Lithography Wavelength Research Articles

Deep Learning-Driven Simultaneous Layout Decomposition and Mask Optimization

Combining multiple patterning lithography (MPL) and optical proximity correction (OPC) pushes the limit of 193nm wavelength lithography to go further. Considering that layout decomposition may generate plenty of solutions with diverse printabilities, relying on conventional mask optimization process to select the best candidate for manufacturing is computationally expensive. Therefore, an accurate and efficient printability estimation is crucial and can significantly accelerate the layout decomposition and mask optimization (LDMO) flow. In this paper, we propose a convolutional neural network (CNN)-based prediction and integrate it into our new high-performance LDMO framework. The optimization process can be considerably improved as the decomposition quality has been inferred in the early phase. To facilitate the network training and ensure better estimation accuracy, we develop sampling strategies for both layout and decomposition. Moreover, we enhance the layout sampling approach by adopting auto-encoder to distance evaluation that promises superior sampling results. The experimental results demonstrate the effectiveness and the efficiency of the proposed algorithms.

Electron trapping: a mechanism for acid production in extreme ultraviolet photoresists

The photomechanism of extreme ultraviolet (EUV) exposures in chemically amplified photoresists is much different than that of previous lithographic wavelengths. Electrons generated during EUV exposure are demonstrated to be a source of acid production through a process referred to as electron trapping. Density functional theory modeling indicates that it is energetically favorable for the photoacid generator (PAG) molecule to decompose if an electron is trapped. Low-energy electrons (<10 eV) that are unlikely to produce holes and secondary electrons generate acid-indicating electron–PAG interactions that are capable of inducing decomposition. Additionally, solution phase reduction in PAGs via electrolysis is shown to produce acid. Furthermore, a more easily reduced PAG (i.e., higher likelihood of trapping an electron) produces a higher acid yield, further supporting electron trapping as a process of acid production regardless of the polymer matrix. An acid indicator, Coumarin 6, was used to determine the number of acids generated per absorbed EUV photon. The results of these measurements indicate that electron–PAG interactions are a source of acid production through electron trapping; thus, an increase in the number of electron-hole pairs available to induce chemical reactions would improve sensitivity.

A soft lithographic approach to fabricate InAs nanowire field-effect transistors

The epitaxial layer transfer process was previously introduced to integrate high-quality and ultrathin III-V compound semiconductor layers on any substrate. However, this technique has limitation for fabrication of sub-micron nanoribbons due to the diffraction limit of photolithography. In order to overcome this limitation and scale down its width to sub-50 nm, we need either a costly short wavelength lithography system or a non-optical patterning method. In this work, high-quality III-V compound semiconductor nanowires were fabricated and integrated onto a Si/SiO2 substrate by a soft-lithography top-down approach and an epitaxial layer transfer process, using MBE-grown ultrathin InAs as a source wafer. The width of the InAs nanowires was controlled using solvent-assisted nanoscale embossing (SANE), descumming, and etching processes. By optimizing these processes, NWs with a width less than 50 nm were readily obtained. The InAs NWFETs prepared by our method demonstrate peak electron mobility of ~1600 cm2/Vs, indicating negligible material degradation during the SANE process.

Lithography technology for advanced devices and introduction to integrated CAD analysis for hotspot detection

Optical projection lithography has been the workhorse of the integrate circuit (IC) manufacturing industry to transfer the computer-aided design (CAD) to semiconducting material wafers. The resolution limit of the 193 nm wavelength lithography which was initially targeted for the 90 nm design rule has been further extended to realise ∼10–20 nm devices with ingenious interventions. The three-dimensional fin-shaped field-effect transistor device structure now realise the <20 nm design rule still using 193 nm projection lithography as the widely accepted solution. The extreme ultraviolet wavelength source systems are still in development and testing phases with some recent success reported, but still falling short of supporting volume production requirements. This study reviews the current trends in lithography and the associated resolution enhancement techniques with brief introduction to an integrated CAD analysis for hotspot detection.

Lithographic wavelength control of an external cavity laser with a silicon photonic crystal cavity-based resonant reflector.

