An integrated imaging system for the 45-nm technology node contact holes using polarized OAI, immersion, weak PSM, and negative resists

Abstract

Imaging contact holes has become a major technology barrier for optical lithography in the deep subwavelength era. Using hyper-numerical aperture, extreme off-axis illumination with TE-polarization, weak PSM and negative-acting resists 50nm contacts on a 90nm pitch can be produced with better than 0.3 micron depth-of-focus with 5% exposure latitude and maximum exposure latitude of greater than 15% at best focus. Large depth-of-focus across-pitch range solutions for 50nm contacts require the use of multiple exposures using unique sources but smaller focus budgets can be reduced to single exposure. This work defines possible integrated imaging systems that will allow imaging of deep sub-wavelength sized contact holes and then compares these to other solutions that have been proposed in the literature. Specifically, source design through normalized-image-log-slope, normalized-resist-image-log-slope and process window mapping, development of contact hole primitives using full mask transform correction (where the mask pattern shape, material and topography are taken into account) and resist requirements will be discussed for developing dense, mid-range and isolated pitch contact hole imaging solutions for the 45nm technology node. IntroductionStarting with the 130nm technology node, resolving contact holes is the primary feature size and pitch limiter. Relative to lines and spaces the normalized-image-log-slope (NILS) and intensity maximum of the projected image are significantly worse for contacts imaged in positive-tone resists. Our work shows NILS of less than 1.5 is typical for 160nm pitches imaged with 0.75 NA 193nm and c-Quasar. This is due in large part to the loss in cross term diffraction information that is filtered by the pupil reducing both contrast and intensity and that is then compensated by increasing the size of the contact and sampling the low NILS region near the intensity maximum to attain sizing through underexposure. It is also due to the type of off-axis illumination scheme used to attain the small pitch. Using an off-axis illuminator poles placed at the 45 degree position relative to the optical axis limits resolution to a pitch factor of 1/√2 whereas with the poles oriented on the optical axis resolution can extend to 1/2. However, while increasing resolution, this is done at a loss to contrast due to two poles being ideally oriented to form good diffraction information for each x-orientation or y-orientation feature edge while the other two are not. 1 This problem can be mitigated by using y-polarization for x-edge and x-polarization for each y-edge in a dual dipole exposure or by using azimuthally polarized source in a single exposure. 2 Yet after doing this, the lithographer is still faced with the problems inherent with underexposing low contrast images, poor process latitude and a greater propensity for line-edge-roughness in positive resist.

Revisiting the linear programming framework for leakage power vs. performance optimization

“…Table 3 summarizes our simulation settings for trim exposure of all layers. Consistent with our previous work [16], chromeless phase assist (CPA) masks provide the best-quality trim exposure. …”

Imaging study of positive and negative tone weak phase-shifted 65 nm node contacts

“…Research at PAL, published elsewhere 13 , shows that the use of azimuthally polarized sources, negative resist and CPL contacts provide extensibility to 50nm contacts on pitches from 90nm and larger. This image design system has NILS greater than 2 and as high as 3 to 4.…”