Immersion lithography is proposed as a method for improving optical microlithography resolution to 45 nm and below via the insertion of a high-refractive-index liquid between the final lens surface and the wafer. Because the liquid acts as a lens component during the imaging process, it must maintain a high, uniform optical quality. One potential source of optical degradation involves changes in the liquid's index of refraction caused by changing temperatures during the exposure process. Two-dimensional computational fluid dynamics models from previous studies investigated the thermal and fluid effects of the exposure process on the liquid temperature associated with a single die exposure. We include the global heating of the wafer from multiple die exposures to better represent the "worst-case" liquid heating that occurs as an entire wafer is processed. The temperature distributions predicted by these simulations are used as the basis for rigorous optical models to predict effects on imaging. We present the results for the fluid flow, thermal distribution, and imaging simulations. Both aligned and opposing flow directions are investigated for a range of inlet pressures that are consistent with either passive systems or active systems using filling jets.
Immersion lithography has been proposed as a method for improving optical microlithography resolution to 45 nm and below via the insertion of a high refractive index liquid between the final lens surface and the wafer. Because the liquid will act as a lens component during the imaging process, it must maintain a high, uniform optical quality. One potential source of optical degradation involves changes in the liquid’s index of refraction caused by changing temperatures during the exposure process. Two-dimensional computational fluid dynamics models from previous studies have investigated the thermal and fluid effects of the exposure process on the liquid temperature associated with a single die exposure. Here, the global heating of the wafer from multiple die exposures has been included to better represent the “worst case” liquid heating that will occur as an entire wafer is processed. The temperature distributions predicted by these simulations were used as the basis for rigorous optical models to predict effects on imaging. This paper presents the results for the fluid flow, thermal distribution, and imaging simulations. Both aligned and opposing flow directions were investigated for a range of inlet pressures that are consistent with either passive systems or active systems using filling jets.
A simulation package has been developed for predicting the influence of immersion, i.e., the presence of a uniform liquid layer between the last objective lens and the photoresist, on optical projection lithography. This technology has engendered considerable interest in the microlithography community during the past year, as it enables the real part of the index of refraction in the image space, and thus the numerical aperture of the projection system, to be greater than unity. The simulation program described here involves a Maxwell vector solution approach, including polarization effects and arbitrary thin film multilayers. We examine here the improvement in process window afforded by immersion under a variety of conditions, including λ = 193 nm and 157 nm, annular illumination, and the use of alternating phase shift mask technology. Immersion allows printing of dense lines and spaces as small as 45 nm with acceptable process window. We also examine the effect of variations in liquid index on the process window and conclude that the index of the liquid must be known to and maintained within a few parts per million. This has important implications for the temperature control required in future liquid immersion projection systems.
A simulation package has been developed for predicting the influence of immersion, i.e. the presence of a uniform liquid layer between the last objective lens and the photoresist, on optical projection lithography. This technology has engendered considerable interest in the microlithography community during the past year, as it enables the
real part of the index of refraction in the image space, and thus the numerical aperture of the projection system, to be greater than unity. The simulation program described here involves a Maxwell vector solution approach, including polarization effects and arbitrary thin film multilayers. We examine here the improvement in process window afforded by immersion under a variety of conditions, including λ = 193 nm and 157 nm, annular illumination, and the use of alternating phase shift mask technology. Immersion allows printing of dense lines and spaces as small as 45 nm with acceptable process window. We also examine the effect of variations in liquid
index on the process window and conclude that the index of the liquid must be known to and maintained within a few parts-per-million. This has important implications for the temperature control required in future liquid immersion projection systems.
KEYWORDS: Manufacturing, Microelectronics, Computer aided design, Semiconductors, Design for manufacturability, Yield improvement, Nanoelectronics, Lithography, Field effect transistors, Control systems
A perspective is presented on how the semiconductor integrated circuit industry has evolved and what we can expect over the next decade or two. However, this 'forecast' is given in only the broadest sense, to make it relatively independent on innovations and discoveries that are likely to strongly shape the industry over this time period. Rather, trends are examined, as well as general 'tools' that will undoubtedly be important in advancing from our present microelectronics era to our presumable future in nanoelectronics.
The modeling of the resist development is an important tool in the study of lithography. Many papers reported the importance of the develop rate change near the resist surface, but Mack's lumped parameter model ignored the develop rate change near the resist surface and they treated the absorption coefficient as a constant. We included the resist surface effect by changing the absorption coefficient as a function of resist depth and we can predict more realistic resist sidewall angle near the resist surface. We also noticed that the resist sidewall angle can be changed by numerical aperture and partial coherence variation. Higher numerical aperture and smaller partial coherence give not only better resolution at the resist bottom, but also more vertical sidewall angle around the resist surface.
In order to make next generation ultra large scale integrated circuits, we have to form sub- quarter micron patterns. Among the several lithographic choices, the enhanced optical lithography techniques of using deep UV sources are strong candidates. The aerial image study shows the combination of annular illumination, binary intensity mask and pupil filter can be applied to all kinds of patterns. This optimum combination is applied to the resist profile study to find out the process latitude. We also investigated the process latitude variation by changing the sublayers such as anti-reflection coating, polysilicon, oxide and nitride.
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