New forms of cancer cell identification coupled with faster detection and better accuracy may enhance diagnostic capabilities. The purpose of this study is to improve recognition of minimal residual disease from peripheral blood samples. Spectral images are generated by optical microscopy using filtered broadband visible light elastically scattered from human blood and cancer cells. Exogenous tags, like CD markers may introduce a label bias and are not required. A training cell may be validated without detailed knowledge of intra-cellular spectra used to classify random cells. Spectral object classification is scalable to any number of cell types. Small samples of erythrocytes, leukocytes, Jurkat cancer and non-small lung cell adenocarcinoma are accurately classified and associated with unique spatial-spectral characteristics.
A raster multibeam lithography tool is in Etec’s roadmap to meet the stringent requirements of sub 100 nm mask fabrication. The tool leverages the long experience obtained with the ALTA laser pattern generators and the high resolution capabilities of e-beam lithography. A photocathode controlled by acousto-optic modulated 257nm laser beams is utilized to generate 32 electron beams. The beams are accelerated at 50 KV in an electron column, demagnified and focussed on the mask or wafer substrate. The performance of the photocathode and other system components will be presented together with preliminary lithographic patterning.
Photomask complexity is rapidly increasing as feature sizes are scaled down and as optical proximity correction (OPC) methods become widespread. The growing data content of critical mask levels requires that pattern generator solutions be adapted to maintain productivity. Raster shaped beam (RSB) technology has been developed to enable the production of 70 nm photomasks and the development of 50 nm masks. RSB is built on and extends the capability of the 50 kV MEBES platform. The beam is shaped as it is scanned, printing the mask pattern on a calibrated flash grid. Complex OPC patterns are efficiently tiled by combining a relatively small maximum shape size with a high flash rate of 100 MHz. The maximum shape size and the current density can be adjusted to match a wide set of mask applications. Proximity effects are corrected with dose modulation using a real-time computation.
Photomask complexity threatens to outpace mask pattern generator productivity, as semiconductor devices are scaled down and optical proximity correction (OPC) becomes commonplace. Raster scan architectures are well suited to the challenge of maintaining mask throughput and mask quality despite these trends. The MEBES eXara mask pattern generator combines the resolution of a finely focused 50 keV electron beam with the productivity and accuracy of Raster Graybeam writing. Features below 100 nm can be imaged, and OPC designs are produced with consistent fidelity. Write time is independent of resist sensitivity, allowing high-dose processes to be extended, and relaxing sensitivity constraints on chemically amplified resists. Data handling capability is enhanced by a new hierarchical front end and hiearchical data format, building on an underlying writing strategy that is efficient for OPC patterns. A large operating range enables the MEBES eXara system to support the production of 100 nm photomasks, and the development of 70 nm masks.
MEBESR 50 kV mask pattern generators use Raster GraybeamTM writing, providing an effective grid that is 32X finer than the print grid. The electron beam size and print pixel size are variable between 60 nm and 120 nm, allowing a tradeoff between resolution and write time. Raster scan printing optimizes throughput by transferring precisely the amount of data to the mask that is consistent with the chosen resolution. As with other raster output devices, mask write times are not affected by pattern complexity. This paper examines the theoretical performance of Raster Graybeam for model-based optical proximity correction (OPC) patterns and provides examples of mask patterning performance. A simulation tool is used to model the MEBES eXaraTM system writing strategy, which uses four writing passes, interstitial print grids, offset scans, and eight dose levels per pass. It is found that Raster Graybeam produces aerial image quality equivalent to the convolution of the input pattern data with a Gaussian point spread function. Resolution of 90 nm is achieved for equal lines and spaces, supporting subresolution assist features. Angled features are a particular strength of raster scan patterning, with feature quality and write time that are independent of feature orientation.
The complexity of photomasks is rapidly increasing as semiconductor devices are scaled down and optical proximity correction (OPC) becomes commonplace. Raster scan architectures are well suited to the challenge of maintaining mask throughput despite these trends. Electron-beam techniques have the resolution to support OPC requirements into the foreseeable future. The MEBES® eXara mask pattern generator combines the resolution of a finely focused electron probe with the productivity and accuracy of Raster Graybeam patterning. Features below 100nm can be created, and OPC designs are produced with consistent fidelity. Write time is independent of resist sensitivity, allowing high-dose processes to be extended, and relaxing sensitivity constraints on advanced chemically amplified resists. The system is designed for the production of 100nm photomasks, and will support the development of 70nm masks.
