Outside Front Cover: Plasma Process. Polym. 10/2022

Microwave Kinetic Inductance Detectors (MKIDs) provide a compelling path forward to the large-format polarimeter, imaging, and spectrometer arrays needed for next-generation experiments in millimeter-wave cosmology and astronomy. We describe the development of feedhorn-coupled MKID detectors for the TolTEC millimeter-wave imaging polarimeter being constructed for the 50-meter Large Millimeter Telescope (LMT). Observations with TolTEC are planned to begin in early 2019. TolTEC will comprise ∼7,000 polarization sensitive MKIDs and will represent the first MKID arrays fabricated and deployed on monolithic 150 mm diameter silicon wafers - a critical step towards future large-scale experiments with over 105 detectors. TolTEC will operate in observational bands at 1.1, 1.4, and 2.0 mm and will use dichroic filters to define a physically independent focal plane for each passband, thus allowing the polarimeters to use simple, direct-absorption inductive structures that are impedance matched to incident radiation. This work is part of a larger program at NIST-Boulder to develop MKID-based detector technologies for use over a wide range of photon energies spanning millimeter-waves to X-rays. We present the detailed pixel layout and describe the methods, tools, and flexible design parameters that allow this solution to be optimized for use anywhere in the millimeter and sub-millimeter bands. We also present measurements of prototype devices operating in the 1.1 mm band and compare the observed optical performance to that predicted from models and simulations.

The complexification of integrated circuit designs along with downscaling introduces new patterning challenges. In logic process integration, it is found that the gate etch process flow introduces a few nanometer displacement of the gate patterns from their original position fixed by the lithography layout. This phenomenon referred to gate shifting (GS) generates a contact to gate overlay misplacement that compromises the transistor electrical performance. HBr cure plasma, which is a well-established postlithography treatment to increase photoresist stability and improves both line edge roughness (LER) and critical dimension uniformity during pattern transfer, has been identified as the root cause of the gate shifting phenomenon. The vacuum ultraviolet (VUV) irradiation emitted by HBr plasma leads to an asymmetric flowing of the two-dimensional resist patterns, and thus to a displacement of the gate patterns. Based on plasma optical emission measurements, the HBr plasma conditions are optimized to limit the VUV irradiation. If the GS phenomenon can indeed be eliminated using low VUV dose HBr plasma conditions, it introduces some strong LER issue during the subsequent Si antireflective coating (Si ARC) fluorocarboned plasma process. Indeed, low VUV dose HBr cure plasma does not play anymore its hardening role. The elimination of the GS issue is a priority for the transistor electrical performance. The strategy adopted in this study is to remove the HBr cure treatment and to optimize the subsequent Si ARC etch plasma process to minimize LER degradation during this step. The developed SF6/CH2F2 Si ARC plasma etching process uses low energy ion bombardment combined with a fluorine rich chemistry to avoid the formation of a fluorocarbon polymer on the resist pattern, which is the main contributor for resist surface and sidewalls roughening. The new gate patterning process flow that is proposed in this article allows to eliminate the GS phenomenon but also to improve the final gate LER from 3.5 to 2.8 nm. Moreover, the study highlights the capability of the developed SF6/CH2F2 Si ARC plasma chemistry to address the most advanced nodes with even more aggressive gate dimensions by eliminating the wiggling phenomenon occurring with previous Si ARC plasma chemistries for gate dimension inferior to 25 nm.

In this article, we report the absolute intensities of ultraviolet light between 4.9 and 24 eV (250 to 50 nm) striking a silicon wafer in a number of oxide etch processing discharges. Our emphasis is on photons with energies greater than 8.8 eV, which have enough energy to damage SiO2. These discharges were in an inductively driven Gaseous Electronics Conference (GEC) reference cell which had been modified to more closely resemble commercial etching tools. Comparisons of measurements made through a side port in the cell and through a hole in the wafer indicate that the vacuum ultraviolet (VUV) light in these discharges is strongly trapped. For the pure halocarbon gases examined in these experiments (C2F6, CHF3, C4F8), the fluxes of VUV photons to the wafer varied from 1 to 3×1015 photons/cm2 s or equivalently from 1.5 to 5 mW/cm2. These measurements imply that 0.1%–0.3% of the rf source power to these discharges ends up hitting the wafer as VUV photons for our typical 20 mT, 200 W rf discharges. For typical “ashing” discharges containing pure oxygen, the VUV intensities are slightly higher—about 8 mW/cm2. As argon or hydrogen diluents are added to the fluorocarbon gases, the VUV intensities increase dramatically, with a 10/10/10 mixture of Ar/C2F6/H2 yielding VUV fluxes on the wafer 26 mW/cm2 and pure argon discharges yielding 52 mW/cm2. Adding a rf bias to the wafer had only a small effect on the VUV observed through a side port of the GEC cell.

