Neste trabalho foi desenvolvida a técnica de Litografia Interferométrica para a gravação de nano-estruturas periódicas em relevo, uni e bidimensionais, sobre substratos de vidro e de silício. Em particular, o trabalho se concentrou em duas frentes: no estudo no perfil das estruturas gravadas em fotorresina, através da superposição de padrões interferométricos, e na integração desta técnica com as demais tecnologias usuais de processamento do Si para microeletrônica. A partir dos padrões luminosos, gerados pela superposição de franjas de interferência, o perfil em relevo das estruturas gravadas em fotorresina foi simulado para estudar a influência de alguns dos parâmetros do processo de exposição e revelação. Para a associação desta técnica de litografia interferométrica com as demais tecnologias de processamento de Si foi necessário desenvolver um processo para gravação sobre substratos de Si. Para isto foi preciso reduzir o efeito das ondas estacionárias na litografia. A solução encontrada foi crescer termicamente uma camada de SiO2, com espessura apropriada sobre o substrato de Si, antes da aplicação da fotorresina. Para demonstrar o potencial dos processos desenvolvidos para fabricação de componentes e dispositivos baseados em nano-estruturas...
We describe the design of an instrument that can fully implement a new nanopatterning method called ice lithography, where ice is used as the resist. Water vapor is introduced into a scanning electron microscope (SEM) vacuum chamber above a sample cooled down to 110 K. The vapor condenses, covering the sample with an amorphous layer of ice. To form a lift-off mask, ice is removed by the SEM electron beam (e-beam) guided by an e-beam lithography system. Without breaking vacuum, the sample with the ice mask is then transferred into a metal deposition chamber where metals are deposited by sputtering. The cold sample is then unloaded from the vacuum system and immersed in isopropanol at room temperature. As the ice melts, metal deposited on the ice disperses while the metals deposited on the sample where the ice had been removed by the e-beam remains. The instrument combines a high beam-current thermal field emission SEM fitted with an e-beam lithography system, cryogenic systems, and a high vacuum metal deposition system in a design that optimizes ice lithography for high throughput nanodevice fabrication. The nanoscale capability of the instrument is demonstrated with the fabrication of nanoscale metal lines.; Engineering and Applied Sciences; Molecular and Cellular Biology; Physics
We report on the process parameters of nanoimprint lithography (NIL) for the fabrication of two-dimensional (2-D) photonic crystals. The nickel mould with 2-D photonic crystal patterns covering the area up to 20mm² is produced by electron-beam lithography (EBL) and electroplating. Periodic pillars as high as 200nm to 250nm are produced on the mould with the diameters ranging from 180nm to 400nm. The mould is employed for nanoimprinting on the poly-methyl-methacrylate (PMMA) layer spin-coated on the silicon substrate. Periodic air holes are formed in PMMA above its glass-transition temperature and the patterns on the mould are well transferred. This nanometer-size structure provided by NIL is subjective to further pattern transfer.; Singapore-MIT Alliance (SMA)
This dissertation describes meniscus-mask lithography (MML): a planar top-down method for the fabrication of precisely positioned narrow graphene nanoribbons (GNRs) and metallic and semiconducting nanowires. The method does not require demanding high resolution lithography tools. The mechanism behind the method involves masking by atmospheric water adsorbed at the edge of the lithography pattern written on top of the target material.
Chapter 1 describes the fabrication of sub-10 nm GNR from graphene sheets using MML technique. The electronic properties of resulting GNRs depend on the graphene etching method with argon reactive ion etching yielding remarkably consistent results. The influence of the most common substrates (Si/SiO2 and BN) on the electronic properties of GNRs is demonstrated. The MML technique is also shown to be applicable for fabrication of narrow metallic wires, underscoring the generality of MML for narrow features on diverse materials.
