Development Of Lithography Research Articles

A review on contemporary practices in Lithography

This paper discusses the basic concepts and current state of development of LITHOGRAPHY i.e., EUV lithography (EUVL), lithography that uses extreme ultraviolet (EUV) radiation with a different wavelengths in the range of 32 to 22 nanometers (nm) to carry out projection imaging. Currently, and for the last several decades, optical projection lithography has been the lithographic technique used in the high volume manufacture of integrated circuits. It is widely anticipated that improvements in this technology will allow it to remain in semiconductor industry's workhorse through the 100 nm generation of devices. However, sometime around the year 2005, so-called NGL is used. EUVL is one such technology vying to become the successor to optical lithography. This paper provides an overview of the capabilities of EUVL, and explains how EUVL might be implemented.

Resist outgassing assessment for multi electron beams lithography

The outgassing of e-beam resist materials has to be carefully considered in the research and development of multi e-beams lithography. The release of hydrocarbonaceous species by outgassing in high-vacuum e-beam exposure tool is indeed unavoidable and may lead to premature contamination of optics projection systems. Such a contamination may affect the incident electrons path and hence the final imaging performances. In this work, we present an experimental methodology for the purpose of e-beam resist outgassing qualification. A specific experimental setup was designed in CEA-Leti in order to perform electron bombardment of the e-beam resists coated on 100mm silicon wafers and to monitor the induced outgassing phenomena. The wafer stage was designed in order to allow suitable displacements of the resist coated surface with respect to the incident e-beam. In addition, the wafer can be exposed through specific silicon micromachined membranes (called mimic) that are representative of the optics projection system usually embedded in real multi e-beam exposure tools. Finally, a Quadrupole Mass Spectrometer (QMS) is plugged into the vacuum chamber and enables in situ analysis of the by-products outgassing. Combining this tool with the Thermo Desorption–Gas Chromatography coupled to Mass Spectroscopy and Flame Ion Detector (TD/GC/MS–FID) analysis, we could not only determine the outgassing amount of four different resists but also identify all by-products outgassed and their origin. This paper also shows that the use of a thin top-coat can considerably reduce the outgassing. The outgassing amount as well as the top-coat efficiency was shown to be dependent on the resist chemical properties.

Thermal Modeling of Ultraviolet Nanoimprint Lithography

Nanoimprint lithography (NIL) is a promising nanomanufacturing technology that offers an alternative to traditional photolithography for manufacturing next-generation semiconductor devices. This technology involves coating an ultraviolet (UV)-curable monomer layer on the substrate and then imprinting it with a template containing topography corresponding to the desired substrate features. While the template is close to contact with the substrate, the monomer is cured by UV exposure. This results in definition of desired features on the substrate. While NIL has the potential of defining very small feature sizes, thermal management of this process is critical for ensuring accuracy. Heat generation in the monomer layer due to UV absorption needs to be managed and dissipated in order to avoid thermal expansion mismatch and consequent misalignment between the template and wafer. In addition, thermal dissipation must occur in a timeframe that does not adversely affect the required lithography throughout. This paper develops a numerical simulation model of the nanoimprinting process and utilizes the model to study the effect of various geometrical parameters on the accuracy and throughput of the process. The effect of the UV power characteristics on heat dissipation and consequently on misalignment due to thermal expansion is studied. Results indicate that the thermal expansion mismatch due to commonly used UV exposure parameters may be minimized by utilizing a lower exposure power for longer time. A transient model enables a study of the effect of die imprint sequencing on the overall temperature rise during the process. Results indicate a critical trade-off between minimizing temperature rise on one hand, and maximizing system-level throughput on the other. By identifying and quantifying this trade-off, this work contributes to development of error-free nanoimprint lithography for future technology nodes.

Pattern transfer using block copolymers

To meet the increasing demand for patterning smaller feature sizes, a lithography technique is required with the ability to pattern sub-20 nm features. While top-down photolithography is approaching its limit in the continued drive to meet Moore's law, the use of directed self-assembly (DSA) of block copolymers (BCPs) offers a promising route to meet this challenge in achieving nanometre feature sizes. Recent developments in BCP lithography and in the DSA of BCPs are reviewed. While tremendous advances have been made in this field, there are still hurdles that need to be overcome to realize the full potential of BCPs and their actual use.

Development of Selective Blue-Laser Lithography for Biomedical Applications: A Pilot Study

The study aimed to investigate the selective blue-laser lithography that can fabricate the biomedical materials. The major advantage of using blue-laser instead of UV laser is to lower the machine and operating costs but still keeping the proper part quality for biomedical applications. The material used in the study is the bisphenol a diglycidylether methacrylate (BisGMA) which is specific formulated for photo-polymerizing with blue laser (wavelength = 473nm). The fabricated parts were preliminarily examined by flexural strength testing and in vitro testing of toxicity by direct contact test. The results showed that the flexural strength of fabricated part was about 92% as compared to the flexural strength of hand-pressed PMMA. The in vitro testing of toxicity, confirmed that the fabricated part by the selective blue-laser lithography with BisGMA material has good biocompatibility.

