Bottom Anti-reflective Coating Research Articles

Sustainable solvent metal lift-off for compound semiconductor fabrication with improved manufacturability

Due to concerns regarding substrate damage, wet photoresist removal has been adopted over dry etch techniques for certain metal lift-off processes on substrates and metals that are susceptible to plasma damage. Wet photoresist removal generally requires the use of polar aprotic solvents and historically n-methyl pyrrolidone (NMP) has been broadly adopted. A successful lift-off process requires consideration of both the solvent used to remove the photoresist as well as the correct photoresist retrograde profile. As features become smaller and more critical, the overall photoresist profile becomes more challenging. The use of bottom anti-reflective coatings (BARC) has become necessary to better control the reflected light and minimize potential defectivity during patterning. However, addition of the BARC layer complicates the resist removal process by requiring a secondary cleaning step since wet photoresist strip chemistries, such as NMP, generally do not remove it. There have been several developmental efforts in the metal lift-off industry to formulate a solvent, which could remove both photoresist and BARC, concurrently. In the first half of this paper, various wet photoresist removers are compared to determine the most effective wet resist strip for removal of both photoresist and BARC in one step. The second half of the paper summarizes two different metal liftoff processes and compares the performance of the best chemistry from initial experimentation, Technistrip® MLO-07, to NMP.

Wafer-scale nanofabrication of sub-100 nm arrays by deep-UV displacement Talbot lithography

In this manuscript, we demonstrate the potential of replacing the standard bottom anti-reflective coating (BARC) with a polymethylglutarimide (PMGI) layer for wafer-scale nanofabrication by means of deep-UV displacement talbot lithography (DTL). PMGI is functioning as a developable non-UV sensitive bottom anti-reflective coating (DBARC). After introducing the fabrication process using a standard BARC-based coating and the novel PMGI-based one, the DTL nanopatterning capabilities for both coatings are compared by means of the fabrication of etched nanoholes in a dielectric layer and metal nanodots made by lift-off. Improvement of DTL capabilities are attributed to a reduction of process complexity by avoiding the use of O2 plasma etching of the BARC layer. We show the capacity of this approach to produce nanoholes or nanodots with diameters ranging from 95 to 200 nm at a wafer-scale using only one mask and a proper exposing dose. The minimum diameter of the nanoholes is reduced from 118 to 95 nm when using the PMGI-based coating instead of the BARC-based one. The possibilities opened by the PMGI-based coating are illustrated by the successful fabrication of an array of nanoholes with sub-100 nm diameter for GaAs nanowire growth on a 2″ GaAs wafer, a 2″ nanoimprint lithography (NIL) master stamp, and an array of Au nanodots made by lift-off on a 4″ silica wafer. Therefore, DTL possess the potential for wafer-scale manufacturing of nano-engineered materials.

Optimization of Single-Step UV Exposure for Fabrication of Integrated Optical Device by Imprinting

In this paper, a single ultra-violet exposure for multi-height structure was used to fabricate an optical-fiberintegrated planar lightwave circuit (PLC) splitter using a thermal imprinting technique. The 1 × 8 tapered multimode PLC splitter was designed with a trench at a depth of 50 μm and a variable width ranging from 50 μm to 690 μm for the insertion of waveguide and fiber structures measuring 125 μm × 87.5 μm in order to minimize insertion loss. Photolithography with a Cr layer and bottom anti-reflection coating (BARC) was utilized to fabricate a multi-height photoresist structure, and the effect of the thick Cr layer and BARC on the geometry was investigated. Scanning electron microscopy of the fabricated structures showed that a Cr thickness of 50 nm and BARC provided the ideal geometry with a minimal undercut and sidewall roughness. Based on the characterization of the imprinted splitter, the average value and uniformity of optical loss between the channels were 10 dB and less than 0.42 dB, respectively.

