Toshiyuki Ohta

Practical Monte Carlo sputter deposition simulation with quasi-axis-symmetrical (QAS) approximation

A practical Monte Carlo (MC) sputter deposition profile model has been developed to achieve accurate profile simulation within reasonable calculation time. The key features of the model are: (1) a quasi-axi-symmetrical (QAS) approximation which enables to convert 3D trajectories of incident atoms into 2D sputter deposition profiles in terms of the string model, and (2) calculation of the collision cross-section by means of Lennard-Jones potential. The simulated profiles of collimated-sputter titanium (Ti) in contact holes well agree with the experimental SEM profiles within 5% accuracy.<<ETX>>

A sputter equipment simulation system including molecular dynamical target atom scattering model

We have developed an advanced sputter equipment simulation system to design the deposition equipment for ULSI with high aspect ratios contact holes. The system is composed of a newly developed target atom scattering model and die profile model with the Monte Carlo (MC) method. The target atom scattering model uses the Molecular Dynamics (MD) technique combined with thermal analysis and derives ejection angle distribution. The simulated results of titanium (Ti) bottom coverage vs. applied voltage agree with experiments within 10% accuracy.

Practical 3D lithography simulation system

We have developed a 3D practical lithography simulation system and realized the practical parameter optimization. A very fast 3D profile computation is performed by using the FFT algorithm in aerial images and the post exposure bake. The optimization system is developed by using object- oriented technology in order to reduce the computation time. The resulted computational time is less than one tenth of the conventional system. The total parameter optimization time is also reduced.

Simulation of the optical effects of particles residing on top antireflective coatings for KrF positive photoresist films

The reflection effects of particles on developed cross‐sectional photoresist patterns are simulated by using a two‐dimensional waveguide model. The particles were assumed to reside on top antireflective coatings used for chemically amplified positive photoresist films. In order to improve the accuracy of the analysis, the exposure dose of KrF excimer laser light and focus position in the resist were optimized. The top antireflective coating film thickness was also adjusted to the optimum thickness for obtaining the critical dimension of 0.25 μm. Under these conditions, the light intensity distributions in the resist depth and in the lateral direction on the focal plane are discussed, and it is revealed that the influence of the particles is enhanced for the case of weaker light intensity. Finally, it is described that the antireflective coating gives a wider process margin on the smallest critical sizes of particles capable of causing pattern shorts. In conclusion, the light intensity obtained from three‐dimensional Fresnel approximation is also taken into account.The reflection effects of particles on developed cross‐sectional photoresist patterns are simulated by using a two‐dimensional waveguide model. The particles were assumed to reside on top antireflective coatings used for chemically amplified positive photoresist films. In order to improve the accuracy of the analysis, the exposure dose of KrF excimer laser light and focus position in the resist were optimized. The top antireflective coating film thickness was also adjusted to the optimum thickness for obtaining the critical dimension of 0.25 μm. Under these conditions, the light intensity distributions in the resist depth and in the lateral direction on the focal plane are discussed, and it is revealed that the influence of the particles is enhanced for the case of weaker light intensity. Finally, it is described that the antireflective coating gives a wider process margin on the smallest critical sizes of particles capable of causing pattern shorts. In conclusion, the light intensity obtained from three‐...

Simulation of influence of particles on photoresist films for lithography

The influence of the particles existing on photoresist films, the sizes of which are comparable or smaller than the exposure light wavelength, on the developed cross‐sectional pattern is investigated by using the two‐dimensional waveguide model. Then, the smallest sizes of particles capable of causing pattern shorts are obtained as a function of the device design rule, taking into account the calculation results using a three‐dimensional Fresnel diffraction approximation. The simulated results show good agreement with the actual critical sizes on the starting material silicon wafers at the 0.5, 0.35, and 0.25 μm design rule periods.

A practical CMP profile model for LSI design application

We have developed a practical CMP model. The model is based on elastic mechanics. For practical use, some numerical treatments including a new time iteration method are developed. Using the model, numerical errors in a test chip are reduced to less than 1% with 5 minutes EWS calculation time. The simulated results agree with experiments within 5% error.

Interactive OPC simulator for memory devices

The practical OPC simulation system suitable for memory devices is developed with a simple threshold model considering acid diffusion in chemically amplified resists. And the resist parameter extraction method is also presented. The simulation performance is within 0.01 micrometer CD error, and within a few second computation time for 4 micrometer2 area memory cell on a EWS.