Dry Lithography Research Articles

Organic Semiconductors: Dry Lithography of Large‐Area, Thin‐Film Organic Semiconductors Using Frozen CO2 Resists (Adv. Mater. 46/2012)

Organic Semiconductors: Dry Lithography of Large‐Area, Thin‐Film Organic Semiconductors Using Frozen CO₂ Resists (Adv. Mater. 46/2012)

Dry Lithography of Large‐Area, Thin‐Film Organic Semiconductors Using Frozen CO2 Resists

To address the incompatibility of organic semiconductors with traditional photolithography, an inert, frozen CO(2) resist is demonstrated that forms an in situ shadow mask. Contact with a room-temperature micro-featured stamp is used to pattern the resist. After thin film deposition, the remaining CO(2) is sublimed to lift off unwanted material. Pixel densities of 325 pixels-per-inch are shown.

Through-Silicon-Via (TSV) for silicon package: ″via-bridge″ approach

We present in this paper an alternative Through-Silicon-Via approach that can meet the new requirements of Si package. In this wafer level packaging scheme, a thick silicon interposer (200 to 300μm) is directly reported on a PCB. In 200mm Si wafers, we made a two steps TSV composed of two vias: a top via and a bottom via. The top via is etched with DRIE (diameter 60μm, depth 180 μm, Aspect Ratio = AR>3), and insulated with high temperature dielectric. After dry film lithography, the TSV is partially plated with Cu limiting the process costs (short plating time, no CMP) and the stress inside the TSV. After temporary carrier bonding, the wafer is backgrinded so that 15μm remains below the bottom of the main TSV. Backside lithography and DRIE process create the bottom via (four different diameters: 10-20-30 and 40μm) to contact main TSV. A final backside Cu plating of the opening completed the process. This via bridges the gap between via-last (AR<2) and via-middle (AR>7) and combines high temperature process from via-middle and low-cost processing from via-last. The mechanical simulations show that this ″TSV bridge″ has reduced residual stresses inside the TSV. Our electrical measurements exhibit an average single TSV resistance below 10mOhms with excellent yield (∼95% on Kelvin and 82 TSV chains), and low contact resistances (4.7×10−9 Ω.cm2) extrapolated on 4 different contact diameters. This 200μm deep TSV seems therefore very promising for low-cost thick interposer applications.

Probe-Based Nanolithography: Self-Amplified Depolymerization Media for Dry Lithography

Probe-Based Nanolithography: Self-Amplified Depolymerization Media for Dry Lithography

Immersion Lithography: Photomask and Wafer-Level Materials

Optical immersion lithography utilizes liquids with refractive indices >1 (the index of air) below the last lens element to enhance numerical aperture and resolution, enabling sub-40-nm feature patterning. This shift from conventional dry optical lithography introduces numerous challenges requiring innovations in materials at all imaging stack levels. In this article, we highlight the recent materials advances in photomasks, immersion fluids, topcoats, and photoresists. Some of the challenges encountered include the fluids' and photomask materials' UV durability, the high-index liquids' compatibility with topcoats and photoresists, and overall immersion imaging and defectivity performance. In addition, we include a section on novel materials and methods for double-patterning lithography—a technique that may further extend immersion technology by effectively doubling a less dense pattern's line density.

Investigation of Resolution Enhancement by Using Interferometric Immersion Lithography with a Lloyd Mirror

The minimum feature size of semiconductor devices will be smaller and smaller because of the increasing demand for high integration of such devices. The resolution limit of an optical lithography system is described by Rayleigh's criterion. While it is hard to achieve a small critical dimension by reducing the illumination wavelength and the processing-dependent factors, the critical dimension can be reduced by increasing the refractive index of the material between the lens and the wafer. We have used an interferometric immersion lithography system. This system uses a Lloyd mirror for interference between the 1st and the 1st di raction order and deionized water with a refractive index of 1.437 at 193 nm. The experimental result showed that immersion lithography, compared to conventional dry lithography, improved not only the resolution but also the depth of focus. The simulation result con rmed this behavior, showing a larger depth of focus for immersion compared to dry lithography. Also, the linewidth with immersion lithography was smaller than the linewidth with dry lithography.

