Mask data file sizes are increasing as we move from technology generation to generation. The historical 30% linear
shrink every 2-3 years that has been called Moore's Law, has driven a doubling of the transistor budget and hence feature
count. The transition from steppers to step-and-scan tools has increased the area of the mask that needs to be patterned.
At the 130nm node and below, Optical Proximity Correction (OPC) has become prevalent, and the edge fragmentation
required to implement OPC leads to an increase in the number of polygons required to define the layout. Furthermore,
Resolution Enhancement Techniques (RETs) such as Sub-Resolution Assist Features (SRAFs) or tri-tone Phase Shift
Masks (PSM) require additional features to be defined on the mask which do not resolve on the wafer, further increasing
masks volumes. In this paper we review historical data on mask file sizes for microprocessor, DRAM and Flash memory
designs. We consider the consequences of this increase in file size on Mask Data Prep (MDP) activities, both within the
Integrated Device Manufacturer (IDM) and Mask Shop, namely: computer resources, storage and networks (for file
transfer). The impact of larger file sizes on mask writing times is also reviewed. Finally we consider, based on the trends
that have been observed over the last 5 technology nodes, what will be required to maintain reasonable MDP and mask
manufacturing cycle times.
In this contribution we will demonstrate how the use of negative tone CAR can significantly improve the CD control of mask layers in which CD is measured on opaque features. A thorough investigation of the individual contributions of sequential process steps in mask making revealed that the final CD uniformity can by improved by 20% when a negative tone resist is used. In case of 50 keV electron beam (EB) mask writing systems, that employ variable shaped beam (VSB) writing, the writing time can be reduced by 40-50 % when a chemically amplified resist (CAR) is applied. Therefore we have evaluated and characterized a commercially available negative-tone CAR. The resist showed good pattern performance down to 150 nm for isolated and semi-isolated opaque lines thus having the ability to form assist bar features. Vertical profiles have been obtained. Line edge roughness (LER) is more pronounced for this material when compared to standard EB resist ZEP 7000. But analysis of CD uniformity (3σ) of 500 nm opaque lines in local area with negative CAR and with positive tone ZEP 7000 showed 4,8 nm and 6,2 nm, respectively. Thus substantiating that the negative CAR is advantageous in terms of opaque line CD control. Regarding soft bake (SB) and post exposure bake (PEB) latitude, the CAR is stable with respect to soft bake temperature variation (3,7 nm/°C). Much more severe is the steep PEB latitude with respect to dose of 0,7-1,3 (μC/cm2)/°C. This requires the use of high precision baking tools for the PEB step. Since all mask blanks have been coated in-house, we have investigated a variety of pre-treatment steps. The influence of each step was characterized by contact angle measurement. We found out that the best results have been achieved when the sequence H2SO4/H2O2-cleaning-UV/ozone-clean-dehydration bake is applied to virgin blanks as delivered by the blank supplier.
In optical lithography balancing the aerial image of an alternating phase shifting mask (alt. PSM) is a major challenge. For the exposure wavelengths (currently 248nm and 193nm) an optimum etching method is necessary to overcome imbalance effects. Defects play an important role in the imbalances of the aerial image. In this contribution defects will be discussed by using the methodology of global phase imbalance control also for local imbalances which are a result of quartz defects. The effective phase error can be determined with an AIMS-system by measuring the CD width between the images of deep- and shallow trenches at different focus settings. The AIMS results are analyzed in comparison to the simulated and lithographic print results of the alternating structures. For the analysis of local aerial image imbalances it is necessary to investigate the capability of detecting these phase defects with state of the art inspection systems. Alternating PSMs containing programmed defects were inspected with different algorithms to investigate the capture rate of special phase defects in dependence on the defect size. Besides inspection also repair of phase defects is an important task. In this contribution we show the effect of repair on the optical behavior of phase defects. Due to the limited accuracy of the repair tools the repaired area still shows a certain local phase error. This error can be caused either by residual quartz material or a substrate damage. The influence of such repair induced phase errors on the aerial image were investigated.