It is commonly accepted in the semiconductor industry that optical lithography will be the most cost-effective solution for 150 nm and 130 nm device generations. Some selected layers at the 130 nm device generation may be produced using electron-beam direct-write or x-ray during the development phase. However, for the production phase, it is expected that 193 nm optical lithography with reticle enhancement techniques such as optical proximity correction (OPC) and phase shift masks (PSM) will be the technology of choice. What about post 193 nm. The range of solutions is more diverse and a clear winner has not yet emerged. The topic, however, is becoming more visible and has taken a prominent place in technical conferences in the past year. The five leading potential alternatives to optical lithography are proximity x-ray, e-beam projection (EBP), extended UV (EUV), ion projection lithography (IPL), and e-beam direct write. The search for the right answer will most likely continue for a few years, and possibly more than one alternative will emerge as an effective solution at and below 100 nm. All of the alternatives, with the exception of e-beam direct write, have one thing in common, the mask. Except for proximity x- ray, all solutions at present envision a 4x reduction of the mask-to-wafer image plane. Instead of chrome-coated quartz, a silicon wafer substrate is used. Aside from patterning, mask fabrication varies depending on the lithography absorbing substrate, and EUV requires a reflective multilayer stack. Most key lithography requirements needed to pattern the imaging layer are common to all of the candidates, at least for the reduction methods. For x-ray lithography, the requirements are significantly more stringent but at a smaller field. This paper will consolidate the requirements of the various types of masks from a pattern generation point of view and will focus on the pattern generation tool requirements to meet those mask requirements. In addition, it will explore key technologies that enable the development of the pattern generation tools.
Etec Systems, Inc. has developed a new e-beam mask lithography system, the MEBES 4500S, featuring a higher productivity writing strategy called multipass gray and a number of mechanical and electrical improvements. This new system, based on the proven technologies introduced in the MEBES 4500 system, provides improved throughput and accuracy. The MEBES 4500S system with multipass gray supports smaller mask design addresses needed for high resolution masks, while providing higher dose for high contrast processes with low sensitivity and improved CD linearity. Improved print performance is achieved by the introduction of several system design changes that work in conjunction with the multipass gray writing mode. These changes include improved column deflection system temperature control, enhanced TFE current control, improved work chamber thermal management, and improved stage drive vibration damping. Details of these features are presented along with first performance data for the new system.
Performance data from a prototype 50 kV shaped electron-beam (e-beam) pattern generator is presented. This technology development is targeted towards 180-130 nm device design rules. It will be able to handle 1X NIST X-ray membranes, glass reduction reticles, and 4- to 8-inch wafers. The prototype system uses a planar stage adapted from the IBM EL-4 design. The electron optics is an 50 kV extension of the AEBLE%+TM) design. Lines and spaces of 0.12 micrometers with < 40 nm corner radius are resolved in 0.4 micrometers thick resist at 50 kV. This evolutionary platform will evolve further to include a new 100 kV column with telecentric deflection and a 21-bit (0.5 mm) major field for improved placement accuracy. A unique immersion shaper, faster data path electronics, and 15-bit (32 micrometers ) minor field deflection electronics will substantially increase the flash rate. To match its much finer address structure, the pattern generator figure word size will increase from 80 to 96 bits. The data path electronics uses field programmable gate array (FPGA) logic allowing writing strategy optimization via software reconfiguration. An advanced stage position control (ASPC) includes three-axis, (lambda) /1024 interferometry and a high bandwidth dynamic corrections processor (DCP). Along with its normal role of coordinate transformation and dynamic correction of deflection distortion, astigmatism, and defocus; the DCP improves accuracy by modifying deflection conditions and focus according to measured substrate height variations. It also enables yaw calibration and correction for Write-on-the FlyTM motion. The electronics incorporates JTAG components for built-in self- test (BIST), as well as syndrome checking to ensure data integrity. The design includes diagnostic capabilities from offsite as well as from the operator console. A combination of third-party software and an internal job preparation software system is used to fracture patterns. It handles tone reversal, overlap removal, sizing, and proximity correction. Processing of large files in a commercial mask shop environment is made more efficient by retaining hierarchy and using parallel processing and data compression techniques. Large GDSIITM and MEBES data files can be processed. Data includes timing benchmarks for a 1 Gbit DRAM on both proximity and reduction reticles. The paper presents 50 kV results on silicon and quartz substrates along with examples of overlay to an external grid, field butting, and critical dimension (CD) control data. Selective experiments testing system stability, calibration accuracy, and local correction software implementation on a VAX control computer are also given.