B. Beeman, A. Carpenter, J. Kimbrough, T. Clancy, R. Chow, E. Bond, Z. Zayas-Rivera, P. Bell, J. Celeste, A. MacPhee, W. Widmann, T. Golod, E. Miller, R. Abbott, K. Lee, J. Peterson, S. Gordoni, J. Buckley, W. Donaldson
We present lessons learned from the fielding of various Mach-Zehnder (MZ) based diagnostic systems
on the National Ignition Facility (NIF) and potential solutions. The DANTE X-ray diagnostic is the next in a
series of applications for Mach-Zehnder based signal transport and acquisition systems on NIF and as such
will incorporate many of these upgrades. In addition to extended dynamic-range performance and improved
reliability, the upgrades presented also enable multiplexing of the signals from DANTE’s 18 X-Ray Diodes
(XRD) to economize on system cost and rack space. Previous deployments on other NIF diagnostics
highlighted the necessity to decouple the input light intensity from the bias point of the Mach-Zehnder. Areas
of concern including polarization, temperature, bias point and optical power level control will be addressed.
KEYWORDS: Comets, Signal detection, National Ignition Facility, Diagnostics, Signal to noise ratio, Multiplexing, Modulators, Pulsed laser operation, Interference (communication), X-rays
We present performance characterization measurements for Mach-Zehnder optical modulators to be fielded on NIF as a signal path upgrade for various diagnostics. Two different operating configurations will be explored including in phase quadrature and 90deg I/Q operation. Impulse response functions of x-ray emissions were conducted using the COMET laser facility at the Lawrence Livermore National Laboratory. Results from these short pulse laser driven plasma experiments are given along with comparisons to other recording instrumentation
The National Ignition Facility (NIF) has a need for measuring gamma radiation as part of a nuclear diagnostic program.
A new gamma-detection diagnostic uses 90° off-axis parabolic mirrors to relay Cherenkov light from a volume of
pressurized gas. This nonimaging optical system has the high-speed detector placed at a stop position with the
Cherenkov light delayed until after the prompt gammas have passed through the detector. Because of the wavelength
range (250 to 700 nm), the optical element surface finish was a key design constraint. A cluster of four channels (each
set to a different gas pressure) will collect the time histories for different energy ranges of gammas.
Development of OPC strategies, both model-based and rules-based, can be greatly accelerated by identifying and minimizing metrology bias during OPC iterations. The CD-SEM edge-detection algorithms best suited for precision on 90 nm and 65 nm node ground-rule structures often do not provide linear response across a wide range of line sizes, line-end gaps and other structures of interest during OPC refinement. To ensure that reliable metrology data is being fed into the OPC calculation engine, reference measurements that are independent of (a) feature size, (b) feature shape and (c) material composition must be made to optimize CD-SEM edge-detection for this application. We show the importance of on-line atomic force microscopy (AFM) measurements to improve CD-SEM measurements and speed turnaround of OPC model generation. Measurements are made on through-pitch and through-size lines and spaces, both after litho and after etch and compared with CD-SEM measurements.
The decrease in critical dimension (CD) of integrated circuits (IC) always challenges metrology tools capabilities. In less than ten years we will reach the limit of CMOS technology with typical printed gate length less than 20 nm and physical gate length of less than 15nm. Advanced R&D departments must already address today all the issues related to so small devices otherwise the roadmap requirements would not be fulfilled. Indeed most of the issues are directly related to metrology capabilities such as precise control of the shape of etched features, sidewall roughness, wafer CD uniformity, and mask inspection (. . .). All these parameters will represent a bottleneck for advanced patterning if metrology tools are unable to measure them with a precision better than few nanometers. In this paper we show that 3D metrology is mandatory to succeed in reaching future roadmap requirements. We address in details the CD AFM technique capabilities which is a potential candidate for advanced patterning metrology. The experimental data are compared with today’s reference: cross-sectional analysis (X-SEM). We also discuss on other techniques such as scatterometry and top view CD-SEM which are also candidates for 3D metrology.
We discuss the aspects of three-dimensional AFM metrology relevant to 90 nm node processes, with extensions to 65 nm node and beyond. Important advances have been made, including deployment of silicon tips with diameter less than 70 nm as well as development of a novel algorithm for tip shape deconvolution. As primary case studies, we present detailed analyses of process and materials issues encountered during poly silicon etch and during 193 nm photolithography. Etched poly silicon shows shape details at the bottom of the line that are known to impact device performance both directly (by defining the physical gate length) and indirectly (by screening ion implantation). Our data from one particular process show that etch shape (CD and sidewall angle) varies strongly as the line pitch decreases from 500 nm to 260 nm, with sidewall angle changing by approximately 0.8 degrees per 100 nm pitch change. We also present data for a different etch process in which both CD and sidewall angle vary systematically across the wafer from center to edge, with the range of sidewall angles being ~2 degrees and CD varying by 20 nm. Resist is seen to have height and sidewall angle variation with pattern density and with linewidth at a given focus-exposure process point. In addition, resist profiles before resist trim show footing, standing waves and 3-dimensional sidewall roughness that are readily visualized and quantified with AFM measurements.
