J. Romijn

Nanometer-scale lithography for large lateral structures

Abstract Nanometer-scale lithography for structures with large overall dimensions requires an electron beam lithography tool with high resolution capabilities and high positioning accuracy. The specific properties of a commercial electron beam pattern generator and a modified scanning (transmission) electron microscope are described. In addition to the exposure process, good anisotropic etching facilities are crucial. A review is given of high resolution mask techniques illustrated with practical examples.

Experimental study on proximity effects in high voltage e-beam lithography

Abstract For accurate realization of patterns by e-beam lithography it is essential to know the proximity exposure effect. However, both experimental and theoretical results are available mainly for single layer masks on Si in the acceleration voltage range of 20 kV to 30 kV. In this work an experimental study on proximity effects is presented with exposure conditions and substrate systems being typical for modern high resolution lithography, i.e. exposures of single layer and multilayer masks at an acceleration voltage of 50 kV or 100 kV on both Si and substrate layers with a different atomic number. Significant deviations from the two-gaussian model were observed.

Proximity effect in high voltage electron beam lithography on Ti/Pt/Au metallization

Abstract The point exposure distribution function (PEDF) for electron beam lithography on Ti/Pt/Au has been measured for 50 keV and 100 keV electrons. The PEDFs show strong non-Gaussian behaviour. The range of the backscattered electrons does not change whereas the backscatter coefficient is significantly reduced when the electron energy is increased from 50 keV to 100 keV. The data is used in calculations of the dose distribution for a typical Ti/Pt/Au metallization pattern of a microwave bipolar transistor. The results combined with the measured contrast function, provide information over the process parameters needed for well-defined resist patterns and confirm the narrow parameter range observed in preliminary experimental work.

High contrast marks for e-beam direct write made by reactive ion etching

Abstract Square wells, etched in silicon (111) substrates by reactive ion etching, are characterized as alignment marks for direct write electron beam lithography. In addition to compatibility with subsequent silicon bipolar processing steps, the contrast of the marks is comparable to etched V-shaped holes in silicon (100). The mark properties are investigated systematically by varying the size, the depth and the slope of the edges. Marks with a size smaller than 10 μm and a depth larger than about 1 μm have a sufficient contrast (>0.1) for automatic detection by a Philips EBPG-3 after deposition of 0.4 μm SiO 2 and 0.25 μm Ti/ 0.2 μm Pt/0.6 μm Au. Although the slope of the mark edges degrades after deposition of the layers, the marks allow an overlay accuracy between 50 to 100 nm. The application of the marks is not restricted to silicon (111) since the fabrication of the marks only depends on the anisotropic nature of reactive ion etching and this technique is applicable to many other substrates.

Fabrication of 35mm linewidth gold rings and observation of h/e and h/2e magnetoconductance oscillations

Abstract A detailed description is given of the fabrication of gold rings with a diameter of ∼700 nm and a linewidth between 25 and 50 nm. The fabrication technique is based on electron beam lithography in combination with lift-off. In contrast to previous work, the magnetoconductance of these rings shows at low magnetic field oscillations with flux period h/2e superimposed on oscillations with flux period h/e. At high magnetic fields, only the h/e oscillations are observed.

Tungsten calibration markers for electron beam pattern generators

Abstract Tungsten markers have been fabricated with reactive ion etching (RIE) using a trilevel resist stencil as a mask. A low pressure SF 6 -plasma has been used for the etching of tungsten, resulting in sharp edges of the marker. The influence of the metal layer thickness and the type of substrate on the performance as a marker for automatic calibration has been investigated. The thickness has been varied from 12.5 nm to 100 nm. Both silicon and carbon have been applied as substrates. Spot sizes smaller than 40 nm to 100 nm. Both silicon and carbon the marker edge showed to be about 30 nm. After correction for the marker edge the minimum value for the actual spot size which can be obtained, is about 15 nm. At 50 keV beam energy the contrast of the markers on carbon is considerably better compared to the markers on silicon substrates. As a consequence the contrast in the detector signal of the 12.5 nm thick marker on silicon was not sufficient for automatic calibration, contrary to 12.5 nm thick markers on carbon. The measured spot sizes on silicon substrates are up to 30 % smaller than the actual spot size. The overlay accuracy showed to be better than 30 nm.

High resolution patterning of aluminumoxide for intedrated optical devices

Abstract Patterning of aluminumoxide (Al 2 O 3 ) by wet etching or ion milling is not adequate for the fabrication of integrated optical devices with dimension control far within the sub 100 nm range. In this context a high resolution patterning process for Al 2 O 3 is presented, with a trilevel mask system consisting of a bottom layer of chromium (Cr), an intermediate layer of photoresist AZ 1470 and a top layer of high resolution silicon negative electron beam resist SNR. After e-beam exposure and wet development of the SNR resist the pattern transfer is a sequence of dry processing steps. During the processing of chromium a residue was formed. By Auger, X-ray photo-electron spectroscopy and Electron Microprobe Analysis it is shown that the Si from the silicondioxide (SiO 2 ) cover plate on the powered electrode reacts with Cr, O and Cl to form the observed residue. Reactive ion etching (RIE) with a titanium electrode yields a clean surface. The adequacy of the patterning process is demonstrated with the fabrication of an optical filter, containing two gratings with a period of 250 nm, used as reflectors in an integrated Fabry-Perot resonator

Blazed x-ray reflection gratings fabricated by electron beam lithography.

We show that blazed gratings with well-controlled extremely small vertical dimensions can be made in electronresist (PMMA) using electron beam lithography.

Patterning of a Ti/Pt/Au metallization for submicron bipolar transistors made by direct write e-beam lithography

Abstract To fabricate interdigitated bipolar transistors with lateral dimensions well below 1 μm, electron beam lithography and dry etching have been implemented in an on optical lithography based production process. The most demanding step is the patterning of the Ti/Pt/Au metallization layer traditionally used in these devices. Pattern definition by electron beam lithography is severely hampered by the proximity effect. This problem has been studied in detail and local exposure dose corrections are applied to realize well defined resist patterns. The resist pattern is transferred to the Au/Pt layers by argon sputter etching. In this work with lateral dimensions smaller than the thickness of the metal layers the quality of the etch profiles is seriously degraded by redeposition phenomena. However with a Ti layer patterned by lift-off as etch mask, gaps with a defined width as small as 0.6 μm have been opened.

Critical pair-breaking current in superconductors far below Tc

Abstract The critical pair-breaking current in narrow aluminium filaments is measured as a function of temperature to about T T c = 0.3 . Down to T T c = 0.5 agreement with theoretical predictions based on Eilenbergers equations is found.