Gate critical dimension (CD) common window (UDOF) is less than 0.25μm below 110nm-node. It's a serious
impact by scanner leveling tilt due to it'll result in defocus, profile changed and then suffer etch bias. Here, we
provide an easy and convenient method to monitor daily leveling tilt of ASML 193nm by SCD. Of course, it can
also be used for other vendors' scanner including DUV 248nm, 193nm & immersion 193nm.
SCD can measure side wall angle (SWA) of photo resist and it's a factor of focus. We can design one mask with
SCD grating pattern and layout them at four corners of mask. Collect the SWA data of four corners by different tilt
at x and y direction and then we can find the correlation within SWA bias and leveling. It's an easy method to
monitor scanner leveling issue and early alert for excursion case.
As the leading edge semiconductor technology development, the gate critical dimension (CD) shrinks below
90nm. The microlithography capability is limited by the exposure utility. The development of scanner is
focusing on low k that is implying that the high NA scanner is the main stream in the future. In addition, the
high NA reticle requirement is stricter than previous one. In aspect of mask manufacturing, reducing mask
topography effect is one of the various solutions, which is like lower mask blank flatness, should be lower than
1T flatness type or else. Unless the mask flatness, the absorber profile also could be a considerate effect element,
which is local topography effect contribution in wafer print window.
The main purpose of this study is verifying how much wafer prints window discrepancy between different
absorber profiles. The experiment pattern is designed for five kind of MoSi sidewall angle (SWA) on the same
mask, which could simultaneously gathers the wafer print window data. In addition, the other purpose is getting
exactly the same process condition of five kinds MoSi profile in both mask house and lithography of wafer
manufacturing Fab. The mask layout pattern is poly layer of logical 90 nm generation that is more critical among
all of lithography and was exposed by 193nm ArF.Then, we offer the effected level between absorber profile
and lithography process window. The process window of different SWA pattern will be compare to check the
relationship between process windows and mask profile. We also investigate how the profile affects the optical
Photomask blank flatness is more important for wafer lithography so far. In view of economic and capital concern, venders of mask blank always provide several level flatness of blank what mask house request. And the wafer fabricators would request the flatter photomask to fit the next generation requirement. The topography effect of photomask should be a contribution of lithography process window. The effect includes quartz substrate flatness and distortion and the film of Cr and MoSi deposit. Besides, the Mask blanks have several shapes that are flat, concave and convex. Reducing the effect from mask is the main consideration of depth of focus improvement. In this study, we made two masks of different type, 0.5T and 2.5T. Flatness measurement is directly provided by interferometer. To verify the effect between mask blank flatness and wafer printing window. Furthermore, we also check patterned mask effect of flatness. The pattern we use is poly layer of logical 90 nm generation that is more critical among all of lithography process and was exposed by 193nm ArF environment. Primary purpose of the ADI (after develop inspection) performance concern is process window of wafer print. Then, we offer the effected level between mask blank flatness and lithography process window.
Lot-to-lot ADI CD data are generally used to tighten the variation of exposure energy of an exposure tool through an APC feedback system. With decreasing device size, the process window of an exposure tool becomes smaller and smaller. Therefore, whether the ADI CD can reveal the real behavior of a scanner or not becomes more and more a critical question, especially for the polysilicon gate layer. CD-SEM has generally been chosen as the metrology tool for this purpose. Because of the limitations of top-down CD-SEMs, an APC system could be easily misled by improper ADI CD data if the CD data were measured on a T-topped photo resist. ArF resist shrinkage and line edge roughness are also traditional causes for improper CD feedback if the user did not operate the CDSEM carefully. Another candidate for this APC application is spectroscopic-ellipsometry-based scatterometry technology, commonly referred to as SpectraCD. In recent studies, SpectraCD was proven to be able to reveal profile variation with excellent stability. The feasibility of improving a CDSEM-based APC system by a SpectraCD-based system in a high-volume manufacturing fab is therefore worthy of study.
This study starts from an analysis of the historical data for the polysilicon ADI CD of a 130 nm product. Two different sets of CD measured from the two different metrology tools were analyzed. In the fab, CDSEM was the metrology tool chosen for the APC feedback. The CD data measured by SpectraCD over a 2 month timeframe were plotted as a CD trend chart of the specific exposure tool. There are several trend-ups and trend-downs observed, even though the overall CD range is small. After a series of analyses, the exposure tool has been proven to be quite stable and the CD data measured by SpectraCD also reveal the real behavior of the exposure tool correctly. The scanner is shown to have been misled by improper CD feedback. In comparison with CDSEM, the linearity of the correlation between ADI and AEI CDs, which represents the consistence of etch bias, can also be improved from 0.4 to 0.8 by SpectraCD. The root causes are still under investigation, but one suspected reason is related to resist profile. All the analysis results will be reported in this paper. The data provided sufficient motivation for switching the APC feedback system of the fab from a CDSEM-based system to a SpectraCD-based system. The results of the new APC system will also be discussed.