As reduction of k1 factor continues, it becomes more extensive to apply resolution enhancement techniques (RETs) such as phase shift mask (PSM), optical proximity correction (OPC) and off axis illumination (OAI). OPC has been playing a key role to control of pattern printing accuracy and maximize the overlapping process window especially for logic devices. However, RETs, including OPC, tend to increase the sensitivity of printed images to the projection lens aberrations. In order to improve the pattern uniformities and image qualities, lens aberration should be considered as one of the most important factor to OPC modeling. In this paper, we investigated the impact of lens aberration on data set for OPC model generation. The data of projection lens aberrations on exposure tools were extracted by LITEL In-situ Interferometer (ISI) and the sensitivity of CD variation with each lens aberration was simulated by SIGMA-C Solid-E Simulator. Among the lens aberrations, the significant error sources contributing to setting a limit to use one general OPC model with multiple exposure tools were analyzed. Also, the lens aberration specification to use one general OPC model was proposed. By considering the effect and specification of lens aberrations, further improvement of the OPC model accuracy and prevention of device yield loss originated from lens aberrations are expected.
We investigated the influence of lens aberration on the lithographic performance according to the phase error and topography effects of phase-shift mask (PSM). Twin-bar and isolated pattern showing high sensitivity to lens aberration were used for this study. The simulation of aberrated images was carried out using the Solid-CTM simulator. Specially, we quantified the relationship between patterning behaviors such as the isofocal tilt, the left-right (L-R) CD difference and the Z7 and Z9 individual Zernike coefficients. Isofocal tilt aberration sensitivity for Z9 was 0.4nm/nm, which resulted in 2nm CD variation using lens with 5nm Z9 value. When using the lens with 5nm Z7 value, the L-R CD difference and its sensitivity are 10nm and 2nm/nm, respectively. Finally, we evaluated the patterning performance by phase error effect, and determined the phase error criteria for PSM. The pattern placement error was increased by increasing phase error as well as Z7 value, while its slope to the defocus was similar regardless of lens aberration. However, it was found that the aberration sensitivity was not affected by phase error. The simulation predicted that the sensitivity of lens aberration could be increased due to mask topography effect. The nominal shift of phase edge attributed to mask topography was measured.
We demonstrated the impact of space between assist bar and main pattern, width of assist bar, defect size, and the location of defect between assist bar and main pattern on main pattern distortion. The sizes of designed defect on mask were 400, 1600, 3600, and 6400 nm2 (1X) and the locations of defect were varied with 20 nm intervals between assist bar and main pattern. The widths of assist bar were varied from 60nm to 100nm with 10nm intervals and the spacing between assist bar and main pattern with 130- and 150-nm-width were 200nm, 240nm, and 280nm. The ΔCD, which is the difference of CD values between normal main pattern and distorted main pattern adjacent to defects, values were decreased with increasing space between assist bar and main pattern, while width variation of assist bar does not affect on the ΔCD value. Concerning the effect of defect location, we observed that the isolated defects with ≥1600 nm2, located between assist bar and main pattern, were printed on wafer. In sharp contrast, the defect attached to assist bar were not printed at all for all sizes of defects. In addition, ΔCD values were linearly increased as the defect location is close to main pattern regardless of process conditions. These results indicate that the location of defect plays a major role to specify the defect criteria, especially for assist bar OPC mask. The change of process latitude and defect printability with the illumination conditions and mask bias was also investigated
We have optimized the standard method for the extraction of MEEF at 200nm contact hole with regard to the pitch and mask CD variations, which resulted in 4.8. Additionally, we have evaluated the impact of mask bias, surrounding pattern size and asymmetric change of mask CD.
The pitch has greatly influenced the MEEF of the contact hole, and the contact holes with the minimum pitch show higher MEEF than isolated or semi-dense contact holes. The MEEF was little affected by the mask bias, ranging from 10 to 30nm. The MEEF remains independent despite the changes of the mask CD occurring around the holes within ±10nm range. The variations of the mask CD in one direction or another are not related to the MEEF determination. In addition, the pitch has influence on the defect printability. Other things that influence the defect printability are the defect types and their location. The defect of Cr intrusion has more intensive effect on the printed CD change. The more the defect is close to the center of the hole pattern, the more the defect printability increases.
