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The electron-beam forward scattering parameter α characterizes the width of the incident beam plus an additional radius due to scattering of primary electrons in the resist. These “forward scattering” effects can be included in proximity-effect correction algorithms by using the point-spread energy function generated by a Monte Carlo simulation. Alternatively, correction algorithms may use a superposition of Gaussian functions to fit Monte Carlo simulations or to fit experimental data. Long-range (β>10μm) effects due to electrons backscattered from the substrate are well characterized by simulations; however, forward scattering effects are difficult to model or measure. Experimental methods of measuring α include the exposure of dot arrays, line arrays, or so-called “doughnut” patterns over a large range of doses. Proximity parameters are then inferred indirectly through fitting line and dot widths. We have instead used a simpler and faster technique based on the method of [Dubonos et al., Microelectron. ...

Magnetic head fabrication for >100 Gbit/in.2 areal density requires minimum lithographic feature size

Experimental measurements of emission stability and energy distributions from a Schottky emitter have been conducted at a tip temperature range from 1330 to 1800 K. The changes of emission properties have been observed at reduced tip temperatures. Noise fluctuations of the probe current increase with decrease of the tip temperature at a constant extraction voltage. The work function of the Schottky emitter increases with decrease of tip temperature. The energy distribution measurements show that the energy width at a given temperature increases with increasing angular emission current density. The energy width also increases with decreasing tip temperature at a given angular emission current density. The results indicate that the energy broadening is mainly contributed by electron tunneling. A comparison of the measured energy width with the theoretical predictions is discussed.

Lithography with an array of miniaturized scanning electron‐beam columns presents one of the most promising high‐throughput possibilities for fabrication of devices with feature sizes less than 100 nm. With scanning electron beams no mask is required and the necessary resolution and alignment of overlay structures are realizable. With arrays of microcolumns, the lithography throughput of a single column can be multiplied. The approach can also be used for a number of lithography related applications such as metrology, inspection, testing, etc. We review the status of the microcolumn program and discuss opportunities and challenges of this approach to high‐throughput nanolithography and related applications. Special emphasis is given to lithography in the 100 nm regime.

A miniaturized 1 kV electron beam column with a 20×20 mm square footprint for application in arrayed lithography was developed. The actual beam forming optics measured from the electron emitter to the last electrode in the beam focusing Einzel lens is only 3.5 mm in length. The electron source is a miniaturized, high brightness (120 μA/sr), low heating power (

A miniature Schottky electron source has been developed and evaluated for applications in a new generation of scanning tunneling microscope aligned field emission microcolumns. Both the physical dimensions and the heating power of this source have been significantly reduced from a conventional source of the same kind. Operating parameters for such a source in a microcolumn environment in terms of emission characteristics, suppressor operating range, etc., have been evaluated. Test results show that very good emission stability at ≥100 μA emission current over several hours, and axial angular current densities in excess of 100 μA/sr can be obtained. Energy distributions have been measured using a carefully calibrated analyzer, and the results show a full width at half‐maximum of 0.4 to 0.76 eV for a 0.3 μm radius Schottky source operating over an angular current density range of 1 to over 100 μA/sr. A significant change in the shape of the energy distribution was observed over this range of operation, indi...

We have built and tested a 1 keV electron‐beam microcolumn that focuses 1 nA of beam current into a 10 nm full width half‐maximum beam diameter at a working distance of 1 mm. The electron source is a miniaturized Zr/O/W Schottky field emitter with 150 μA/sr angular emission current density operating at about 1800 K at a distance of only 100 μm from a silicon membrane extractor electrode. The actual microcolumn is 3.5 mm long assembled mainly from silicon membrane electrodes. Improved einzel lens design and fabrication allowed the operation of this beam focusing element in the accelerating mode. Spherical and chromatic aberrations were reduced by factors of about 2–3, respectively, as compared to the retarding lens mode. Excellent beam current stability with less than 1% variation over several hours has been observed.

A small, 2×2×1.1 cm (height), three‐axis micropositioner has been developed. It combines sub‐nm positioning capability with a large range of travel of more than 1 mm in each direction. Its applications range from scanning proximal probe instruments to sample stages for electron or light microscopes. Two shear piezos are provided in each direction to facilitate motion. They are located at opposite sides of a moving frame which is guided by V grooves on sapphire balls (or rods). A critical point in designing this kind of positioners is how to generate the ‘‘attachment’’ force that holds the parts of the positioner together. Gravity cannot be used as the stage needs to work in all orientations. Springs, connecting the two parts moving relative to each other, generate a force in the direction of the desired motion that is changing with position, making the stage motion nonlinear. Magnets are not appropriate when low‐energy electrons are involved in the vicinity. This problem is solved by especially designed leaf springs coupled to V grooves and balls (or rods). This design allows the attachment force to remain constant and orthogonal to the direction of motion when the stage moves, thus making the motion very linear and independent of the orientation of the positioner. The positioner is exceptionally compact and can be operated in ultrahigh vacuum. These properties make the positioner attractive for atomic scale resolution scanning proximal probe microscopes and a wide range of other applications.

