Μm Critical Dimension Research Articles

Large aperture high diffraction efficiency off-axis Fresnel lens fabrication and analysis.

Large aperture high diffraction efficiency off-axis Fresnel lens is one of the most important optical elements in future 10m scale aperture transmissive space telescope systems. Improving diffraction efficiency and effective aperture are long-term goals and bottlenecks for engineering applications. A 4-level off-axis fresnel lens with Ф350 mm effective aperture and 2 µm critical dimension was fabricated through overlay etching technique bylaser direct writing system. Average diffraction efficiency of 75.9% was achieved and certain distribution pattern was observed. Influence of alignment errors on diffraction efficiency distribution was analysed and discussed in detail. This work presented the best results to our knowledge among the same field with similar aperture and critical dimension in open publications, and layed a solid foundation for future large aperture diffractive telescope development.

Surface kinetics and feature scale particle model of SixNy atomic layer deposition using Si2Cl6 precursor

One of the important steps in the fabrication of semiconductor memory devices is the deposition of ultrathin silicon nitride films with uniform film thickness and electrical properties. Such high-quality films have made atomic level control during deposition a necessity and can be achieved via atomic layer deposition (ALD) with excellent step coverage. While ALD has been studied experimentally by many authors, there exist significant gaps between their observations and the practical application of the ALD process in large-scale manufacturing. In this work, a computational model of thin film deposition for a silicon based ALD application was developed. The model includes a surface chemistry mechanism for the deposition of hexachlorodisilane (Si2Cl6) on a growing SixNy film. This mechanism quantifies the sticking probability of the Si2Cl6 precursor on the growth surface as well as an effective active reaction site density on these surfaces. This surface reaction chemistry was used in the context of a feature scale particle transport model to simulate ALD in 100 nm–1 μm critical dimension, ∼10–100 high aspect ratio holes. The model demonstrates the effects of hole size and aspect ratio dependence on the overall kinetics of the deposition process. An increase in the completion time for ALD processes with increasing hole aspect ratio and the increasing statistical nature of the deposition process with smaller critical dimension of the hole were predicted.

Reversible chemocapacitor system based on PDMAEMA polymers for fast sensing of VOCs mixtures

A sensing system, based on tailor-made qPDMAEMA polymers, with the ability to discriminate between methanol and ethanol vapors in the presence or absence of humidity without the need of a separation column and at room temperature is designed and implemented. The miniaturized sensing system is comprised of four polymer coated planar capacitors along with the readout electronic module. The capacitors are fabricated with mainstream microelectronic/micromachining processes forming a planar InterDigitated Electrodes outline with 1 μm critical dimension. Tailor-made, hydrophilic homopolymers and a copolymer based on poly((2-dimethylamino)ethyl methacrylate), synthesized via GTP and quaternized with either methyl iodide or 1-(chloromethyl)naphthalene were used as the sensing layer and were compared to a hydrophobic, commercially available polymer. The sensing system was evaluated upon exposure to humidity, volatile organic compounds and binary mixtures of the latter. Data processing with Principal Component Analysis (PCA) highlights the ability of the proposed sensing system to discriminate between polar analytes, and more importantly between low molecular weight alcohol vapors, ethanol and methanol, in the presence of humidity.

Development of a Microchip CE-HPMS Platform for Cell Growth Monitoring.

Improvements were made to a previously developed platform coupling microchip capillary electrophoresis (CE) with high pressure mass spectrometry (HPMS). The RF drive frequency was increased to over 30 MHz from less than 10 MHz, and the ion trap was scaled down to 100 μm critical dimensions. A stretched length ion trap was used to improve sensitivity, and a tube lens was used to improve ion transmission. Detection of the 20 common amino acids was demonstrated, resulting in an average improvement of signal-to-noise of 28 times and an average improvement in peak width of 2.6 times over those obtained in previous work. Consumption of amino acids by cells in growth media was monitored over time using the improved CE-HPMS platform, and several amino acids were shown to be consumed at different rates, demonstrating the potential for real-time bioreactor monitoring.