In this paper, we demonstrated the impact of illumination condition on MEEF and investigated the correlation between CD linearity and MEEF according to the illumination conditions and imaging pitches. For all of the illumination conditions, the MEEF increased appreciably as the CD decreased beyond a CD linear region. The aerial image intensity and NILS change with the pattern size and illumination conditions were also investigated. We also measured and analyzed the printability of mask defect according to the MEEF. Two types of mask defects; chrome and clear mask intrusion defects were designed in the cell. The designed mask defect was split from 0.02 μm2 to 0.72 μm2(5X) in area. While within a linear CD region the slope of the CD response to the defects are similar regardless of the illumination condition and 0.08 μm2(5X) clear defect size was not printed, within a linear CD region the slope of the CD response to the defects increased as the illumination NA decreased and only 0.02 μm2(5X) chrome defect size was printed within a linear CD region, where the defect printability criteria is out side ±5% target CD range. We could also show that as the process is operated under the linearity limit, the dependency of aspect ratio to the defect printability would be increased.
Due to its low resistance and high electromigration performance, copper is now considered as a better metalization than the currently used aluminum based alloys. Dual damascene architecture is generally proposed for fabrication of multilevel copper interconnection. However, in the case of via first dual damascene scheme, we have great difficulties in M2 Trench photoprocess such as alignments and overlay measurements because this scheme makes too high topography of via patterns. Alignment marks and overlay targets made during via patterning process do not have good image contrasts after coating BARC and photoresist. Deteriorated image contrast of alignment marks and overlay targets increases the uncertainty in the alignment and overlay measurement. The image contrasts of alignment mark become worse after coating BARC and photoresist, resulting in weak, noisy, and asymmetric alignment signals. In this paper, we evaluated the impacts of mark structure, geometry, and BARC processing for the alignments and the overlay measurements using convex or concave structures, bar or slit structures, and special designed structures in M2 trench photo process. We also investigated the copper filled keys on M1 trench layer as alternative alignment targets.
In this paper, we will describe why the calibration process between CD-SEM and transmission electron microscopy (TEM) was performed. TEM is considered to be a unique solution such that we could obtain CD and sidewall angle accurately. TEM has the merit of having good resolution, but the measurement is performed over small segments of device features. The CD measurement error related to line edge roughness (LER) was also investigated in order to avoid the degradation in the accuracy of TEM measurement of CD. Many efforts were performed to reduce the uncertainty in TEM measurement of CD. The amount of the uncertainty related to TEM CD measurement was approximately 5 nm. We could obtain the linear relationship between CD-SEM and TEM measurements of CD Of logic gate lines ranging form 0.12 micrometers to 0.20 micrometers . The average CD measured using TEM was 15 nm lower than the CD measured with CD-SEM at poly silicon etched profile which had the sidewall angle of 86 degrees. Such difference is unacceptable in the CD measurement. The CD measurement error could be compensated with the modification of the measurement algorithms. The reproducibility of CD measurement for various algorithms was also investigated. It was shown that TEM measurement of CD could be applicable for the calibration with CD-SEM measurement to control various processes with different sidewall angles.
The bi-layer resist (BLR) process, which first accomplish imaging on a thin top layer and transfer it down to a thick organic layer, is one of newly emerging patterning techniques in silicon processing. In this work, we studied the lithographic performance of the BLR process adopting FK- SPTM (Fujifilm Olin Co.) as top layer material and various organic material as bottom layer. Generally, considerable advantages of planarization, reduced substrate reflection, improved process latitude, and of enhanced resolution are achieved. However, the resolution and the process latitude are highly affected by surface interaction between the top resist and the bottom material. Moreover, the BLR process has a sidewall roughness problem related to the material factors of the resist and the degraded aerial image contrast, which can affect the reliability of the device. We found that thermal curing treatment applied after development with the consideration of the glass transition temperature are very effective in reducing the line edge roughness. More smooth and steep patterning is achieved by the thermal treatment. The linewidth controllability is below 10 nm and the k1 value is reduced from 0.5 down to 0.32 in this process. The reactive ion etching adopting O2 gas demonstrated selectivity of the top resist over bottom material more than 15:1, together with residue-free and vertical wall profile.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.