Exposure of binary masks using ArF (193nm) photolithography processing is a common practice for layers with less critical imaging requirements, but they may experience obstacles for high volume manufacturing; mainly defectivity or requalification cost concerns. The usage of chrome on glass (COG) mask types under ArF wavelength exposure has been shown to lead to chrome migration issues, impacting mask integrity and critical dimensions (CDs) on wafer. While not experiencing the same defectivity concerns as COG, using opaque MoSi on glass (OMOG) as a replacement greatly increases the cost to build the mask but reduces the requalification efforts. We have observed that attenuated phase shift masks (PSMs) built for KrF wavelength (248nm) exposure show the same functional performance as a binary mask under ArF exposure for 45nm node technology. Initial feasibility investigation involved simulating wafer exposure with an OMOG mask and a KrF PSM mask under the same conditions. To demonstrate wafer performance, masks with and without 2nd level processing were built to verify exposure and tool handling capabilities. The application of KrF PSM as a binary mask under ArF photolithography processing for less critical layers of mature technology nodes shows to maintain pattern integrity at a lower total lifetime cost, compared to COG or OMOG, while providing comparable results on wafer.
Reticle process of record (POR) sometimes needs fine tuning for some reasons such as multiple layer process, better
critical dimension uniformity (CDU) or new etch chamber. The sidewall angle and corner rounding will be varied due to
the reticle processing tuned comparing to previous POR. However, because the reticle critical dimension (CD)
measurement is based on middle side lobe measurement or other algorithm, the reticle CD cannot reflect the changes of
reticle sidewall angle and corner rounding variation which are critical for 65nm node and below. Each of the scanner,
wafer process, reticle and metrology tool contributes to the intra-field wafer CD. Normally, the reticle contribution to the
wafer CDU should be as small as possible, that is less than 33%. By averaging all wafer CD of individual features to
obtain a wafer CD reference independent of feature location and wafer die, the correlation of wafer measurement to
target (MTT) and reticle MTT can be obtained. The correlation can accurately qualify and monitor the tuning processing
of reticle.
We have manufactured two masks for active layer of 65nm tech node by different reticle process. One used the original
POR process of active layer, while another used multi-layer-reticle (MLR) process. The correlations between wafer
CDU and reticle CDU of these reticles are demonstrated for both isolated and dense features in vertical and horizontal
direction, respectively. Similar experiments were implemented and the correlations for both dense and isolated structures
are demonstrated as well, for two different POR process for first metal layer of 40nm tech node. Referring to the wafer
and reticle MTT correlation, the contribution of reticle CDU to wafer CDU can be used as an evaluation methodology
for reticle processing. The wafer and reticle CDU correlations for 45nm node poly and contact layers POR process are
also demonstrated.
A persistent industry problem impacting photomask yield and costs has been haze formation. The haze nucleation
and growth phenomenon on critical photomask surfaces has periodically gained attention as it has significantly
impacted wafer printability for different technology nodes over the years. A number of process solutions have
been promoted in the semiconductor industry which has been shown to suppress or minimize the propensity for
haze formation, but none of these technologies can stop every instance of haze. Thus some capability will always
be needed to remove haze on photomasks with their final pellicles mounted both at the manufacture and long term
maintenance stages of a mask's lifetime. A novel technology is reviewed here which uses a dry (no chemical
effluents) removal system to sweep the entire printable region of a pelliclized photomask to eliminate all removable
haze regardless of the mask substrate materials or the presence of critical patterns. An operational process
technique for this system and performance in removal is shown for haze located on the mask pattern surface.
Finally, preliminary data from tool acceptance and preliminary use in a production environment will also be reviewed.
In this paper, a novel optical proximity correction (OPC) method for contact hole patterning is demonstrated.