Fin field effect transistor directionality impacts printing of implantation shapes

In modern integrated circuit (IC) fabrication processes, the photoresist receives considerable illumination energy that is reflected by underlying topography during optical lithography of implantation layers. Bottom antireflective coating (BARC) is helpful to mitigate the reflection. Often, however, BARC is not used, because its removal is technically challenging, in addition to its relatively high economic cost. Furthermore, the advanced technology nodes, such as 14/10-nm nodes, have introduced fin field effect transistor (FinFET), which makes reflection from nonuniform silicon substrates exceptionally complicated. Therefore, modeling reflection from topography becomes obligatory to accurately predict printing of implantation shapes. Typically, FinFET is always fixed in one direction in realistic designs. However, the same implantation rectangle may be oriented in either horizontal or vertical direction. Then, there are two types of relations between the critical dimension (CD) and FinFET, namely a parallel-to and a perpendicular-to relation. We examine the fin directionality impact on CD. We found that this impact may be considerable in some cases. We use our in-house rigorous optical topography simulator to reveal underlining physical reasons. One of the major causes of the CD differences is that in the parallel orientation, the solid sidewalls of the fins conduct considerable light reflections unlike for the perpendicular orientation. This finding can aid the compact modeling in optical proximity correction of implantation masks.

Modification Pathways for Copoly(2-oxazoline)s Enabling Their Application as Antireflective Coatings in Photolithography.

Chromophore-functionalized copoly(2-oxazoline)s are successfully evaluated as bottom antireflective coatings (BARCs) in high-resolution photolithography. With respect to UV light sources used in photolithographic production routines, anthracene is chosen as a chromophore. For application as polymer in BARCs, the copolymer poly(2-ethyl-2-oxazolin)45 -stat-poly(2-dec-9'-enyl-2-oxazolin)20 -stat-poly(2-(3'-(1"-(anthracen-9-ylmethyl)-1",2",3"-triazol-4-yl)propyl)-2-oxazolin)35 can be synthesized by the Huisgen cycloaddition click reaction of the copolymer poly(2-ethyl-2-oxazolin)45 -stat-poly(2-dec-9'-enyl-2-oxazolin)20 -stat-poly(2-pent-4'-inyl-2-oxazolin)35 and the corresponding azide-functionalized anthracenes. These copolymers can be crosslinked by the thermally induced thiol-ene reaction involving the unsaturated C=C bonds of the poly(2-dec-9'-enyl-2-oxazoline) repetition units and a multifunctional thiol as crosslinker. Tests of this BARC in a clean room under production conditions reveal a significant decrease of the swing-curve of a chemically amplified positive photoresist by more than 50%, hence significantly increasing the resolution of the photoresist.

Optoelectronic simulation and optimization of unconstrained four terminal amorphous silicon/crystalline silicon tandem solar cell

Optoelectronic two dimensional technology computer aided design simulation of unconstrained four terminal hydrogenated amorphous silicon/crystalline silicon (a-Si:H/c-Si) tandem solar cells have been carried out. Tandem solar cell approach is one of the promising approaches to achieve high efficiency solar cell by reducing lattice thermalization loss, but needs extensive optimization as the efficiency depends on a number of parameters. The optoelectronic properties of various materials involved have been taken into consideration and a range of parameters such as top anti reflection coating (ARC) thickness, bottom ARC thickness, a-Si:H solar cell thickness, optical connecting layer thickness, a-Si:H solar cell doping, crystalline silicon solar cells doping etc. have been optimized. The optimization resulted in a simulated efficiency of 19.29 % for an untextured planar solar cell.

The effects of the bottom anti-reflective coating with different baked temperatures and thicknesses on nanoscale patterns

The bottom anti-reflective coating (BARC) material can enhance the resolution of the nanopatterns structures in laser interference lithography process. In this study, WIDE-B ARC material was investigated to confirm the reduction of the vertical standing wave which leads to defect of nanopatterns. And the critical dimension (CD) of 100nm L/S patterns with and without the application of BARC material was fabricated by laser interference lithography technology. The compared results showed that BARC can effectively reduce CD swing and obtain more uniform nanopatterns. Meanwhile, we also verified the influence of cured temperature and film thickness of BARC on the uniformity of nanopatterns.

