SPRINTCAD QUARTERLY SUMMARY
Apr. 1 - June 30, 1996
ORGANIZATION: Stanford University
Robert W. Dutton, dutton@gloworm.Stanford.EDU, (650) 723-4138
Kincho H. Law, law@cive.Stanford.EDU, (650) 725-3154
Krishna Saraswat, saraswat@ee.Stanford.EDU, (650) 725-3610
Peter Pinsky, pinsky@ce.Stanford.EDU
Edwin C. Kan,
kan@gloworm.Stanford.EDU, (415) 723-9796
TITLE OF EFFORT:
-Networked TCAD using Shared Parallel Computers
The URL for Stanford TCAD projects is:
OBJECTIVE: First-time capabilities to bridge solid modeling, FEM-based
parallel computation of fabrication processes and electrical analysis
of the resulting IC structures will be developed. Models needed to
represent diffusion, etching, deposition, oxidation and stress analysis
resulting from a sequence of process steps necessary in the creation
of electrical devices will be developed. This effort will provide a
radically new HPC framework for technology-based 3D process/device
modeling as well as realistic benchmarks to test HPC architectures
APPROACH:We will build, integrate and test TCAD modules based on an
object-oriented approach that both develops and uses information
models in support of CFI-based standards. The modules and software
engineering methodology will be designed specifically to exploit
parallel computers and library components. The 3D process simulation
modules will utilize HPC platforms and provide new functional
capabilities for "computational prototyping" of the following key
technology fabrication steps:
- 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
- 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
APCVD has become very important for intermetal dielectric deposition
processes in the deep submicron technology owing to its excellent
capabilities in void-free filling of narrow and deep trenches.
Physical modeling of conformal and flow-like behaviors in APCVD
processes are rigorously derived from a generic surface reaction
kinetics. Surface reaction follows adsorption of gas-phase
precursors on surface sites. When the surface sites are saturated,
the deposition rate approaches zero-order reaction and the
nonuniform surface site density effects become more apparent.
A widely applicable parameter set, which accounts for the 0th
(planar), 1st (shape) and 2nd (curvature) geometrical effects,
can be extracted from the experimental deposition rates and detailed
boundary profiles on test structures. The level-set method is
especially appropriate for this formalism owing to its accurate
curvature estimation and boundary movement according to the entropy
condition. Very good agreement with experimental measurements are
obtained for various grove sizes and elbow-shaped 3D structures
with the same parameter set.
The numerical undershoot near sharp concentration gradients in the
transient simulation of diffusion equation may be shunned through
time step selection, mass lumping schemes and geometrical element
constraints, all of which need to satisfy the maximum
principle in the finite element analyses with the solutions in all
time steps bounded by the initial solution. The maximum principle
may put lower bounds for the magnitude of time steps, but this approach
is usually unacceptable since time steps need to be controlled by
accuracy and stability. In 1-D, mass lumping is most effective with
arbitrary spatial discretization. However, in 2D and 3D, mass lumping
is not very useful without constraints on geometrical elements.
For various element types including triangles, quads, bricks, prisms
and tetrahedra, a formal analysis is performed to give geometrical
constraints for satisfying the maximum principle. Influence from
the reactive term is still under study.
Time domain error estimation for general trapezoidal schemes including
local and global discretization errors has been formulated. The local
truncation error is based on the divided difference approximation
and the global error is calculated using the mass and Jacobian
matrices in the nonlinear iteration. The formulation is tested
against the standard van der Pol equation for nonlinear systems.
The conventional constant-step backward Euler method, although stable and
convergent, is not only less efficient owing to unnecessary fine steps
in slow transient regions, but also heavily polluted by global
errors and hence very inaccurate after a fast transient region.
Adaptation criteria in consideration with the spatial error estimation
and acceleration methods are still under investigation.
Lack of universally appropriate gridding schemes in 3D in view
of boundary conformability and movement, a hybrid set of gridding
tools has been collected under the SprintCAD project. For supporting
a wide range of 3D TCAD tools, gridders based on unstructured
and the nonconformal Eulerian
scheme (level-set) have their respective advantages in different
applications and are included in the specification of the minimalistic
geometry/field service interface. The geometry is maintained
consistent in all spatial discretization, which has greatly simplified
the interface design and communication between gridders.
- Physical modeling of conformal and flow-like behaviors in APCVD
processes are derived from surface reaction kinetics. A widely
applicable parameter set, which accounts for the 0th (planar),
1st (shape) and 2nd (curvature) geometrical effects, is obtained
from the surface-site theory and the level-set method.
- Geometrical and mass lumping criteria for satisfying maximum
principles in the 1-2-3D diffusive systems are derived for various
element types including triangles, quads, bricks, prisms and tetrahedra.
- Time domain error estimation including local and global
discretization errors has been formulated and tested against the
standard van der Pol equation for nonlinear systems.
- Geometry/Field services combining CAMINO, EUCLID and the level-set
method have been provided through a unified geometry class and a
minimalistic procedural interface.
- Parallelization of ALAMODE and the geometry/field server functions
through the static domain decomposition techniques.
- 3D conformal gridding tools to provide 3D elements that satisfy the maximum
principle in various mass lumping schemes for the diffusive-reactive systems.
- Validation of the 1-2-3D geometry/field server using fully adaptive schemes
for semi-discrete finite-element based TCAD tools.
- 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.
has been selected as the benchmark platform for
the bulk diffusion models developed under the SRC/National Labs
CRADA projects. A common 1D field interface is defined by Dr.
Martin Giles of Intel to facilitate easy calibration process.
Extension to 2D and 3D with various element technology is readily
available in ALAMODE. Due to the dial-an-operator design and
many finite-element numerical control in ALAMODE, new models and
their numerical algorithms will be entirely encapsulated in the
extension language level without touching the source code, and
hence eliminate problematic comparisons of physical models implemented
on different platforms. The binary code is scheduled for release
in early August of 1996.
Edwin C. Kan
CIS-X 334, Stanford University, Stanford, CA 94305
Date prepared: 7/31/96