Advanced Photolithography Research Articles

Free-standing nanowire printed surfaces with high variability in substrate selection for boiling heat transfer enhancement

Nanowires (NWs) constitute a promising solution to the overheating of high-heat-load surfaces in multiphase heat transfer. Typical nanostructure fabrication methods such as complex photolithography and metal-assisted chemical etching (MACE) that utilize patterned templates are limited by high manufacturing costs and type of substrate materials. These limitations significantly hinder the industrial applicability of NW structures in high heat flux units. In this study, we first examine the effect of the morphology of Zinc oxide (ZnO) NW printed substrates, fabricated via microcontact printing (µCP) and solution based growing, on the heat transfer characteristics in pool boiling. Unlike advanced photolithography, µCP offers greater variability and convenience in terms of the substrate selection and large area creation for NW fabrication. Compared with the silicon substrate, the underlying mechanisms for enhancing both the critical heat flux and heat transfer coefficient of ZnO NW substrates are explored by analyzing the surface morphology, bubble, and wicking characteristics of the test surfaces, in order to determine the applicability of boiling heat transfer using ZnO NWs in industrial fields.

Continuous roller nanoimprinting: next generation lithography.

Nanoimprint lithography (NIL) is a cost-effective and high-throughput technique for replicating nanoscale structures that does not require expensive light sources for advanced photolithography equipment. NIL overcomes the limitations of light diffraction or beam scattering in traditional photolithography and is suitable for replicating nanoscale structures with high resolution. Roller nanoimprint lithography (R-NIL) is the most common NIL technique benefiting large-scale, continuous, and efficient industrial production. In the past two decades, a range of R-NIL equipment has emerged to meet the industrial needs for applications including biomedical devices, semiconductors, flexible electronics, optical films, and interface functional materials. R-NIL equipment has a simple and compact design, which allows multiple units to be clustered together for increased productivity. These units include transmission control, resist coating, resist curing, and imprinting. This critical review summarizes the hitherto R-NIL processes, their typical technical problems, and corresponding solutions and gives guidelines for developing advanced R-NIL equipment.

Fast wafer focus measurement system for photolithography using on-axis structure illumination method

Wafer focus-measuring system (WFMS) with high efficiency and robustness is crucial to ensure the exposure quality when advanced optical projection photolithography method is applied. In this work, we proposed a structure-illumination based wafer focus measuring system (SI-WFMS) which requires only single-step sampling process to implement the measurement of vertical defocus distance of exposure area, with less than 0.06 μm error. Both the surface profile and tilt angle of the wafer are also available to be rapidly measured through SI-WFMS, thereby saving the time of the measuring process and improving the manufacturing efficiency.

Label-free neural networks-based inverse lithography technology.

Neural network-based inverse lithography technology (NNILT) has been used to improve the computational efficiency of large-scale mask optimization for advanced photolithography. NNILT is now mostly based on labels, and its performance is affected by the quality of labels. It is difficult for NNILT to achieve high performance and extrapolation ability for mask optimization without using labels. Here, we propose a label-free NNILT (LF-NNILT), which is implemented completely without labels and greatly improves the printability of the target layouts and the manufacturability of the synthesized masks compared to the traditional ILT. More importantly, the optimization speed of LF-NNILT is two orders of magnitude faster than the traditional ILT. Furthermore, LF-NNILT is simpler to implement and can achieve better solvers to support the development of advanced lithography.

Applicability of the Van Cittert-Zernike theorem in a Ronchi shearing interferometer.