We report the experimental demonstration of a new design for external cavity hybrid lasers consisting of a III-V semiconductor optical amplifier (SOA) with fiber reflector and a photonic crystal (PhC)-based resonant reflector on SOI. The silicon reflector is composed of an SU8 polymer bus waveguide vertically coupled to a PhC cavity and provides a wavelength-selective optical feedback to the laser cavity. This device exhibits milliwatt-level output power and side-mode suppression ratios of more than 25 dB.

Comparison of line x-ray emission from solid and porous nano-layer coated targets irradiated by double laser pulses

Enhancement of line x-ray emission from both solid and porous iron targets induced by irradiation of single and double laser pulses is studied numerically. The line emission from laser produced plasma is calculated within the extreme ultra-violet lithography wavelength range of 13.5–13.7 nm. The effects of pre-pulse intensity and delay time between two pulses (pre-pulse and main pulse) are examined. The results show that using double pulses irradiation in the conditions of porous target can reduce the x-ray enhancement. According to the results, the use of both pre-pulse and porous target leads to efficient absorption of the laser energy. Calculations also show that such enhanced laser absorption can ionize atoms of the target material to very high degrees of ionization, leading to decrease of the density of appropriate ions that are responsible for line emission in the selected wavelength region. By increasing the target porosity, x-ray yield was more reduced.

Enhancement of line X-ray emission from iron plasma created by laser irradiation of porous targets

AbstractEnhancement of the line X-ray emission from iron plasma is investigated by simulating laser irradiation of both porous and solid targets. Spectral line intensities are calculated for selected lines of the iron plasma within the extreme ultra-violet lithography wavelength range 13.3–13.7 nm. The calculations show that X-ray yield in porous targets can be enhanced significantly in comparison with solid density targets. The results also show that for specified conditions of the driving laser, there are optimums conditions of the porous target in which maximum yield can be obtained.

Near‐Bulk Conductivity of Gold Nanowires as Nanoscale Interconnects and the Role of Atomically Smooth Interface

The electronics industry has consistently decreased the dimensions of structural components and they are now well into the nanoscale range. Naturally, a significant portion of the chip is composed of interconnects. Besides, the engineering problems associated with short wavelength lithography to achieve smaller components, the performance of increasing number of interconnections has become one of the biggest limiting factors in device performance. [1,2] The power loss, signal degradation, interconnection delays, and other performance limitations related to interconnects should be minimized. The importance of such a task can be seen from the perspective of power dissipation by computation elements. The energy dissipation density in electronic chips approaches that in nuclear reactors. [3,4] Therefore, the decrease of the resistivity of metal interconnects is one of the key challenges in the design of nanoscale electronic circuits. Intense studies on methods of preparation of interconnects by advanced lithographic techniques including e-beam lithography lead to the preparation of Au, Pd, Pt, and Cu nanowires (NWs) with resistivities much greater than the bulk metal value (see Supporting Information). [5‐11] The reason for the drastic increase in resistivity for NWs is that charge carriers experience grain boundaries reflections and surface scattering. The smaller the diameter of the conductor, the greater this effect becomes. Even NWs with diameters much above the nanometer scale can exhibit resistivities as high as two orders of magnitude greater that the bulk. [12]

A compact, quasi-monochromatic laser-plasma EUV source based on a double-stream gas-puff target at 13.8 nm wavelength

A compact, high-repetition table-top EUV source, based on a gas-puff target, is presented. This source was developed in our group and is capable of emitting quasi-monochromatic radiation at 13.8 nm wavelength with the inverse relative bandwidth of 140 and pulse energies up to ∼1.3 μJ/pulse at 10-Hz repetition rate. The source is debris-free, operates near the lithographic wavelengths and offers the energy density of ∼0.4 mJ/cm2 in each EUV pulse. These three features make the source attractive for lithographic experiments. The timing optimization of the source, its energy per pulse, spectral and spatial distributions are pointed out in detail as well as the enhancement in energy density achievable with a multi-layer collector mirror compared to a planar mirror of equal reflectivity.