Recent progress in source development for lithography at 6.x nm

In 2009 industry announced that sources would be needed at 6.x nm for future lithography. The brightest sources in this wavelength region are plasmas containing gadolinium and terbium. The strongest lines result from 4d–4f lines in the spectra of Ag-like Gd XVIII and Tb XIX through Rh-like Gd XX and Tb XXI. Assuming collisional radiative equilibrium, the optimum plasma temperature for producing these species is expected to be in the range 100–130 eV. Time integrated experimental spectra have been recorded with a variety of lasers and a maximum measured conversion efficiency (CE) for 150 ps pulses was 0.4%. The extreme ultraviolet (EUV) emission was observed to be anisotropic while the ion energy decreases with decreasing pulse length. The optimum laser intensity for efficient 6.7 nm EUV emission was determined to be close to 7 × 1013 W cm−2, which gives an electron temperature of ∼ 130 eV. The use of prepulses increases the CE which is limited by plasma opacity. To improve radiation transport low initial density targets and/or low electron density plasmas such as CO2 LPPs are required.

Three-dimensional deep sub-diffraction optical beam lithography with 9 nm feature size

The current nanofabrication techniques including electron beam lithography provide fabrication resolution in the nanometre range. The major limitation of these techniques is their incapability of arbitrary three-dimensional nanofabrication. This has stimulated the rapid development of far-field three-dimensional optical beam lithography where a laser beam is focused for maskless direct writing. However, the diffraction nature of light is a barrier for achieving nanometre feature and resolution in optical beam lithography. Here we report on three-dimensional optical beam lithography with 9 nm feature size and 52 nm two-line resolution in a newly developed two-photon absorption resin with high mechanical strength. The revealed dependence of the feature size and the two-line resolution confirms that they can reach deep sub-diffraction scale but are limited by the mechanical strength of the new resin. Our result has paved the way towards portable three-dimensional maskless laser direct writing with resolution fully comparable to electron beam lithography.

33.4L: Late‐News Paper: High Resolution Vacuum Patterning of Organic‐ and Metal‐Layers for Organic Electronic Devices

AbstractIn this paper, we describe the recent progress made in the development of the Flash Mask Transfer Lithography for AMOLED‐pixel patterning. Basic principles of the technology are discussed, recent results on resolution and processing are presented and patterns and materials were analyzed. Based on the technology a lab scale cluster‐tool was manufactured to demonstrate the feasibility of pixel patterning in OLED displays.

Effect of Molecular Weight and Protection Ratio on Latent Image Fluctuation of Chemically Amplified Extreme Ultraviolet Resists

Line edge roughness (LER) has been the most serious problem in the development of high-resolution lithography for manufacturing semiconductor devices. LER is caused by the stochastic effects in resist pattern formation. In this study, the effects of the molecular weight and protection ratio of a resist backbone polymer on latent image fluctuation were investigated by a Monte Carlo method. From the viewpoint of latent image fluctuation, a high molecular weight and a high protection ratio were found to be favorable for the reduction in LER.

Effect of Injection Parameters on Immersion Liquid during Wafer Scanning

Double patterning improves the development of immersion lithography, but it brings new challenges including the higher scanning velocity of wafer. In this paper, considering two typical injection types, the three-dimensional computational fluid dynamics model is developed to investigate the effect of injection parameters on immersion liquid during wafer scanning. By analyzing the velocity distribution of immersion flow and normal stress on the lens, the proper parameters of injection are proposed under the typical conditions, and the appropriate parameters which lead to effective renovation with low lens distortion are also given.

The Study of X-ray Lithography Using the DNQ-Novolak Type Photoresist

As a result of the rapid development of lithography, it enables semiconductor technology to design more devices in the same area, which therefore makes electronic products faster, more functional, and hold more components. The photoresist, playing an important role in lithography, constantly develops with a light wavelength used for exposure from early entire wavelengths to present optical and non-optical lithography. The light sources of optical lithography have moved from the early 436nm and 365nm wavelength to short-wavelength light gradually. It is a big issue to find a suitable photoresist under the exposure of 0.578nm X-Ray light source. In this paper we first proposed to use DNQ / Novolak photoresist sold in the market for the 0.578nm X-Ray lithography. In the experiment, it is discovered that the exposure amount of X-Ray can determine if the photoresist is positive or negative; in low doses, when the photoresist film thickness is increased with the reduced exposure time, and a critical level is reached, the Novolak liquid will become positive photoresist after it is exposed in certain time. The high-dose X-Ray beam will make Novolak resin bond break and result in free radicals, which, through resin crosslinking, can improve the internal strength, and reduce developer solubility so the Novolak liquid can become a negative photoresist. By using synthesized DNQ / Novolak photoresist under X-Ray exposure, we can reduce the process line width, and explore principles of photoresist imaging analysis under the different exposure doses.

