Electron Beam Nanolithography Research Articles

Single-domain magnetic pillar array of 35 nm diameter and 65 Gbits/in.2 density for ultrahigh density quantum magnetic storage

Using electron beam nanolithography and electroplating, arrays of Ni pillars on silicon that have a uniform diameter of 35 nm, a height of 120 nm, and a period of 100 nm were fabricated. The density of the pillar arrays is 65 Gbits/in.2—over two orders of magnitude greater than the state-of-the-art magnetic storage density. Because of their nanoscale size, shape anisotropy, and separation from each other, each Ni pillar is single domain with only two quantized perpendicular magnetization states: up and down. Each pillar can be used to store one bit of information, therefore such nanomagnetic pillar array storage offers a rather different paradigm than the conventional storage method. A quantum magnetic disk scheme that is based on uniformly embedding single-domain magnetic structures in a nonmagnetic disk is proposed.

Fabrication of single-domain magnetic pillar array of 35 nm diameter and 65 Gbits/in.2 density

Using electron beam nanolithography and electroplating, arrays of Ni pillars on silicon have been fabricated. The effects of plating current and feature size on the plating rate were investigated. The pillar arrays have a period of 100 nm and the pillar diameters are uniform and as small as 35 nm. Because of their nanoscale size, shape anisotropy, and separation from each other, each Ni pillar is single domain with only two quantized perpendicular magnetization states: up and down. If each pillar were to represent one bit of information, the density of the pillar arrays would be 65 Gbits/in.2—over two orders of magnitude greater than the state-of-the-art magnetic storage density. The ultrahigh density, together with the single-domain formation, make these pillar arrays very attractive for high-density magnetic storage devices and fundamental magnetics studies.

Electron diffraction from gratings fabricated by electron beam nanolithography

The ability to produce nanometre-scale features in certain inorganic films offers the possibility of phase manipulation of electron waves. Gratings consisting of a square array of 100×100 holes with a spacing as low as 10 nm were drilled in thin films of AlF 3 using the 0.5 nm electron probe of a VG HB501 scanning transmission electron microscope (STEM). The sample thickness was chosen so that its inner potential would change the phase of a 200 keV transmitted electron wave by approximately 2 π with respect to a reference wave through a complete hole. Both constant phase and graded phase gratings have been produced. Electron diffraction patterns from these nanostructures have been observed in a JEOL 2000EX TEM at 200 keV. Simple computer simulations were used to aid the interpretation of the diffraction patterns. The graded phase gratings demonstrate conclusively that the phase of the diffracted electron wave can be manipulated by exploiting the effect of the inner potential.

Design and characterization of compact 100 nm-scale silicon metal–oxide–semiconductor field effect transistors

Ultracompact n-channel silicon metal–oxide–semiconductor field effect transistors (MOSFETs) have been fabricated using electron beam nanolithography for all critical levels leading to a first demonstration of silicon MOSFETs which meet 100 nm ground rules. The smallest devices fabricated have active areas which measure only 700 nm×150 nm and are enclosed by a narrow trench isolation scheme. Devices of this size and with physical gate lengths of 120 nm and widths of 150 nm display an extrinsic transconductance of 410 mS/mm at room temperature. This level of miniaturization and performance arises in part from direct application of conventional scaling principles and in part from implementation of a novel device configuration. This article discusses the design of these devices as well as details of their electrical characteristics.

Fabrication of compact 100 nm-scale silicon metal–oxide–semiconductor field effect transistors

The fabrication of exploratory silicon metal–oxide–semiconductor field effect transistors in which all device levels meet 100 nm groundrules is reported. The device design incorporates several novel features which allow for an ultracompact structure. These features include shallow trench isolation, over-the-gate contacts, fully overlapped source, drain and gate contacts and shallow source and drain extensions. This article offers a detailed description of the fabrication process, with an emphasis on high resolution, high accuracy electron beam nanolithography and new reactive ion etching processes. Complete process integration is described which culminates in the successful fabrication of functional compact devices.

The proximity effect in electron beam nanolithography

We have investigated the mechanisms which governs the increase in the width of structures produced by high energy electron beam lithography taking into account the effects of secondary electrons arising from exposure of neighbouring structures.

