Thomas Elster

Optimization of MSB for future technology nodes

In the ITRS roadmap [1] increasingly long mask write and cycle time is explicitly addressed as a difficult challenge in mask fabrication for the 16nm technology node and beyond. Write time reduction demands have to be seen in relation to corresponding performance parameters like Line Width Roughness (LWR), resolution, placement as well as CD Uniformity. The previously presented Multi Shaped Beam (MSB) approach [2, 3] is considered a potential solution for high throughput mask write application. In order to fully adapt the MSB concept to future industrys requirements specific optimizations are planned. The key element for achieving write time reduction is a higher probe current at the target, which can be obtained by increasing the number of beamlets as well as applying a higher current density. In the present paper the approach of a 256 beamlet MSB design will be discussed. For a given image field size along with a beamlet number increase both beamlet pitch and size have to be optimized. Out of previous investigations, one finding was that by changing the demagnification after the beam forming section of the MSB column the overall performance can be optimized. Based on first electron-optical simulations for a new final lens a larger demagnification turned out to be advantageous. Stochastic beam blur simulation results for the MSB reduction optics will be presented. During the exposure of a pattern layout the number of used beams, their shape and their distribution within the image field varies, which can lead to space charge distortion effects. In regard to this MSB simulation results obtained for an image field of approximately 10x10ìm² will be presented. For the 256 beamlet MSB design and resist sensitivities of 20μC/cm2, 40μC/cm2 and 100μC/cm2 write time and LWR simulations have been performed. For MSB pattern data fracturing an optimized algorithm has been used, which increased the beamlet utilization factor (indicates the mean number of beamlets which are used per multi-shot). Finally an update with regard to the required changes of the data path architecture for the 256 beamlet MSB approach will be given. Data integrity as an important aspect of the production worthiness of such a systems will be discussed specifically.

Coulomb Blur Advantage of a Multi Shaped Beam Lithography Approach

This paper describes a new multi beam approach in electron beam lithography called Multi Shaped Beam (MSB). Based on the well known Variable Shaped Beam (VSB) principle, the single shaped beam arrangement is extended and complemented by an array of individually controlled shaped beams. The positive effect of the MSB approach on resolution limiting stochastic beam blur due to Coulomb interactions will be highlighted applying detailed electron-optical Monte-Carlo simulations. To verify the feasibility of the above-mentioned new approach, there is also depicted a proof-of-lithography test stand based on a complete e-beam-lithography system containing MSB-specific hardware and software components.

Projection maskless lithography

Recent studies have shown the feasibility of Projection Mask-Less Lithography (PML2) for small and medium volume device production (2-5 WPH) for the 45nm technology node. This PML2 tool concept comprises a combined electrostatic-magnetic electron optical column with 200x de-magnification factor. Instead of a mask there is a programmable aperture plate enabling dynamic beam structuring. Wafer exposure is done stripe-by-stripe with a scanning 300mm wafer stage. Detailed calculations of the PML2 optical column (2-step demagnification) including Monte-Carlo simulations of Coulomb interactions are presented. The extendibility of PML2 technology for the 32nm node will be discussed.

Tool and process optimization for 100-nm maskmaking using a 50-kV variable shaped e-beam system

An overview will be presented of high-resolution e-beam lithography equipment issues and processes used in the fabrication of photomasks/reticles needed for 100nm maskmaking. As reported and discussed repeatedly, the emerging advanced optical and next generation lithography for 100nm and beyond requires masks with a well controlled CD variation and high pattern placement accuracy. Our paper shows the possibility of 100nm patterning by using standard resist materials (e.g. ZEP 7000) or other advanced resist materials under optimized processing exposed with a 50keV shaped-beam vector-scan Leica SB350MW mask writer e-beam pattern generator. The presented results will show that this commercially available e-beam system together with built-in exposure optimization methods (proximity, local heating, fogging) meets the challenges of the 100nm device generation with extendibility to at least 70nm. Details of the exposure optimization possibilities, including a flexible determination method of proximity input parameters and resist-pattern transfer methods maintaining the required CD-control will be discussed also.