Wire Sizing and Spacing for Lithographic Printability and Timing Optimization

As the VLSI feature size has already decreased below lithographic wavelength, the printability problem, due to strong diffraction effects, poses a serious threat to the progress of VLSI technology. A circuit layout with poor printability implies that it is difficult to make the printed features on wafers follow designed shapes without distortions. The development of resolution enhancement techniques (RET) can alleviate the printability problem but cannot reverse the trend of deterioration. Moreover, over-usage of RET may dramatically increase photo-mask cost and increase the cycle time for volume production. Thus, there is a strong demand to consider the subwavelength printability problem in circuit layout designs. However, layout printability optimization should not degrade circuit timing performance. In this paper, we introduce a wire sizing and spacing method to improve wire printability with minimal adverse impact on interconnect timing performance. A new printability model is proposed to handle partially coherent illuminations. The complex printability and timing optimization problem is solved in a two-phase approach. The difficulty of the printability optimization due to its multimodal nature is handled with a sensitivity-based heuristic. A coupling aware timing driven continuous wire sizing algorithm is also provided. Lithographic simulation results show that our approach can improve the printability in term of edge placement error (EPE) by 20%-40% without violating timing, wire width, and spacing constraints.

Study of SiOxNy as a bottom antireflective coating and its pattern transferring capability

To meet such challenges for the controlling of critical feature dimension at sub-50–100‐nm, it has been a general industrial trend to employ shorter wavelength (193nm, for example) lithography for better resolution and to use bottom antireflective coating (BARC) for a reduced standing wave formation and thus, a better critical dimensional control. Matching the optical constants (n,k) between the BARC, photoresist, and the underlayer to be patterned is critical for the elimination of such standing waves. SiOxNy and SiOxCy are two attractive inorganic BARC candidates in view of their easily adjustable optical constants by varying the deposition parameters and their etching compatibility with standard semiconductor plasma processes. In this article, SiOxNy films were prepared by plasma enhanced chemical vapor deposition approach. These films have been further characterized using x-ray photoelectron spectroscopy for chemical composition depth profile, Fourier transform infrared spectroscopy for local chemical bonding, and ellipsometry for optical constants. It has been demonstrated that the refractive indices of SiOxNy can be tuned from 1.6 to 2, while the absorption constants k can be adjusted from 0.1 to 0.9 by changing the process parameters, such as SiH4 flow rate, NH3 flow rate, and SiH4∕N2O ratio. To integrate the SiOxNy BARC film into the storage device manufacturing, the pattern transferring capability of SiOxNy has been discussed. A film stack structure of photoresist∕SiOxNy∕carbon or SiC hard mask∕magnetic device layer has been used to evaluate the performance of the SiOxNy BARC. SiOxNy film was opened via inductively coupled plasma etching with CHF3+O2 chemistry, while carbon and SiC hard masks were opened using He–O2 and SF6–He–O2 chemistries, respectively. SiF emission line at 388nm wavelength was used for end point during the SiOxNy etching, while the 778nm O peak and 685nm F peak have been used for carbon and SiC end pointing. The profiles of the etched SiOxNy and carbon∕SiC were analyzed by cross-section transmission electron microscopy.

투과율 조절 포토마스크 기술의 ArF 리소그래피 적용

We report theoretical and experimental results for application of transmittance-controlled photomask technology to ArF lithography. The transmittance-controlled photomask technology is thought to be a promising technique fo critical dimension (CD) uniformity correction on a wafer by use of phase patterns on the backside of a photomask. We could theoretically reproduce experimental results for illumination intensity drop with respect to the variation of backside phase patterns by considering light propagation from the backside to the front side of a photomask at the ArF lithography wavelength. We applied the transmittance-controlled photomask technology to ArF lithography for a critical layer of DRAM (Dynamic Random Access Memory) having a 110-nm design rule and found that the in-field CD uniformity value was improved from 13.8 nm to 9.7 nm in .

