Simulation parameter effects on critical dimension and sensitivity of 193 nm Chemically Amplified Resist
It is helpful in lithography process and developing resist to know the relationship between the critical dimension variation and simulation parameters such as aerial image parameters, the Dill exposure parameters, PEB (Post Exposure Bake) parameters, and development parameters. In this paper the profiles of a 193 nm CAR (Chemically Amplified Resist) were simulated with those various parameter, and those results were analyzed by the response surface methodology (RSM) approach to know the influence of independent factors on a dependent response and to optimize each process. Both the parameter effects of each process and the simulation process effects of the whole process were described about critical dimension and side wall angle so that the sensitivity of lithography process could be assumed. The development parameters were modified with those of flood exposure experiment according to the pattern density and pattern size for more accurate lithography simulation. Also those effects on critical dimension and side wall angle were analyzed. For the validity of our results the quantitative comparison between our results and those of a commercial tool was shown.
Etude de la stabilité et de la précision des modèles utilisés dans la correction des effets de proximité optique en photolithographie
A l’heure actuelle, les modeles photochimiques utilises dans la correction des effets de proximiteoptique (OPC) en photolithographie sont devenus complexes et moins physiques afin de permettre decapturer rapidement le maximum d’effets optiques et chimiques. La question de la stabilite de tels modelespurement empiriques est devenue d’actualite. Dans ce memoire, nous avons etudie la stabilite desmodeles photochimiques actuels en examinant les differentes causes d’instabilite vis-a-vis des parametresdu procede. Dans la suite, nous avons developpe une methode perturbative permettant d’evaluer le criterede la stabilite. L’obtention de modeles simples et stables nous conduit a separer les effets optiques desautres effets chimiques. De plus, les approximations utilisees dans la modelisation des systemes optiquesoperant a grande ouverture numerique entrainent des erreurs residuelles pouvant degrader la precisionet la stabilite des modeles OPC. Ainsi, nous nous sommes interesses a etudier les limites de validitede l’approximation de Kirchhoff, methode qui, jusqu’a present, est la plus utilisee dans la modelisationdu champ proche d’un masque. D’autres methodes semi-rigoureuses, permettant de modeliser les effetstopographiques, ont ete egalement evaluees. Ces methodes approchees permettent de gagner en precisionmais degradent le temps de calcul. Nous avons ainsi propose differentes facons de corriger les effetstopographiques du masque, tout en gardant l’approximation de Kirchhoff dans la modelisation de la partieoptique. Parmi les methodes proposees, nous exploitons celle permettant de reduire les erreurs lieesaux effets topographiques du masque par l’intermediaire d’un second modele empirique. Nous montronsque pour garantir une precision adequate, il est necessaire d’augmenter la complexite du modele en rajoutantdes termes additionnels. Enfin, pour garantir la stabilite numerique du modele empirique, nousintroduirons une nouvelle methode approchee hybride rapide et precise, la methode des multi-niveaux,permettant d’inclure les effets topographiques par decomposition multi-niveaux du masque fin et discuteronsses avantages et ses limites.
Exposure monitor structure
A novel exposure monitor structure (EMS) is proposed as a sensitive means to monitor or measure effective exposure dose in the optical lithographic printing. Like windows of graduated transmittance, it is very sensitive to dose, but not to focus. On the other hand, EMS is compact to allow placement in the kerf or device layouts and it is measurable by automated rctetrology tools. EMS is built in the conventional reticles by arranging a set of stripes of chrome and glass on the period near MTF cut-off in a manner simulating transmission wedges on both sides of a conventional line. Since the fine structure of EMS is not resolved by the optical lithography tool used for printing, it performs like a transmission wedge. Conventional linewidth measurements of a printed EMS image are used to monitor exposure dose. Coupled with a calibration curve, sensitive dose measurements can also be made. Modelling of printing of EMS and of a conventional line on an optical stepper indicates that printed linewidth of EMS changes much faster as the function of dose. EMS also displays relatively little sensitivity to defocus. Conventional 5X reticles with EMS were built. Exposure sequences were carried out on a G-line stepper. Linewidth measurements of printed EMS and of conventional lines were done on a typical linewidth measurement tool. Experiment confirms that linewidth of printed EMS is much more sensitive to dose than that of a conventional line. Once linewidth of EMS is established at the desirable dose, EMS may be used to set that dose in the subsequent runs. With more accurate dose set-up and job disposition decisions, higher product tolerance can be achieved with existing equipment and process.