Shot noise effects are important to take into account both in the design of resists for lithography and in the design of lithography tools. The statistics of electron or photon arrival gives rise to dose variations, which translate to variations in the size of written features. It is possible to model the shot noise effects in an analytical equation, which shows the influence of all relevant parameters. The sequence of subsequent events in the resist: Secondary electron creation, acid generation, and acid diffusion are incorporated in the model. The model then allows the evaluation of the minimum resist sensitivity necessary for a certain required critical dimension control.

To maximize the performance of an electron-beam lithography system the resist sensitivity must be chosen carefully. Very sensitive resists require only a low illumination dose, thus increasing the throughput. However, shot noise effects may give rise to unacceptable line edge roughness and variations in critical dimension (CD). In this study, the physical parameters which influence the effect of shot noise statistics on CD uniformity (CD-u) and linewidth roughness (LWR) are determined and an analytical model for CD-u and LWR is derived. It is found that the CD-u and LWR depend on the dose, the Gaussian beam probe size, the diffusion length dr of secondary electrons and acids in resist. The influence of background dose and non-shot-noise dose variations must also be taken into account. Monte Carlo simulations are performed to obtain the statistical variation of the two-dimensional solubility distribution of illuminated resist in a developer. The results of this simulation are used to validate the model. For the CD-u and the LWR, different expressions were found for describing the effect of the shot noise because, to describe the LWR, an extra factor must be incorporated to include the effect that spatial frequencies lower than 2 CDs do not have a contribution. Also, the area over which the dose must be integrated for the shot noise calculation is different for CD-u and LWR. For CD-u this area depends on dr∙CD, for LWR on dr2. From the model it can be concluded that shot noise has a significant effect on both the CD uniformity and the LWR and cannot be neglected in the optimization of the dose for high-throughput electron-beam lithography. With the specific relation between the current and the resolution of an e-beam tool, an expression for CD uniformity is found from which the throughput can be maximized for the required CD-u by optimizing the dose, probe size, and diffusion parameter. The background dose and the other dose variations are input parameters for such an optimization. For electron-beam systems with a typical resolution of 30nm and a required CD uniformity contribution of 3.5nm (3σ) due to all dose variations, a dose of 30μC∕cm2 is needed if 20% background and 3% (3σ) non-shot-noise dose variations are taken into account.

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MAPPER Lithography is developing a maskless lithography technology based on massively-parallel electron-beam writing with high speed optical data transport for switching the electron beams. In this way optical columns can be made with a throughput of 10-20 wafers per hour. By clustering several of these systems together high throughputs can be realized in a small footprint. This enables a highly cost-competitive alternative to double patterning and EUV alternatives [1].In 2009 MAPPER shipped two systems one to TSMC and one to CEA-Leti. Both systems will be used to verify the applicability of MAPPER's technology for CMOS manufacturing.This paper presents a status update on the development of the MAPPER system over the past year. First an overview will be presented how to scale the current system to a 10 wph machine which can consequently be used in a cluster configuration to enable 100 wph throughputs.Then the results of today's (pre-) alpha systems with 300 mm wafer capability are presented from the machines at MAPPER, TSMC and CEA-Leti.

p-doped silicon field emitters were studied experimentally to assess their usefulness in multibeam electron lithography. Both individual emitters and emitter arrays were fabricated from single crystal Si wafers with several doping levels. Current-voltage curves were measured for different temperatures and illumination conditions. The typical plateaus in the I-V curves and the sensitivity to light known from the literature were reproduced. Stability measurements showed a very stable total emission current even while the angular emission distribution fluctuated strongly, giving unstable currents in apertured beams. Measured light response times varied between 34 ns and 20 µs, depending on experimental conditions. It was found that in the plateau of the I-V curve, the energy of the electrons shifts over up to 100 eV when changing the extraction voltage over a few kilovolts. In operation, when the current is stable, the energy shift is rather unstable. The experimental results are discussed within a model of the emission process involving an induced p-n junction inside the tip. The conclusion is that p-doped silicon field emitters are not particularly useful for applications in electron beam lithography.