Conventional OPC for contact hole patterning involves dimensional biasing, addition of serifs, and sub resolution assist
features (SRAF). A square shape is targeted in the process of applying conventional OPC. As dimension of contact hole
reduces, features on mask appear to be circular due to strong diffraction effect. The process window enhancement of
conventional OPC approach is limited. Moreover, increased encounters of side lobes printing and missing contact holes
are affecting the process robustness. A new approach of changing the target pattern from square to circular is proposed in
this study. The approach involves a change in shape of mask openings and a radial segmentation method for proximity
correction. The contact holes patterns studied include regular contact holes array and staggered contact holes. Process
windows, critical dimension (CD) and aerial image contrast is compared to investigate the effectiveness of the proposed
contact holes patterning approach relative to conventional practice.
Intra-field CD variation can be corrected through wafer CD feedback to the scanner in what is called the Dose Mapper
(DOMA) process. This will correct errors contributed from both reticle and scanner processes. Scanner process errors
include uncorrected illumination non uniformities and projection lens aberration. However, this is a tedious process
involving actual wafer printing and representative CD measurement from multiple sites. A novel method demonstrates
that measuring the full-field reticle transmission with Galileo® can be utilized to generate an intensity correction file for
the scanner DOMA feature. This correction file will include the reticle transmission map and the scanner CD signature
that has been derived in a preliminary step and stored in a database. The scanner database is periodically updated after
preventive maintenance with CD from a monitoring reticle for a specific process. This method is easy to implement as no
extra monitoring feature is needed on the production reticle for data collection and the new reticle received can be
immediately implemented to a production run without the need for wafer CD data collection. Correlation of the reticle
transmission and wafer CD measurement can be up to 90% depending on the quality of CD data measurements and
repeatability of the scanner signature. CD mapping on the Galileo® tool takes about 20 minutes for 1500 data points
(there is no limit to the number of measurement point on the Galileo®), which is more than enough for the DOMA
process. Turn Around Time (TAT) for the whole DOMA process can thus be shortened from 3 Days to about an hour
with significant savings in time and resources for the fab.
A lithography technique for fabricating subwavelength surface relief grating features based on evanescent waves interference is investigated by both analytical and numerical approaches. The analytical expressions for the intensity profiles of evanescent waves interference generated by both s- and p-polarized incident plane waves are deduced. The corresponding resist topologies are computed using a numerical scheme based on a modified cellular automata model, as proposed. The influences of polarization and exposure duration on patterning by evanescent waves interference lithography are investigated. The results suggest that this technique is capable to achieve nanoscale line features with linewidths as small as 15 nm, a pitch size of 105 nm, and an aspect ratio as high as 10.7 by appropriate choice of exposure duration and state of polarization for the incident beams.
In this paper, a defect disposition integrated system for progressive growth and hard defects has been proposed and
discussed for 65 nm and 45 nm immersion lithography. Pre-programmed hard defects on mask with minimum defect size
of 60 nm are studied. These mask defects are scanned by STARlight inspection with pixel size P90 for mask defect
capturing. Aerial Image Measurement System (AIMS) and printed photoresist features are used for modeling. Line,
space and hole in both bright and dark field are used for model setup. Printability for these programmed mask defects is
determined from process critical dimension (CD) variability. Experimental wafer results on the programmed defect mask
are obtained using 193 nm immersion tool with effective NA of 1.2 imaging lens. The resist CDs response to the mask
defect area are measured under the different exposure dose or focus. The correlation of AIMS CD, simulated CD and
wafer CD for different defect types and sizes to printability is performed. Scan result of progressive growth defects are
captured and verification of its printability using AIMS and Automated Mask Defect Disposition (AMDD) from KLATencor
is obtained.
