Microfabricated SERS-arrays with sharp-edged metallic nanostructures

By means of e-beam lithography, vacuum evaporation and ion-beam etching we have developed fabrication routes for the realisation of very small and sharp-edged metallic nanostructures which can be used as substrates for surface enhanced Raman spectroscopy (SERS). The metallic nanostructures are made from gold, are periodically arranged with a pitch of 250 nm and have sharp edges with corner radii of less than 20 nm. These structures show uniform SERS-signals across the whole field size of 200 × 200 μm², and a dependency of the SERS signal intensity and of the signal-to-noise ratio on the pattern geometry. Thus the microfabricated SERS-substrates are suitable for practical applications.     

MCC8: Throughput enhancement of EB direct writer

To obtain higher throughput of more than 5 wafer per hour (WPH), authors propose a high throughput 50 kV e-beam direct writer MCC8 that has eight column. MCC8 has multi column cell (MCC), character projection (CP) with design for e-beam (DFEB) and high current density technologies. Proof-of-concept evaluations for combination between MCC and CP have finished in the MASK-D2I project of ASET, including mix-and-match overlay results of better than 5 nm. By the combination of these proven technologies, MCC8 realizes a throughput of 5 WPH. Furthermore, over 30 WPH can be realized by clustering six MCC8s together.     

Gas sensing of colloidal polyaniline in a chemoresistor consisting of nanometer electrodes

The high conductivity of colloid-conducting polymers is explained by the networking structures and the hopping mechanisms of the metallic particles [1], [2] and [4]. To observe how the metallic region and the networking structures differ in sensing NH₃ gas, E-beam lithography and electromigration were used to make chemoresistors with nanometer-gap electrodes. Colloid Pani was coated on a nanometer gap as a reaction matrix for the gas. The I-V curves were measured in a vacuum and the NH₃ gas was nonlinear. In sensors with a gap of less than 10 nm, there was a two- or threefold increase in the conductivity, and the work function decreased from 600 meV in a vacuum to 250 meV in NH₃ gas. In contrast, the conductivity of sensors with gaps of 200 and 500 nm decreased to 1/1000 in the NH₃ gas environment. The decrease of the conductivity can be explained by electron-hole annihilation, which appears to occur on the surface of the secondary particles. With comb-type electrodes, the operating voltage can be decreased by three orders of magnitude. In electrodes with 200 and 500 nm gaps, the I-V has a step-type response to NH₃ gas.     

Tensile tests of micro anchors anodically bonded between Pyrex glass and aluminum thin film coated on silicon wafer

Micro anchor is a kind of typical structures in micro/nano electromechanical systems (MEMS/NEMS), and it can be made by anodic bonding process, with thin films of metal or alloy as an intermediate layer. At the relative low temperature and voltage, specimens with actually sized micro anchor structures were anodically bonded using Pyrex 7740 glass and patterned crystalline silicon chips coated with aluminum thin film with a thickness comprised between 50 nm and 230 nm. To evaluate the bonding quality, tensile pulling tests have been finished with newly designed flexible fixtures for these specimens. The experimental results exhibit that the bonding tensile strength increases with the bonding temperature and voltage, but it decreases with the increase of the thickness of Al intermediate layer. This kind of thickness effect of the intermediate layer was not mentioned in the literature on anodic bonding.     

Improved properties of Al-doped ZnO film by electron beam evaporation technique

High-quality Al-doped ZnO (AZO) thin films have been fabricated by electron beam evaporation technique. The effect of the growth temperature on the optical and electrical properties of the electron-beam (e-beam) evaporated AZO film is investigated. X-ray diffraction measurements have shown that e-beam evaporated films are highly c-axis oriented at appropriate growth temperature. Transmittance measurement showed that the best optical and structural quality of the e-beam evaporated AZO film occurred at 200 °C. The scanning electron microscope images have shown that the surfaces of the e-beam evaporated AZO became smoother for the growth temperature at and above 200 °C. Finally, the maximum electrical resistivity of 2.5×10⁻⁴ Ω cm and optical transmittance of more than 85% has been found at 200 °C growth temperature, which explains its relation with the crystal quality of the film.     

