One of the main factors driving ICs in complexity is the improvement in photolithography to print small features. The use of immersion imaging and resolution enhancement technology (RET) will extend the ArF lithography to produce small features. With the patterns size decreasing, the absolute CD variation has a bigger relative importance on small features. The process windows are used to see if a certain process is compatible with the dose and focus budget. We discuss the impact of illumination, numeric aperture, phase-shifting mask and polarized light on process windows using ArF immersion lithography to print line pattern exposed features in photo resist on 45nm node. The interaction between the process windows and illumination, numeric aperture, phase-shifting mask and polarized light are calculated using a full photo resist model. The analysis gives fundamental insight into the optimum conditions necessary for printing these patterns both individually and simultaneously. The results show that illumination, numeric aperture, phase-shifting mask and polarized light can contribute to the process capability. The dipole illumination system can enhance the process window about twice than that use conventional illumination. The process capability of semi-dense pattern is insensitive to optical parameters. The 100% attPSMs and altPSMs are strong phase shifting mask, so the process capability can be enhanced. By using the polarized light can enlarge the depth of focus about 4%~11% with specified exposure latitude. According to the rules of process windows, some methods to extend process windows are presented.
To achieve smaller and smaller feature sizes in the semiconductor industry, extreme demands are placed on the lithographic optics, specifically the projection lens. Higher numerical aperture (NA) is adopted to obtain higher resolution. However, higher NA scales the impact of geometrical aberrations on lithography performance. Thus, a detailed understanding of the effect of geometrical aberrations on the lithographic process is indispensable. In this paper, we consider some of the surprising phenomena that occur at such high NA. We discuss the impact of flare, polarization state and MSD on higher-order aberration's sensitivity using ArF immersion lithography to print elbow pattern exposed features in photo resist on 65nm node. The higher-order aberration's sensitivity is analyzed when the annular illumination (NA=1.2, sigma out=0.76, sigma in=0.52) is employed. The 3rd, 5th, 7th, 9th geometrical aberrations according to the Fringe convention are discussed. The sensitivities to individual geometrical aberrations are calculated by introducing a fixed amount of aberration for each Zernike coefficient with all other aberrations being zero. On 65nm node, with annular illumination, the high-order aberration's sensitivity is calculated respectively according to the variation of flare, polarization state, and MSD. The results show that flare, polarization state, and MSD can contribute to the high-order aberration's sensitivity. The aberration sensitivities are increasing with the MSD and flare's value rising. The aberration sensitivities can be decreased when the horizontal linear polarized light is adopted. The merits of adjusting polarization state to choke back the aberration sensitivities are presented.
The semiconductor industry is aggressively pushed to produce smaller and smaller feature sizes from their existing base of lithography systems. With the line-width of integrate circuit (IC) narrowing and ArF immersion lithography technology arising, the mask error factor (MEF) becomes a significant problem because it consumes a large anticipated portion of the CD tolerance budget. This paper discusses the mask error’s impact on the CDs of butting feature using an ArF immersion lithography system. On 65nm node, the variation of image contrast, NILS (Nominal Image Log-Slope), line width and gap width, which results from mask errors, is calculated. The mask errors include puncture, burr, blotch, and mask bias, etc. The rules of mask error’s impact on image contrast, NILS, line width and gap width are concluded. The puncture errors enlarge the gap width, while, the burr and blotch errors reduce the gap width. All mask errors can magnify the resist CD error and result in the FE windows shrinking. The relations of exposure dose and gap width according to butting pattern are presented. The variation of gap width is compensated by exposure dose’s tuning. The relations of polarization state and gap width are discussed. By adjusting polarization state, the variation of gap width, which results from mask errors, can be compensated. After polarization state adjusted, the image contrast, NILS, line width and gap width are calculated again. By comparing the image contrast, NILS, line width and gap width of butting pattern before and after compensated, the merits of adjusting the exposure dose and polarization state to compensate the impact of mask errors are presented.