Recess Photomask Contact Lithography and the fabrication of coupled silicon photonic and plasmonic waveguide switches

A novel lithographic method is presented, based on the use of a mask aligner in the contact mode with a modified photomask, the so-called recess photomask; its goal is the printing of submicron-sized patterns into deep cavities of a chip, which is not manageable with conventional contact lithography. The photomask (initially a standard photomask) is etched in designated sections in order to obtain a surface nearly conformal to the topography of the wafer to be patterned and allowing to maintain the ultimate resolution of UV mask aligners in the contact mode, down to ∼0.5μm critical dimension at 250nm wavelength in spite of the difficult topography of the chip. The technique is successfully applied to the integration of polymer and gold plasmonic structures in silicon photonic SOI chips with 1.9μm deep cavities intended to accommodate the plasmonic waveguide switching technology. In this specific application, coupling of silicon photonic waveguides with small-footprint plasmonic waveguides can assure ultrafast and low-power electrically-driven thermo-optical switching. The method is generic as it can be applied to any pre-existing resist process and has no theoretical recess depth limit. It is potentially widely applicable to emerging technologies in fields including optoelectronic and integrated optical communications devices, but also potentially MEMS and MOEMS.

Large-aperture fast multilevel Fresnel zone lenses in glass and ultrathin polymer films for visible and near-infrared imaging applications.

The ability to fabricate 4-level diffractive structures with 1 µm critical dimensions has been demonstrated for the creation of fast (∼f/3.1 at 633 nm) Fresnel zone lenses (FZLs) with >60% diffraction efficiency into the -1 focusing order and nearly complete suppression of 0 and +1 orders. This is done using tooling capable of producing optics with 800 mm apertures. A 4-level grating fabricated in glass at 300 mm aperture is shown to have <15 nm rms holographic phase error. Glass FZLs have also been used as mandrels for casting zero-thermal-expansion, 20 µm thick polymer films created with the 4-level structure as a route to mass replication of efficient diffractive membranes for ultralight segmented space-based telescope applications.

A miniaturized chemocapacitor system for the detection of volatile organic compounds

A miniaturized gas sensing system suitable for real life applications, consisting of an array of 8 polymer-coated capacitive sensors and low power read-out electronics is designed and realized. The chemocapacitor array is fabricated with standard microelectronics/micromachining processes allowing for the realization of planar InterDigitated Electrodes (IDEs) with 2 μm critical dimension. The read-out electronics sub-module consists of an analog multiplexer for the sequential measurement of the sensor array elements, a capacitance to 24-bit converter and a USB to I 2 C interface. The electronic sub-module developed, was evaluated against a standard capacitance meter and presents a noise of ∼0.2 fF and therefore capacitance signal (Δ C ) of 0.6 fF (S/N = 3) is detectable. The compact module has been successfully applied in the detection of low concentrations of p-xylene and toluene, according to the international health standards, in the presence of humidity.

Backside Infrared Interferometric Patterned Wafer Thickness Sensing for Through-Silicon-Via (TSV) Etch Metrology

A quantitative metrology technique is required to provide quality control necessary for production-worthy through-silicon-via (TSV) etch. This paper reports on backside infrared interferometric wafer thickness sensing for highly repeatable, nondestructive, and high-throughput determination of TSV depth, unlimited by aspect ratio (AR). Selected etch depth measurements for 1-18 μm critical dimension TSVs with AR up to 28:1 are demonstrated with 3 sigma measurement repeatability of less than 50 nm. On the 5 μm×25 μm TSV etch process baseline on 300 mm wafers, lot-to-lot, run-to-run, and within wafer etch depth variations have been quantified in a production-worthy fashion. This technique has found no appreciable depth differences between dense and isolated TSVs within run, and has identified improvements in run-to-run variability when using oxide conditioning wafers.

High-rate Ru electrode etching using O 2/Cl 2 inductively coupled plasma

We have studied the characteristics of Ru etching using O 2/Cl 2 plasmas in an inductively coupled plasma (ICP) etcher. The changes of Ru etch rates and Ru electrode etching slopes by varying Cl 2/(O 2+Cl 2) gas flow ratio, total flow rate, source power, bias power, and pressure were investigated. A high Ru etch rate of >1400 Å/min with a high etching slope of >85° was demonstrated using 0.15 μm critical dimension (CD) patterned wafers. The mechanism of high-rate Ru etching is studied.