Titanium-aluminum oxynitride (TAON) as high-k gate dielectric for sub-32 nm CMOS technology

High-k insulators for the next generation (sub-32 nm CMOS (complementary metal-oxide-semiconductor) technology), such as titanium-aluminum oxynitride (TAON) and titanium-aluminum oxide (TAO), have been obtained by Ti/Al e-beam evaporation, with additional electron cyclotron resonance (ECR) plasma oxynitridation and oxidation on Si substrates, respectively. Physical thickness values between 5.7 and 6.3 nm were determined by ellipsometry. These films were used as gate insulators in MOS capacitors fabricated with Al electrodes, and they were used to obtain capacitance-voltage (C-V) measurements. A relative dielectric constant of 3.9 was adopted to extract the equivalent oxide thickness (EOT) of films from C-V curves under strong accumulation condition, resulting in values between 1.5 and 1.1 nm, and effective charge densities of about 10¹¹ cm⁻². Because of these results, nMOSFETs with Al gate electrode and TAON gate dielectric were fabricated and characterized by current-voltage (I-V) curves. From these nMOSFETs electrical characteristics, a sub-threshold slope of 80 mV/dec and an EOT of 0.87 nm were obtained. These results indicate that the obtained TAON film is a suitable gate insulator for the next generation (MOS) devices.     

Fabrication of large scale arrays of metallic nanodots by means of high resolution e-beam lithography

We present the fabrication of large nanodot arrays with very small single dot sizes made of different metals and on different substrates using e-beam lithography and lift-off techniques. Nanodot arrays have a high potential for bioanalytical applications aiming towards single molecule detection. In addition, they can be used as well defined models of heterogeneous catalysts. For this purpose an independent control of the dot size and the distance between the dots is necessary. This is a limitation for many fabrication techniques, which can be overcome by e-beam lithography. However, aiming for the dot size of few tens of nanometers, we observed a strong influence of the beam focusing and astigmatism on the quality of the fabricated nanodot arrays. A significant improvement, i.e. reduction of defect density as well as better control of the dot size, was achieved by modification of the fine focus and stigmation system of the used e-beam writer. Using lift-off technique, we successfully fabricated platinum dot arrays on glassy carbon with target dot diameter ranging from 25 to 35 nm. By applying additional annealing step, we could fabricate nanodot arrays made of gold on SiO₂ with very small dot sizes down to 6 nm and pitch of 100 nm. Furthermore, the generation of large area arrays of nanosized pillars was demonstrated using the same exposure strategy in a negative tone HSQ resist.     

Fabrication of sub-micron high aspect ratio diamond structures with nanoimprint lithography

Polycrystalline diamond with optical quality has been patterned using nanoimprint lithography. Nanoimprint lithography is a rather new method for fabrication of resist structures with features sizes down to at least 20 nm. The pattern used in this article is a grating with a period of 600 nm and a fill factor of 0.5. Using plasma etching the nanoimprinted grating is etched into a freestanding diamond substrate. We have accomplished the fabrication of 300 nm diamond features with a depth of about 2 μm, which corresponds to an aspect ratio of 7.     

Quantitative TEM characterizations of La/B4C and Mo/B4C ultrathin multilayer gratings by the geometric phase method

Artificially fabricated multilayers that exploit the effect of Bragg diffraction at long wavelengths are used as X-ray optical components. Periodic ultrathin bilayer stacks of, alternatingly, a metallic reflection layer and a non-metallic spacer layer prepared as μm-scaled surface grating promise particularly high performance in applications as X-ray filters for high-resolution spectroscopy. Such gratings can be prepared by multilayer deposition onto Si(0 0 1) gratings or by coating flat Si(0 1 1) substrate surfaces with a multilayer, followed by subsequent etching of a grating structure. The structural quality of ultrathin multilayer gratings of both types has been characterized quantitatively combining TEM bright-field imaging of specimen cross-sections and applying a geometric phase method. The geometric phase method has been originally developed for the analysis of local displacement fields from HREM images and allows to obtain the relevant structure parameters. The application of this method to the characterization of Mo/B₄C and La/B₄C multilayer systems shows that the functionally decisive structure parameters, such as layer perfection, layer periodicity, and layer orientation, can be obtained with high precision from evaluation of TEM bright-field images. The essential role of such data analyses for a quantitative characterization of multilayer systems and for optimising the layer deposition techniques in the fabrication of X-ray optical layer systems will be demonstrated and discussed.     