Ronchi shearing interferometry is a promising technique for in situ wavefront aberration measurement of the projection lens in advanced photolithography systems. The Van Cittert-Zernike theorem has been used to analyze the interference signal of a Ronchi shearing interferometer in the effective interference area (overlapping area of the ±1st diffraction orders produced by the image grating). However, the applicability of this theorem has not been systematically studied. In this work, the analytical expression of the Ronchigram in this area is derived based on the theory of scalar diffraction and incoherent imaging. The results show that only the object and image grating with infinite diffraction orders can fully satisfy the Van Cittert-Zernike theorem. In the finite diffraction orders case, the theorem can be considered approximately applicable in the overlapping area of the ±3rd diffraction orders produced by the image grating. The applicable area extends to the overlapping area of the ±2nd diffraction orders under a shear ratio of less than 1%, which accounts for 97% of the effective interference area. The theoretical analysis has been verified by simulation and fundamental experiments.

Study of the ordered assembly morphologies of diblock copolymers on the same substrate.

With the development of frontier technology in emerging semiconductor processes, self-assembling (SA) and directed self-assembly (DSA) of block copolymers (BCPs) have attracted great attention from scientific researchers and become promising candidates for advanced photolithography. Using an optimal coating and baking process, highly ordered assembly morphologies (e.g., cylinder and lamella) of two BCPs in thin films were obtained without an additional topcoat material layer. Moreover, the whole experimental study also provides an optimal process for integrating the two BCPs into the same topographic guiding pattern substrate fabricated by electron beam lithography (EBL) to achieve specific self-assembly. This topographic guiding substrate achieves not only lamellar micro-domains aligned perpendicular to the sidewalls of trench edges but also cylindrical micro-domains (PMMA phase in a PS matrix) aligned parallel to trench edges respectively, which provides insights and valuable information for further applications in lithography and electronic devices.

Evolution and Updates of Advanced Photolithography Technology

Evolution and Updates of Advanced Photolithography Technology

Improving the electrical performance of vertical thin-film transistor by engineering its back-channel interface

This paper reports the effect of the properties of a back-channel region of a vertical thin-film transistor (VTFT) on its electrical performance. The deposition of a thin layer of SiO2 on a damaged back-channel region was found to improve the subthreshold swing (SS) from 0.25 to 0.12 V/dec, while maintaining the field-effect mobility. Detailed analysis of the surface morphology of the back-channel region revealed that the application of advanced photolithography resulted in a significantly smoother back-channel interface, yielding higher-performing VTFTs. The VTFT fabricated using a high-resolution, stepper photolithography system exhibited a linear mobility (μlin) of 14.60 cm2/Vs, a saturation mobility (μsat) of 23.69 cm2/Vs, and an SS value of 0.13 V/dec. Meanwhile, the VTFT fabricated using a standard projection aligner displayed μlin, μsat, and SS values of 5.74 cm2/V·s, 13.87 cm2/V·s, and 0.27 V/dec, respectively. These results revealed the electrical performance of the VTFT to be strongly influenced by the properties of the back-channel region.

On-Wafer FinFET-Based EUV/eBeam Detector Arrays for Advanced Lithography Processes

A novel microdetector array (MDA) for monitoring electron beam (eBeam) and extreme ultraviolet (EUV) lithography processes in 5 nm and beyond FinFET technology is first-time presented. This on-wafer detector array consists of high-density sensing cells which are fully compatible with standard FinFET CMOS processes. Fin coupling structures and energy-sensing pads are first applied in an ultrasmall detector for realizing efficient eBeam and EUV photon detection. In advanced lithography process, eBeam or EUV level projected on the wafer can be precisely recorded on the on-wafer MDA without power or batteries. The distributions and variations on the beam intensities collected by MDA can be electrically measured in real time or inline through wafer level test after eBeam or EUV exposures. The proposed MDA is expected to provide real-time feedback for the optimization and stable maintenance of advanced photolithography processed critical to the development nanometer CMOS technologies.