Resist Properties Required for 6.67 nm Extreme Ultraviolet Lithography

The reduction of wavelength is a trend in the development of lithography used for high-volume production of semiconductor devices. The lithography using 13.5 nm extreme ultraviolet (EUV) radiation has been intensively developed and is approaching realization. After the use of 13.5 nm EUV, the wavelength is expected to be reduced to 6.67 nm. In this study, we theoretically examined the resist properties required for 6.67 nm EUV lithography. Using an exposure tool with the numerical aperture of 0.5, the fabrication of 11 nm line-and-space patterns with 0.9 nm line width roughness (LWR) with 10 mJ cm-2 sensitivity requires >30× enhancement of the absorption coefficient, >30 wt % acid generators, and >5× enhancement of the effective reaction radius for deprotection from the current resists in order to simultaneously meet the requirements for resolution, LWR, and sensitivity.

Resist Properties Required for 6.67 nm Extreme Ultraviolet Lithography

The reduction of wavelength is a trend in the development of lithography used for high-volume production of semiconductor devices. The lithography using 13.5 nm extreme ultraviolet (EUV) radiation has been intensively developed and is approaching realization. After the use of 13.5 nm EUV, the wavelength is expected to be reduced to 6.67 nm. In this study, we theoretically examined the resist properties required for 6.67 nm EUV lithography. Using an exposure tool with the numerical aperture of 0.5, the fabrication of 11 nm line-and-space patterns with 0.9 nm line width roughness (LWR) with 10 mJ cm-2 sensitivity requires >30× enhancement of the absorption coefficient, >30 wt % acid generators, and >5× enhancement of the effective reaction radius for deprotection from the current resists in order to simultaneously meet the requirements for resolution, LWR, and sensitivity.

Lithography for enabling advances in integrated circuits and devices

Because the transistor was fabricated in volume, lithography has enabled the increase in density of devices and integrated circuits. With the invention of the integrated circuit, lithography enabled the integration of higher densities of field-effect transistors through evolutionary applications of optical lithography. In 1994, the semiconductor industry determined that continuing the increase in density transistors was increasingly difficult and required coordinated development of lithography and process capabilities. It established the US National Technology Roadmap for Semiconductors and this was expanded in 1999 to the International Technology Roadmap for Semiconductors to align multiple industries to provide the complex capabilities to continue increasing the density of integrated circuits to nanometre scales. Since the 1960s, lithography has become increasingly complex with the evolution from contact printers, to steppers, pattern reduction technology at i-line, 248 nm and 193 nm wavelengths, which required dramatic improvements of mask-making technology, photolithography printing and alignment capabilities and photoresist capabilities. At the same time, pattern transfer has evolved from wet etching of features, to plasma etch and more complex etching capabilities to fabricate features that are currently 32 nm in high-volume production. To continue increasing the density of devices and interconnects, new pattern transfer technologies will be needed with options for the future including extreme ultraviolet lithography, imprint technology and directed self-assembly. While complementary metal oxide semiconductors will continue to be extended for many years, these advanced pattern transfer technologies may enable development of novel memory and logic technologies based on different physical phenomena in the future to enhance and extend information processing.

Relationship between Stochastic Effect and Line Edge Roughness in Chemically Amplified Resists for Extreme Ultraviolet Lithography Studied by Monte Carlo Simulation

The fluctuation of the line edge of resist patterns, called line edge roughness (LER), has been the most serious problem in the development of next-generation lithography. The major root cause of LER is the chemical inhomogeneity at the boundary between the insoluble and soluble regions of the resist. In this study, the stochastic effect induced in the processes of formation of resist patterns was investigated using a Monte Carlo method. The relative standard deviation of acid concentration was smaller than that of absorbed photons. The relative standard deviation of protected units was smaller than that of acid concentration. By comparing the simulation results with the reported values of LER, it was found that the stochastic effect is further reduced in the development and rinse processes.