Characterization of electron beam evaporated ZnO thin films and stacking ZnO fabricated by e-beam evaporation and rf magnetron sputtering for the realization of resonators

High quality Zinc oxide thin films have been fabricated by reactive e-beam evaporation in an oxygen environment. The effect of air annealing on the optical and structural properties of the e-beam evaporated ZnO is investigated. Raman spectroscopy has been found to be an efficient tool to evaluate the residual stress in the as-grown ZnO films from the position of the E₂ (high) mode. Photoluminescence and transmittance measurements showed that the best optical and structural quality of the e-beam evaporated ZnO occurred at 300 °C. Finally, thin films of ZnO evaporated by e-beam technique have served to eliminate the compressive stress due to the sputtered piezoelectric ZnO and therefore to improve the quality of the fabricated resonators by stacking these ZnO layers fabricated by electron beam technique and rf magnetron sputtering, respectively.     

拓展临近效应由纳米连接制备亚20nm金属Nanogaps

描述了一种拓展电子束光刻中的临近效应来制备特征尺寸在亚20nm的金属Nanogap的方法. 结合图形转移过程（如去胶等）,利用临近效应灵活有效地制备了金属（如Au或者Ag等）Nanogap结构及其阵列. 采用GDSII软件设计图形,以电子束光刻为手段制备Nanogap的原始纳米连接图形,然后通过去胶过程获得金属的Nanogap. 另外,通过控制电子束光刻的剂量,能够把Nanogap的尺寸降低到约10nm.     

拓展临近效应由纳米连接制备亚20nm金属Nanogaps

描述了一种拓展电子束光刻中的临近效应来制备特征尺寸在亚20nm的金属Nanogap的方法.结合图形转移过程(如去胶等),利用临近效应灵活有效地制备了金属(如Au或者Ag等)Nanogap结构及其阵列.采用GDSII软件设计图形,以电子束光刻为手段制备Nanogap的原始纳米连接图形,然后通过去胶过程获得金属的Nanogap.另外,通过控制电子束光刻的剂量,能够把Nanogap的尺寸降低到约10nm.     

Comparison of quartz and silicon as a master mold substrate for patterned media UV-NIL replica process

Nanoimprint lithography (NIL) is a promising candidate technology to fabricate patterned media for the next generation hard disk drives (HDD). The requirement of pattern pitch for the HDD or discrete-track recording (DTR) media will be as small as from 40 to 50 nm by 2011 or 2012. However not only to create such fine pitch but also long e-beam writing time such as 1 week with conventional high resolution resist ZEP520A are critical. This paper addresses the fabrication processes to combine silicon substrate and a new chemically amplified resist (CAR) for the master molds of this NIL. The e-beam writing speed with this new CAR was achieved over 3-times faster while 50 nm fine DTR patterns were demonstrated with rotary stage e-beam writer. Furthermore, the replication with J-FIL from the master mold into quartz working mold was also demonstrated.     

Improvement of PMMA electron-beam lithography performance in metal liftoff through a poly-imide bi-layer system

Poly(methyl methacrylate) (PMMA) is a commonly used resist for electron-beam lithography. Some primary reasons for the widespread popularity of PMMA include high resolution and low cost. Single layer PMMA has notably poor characteristics in metal liftoff and sub-15 nm resolution as well as poor line edge roughness. Standard problems with liftoff such as tags, feature removal and lack of solvent penetration were alleviated with a poly-imide lift-off layer which increased resolution and allowed better liftoff. The effect of dense feature proximity over-dose was also reduced with this method. Single lines in metal as small as 23 nm were achieved and denser patterns were resolved with a pitch of 50 nm. These results increase the utility of PMMA as a nanolithographic material for fabricating small metallic features by the use of a liftoff technique.     

Platinum zone plates for hard X-ray applications

We describe the fabrication and evaluation of platinum zone plates for 5-12 kV X-ray imaging and focusing. These nano-scale circular periodic structures are fabricated by filling an e-beam generated mold with Pt in an electroplating process. The plating recipe is described. The resulting zone plates, having outer zone widths of 100 and 50 nm, show good uniformity and high aspect ratio. Their diffraction efficiencies are 50-70% of the theoretical, as measured at the European Synchrotron Radiation Facility. Platinum shows promise to become an attractive alternative to present hard X-ray zone plate materials due to its nano-structuring properties and the potential for zone-plate operation at higher temperatures.     