Intelligent Photolithography Corrections Using Dimensionality Reductions

With the shrinking of the IC technology node, optical proximity effects (OPC) and etch proximity effects (EPC) are the two major tasks in advanced photolithography patterning. Machine learning has emerged in OPC/EPC problems because conventional optical-solver-based OPC is time-consuming, and there is no physical model existing for EPC. In this work, we use dimensionality reduction (DR) algorithms to reduce the computation time of complex OPC/EPC problems while the prediction accuracy is maintained. Also, we implement a pure machine learning approach where the input masks are directly mapped to the output etched patterns. While one photolithographic mask can generate many experimental patterns at once, our pure ML-based approach can shorten the trial-and-error period in the photolithographic correction. Additionally, we demonstrate the automation in SEM images preprocessing using feature detection, and this facilitates intelligent manufacturing in semiconductor processing. The input vector dimensions are effectively reduced by two orders of magnitude while the observed mean squared error is not affected significantly. The computation runtime is reduced from 4804 s of the baseline calculation to 10 s-200 s The MSE values changed from the baseline 0.037 to 0.037 for singular value decomposition (SVD), to 0.039 for independent component analysis (ICA), and to 0.035 for factor analysis (FA).

Low-cost top-down zinc oxide nanowire sensors through a highly transferable ion beam etching for healthcare applications

In this work, we demonstrate a wafer-level zinc oxide (ZnO) nanowire fabrication process using ion beam etching and a spacer etch technique. The proposed process can accurately define nanowires without an advanced photolithography and provide a high yield over a 6-inch wafer. The fabricated nanowires are 36nm wide and 86nm thick and present excellent transistor characteristics. The pH sensitivity using a liquid gate was found to be 46.5mV/pH, while the pH sensitivity using a bottom gate showed a sensitivity of 366mV/pH, which is attributed to the capacitance coupling between the top- and bottom-gates. The maximum process temperature used in the fabrication of the nanowire sensors is optimized to be 200°C (after wet oxidation) which makes it applicable to low-cost substrates such as glass and plastic. The Ion Beam Etching (IBE) process in this work is shown to be highly transferable and can therefore be directly used to form nanowires of different materials, such as polysilicon and molybdenum disulfide, by only an adjustment of the etch time.

Construction of in situ cell separation system by visible light irradiation

Event Abstract Back to Event Construction of in situ cell separation system by visible light irradiation Chie Kojima1*, Yusuke Nakajima1*, Naoya Oeda1*, Takeshi Kawano2* and Yusuke Taki2* 1 Osaka Prefecture University, Dept. Applied Chemistry, Japan 2 Nikon, Japan Introduction: Separation of functional cells from cultured cells is important for cell engineering and regenerative medicine. We designed a visible light-induced in situ single cell detachment system as an advanced photolithography technology. Gold nanoparticle (AuNP) was embedded in a collagen gel to produce a visible light-responsive cell scaffold. When green light is irradiated at the target cells cultured on the AuNP/collagen hybrid gel, the photo-irradiated collagen gel is thermally denatured into the gelatin sol due to the photothermogenic property of the AuNP. Consequently, the irradiated cells are possibly detached from the scaffold (Fig. 1). In this paper, we prepared AuNP/collagen hybrid gels and performed the in situ single cell detachment by irradiating visible light. Experiments: AuNPs with different diameters were prepared by a seeded growth method using hydroquinone [1]. The collagen sol (Cell matrix IA (Nitta Gelatin)) and the AuNPs were mixed and then induced the gel formation according to the manufacturer’s instruction (Collagen 0.08% and [Au]=0.25mM). Several model cells were cultured on the hybrid gel. Laser (532 nm and 50 mW) was irradiated at the center of target cells for 10 s, 30 s or 60 s, followed by the collection of the medium at the above of the gel. Live/dead assay was performed by using calcein-AM and propidium iodide (PI). Results and Discussion: The average sizes of the AuNPs were estimated by TEM. The most effective photochemical property was observed from the 50 nm-sized AuNP, which was consistent with our previous report [2]. The AuNP with 50 nm was embedded in the collagen gel. The hybrid gel exhibited the photochemical properties due to the AuNP, and dissolved around 50 oC. Some kinds of cells (HeLa cells, MCF-7 cells, MDCK cells, GFP-expressing colon26 cells and so on) were cultured on the gel. No significant cytotoxicity was observed before and after the photoirradiation, indicating that our system was biocompatible. The target cells were surveyed, and the green laser was irradiated by using microscopy equipped with the laser irradiation system. The photo-irradiated cells were detached after the collection of the medium. We have attempted to culture the collected cells further. Conclusion: We succeeded in construction of visible light-induced in situ cell detachment system by using the AuNP and the collagen gel. The materials and the separation system are cell-friendly. This technology is useful for cell separation system of desired cells from the cultured cells, which will become a key technology in a wide range of biomedical studies.