Processing of an Integrated Optical Sensor with Almost 100% Quantum Efficiency

We report on a new fabrication process of integrated PIN photodetectors with very high quantum efficiencies into a 0.35μm CMOS process, including improved processing for bottom antireflective coating (BARC). The integration process is such that complete modularity of the CMOS process remains untouched by the implementation of the highly efficient photodetectors. Due to the fact that only two additional masks and one ion implantation step are necessary for the implementation of PIN photodetectors including BARC, this integration process also proves to be very cost effective. In-house processed p-doped intrinsic layers with EPI doping levels as low as 1∙1012/cm3 serve as CMOS base material. This is a doping level that major semiconductor vendors could not provide. With just one additional mask and ion implantation we provide doping concentrations very similar to standard CMOS substrates to areas outside the photoactive regions. Thus full functionality of the standard CMOS logic can be guaranteed while the photodetectors highly benefit from the low doping concentrations of the intrinsic EPI. Special surface protection techniques are performed to maintain the low doping concentrations of the substrate during the complete CMOS processing. To further enhance the photosensor’s quantum efficiency especially of photodetector arrays we present a new BARC process. With this new BARC process we can lower the dark current in photodiode arrays by at least one order of magnitude compared to currently established plasma-etch methods. The following photodiode parameters could be accomplished for 100x100μm2 single photodiodes with BARC: quantum efficiencies of 76%, 99.8% and 74% at wavelengths of 500nm, 675nm and 850nm, respectively, capacitances of 0.13pF and dark currents of 1.18pA for unbiased photodiodes.

Reflectivity Control at Substrate / Photoresist Interface by Inorganic Bottom Anti-Reflection Coating for Nanometer-scaled Devices

More accurate CD (Critical Dimension) control is required for the nanometer-scaled devices. However, since the reflectivity between substrate and PR (Photoresist) becomes higher, the CD (Critical Dimension) swing curve was intensified. The higher reflectivity also causes PR notching due to the pattern of sub-layer. For this device requirement, it was optimized for the thickness, refractive index(n) and absorption coefficient(k) in the bottom anti-reflective coating(BARC; SiON) and photoresist with the minimum reflectivity. The computational simulated conditions, which were determined with the thickness of 33 nm, n of 1.89 and k of 0.369 as the optimum condition, were successfully applied to the experiments with no standing wave for the 0.13um-device. At this condition, the lowest reflectivity was 0.44%. This optimum condition for BARC SiON film was applied to the process for 0.13um-device. The optimum SiON film as BARC to PR and sub-layer could be formed with the accurate CD control and no standing waver for the nanometer-scaled semiconductor manufacturing process.

Dispersion and origin of surface optical-like waves in a two-dimensional antidot-patterned structure with a soft intervening layer

The phonon dispersion of a square-lattice antidot-patterned Ni80Fe20 film on a bottom-anti-reflective coating (BARC)/Si substrate has been investigated by Brillouin spectroscopy and finite element simulations. Band structures, measured along Γ-M and Γ-X, exhibit Bragg gap openings, surface optical-like and acoustic-like waves, and an acoustically isolating feature arising from the soft BARC layer. A qualitative explanation of the origin of the optical-like waves is presented, by mapping their displacement fields onto reciprocal space. Interestingly, these waves can be frequency shifted, almost independently of the acoustic-like mode frequencies, by varying one of the dimensions of the patterned array on the Ni80Fe20 film.

