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In this paper, the feasibility of a large area exposure for the manufacturing of a NIL master (silicon wafer) dealing with a long writing time is shown. Fraunhofer CNT succeeded in a 355h exposure with a variable shaped e-beam using a commercially available positive tone chemically amplified resist. The wafer has been evaluated in terms of resist contrast and stability, CD uniformity, linearity, pattern quality and defectivity. Electron beam tool parameters like Wehnelt voltage and stage temperature have been analyzed. Different writing strategies and concepts will be considered to optimize the exposure and minimize stitching error defects.

The fabrication of high aspect ratio silicon trenches (critical dimension < 100 nm, aspect ratio > 10:1) by dry etch processing has proven to be a challenge mainly due to limited etch selectivity of conventional hardmask materials to Si. Moreover, for future technology nodes the hardmask thickness will be limited by the thickness of the photoresist. This work focuses on a concept to enable the usage of very thin resist layers (< 100 nm) for patterning of silicon trenches by the integration of an unconventional hardmask stack consisting of SiO2 and ZrO2. Deposition of such material films has been investigated, as well as e-beam lithography exposure and finally pattern transfer by dry etching. Using this hardmask stack and 100 nm thin resist, the fabrication of 35 nm wide trenches with an aspect ratio of ~ 20:1 is demonstrated revealing a very high selectivity (> 100:1) of the ZrO2 layer to Si during the deep silicon etch. A silicon etch rate > 1.5 µm/min was achieved. The ZrO2 layer itself provides the main selectivity improvements of the final hardmask stack.

To realize fast and efficient integrated circuits the interconnect system gains an increasing importance. In particular, this is the case for logic and processor circuits with up to 12 metallization layers. In order to optimize this technology and the according processes it is desirable to generate flexible test structures in small lot production. In opposition to standard optical lithography using masks, Electron Beam Direct Write (EBDW) lithography can rapidly deliver special test structures at low cost. Furthermore, critical dimensions of future technology nodes which are not yet manufacturable by standard optical lithography tools can be produced. In this paper we demonstrate the potential of the 50kV variable shaped EBDW cluster for patterning of future back-end-of-line (BEOL) structures on full 200mm wafers. The patterned wafers have been used to develop next generation copper damascene interconnect processes for critical dimensions down to 50nm.

Electron beam direct write (EBDW) provides high resolution for device and technology development. A new variable shaped beam system with improved electron optics was introduced, which features the capability for the 32nm node. Because of the limited resolution of commercially available chemically amplified resists at this node, it is important to determine a stable and optimum resist process window. To compare a process window under different premises, a universally applicable and low error-prone method is needed. The isofocal dose method is investigated with regard to these properties for its use in EBDW. Experiments were performed on 50kV variable shaped electron beam direct writers using the new electron-optical column SB3050 DW (Vistec Electron Beam GmbH). Exposures are performed at different sites in Dresden (Fraunhofer CNT/Qimonda Dresden), Jena (Vistec) and Stuttgart (IMS Chips); also patterns are exposed on different layer stacks at one site. The strong need for a process window can be fulfilled by the isofocal dose method, which will be shown by contour plots.

Electron beam direct write (EBDW) with a variable shaped beam writer can be applied for very low volume applications like prototyping and personalization. Together with Infineon Technologies, the Center of Competence E-Beam Lithography of Qimonda in Dresden has demonstrated the integration of an E-Beam written back end of line metal layer into a productive 220nm node microcontroller fabrication process. For this purpose an electron beam lithography unit process was developed, and all necessary steps like data prep, proximity correction, alignment and overlay processes and etching processes were reviewed. Several test wafers have been completed in fabrication and measured electrically. At first go, full electrical functionality with a yield >70% could be demonstrated.

When using electron beam direct write for patterning, resist selection (positive or negative) plays an important role. This is because writing time for shaped beam machines is proportional to the mean density of exposed shapes. There is an optimum with respect to writing time when using either the direct exposure or the complementary exposure with reversed resist tonality. Switching from positive to negative resist or vice versa has an impact on writing time. In this paper, we derive the fundamental differences on CD accuracy when using direct or complementary exposure, which is given by the local registration error. Additionally, a simple method is developed to measure this local registration error by simple CD SEM measurement of 1:1 line/space patterns.

Organic photorefractive materials have attracted a lot of interest recently. Their optical response times of a few milliseconds, however, are not yet adequate for the desired commercial applications. We present an investigation on the correlation between the optical response time and photoelectric quantities, such as the hole mobility and the dispersivity of charge carrier transport.