Simulation of the optical effects of particles residing at the bottom of KrF positive photoresist films coated on Si substrates

The reflection effects of Si, SiO2, and Al particles on developed cross-sectional photoresist patterns are simulated by using a two-dimensional waveguide model. The particles were assumed to reside at the bottom of chemically amplified positive photoresist film coated on the Si substrates. The reflection effects were investigated in both cases of particles on the flat surface and on the side slope of the stepped pattern of the substrates. The smallest sizes of particles capable of causing pattern shorts are discussed through a comparison between this work and the authors’ previous work, where the particles reside at the top of photoresist film. In conclusion, the smallest sizes of particles residing at the bottom of the resist film are larger than those of particles residing at the top of the resist film. In addition, because the reflecting light exposes the bottom of the positive resist, after development it apparently helps to realize 0.2 μm critical dimension. Thus the smallest size of the Al particle is larger than that of the Si particle. The reflection from the side of the steps on the Si wafer surface influences the cross-sectional developed pattern of the photoresist film.

InGaP HBT technology for RF and microwave instrumentation

An InGaP emitter HBT IC process developed for RF and microwave instrumentation is described. The process is based on MOCVD epitaxial material, 1 μm critical dimension (CD), G-line, stepper aligned lithography and SiCl 4 based reactive ion etching. F t and F max values of 65 and 75 GHz, respectively are achieved. The HBT technology is well suited for instrument applications in that it can simultaneously achieve both excellent reliability and high performance in terms of broad bandwidth, low phase noise, high gain and linearity. Circuits designed in the process include a Darlington feedback amplifier, which achieves 9.8 dB gain from dc to 20 GHz and dc to 16 GHz dividers. The circuits have been utilized in numerous instrument applications and have resulted in improvements in dynamic range, bandwidth and time-domain jitter. Extensive reliability testing of the InGaP emitter process indicates that MTTF values at T j=150°C and J C=6×10 4 A/cm 2 are greater than 4×10 5 h and are an order of magnitude larger than MTTF values for AlGaAs emitter devices.

Imaging interferometric lithography: A wavelength division multiplex approach to extending optical lithography

The critical dimension (CD) limits of conventional optical lithography follow directly from the low-pass filter characteristics of the imaging optical system (|k|≲2πNA/λ where λ is the optical wavelength and NA the numerical aperture). In contrast, the linear systems limits of optics extend to spatial frequencies of 4π/λ (interference between counterpropagating beams at grazing incidence). Imaging interferometric lithography is introduced as a technique to approach this linear systems limit while retaining the arbitrary pattern capability of an imaging optical system. Multiple, wavelength-division-multiplexed exposures are used, each exposure recording a different portion of frequency space. A conventional, coherent illumination exposure provides the low frequency information, within the lens passband. Offset exposures provide the high spatial frequency information. Off-axis illumination shifts a portion of the high spatial frequency diffraction from the mask into the lens passband and interference with a reference beam resets the frequencies once they are transmitted through the optical system. For a typical x-y geometry pattern, offset exposures in the x and y directions provide a sufficient coverage of frequency space. Model calculations illustrate that the imaging capabilities of imaging interferometric lithography (IIL) for dense features extend to ∼λ/3 (130 nm at I line; 65 nm at an ArF exposure wavelength). Initial experiments are reported at I line with a modest (NA=0.04) optical system. The results are in good agreement with the model calculations. A resolution enhancement of ∼3× from dense 6 μm CDs for a conventional, coherent illumination exposure to ∼dense 2 μm CDs for an IIL exposure sequence is demonstrated.

High performance positive DUV photoresists AZ ® DX 1100P, AZ ® DX 1200P. AZ ® DX 1300P, AZ ® DX 2034P, AZ ® DX 2058P for advanced lithographic applications

