Focused ion beam repair of opaque defects in 5X reticles produces post repair stains which result... more Focused ion beam repair of opaque defects in 5X reticles produces post repair stains which result in ghost defects in wafer prints produced at G-line, I-line, and DUV wavelengths. These stains can be removed using a post repair plasma process which restores transmission to almost 100%. However, a new in situ process is preferred which reduces stains to acceptable levels. The key to the new process is an understanding of factors affecting sputter yield. The effectiveness of the in situ antistain procedure is demonstrated through wafer lithography at all three wavelengths showing an absence of ghost defects following repair.
... 3ym thck) was carried out using chemical vapour deposition at a target temperature of 625°C. ... more ... 3ym thck) was carried out using chemical vapour deposition at a target temperature of 625°C. The deposited layers were subsequently implanted with boron at 6OkeV in order to producep-type polycrystalline ... 4. 5. 6 EC Boswell, and PR Wilshaw, J.Vac.Sci.Technol., B 11 (1994 ...
Electron beam resists having high sensitivity and high resistance to dry etching are under invest... more Electron beam resists having high sensitivity and high resistance to dry etching are under investigation for sub-half micron device production using 5x reticle masks. The effects of dry etch process conditions on the performance of the novolac based chemically amplified AZPN114 and onium salt ...
An application of a simple and low-cost novel volumetric linewidth measurement technique to e-bea... more An application of a simple and low-cost novel volumetric linewidth measurement technique to e-beam lithography process optimization for the positive CAR UVIII demonstrates clearly its efficiency and accuracy. It helps to optimize exposure, PEB and development procedure to get the highest possible process latitude. For this optimized procedure structure linewidth does not exceed 10% for a 20% exposure variation. PEB temperature and time deviation for 1 degree(s)C and 1 second lead to a 0.5 nm and a 2.5 nm linewidth run-out correspondingly.
As the critical dimensions of masks and reticles approach i ~m, the limitations of the laser repa... more As the critical dimensions of masks and reticles approach i ~m, 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.
A high-efficiency focusing waveguide grating coupler (FWGC) using parallelogramic groove profiles... more A high-efficiency focusing waveguide grating coupler (FWGC) using parallelogramic groove profiles is proposed, designed and fabricated. A new waveguide grating structure has been employed which consists of bilayered grating with one grating etched into the guiding layer and the other into a high-index cladding layer. Computer simulation shows that both high directionality and large radiation decay factor are obtainable with this structure. Fabrication of this FWGC by electron beam lithography is described. A coupling efficiency of 86% and focusing spot size full-width at half maximum (FWHM) of around 10 m have been achieved.
Field emission characterisation of gridded silicon FEAs was carried out before and after anodisat... more Field emission characterisation of gridded silicon FEAs was carried out before and after anodisation. Each sample contains ten gridded FEAs with array sizes varying from 1 to 10x1 0. For each sample, both current-voltage and current-time measurements of each FEA were carried out before and after anodisation. The morphology and thickness of the porous silicon layer on the emitters were controlled by the anodising current density and duration of the anodisation process. The emission uniformity of FEAs was evaluated by comparing the I-V curves from different FEAs, which show that the emission uniformity had been improved after anodisation. In addition, the I-t measurements show that the emission stability of FEAs is very sensitive to anodisation time, and it is essential to use a very short anodisation time (-0.1 second) to obtain stable emission currents. Under these conditions no adverse effects of the anodisation process on emission stability have been found whilst the improvements in operating voltage and unifornzity are maintained. I. INTRODUCTION It has been demonstrated that the performance of ungridded single crystal silicon field emitters is improved by the formation of porous silicon on their surface, using a process known as anodisation[l]. A large improvement in maximum field emission current and lower starting voltages can be obtained. Anodisation is a simple process and can be easily integrated into the fabrication processes of gridded silicon field emitter arrays, investigation of the effect of anodisation on gridded FEAs to date [2] showed that the operating voltage was lowered after anodisation. However, the investigation was limited to n-type silicon FEAs. No studies of the effect of anodisation on emission stability and lifetime of silicon FEAs have been previously reported. In this study we investigate the effect of anodisation on the field emission performance of p-type silicon FEAs, with the emphasis on the emission uniformity and stability.
