Overlay control for semiconductor devices is getting tighter in recent years. In the past, we may only concern the whether the overlay are in spec or not. However, the spec we concerned was the same for both X and Y directions. To achieve the tighter spec in the future, we may consider the asymmetry specs for X and Y directions separately for some specific layers, such as CONT layer. For example, if the spec of X direction is tighter than Y direction, we can lose the precision of overlay from Y direction to let overlay from X direction more precise. Theoretically, the common overlay models such as HOPC or iHOPC set X and Y directions independently. To reach the goal of loss overly from one direction to preserve the overlay from the other direction, we consider the full map measurement overlay historical data. From these data, we can analyze the data to find which overlay targets are more important to X direction, and we can set these corresponding targets as the new measurement locations. This is one concept of “asymmetry” since the chosen measurement locations can provide more precisely correction for the overlay of specific direction. On the other hand, we use the in spec ratio (ISR) index for all measurement overlay targets on wafer to replace the traditional mean plus 3 sigma (M3S) index, since we have the budgets of both X and Y directions. The in spec ratio is defined as ratio that the residuals of X and Y directions fill the corresponding budgets, simultaneously. Since our goal is to maximize the ISR, the traditional M3S optimization algorithm can be replaced by ISR optimization with different overlay specs. That is the reason we call “asymmetry overlay correction”.
Ability to predict process behavior under defocus has until now relied on explicit calculations, which while accurate, cannot be realistically used in full-chip optical and process correction strategies due to the long run times. In this work, we have applied a vector model for the optics, and a compact model for the resist development process. Simulations with these models are fast enough to be the basis of full-chip OPC. We verify this strategy with an independent set of measurements, and compare it to current lithographic process fitting strategies. The results indicate that by describing optical processes as accurately as possible, the model accuracy improves over a wider range of defocus conditions when compared to the traditional calibration method. As long as the calibration process successfully decouples optical and resist effects, relatively simple resist models deliver excellent accuracy within the noise level of the metrology measurements. Our data are based on one-dimensional and two-dimensional results using a 193nm system using 0.75 NA and off axis illumination with 6% attenuated phase shift mask. In all cases, a wide variety of sub-resolution assist feature rules were used in order to further test the ability of the models to predict various optical and resist environments.
As 6% attenuated phase shift masks (PSM) become commonly used in ArF advanced lithography for the 90nm Technology and mass production to print lines/ spaces as well as contacts, the specification and control of the phase angle and the width of the distribution of phase angles becomes critical to maintain the quality of the lithography process. The influence of the mean phase angle and the width of the distribution of phase angles on the best focus, the through pitch behavior and uniformity of the critical dimension (CD uniformity) has been studied experimentally using a 6% attenuated PSM whose phase angle has been affected by several reticle cleans. The results are consistent with aerial image simulations. Independent specifications for the mean phase angle and the width of the distribution of phase angles have been derived and could be applied for the production of masks in the future.
A multiple exposure with matching illumination settings has been applied to the advanced photo process. We combine some special illumination settings which are good for each specific duty ratio and produce a good through-pitch performance. For example, we can combine OAI for dense and conventional with low sigma for Iso to optimize through pitch performance. With this method we can fine tune all illumination parameters, including NA, sigma, exposure dose, focus and pupil type. For sub-wavelength photolithography, the proximity effect of single illumination setting causes limited DOF through pitch so a compromise between isolated and dense pattern performance must be taken. Traditional exposure method using a single illumination setting can not fulfill the optimal illumination setting for patterns at all pitches. With this invention using multi-illumination settings, we can combine multiple exposures with the advantage of different illumination settings to perform better process capability include DOF and proximity through all pitches. Experimental data shows that the single exposure DOF of isolated hole and dense hole are below 0.2um but DOF can be enlarged to 0.4um by multiple exposure. And we get smaller proximity effect at the same time.
In an attempt to develop the dual damascene process in 0.13 micrometer design rule, the trench optics, resist usage, reflectivity control and BARC strategy for 0.18 micrometer S/L on 0.20 micrometer via dual damascene process are discussed. The difficulty of 0.18 micrometer trench process will be concentrated by two reasons: First, the trench optics is totally different from the traditional L/S patterns either observing the pupil plane wave vector or the aerial image versus defocus, it contains the intrinsic limitation to drive and enough process DOF. Secondly, the PR residues remain in via due to the weak light incidence into via as soon as trench exposure. The side issues are the MEEF problem in dark field exposure and lens aberration problem enhanced in the use of PSM or some kinds of special customized illumination filter CIFs. As a result, the negative resist together with NA equals 0.55, (sigma) equals 0.8, annular 1/2 illumination were applied, it reveals that all mentioned issues are properly compromised by this optimized condition. It is also found that the PR window and profile is quite sensitive to substrate acidity and reflectivity. When BARC protecting coating and reflectivity control problems are taken into account simultaneously, the thin conformal BARC and fully filled polymer on dual SiO<SUB>X</SUB>N<SUB>Y</SUB> underlayer are introduced to get a good profile and CD control. Experimental results exhibit the feasibility in manufacturing.