Validity of the diffused aerial image model: an assessment based on multiple test cases

Abstract

Lithography modeling is a very attractive way to predict the critical dimensions of patterned features after lithographic processing. In a previous paper [1] , we have presented the assessment of three different simplified resist models (aerial image model, aerial image convolved with fixed gaussian noise and aerial image convolved with variable gaussian noise) by using a systematic comparison between experimental and simulated data. It has been shown that the aerial image convolved with fixed gaussian noise, or "diffused aerial image model" (DAIM), exhibits surprisingly good results of CD prediction for lines @ 193nm: using these datasets, the DAIM appears as a fast and accurate model for CD prediction. This approach allows also an easy run, and because it needs only four adjustable parameters, it avoids the difficult task of resist parameters extraction associated to full resist models, with. In this paper, we enlarge the datasets used for the assessment of the DAIM by considering both lines and contact holes of various sizes printed at different wavelengths. The reference wafers have been printed at 248nm, 193nm and 157 nm. The procedure used to extract the model parameters has been improved and now needs less data to provide acceptable values. We will show that the validity of the DAIM extends well outside the results presented in ref.1. Experimental data printed using various wavelengths, resists and exposure tools can be simulated accurately with CD prediction error ranging within few percents. It is to be noted that the results that will be presented on contact holes data indicate that the model is valid for 2D features. Finally, a comparison with full resist models shows that the accuracy of DAIM is comparable to more sophisticated and heavier models .

Process variation aware OPC with variational lithography modeling

“…to its simple analytical formulation. It has also been demonstrated in [7] that it predicts CD fairly accurately. This model assumes the printed contour can be computed by applying a constant bias to the contour where the intensity is equal to an intensity threshold I th .…”

Comparison of various lithography strategies for the 65- and 45-nm half pitch using simulation

“…CD and dose offsets are added that improve the accuracy of the simulations, and finally the DAIM uses only four parameters. A previous work [2] show that the DAIM is predictive and can simulate accurately CDs outside the set of data that have been used for fitting the model parameters. The DAIM coefficients depend of the whole resist process (resist thickness, layer stack, PAB, PEB, development conditions), and metrology conditions.…”

“…This fit is based on functions that rely on physical considerations and that include the isofocal dose or threshold as explicit coefficients. [2] The four DAIM parameters are drawn together. All the masks and optical tools considered for the following work are considered as perfect (for process windows evaluation, it is highly improbable that non ideal objects would lead to improved process margins).…”

“…Simulation gives information on expected process latitudes and is an important tool to help this technical choice. Previous works [1,2] have shown that the "Diffused Aerial Image Model" (DAIM) [3] is accurate for CD prediction. Reliable process latitudes can be extracted from the simulated focus-exposure matrices (FEM).…”

Estimating resist parameters in optical lithography using the extended Nijboer-Zernike theory

“…In various publications, the validity of the diffused aerial image model ͑DAIM͒ was assessed. 8,9 It was concluded that DAIM is a good predictor not only for lines and spaces, but also for 2-D structures such as contact holes. The accuracy of DAIM was found to be comparable to full resist models.…”