Metal direct nanoimprinting for photonics

In this paper metal direct nanoimprinting (embossing) for the production of metallic microparts is discussed, with a main focus on its suitability for the fabrication of metal-containing optical devices such as photonic crystals, plasmon waveguides or chiral structures. Silver and gold were chosen, since they have the lowest light absorption in the near infrared and visible range. They are also easily formable due to their good ductility, which can be further enhanced by processing at elevated temperature. The mold material, which may form part of the optical device, usually consisted of silicon, but other dielectric materials such as silicon oxide and silicon nitride were also successfully tested.Cylindrical and line-shaped holes with lateral dimensions down to 250 nm and aspect ratios of up to 5 were etched in silicon wafers. All the structures were successfully filled with silver and gold, and the filling of smaller dimensions is also deemed possible. This technique is therefore suitable for producing metal-containing optical devices working in the infrared, at least down to the standard telecom wavelength of 1.5 μm, which requires metallic dimensions of 200-300 nm.     

New selector based on zinc oxide grown by low temperature atomic layer deposition for vertically stacked non-volatile memory devices

We report on the fabrication of Schottky diodes based on n-type zinc oxide (ZnO) grown by atomic layer deposition (ALD) at low temperature (100 °C). These structures are suitable as selector elements in highly integrated non volatile memories based on crossbar architecture. The junctions are fully realized by optical lithography and the smallest investigated structures are 3 × 3 μm² area. Several metals have been tested to single out the most suitable ohmic and Schottky contact materials. The electrical characterisation shows good properties with a forward current above 10⁴ A/cm² and a rectifying ratio of 10⁵.     

E-beam lithography of computer generated holograms using a fully vectorial 3D beam propagation method

A fully vectorial 3D beam propagation method (BPM) has been applied to obtain a required pattern of computer generated hologram (CGH) with a variable profile of four phase levels. The computer reconstruction of the CGH image having one and two focal spots was performed by application of the fully vectorial 3D BPM method. After transferring the CGH by EBL technique an adequate phase profile was obtained. Inter-level parameter method was developed to obtain the estimated an electron beam dose required for the even topographical patterning. Using this method, an EBL exposure dose determined to achieve the required relief amplitude of 1.29 μm was 43 μC/cm². The manufactured holograms showed that the overall proposed production process, from the 3D BPM computer simulation to e-beam lithography, can be used to obtain good quality product with reasonable time and computational resources.     

Electrical properties of Pt interconnects for passive crossbar memory arrays

We report on the fabrication and the electrical characterization of platinum interconnects for novel non-volatile memory technologies. These nanowires present an important and essential contribution to the deep nanometer scaling of alternative architectures beyond CMOS, e.g. nanocrossbar arrays with resistance switching junctions. The nanowires, which have a thickness of 25 nm and a width ranging from 200 nm down to 40 nm, were patterned using electron beam direct writing. They were deposited by UHV electron beam evaporation in combination with a lift-off process.The electrical characteristic is increasingly affected by the contribution of surface effects like scattering at grain boundaries and scattering at the surfaces as the wire dimensions become smaller. With decreasing width of the platinum wire an increasing resistivity was observed, which is consistent with the theories of Fuchs-Sondheimer and Mayadas-Shatzkes. Our studies have shown that the investigated structures possess a high stability concerning the operational current densities up to 4 × 10⁷ A/cm², and an additional annealing step results in an improvement of the electrical wire properties, which is explained by a higher quality of the grain boundaries and side walls.     

Sputtered Ru-Ti, Ru-N and Ru-Ti-N films as Cu diffusion barrier

Ultrathin Ru-Ti alloy, Ru-N and Ru-Ti-N films were fabricated as diffusion barriers to Cu metallization. The thermal stability, phase formation, surface morphology and atomic depth profile of the Cu/Ru-Ti(10 nm)/Si, Cu/Ru-N(10 nm)/Si and Cu/Ru-Ti-N(10 nm)/Si structures after annealing at different temperatures were investigated. Comparing to the single Ru layer, both N doping and Ti alloying improve the thermal stability and diffusion barrier properties to Cu. The Cu on the Ru-Ti layer has better morphology than Cu on the Ru-N layer, while the Ru-Ti-N layer has the best thermal stability and has great potential to be applied as a single layer diffusion barrier.