Embedded metal mask enhanced evanescent near field optical lithography

Simulation of evanescent optical lithography using an embedded metal mask (EMM) shows that resolution and throughput are significantly enhanced over conventional ENFOL, due to coupling between surface plasmons and cavity mode excitations. The key role played by surface plasmon polaritons and the effects of wave vector matching between the incoming photon and the EMM mask grating are clear from the simulation. In particular a double peaked resonant intensity distribution is revealed for the first time within the dielectric filled mask cavity, for the shorter wavelengths only. This effect is highly conducive to efficient sub wavelength lithography and has not been discovered by previous simulations. The EMM–ENFOL process has considerable potential for cheap, high throughput nanolithography with resolution well below diffraction limits.

Linear birefringence in CaF2 measured at deep ultraviolet and visible wavelengths

We describe the application of a linear birefringence measurement system at the optical lithographic wavelengths (157, 193, and 248 nm). Using this instrument, we obtain linear birefringence maps of a variety of calcium fluoride samples with different crystal orientations and at different DUV (deep ultraviolet) wavelengths. Comparing the birefringence results measured at DUV and visible wavelengths, we find that some calcium fluoride samples show a strong correlation in birefringence measured at different wavelengths while others do not. Significant differences in birefringence patterns are observed at 157 and 633 nm for certain calcium fluoride samples when the light beam propagates along the [111] crystal axis. We explain the discrepancy in the birefringence patterns observed at 157 and 633 nm based on the crystalline structural quality of calcium fluoride samples.

Quantum chemical modeling for 157 nm photolithography

In its continuing quest for smaller length scales, the electronics industry plans to introduce 157 nm as the next lithographic wavelength. Accordingly, there is a pressing need to develop photoresists that are more transparent, and pellicles that are both more transparent and more durable. With the advent and popularization of time-dependent density functional theory (TD-DFT), we now have a practical quantum chemical method for calculating excitation energies and transition moments in the vacuum ultraviolet (VUV) which can greatly assist in the scouting of highly transparent materials. We have performed TD-DFT calculations for a broad variety of fluorinated molecules and we will report calculated VUV photoabsorption spectra for a large family of model fluorohexanes. These calculations, which span a range from 1-fluorohexane to CH 3CF 2CF 2CF 2CF 2CH 3, illustrate some of the principles one may use to design low absorption polymeric materials.

Novel hydrofluorocarbon polymers for use as pellicles in 157 nm semiconductor photolithography: fundamentals of transparency

With the advent of 157 nm as the next photolithographic wavelength, there has been a need to find transparent and radiation durable polymers for use as soft pellicles. Pellicles are ∼1 μm thick polymer membranes used in the photolithographic reproduction of semiconductor integrated circuits to prevent dust particles on the surface of the photomask from imaging into the photoresist coated wafer. Practical pellicle films must transmit at least 98% of incident light and have sufficient radiation durability to withstand kilojoules of optical irradiation at the lithographic wavelength. As exposure wavelengths have become shorter the electronics industry has been able to achieve adequate transparency only by moving from nitrocellulose polymers to perfluorinated polymers as, for example, Teflon ® AF 1600 and Cytop™ for use in 193 nm photolithography. Unfortunately, the transparency advantages of perfluorinated polymers fail spectacularly at 157 nm; 1 μm thick films of Teflon ® AF 1600 and Cytop™ have 157 nm transparency of no more than 38 and 2%, respectively, with 157 nm pellicle lifetimes measured in millijoules. Polymers such as [(CH 2CHF) x C(CF 3) 2CH 2] y , or (CH 2CF 2) x [2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole] y  with chains that alternate fluorocarbon segments with either oxygen or hydrocarbon segments frequently show >98% transparency at 157 nm, if amorphous. These polymers are made from monomers, such as vinylidene fluoride (VF 2) and hexafluoroisobutylene, which themselves exhibit good alternation of CH 2 and CF 2 in their structures. In addition, we find that ether linkages also can serve to force alternation. In addition, we find that fluorocarbon segments shorter than six carbons, and hydrocarbon segments less than two carbons or less than three carbons if partially fluorinated also promote 157 nm transparency. We also find that even with these design principles, it is advantageous to avoid small rings, as arise in the cyclobutanes. These results suggest a steric component to transparency in addition to the importance of alternation. Upon irradiation these polymers undergo photochemical darkening and therefore none has demonstrated the kilojoule radiation durability lifetimes required to be commercially attractive. This is likely because these exposure lifetimes require every bond to absorb ∼10 photons, each photon having an energy roughly twice common bond energies. We have studied intrinsic (composition, molecular weight) and extrinsic (trace metals, impurities, environmental contaminants, oxygen, water) contributions to optical absorption and photochemical darkening in these polymers. Studies of photochemical darkening in model molecules illustrate the dynamics of photochemical darkening and that appreciable lifetimes can be achieved in fluorocarbons. To a first approximation the polymers that have lower 157 nm optical absorbance also tend to show the longest lifetimes. These results imply that quantum yield, or the extent to which the polymer structure can harmlessly dissipate the energy, can be important as well.