In chapter 2 the MML method is shown to be effective for fabrication of narrow wires in a variety of materials. Si, SiO2, Au, Cr, W, Ti, TiO2, Al nanowires are fabricated and characterized. A wide range of materials and etching processes are used and the generality of approach suggests possible applicability of MML to a majority of materials used in modern planar technology. High reproducibility of MML method is shown and some fabrication issues specific to MML are addressed. Crossbar structures produced by MML demonstrate that junctions of nanowires could be fabricated as well...
peer-reviewed; Focused Ion Beam (FIB) lithography has
significant advantages over the electron beam counterpart in terms
of resist sensitivity, backscattering and proximity effects.
Applying the Top Surface Imaging (TSI) principal to FIB
lithography could further enhance its capability. In this paper we
review different FIB lithography processes which utilise both wet
and dry development. As of further development of this
technology, we report a novel lithography process which
combines focused Cia' ion beam (Cia' FIB) exposure, silylation
and oxygen dry etching. The Negative Resist Image by D q
Etching (NERIME) is a TSI scheme for DNQhovolak based
ICS~SIS and can result in either positive or negative resist images
depending on the extent of the ion beam exposure dose. The
NERlMF process can resolve nanometer resist patterns as small
as 30nm yet maintaining high aspect ratio of up to 15. The
proposed lithography scheme could be utilised for advanced
prototype IC's fabrication and critical CMOS lithography process
As an emerging technique, immersion lithography offers the capability of reducing critical dimensions by increasing
numerical aperture (NA) due to the higher refractive indices of immersion liquids than that of air. Among the candidates
for immersion liquids, water appears to be an excellent choice due to its high transparency at a wavelength of 193 nm, as
well as its immediate availability and low processing cost. However, in the process of forming a water fluid layer
between the resist and lens surfaces, air bubbles are often created due to the high surface tension of water. The presence
of air bubbles in the immersion layer will degrade the image quality because of the inhomogeneity induced light
scattering in the optical path. Therefore, it is essential to understand the air bubble induced light scattering effect on
image quality. Analysis by geometrical optics indicates that the total reflection of light causes the enhancement of
scattering in the region where the scattering angle is less than the critical scattering angle, which is 92 degrees at 193
nm. Based on Mie theory, numerical evaluation of scattering due to air bubbles, polystyrene spheres and PMMA
spheres was conducted for TE, TM or unpolarized incident light. Comparison of the scattering patterns shows that the
polystyrene spheres and air bubbles resemble each other with respect to scattering properties. Hence polystyrene spheres
are used to mimic air bubbles in studies of lithographic imaging of “bubbles” in immersion water. In direct interference
The physical limitations of lithographic imaging are ultimately imposed by the refractive indices of the materials
involved. At oblique collection angles, the numerical aperture of an optical system is determined by nsin(theta) , where n is
the lowest material refractive index (in the absence of any refractive power through curvature). For 193nm water
immersion lithography, the fluid is the limiting material, with a refractive index of near 1.44, followed by the lens
material (if planar) with a refractive index near 1.56, and the photoresist, with a refractive index near 1.75. A critical
goal for immersion imaging improvement is to first increase the refractive indices of the weakest link, namely the fluid
or the lens material. This paper will present an approach to immersion lithography that will allow for the exploration
into the extreme limits of immersion lithography by eliminating the fluid altogether. By using a solid immersion
lithography (SIL) approach, we have developed a method to contact the last element of an imaging system directly to the
photoresist. Furthermore, by fabricating this last element as an aluminum oxide (sapphire) prism, we can increase its
refractive index to a value near 1.92. The photoresist becomes the material with the lowest refractive index and imaging
becomes possible down to 28nm for a resist index of 1.75 (and 25nm for a photoresist with a refractive index of 1.93).
Imaging is based on two-beam Talbot interference of a phase grating mask...
Recent advances in immersion lithography have created the need for a small field microstepper to carry out the early
learning necessary for next generation device application. Combined with fluid immersion, multiple-beam lithography
can provide an opportunity to explore lithographic imaging at oblique propagation angles and extreme NA imaging.