Alternating phase shift mask will be one of the most possible solutions for 65nm technology node as the further delay of 157nm lithography and next generation lithography. In this paper, alternating phase shift mask is used to pattern 65nm poly gate on logic device using 193nm lithography. Double exposure of dark field phase mask and binary trim mask were superimposed on wafers using 193nm scanner. Both mask making process and wafer exposure process are optimized in order to obtain maximum process margin on wafer for 65nm gate CD for pitch of 170nm. The amount of intensity imbalance on alternating phase shift mask with various mask making processes is fully characterized to improve mask making process. Furthermore, the impact of mask making process on process margin is evaluated with and without mask process optimization. The results show that with mask process optimization, large DOF of 0.50μm can be achieved for 65nm line with 170nm pitch. However, without mask process optimization, resolution is limited to 240nm pitch only due to intensity imbalance in 0 degree and 180 degree features. In addition, the study also shows that with alternating phase shift mask, intermediate NA of 0.70 is suitable for 65nm technology as high NA of larger than 0.75 will decrease DOF performance.
Resolution enhancement techniques (RET) have been widely used to extend existing lithography to print features below the wavelength of the light source. One of such techniques is phase shifting. Due to the relative ease of implementation, the application of attenuated phase shift mask (PSM) is relatively more common compare to the strong alternating phase shift mask. The impact of the mask error critical dimension (CD) and its effect on printing onto wafers have widely been studied. However, the transmission error incurred in the blank and mask making has not been popularly investigated. This paper will study the impact of transmission error on the CD of wafer printing level. Simulation studies have be preformed for isolated lines as well as dense lines with assist features using 248nm laser source. In addition, the effect of phase error by on-axis as well as annular illumination type of light source will also be investigated.
Mask error factor (MEF) plays an important role as lithography progresses to sub wavelength patterning. For patterning feature in the sub wavelength region of the illuminating system, namely 0.10 um line and space feature, resolution enhancement techniques (RET) such as optical proximity correction (OPC), and assist features (AF) are applied. A study on the impact of MEF on 248 nm lithography will be investigated. Experimental results for both isolated line and dense lines up to 0.10 um with AF will be obtained and analyzed. A through pitch experimental study shows a decrement in MEF from dense line to semi-isolated line. Experimental studies on varying the placements of the assist features for both isolated will be conducted. Furthermore, the study also included the comparison by conventional and annular illumination for both line and space. Simulation results will also be utilized as a comparison.
Resolution enhancement techniques, such as phase shifting, OPC and assist features were greatly used to enable sub-wavelength features printing using 248nm lithography due to the delay of 193nm lithography. Assist features, also known as scattering bars, was utilized to improve the image quality for isolate lines for the sub-wavelength features as well as to improve the overlapping process latitude. In this study, MEEF was fully characterized with assist features. Great improvement in MEEF was observed by applying assist features to the sub-0.13 micrometers technologies. The effect of mask error enhancement by the deviation from the designed line width of the image line with different sets of placement and width sizes of the assist features was been studied. The impact of MEEF by different placement of the assist features was observed. In addition, a simulation program had been used for the study of the deviation in the placement of the scattering bars as well as its size. It was shown that simulation aerial image results were quite matching with imperial results. The effect of annular illumination had also been examined as compared to conventional illuminations.
Mask Error Enhancement Factor (MEEF) has become one of the critical concerns with the recent technology progress into producing pattern features far smaller than the wavelength of light, as in the case of 0.13 micrometer lithography and below. In this paper, we present MEEF study on different illumination conditions for 0.13 micrometer technology using 248 nm KrF Lithography. Both simulation results using Prolith/2 tool and experimental results using 248 nm DUV scanner, for varying the illumination conditions namely, annular versus conventional with different Numerical Aperture (NA) and Partial Coherent (PC) settings will be discussed. The study shows MEEF varies for different illumination conditions. MEEF was lower with high NA setting as compared to low NA, and annular illumination shows slight improvement of MEEF. In addition, experiments using different types of reticle specifically; Binary mask, 6% half tone Phase Shift Mask (PSM) and 18% High Transmittance Mask (HTM) were also analyzed to characterize its relationship with MEEF.
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.