Wafer Edge Process Integration and Defect Inspection with the Immersion Lithography Process

The study aims at the wafer edge engineering with defect reduction and the corresponding inline inspection methodology. The BARC (bottom anti-reflective coating) step of the immersion lithography in the front-end-of-the-line (FEOL) process was found that would lead to metal film peeling defects at the very later process in middle-end-of-the-line (MEOL). In this work, the wafer-edge inspection tool was used to scan the BARC profile in the wafer edge, including the front-side, apex and the back-side edges and which presents an effective inline routine monitor for EBR (edge bead removal) control of the BARC. The silicon residues were found after the etch process and caused by the bad edge BARC profile at wafer edge. The intrinsic stress of the Ti/N metal film would lead to the delamination and peel off from the wafer-edge silicon residue with poor adhesion. After cycles of experiments, an innovative bevel etching step with oxygen-based gas was added to tailoring the wafer edge profile after active area (AA) lithography, and the peeling defect dramatically trended down to zero.

Precise Cross-Sectional Measurement of Photoresist Shrinkage Caused by Electron Beam Irradiation

A mechanism of the photoresist shrinkage induced by electron-beam (EB) irradiation was studied in detail. A precise cross-sectional profile of a photoresist pattern is obtained by a scanning transmission electron microscope (STEM) after HfO2 atomic layer deposition on a sample. Photoresist lines and spaces formed on either of bottom anti-reflective coating (BARC) layer or spin-on-glass (SOG) layer were exposed to EB at a much higher dose than a practical dose (to accelerate shrinkage intentionally). The obtained STEM images of the patterns before and after EB irradiation showed that EB irradiation causes necking of the pattern profile as well as linewidth slimming. In addition, it was suggested that the BARC layer shrinkage results in the elastic deformation of the pattern profile, whereas the SOG layer does not shrink. Furthermore, EB irradiation only to the lines or spaces was performed. The EB irradiation to spaces caused sidewall shrinkage and necking of the pattern profile, although no electron was irradiated directly into the pattern. This result is considered to be due to the electrons scattered from the spaces to the pattern sidewall. Finally, a Monte Carlo simulation showed that the distribution of the deposited energy on the pattern surface corresponds to the change of the pattern shape. Consequently, our study clarifies the importance of the effect of elastic shape change and the impact of the electrons scattered from the underlying layer to the sidewall on photoresist shrinkage.

Substrate effect on CD Control for Ion Implantation Layer Lithography Beyond 45 nm Node

Implant level photolithography processes are becoming more and more challenging due to decreasing CD and photoresist edge placement requirements. In addition to the traditional proximity effects associated with the implant layer mask, the underlying active and gate layers can interact through a variety of mechanisms to influence the edge placement of the developed implant layer. For many implant layers, the impact of underlying topography cannot be subdued, because, because it is not desirable to employ bottom anti-reflection coating (BARC) for various reasons. Therefore, the implant OPC models calibrated on bare silicon wafers must include additional compensation components to counter the various substrate complexities from real device/design scenarios. In this paper, we show our systematic study on substrate effect (AA/STI) on implant level lithography CD printing including real wafer data analysis and simulation with wafer 3D OPC. Besides, we also show some study of the poly effect on CD. Based on the results, we generate an empirical model to match the substrate effect, and also proposed an approach with additional substrate-aware OPC rule to correct such effect.

Humidity Induced Defect Generation and Its Control during Organic Bottom Anti-reflective Coating in the Photo Lithography Process of Semiconductors

Defect generation during organic bottom anti-reflective coating (BARC) in the photo lithography process is closely related to humidity control in the BARC coating unit. Defects are related to the water component due to the humidity and act as a blocking material for the etching process, resulting in an extreme pattern bridging in the subsequent BARC etching process of the poly etch step. In this paper, the lower limit for the humidity that should be stringently controlled for to prevent defect generation during BARC coating is proposed. Various images of defects are inspected using various inspection tools utilizing optical and electron beams. The mechanism for defect generation only in the specific BARC coating step is analyzed and explained. The BARC defect-induced gate pattern bridging mechanism in the lithography process is also well explained in this paper.

