David K. Lam

Multiple columns for high-throughput complementary e-beam lithography (CEBL)

Developers of e-beam lithography systems are pursuing diverse strategies to bolster throughput. To achieve parallelism, some e-beam efforts focus on building multiple-columns, and others focus on developing columns with multiple beamlets. In this paper, we discuss the benefits and throughput of a multiple column approach for a particular application: Complementary E-Beam Lithography (CEBL). CEBL is a novel approach where the e-beam lithography system is used only to pattern the smallest features. Everything else is patterned with existing optical lithography equipment. By working hand-in-hand with optical lithography, CEBL provides an urgently needed solution to create next-generation microchips. Moreover, CEBL is extendable for multiple technology generations. We show how a multiple column approach is the best way to meet the requirements for CEBL, including high throughput, high resolution and overlay accuracy, without excess complexity or cost.

Analysis of multibeam's scalable column for complementary e-beam lithography (CEBL)

We present an analysis of the performance of an all electro-static electron-beam column designed for CEBL (Complementary Electron Beam Lithography). To meet the requirements of CEBL at advanced technology nodes (16 nm half-pitch and beyond), a beam size of < 20 nm FWHM (Full Width Half Maximum) and overlay accuracy of < 4 nm are needed. Beam current and beam energy must be optimized to achieve these specifications while meeting throughput requirements. In this paper, we present an in-depth analysis of the resolution of Multibeams electron beam column as a function of beam energy. We focus on an analysis of beam energy below 30 keV, to avoid wafer heating and improve overlay accuracy. The beam size is analyzed with respect to aperture size and current. Spherical aberrations, chromatic aberrations and other effects at various beam energy levels are analyzed. At 7.5 or 5 keV beam energy, the 2 dominating factors in the beam spot size are the image size of the virtual source of the TFE (thermal field emitter) electron gun, chromatic and spherical aberrations. Performance of the column and process window to meet patterning requirements will be discussed.

Image contrast of line-cut / contact hole features in Complementary E-Beam Lithography (CEBL)

Image contrast of line-cut and contact hole features patterned using Complementary E-Beam Lithography (CEBL) at advanced technology nodes are analyzed. The study assumes one beam in each column is used to pattern features less than 20 nm (Full Width Half Maximum, FWHM), consistent with Multibeam’s multi-column vector-scan approach for CEBL patterning. When the feature size approaches the resolution of the e-beam column design, the dose intensity profile follows a Gaussian model. Using Gaussian profiles, the image contrast of line cut or contact hole features can be studied as a function of beam FWHM size, spacing between features, and proximity effect. As expected, the image contrast was dominated by contact hole stepping distance (i.e., spacing between neighboring contact holes) and proximity effect. The plot of image contrast versus contact position becomes very useful in studying the impact of contact spacing, proximity effect and process window in writing line-cut or contact features in CEBL applications. Based on a given design rule of contact hole size and spacing, we can determine the appropriate e-beam size and resist contrast to achieve good image contrast. The relationship between resist contrast and image contrast is discussed to estimate the process window in CEBL applications. Finally, the impact of electron forward scattering in resist is analyzed, including the effects of resist thickness and beam voltage selections. We determined that the influence of back scattered electrons is not a significant factor in CEBL applications when feature pattern density is less than 11%.