The Application of AGILE for 40nm Via Hole Development of Lithography Process and Solutions

As the chip industry enters 45/40 nm technology node and beyond, Via photolithography process is becoming more and more challenging due to decrease of critical dimension (CD) and narrow process window. The effective control on Via CDU becomes more important to improve SRAM yield, however, the CDU has shown highly sensitive to the variations of wafer topography and the leveling capability of a scanner. The Air Gauge Improved Process Leveling (AGILE) function of ASML immersion scanner is a very effective leveling system for the improvement of CDU performance. This paper studies on the implementation and performance of AGILE focus corrections for advanced photo lithography in volume production as well as advanced development in Huali’s 300 mm facility. In particular, a logic hierarchy that manages the air gage sub-system corrections to optimize tool productivity with sufficient sampling frequency to ensure focus accuracy for stable production processes is described.

Nanolithography in microelectronics: A review

The current status of basic photolithographic techniques allowing researchers to achieve results that seemed to be unrealistic even a short time ago is reviewed. For example, advanced DUV photolithography makes it possible to exactly reproduce IC elements 25 times smaller in size than the wavelength of an excimer laser used as a lithographic tool. Approaches owing to which optical lithography has pushed far beyond the Rayleigh-Abbe diffraction limit are considered. Among them are optical proximity correction, introduction of an artificial phase shift, immersion, double exposure, double patterning, and others. The prospects for further advancement of photolithography into the nanometer range are analyzed, and the capabilities of photolithography are compared with those of electronolithography, EUV lithography, and soft X-ray lithography

Study on advanced nanoscale near‐field photolithography

At present, applying a near-field optical microscope to photolithographic line segment fabrication can only obtain nanoscale line segments of equal cutting depths, and cannot result in 3D shape fabrication. This study proposes an innovative line segment fabrication model of near-field photolithography that adjusts an optical fiber probe's field distance to control the exposure energy density, and moreover constructs an exposure energy density analysis method of the innovative photolithographic line segment fabrication. During the exposure simulation process of the innovative line segment fabrication model of near-field photolithography, the near-field distance between the optical fiber probe and the photoresist surface increases gradually, whereas the exposure energy density distribution decreases gradually. As a result, the cutting depth becomes shallower and the full-width at half maximum (FWHM) increases. The results of this study can serve as a theoretical reference for developing advanced nanoscale near-field photolithography techniques, to which an important and groundbreaking contribution is made.

P‐5: Spacer Technique to Fabricate pSi TFTs with 50nm Nanowire Channels

AbstractIn this work, polycrystalline silicon thin‐film transistors (poly‐Si TFTs) with 50‐nm nanowire (NW) channels fabricated without advanced photolithography by using a sidewall spacer formation technique are proposed for the first time. Because the poly gate electrode is perpendicularly across poly‐Si NW channels to form a tri‐gate‐like structure, the proposed poly‐Si NW TFT owns an outstanding gate controllability. In summary, a simple and low‐cost scheme is proposed to fabricate high‐performance poly‐Si NW TFT suitable for future display manufacturing and practical applications.

