Inverse lithography for 45-nm-node contact holes at 1.35 numerical aperture

Abstract

Inverse lithography technology ͑ILT͒ is a procedure that optimizes the mask layout to produce an image at the wafer with the targeted aerial image. For an illumination condition optimized for dense pitches, ILT inserts model-based subresolution assist features ͑AF͒ to improve the imaging of isolated features. ILT is ideal for random contact hole patterns, in which the AF are not at intuitive locations. The raw output of ILT consists of very complex smooth shapes that must be simplified for an acceptable mask write time. It is challenging for ILT to quickly converge to the ideal pattern as well as to simplify the pattern to one that can be manufactured quickly. ILT has many parameters that effect process latitude, background suppression, conversion run time, and mask write time. In this work, an optimization procedure is introduced to find the best tradeoff between image quality and run time or write time. A conversion run time reduction of 4.7ϫ is realized with the outcome of this optimization procedure. Simulations of mask write time quantify the ability of ILT to be used for full chip applications. The optimization procedure is also applied to alternate mask technologies to reveal their advantages over commonly used 6% attenuated phase shift masks. ©

Modeling and characterization of contact-edge roughness for minimizing design and manufacturing variations

“…In reality, due to the relatively small process margin, contact patterning is one of the most challenging tasks in hyper-NA lithography. 10,12 The increased imaging challenges for advanced node contacts lead to strong off-axis illumination 19 and inverse lithography techniques, 11,20 which implies that modern contact patterning still suffers from the CD and area variation due to the lithography proximity and process variation. Both variations cause the area change of contact plug, which induces device performance degradation.…”

“…[7][8][9][10] That is because a patterned photoresist (PR) layer used to produce such small 1932-5150/2010/$25.00 C 2010 SPIE feature sizes typically has a high aspect ratio, and maintaining a desired critical dimension (CD) can be very difficult due to small process margins. 11,12 Despite intensive attention on line-edge roughness (LER), [13][14][15][16] CER has been relatively less studied even though contact patterning is one of the most difficult lithography processes. As aggressive scaling continues into the nanometer regime, CER does not scale accordingly and becomes an increasingly larger fraction of the contact pattern.…”

Wavefront-based pixel inversion algorithm for generation of subresolution assist features

“…Thus, in recent years another resolution enhancement technique known as inverse lithography (IL) or inverse mask technology has been proposed. [10][11][12][13][14][15] IL is a technique that theoretically calculates/corrects the full mask to compensate for strong image distortion from optical diffraction loss. IL calculates the full mask correction using a nonlinear regression that incorporates the inverse optimization algorithm to obtain a theoretically optimal mask after an elaborate computation.…”