Linear birefringence measurement at 157 nm

The author describes a linear birefringence measurement instrument designed for the new optical lithography wavelength—157 nm. This instrument contains a deuterium lamp with magnesium fluoride window, a monochromator, a polarizer-photoelastic modulator (PEM) combination, a PEM-polarizer combination, and a photomultiplier tube. The sample is placed between the two PEMs. For measuring linear retardation, the signals carried on the first harmonics of the two PEMs are analyzed using lock-in amplifiers. A computer program calculates and displays both the retardation magnitude and angle of fast axis. The instrument reported here is a special polarimeter designed for measuring linear retardation in high quality optical components at 157 nm and other deep-ultraviolet wavelengths. It provides a retardation sensitivity of 0.01 nm at 157 nm.

Progress in deep-UV photoresists

Higher resolution can be achieved in lithography by decreasing the wavelength of the exposure source. However, resist material and their processing are also important when we move to a shorter wavelength lithography technology. This paper reviews the recent development and challenges of deep-UV photoresists and their processing technology.

Enabling alternating phase shifted mask designs for a full logic gate level

The International Technology Roadmap for Semiconductors lists F2 (157 nm exposure wavelength) optical lithography and extreme ultraviolet (EUV) next generation lithography as the two most feasible lithography solutions for the 70 nm technology node. It is very likely that both of these lithography solutions will be late, forcing ArF (193 nm exposure wavelength) lithography to operate at unprecedented resolution levels. Lithographically, alternating phase shifted masks (altPSM) can achieve the resolution required to manufacture 70 nm logic products with ArF lithography equipment [P. Schiavone, F. Lalanne, and A. Prola, Clear field alternating PSM for 193 nm lithography, Proc. SPIE 3679, 582-589 (1999) and M. Fritz et al., Application of chromeless phase-shift masks to sub-100 nm SOI CMOS transistor fabrication, Proc. SPIE 4000, 388-407 (2000)], but technical and logistical challenges associated with the broad implementation of altPSM require novel and invasive EDA solutions which have caused the industry to shy away from altPSM in the past. Since the resolution capabilities of altPSM are well understood in the lithography community, this paper will focus on the challenges facing altPSM implementation for the polysilicon gate level and will present the results of a detailed altPSM design feasibility study done at IBM for the 180 nm technology node. While the 70 nm technology node will push resolution harder then ever before, the design rules, EDA tools, and layout methodologies developed in the past lay the foundation for our attack on this challenging technology node.

Implementing advanced lithography technology: A 100 MHz, 1 V digital signal processor fabricated with phase shifted gates

To demonstrate the effectiveness of alternating aperture phase shift lithography for integrated circuit manufacturing, a demonstration device was designed and processed. A 2 million transistor integrated circuit was processed with a phase shifted gate level using 248 nm wavelength lithography. The lithographic results were confirmed by careful feature size measurements throughout the process sequence and finally by the performance of the devices themselves. Gate lengths were reduced from 240 to 120 nm, resulting in fully functional chips with 100 MHz circuit speed at 1.0 V operation, more than a two-fold speed improvement and a record for communication circuits of this type at a low supply voltage.