Microneedle patches have received much interest in the last two decades as drug/vaccine delivery ... more Microneedle patches have received much interest in the last two decades as drug/vaccine delivery or fluid sampling systems for diagnostic and monitoring purposes. Microneedles are manufactured using a variety of additive and subtractive micromanufacturing techniques. In the last decade, much attention has been paid to using additive manufacturing techniques in both research and industry, such as 3D printing, fused deposition modeling, inkjet printing, and two-photon polymerization (2PP), with 2PP being the most flexible method for the fabrication of microneedle arrays. 2PP is one of the most versatile and precise additive manufacturing processes, which enables the fabrication of arbitrary three-dimensional (3D) prototypes directly from computer-aided-design (CAD) models with a resolution down to 100 nm. Due to its unprecedented flexibility and high spatial resolution, the use of this technology has been widespread for the fabrication of bio-microdevices and bio-nanodevices such as microneedles and microfluidic devices. This is a pioneering transformative technology that facilitates the fabrication of complex miniaturized structures that cannot be fabricated with established multistep manufacturing methods such as injection molding, photolithography, and etching. Thus, microstructures are designed according to structural and fluid dynamics considerations rather than the manufacturing constraints imposed by methods such as machining or etching processes. This article presents the fundamentals of 2PP and the recent development of microneedle array fabrication through 2PP as a precise and unique method for the manufacture of microstructures, which may overcome the shortcomings of conventional manufacturing processes.
This work is concerned with the performance evaluation of thermally activated bimorph cantilevers... more This work is concerned with the performance evaluation of thermally activated bimorph cantilevers. A range of cantilevers has been fabricated using state of the art microfabrication techniques. The cantilevers are 600 μm long and have initial (non-resonant) displacement of 250 μm. Following the successful fabrication of wafer-scale bimorph cantilevers thermal/mechanical tests have been carried out under loaded and non-loaded conditions.
An experimental investigation at energies of 2-6keV has been carried out on the positive chemical... more An experimental investigation at energies of 2-6keV has been carried out on the positive chemically amplified resist AZPF 514. A new way of suppressing the "T-topping" effect, based on resist shower irradiation with low energy electrons, is suggested. This does not prevent contamination of the upper resist layer, but it does provide an easy method of removing the contaminated layer at the very start of resist development.
We have measured the electrical resistivity of a single strand of a ferromagnetic Ni nanowire of ... more We have measured the electrical resistivity of a single strand of a ferromagnetic Ni nanowire of diameter 55 nm using a 4-probe method in the temperature range 3 K-300 K. The wire used is chemically pure and is a high quality oriented single crystalline sample in which the temperature independent residual resistivity is determined predominantly by surface scattering. Precise evaluation of the temperature dependent resistivity (ρ) allowed us to identify quantitatively the electron-phonon contribution (characterized by a Debye temperature θR) as well as the spin-wave contribution which is significantly suppressed upon size reduction.
We have measured the resistance vs temperature, R͑T͒, and current vs voltage, I͑V͒, for a series ... more We have measured the resistance vs temperature, R͑T͒, and current vs voltage, I͑V͒, for a series of submicrometer YBa 2 Cu 3 O 7−␦ tracks. We find that superconductivity is suppressed when the room temperature resistance is greater than the superconducting resistance quantum, R q = h /4e 2. In addition, we observe regular steps in the I͑V͒ characteristics of some bridges, which we associate with phase slip centers. For one bridge, with resistance just below the resistance quantum, R q , we find a gradual entry into the superconducting state which is well fit by theoretical predictions for thermally activated phase slips in a superconducting wire.