Vacuum ultraviolet (VUV) photons in plasma processing systems are known to alter surface chemistry and may damage gate dielectrics and photoresist. We characterize absolute VUV fluxes to surfaces exposed in an inductively coupled argon plasma, 1–50 mTorr, 25–400 W, using a calibrated VUV spectrometer. We also demonstrate an alternative method to estimate VUV fluence in an inductively coupled plasma (ICP) reactor using a chemical dosimeter-type monitor. We illustrate the technique with argon ICP and xenon lamp exposure experiments, comparing direct VUV measurements with measured chemical changes in 193 nm photoresist-covered Si wafers following VUV exposure.

Fast on-line detection of organic compounds from complex mixtures, such as industrial process gas streams, require selective and sensitive analytical methods. One feasible approach for this purpose is the use of mass spectrometry (MS) with a selective and soft (fragment-free) ionization technique, such as chemical ionization (CI) or photo ionization (PI). Single photon ionization (SPI) with vacuum ultraviolet (VUV) light is a particularly sof tionization technique, well-suited for detection of both aromatic and aliphatic species. Problematic, however, is the generation of the VUV light. In general, the vacuum ultraviolet (VUV) light sources for SPI-MS are based either on lasers (e.g., 118-nm radiation generated by frequency-tripling of the third harmonic of a Nd:YAG laser) or on conventional VUV lamps, such as deuterium lamps. Althoughthe laser-based techniques are very sophisticated and expensive, the conventional lamps have serious drawbacks regarding their optical parameters, such as low-output power, low spectral power density, and broad emission bands. In this work, a novel excimer VUV light source, in which an electron beam is used to form rare gas excimer species, is used. The excimer VUV light sourceproduces brilliant and intense VUV light. The novel VUV light source was coupled to a compact and mobile time-of-flight mass spectrometer (TOFMS). A special interface design, including optical (VUV optics) as well as electronic measures (e.g., pulsed ion extraction) was realized. The use of the excimer VUV lamp for SPI will allow the realization of very compact, rugged, and sensitive SPI-TOFMS devices, which preferably will be adapted for process analytical application or monitoring issues (e.g., chemical warfare detection). The excimer VUV-lamp technology delivers VUV light with a good beam quality and high-output power at low costs. Furthermore, it allows changing the emitted wavelength as well as the bandwidth of the excimer VUV lamp in t he 100-200-nm region by changing the gas filling. Consequently, SPI-TOFMS with an excimer light source is a fast detection technique that can be used for online monitoring, for example, in environmental studies or industrial manufacturing processes. In this paper, technology and characteristics of the new excimer light source, as well as the combination with the TOFMS, are presented. Furthermore, a first characterization of the SPI-TOFMS instrument, regarding analytical parameters such as detection limits and selectivity, is given. This includes a discussion of potential improvements that probably will be achievable within a future prototype genertation. Finally, first applications of the system for on-line measurement of organic trace species in a complex gas mixture (here, motorcycle exhaust gas) are presented.

In this study, an optical system for simultaneous measurement of physical thickness, group refractive index, bow, and warp of a large silicon wafer is first proposed based on a reflection-type spectral-domain interferometer. Such key parameters are determined by combining four different optical path differences (OPDs) measured at each sampling point throughout two-axis sample scanning within area of 250 mm by 250 mm. To overcome the measurement limitations by the deflection of a free, unclamped large-sized wafer, two OPDs representing the surface profiles of both sides are utilized to facilitate the thickness and refractive index measurements insensitive to sample inclination. For verification of the proposed method, a 300 mm diameter silicon wafer with nominal thickness of 775 μm was used as a test sample. For measuring the bow and warp with gravity effect compensation, a silicon wafer was measured once again after turning over. Through theoretical analysis on the changes of OPDs with the wafer tilted based on the measured surface profiles, it was verified that the effect of wafer bending on thickness and refractive index measurements can be ignored. The measurement uncertainties (k = 1) of physical thickness, group refractive index, bow, and warp were evaluated to be approximately 0.692 μm, 0.003, 0.416 μm, and 0.589 μm, respectively.