Besides halftone phase shifting masks (HTPSM) in combination with off-axis illumination alternating phase shifting masks (altPSM) are becoming more and more an important resolution enhancement technique. Their obvious benefits can only yield profit in production if certain mask properties like intensity and phase balance are controlled to a requisite extent. In order to achieve production capable masks within a reasonable time and cost frame simulation tools are of essential importance for mask development and manufacturing. Four our studies we employed solid-CMTM, a 3D EMF (electro magnetic field) simulator that handles arbitrary topographical masks. It is demonstrated by examples that these capabilities are mandatory for altPSM development. In this paper we discuss the effects of various issues relevant for development and manufacturing of altPSM on a basis of systematic 3D EMF simulations. For different balancing options sensitivity to phase errors, mask CD errors and pitch/feature size were investigated. Comparisons to 2D simulation are made for further illustration. We show the influence of certain mask errors on process window and draw conclusions for optimizing altPSM manufacturing.
Besides assist features in combination with HTPSM (half-tone phase shifting mask} and off-axis illumination altPSM (alternating phase shifting mask} is the major resolution enhancement technique to extend optical lithography to low k1. AltPSM in addition has the potential of superior CD control. However to achieve this in production altPSM has to fullfil a number of specifications with respect to phase and transmission. Another important aspect to obtain maximum CD control and overlapping process window for all kinds of structures at different pitches is that the phase shifters need to be optimized. Optimizing shifters by means of simulation results provides valuable input for both setting up design rules for altPSM application and for development of OPC strategies and software. Therefore various systems with different widths of lines and shifters were studied with special focus on basic asymmetric cases. We applied Solid-CM TM, a 3D EMF (electro magnetic field) simulator for our studies. Some results obtained from simulation were experimentally verified by wafer printing results (SEM imaging and CD measurement}. In addition, comparison to 2D simulation results clearly allows the determination of cases in which 3D effects have to be taken into account. The effect of varying shifters is monitored by pattern placement and process window analysis. We apply this investigation to develop solution strategies and to optimize shifter dimensions.
Phase shifting mask technology will be necessary to product integrated circuits at the 130 nm node using KrF wavelength steppers. In order to successfully accomplish this goal, it is necessary to detect and repair phase shifting defects that may occur in the manufacture of these reticles. An inspection algorithm has been developed to improve the phase shift defect detection rate of an UV reticle inspection system and is based upon the simultaneous use of the transmitted and reflected light signals. This paper describes the phase defect sensitivity improvement over transmitted light only pattern inspection results and simultaneous transmitted and reflected light based contamination inspection results.
Alternating phase shifting masks have proven their capability to enhance the process window and to reduce the mask error enhancement factor effectively. The application of this mask type requires additional mask-properties compared to binary masks or halftone PSM. In this paper two of these mask-properties, the intensity and the phase balancing, are investigated experimentally for 4X and 5X masks at DUV and compared with simulations applying the T-Mask configuration of the SOLID-CM™ program. In a first part the experimentally determined balancing results are discussed. For the measurements two independent methods are compared: Balancing measurements with an AIMS-system (MSM100) and direct optical phase and transmission measurements using a MPM-248 system. The T-Mask as a 3D Maxwell solver allows the simulation of real 3D mask topography. We compare the results of simulations with measured AIMS data. All available mask data like depth of trenches, thickness and composition of chromium/CrxOy layers, etc. are taken as input for the simulations. The comparison enables an assessment of the possibilities and limitations of 3D mask- simulation. Based on 3D mask simulations CD-sensitivity of the different balancing methods was investigated also taking the influence of proximity into account. The simulations allow an assessment of the CD-sensitivity for four analyzed mask types for feature sizes below 150nm on the wafer.
This paper describes mask topography effects of alternating phase shift masks for DUV lithography. First two options to achieve intensity balancing are discussed. Global phase errors of +/- 10 degrees cause a CD change of 3 nm and 8 nm CD placement errors. The CD placement appears to be the parameter affected most by phase errors. A sloped quartz edge with an angle of 3 degrees causes a CD change of 10 nm. The CD sensitivity on local phase errors, i.e. quartz bumps or holes was also studied. The critical defect size of a quartz bump was seen to be 150 nm for 150 nm technology. For the investigation the recently developed topography simulator T-mask was used. The simulator was first checked against analytical tests and experimental results.