Schottky emission tips have been evaluated with microlenses for applications in scanning tunneling microscope aligned field emission microcolumns. Operation of Zr/O/W 〈100〉 Schottky emission tips at 1800 K with an axial separation of 50–100 μm between the tip and a microlens has been successfully tested. The microlens consists of an extraction electrode with a 5‐μm‐diam hole in a 1‐μm‐thick silicon membrane. The preliminary results of this study show that thermal field emission tips can be operated continuously in close proximity to a microlens over a long period of time, and that good emission stability of less than 1% noise fluctuation over 10 h is achieved with emission currents up to at least 100 μA.

Electron sensitive resists have been exposed on optical masks in a variably shaped spot electron beam lithography system, EL3, at 25 and 50 kV and beam current densities up to 50 A/cm2 to evaluate the effects of resist heating during electron exposure. Resist heating effects are primarily observed in dense patterns at high electron exposure dose. For the purpose of comparison resist heating effects are quantified in terms of the development rate change that is caused by the temperature rise in the resist during electron beam exposure. From an energy density point of view the maximum temperature rise in the resist during exposure is very similar for both 25 and 50 kV exposures. The area on the mask over which the temperature rise in the resist can change resist properties is significantly larger at 50 kV: up to 20 μm at 50 kV compared to ∼5 μm at 25 kV. Using sensitive electron beam resists requiring 1–5 μC/cm2 exposure dose no resist heating effects are observed at beam current densities up to 50 A/cm2.

A new method for computing proximity effect corrections for submicron electron‐beam lithography is introduced. It is based on a fast algorithm for shape partitioning to gain better control for resultant exposure intensity distribution across each shape in the pattern. By careful investigation of the intrashape and the intershape proximity effects the program supplies a means of controlling the submicron pattern delineation. Values for the parameters of the double Gaussian function used in the calculation of the dose variation factors are given for a variety of exposure conditions. Results of the application of the program to delineation of submicrometer patterns in PMMA and AZ 1350 resist on silicon substrate are presented.

AlF3 evaporated thin films of 20–80 nm thickness have been used as self‐developing positive resists and also as negative resists forming metallic Al structures. The exposure mechanism of AlF3 resist has been investigated, and nanometer scale features have been fabricated in both cases at exposure doses of about 20 C/cm2 and 2 C/cm2 at 100 keV, respectively. Using reactive ion etching, AlF3 resist patterns have been transferred into Si3N4, resulting in feature sizes as small as 20 nm.

A piezo‐actuated locking stage is described, which minimizes stage mechanical vibrations relative to the column in a nanometer electron beam lithography system capable of using large 5‐in. diameter substrates. The performance of the piezo locking stage is compared to the performance of a laser position servo system with a resolution of about 5 nm. The measurements show that mechanically locking the stage with respect to the objective lens is far more effective than the servo loop in suppressing mechanical vibrations. With the stage locked, total beam position noise with respect to the substrate has been measured as 2.5‐nm peak‐to‐peak compared to 10‐nm peak‐to‐peak total noise for the servo loop within a bandwidth of 0.25 to 200 Hz. A more detailed analysis of the beam position noise shows that the piezo locking stage reduces the noise component which is caused by mechanical vibrations to 0.4‐nm rms.

Field emitters offer a particularly high potential in e‐beam lithography when writing in the nanometer range. Using a modified VG Microscopes Ltd., model HB 501 STEM, a current of 0.1 nA can be focused into a diameter of 2.5 nm at 100 kV with a final beam aperture of 1.6 mrad. In order to fulfill the demands of microlithography, an objective lens of 15 mm nominal focal length is used. Stage travel in the system is 5 mm in the X and Y directions and the maximum scan field is 250×250 μm2. The beam is deflected electromagnetically under computer control and vector scanning is used during lithography. The 14 bit digital pattern generator has been electrically isolated by optocouplers from the host computer and is connected via analog differential buffers to the deflection amplifiers. The cold tungsten field emitter exhibits a linear decrease in current of about 20% within 20 min of continuous writing. The decrease in current is corrected during lithography by a feedback to the clock frequency of the digital p...

Factors affecting the ultimate resolution of ion beam lithography are discussed. These factors are primary ion scattering, recoil atom scattering, range of secondary electrons, and resist properties (i.e., resist sensitivity and molecule size in the resist). From a consideration of these factors, it is estimated that minimum linewidths of ≲10 nm can be achieved in polymethyl methacrylate (PMMA) using light ions. For heavy ions such as gallium, the resolution limit is estimated to be ∼30 nm with the limitation being due to recoil atom scattering. Fabrication of high resolution silicon nitride stencil masks is described and replication of the masks with protons in PMMA is demonstrated with features as small as 20 nm.

Thin films of metal fluorides such as AlF3, FeF2, CrF2, CsF, LaF3, BaF2, and SrF2 have been used as electron beam sensitive resists. When exposed in an ultrahigh vacuum system by a high intensity electron beam at line doses of 0.5 to 400 μC/cm at 100 keV on a thin membrane substrate, the films act as positive resists. At line doses of typically an order of magnitude less than in the case of the positive resist mode, the films also act as negative resists requiring the use of an appropriate developer. The exposure properties for these metal fluoride resists are discussed along with their film properties, sensitivity, and etching characteristics.

A technique for the measurement of the beam diameter and the positional stability of an electron beam with respect to the substrate using an anisotropically etched silicon edge is described. Measurements are done either in a scanning beam mode to measure the beam diameter or in a stationary beam mode to measure beam positional noise. This technique has been used for a quantitative analysis of the resolution and stability in a 8‐nm spot size electron beam lithography system. The detection limit of the beam position stability measurements is