The lithographic requirements for the thin film head industry are comparable to the semiconductor industry for certain parameters such as resolution and pattern repeatability. In other aspects such as throughput and defectivity, the requirements tend to be more relaxed. These requirements match well with the strengths and weaknesses reported concerning nanoimprint lithography (NIL) and suggest an alternative approach to optical lithography. We have demonstrated the proof of concept of using NIL patterning, in particular Jet and FlashTM Imprint Lithography (J-FILTM) 1 , to build functional thin film head devices with performance comparable to standard wafer processing techniques. An ImprioTM 300 tool from Molecular Imprints, Inc. (MII) was modified to process the AlTiC ceramic wafers commonly used in the thin film head industry. Templates were produced using commercially viable photomask manufacturing processes and the AlTiC wafer process flow was successfully modified to support NIL processing. Future work is identified to further improve lithographic performance including residual layer thickness uniformity, wafer topography, NIL→NIL overlay, and development of a large imprint field that exceeds what is available in optical lithography.
The lithographic requirements for the thin film head (TFH) industry are comparable to the semiconductor industry for certain parameters such as resolution and pattern repeatability. In other aspects such as throughput and defectivity, the requirements tend to be more relaxed. These requirements match well with the strengths and weaknesses reported concerning nanoimprint lithography (NIL) and suggest an alternative approach to optical lithography. We demonstrate the proof of concept of using NIL patterning, in particular Jet and Flash™ Imprint Lithography (J-FIL™) (Imprio, Jet and Flash Imprint Lithography, and J-FIL trademarks are the property of Molecular Imprints, Inc.), to build functional TFH devices with performance comparable to standard wafer processing. An Imprio™ 300 tool from Molecular Imprints, Inc. (MII) was modified to process the AlTiC ceramic wafers commonly used in the TFH industry. Templates were produced using commercially viable photomask manufacturing processes and the AlTiC wafer process flow was successfully modified to support NIL processing. Future work is identified to further improve lithographic performance including residual layer thickness uniformity, wafer topography, NIL→NIL overlay, and development of a large imprint field that exceeds what is available in optical lithography.
One of Cypress’ primary goals for 90-nm generation mask strategy is to control mask costs while not compromising on performance. One key objective is to replace the use of 50-ke V electron beam pattern generation with DUV laser mask lithography where possible. The higher productivity of the DUV laser systems compared to the 50Ke V e-beam platforms offers a unique opportunity for mask cost reduction. Compared to previous i-line generations of laser lithography systems, the DUV laser systems provide significantly improved resolution and pattern fidelity that more closely approaches that of ebeam lithography. We have previously published experimental results demonstrating that the difference in fidelity on the mask between the laser and EB platforms does not always translate to a measurable difference in wafer litho performance or even more importantly to a measurable difference in electrical performance. Through this work, Cypress was able to eliminate the use of 50Ke V ebeam writers for all of their 130nm technology node layers. In some cases the improved performance of the DUV tools was sufficient to replace i-line produced masks where wafer performance was marginal without having to resort to EB lithography. This study addresses the conversion of 50Ke V ebeam layers to DUV laser platform specifically for the critical layers of the Cypress’ 90nm Technology node. EB lithography was originally specified for these layers as a conservative approach in part due to the timing of 90-nm technology development relative to the maturation of the DUV laser mask lithography process. In this study, the electrical performance and wafer yield are evaluated for equivalency in order to take advantage of the lower cost and faster cycletime that use of a ALTA DUV system provides over the 50Ke V VSB systems. In addition, the wafer OPC is not changed between the two mask writing systems in order to allow interchangeable use of the two writing systems if the experimental results indicated no difference in wafer performance.
