Computer-aided design and analysis of circuits and semiconductor – Nanotechnology related integrated circuit design
Reexamination Certificate
1998-07-24
2001-01-23
Teska, Kevin J. (Department: 2763)
Computer-aided design and analysis of circuits and semiconductor
Nanotechnology related integrated circuit design
C703S014000
Reexamination Certificate
active
06178544
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns a simulation mesh generation method for generating, at high speed, meshes having a boundary protection layer for use in semiconductor processes and device simulations. The present invention also concerns an apparatus for generating these meshes and a computer program product for causing a computer to generate meshes.
2. Description of the Related Art
In semiconductor manufacturing processes using process simulators and in analyzing the electrical properties of transistors using device simulators, it is necessary to solve diffusion continuity equations, Poisson equations, and other partial differential equations in order to determine impurity distributions, current densities, and other physical quantities. Because partial differential equations cannot be solved analytically, however, computations are performed after subdividing analysis domains into small domains and discretizing the partial differential equations. The method of such discretization widely and generally used is mesh generation using triangular meshes, a method that affords outstanding shape compatibility. With this method it is possible to accurately represent the complex shapes found in semiconductors.
When such triangular.meshes are used for MOSFET simulations, however, there are problems, as demonstrated by Kumashiro and Yokota in “NUPAD-V,” pp. 167-170. It has also been demonstrated that the boundary protection layer disclosed in Unexamined Japanese Patent Publication No. A-7-161962 [1995] is an effective measure for resolving these problems.
A technique for generating this boundary protection layer is represented in the flowchart given in FIG.
14
. The processing procedures are as follows. In processing step
1201
, a boundary protection layer is generated that comprises an orthogonal mesh that is locally matched with the boundary line segments. In processing step
1202
, mesh points are placed inside an area separated at least by some reference distance from the boundary protection layer. In processing step
1203
, the mesh points are connected together, and a triangular mesh is generated by the method of maximizing the apparent angle. The method of maximizing the apparent angle, as disclosed in Unexamined Japanese Patent Publication No. A-7-219977 [1996], is a method wherein attention branch terminal mesh points and branch vicinity mesh points are connected, and mesh points are thereupon selected wherewith the apparent angle is maximized.
The method of maximizing the apparent angle is now briefly described with reference to FIG.
15
. Taking the line segment A
14
-B
14
as an attention branch, in a case where the connectable mesh points are C
14
, D
14
, E
14
, and F
14
, these respective mesh points are connected with the branch terminal mesh points A
14
and B
14
, and the mesh point wherewith the apparent angle is maximized is selected. By apparent angle is meant, for example, ∠ A
14
C
14
B
14
. In the example diagram given in this figure, the apparent angle is maximized when A
14
and B
14
are connected to mesh point C
14
. Because the chord A
14
B
14
is common, the apparent angle reaches maximum at the mesh point where the radius of the circumscribed circle is maximum. When the circumscribed circle radius reaches minimum, there will be no other mesh point contained inside the triangle A
14
B
14
C
14
. For this reason, Delaunay division can be performed efficiently with the method of maximizing the apparent angle. It is also possible to generate a triangular mesh that spirals in toward the interior of a domain from the periphery.
Next, in processing step
1204
, a search is made for a triangular mesh that destroys the boundary protection layer. When a triangular mesh exists which destroys the boundary protection layer, in processing step
1205
, of the apexes of the triangular mesh that destroys the boundary protection layer, the mesh point inside the domain is projected onto the boundary line segment, and that projection point is added as a new mesh point. Thereupon, processing step
1201
is returned to, and the routines from that step on are repeatedly executed until the generation of new projection points ceases. In processing step
1204
, moreover, if no triangular mesh exists that destroys the boundary protection layer, all processing for generating the boundary protection layer terminates.
By using the technique described in the foregoing, it is possible to make the cross-sectional area in the normal direction relative to the control volume boundary constant. When that is done, it is possible to accurately compute inversion layer currents for MOSFETs having Si—SiO
2
boundary surfaces facing in any direction without producing mesh-induced parasitic resistance.
When this technique is used, however, in cases where a triangular mesh exists which destroys the boundary protection layer, the triangular mesh produced in processing step
1203
will be thrown out. In general, when mesh points become numerous, more time is required to generate triangular meshes, so that, when triangular meshes exist that destroy the boundary protection layer and there are many mesh points, time is lost. For this reason, there is still room for improvement in the high-speed generation of meshes having boundary protection layers in cases where there are triangular meshes that destroy the boundary protection layer.
More specifically, in the prior art described above, there are the following problems.
A first problem is that, while triangular meshes exist that destroy the boundary protection layer, time is wasted in generating triangular meshes that cannot destroy the boundary protection layer, as with triangular meshes inside the domain.
A second problem is that boundary protection layers are also added to the surfaces of device walls or device bottoms wherein reflection type boundary conditions are established, whereupon time is wasted in subsequent process diffusion simulations, etc., because of the boundary protection layer generation time and the increase in the number of meshes.
The present inventor determined by analysis that the cause of these difficulties lies in the fact that the search for triangular meshes destructive of the boundary protection layer is conducted after the triangular meshes have been completed inside the domain. In the prior art, moreover, boundary protection layers are generated for all boundary surfaces, so that boundary protection layers are added also to device wall and bottom surfaces.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method, apparatus, and program product for producing improved triangular meshes wherewith triangular meshes having boundary protection layers can be generated at high speed.
Another object of the present invention is to provide a method, apparatus, and product wherewith the number of generated meshes that are cancelled can be reduced, and post-processing diffusion simulations, etc., can be speeded up.
A further object of the present invention is to provide a method, apparatus, and product wherewith analyses using triangular meshes can be performed at high speed as compared to the processes for solving diffusion equations.
Therefore, in the present invention, triangular meshes are generated by the following procedure.
a. Device shape data are received;
b. mesh points that define a boundary protection layer having orthogonal meshes matched locally with boundary line segments are generated as boundary protection points;
c. mesh points are placed inside domains separated by at least a reference distance from the boundary protection layer;
d. from among the domains defined by the plurality of mesh points, those domains capable of destroying the boundary protection layer are specified, and, at the same time, the mesh points inside those domains are connected;
e. the presence or absence of triangular meshes destructive of the boundary protection layer is determined by having, in a side or sides, branches wherein the boundary protecti
Choi Kyle J.
NEC Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
Teska Kevin J.
LandOfFree
Simulation mesh generation method, apparatus, and program... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Simulation mesh generation method, apparatus, and program..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Simulation mesh generation method, apparatus, and program... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2444835