L. P. Muray

Microminiaturization of electron optical systems

The performance of miniaturized electron optical systems comprising a field emission microsource and a microlens for probe forming has been studied. A complete system measuring millimeters in length and diameter with performance exceeding that of a conventional system over a wide range of potentials (100 V–10 kV) and working distances (up to 10 mm) appears to be feasible. A scanning tunneling microscope aligned field emission microsource offers performance well suited for this application and a selective scaling approach has been developed to allow a wide range of potentials to be applied. Such miniaturized systems can be of significant importance to many areas of electron‐beam applications.

Miniature electron-optical columns

Miniaturized electron-optical systems based on a field emission microsource and a microlens for probe forming have been studied. The performance of systems with dimensions (length and diameter) in the submillimeter to millimeter range can exceed that of a conventional system over a wide range of potentials (100 V to 10 kV) and working distances (up to 10 mm). Electron-optical studies show that not only can a significant reduction in size be achieved but the performance in terms of resolution and especially beam current can also be greatly improved. A key component of the miniaturized system is the field emission microsource which provides an improvement of two to three orders of magnitude in effective brightness over the conventional field emission source. Among the options, the STM aligned field emission (SAFE) microsource appears most promising and a selective scaling approach has been developed to allow this source to operate over a wide range of potentials. Preliminary experimental studies of the microsource have been conducted. >

Experimental evaluation of a scanning tunneling microscope-microlens system

This paper presents the results of the first successfully fabricated scanning tunneling microscope (STM) aligned field emission (SAFE) microsource. SAFE sources have been shown to produce 2–3 orders of magnitude improvement in brightness over conventional field‐emission sources. Lens electrodes were fabricated from 1‐μm thick silicon membranes by electron‐beam lithography and reactive‐ion‐beam etching. Two‐element microlenses were tested in an ultrahigh vacuum (UHV) chamber with a piezo mounted tungsten tip and a dual feedback system. The sources demonstrated stable emission for periods of hours at beam energies of up to 1 kV. Measurement of the virtual source position showed good agreement with calculated values.

Performance measurements of a 1-keV electron-beam microcolumn

A complete 1‐keV electron‐beam microcolumn, measuring only 2.5 mm in length, has been assembled and tested. The microcolumn combines a scanning tunneling microscope aligned field‐emission source with a miniaturized octupole scanner and a microfabricated einzel lens. Expected performance of this configuration, at a working distance of 1 mm and semiconvergent angle of 2.5 mrad, has been calculated to be a probe size of 8 nm with current density exceeding 104 A/cm2. The microcolumn has been successfully operated at 1 keV in scanning transmission mode using a 1‐μm grid sample. Images were acquired with scan fields ranging from 10 to 100 μm and preliminary resolution measurements indicated Gaussian beam diameter of 200 nm. Significant improvements are expected in the near term.

A scanning tunneling microscope controlled field emission microprobe system

A novel approach based on scanning tunneling microscopy controlled field emission with microlens to form an exceptionally high brightness electron source and low aberration electron probe forming system has been explored. Electron optical studies of such a microsource have shown it to have a brightness two to three orders of magnitude greater than conventional field emission sources at energies in the low keV range and the ability to form an ultrahigh resolution probe with diameter in the 1 to 10 nm range in conjunction with additional microlenses. Encouraging preliminary experimental results have been obtained.

Investigation of emitter tips for scanning tunneling microscope‐based microprobe systems

This paper reports the preparation and characterization of field emitter tips for use in a scanning tunneling microscope aligned field emission (SAFE) microprobe system. With the tip being at close proximity to the extraction electrode, new demands are imposed on the emitter tips: (1) a low extraction voltage, (2) a well‐defined emission pattern, preferably a single lobe emission, and (3) a high angular emission density. A combined field ion–field electron emission microscope equipped with a special stage for mounting a small aperture in close proximity to the emitter tip, which was used to simulate the first element of the electro‐optical system of the SAFE microprobe, was used to analyze different tip preparation techniques. A low‐temperature field‐assisted thermal annealing process has been developed to routinely produce sharp W 〈111〉 tips well suited for SAFE operation. Tips having an effective tip radius of less than 500 A, an emission half cone angle of less than 10°, and a peak angular emission den...

Arrayed miniature electron beam columns

Abstract This paper discusses the development of a new approach based on scanning tunneling microscope (STM), microfabricated lenses and field emission technology to form an exceptionally high brightness electron source and miniaturized electron probe forming columns. Electron optical studies have shown that such miniaturized columns, measuring millimeters in length and diameter, can have performance surpassing conventional columns at the same potential. Processes for fabricating microlenses from silicon membrane using electron beam lithography and reactive ion etching (RIE), and a special W field emission tip preparation and annealing procedure have been developed. Prototype 1kV microcolumns based on this concept measuring 2.5 mm have been successfully fabricated and demonstrated to be fully operational. Scanning electron microscope images in the transmission mode have been achieved. The expected performance of such microcolumns coupled with the very significant reduction in physical column size can open new possibilities in many applications which include lithography, microscopy, metrology, testing, storage, etc.. It can be shown that by the use of an array of these miniaturized columns, high throughput sub-100nm lithography can be achieved.

Arrayed lithography using STM-based microcolumns

This paper outlines a novel method based on arrays of electron microcolumns for lithography in the 100nm and below linewidth regime. Throughput on the order of 10 to >50 wafers per hour for 100nm lithography on 200 mm wafers is believed to be achievable depending on the number of columns employed. It requires no mask and can be extended to the sub-100A linewidth regime. It offers the potential of a breakthrough for a low cost high throughput manufacturing process for the new generation of ultra -high density devices. The proposed microcolumns are to be based on a new concept which combines scanning tunneling microscope (STM), microfabricated lenses and field emission technologies to achieve a performance that is expected to surpass the conventional column. The proposed approach will embody an array of these microcolumns, each with its own pattern generation capability, operating in parallel at low voltage to achieve high throughput. The low voltage operation is attractive because proximity effect corrections may not be needed. In addition, an arrayed microcolumn system also has the potential of reducing the cost of the overall system through the compaction of the mechanical system.