Electrochemistry on microcircuits. I: Copper microelectrodes in oxalic acid media

Microelectrode size and connections are the two main limitations to conceive microelectrode arrays with a micrometric scale to study the electrochemical phenomena involved in the damascene process. A new chip consisting of an array of microelectrodes realized in an industrial CMOS process addresses these issues. This new fabrication technique for the realization of copper microelectrode arrays was reported. The design and the manufacturing of this device were aimed at studying the behaviour of copper by electrochemical measurements at small scale in media of interest for the microelectronic industry. In this paper, the design and the manufacturing of microelectrode array composed of copper electrode couples of various geometries were described. An advanced photolithography technique developed for the semiconductor industry was used to fabricate them. The tools permitting their characterization are also presented in order to study the wet processes involved in the damascene process by various electrochemical techniques, namely voltammetry and electrochemical impedance measurements.

A Simple Spacer Technique to Fabricate Poly-Si TFTs With 50-nm Nanowire Channels

In this letter, polycrystalline-silicon thin-film transistors (poly-Si TFTs) with 50-nm nanowire (NW) channels, which are fabricated without advanced photolithography by using a sidewall spacer-formation technique, are proposed for the first time. Because the polygate electrode is perpendicularly across poly-Si NW channels to form a trigatelike structure, the proposed poly-Si NW TFT owns outstanding gate controllability. In summary, a simple and low-cost scheme is proposed to fabricate high-performance poly-Si NW TFT suitable for future display manufacturing and practical applications.

Polymer nanostructures in sub-micron lithographically defined channels: film-thickness effects on structural alignment of a small feature size polystyrene-polyisoprene-polystyrene block copolymer.

The use of phase separation in block copolymer systems to generate regular nanopatterns at surfaces may be an alternative to advanced photolithography. Here, substrates with photolithographically defined rectangular channels (of depth 60 nm and widths 166-433 nm) are used to direct nanoscale phase separation of a polystyrene--polyisoprene--polystyrene (PS-PI-PS) block copolymer into aligned periodic superstructures. This nanoscale phase separation results in the rapid formation of parallel and narrow polystyrene (PS) cylinders orientated in a 2D hexagonal arrangement within a polyisoprene (PI) matrix for the polymer composition used here. The PS-PI-PS system is shown to be extremely amenable to simple processing methods allowing precise and homogeneous coating of the substrates. Effects of polymer film thickness are investigated in depth, given that polymer film thickness plays an essential role in the orientation/architecture of the structure formed. It was observed that control of film thickness can determine the orientation of cylinders (parallel or vertical) with respect to the substrate surface. In films where the PS cylinders are aligned parallel to the substrate surface careful control of the processing parameters facilitates the fabrication of regular multi-layer systems ( layers of cylinders) within the channel. The directional effect imposed by the channels is not limited to polymer nanostructures within the channels as long-range order and alignment can be observed at film thicknesses that extend above the channels and onto the outer surface of the substrate. However, as thickness increases, this 'directing' effect conferring alignment is lost.

Fabrication and characterization of two-color midwavelength/long wavelength HgCdTe infrared detectors

High-performance 20-µm unit-cell two-color detectors using an n-p+-n HgCdTe triple-layer heterojunction (TLHJ) device architecture grown by molecular beam epitaxy (MBE) on (211)-oriented CdZnTe substrates with midwavelength (MW) infrared and long wavelength (LW) infrared spectral bands have been demonstrated. Detectors with nominal MW and LW cut-off wavelengths of 5.5 µm and 10.5 µm, respectively, exhibit 78 K LW performance with >70 % quantum efficiency, reverse bias dark currents below 300 pA, and RA products (zero field of view, 150-mV bias) in excess of 1×103 Ωcm2. Temperature-dependent current-voltage (I–V) detector measurements show diffusion-limited LW dark current performance extending to temperatures below 70 K with good operating bias stability (150 mV ± 50 mV). These results reflect the successful implementation of MBE-grown TLHJ detector designs and the introduction of advanced photolithography techniques with inductively coupled plasma (ICP) etching to achieve high aspect ratio mesa delineation of individual detector elements with benefits to detector performance. These detector improvements complement the development of high operability large format 640×480 and 1280×720 two-color HgCdTe infrared focal plane arrays (FPAs) to support third generation forward looking infrared (FLIR) systems.