P.D. Prewett

Sub10nm silicon field emitters produced by electron beam lithography and isotropic plasma etching

There is a growing interest in the fabrication of nanometer scale silicon tips for use as field emitters for that panel displays. Advantages include brightness, efficiency and spatial resolution. Additionally, field emission devices offer an alternative technology for high speed, radiation-resistant microcircuits operating over wide temperature ranges. This paper reports on a new fabrication route for producing arrays of silicon nanotips with precise control of tip size and geometry without any oxidation sharpening step.

Focused ion beam deposition of carbon for photomask repair

Abstract Initial results from a series of experiments to study focused ion beam deposition (FIBD) of carbon from a hydrocarbon gas are reported. Deposition and resputtering are the competing processes which determine the overall growth rate of the carbon patch material in mask repair. Deposition and resputtering sensitivities have been measured for a range of hydrocarbon gas pressures and different scan strategies. There is evidence of pixel dose rate related effects associated with different scan strategies. A model for the deposition process has been developed, which is consistent with the results.

Fabrication of sub‐10 nm silicon tips: A new approach

Nanometer scale silicon tips are becoming increasingly important for use as field emitters. Applications include high resolution field emission displays and ultrahigh‐speed devices. Of crucial importance is the precise control of tip shape and size if field emitters are to be used as microelectronic elements. This article reports on the fabrication procedure of silicon based gridded field emitter tips, using a new fabrication route which eliminates the need for an oxidation sharpening step.

Comparison of focused ion beam and laser techniques for optimal mask repair

Abstract As the critical dimensions of masks and reticles approach 1 μm, the limitations of the laser repair technique are becoming increasingly apparent. The use of focused ion beams for mask repair offers a process with significantly improved resolution over that achievable using lasers. A comparison of the two techniques for opaque defect repair reveals a significant degree of mask damage associated with laser repair. In contrast, the FIB process shows much better edge acuity with little damage to the mask. Some staining of the glass substrate does occur but this is found not to be a problem during subsequent printing using standard processes.

Laminated dry film resist for microengineering applications

Abstract An innovative technology with a dry film resist (Riston) for use in microsystem engineering applications is presented. In view of the simplicity of forming a controllable resist thickness (20 – 100 μm/level), inherent planarization for multilevel processes in 3D microsystems and high, stable over-wafer thickness uniformity, we have investigated the use of dry film resists to realise high aspect ratio microstructures > 10:1 using both reactive ion etching (RIE) and excimer laser ablation.

Effects of focused ion beam reticle repair on optical lithography at i‐line and deep ultraviolet wavelengths

The repair of opaque defects in photomasks and reticles using focused ion beams (FIBs) can give rise to staining of the quartz substrate. A purpose built system is used to measure the transmission properties of stained regions and reveals relative fractional transmission of 60% at i line, falling to 25% in the deep ultraviolet (DUV). A series of printability trials using commercial steppers and processes at i line and DUV wavelengths shows the effects in resist images due to these stains in comparison with the original defects. The negative resist process used at DUV affords some protection against the printability of stained areas. However, the results confirm that antistain processes must be used with FIB repair which can be counter productive without them.

Electron beam lithography using chemically-amplified resist: resolution and profile control

The effect of post exposure bake and softbake conditions on the sensitivity of AZPN114 has been investigated experimentally. A bilayer system for undercut structures has been achieved using two layers of AZPN114 with different softbake temperatures. A single layer of AZPN114 has also been used to produce undercut and tailored resist profiles by two different multiple exposure strategies at different beam energies.

Gallium staining in FIB repair of photomasks

Abstract Focused ion beam repair of opaque defects in photomasks using Ga+ions, produces a stain which may be measured using a purpose built photometric system. A simple model for the absorption due to the implanted gallium has been developed. The stain may be removed by an RIE plasma etch process, combined with chemical cleaning which restores the relative fractional transmission to 100%.

A new e-beam method for grey scale 3D optical elements

A new e-beam lithography grey scale method has been developed for phase shift optical elements production. It could be used only for 3D elements with lateral dimensions of constant height regions much greater than the resist height and provides an extremely precise structure height control with a very high process latitude. Resist structure height in it is controlled not by the local dose but by the exposed cell area.

X-ray micro- and nanofabrication using a laser–plasma source at 1 nm wavelength

A picosecond excimer laser–plasma source has been constructed, which generates an x-ray average power of 2.2 and 1.4 W at the wavelengths required for proximity x-ray lithography: 1.4 nm (steel target) and 1 nm (copper target), respectively. The plasma source could be scaled to the 50–75 W x-ray average power required for industrial lithographic production by scaling the total average power of the commercial excimer laser system up to 1 kW. The 1 nm x-ray source is used to micromachine a 2.5 THz microwave waveguide–cavity package with a 48 μm deep, three-dimensional structure, using the LIGA technique. The 1 nm x-ray source is also used to print 180 nm long transistor gates in the fabrication process of field-effect transistors.