Using the phase preserving properties of Smith Talbot interferometry, the Amphibian XIS immersion lithography
microstepper has been created for research and development applications directed toward sub-90nm patterning. The
system has been designed for use at ArF and KrF excimer laser wavelengths, based on a fused silica or sapphire prism
lens with numerical aperture values up to 1.60. Combined with a chromeless phase grating mask, two and four beam
imaging is made possible for feature resolution to 35nm. The approach is combined with X-Y staging to provide
immersion imaging on a microstepper platform for substrates ranging up to 300mm. The Amphibian system consists of
single or dual wavelength sources (193nm and 248nm), a 2mm exposure field size, stage accuracy better than 1 um,
polarization control over a full range from linear polarization to unpolarized illumination, full control of exposure dose
and demodulation (to synthesize defocus)...
Interference imaging systems are being used more extensively for R&D applications where NA manipulation,
polarization control, relative beam attenuation, and other parameters are explored and projection imaging approaches
may not exist. To facilitate interferometric lithography research, we have developed a compact simulation tool, ILSim,
for studying multi-beam interferometric imaging, including fluid immersion lithography. The simulator is based on full-vector
interference theory, which allows for application at extremely high NA values, such as those projected for use
with immersion lithography. In this paper, ILSim is demonstrated for use with two-beam and four-beam interferometric
immersion lithography. The simulation tool was written with Matlab, where the thin film assembly (ambient, top coat,
resist layer, BARC layers, and substrate) and illumination conditions (wavelength, polarization state, interference angle,
demodulation, NA) can be defined. The light intensity distributions within the resist film for 1 exposure or 2-pass
exposure are displayed in the graph window. It also can optimize BARC layer thickness and top coat thickness.
In a photolithographic system, the mask patterns are imaged through a set of lenses on a resist-coated
wafer. The image of mask patterns physically can be viewed as the interference of the plane waves of the diffraction
spectrum captured by the lens set incident on the wafer plane at a spectrum of angles. Two-beam interference fringe
is the simplest format of the image. Consequently, two-beam interferometric lithography is often employed for
photolithographic researches. For two-beam interferometric lithography, beam pointing instability of the
illumination source can induce fringe displacement, which results in a loss of fringe contrast if it happens during the
exposure. Since some extent of beam pointing instability is not avoidable, it is necessary to investigate its effects on
the contrast of the interference fringe. In this paper, the effects of beam pointing instability associated with a two beam
interferometric lithography setup are analyzed. Using geometrical ray tracing technique and basic interference
theory, the relationship between the beam tilt angle and interference fringe displacement is established. For a beam
pointing instability with random distribution, the resulted fringe contrast is directly proportional to the Fourier
transform of the pointing distribution evaluated at 1/2(pi). The effect of a pointing instability with normal distribution
on interference contrast is numerically investigated.
Immersion interferometric lithography has been applied successfully to semiconductor device applications, but its
potential is not limited to this application only. This paper explores this imaging technology for the production of three-dimensional
nano-structures using a 193 nm excimer laser and immersion Talbot interferometric lithographic tool. The
fabrication of 3-D photonic crystals for the UV spectrum is still considered to be a challenge. A systematic analysis of
immersion lithography for 3-D photonic crystal fabrication will be provided in this paper. Significant progress has been
made on optical immersion lithography since it was first proposed. Two-beam immersion interferometric lithography can
provide sub-30nm resolution. By changing the exposure parameters, such as the numerical aperture of the exposure
system, the polarization states and wavelength of the illumination source, 30 nm polymeric nanospheres with different
crystal structures can be fabricated.
Dot gain is the enlargement which takes place in a dot from the time
the dot is captured or generated on the film until it is printed. Dot gain
can cause many problems, including color variation and loss of contrast,
and if uncontrolled is one of the main contributors to waste in offset
lithography. Of the many factors influencing dot gain, inks have been
found to be a major contributor. One property recommended for further
investigation is ink viscosity, which is the resistance to flow of an ink.