An increasing number of DUV resists, which have taken considerable steps on the maturity curve, is available on the market these days. It becomes obvious that - similar to i-line application - there is not the universal resist giving the best fit for every aspect of DUV handling. Meanwhile this seems to find wide acceptance by the majority of the user community. Classifying major commercial PHS based resists according the protective group: acetal, t-BOC and acrylate type with the chemistry concept of low, medium and high activation energy may be distinguished. In order to satisfy specific customer needs Clariant have a commercially available family of AZ® DUV products. These recently developed products include on the positive resist side AZ® DX 1100P, AZ® DX 1200P, AZ® DX 1300P, AZ® DX 21134P and AZ® DX 2058P, all two component acetal-based systems. The details of this resist chemistry are described elsewhere 1 . Dose-to-print versus dose-to-clear ratio is about 2.4 indicating high contrast. Process parameters, as well as selected characteristics and performance items are highlighted in this contribution. AZ® DX 1100P is intended for use on weakly reflective substrates, such as bottom antireflective coatings (BARCs) of organic or inorganic nature. On AZ® BARLi, a BARC originally developed for i-line application, AZ® DX 1100P shows a lines and spaces resolution well below 0.2 μm. Depth of focus (DOF) amounts to 1.05 μm for 0.25 μm critical dimension (CD). Excellent post exposure bake (PEB) latitudes are found where CD change is below 1 nm/°C. Post exposure delay stability for CD 0.2 μm is better than 12 hours for amine concentrations at around 5 ppb. Good substrate compatibility is also found on TiN and Tungsten (W). AZ® DX 1200P is targeted for contact hole (C/H) printing. Besides an excellent sensitivity with the C/H dose to print at around 40 mJ/cm 2 for 0.96 μm resist thickness. C/H ultimate resolution goes down to < 0.2 μm. For CD 0.25 μm the DOF is determined to be greater than 1.2 μm. As far as the baking parameters are concerned, there is full processing compatibility with conventional diazonaphtoquinone/novolak based resists. This is also valid for AZ® DX 1300P, an allround resist, aimed for a wide range of applications on standard and highly reflective substrates. Evaluation highlights of AZ® DX 1300P include high sensitivity of around 20 mJ/cm 2 , excellent resolution down to 0.2 μm and a large DOF of 1.2 μm for 0.25 μm l/s. To respond to most advanced sub 0.2 μm CD needs AZ® DX 2034P comparable to AZ® DX 1100P addresses BARC and AZ® DX 2058P analogous to AZ®DX 1300P covers the remaining more general areas of use.

Ultrathin resist films patterning using a synchrotron radiation lithography system

Ultrathin polymethylmethacrylate (PMMA) films with a width of 17–59.5 nm have been prepared for X-ray resist by Langmuir-Blodgett (LB) technique on a trough using a steady laminar flowing subphase for monolayer compression. Using a synchrotron radiation (SR) lithography system as an exposure tool, patterns with 0.2 μm critical dimensions have been obtained, limited to the mask used.

Fabrication of x-ray masks for giga-bit DRAM by using a SiC membrane and W–Ti absorber

Advanced x-ray masks for giga-bit DRAM require an optimization of the mask fabrication process and a stress-free absorber. In this article, we will describe the performance of the x-ray masks fabricated by a membrane process where back-etch is performed prior to electron beam writing. With other techniques such as stress control by step-annealing and electron beam (EB) multiple writing, mask-to-mask overlay was reduced to less than 40 nm. In spite of multiple EB writing, the pattern size accuracies of 0.14 μm critical dimension were about 10% and 20% for the line and two-dimensional patterns, respectively. For further improvement in the uniformity of absorber stress and resultant higher placement accuracy, a space variant annealing method is proposed, where the nonuniformity of the absorber stress is corrected by spatially variant temperature distribution during the annealing. Under this method, the uniformity of the amorphous W–Ti absorber improved to about 10 MPa in a 50 mm diam region.

Micropatterning for Advanced Interconnections.

Ultra-large integrated devices require an increase in density and number of interconnection levels. The design rules for 0.18μm technologies are 0.2μm for the holes and 0.3μm lines and spaces patterns for the metal level. DUV lithography using advanced techniques will achieve such design rules. However, DUV materials based on chemical amplification have not yet reached full maturity. In this paper, we have investigated their ability to achieve advanced interconnections for both lithography and etching.Regarding the lithographic performance, the two main problems to be overcome are the sensitivity to both delay time and substrate type. We propose a physico chemical method based on DSC measurements to screen the materials able to be processed with minimized sensitivity to both delay and substrates.The selected materials, positive and negative tones, as well as optimized lithographic processes have been used to investigate their etching durability.For the etching step, the main parameters to be considered are the resist selectivity to the etched layer and the resist mask integrity during etching. When using High Density Plasma for oxide etching, the resist mask is modified, leading to striations on the sidewalls of the holes which requires optimization for 0.2μm critical dimensions. In the case of Aluminum etching, the selected DUV resist shows a reduced selectivity as well as a bad sidewall passivation by the polymers compared to I-line photoresists. This will be a limitation to the conventional metal architecture which will be accentuated with the use of copper. The invert metallization schemes are promising as they only require dielectric etching which is less sensitive to the resist process.

Analysis and optimization of x-ray masks using finite element methods

The development of stable, low-distortion masks is one key to the success of x-ray lithography. The 0.25 μm critical dimensions desired require that the membrane distortions due to mounting be minimized. This paper presents some of the analyses, optimizations, and modelling techniques developed at the Center for X-ray Lithography in the area of mask mounting.