Focused ion beam (FIB) systems are widely used as a versatile tool for nanofabrication prototypin... more Focused ion beam (FIB) systems are widely used as a versatile tool for nanofabrication prototyping, device modification and ion beam lithography. However, there are still many unexplored effects due to the different methods that ion implantation could perform during FIB milling using Ga as a liquid metal ion source. In this report we studied the effects of pixel spacing when FIB is used for direct milling of a substrate at different milling currents for constant implantation doses. The experiment consists of FIB milling of a Si substrate at 30 keV using currents of 50 pA and 100 pA for a dose of 5×1016 ions/cm2. The dwell time was set to be 1 μs and the pixel spacing varied from 6.2 nm to 34.2 nm. The surface topographies of machined regions were examined using the atomic force microscope and the quality is described by comparing the intensities of a crystal to amorphous peak of the recorded trace from Raman spectroscopy measurements. This method was introduced by Wagner. In order to more accurately consider the sputtering yield the effect of second order deposition was neglected. It was observed that by increasing the pixel spacing the sputtering yield starts to increase and then gradually decreases for both currents. Ion implantation breaks the crystal structure and the process involves displacement of the atoms from the atomic rows which consequently increases the effect of de-channeling in ion implantation. The increase in sputtering yield could be because of the enhanced de-channeling which is due to the changes of the substrate structure which increases the collisions between implanted ions and the substrate atoms. After a threshold, the sputtering yield gradually decreases, which is due to having less implanted ions per unit of volume for each scan and therefore less applied damage. Pixel spacing at different currents and dose rates can yield different behavior due to the concentration of implanted ions per pixel dwell time. In our study the maximum concentration of implanted ions per pixel dwell time is about 5×1017 ions/cm3 and 1018 ions/cm3 for currents of 50 pA and 100 pA respectively; this concentration is lower than 1019 ions/cm3 which is the saturation point of Ga solubility in Si. It was observed that increasing the pixel spacing leads to rougher surfaces. It was also found that the quality of Si is at its highest when the pixel spacing is 14.8 nm. This is consistent with the topography results which were described by the de-channeling effect. As the de-channeling increases, the depth of implanted ions is decreased, and therefore fewer layers of substrate are damaged. In this study, we investigated the effect of FIB milling pixel spacing on substrate physical and structural changes at a dose of 5×1016 ions/cm2. We observed the sputtering yield is first increased and then decreased, which is mainly due to structural changes in substrate. The quality of substrate was also studied, revealing less damage when the pixel spacing is 14.8 nm for both currents.
A laser-plasma X-ray source has been developed at the Rutherford Appleton Laboratory for applicat... more A laser-plasma X-ray source has been developed at the Rutherford Appleton Laboratory for application to x-ray lithography at 0.18μm and beyond, as well as for generation of deep structures. This source provides a calibrated X-ray output of up to 1W (average power) 1nm wavelength (Cu L-shell emission) and 1.5W @ 1.4nm (Fe L-shell)1. Fig. 1 shows a schematic of the RAL laser-plasma x-ray source.
SEM linewidth measurement in the process latitude investigation procedure can be replaced with a ... more SEM linewidth measurement in the process latitude investigation procedure can be replaced with a resist reflow technique for PMMA and other positive resists. The linewidth dependence on technical parameters can be measured quickly and cheaply with specialised test structures.
Focused ion beam repair of opaque defects in 5X reticles produces post repair stains which result... more Focused ion beam repair of opaque defects in 5X reticles produces post repair stains which result in ghost defects in wafer prints produced at G-line, I-line, and DUV wavelengths. These stains can be removed using a post repair plasma process which restores transmission to almost 100%. However, a new in situ process is preferred which reduces stains to acceptable levels. The key to the new process is an understanding of factors affecting sputter yield. The effectiveness of the in situ antistain procedure is demonstrated through wafer lithography at all three wavelengths showing an absence of ghost defects following repair.
... 3ym thck) was carried out using chemical vapour deposition at a target temperature of 625°C. ... more ... 3ym thck) was carried out using chemical vapour deposition at a target temperature of 625°C. The deposited layers were subsequently implanted with boron at 6OkeV in order to producep-type polycrystalline ... 4. 5. 6 EC Boswell, and PR Wilshaw, J.Vac.Sci.Technol., B 11 (1994 ...
Electron beam resists having high sensitivity and high resistance to dry etching are under invest... more Electron beam resists having high sensitivity and high resistance to dry etching are under investigation for sub-half micron device production using 5x reticle masks. The effects of dry etch process conditions on the performance of the novolac based chemically amplified AZPN114 and onium salt ...
An application of a simple and low-cost novel volumetric linewidth measurement technique to e-bea... more An application of a simple and low-cost novel volumetric linewidth measurement technique to e-beam lithography process optimization for the positive CAR UVIII demonstrates clearly its efficiency and accuracy. It helps to optimize exposure, PEB and development procedure to get the highest possible process latitude. For this optimized procedure structure linewidth does not exceed 10% for a 20% exposure variation. PEB temperature and time deviation for 1 degree(s)C and 1 second lead to a 0.5 nm and a 2.5 nm linewidth run-out correspondingly.
As the critical dimensions of masks and reticles approach i ~m, the limitations of the laser repa... more As the critical dimensions of masks and reticles approach i ~m, 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.