This work involved a demonstration of the infrastructure and the ability of mask-making equipment to produce 9 inch reticles. While the choices for this particular work made the timing and logistics long and complicated, we find that there currently exists adequate infrastructure to create 9 inch reticles and we have used this ability to produce several demonstration quality examples.
We present nanometer-scale physical structures and analysis algorithms for characterizing tip width and shape for critical dimension atomic force microscopy (CD-AFM). Automated CD-AFM measurements will be used in future generation, and a robust methodology is demonstrated for ensuring long-term repeatability of width measurements on sub-100 nm structures. Structures are designed and chosen for their width uniformity on the sub-nm scale, as well as for their well defined shapes that can be deconvolved from the scan data to yield a precise image of the tip. We apply our tip characterization techniques to measurements of photoresist linewidth, contact etch and poly Si gate width in a manufacturing environment, and show that tool performance and characterization strategy can combine to give excellent long-term repeatability.
KEYWORDS: Semiconducting wafers, Metrology, Chemical mechanical planarization, Copper, Image resolution, Logic, System on a chip, Optical lithography, Stereoscopy, Lithography
We present 3-dimensional atomic force profiler (AFP) measurements on die-scale flatness after copper and STI CMP. True metrology is achieved for patterned wafers. Wafers are vacuum-mounted on a flat chuck, as they would be in a stepper, so wafer warpage and strain-related non-planarity are not present. The results of this new technique are compared against current measurement techniques. For logic, memory and System-on-a-chip, we discuss the implications of wafer planarity going into subsequent photolithography steps.
With the advent of alternating aperture phase shift masks it has become necessary to Monitor quartz etch depth to ensure quality mask fabrication. To date, optical tools have been primarily used for the phase metrology of these masks. Optical tools have the advantage of using actinic light, but they also have several limitations, most notably: restrictions on the minimum aperture size to be measured, prior knowledge of which aperture is etched and alack of automation. Atomic force microscopes have a long history of depth metrology and the current tip technology is small enough to extend for the next four reticle generations while new tips are being developed to meet semiconductor device roadmaps. We examine several practical issues of using an AFM based system for the phase metrology of APSM masks; matching of AFM to optical tools automation of phase measurement and an examination of the theoretical difference between AFM and optical measurements.
In this paper we will discuss the results obtained from five alternating aperture phase-shifting masks (altPSM), each with an identical layout but manufactured using a different technique. We will show the results obtained for mask CD performance measured on a SEM for a number of dimensions and duty cycles. We will show how the results obtained from conventional mask metrology compare with results from advanced analysis including mask topography information obtained using an automated atomic force microscope (AFM). Comparison will be made showing how the metrology structures on the mask compare to the actual structures in the patterning area. A comparison of the results achieved from each mask manufacturing technique will also be made.
We present a study of the micro-trenching caused by different quartz etch processes during the fabrication of phase-shift photomasks. Six different photomasks with quartz etches 320nm - 720nm deep were measured non-destructively by Atomic Force Microscopy (AFM) to explore the details of micro-trenching that occurs at the base of vertical walls. Results of etch profiles obtained using AFM metrology are correlated with electromigration (EM) modeling of alternating aperture phase shift masks for use with KrF 4X reduction steppers. The metrology and EM modeling results clearly differentiate each of the generic etch processes and predict the process window changes resulting from modeled micro-trenching relative to an ideal etch case. In particular, the ICP + wet etches show 50 percent less micro-trenching relative to three of the four RIE-only etch processes. Comparisons of micro-trenching lengths measured during these experiments with the results of trenching bias across different etched space widths as reported by McCallum, et al. suggest that micro-trenching is a universal phenomenon occurring during quartz etches. We propose that micro-trenching more correctly defines the geometries responsible for trenching bias. Finally, to show the effect of local geometry to the extent which trenching occurs, we study the depth detail in the vicinity of an unusually shaped phase bump defect. Trenching is more than 50 percent greater at the base of concave or acute defects as compared to convex defects. Local trenching may make repair more difficult for phase bump defects near or touching a vertical trench wall.