We present a detailed study of the photoelectric as well as the holographic properties of a novel organic photorefractive glass based on triphenylamine. We studied the quantum efficiency Φ of the photogeneration of charges by means of photoinduced discharge measurements. The photoconductivity σ and the charge carrier mobility μ were obtained via dc photoconduction and pulsed time-of-flight experiments, respectively. The holographic characterization was performed by two-wave and degenerate four-wave mixing experiments allowing for the determination of properties such as diffraction efficiency η, modulation of the refractive index Δn, gain coefficient Γ, and phase-shift φp of the investigated system. The experimental data for Φ could be successfully described by the Onsager formalism with a thermalization radius of r0=24 A and a primary quantum yield of Φ0=40%. We evaluated the E field and temperature-dependent measurements of μ using the Bassler formalism yielding a width of the density of states of σ=0.13 eV and a disorder parameter Σ=3.6. On this basis the lifetime and the average drift length of the charge carriers could be estimated from the dc photoconduction experiments. From the photoelectric measurements we also calculated the holographic response time that matched very well to the measured response time and described the E-field dependence satisfactorily. The presented photorefractive system shows outstanding optical properties and stability with respect to degradation. We measured a gain coefficient of Γ=90 cm-1, and a diffraction efficiency of η=27% at a response time of 30 ms for only 40-μm-thick samples. Orientational enhancement was observed and evaluated quantitatively. To our knowledge, this work presents the first determination of each of the above quantities all in one single organic photorefractive material.

A novel organic photorefractive composite system is presented consisting of the amorphous multifunctional low-molar mass compound DR1-DCTA, doped with C 60 as sensitizer and diisooctyl phthalate (DOP) as plasticizer. DR1-DCTA, a carbazole substituted triphenylamine with a covalently attached nonlinear optical azo chromophore unit has been synthesized in a 4 step reaction. The compound forms a stable glass. Its thermal, optical and electrochemical properties are discussed. Holographic experiments (2BC, DFWM) of the photorefractive composite exhibit a fast response time in the range of only 30 ms and a maximum gain coefficient of 90 cm –1 .

A variety of new functional materials based on triarylamines, such as low molecular weight glasses which possess hole conducting/photoconductive properties as well as amorphous bifunctional materials which combine photoconductive and non-linear optical (NLO) properties in one compound, have been synthesized. The new hole transporting glasses belong to the class of 1,3,5-tris(triaryldiamino)benzenes (TTADB). The hyperbranched structure and the large aryl groups attached as substituents lead to high glass transition temperatures (Tg) of up to 141°C in these compounds. The TTADBs do not recrystallize upon cooling from the melt, but form stable glasses. Cyclic voltammetry studies reveal multi-oxidation stages for these compounds of which the first oxidation is reversible. The HOMO energy values determined from CV for TTADB-1 and TTADB-2 are -4.82 and -4.94 eV, respectively. Light emitting diodes with the structure ITO/TTADB-2/Alq3/Al (where ITO=indium tin oxide) show high efficiency and large current carrying capacity. Further, bifunctional compounds have been synthesized in which a photoconductive moiety such as bis(carbazolyl)triphenylamine or bis(diphenylamino)triphenylamine is covalently bound to different NLO chromophores. Some of these compounds are thermally and morphologically stable amorphous materials, possessing Tg in the range from 85 to 122°C. Cyclic voltammetry measurements reveal that the HOMO energy values are between -4.81 and -5.45 eV. In photorefractive measurements using 40 µm thick samples, a diffraction efficiency of 27%, which corresponds to a refractive index modulation (Δn) of 3.5×10-3, a maximum two beam coupling gain coefficient (Γ) of 90 cm-1 and a response time of 40 ms were obtained.

Hydrogen silsesquioxane (HSQ) has interesting applications as an electron-beam resist and hardmask. In this work, HSQ was investigated with regard to the postcoat delay, isofocal dose for an optimum process window, a-beam proximity effect correction, and the molecular structure in order to better understand the processing. Several independent methods were set up and applied to characterize the structuring of HSQ with e-beam including contrast measurements, basedose-over-critical-dimension tests, the isofocal dose method, the doughnut test, and Fourier transform infrared analysis. HSQ was coated on 300 mm bare silicon wafers and exposed with a 50 kV variable shaped e-beam writer in the dynamic random access memory pilot line environment of Qimonda Dresden and Fraunhofer CNT. The postcoat delay showed no significant influence on the exposure results. A dose difference between the basedose and the isofocal dose was observed, which indicates a working point-in a suboptimal process window related to the poor contrast. The FTIR analysis showed a molecular structure change up to 600 mu C/cm(2). Finally, a point-spread-function for HSQ has been generated for the first time. In summary, the results from this detailed characterization show promise for a manageable process.

A series of different fluorinated polymer platforms used for early and current 157-nm photoresists is investigated with regard to blanket etch properties and surface roughness. Besides methacrylic-based polymers applied for 193-nm lithography, fluorine containing norbornene homopolymers, fluorinated cycloolefines, and tetrafluoroethylene (TFE) norbornene copolymers are chosen. Etch rates in different plasmas used for several applications, such as poly, SiN mask open, and selective/nonselective SiO2 etch, are determined and compared to standard 193-nm platforms currently used for DRAM manufacturing. Looking at various base resins, significant differences can be found using HBr- or Cl2-based poly etch conditions and various fluorocarbon-based oxide etch chemistries. Up to 2.4 times higher etch rates in Cl2 and the different CxFy oxide etch recipes are observed for the highly fluorinated cycloolefines and the TFE norbornenes, showing a strong correlation between fluorine content and etch rate. After stress by different etch conditions, the polymer surfaces are characterized using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Surprisingly, the surface roughness of the methacrylic platforms and the norbornene base resin (determined by AFM) are found to be substantially higher than that of the highly fluorinated platforms. These results can directly be correlated to pictures obtained by optical methods (SEM).