Marco Jan-Jaco Wieland

MAPPER: high-throughput maskless lithography

MAPPER Lithography is developing a maskless lithography technology. The technology combines massively-parallel electron-beam writing with high speed optical data transport used in the telecommunication industry. The electron optics generates 13,000 electron beams that are focused on the wafer by electrostatic lens arrays which are manufactured by using MEMS manufacturing techniques. Each beam has its own optical column to avoid a central cross-over. This secures high throughput (> 10 wafers per hour) at high resolution (< 45 nm half pitch). The 13,000 e-beams are generated by splitting up a single electron beam that originates from a single electron source and are finally accelerated to 5 kV to expose the resist on the wafer. The e-beams are arranged in such a way that they form a rectangular slit with a width of 26 mm, the same width of a field in an optical stepper. During exposure the e-beams are deflected over 2 μm perpendicular to the wafer stage movement. This means that with one scan of the wafer a full field of 26 mm x 33 mm can be exposed. During the simultaneous scanning of the wafer and deflection of the electron beams the beams are switched on and off by 13,000 light signals, one for each e-beam. The light beams are generated in a data system that contains the chip patterns in a bitmap format. This bitmap is divided over 13,000 data channels and streamed to the ebeams at 1-10 GHz. This paper will explain the design drivers behind the system and provide more detail on the current design. Finally, results of our technology Demonstrator are presented, showing the viability of MAPPERs concept.

Optimum dose for shot noise limited CD uniformity in electron-beam lithography

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. Fo...

Predicted effect of shot noise on contact hole dimension in e-beam lithography

The requirements on dimensional control of contact holes scale with the technology node and are reaching values of only a few nanometers. The allowed 3σ variation of the diameter is typically 10%. In traditional optical lithography, cross section variations occur mainly on a global scale as a result of slowly varying image or process parameters. For electron beam lithography and extreme ultraviolet (EUV) lithography, local variations need more attention. The authors have developed a model for the critical dimension (CD) variations resulting from shot noise and checked the results with Monte Carlo simulations. The model predicts that the necessary number of particles to write a contact is independent of the contact diameter, when both the requirements, the resolution, and resist’s acid diffusion length scale with the size of the contacts. The minimum number of particles required under ideal circumstances is about 500 per contact, but under more realistic circumstances, e.g., for electron beam lithography a...

MAPPER: progress toward a high-volume manufacturing system

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 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 solution for either direct patterning or complementary patterning approach, [1, 2]. For a 10 wph throughput per unit MAPPER will use 13,260 parallel electron beams, delivering 170 μA to the wafer. To realize this large current at the wafer MAPPER uses its patterned beam approach where each beam consists of 49 subbeams [3]. MAPPER is currently realizing its MATRIX platform. This system is one unit in the cluster depicted above and will have a capability of 10 wph (containing the patterned beams approach) and have full overlay capability. One 10 wph unit will have a footprint of 1.1 m x 1.65m. This paper will provide an overview of the development status of this MATRIX platform.

Demonstration of real-time pattern correction for high-throughput maskless lithography

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 electron optical columns can be made with a throughput of 10 wafers per hour. The amount of data for each 26mm x 33mm field is 8 Tbyte. The data rate is approximately 3 Tbyte per second. In order to realize overlay the patterns for different fields on the wafer need to be slightly adjusted. Additionally it is beneficial for the electron optics design to be able to correct a number of tool parameters on the data. For this it is desirable to be able to correct the pattern data in real time. By implementing the correction algorithms on an FPGA test board it has been demonstrated that it is possible to perform the corrections on the exposed data real time. By using a pixel size of 3.5nm, a CDu and overlay contribution of smaller than 1nm 3s is obtained. A datapath for 10wph based on an FPGA implementation that stores the switching data uncompressed in DRAM fits in 4 racks of 2 meters high, with a footprint of 600mm x 700mm each. By replacing the FPGA by an ASIC implementation, and by using real time decompression, the footprint can be reduced in a later stage.