Optical Biochip with Multichannels for Detecting Biotin–Streptavidin Based on Localized Surface Plasmon Resonance

A rapid and accurate detection of molecular binding of antigen-antibody signaling in high throughput is of great importance for biosensing technology. We proposed a novel optical biochip with multichannels for the purpose of detection of biotin–streptavidin on the basis of localized surface plasmon resonance. The optical biochip was fabricated using photolithography to form the microarrays functioning with multichannels on glass substrate. There are different nanostructures in each microarray. Dry etching and nanosphere lithography techniques were applied to fabricate Ag nanostructures such as hemispheres, nanocylindricals, triangular, and rhombic nanostructures. We demonstrated that 100-nM target molecule (streptavidin) on these optical biochips can be easily detected by a UV-visible spectrometer. It indicated that period and shape of the nanostructures significantly affect the optical performance of the nanostructures with different shapes and geometrical parameters. Our experimental results demonstrated that the optical biochips with the multichannels can detect the target molecule using the microarrays structured with different shapes and periods simultaneously. Batch processing of immunoassay for different biomolecular through the different channels embedded on the same chip can be realized accordingly.

PECVD Bi-Layer ARC for BARC-less Immersion Lithography

A PECVD bi-layer Dielectric Anti-Reflective Coating (DARC®) process has been developed as a cost-effective solution for immersion lithography. The proposed bi-layer DARC scheme eliminates the need for a Bottom Anti-Reflective Coating (BARC) which is commonly used in both dry and immersion lithography processes, thereby reducing manufacturing cost and improving etch margin for better CD control. The bi-layer DARC film properties are highly tunable for different underlayers to provide optimal reflectivity control. With the bi-layer DARC scheme, we have demonstrated a minimum line width of 30 nm with a wider process window and comparable line edge roughness (LER) as a BARC scheme. The patterning performance is stable after multiple rework cycles and extended queue time, proving the manufacturability of the bi-layer DARC process.

Double-patterning requirements for optical lithography and prospects for optical extension without double patterning

Double patterning (DP) has now become a fixture on the development roadmaps of many device manufacturers for half pitches of 32 nm and beyond. Depending on the device feature, different types of DP and double exposure (DE) are being considered. This paper focuses on the requirements of the most complex forms of DP, pitch-splitting (where line density is doubled through two exposures) and spacer processes (where a deposition process is used to achieve the final pattern). Budgets for critical dimension uniformity and overlay are presented along with tool and process requirements to achieve these budgets. Experimental results showing 45-nm lines and spaces using dry ArF lithography with a k1 factor of 0.20 are presented to highlight some of the challenges. Finally, alternatives to DP are presented.

Fluorescent photoimaging with polymers having protected quinizarin dye precursors by a dry process based on chemical amplification

Styrene monomers, possessing three kinds of protected quinizarin (Qz) dye precursors such as tBOC, acetyl and tosyl groups, have been prepared and copolymerized with MMA in high yields to obtain protected-Qz precursor polymers (pr-QzP). Thermal and photoinduced acidolytic deprotection behaviors were investigated to confirm the regeneration of the Qz moieties in the polymer films by thermal and spectral analyses. Lithographic fluorescent photoimaging on spin-cast films of pr-QzP containing a photoacid generator resulted in high resolution and sensitivity by a dry process based on chemical amplification. In the dry lithography process, finely resolved sub-0.4-micrometer fluorescent patterns were delineated on the thin precursor polymer films without using a developer.