A high-efficiency focusing waveguide grating coupler (FWGC) using parallelogramic groove profiles... more A high-efficiency focusing waveguide grating coupler (FWGC) using parallelogramic groove profiles is proposed, designed and fabricated. A new waveguide grating structure has been employed which consists of bilayered grating with one grating etched into the guiding layer and the other into a high-index cladding layer. Computer simulation shows that both high directionality and large radiation decay factor are obtainable with this structure. Fabrication of this FWGC by electron beam lithography is described. A coupling efficiency of 86% and focusing spot size full-width at half maximum (FWHM) of around 10 m have been achieved.
Field emission characterisation of gridded silicon FEAs was carried out before and after anodisat... more Field emission characterisation of gridded silicon FEAs was carried out before and after anodisation. Each sample contains ten gridded FEAs with array sizes varying from 1 to 10x1 0. For each sample, both current-voltage and current-time measurements of each FEA were carried out before and after anodisation. The morphology and thickness of the porous silicon layer on the emitters were controlled by the anodising current density and duration of the anodisation process. The emission uniformity of FEAs was evaluated by comparing the I-V curves from different FEAs, which show that the emission uniformity had been improved after anodisation. In addition, the I-t measurements show that the emission stability of FEAs is very sensitive to anodisation time, and it is essential to use a very short anodisation time (-0.1 second) to obtain stable emission currents. Under these conditions no adverse effects of the anodisation process on emission stability have been found whilst the improvements in operating voltage and unifornzity are maintained. I. INTRODUCTION It has been demonstrated that the performance of ungridded single crystal silicon field emitters is improved by the formation of porous silicon on their surface, using a process known as anodisation[l]. A large improvement in maximum field emission current and lower starting voltages can be obtained. Anodisation is a simple process and can be easily integrated into the fabrication processes of gridded silicon field emitter arrays, investigation of the effect of anodisation on gridded FEAs to date [2] showed that the operating voltage was lowered after anodisation. However, the investigation was limited to n-type silicon FEAs. No studies of the effect of anodisation on emission stability and lifetime of silicon FEAs have been previously reported. In this study we investigate the effect of anodisation on the field emission performance of p-type silicon FEAs, with the emphasis on the emission uniformity and stability.
Microneedle patches have received much interest in the last two decades as drug/vaccine delivery ... more Microneedle patches have received much interest in the last two decades as drug/vaccine delivery or fluid sampling systems for diagnostic and monitoring purposes. Microneedles are manufactured using a variety of additive and subtractive micromanufacturing techniques. In the last decade, much attention has been paid to using additive manufacturing techniques in both research and industry, such as 3D printing, fused deposition modeling, inkjet printing, and two-photon polymerization (2PP), with 2PP being the most flexible method for the fabrication of microneedle arrays. 2PP is one of the most versatile and precise additive manufacturing processes, which enables the fabrication of arbitrary three-dimensional (3D) prototypes directly from computer-aided-design (CAD) models with a resolution down to 100 nm. Due to its unprecedented flexibility and high spatial resolution, the use of this technology has been widespread for the fabrication of bio-microdevices and bio-nanodevices such as microneedles and microfluidic devices. This is a pioneering transformative technology that facilitates the fabrication of complex miniaturized structures that cannot be fabricated with established multistep manufacturing methods such as injection molding, photolithography, and etching. Thus, microstructures are designed according to structural and fluid dynamics considerations rather than the manufacturing constraints imposed by methods such as machining or etching processes. This article presents the fundamentals of 2PP and the recent development of microneedle array fabrication through 2PP as a precise and unique method for the manufacture of microstructures, which may overcome the shortcomings of conventional manufacturing processes.
This work is concerned with the performance evaluation of thermally activated bimorph cantilevers... more This work is concerned with the performance evaluation of thermally activated bimorph cantilevers. A range of cantilevers has been fabricated using state of the art microfabrication techniques. The cantilevers are 600 μm long and have initial (non-resonant) displacement of 250 μm. Following the successful fabrication of wafer-scale bimorph cantilevers thermal/mechanical tests have been carried out under loaded and non-loaded conditions.
An experimental investigation at energies of 2-6keV has been carried out on the positive chemical... more An experimental investigation at energies of 2-6keV has been carried out on the positive chemically amplified resist AZPF 514. A new way of suppressing the "T-topping" effect, based on resist shower irradiation with low energy electrons, is suggested. This does not prevent contamination of the upper resist layer, but it does provide an easy method of removing the contaminated layer at the very start of resist development.