Ready for multi-beam exposure at 5kV on MAPPER tool: lithographic and process integration performances of advanced resists/stack

Maskless electron beam lithography is an attractive solution to address sub-90 nm technology nodes with high throughput and manufacturing costs reduction. One of the key challenges is to meet entirely process/integration specifications in terms of resolution, resist sensitivity, roughness and etch transfer into underlayers. In this paper, we evaluate and identify the optimal stack to fit printing performance using e-beam exposures and etch transfer patterning. Besides imaging performance, other key parameters such as outgassing and charge dissipation due to high current density are also considered to fully achieve targets for the machine developed by MAPPER Lithography.

Resolution of the multiple aperture pixel by pixel enhancement of resolution electron lithography concept

For the sub 100 nm integrated circuit generations we investigate the potential of a new lithography concept: multiple aperture pixel by pixel enhancement of resolution. The wafer is illuminated by a large number of electron beams which are triggered by an equal number of light beams. The light beams are switched on and off by an optical mask. The electron beams are focused by parallel electric and magnetic fields [P. R. Malmberg, T. W. O’Keeffe, and M. M. Sopira, J. Vac. Sci. Technol. 10, 1025 (1973); J. P. Scott, ibid. 15, 1016 (1973)]. By means of computer simulation we determine the point spread function of the electron beam at the wafer. The requirements on the magnetic field form and the alignment are evaluated. It is concluded that the resolution can be better than 1:1 image projection. For 100 nm lines and spaces there is a wide process window.

Cathode ray tube type electron gun as a source for multibeam electron lithography

The authors have investigated the potential of using a dispenser cathode in space charge limited regime for employment in an electron beam lithography electron source. The space charge limitation guarantees stable and uniform emission even if there are small work function variations or bumps and depressions on the surface. Employment of a dispenser cathode in the space charge limited regime enables high beam currents and splitting of the electron beam into many sub-beams for parallel multibeam electron lithography. In the reported experiment, the electron beam is split into 194 sub-beams. The reduced brightness, defined as current divided by normalized emittance, was measured at different cathode temperatures and extraction potentials for a cathode ray tube type electron source equipped with an I-type dispenser cathode. In the central 25 sub-beams, reduced brightness values of up to 106Am−2sr−1V−1 were observed. Such a high reduced brightness in combination with a high total emission current (up to 20mA) ...

Fabrication and characterization of p-type silicon field-emitter arrays for lithography

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 ...

Patterning Fidelity on Low-Energy Multiple-Electron-Beam Direct Write Lithography

The Multiple E-beam Direct Write (MEBDW) technology has been considered a promising solution for the next generation lithography to delineate 32-nm half-pitch and beyond. A low-energy, say 5 keV, e-beam direct writing system has advantages in lower exposure dosage, less heating effect on resist, and less damage to devices underneath, comparing with a high energy one, such as 50 keV or 100 keV. However, the low-energy electron-beam is easily blurred due to forward scattering in the substrate due to its shallow penetration and hence loses resolution. In this paper, variables affecting patterning fidelity of a raster-scan MEBDW system are investigated. In order to realize a MEBDW system with acceptable throughput, a relatively large beam size is chosen for sufficient beam current to sustain throughput while maintaining enough resolution. The imaging resolution loss and the proximity effect, due to beam blurring through the resist, have been observed. The in-house software MOSES, incorporating the Monte Carlo simulation and the Double Gaussian model was used to evaluate 1-D and 2-D pattern fidelity with various exposure conditions. The line width roughness, which represents 1-D fidelity, was evaluated on 32-nm dense lines. Pattern fidelity of 2-D features such as the zigzag poly line and dense metal patterns was also examined. The impact to LWR of using the edge dithering method, instead of dosage modulation, to control the line width accuracy beyond the pixel size was studied.