Optimum design of photoresist thickness for 90-nm critical dimension based on ArF laser lithography

In this work, a 90-nm critical dimension (CD) technological process in an ArF laser lithography system is simulated, and the swing curves of the CD linewidth changing with photoresist thickness are obtained in the absence and presence of bottom antireflection coating (BARC). By analysing the simulation result, it can be found that in the absence of BARC the CD swing curve effect is much bigger than that in the presence of BARC. So, the BARC should be needed for the 90-nm CD manufacture. The optimum resist thickness for 90-nm CD in the presence of BARC is obtained, and the optimizing process in this work can be used for reference in practice.

Influence of Photoresist and BARC Selection on the Efficiency of a Post-Etch Wet Strip in BEOL Applications

All-wet processes are gaining a renewed interest for the removal of post-etch photoresist (PR) and Bottom AntiReflective Coating (BARC) in the back-end-of-line (BEOL) semiconductor manufacturing, as plasma ash, traditionally used to remove the PR and BARC layer after etch, cause damage to the low-k dielectric. This study investigates the modification of 193 nm post-etch PR and BARC layer by UV irradiation, that can be used as an intermediate step to enhance PR and BARC wet strip by O3/H2O.

Towards Fully Aqueous Ozone Wet Strip of 193 nm Photoresist Stack Using UV Pre-Treatments in Low-k Patterning Applications

All-wet processes are gaining a renewed interest for the removal of post-etch photoresist (PR) and Bottom Anti Reflective Coating (BARC) in the Back-End-Of-Line (BEOL) semiconductor manufacturing, as an alternative to plasma strip, which may cause damage to advanced porous low-k materials. However, degradation of DUV PR by etch plasmas results in a modified top layer that is cross-linked (so-called crust) and therefore not soluble anymore using pure organic solvents. This study investigates the combination of UV with ozonated processes to remove PR and BARC in BEOL applications. Treatment of PR and BARC by UV irradiation was proved to be an interesting process to increase the concentration of reactive C=C bonds in the post-etch PR and BARC layer. Another effect of UV irradiation is that it can cause scissioning of C–C bonds in the PR main chain, thereby improving the dissolution of the PR in solvents. This UV pre-treatment was used as a preliminary step to enhance PR and BARC removal by ozonated wet strips. Different pathways were studied in detail, leading to the development of a fully aqueous ozonated wet strip process.

PR and BARC Wet Strip in BEOL Patterning Using a UV-Enabled Aqueous Process

Conventional plasma strip processes are prone to cause damage to advanced porous low-k materials. Therefore, all-wet processes are gaining a renewed interest for the removal of post-etch photoresist (PR) and Bottom Anti Reflective Coating (BARC) in Back-End-of-Line (BEOL) semiconductor manufacturing. A two step process with a UV pre-treatment and an ozonated strip process is considered. The UV pre-treatment under O2 at high temperature enhances PR and BARC removal. With a subsequent fully aqueous ozone wet strip, complete removal is feasible.

Interactions between Developable Bottom Anti Reflective Materials and Surface Preparations

Latest generations of integrated circuits require some tight control of critical dimensions during photolithography's operations. Hence the introduction of dBARCs (developable Bottom Anti Reflective Coating) at many litho steps. This greatly improves the optical performances [1], especially when the photo lithography is performed on wafers with irregular topology. Nonetheless a high care is required on the areas where the resist is developed. Indeed, organic residues are often left on these surfaces with serious consequences. This article brings some characterizations' data and solutions.

Use of DBARCs Beyond Implant

Almost a decade ago, the integrated circuit (IC) industry realized that traditional implant layers required new technology to achieve the specifications of the shrinking design rules and increased topography effects. In response, developer-soluble bottom anti-reflective coatings (DBARCs) were introduced as a solution. DBARCs offered the resolution and critical dimension (CD) control needed for the increasingly critical implant layers. In this paper the benefits DBARCs can bring to other lithographic processes are reviewed. Back-end-of-line (BEOL) dual damascene processes are surveyed. Front-end-of-line (FEOL) processes are examined, including high-k metal gate (HKMG), double patterning, and spacer. All processes are defined, and the value that a DBARC brings to each process is examined, along with potential challenges.