S. Thoms

Fabrication of 3 nm wires using 100 keV electron beam lithography and poly(methyl methacrylate) resist

We report the fabrication of 3 nm NiCr wires on a solid silicon substrate. The process uses conventional 100 keV electron beam lithography and poly(methyl methacrylate) resist. The wires consist of short, continuous, lengths of metal that are attached at either end to 20 nm wide wires. Instead of exposing continuous lines in the resist, we blank the beam for several pixels to leave a gap. The resist in the gap is therefore exposed only by the secondary electrons from the neighboring regions that are directly exposed by the beam. The technique is repeatable and we demonstrate that it is possible to make 3 nm features on demand.

Passivation of donors in electron beam lithographically defined nanostructures after methane/hydrogen reactive ion etching

We show that while the methane/hydrogen gas mixture is capable of etching GaAs and AlGaAs controllably and with little residual damange, it leads to the passivation of donors in both semiconductors. The passivation can, however, be annealed out with a short thermal cycle to 300 °C. The effects of passivation are illustrated and characterized by processing uniform epilayers and quantum wires in n+‐GaAs and modulation doped AlGaAs/GaAs heterostructures.

Fabrication of multipassband moiré resonators in fibers by the dual-phase-mask exposure method

We report on the fabrication of in-fiber moiré filters by dual exposure of a nondedicated chirped phase mask. This simple technique produces broadband filters whose structure depends only on an intermediate stretch between two identical UV exposures. We demonstrate moiré filters with as many as four narrow passbands within a 2-nm stopband.

Direct imprint of sub-10 nm features into metal using diamond and SiC stamps

We demonstrate the transfer of sub-10nm features into nickel using a hard stamp. Nanostructures were transferred directly from diamond and SiC in a single step by pressing the stamp into nickel at room temperature. The patterns were generated using ultrahigh resolution electron beam lithography. Patterns were transferred to the diamond and SiC using RIE etching with an O2 plasma used for the diamond and a SF6+O2 mixture used for the SiC. Hydrogen Silsesquioxane was used as a resist and served as a mask in the plasma etching.

Generic scanned-probe microscope sensors by combined micromachining and electron-beam lithography

We present a novel method for the fabrication of generic scanned-probe microscope probes by performing multiple level direct-write electron-beam lithography on the apex of micromachined atomic force microscope tips. Pattern transfer is by conventional etching or liftoff in a wide range of materials. Lithographic resolution is 50 nm or better. The substrates support the use of automatic alignment and allow for the fabrication of 50 probes/in2. The integration of a force-sensing cantilever permits simple height regulation of the probes during operation. The technology is illustrated by the fabrication of thermocouple and near-field optical probes.

Dry etching damage in III–V semiconductors

Dry etching using ions can cause damage to the underlying semiconductor. This paper discusses damage in III–V semiconductors and presents examples of etching conditions under which it can be effectively eliminated. A distinction between surface and sidewall damage is made and methods of measuring both parameters are reviewed. It is noted that the noble gases cause relatively deep damage, while under the correct circumstances, etchants that have a marked chemical effect can cause much less damage. The present state of understanding of the mechanisms for the damage is discussed.

The fabrication of high resolution features by mould injection

This paper describes work carried out to develop a relatively simple procedure to mass produce high resolution and large area features in polymer by mould injection. Fabrication of the injection mould using high resolution electron beam lithography is described and the results of production runs evaluated. Feature sizes of less than 100 nm were obtained and 4 centimetre long 1:1 gratings with periods down to 1μm produced. Features with high aspect ratio proved difficult to form routinely however it is envisaged that further optimisation of the process will resolve these difficulties. It is our belief that the ultimate resolution of this technique is limited largely by the quality of mould tool manufacturing.

Electron Mobility in Surface- and Buried-Channel Flatband

In this letter, we investigate the scaling potential of flatband III-V MOSFETs by comparing the mobility of surface and buried-channel In_0.53Ga_0.47As devices employing an atomic layer-deposited Al₂O₃ gate dielectric and a delta-doped InGaAs/InAlAs/InP heterostructure. Peak electron mobilities of 4300 cm²/V · s and 6600 cm²/V · s at a carrier density of 3 × 10¹² cm^-2 were determined for the surfaceand buried-channel structures, respectively. In contrast to similarly scaled inversion-channel devices, we find that the mobility in surface channel flatband structures does not drop rapidly with the electron density, but rather high mobility is maintained up to carrier concentrations around 4 × 10¹² cm^-2 before slowly dropping to around 2000 cm²/V · s at 1 × 10¹³ cm^-2. We believe these to be world leading metrics for this material system and an important development in informing the III-V MOSFET device architecture selection process for the future low-power highly scaled CMOS.

\hbox{In}_{0.53}\hbox{Ga}_{0.47}\hbox{As}

In this letter, we investigate the scaling potential of flatband III-V MOSFETs by comparing the mobility of surface and buried-channel In_0.53Ga_0.47As devices employing an atomic layer-deposited Al₂O₃ gate dielectric and a delta-doped InGaAs/InAlAs/InP heterostructure. Peak electron mobilities of 4300 cm²/V · s and 6600 cm²/V · s at a carrier density of 3 × 10¹² cm^-2 were determined for the surfaceand buried-channel structures, respectively. In contrast to similarly scaled inversion-channel devices, we find that the mobility in surface channel flatband structures does not drop rapidly with the electron density, but rather high mobility is maintained up to carrier concentrations around 4 × 10¹² cm^-2 before slowly dropping to around 2000 cm²/V · s at 1 × 10¹³ cm^-2. We believe these to be world leading metrics for this material system and an important development in informing the III-V MOSFET device architecture selection process for the future low-power highly scaled CMOS.

MOSFETs With ALD

A new process has been developed to fabricate T-shaped gates and Γ-shaped gates for high performance metal–semiconductor field effect transistors and high electron mobility transistors using a bilayer of Shipley UVIII DUV resist and poly(methylmethacrylate). The two resists are separated by a 20–30 nm thick layer of aluminum and after patterning by electron beam lithography a two-stage development technique is used to remove the aluminum and to produce well-defined resist profiles. The process can be used to fabricate T-shaped and Γ-shaped gates with footwidth sizes as small as 50 nm and headwidth to footwidth ratios in excess of 40:1 for T gates and 35:1 for Γ gates. The ability to fabricate gates with these dimensions arises from the fact that the UVIII resist is considerably more sensitive to electron beam exposure than PMMA. Further benefits derived from using a UVIII: PMMA bilayer are better control of footwidth dimensions and shorter electron beam patterning times compared to bilayers of PMMA with c...