The purpose of this study was to investigate the effect of ink
viscosity on dot gain in offset lithography. It was found that as ink
viscosity increases, dot gain will decrease, and if ink viscosity is
optimized, dot gain will be optimized. Experimentation was done on a
single color, single impression sheet-fed lithographic press, with five
inks of different viscosities.
Results of this experiment show that ink viscosity is significant in
affecting the amount of dot gain that occurs. Inks with 15 and 20 percent
solvent added, which were less than 1000 poise viscosity, were found cause
the significant difference. Other factors found to be significant were
screen ruling and paper absorbency. The Yates Method of Analysis of
Variance and graphing were used to analyze the data.
The evolution of optical lithography to pattern smaller geometries was witnessed
the shrinkage of source wavelength as a way to increase optical resolution. Shrinking of
source wavelength into vacuum ultra-violet (VUV) faces a number of technical barriers
with respect to imaging materials. Instead of source wavelength shrinking, the optical
resolution can also be enhanced by increasing numerical aperture (NA) with immersion
techniques. This dissertation is devoted to experimentally studying the imaging behaviors
of hyper-NA optics in the context of liquid immersion and solid immersion lithography.
In this dissertation, the full-vector interference theory is described for two-beam
and multi-beam interference. Polarization effects, resist absorption effects and BARC
optimization are analyzed respectively. The experimental setup is analyzed in
consideration of vibration, source temporal coherence and spatial coherence. Imaging
with TE and TM polarization is studied respectively. A solid immersion technique is
investigated experimentally to push the NA beyond what are available using fluids and
imaging at NA values up to the index of the photoresist has been investigated. Moreover,
NA values have been pushed higher than the refractive index of the resist...
Waterless lithography is one of the printing processes that was developed around 1968. It
has a strong impact in the current printing industry. Like other printing processes,
waterless lithography has both advantages and disadvantages. It is said that waterless
lithography can print with more consistency and less dot gain than conventional
lithography. However, it has one significant disadvantage, currently there is only one
waterless lithographic plate supplier in the industry.
There is very little quantitative data describing the waterless lithographic process
to support the arguments that waterless lithography prints with more consistency and less
dot gain. There is even a report that conflicts with such arguments. Consequently, this
research investigates waterless lithography to provide more quantitative data and a better
understanding with its conventional counterpart.
The purpose of this research was to compare a process capability index
(consistency) in terms of solid ink density and the magnitude of dot gain between
waterless lithography and conventional lithography. This research performed a series of
test runs in an academic environment. The densities of the sample press sheets were
measured and used to calculate dot gain. Several statistical methods were used to analyze
data and compute process capability indices. From the data analysis...
Current assumptions for the limits of immersion optical lithography include NA values at 1.35, largely based on the lack of high-index materials. In this research we have been working with ultra-high NA evanescent wave lithography (EWL) where the NA of the projection system is allowed to exceed the corresponding acceptance angle of one or more materials of the system. This approach is made possible by frustrating the total internal reflection (TIR) evanescent field into propagation. With photoresist as the frustrating media, the allowable gap for adequate exposure latitude is in the sub-100 nm range. Through static imaging, we have demonstrated the ability to resolve 26 nm half-pitch features at 193 nm and 1.85 NA using existing materials. Such imaging could lead to the attainment of 13 nm half-pitch through double patterning. In addition, a scanning EWL imaging system was designed, prototyped with a two-stage gap control imaging head including a DC noise canceling carrying air-bearing, and a AC noise canceling piezoelectric transducer with real-time closed-loop feedback from gap detection. Various design aspects of the system including gap detection, feedback actuation, prism design and fabrication, software integration, and scanning scheme have been carefully considered to ensure sub-100 nm scanning. Experiments performed showed successful gap gauging at sub-100 nm scanning height. Scanning EWL results using a two-beam interference imaging approach achieved pattern resolution comparable to static EWL imaging results. With this scanning EWL approach and the imaging head developed...
