We selected alternating phase shift technology to image 90nm dense lines with a pitch of 200nm for volume production purposes. We simulated which settings of illumination were needed to achieve these pitches taking into account the boundary condition of the exposure tool with the wavelength of 248nm and its maximum NA of 0.68. The simulations showed, that normalized image log slope (NILS) is above 2 for a focus range of at least 600nm, if an alternating phase shift mask is used at the very low σ of 0.2 Typical manufacturing conditions with process variations, lens errors and mask deviations were included in the simulations. Based on these results, on the one hand the mask was specified and manufactured; on the other hand the tool was adaptated to the low σ requirement and the specific lens error sensitivities. Shipley's UV212 on BARC AR7 was used at a resist thickness of 250nm. The resist process was optimized by reducing the concentration of the developer. Finally, experimental verification of this entire system with wafer exposures shows that 90nm lines with a pitch of 200nm could be printed with a focus window of more than 600nm.
New metrology capabilities available on a state-of-the-art CD-SEM system are discused that allow quantification of contact and via profiles directly after lithography processing. The so-called Profile Grade (PG) analysis capability is based on secondary electron emission information obtained while scanning the contact or via holes. Three PG ranges can be distinguished to quantify contact profile quality; 0 < PG < 1.4 for closed contacts, 1.4 < PG < 1.7 for semi-opened contacts, and 1.7 < PG < 5 for fully opened contacts. These ranges are independent of resist type. The PG analysis is shown to be more accurate and sensitive in predicting contact profile marginality than classical CD measurements. A common practice in lithography processing is to use overexposure conditions to built in a safety margin ensuring that contacts are fully opened. The present work demonstrates that monitoring the lithography process by using the PG profile analysis with a lower spect limit in addition to the classical CD measurement enables the use of a lower exposure dose which increases stepper throughput. In addition, risk to yield loss is decreased because the quality of the contacts in the lower CD range can be quantified by using the PG profile analysis methodology.
KEYWORDS: Data modeling, Diffusion, Lithography, Scanning electron microscopy, Calibration, Optimization (mathematics), Performance modeling, Critical dimension metrology, Computer simulations, Picture Archiving and Communication System
The simulation of photolithographic processes depends on accurate resist modeling parameters. In this paper we present an automated fitting procedure which can be applied to arbitrary combinations of experimental data and model parameters. The procedure is applied to a typical i-line process. The resulting models are evaluated with respect to their performance for the full set of experimental data. The correlation of model parameters with certain experimental data is discussed and an optimum automatic parameters extraction procedure for i-line resists is proposed. Finally, we evaluate the extracted parameters by comparing different simulated profiles with cross-section SEM pictures.
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