Aerial image formation of quantum lithography for diffraction limit

Since the diffraction limit of Rayleigh criterion hardly creates finer features, the development for the quantum lithography of entangled photons, one of technologies beyond the diffraction limit, is a key merit without the shorter wavelength source tool. In the arbitrary pattern formation for the commercialization of this lithography, however, this quantum lithography is required to implement mask patterns and the conventional optical lithography. In this paper, for the quantum lithography of entangled photons, collective behavior of N-photon entangled states is modeled and simulated to show the effect of photon entangled states for 3-dimensional arbitrary pattern formation by using the rigorous coupled wave analysis (RCWA) and Kirchhoff analysis. For the enhanced resolution from the point of view that the de Broglie wavelength of a quantum state comprised of two entangled photons is half the classical wavelength associated with either photon, simulation results of entangled photons are similar to those of short wavelengths. However, both of simulation results show that the resolution of entangled photons is better than those of the shorter wavelengths. Simulation results can predict realistic better performance of entangled photons.

Performance Comparison between Attenuated PSM and Opaque MoSi on Glass (OMOG) Mask in Sub-32nm Litho Process

During the development of optical lithography that has been extending to 32 nm and beyond, it is found that the selection of mask blank types has a very strong impact on minimum feature process window, or critical dimension performance that can be achieved, which will affect ultimate wafer lithographic performance. Although the industry-standard 6% attenuated phase shifting mask (PSM) with 67nm MoSi has been widely used, as the manufacturing design rule continues to shrink, it will introduce quite a few challenges, such as, defect inspections, imaging contrast, or NILS, and mask error enhancement factor (MEEF) [1]. Meanwhile, the standard chrome-on-glass mask, compared with 6% Att. PSM, is unable to support the minimum feature required in lithographic process windows and through pitch requirements. To alleviate this problem, a new type of binary mask with Opaque MoSi On glass (OMOG) is gradually accepted and used in 32 nm. In this paper, both 6% attenuated PSM and OMOG mask have been evaluated with 28 nm patterns. PSM and OMOG mask's critical dimension uniformities (CDU) are compared. Further more; we have also compared wafer line width roughness (LWR), After Development Inspection (ADI) CDU, MEEF, through pitch process window including Depth of Focus (DOF) and Exposure Latitude(EL). Our result shows that, for bright field and dark field mask, OMOG mask show different behavior than PSM mask in lithographic process performance. As above, whether OMOG can replace 6% attenuated PSM as 32 nm/28 nm main stream mask blank will depend on mask performance, litho performance, and device requirements.

Dielectronic recombination of Pd-like gadolinium

As research and development of extreme ultraviolet lithography (EUVL) sources at 6.7 nm (which will be based on emission from ionized gadolinium) has already begun, reliable atomic data are required in order to determine the optimum plasma conditions. However, the complexity of the atomic structure means that ab initio level-resolved dielectronic recombination (DR) calculations are currently unavailable for the ions of interest. Here we report the first detailed calculation of the DR rate coefficients for the ground state and first excited states of Pd-like gadolinium. Energy levels, radiative transition probabilities, and autoionization rates of Ag-like gadolinium for [Kr]4${d}^{9}$4$fnl$, [Kr]4${p}^{5}$4${d}^{10}$4$fnl$, [Kr]4${d}^{9}$5$l$\ensuremath{'}$nl$, and [Kr]4${d}^{9}$6$l$\ensuremath{'}$nl$ ($n$ \ensuremath{\leqslant} 18) complexes were calculated using the flexible atomic code (FAC). It was found that inclusion of 4${p}^{5}$4${d}^{10}$4$fnl$ configurations has significant influence on the total DR rate coefficient. The DR rate coefficients obtained here are compared with radiative recombination and three-body recombination coeffcients. The results show that the DR rate coefficient is almost an order of magnitude higher than the coefficients for the other two recombination processes combined at plasma electron temperatures around 110 eV, which suggests that the DR process should be included in theoretical modeling for Pd-like gadolinium in EUVL source plasmas.

Development of extreme ultraviolet lithography for manufacturing of nanodevices

Development of extreme ultraviolet lithography for manufacturing of nanodevices

Comparison of EUV Patterning between PTD and NTD for 2Xnm DRAM

The patterning performance of 3Xnm half pitch contact hole for 2Xnm DRAM was achieved from NXE3100, EUV pre-production tool last year. The local CD uniformity of EUV was comparable to that of immersion DPT (Double Patterning Technology), so the EUV patterning performance of 3Xnm half pitch is ready for mass production. But productivity progress of EUV source power is behind the plan and EUV shot noise is still problematic, so EUV resist process need to be improved for sub 3Xnm half pitch contact hole patterning. And also the patterning of sub 20nm half pitch line and space was gathered from NXE3100 but LWR and collapse are critical issues to be improved. Recently we introduced negative tone development (NTD) in immersion lithography for mass production and achieved excellent patterning performance compared to positive tone development (PTD) because negative tone development (NTD) showed better optical contrast on contact hole patterning and swelling-free property of resist film against developer. In this paper, we describe necessity of negative tone development (NTD) on EUV, optimization of mask cell size, upgrade status of resist and resolution limit between positive (PTD) and negative tone development (NTD).