Several ion source related research and development projects are in progress at the Department of Physics, University of Jyväskylä (JYFL). The work can be divided into investigation of the ion source plasma and development of ion sources, ion beams, and diagnostics. The investigation covers the Electron Cyclotron Resonance Ion Source (ECRIS) plasma instabilities, vacuum ultraviolet (VUV) and visible light emission, photon induced electron emission, and the development of plasma diagnostics. The ion source development covers the work performed for radiofrequency-driven negative ion source, RADIS, beam line upgrade of the JYFL 14 GHz ECRIS, and the development of a new room-temperature-magnet 18 GHz ECRIS, HIISI.

A new silicon wafer bonding process based on dielectric heating of an intermediate layer has been developed and characterized. This method uses a capacitive RF field to heat a dielectric interlayer up to its glass transition temperature and permanently join two wafers. A 500 W 14 MHz source was used to deliver RF power to the substrates. Two inches diameter silicon wafers with 2-20 /spl mu/m thick polyimide intermediate layers were successfully bonded (> 95% bond area) in less than 7 minutes. The silicon substrate temperature remained below 280/spl deg/C throughout the bonding process. The results of the pull tests indicate a bond strength of >1.5 MPa for fully cured substrates, which is greater than the strength of other low-temperature adhesive bonds.

We have successfully grown ultrathin oxides on large area of silicon wafers by the microwave plasma afterglow oxidation method. Analysis of the Fourier transform infrared spectra indicates that the general bonding structures of the ultrathin oxides grown by microwave plasma afterglow oxidation at 700 °C could be identical to those grown by dry O2 thermal oxidation. Electrical property measurements (e.g., time-zero dielectric breakdown and time-dependent dielectric breakdown) are also investigated. Based on our results, we conclude that microwave plasma afterglow oxidation is a useful method for the preparation of large area ultrathin oxide films on silicon substrates.

Zinc oxide (ZnO), as a wide band gap (3.37 eV) semiconductor, are useful materials for wide range of applications in thin-film transistor (TFT), photovoltaics, photocatalysts, sensors, and so on. Large exciton binding energy (60 meV) at room temperature (RT) makes ZnO a promising luminescent material especially in optoelectronic devices such as UV lasers and light emitting diodes (LED). Among them, ZnO nanocrystals (quantum dots) has attracted increasing attention because their optical properties can be tuned by varying the crystal size. However, its nanoscale crystallites tend to aggregate to undergo Ostwald ripening due to their high surface energy. To stabilize them, surface modification are usually necessary. At the same time, the whole processes for nanocrystal synthesis and film fabrication become complicated.Here, we report a simple novel photochemical gel conversion approach for one-step preparation of ZnO thin films with an average nanocrystals in about 2-3 nm size (inset in Fig. 1a), by employing vacuum ultraviolet (VUV) light irradiation in dry N2. Systematic characterization is performed to understand the surface chemistry and the optical properties of ZnO nanocrystals. Thus obtained ZnO films show unique absorption peak at 294 nm (4.2 eV) (Fig. 1a) and strong tunable photoluminescence in the range of 386-496 nm when expose to UV light, from violet, blue to bluish-green upon increasing time of VUV irradiation (Fig. 1b). Clearly blue-shifted absorption peaks of the VUV treated samples are indicative of quantum-confinement effect, as contrasted to the broad character of the annealed film, which originates from band structure of bulky ZnO. The extension of VUV time only results in increase of absorbance, with no change of the peak wavelength, indicating population increase but no crystal growth by Ostwald ripening during the VUV irradiation. Therefore, the color change of the emitted light should be associated with the change of defect state distribution, rather than the size effect. However, such photoluminescence from defects was fairly strong to be clearly recognized by naked eyes, so that the university logo could be patterned by photomasking VUV to be seen under black light was demonstrated (inset in Fig. 1b). Figure 1