The integration of 193nm Lithography is close to full production for the 90nm node technology. With the potential of emerging 193nm lithographic resolution down to 65nm, the quality of 193nm reticles including binary, EAPSM and AAPSM must be outstanding so that low K1 factor reticles may be used in production. One area of concern in the IC industry is haze contamination on the mask once the reticle has been exposed to ArF radiation. In this study, haze was found outside of the pellicle and on the quartz side of the mask. Standard through-pell inspections will typically miss the contamination, yet its severity can ultimately affect mask transmission. For this reason, DuPont Photomasks and Cypress joined forces to quickly decipher how it develops. In this investigation, tests were devised which altered conditions such as mask environment, exposure, traditional and advanced cleaning chemistry. This paper describes the relationship between surface and environmental photochemical reactions, the resultant growth, analysis, and how it is controlled.
Mask CD resolution and uniformity requirements for back end of line (BEOL) layers for the 90nm Technology Node push the capability of I-line mask writers; yet, do not require the capability offered by more expensive 50KeV ebeam mask writers. This suite of mask layers seems to be a perfect match for the capabilities of the DUV mask writing tools, which offer a lower cost option to the 50KeV platforms.
This paper will evaluate both the mask and wafer results from all three platforms of mask writers (50KeV VSB,ETEC Alta 4300TM DUV laser and ETEC Alta 3500TM I-line laser) for a Cypress 90nm node Metal 1 layer, and demonstrate the benefits of the DUV platform with no change to OPC for this layer.
It has long been understood that there is an image fidelity difference between the integrated circuit design pattern and the photomask made from that pattern, largely due to the finite spot size of pattern generators. Furthermore, there are known differences in photomask image fidelity (rounding, jogs, etc.) between e-beam and laser pattern generators. Using a novel technique developed by DuPont Photomasks, Inc. (DPI), actual photomask fidelity has been simulated from design data to produce a more true-to-life representation of the mask. We have performed analytical simulations and printed-wafer measurements on Cypress 100-nm technology designs to determine the differences and effects on optical proximity correction (OPC) of two types of pattern generators: 50 keV e-beam and DUV laser. Both JEOL 9000MV-II+ and ETEC ALTA 4000 images were simulated and saved in GDSII format (“mask-GDSII”). These new mask images were processed through standard lithography simulation software to predict the effects each mask writer has on localized optical proximity effects. Simulations were compared to printed wafer results. A detailed comparison of the accuracy of the mask-GDSII and original design GDSII is performed. Furthermore, comparison of 50 keV e-beam and DUV laser image fidelity is completed, and recommendations are made on how to correct OPC models for each type of photomask generator. Lastly, conclusions are drawn about the use of DUV laser and 50 keV e-beam photomasks.
Proc. SPIE. 4689, Metrology, Inspection, and Process Control for Microlithography XVI
KEYWORDS: Electron beams, FT-IR spectroscopy, Optical lithography, Amplifiers, Scanning electron microscopy, Photoresist materials, Monte Carlo methods, Scanning probe microscopy, Systems modeling, 193nm lithography
As photolithography platforms move from 248nm to 193nm resist systems, the industry's established dimension measurement technique (CD-SEM) causes significant shrinkage of the resist structures during measurement. Many studies have been done to characterize this effect and look for the factors that influence / reduce this shrinkage. While numerous anecdotal mechanisms have been proposed to explain the shrinkage, few theoretical / empirical equations have been proposed to connect the observed effects to fundamental mechanisms. Models are proposed relating physical properties (accelerating voltage, photoresist density, resist e-beam film shrinkage) to the commonly observed CD 'hammer test' shrinkage profiles. The validity of the model assumptions is tested via Monte Carlo simulations, FTIR, e-beam curing, SPM and ellipsometry. These models explain the shape of the CD response to repeated measurements (exponential decay curve) and the magnitude of the shrinkage. These models also offer insight into why lower accelerating voltages cause reduced CD shrinkage, although the models predict that accelerating voltage should be a much more dominant parameter for CD shrinkage than literature has shown to date. Mass loss and density changes were also characterized during e-beam cure to check the validity of the model assumptions.