Improving lithography pattern fidelity and line-edge roughness by reducing laser speckle

In this article the authors discuss the impact of coherence, or laser speckle, of current generation 193nm argon fluoride (ArF) excimer sources on lithographic patterning. They report a new metrology capability to characterize single-pulse speckle patterns at the exit of the laser aperture and quantify the speckle dependence on time integral square (TIS) pulse duration for different system configurations. The authors performed lithographic exposures on high-numerical-aperture immersion and dry ArF systems as a function of source pulse duration and have quantified the speckle impacts on measured photoresist line-edge roughness (LER) and linewidth roughness (LWR) using immersion and dry lithography processes. Measurements were obtained for multiple feature sizes, pitches, and illumination modes using both static and scanning exposures. They have compared the measured LWR due to laser speckle to results of a line-roughness image model, which accounts for the LER, LWR, and critical dimension uniformity due to the effective dose variation from laser speckle. Finally, the authors present measurements that demonstrate the proportionality between laser speckle contrast and the inverse root of the TIS pulse duration and find that the lithographic LWR exhibits a similar relationship with pulse duration.

A new circular Dammann grating using a Hankel transform

A new circular Dammann grating using a Hankel transform is proposed to generate a number of optical ring patterns. This grating shows that it can achieve high efficiency and excellent uniformity. A numerical solution is also presented together with the fabrication of a third-order CDG by dry etch lithography. Experimental results agree well with the scalar diffraction theory. This grating has the potential to be further developed into practical applications.

A Novel Resist Freeze Process for Double Imaging

In this study we explore a novel resist freeze process for dual imaging with broad resist and lithography track compatibility. The Vapor Reaction Chamber (VRC) hardware is similar to a HMDS prime chamber. Freeze liquids are selected based on their ability to freeze a positive resist image, and among the materials tested, low boiling point diamines were found to be the most effective. Temperature, freeze material, gas flow rate and time are varied to adjust the process and investigate the impact on dual image profiles. Rapid freezing of the 1st photoresist image is achieved when the VRC temperature is near the Tg of the photoresist polymer, and process times are compatible with track wafer flows. The process has been used to create dual imaging features with dry lithography to achieve 45 nm dense L/S patterns.

Plated through-hole vias in a porous polyimide foil for flexible printed circuit boards

A fabrication process for high aspect ratio plated through-hole vias is presented for flexible printed circuit boards. A 75 µm thick porous Kapton foil that allows direct definition of high aspect ratio through-hole vias by dry photoresist film lithography and electrodeposition is presented. Pretreatment with swift heavy ion irradiation and wet etching define the pore density and porosity of the foil, similar to ion-track-etched filter membranes. Thin film metallization of a seed layer and lithography of a laminated dry photoresist film define the via sizes and positions. Subsequent through-hole electrodeposition produces vias consisting of multiple wires, where each open pore defines one wire. The via geometries are characterized by scanning electron microscopy. The electrical properties of the vias are characterized by resistance measurements. Vias with an aspect ratio over 2 and a side length of 33 µm show high yield with low resistance and low variation in resistance.

Double patterning overlay budget for 45nm technology node single and double mask approach

Double patterning (double exposure and double etch) is definitely a viable solution for overcoming the physical resolution limit of k1=0.25 of imaging systems. This article presents the overlay budget for a double patterning technique using a 45nm technology node flash memory device with k1∼0.20 and 193nm dry lithography. Adopting double exposure, the final pattern is composed of two lithography patterns within the resolution capability of the exposure tool and then combined with the double etching processes. The photoetch photoetch approach creates the overlay between the two exposures which is the most critical issue to be addressed. This article presents the adopted scanner setup, mask requirements, and efficient overlay metrology setup in order to achieve the overlay roadmap of 6nm for the 45nm technology node.

