optimized for processing of advanced substrates for semiconductor packaging. This paper reports on design, technology, characterization and application results of the new SLM. With a resolution of 8192 pixels that can be modulated in the MHz range and the capability to generate intensity gray-levels instantly without time multiplexing, the SLM is applicable also in many other fields, wherever modulation of ultraviolet light needs to be combined with high throughput and high precision.