We have measured the electrical resistivity of a single strand of a ferromagnetic Ni nanowire of ... more We have measured the electrical resistivity of a single strand of a ferromagnetic Ni nanowire of diameter 55 nm using a 4-probe method in the temperature range 3 K-300 K. The wire used is chemically pure and is a high quality oriented single crystalline sample in which the temperature independent residual resistivity is determined predominantly by surface scattering. Precise evaluation of the temperature dependent resistivity (ρ) allowed us to identify quantitatively the electron-phonon contribution (characterized by a Debye temperature θR) as well as the spin-wave contribution which is significantly suppressed upon size reduction.
We have measured the resistance vs temperature, R͑T͒, and current vs voltage, I͑V͒, for a series ... more We have measured the resistance vs temperature, R͑T͒, and current vs voltage, I͑V͒, for a series of submicrometer YBa 2 Cu 3 O 7−␦ tracks. We find that superconductivity is suppressed when the room temperature resistance is greater than the superconducting resistance quantum, R q = h /4e 2. In addition, we observe regular steps in the I͑V͒ characteristics of some bridges, which we associate with phase slip centers. For one bridge, with resistance just below the resistance quantum, R q , we find a gradual entry into the superconducting state which is well fit by theoretical predictions for thermally activated phase slips in a superconducting wire.
Focused ion beam (FIB) systems are widely used as a versatile tool for nanofabrication prototypin... more Focused ion beam (FIB) systems are widely used as a versatile tool for nanofabrication prototyping, device modification and ion beam lithography. However, there are still many unexplored effects due to the different methods that ion implantation could perform during FIB milling using Ga as a liquid metal ion source. In this report we studied the effects of pixel spacing when FIB is used for direct milling of a substrate at different milling currents for constant implantation doses. The experiment consists of FIB milling of a Si substrate at 30 keV using currents of 50 pA and 100 pA for a dose of 5×1016 ions/cm2. The dwell time was set to be 1 μs and the pixel spacing varied from 6.2 nm to 34.2 nm. The surface topographies of machined regions were examined using the atomic force microscope and the quality is described by comparing the intensities of a crystal to amorphous peak of the recorded trace from Raman spectroscopy measurements. This method was introduced by Wagner. In order to more accurately consider the sputtering yield the effect of second order deposition was neglected. It was observed that by increasing the pixel spacing the sputtering yield starts to increase and then gradually decreases for both currents. Ion implantation breaks the crystal structure and the process involves displacement of the atoms from the atomic rows which consequently increases the effect of de-channeling in ion implantation. The increase in sputtering yield could be because of the enhanced de-channeling which is due to the changes of the substrate structure which increases the collisions between implanted ions and the substrate atoms. After a threshold, the sputtering yield gradually decreases, which is due to having less implanted ions per unit of volume for each scan and therefore less applied damage. Pixel spacing at different currents and dose rates can yield different behavior due to the concentration of implanted ions per pixel dwell time. In our study the maximum concentration of implanted ions per pixel dwell time is about 5×1017 ions/cm3 and 1018 ions/cm3 for currents of 50 pA and 100 pA respectively; this concentration is lower than 1019 ions/cm3 which is the saturation point of Ga solubility in Si. It was observed that increasing the pixel spacing leads to rougher surfaces. It was also found that the quality of Si is at its highest when the pixel spacing is 14.8 nm. This is consistent with the topography results which were described by the de-channeling effect. As the de-channeling increases, the depth of implanted ions is decreased, and therefore fewer layers of substrate are damaged. In this study, we investigated the effect of FIB milling pixel spacing on substrate physical and structural changes at a dose of 5×1016 ions/cm2. We observed the sputtering yield is first increased and then decreased, which is mainly due to structural changes in substrate. The quality of substrate was also studied, revealing less damage when the pixel spacing is 14.8 nm for both currents.
A laser-plasma X-ray source has been developed at the Rutherford Appleton Laboratory for applicat... more A laser-plasma X-ray source has been developed at the Rutherford Appleton Laboratory for application to x-ray lithography at 0.18μm and beyond, as well as for generation of deep structures. This source provides a calibrated X-ray output of up to 1W (average power) 1nm wavelength (Cu L-shell emission) and 1.5W @ 1.4nm (Fe L-shell)1. Fig. 1 shows a schematic of the RAL laser-plasma x-ray source.
SEM linewidth measurement in the process latitude investigation procedure can be replaced with a ... more SEM linewidth measurement in the process latitude investigation procedure can be replaced with a resist reflow technique for PMMA and other positive resists. The linewidth dependence on technical parameters can be measured quickly and cheaply with specialised test structures.
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Papers by Philip Prewett