Rigorous electromagnetic field mask modeling and related lithographic effects in the low <inline-formula><math altimg="none" display="inline" overflow="scroll"><mrow><msub><mi>k</mi><mn>1</mn></msub></mrow></math></inline-formula> and ultrahigh numerical aperture regime

As smaller feature sizes and hyper-numerical apertures (>1.0) are approached, rigorous electromagnetic field (EMF) simulation of light diffraction from the mask predicts a more pronounced impact of the mask topography, the optical properties of the mask materials, and the polarization of the incident light on the resulting intensity and the phase of the diffracted light, and on the imaging performance of a lithographic process. This work applies rigorous EMF simulation for the exploration of several aspects of the imaging performance of different binary and 6% attenuated mask stacks at the limits of dry, water immersion, and high index or oil immersion lithography. Several consequences with respect to typical lithographic performance parameters are discussed. The described mask diffraction phenomena have a strong impact on the sensitivity of printed linewidths and process windows with respect to the illumination intensity in the preferred state (IPS) of polarization. Advanced diffraction phenomena are also shown to be important for the lithographic performance of assist features. A new metric, the so-called assist bending efficiency (ABEF), is proposed to quantify the related effects. Modifications of the phase of the diffracted light may result in placement errors and process-window deformations.

Investigation of pupil-fill factors as process window indicators for dry optical lithography

This work presents two pupil-fill factors as process window indicators for optical projection lithography when resolution enhancement techniques are employed. The formulations of these two pupil-fill factors are based on two different concepts of the correlation between the process window and the diffraction orders captured at the pupil of the imaging lens. One pupil-fill factor considers the amplitude of the diffracted orders. The other pupil-fill factor considers the extent of overlap between the 0th and the 1st diffraction orders at the pupil. This work investigates how accurately the variation of the two pupil-fill factors indicates the influences of source configuration and mask features on the process window. The Chromeless Phase Shift Lithography (CPL™) technology, in the context of dry optical lithography, is used as a case study. The results suggest that the pupil-fill factor, which considers the amplitude of the diffraction spectrum, is a better process window indicator than the other.

Leaching mechanisms in immersion lithography with or without top coat

The main difference between dry and immersion lithography lies in the interactions between the immersion medium and photoresist. For example, it has been shown that resists components as PAG or base additive can leach into water. Such leaching could degrade the resist performances and the optical elements such as scanner lens. Moreover, it could be involved in new defectivity mechanisms as watermark formation. That’s why immersion dedicated resists with low leaching rate or top coat protective layers have been designed for immersion lithography. However, they do not permit to prevent all leaching and there is always some residual amount of PAG extracted through the barrier layer. Even if leaching phenomena is now well understood for conventional resists, some questions are still present concerning PAG leaching through top coats. In this paper, we present a study of PAG leaching mechanisms through top coats. It is based on leaching kinetics analysis by HPLC/MS. As described in the literature, PAG leaching from dry resists into a static water volume has been shown to follow a first order kinetics model, however, in the case of a top coat stack, we observed a very different behaviour. A new model, taking into account both resist and top coat surface leaching has been developed to fit the experimental data. It illustrates the presence of two leaching mechanisms: a fast one from the top coat surface and a slow one from an embedded interface. This model also provides interesting data about the leaching process on immersion dedicated resists.

Optical lithography—present and future challenges

Optical lithography has been an industrial workhorse for many decades. It has reached a wavelength of 193 nm, a Numerical Aperture (NA) of 0.93 but was facing difficulties to advance further until the debut of immersion lithography. This review deals with the limit of dry and immersion lithography systems, their present and future challenges to reach these very limits. A discussion of defects in immersion lithography, the status of immersion lithography, polarized illumination, high-index materials, solid-immersion mask, double exposure and double patterning is included. To cite this article: B.J. Lin, C. R. Physique 7 (2006).

Simulation for Optimization of Mask Error Enhancement Factor by Design of Experiments in Both Dry and Immersion ArF Lithography

Simulations for the optimization of the mask error enhancement factor (MEEF) by using Taguchi's design of experiment (DOE) method in both dry and immersion ArF lithography have been demonstrated here. By DOE, MEEF has been successfully reduced, and the process window has also been enlarged. Furthermore, in immersion lithography, MEEF has been significantly reduced, and resolution is also enhanced. In this study, we determined the optimal process and optical parameters to enlarge the process window and reduce MEEFs for different types of mask by DOE.