This paper reports on the application of infrared external reflection spectroscopy (IR-ERS) to the characterization of small surface area addresses prepared on smooth gold surfaces after modification for use as capture substrates in sandwich immunoassays based on surface-enhanced Raman scattering (SERS). Most of the past work with IR-ERS on analyzing coatings formed on highly reflective metals utilized relatively large area samples (e.g., 76 × 25 mm glass microscope slides and ∼51 mm diameter silicon wafers) to accommodate the large size of the elliptical IR beam reflected off the metal surface at grazing angles of incidence. Our interest in employing assay-sized (3 mm diameter) addresses for IR-ERS measurements arises from the need to minimize the consumption, and, thereby, the expense of rare biological reagents like the antibodies under development for immunoassays to detect tuberculosis. The obvious approach to achieving this goal would be to utilize the spatial resolution and sample scanning capabilities of Fourier transform infrared (FT-IR) microscopes. We, however, opted to re-examine the physical optics and geometric layout of the measurement through an analysis of the strength of the mean square electric field at the sample/substrate interface as a function of angle of incidence. These findings suggested that, given the high light throughput and low noise levels of today's FT-IR spectrometers, it may be possible to perform these measurements simply by collecting spectra at a lower angle of incidence when using the optical layout of a standard IR-ERS experiment. Herein, we report both the theoretical analysis and experimental results that demonstrate it is possible to obtain useful spectra from much smaller samples than those traditionally used, e.g., those employed in our SERS-based immunoassays, simply by decreasing the angle at which the IR beam is incident on the sample surface. We also demonstrate that these types of samples can be analyzed by constructing a small jig that allows for the careful positioning of the sample in the IR beam, rather than by extensively modifying the optics of the IR-ERS accessory.

Carbon nanotubes were patterned by a nonphotolithographic, low energy, large area, and high-throughput laser patterning process [material-assisted laser ablation (MALA)]. In this process, a residue layer was observed after the patterning process, requiring an additional cleaning process for the fabrication of electronic devices. In this paper, we investigated the mechanism of the residue layer formation, and optimized the MALA process so that no residue layer is formed after the patterning of carbon nanotubes. We demonstrated patterning of carbon nanotubes on 100 mm diameter silicon wafers, and the patterns of carbon nanotubes were sufficiently clean and sharp to be applicable in high-volume fabrication of electronic devices.

A sensitive method for detecting particle deposition on semiconductor wafers has been developed. The method consisted of generating a monodisperse fluorescent aerosol, depositing the known-size monodisperse aerosol on a wafer in a laminar flow chamber, and analyzing the deposited particles using a fluorometric technique. For aerosol particles in the size range of 0.1–1.0 μm, the mobility classification-inertial impaction technique developed by Romay-Novas and Pui (1988) was used to generate the monodisperse test aerosols. Above a particle diameter of 1.0 μm, monodisperse uranine-tagged oleic acid aerosols were generated by a vibrating-orifice generator. The test wafer was a 3.8-cm diameter silicon wafer placed horizontally in a vertical laminar flow chamber which was maintained at a free stream velocity of 20 cm/s. A condensation nucleus counter and an optical particle counter were used to obtain the particle concentration profile in the test cross section and to monitor the stability of aerosol concentra...

Patterned, chemically reactive poly(methyl)methacrylate can act as a chemical “sponge” via Lewis acid/base adduct formation with metal‐organic reactants commonly used in atomic layer deposition. Extended reactant exposures saturate the reactant within the polymer, and subsequent oxidation removes the polymer and converts the saturated reactant to a metal oxide film that precisely mimics the lateral dimensions of the original polymer. Resulting oxide thickness scales with the starting polymer thickness. Regions without polymer are coated with less than 1 nm of metal oxide. Repeatable nanoscale features are formed simultaneously and uniformly across a 150 mm diameter silicon wafer.

In-line monitoring of silicon dioxide film properties using non-contact or non-destructive techniques is quickly gaining industryacceptance as an alternative to conventional electrical and analytical methods. Mobile ion measurement in oxides using the coronatemperature stress (CTS) technique was first discussed in the early 197Os.1 However, CTS measurements have only recentlybecome available in a new generation ofmeasurement tools. The CTS method may be applied immediately following film growthand does not depend on the fabrication of electrical test structures. This paper addresses the sensitivity and repeatability of theCTS approach with results of measurements performed, using a Semiconductor Diagnostics, Inc. (SDI) mobile charge I plasma damage monitor (MC-PDM) system, on a variety of intentionally contaminated oxides. All oxide growth and characterization wasperformed on 200mm diameter silicon wafers in a state-of -the-art manufacturing facility. Both chlorinated and non-chlorinatedoxides were tested in addition to the effects of growth conditions that resulted in high charge density at the silicon-silicon dioxideinterface. Water solutions containing sodium in the range from 10 to lppba were used to introduce the contamination to theoxides. Photovoltage measurements, conventional C-V (capacitance-voltage) testing, and SIMS analysis were also performed toassess the quality ofthe oxides and to provide correlation to the corona mobile charge measurements.Keywords: corona temperature stress (CTS), mobile ion, surface photovoltage (SPy), contact potential difference (CPD)