Automatic mark detection in electron beam nanolithography using digital image processing and correlation

A method of mark detection for a vector scan eCF1-beam nanolithography system has been developed, in particular, taking into account that fairly low beam currents are used in high resolution writing. The digitally stored image of the scanned mark region is compared to a computer generated template using an advanced correlation technique. This method does not require a threshold determination. It exhibits high immunity to noise and poor contrast in the mark signal. The achieved accuracy is better than one beam step size (LSB) even for partially damaged marks. Due to specially chosen mark shapes, the probability of detecting wrong features is low. This paper describes the method and its hardware implementation along with experimental results for accuracy and repeatability of the mark position evaluation.

Multi-Beam Concepts for Nanometer Devices

To overcome the throughput limitations in electron beam nanolithography, a multi beam system is proposed. Theoretical considerations show that this e-beam comb-probe printer with 1024 probes will be capable of combining 25 nm resolution with a maximum beam current of 5 µA. This allows an exposure speed of 0.1 cm2/s, which is orders of magnitude superior to today's most advanced equipment. In addition, the multi beam principle is considered for nanometer pattern inspection and for ion-beam techniques. The basic concepts for these applications are presented. Practical feasibility investigations are the subject of current research.

High-throughput nanolithography using an oxygen-plasma resistant two-layer resist system

LaB6-based electron beam nanolithography systems suffer from low beam current, resulting in low throughput for nanometer-sized patterns. This drawback is further aggravated by the low sensitivity of the standard high-resolution resist [poly(methylmethacrylate) (PMMA)] and by the reduction of intraproximity effect. We have investigated the lithography aspects (contrast, resolution, exposure latitude, throughput, and statistics) of two-layer resist systems consisting of a sensitive positive electron beam resist poly(3-butenyltrimethylsilane sulfone) (PBTMSS) as the top layer, and a variety of materials such as diamondlike carbon film or polyimide as the bottom layer. In these systems, exposed and developed PBTMSS is first oxidized to SiO2, which masks etching of the bottom layer. The pattern is in turn transferred to the substrate either by wet or dry etching using the bottom layer as a mask. Grating patterns with 0.2- and 0.1-μm pitch can be routinely fabricated on semiconductors, and 0.05-μm pitch patterns have been demonstrated. To achieve such high resolution, a low-strength developer is used, but a throughput about 30 to 50 times higher than that of PMMA can still be obtained. Gratings now can be patterned in a few hours over square-centimeter areas. Such a task would require days for PMMA. Implications of our results on lithography system clock rate and resist resolution–sensitivity tradeoff are also discussed.

Nanolithography with an acid catalyzed resist

Poly(p-t-butyloxycarbonyloxystyrene) resist shows great potential for electron-beam nanolithography, particularly as a negative resist. The resist has been used to fabricate structures with linewidths as narrow as 18 nm. The resist can be processed in both positive and negative modes depending upon the developing solvent, and linewidths <40 nm have been obtained in both cases. The exposure mechanism is based upon a new resist design principle incorporating an acid catalyst. The sensitivity of the resist can be at least six times higher than that of polymethylmethacrylate (PMMA) exposed under the same conditions (i.e., 50 kV, thin membrane substrates). The exposure distribution for the resist in the negative mode has been determined, confirming its resolution potential. These data indicate that the increase in sensitivity realized through incorporation of a gain mechanism in the resist chemistry is not achieved at a large loss in resolution. In its negative mode, the resist exhibits adequate ion etch resistance for device fabrication. The resist compares favorably with other negative resists for nanolithography with regards to both resolution, and its ability to be cleanly removed by rf plasma oxidation after serving as an ion etch mask.

X-ray microscope images with Fresnel zone plates fabricated by electron beam nanolithography

For applications in an imaging X-ray microscope, Fresnel zone plates have been fabricated by electron beam nanolithography and suitable pattern transfer techniques. Images of biological specimens have been taken with a microzone plate of 250 zones and 55 nm outermost ring width at the electron storage ring BESSY in Berlin.

Spatial resolution limits in electron beam nanolithography

Computer simulation of high energy primary electron scattering and subsequent generation of ‘‘fast’’ secondary electrons in thin film targets is demonstrated with Monte Carlo techniques. A hybrid Monte Carlo model is utilized to calculate the generation and subsequent spatial trajectory of each secondary electron in the target. The three-dimensional spatial distribution of energy dissipation by such fast secondary electrons is shown to be the fundamental resolution limit for electron beam lithography with high voltage beams (100 keV) and thin film polymer targets. The dependence of resolution on beam voltage and film thickness is presented, and quantitative comparison is made between these new Monte Carlo calculations and the limited amount of experimental data available in the scientific literature.