With the acceptance of etched phase shift photomasks by most major semiconductor manufacturers, it is necessary to build a significant number of these masks in a cost-effective and controlled manner. Optical methods of metrology used for many years in the photomask industry for binary masks are unsuitable for certain metrology applications related to etched phase shift photomask manufacture and repair. Atomic Force Metrology (AFM), Scanning Electron Microscope (SEM) metrology and optical methods, in combination, are now providing the necessary metrology tools to characterize etched phase shift masks and generate metrology for phase defect repair. Modeling methods such as electromagnetic modeling (EM) are providing insight into the effect of non- ideal processing on the final printed wafer image and the aerial image presented by a lithography system. This paper uses AFM metrology and EM modeling to explore the details of micro-trenching that occurs at the base of vertical walls on etched phase shift masks. Results of etch profiles obtained using AFM metrology are correlated with EM modeling of 320nm - 720nm etched structures in alternating aperture phase shift masks for use with KrF 4x reduction steppers. Three generically different etch processes were used to create the measured structures on six different masks. These six masks were manufactured by four different mask makers. The metrology and EM modeling results clearly differentiate each of the generic etch processes with the ICP + Iso etches showing 50% less micro-trenching relative to three of the four RIE-only etch processes. The simulation predicts the process window changes resulting from modeled micro-trenching relative to an ideal etch case. The models chosen for simulation represent the real etched results observed with the AFM. Comparisons of micro-trenching lengths measured during these experiments with the results of trenching bias across different etched space widths as reported by McCallum, et al. suggest that micro-trenching is a universal phenomenon occurring during quartz etches. It is proposed that micro- trenching more correctly defines the geometries responsible for trenching bias. Depth detail taken from the vicinity of an unusually shaped phase bump defect show the effect of local geometry on the extent to which trenching occurs. Trenching is more than 50% greater at the base of concave or acute defects as compared to convex defects. Further investigation of local trenching sheds light on the reason why phase bump defects near or touching a vertical trench wall appear more difficult to repair.
With the acceptance of AAPSM’s by most major semiconductor manufacturers, it is necessary to build a significant number of these masks in a cost effective and controlled manner. Optical methods of metrology used for many years in the photomask industry for binary masks are unsuitable for certain metrology applications related to AAPSM manufacture and repair. Recent work performed on a Dimension 9000M-PM automated atomic force microscope shows promise for both process control and defect review applications for AAPSM’s and overcome some of the limitations of optical and SEM based metrologies. AFM metrology is shown to be able to quantify shifter step heights and phase error for features as small as 100 nm. Further, these systems are able to read in defect coordinate maps and automatically drive to these sites and scan. The scanned data provides pixel-by-pixel height data that can be used by repair tools to establish the proper dose for defect ablation.
We present experimental evidence that orientation of the polymer chains in semiconducting polymer films leads to lower thresholds for gain narrowing. Two different materials have been investigated: neat films of poly(p-phenylene vinylene) (PPV) and blends of poly(2-methoxy-5-(2'- ethyl-hexyloxy)-1-4-phenylenevinylene) (MEH-PPV) in polyethylene (PE). Gain narrowing is not observed in non- oriented films in either of the two materials. However, free-standing films of PPV drawn to a ratio of (7:1) showed gain narrowing at threshold one order of magnitude lower than typically found for non-oriented films of soluble PPV derivatives. For the MEH-PPV blends, gain narrowing is observed in diluted films with concentrations of the active polymer of approximately 1 percent. The thresholds for these dilute, but chain extended and highly oriented free standing films are comparable to those obtained in neat thin film waveguides of the same material. These result are correlated with the microstructure of the films, as investigated by x- ray diffraction.
We report steady-state photoinduced absorption (PIA) and photoinduced reflectance (PIR) in films of MEH-PPV and BCHA- PPV blended with fullerene-based acceptors. Absorption from the metastable charge-transferred state is probed by PIA; the modulated absorption spectrum causes changes in the real part of the index of refraction, (Delta) n, which can be measured directly by PIR. The charge transfer gives rise to pronounced features in (Delta) n, including vibrational structure in the mid- and near-IR. Our measurements over a wide spectral range allow quantitative comparison of (Delta) n obtained from PIR with that obtained from Kramers- Kronig transformation of the PIA data. We find good agreement throughout the IR, indicating that our method for measuring (Delta) n is useful as an analytical tool for optical characterization and for prediction of optical spectral ranges for nonlinear optical response.
We report photoinduced absorption and photoinduced reflectance spectra of poly(3-octyl thiophene)- methanofullerene films. The data allow direct evaluation of the corresponding changes in the complex refractive index, (Delta) N equals (Delta) n((omega) )+i(Delta) (kappa) ((omega) ), of the films. As a results of the efficient photoinduced intermolecular charge transfer, the magnitudes of (Delta) n((omega) ) and (Delta) (kappa) ((omega) ) are significantly enhanced over those in either of the component materials, with (Delta) n and (Delta) (kappa) approximately equals 10-2 in the infrared at laser pump intensity of only 50mW/cm2. Moreover, the photoinduced absorption shows new features at 1.2 eV and 1.6 eV, both of which are associated with excited state absorptions of the methanofullerene anion. The implications of these photoinduced changes in the index resulting from photoexcitations are discussed in terms of potential optoelectronic and nonlinear optical applications of these materials, indicating that conducting polymer/methanofullerene films are promising as high- performance nonlinear optical materials.
We describe the implementation of an 8 keV microscope that operates with a conventional x-ray source in our lab. Samples are scanned pixel-by-pixel through a focused x-ray spot produced by a phase-modulating zone plate fabricated with the sputtered-sliced technique. The micro-focused x-ray source uses a Cu target and produces 8 keV photons that are detected with a Si(Li) spectroscopy system. The microsope currently achieves 10 um resolution.
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