This paper will start with an overview of the different defect types which can occur on alternating phase shifting masks. A test mask with programmed defects of these different types was fabricated. The defect printability was investigated using an AIMS system. These results were correlated to first printing results in the wafer-fab. The results give an overview of the requirements for an inspection and repair system for alternating phase shifting masks. In order to get a better understanding of this printability behavior first simulations of defects using a 3D mask simulation tool were carried out and compared to the measurements. Several examples of quartz-repairs with different qualities are presented together with the influence on the aerial image.
Dual trench alternating phase shifting masks with an optimized value of the so-called shallow trench depth represents an interesting approach to overcome aerial image imbalances. In order to get a better understanding of the possibilities and limits of this approach, especially for 5X reduction, theoretical and experimental investigations were accomplished. In this paper experimental data obtained from 5X dual trench type alternating PSMs, using DUV-lithography are introduced and compared with 3D-mask simulations. The masks were fabricated with different etch depths and contain parts of typical DRAM patterns. Besides the transmission balancing also the phase balancing has an important influence on the effective process window of an alternating PSM. The effective phase error can be measured with an AIMS-system (MSM100). The comparison with simulated data allows the determination of the phase error. In a second step the influence of different balancing methods on phase and transmission were investigated with the TEMPEST mask simulator for unpolarized light. The optimization of the balancing with respect to the CD-bias, undercut and etch depth will be shown and a first approach of a sensitivity analysis will be presented.
This paper quantifies the expected gain in the process window of 150nm structures printed with DUV for alt PSM vs. COG masks and HT PSM. Most of the analysis was performed for dense lines and isolated lines using lithography simulation. Alt PSM show an increase of dose latitude by 9 percent and an improved DOF by 0.2 micrometers for dense liens. For isolated lines the real advantage is seen in the increase of DOF by 0.7 micrometers . Furthermore it will be demonstrated, that alternating PSM can improve the imagin performance of contacts significantly over competitive techniques. Chromeless PSM may push the ultimate resolution limit. However to vary the linewidth three adjacent quartz edges must be used, since two phase edges are instable in defocus. A phase shifting region needs to exceed a minimum width in order to enhance the contrast of the aerial image of the whole feature. Experimental data and simulations show that the required minimum phase-shifter width for an isolated line is in the region of 400nm. Simulation and experiment show, that 90 degrees edges are very sensitive to defocus and neighboring patterns. Using a 3D mask simulator, correction values for etch depth and parameters for a lateral underetch were determined in order to achieve intensity balancing for alt PSM for various feature sizes.
Nanostructures based on III-V semiconductor materials have reached a status which enables basic physical studies on size effects in device and in nanostructures. The expected benefits of high modulation bandwidth, low laser threshold, and improved linewidth enhancement factor in DFB lasers, to say only a few, which are believed to be based mainly on the changed density of states (DOS) function in low dimensions might be counterbalanced by altered carrier energy relaxation and k-space filling in those structures. To investigate systematically size effects and device aspects, a continuous change of structure and active device size is needed from 2D to 0D dimensions. This requirement can be met by high resolution electron beam lithography in conjunction with low damage etch processes and epitaxial overgrowth. In this presentation we discuss the technology and design considerations of lasers with low dimensional active regions as well as DOS effects and device relevant carrier relaxation effects. The technology part will focus especially on low damage etch processes such as RIE- ECR. Nearly damage free structuring processes can be demonstrated. Based on this low damage dry etch process we obtained electrically pumped wire DFB lasers with relatively high output power (up to 6 mW) and operation temperature (60 degrees C). Time resolved optical ps-spectroscopy as well as high excitation spectroscopy on wire and dot nanostructures demonstrate strongly changed k-space filling and carrier relaxation mechanisms in low dimensions and represent a serious limitation of device speed. Results obtained from electrically pumped wire DFB lasers confirm the carrier relaxation and k-space filling effects in device structures which have been observed by optical pump experiments in nanostructures. Despite the band filling effects in low dimensional structures, the wire DFB lasers show clearly the expected feature of gain coupling and enhanced differential gain which might demonstrate the applicability of mesoscopic laser devices in common data communication approaches.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.