In conventional lithography, a halftone screen is used to photographically convert the continuous- tone image of the original into a grid of very small, closely spaced dots of constant density but varying areas. Screenless or continuous-tone lithography is a printing process capable of reproducing images with gradated tones without the use of a halftone screen. Screenless lithography has a high quality potential because it has few of the inherent problems that limit the quality of the halftone process. This thesis investigates the image mechanisms in screenless lithography and in particular the role of variable water receptivity. It was hypothesized that in screenless lithography which uses a particular image carrier known as the Association Products plate, the continuous-tone image is due to selective emulsification of the ink resulting in a varying ink layer thickness and therefore varying densities. It was theorized that the plate has a water receptivity which varies with exposure to light and that this results in varying degrees of water-in-ink emulsification when the plate is dampened and inked. When transferred to paper and dried this results in an ink layer of varying thickness, which in turn causes a variation in optical density. A mathematical relationship was developed relating optical density...
Advances in the semiconductor industry are mainly driven by improvements in optical lithography technology, which have enabled the continual shrinking of integrated circuit devices. However, optical lithography technology is approaching its limit, and within ten years, it may be substituted by new non-optical approaches. These may include Extreme Ultra Violet (EUV) lithography and charged particle beam projection lithography. While these technologies may have potentially better resolution, they can be very difficult to implement into manufacturing. During the course of the research presented here, the extension of optical lithography to sub 70nm resolution has been investigated. Since optical lithography is mature and well understood, extending it to allow for higher resolution can dramatically reduce manufacturing difficulties, compared to EUV or charged particle beam projection lithography. A majority of the existing infrastructure, such as photoresist materials, sources, optics, and photo-masks, remain applicable with the optical methods explored here. The avenues investigated in this research have concentrated on spatial frequency filtering in alternative Fourier Transform planes, vacuum UV wavelength lithography, and achieving ultra high numerical aperture imaging through the use of liquid immersion imaging. More specifically...
As immersion nanolithography gains acceptance for next generation device applications, experimental data becomes
increasingly important. The behavior of resist materials, fluids, coatings, sources, and optical components in the
presence of a water immersion media presents conditions unique compared to convention “dry” lithography. Several
groups have initiated fundamental studies into the imaging, fluids, contamination, and integration issues involved with
water immersion lithography at 193nm. This paper will present the status and results of the next stage of the
development efforts carried out at RIT. The status of two systems are presented; a small field projection microstepper
utilizing a 1.05 catadioptric immersion objective lens and a 0.50 to 1.26NA interferometric immersion exposure system
based on a compact Talbot prism lens design. Results of the fundamental resolution limits of resist materials and of
imaging optics are presented. Additionally, an exploration into the benefits of increasing the refractive index of water is
addressed through the use of sulfate and phosphate additives. The potential of KrF, 248nm immersion lithography is
also presented with experimental resist imaging results.
It is possible to extend optical lithography by using immersion imaging methods. Historically, the application of
immersion optics to microlithography has not been seriously pursued because of the alternative solutions available. As
the challenges of shorter wavelength become increasingly difficult, immersion imaging becomes more feasible. We
present results from research into 193nm excimer laser immersion lithography at extreme propagation angles (such as
those produces with strong OAI and PSM). This is being carried out in a fluid that is most compatible in a
manufacturable process, namely water. By designing a system around the optical properties of water, we are able to
image with wavelengths down to 193nm. Measured absorption is below 0.50 cm at 185nm and below 0.05 cm' at
193nm. Furthermore, through the development of oblique angle imaging, numerical apertures approaching 1.0 in air and
1.44 in water are feasible. The refractive index of water at 193nm (1.44) allows for exploration of the following:
1. k1 values approaching 0. 17 and optical lithography approaching 35nm.
2. Polarization effects at oblique angles (extreme NA).
3. Immersion and photoresist interactions with polarization.
4. Immersion fluid composition, temperature...