SPRINTCAD QUARTERLY SUMMARY

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PROJECT LEADER

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OBJECTIVE:

APPROACH:

1. deposition/etching module---of special interest are CVD and plasma assisted processes that result in high aspect ratio structures such as trenches and filling/planarization of structures for metal interconnects. Algorithmic work focuses on geometric manipulations and surface evolution.
2. thermal/stress analysis module---that can solve nonlinear constitutive models for key process steps involving growth of dielectric layers and impurity redistribution as well as the resulting stress fields. Advanced formulations for finite elements are being developed that support: parallel computation, adaptive gridding and domain decomposition.

PROGRESS:

Calibration of etching and deposition simulation has been mostly performed on 2D geometrical profiles based on infinite-width approximation, not only because 3D simulation tools are much more computationally expensive and not widely available, but also because 3D profile characterization methodologies are limited by insufficient accuracy in positioning 2D cross-section measurements. An L-shaped test structure is chosen to overcome this characterization difficulty by 45-degree angle cuts at various positions. 3D simulation is performed using the physical models in SPEEDIE, whose parameters are calibrated using 2D infinite-width trench simulation, and the level-set method, which can accurately and robustly model complex 3D boundary movement. Not only that 3D effects, such as the flattening and thinning of the bottom coverage going into the corners, can be clearly observed in both measurement and simulation, good match between various 2D SEM and simulation cross sections also shows the physical model and the boundary movement method are accurate in 3D. This is an important starting point for genuine 3D analyses on more complex structures.

The use of 1D parameters or 2D profiles in creating 3D structures through geometry modelers such as VIP-3D has potential limitations to accurately include important 3D effects. For example, 3D LOCOS structures generated in this way do not show the effects of enhanced oxidant diffusion at mask corners. A new capability to integrate simulated 3D surfaces has been used in VIP-3D to generate more accurate wafer structures. We have chosen a quasi-3D LOCOS modeling algorithm, which uses a combination of parameterized 2D analytic bird's beak shape equations and a fully 3D oxidant diffusion simulation based on the boundary element method to model corner effects in local oxidation. 2D and 3D simulations are combined in order to reduce computational cost. This heterogeneous approach reduces overall complexity which mirrors the goal of VIP as a means for rapid prototyping.

A generalized oct-tree mesh generation algorithm enables mesh refinement and de-refinement in different directions at various regions. A vector level control function is computed and indicates the directions for which the refinement will be performed. In a contour based refinement scheme, the level control function indicates the directions as the gradient, while in an error estimator based scheme, it indicates the direction where the error will be maximally reduced. Every octant can be refined in either one, two or three dimensions. After the tree is generated, detailed tetrahedralization algorithms are implemented to match the complex geometry and ensure mesh conformity. Then after each simulation step, the vector level control function is re-calculated according to the new gradient or error, and the mesh is adapted to reflect the changing areas of simulation significance. With the tree structure, interpolation error is also greatly reduced since the meshes before and after the adaptation share many common nodes. Grid quality required by the maximum principle is degraded during the adaptation. New algorithmic solution is currently under investigation.

RECENT ACCOMPLISHMENTS:

• The minimal SWR specification has been revised for a unified 3D geometry definition and multiple-gridder support.
• Modeling and characterization of 3D effects in etching and deposition have been performed on a test elbow structure. Accurate measurement methods to construct 3D profiles from 2D SEM pictures are devised and SPEEDIE 3D simulation using level-set boundary movement has shown very good agreement.
• 3D oxidation by the boundary element method is linked to the diffusion simulation by the volume element method through the geometrical operations provided by VIP-3D.
• 3D grid adaptation is investigated in ALAMODE/CAMINO for reactive-diffusive systems. Grid quality required by the maximum principle is degraded during the adaptation. New algorithmic solution is studied.

FY-`96 PLANS:

• Test 3D Thermal Module and integration of parallel solver technology.
• Implementation of 3D Oxidation within Thermal Module and transition into unified capabilities (both diffusion and oxidation).
• Implementation of complete server for 3D Deposition/Etching Module, including 3D parallel solver to support flux calculations.
• Benchmark the overall SPRINT-CAD modules in terms of a deep submicron MOS technology. The Thermal Module will demonstrate 3D analysis of locally oxidized isolation and shallow junction diffusion steps. The Deposition/Etching Module will demonstrate first-time functionality of a 3D server-based architecture and implementation.

TECHNOLOGY TRANSITION:

Date prepared: 5/9/96