In this paper, the performance of 6% and 18% attenuated phase-shifting masks (PSM) are investigated to assess their capabilities of printing O.12tm and O.lOjim polysilicon gates, using a 248nm scanner with a high NA of 0.68. The effect of off-axis illumination on process enhancement is also investigated. Simulations were done using PROLITHI3D Version 6.1.2. Experimentation was carried out using test masks with various line pitches. The effect of optical proximity correction (OPC) to enhance the overlapping process windows for 0. 12pm and O.1Otm was also studied.
The attenuated phase shift mask has been sued to delineate 0.22 micrometers contact hole structures for 0.18micrometers technology. Using a scanner with a high NA of 0.68, this is equivalent to a k<SUB>1</SUB> value of 0.60. As device shrinks down to 0.13 micrometers technology, 0.16 micrometers contact holes are to be printed with sufficient process latitudes. Using the existing high NA scanner, the k<SUB>1</SUB> value is a low 0.44. Simulations were done using PROLITH/3D software, and the results show better performance for isolated holes. Higher mask transmissions are required to improve the aerial image of the dense holes. Experimentation was conducted to print 0.16micrometers contact holes using moderate and low (sigma) settings. 6 percent APSM was used with 0.16micrometers , 0.18micrometers and 0.20micrometers contact hole patterns biased by 0.04micrometers , 0.06micrometers and 0.08micrometers . Impact of these parameters on mask error enhancement factor were discussed.
Attenuated phase shift mask (APSM) has been considered a viable technique for contact patterning. For 250 nm lithography technology, 300 nm contact patterns are to be defined. In this paper, Solid-C has been used for aerial image simulations. Conventional and annular illumination settings are optimized for better focus latitudes, that is, large depth-of-focus (DOF), for sufficient throughput. In addition, mask transmission is optimized for different illumination settings. From our simulations of aerial images, it has been shown that a DOF of 1.35 micrometer is achieved when conventional illumination is combined with APSM at high mask transmission (approximately 8 - 10%). However a larger DOF of 1.55 micrometer can be obtained when annular illumination is used with APSM at low mask transmission (approximately 3 - 4%).
Infrared search and track (IRST) system is a wide field of view surveillance system, meant for autonomous search, detection, acquisition, and cue of potential targets. The first and second generation IRSTs utilized detectors with multiple elements followed by discrete preamplifiers for signal read-out. They have many performance limitations. With the advent of infrared focal plane array (IRFPA) sensors, the present trend is to build IRSTs based on line FPA sensors to achieve higher sensitivity and resolution. However, due to system limitations of line IRFPA sensors, scanning mode of IRST cannot be stopped at any desired position to scan a small sector of interest. They also suffer from more false alarms in target detection. In future, it may be desirable to reduce false alarms, and also to use an IRST system for closed-loop- tracking of a potential target, in addition to its surveillance mode. IRST based on area array sensors may be a better option for this purpose, but it may pose some problems when used in a surveillance mode. This paper addresses this issue. Design considerations of all sub-systems of an IRST based on line/area array sensors, such as scanner assembly, interface electronics with the sensor, nonuniformity correction, signal processor, and the display methodology to cover 360 degrees are also discussed.