chapter 19, Technology for LPP Sources

Excerpt

19.1 Introduction

The availability of EUV light sources, measurement tools, and integrated test systems is of major importance for the development of EUVL to be used in high-volume chip manufacturing, which is expected to start in 2009. For economic use of EUVL, a throughput of 100 wafers per hour will be necessary, as estimated from the cost of an EUV exposure tool in combination with sophisticated throughput models. This means that light sources will be necessary that deliver an EUV output power of 115 W at 13.5 nm at the entrance of the illuminator system. The choice of the wavelength is derived from a general convention to use Mo∕Si-based reflection coatings on the near-normal-incidence mirrors of the lithography system. The power specification in combination with the required lifetimes of source components and collector optics makes the source technology the most critical issue in developing EUVL. LPPs as sources for EUV radiation are a promising technical approach because of their physical principle, which allows one to manage the thermal load of source components to provide sufficient component lifetimes. As a result, the EUV output power seems to be scalable to high-volume manufacturing (HVM) requirements.

At XTREME technologies GmbH—a joint venture of Lambda Physik AG, Göttingen, and Jenoptik LOS GmbH, Jena, Germany—EUV sources based on the generation of a plasma by an electrical gas discharge and by laser excitation have been investigated and developed since 2001. This chapter gives an overview of the basics of LPP EUV sources and their technology, the development roadmap, and the current state of the art of these light sources at XTREME technologies. An overview of GDPP EUV sources at XTREME technologies is contained in Chapter 14.

19.1.1 Roadmap

The roadmap for the development of EUV sources until the stage of HVM using EUVL requires so-called microexposure tools (α and β tools), as well as early pre-HVM tools, for the development of the technology. Some of the leading semiconductor manufacturers are expected to ramp up EUVL for HVM at the beginning of 2009, in parallel with 193-nm immersion excimer laser lithography. To support this roadmap, first microexposure tools with small field size were installed in the semiconductor industry as technology pathfinders in 2004. α tools needed to be equipped with sources with 5-W output at lithography exposure-tool manufacturers in 2004. β exposure tools required 15-W EUV sources in 2005. Pre-HVM EUV exposure tools will need the integration of sources with 25–50-W power in late 2006. Finally, HVM sources with 115 W power will be needed starting in 2008.

19.1.2 Requirements for EUV sources for HVM

Lithography exposure-tool manufacturers have agreed to joint top-level specifications of the EUV source performance for HVM using EUVL. The specifications for various EUV source parameters are summarized in Table 19.1. The collector optics module separates the plasma EUV generator from the illumination optics.

The specifications of the EUV source parameters listed in the table hold for the focal plane behind a first-source collector optics. This optics separates the source from the EUV exposure tool. The focal plane defines a clear interface between source and exposure tool—it is often called the intermediate focus (IF). How tremendous these power requirements on LPP EUV sources are becomes clear when the beam path in the source collector from the plasma to the IF is considered. A schematic view of the LPP source collector module is shown in Fig. 19.1.

The source collector to a large extent surrounds the LPP EUV plasma source and is therefore deeply integrated into the source. In Table 19.2, estimates of the necessary EUV power emitted into a 2π-sr solid angle are made, based on the 115-W EUV power specification in the IF for HVM LPP sources. Problems in achieving the necessary power may result from the requirement that the EUV emission volume must show a diameter of about 1 mm or smaller because of the etendue limit defined by the optical system of the exposure tool (see Table 19.1).