Data processing: structural design – modeling – simulation – and em – Simulating electronic device or electrical system
Reexamination Certificate
1998-09-14
2001-02-20
Teska, Kevin J. (Department: 2763)
Data processing: structural design, modeling, simulation, and em
Simulating electronic device or electrical system
C703S014000, C703S002000, C703S003000, C703S006000, C716S030000
Reexamination Certificate
active
06192330
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to recognizing and simulating two-dimensional shapes in evaluating semiconductor elements. In particular, the present invention relates to a simulation method and a simulation apparatus that are used to calculate effective angles (hereinafter referred to as incident angles) on a semiconductor element. The incident angles are used to simulate particles flying toward the surface of the semiconductor element during the manufacturing thereof.
2. Description of the Prior Art
Semiconductor elements and semiconductor integrated circuit devices are mass-produced after making and evaluating experimental pieces.
FIG. 1
is a flowchart showing steps to produce an experimental piece of a semiconductor element. Basic circuits, circuit cells, and processes are designed. Based on the designs, experimental pieces are produced and evaluated in their electric characteristics, etc. If they show good results, the semiconductor element is mass-produced. If the evaluation results are not good, the circuits and/or the processes are redesigned. These steps are repeated to provide satisfactory products. When designing processes and making experimental pieces, process simulations are carried out, and when evaluating the experimental pieces, device simulations are carried out, to improve the quality and performance of semiconductor products.
When designing a semiconductor element, it is necessary to evaluate the electric characteristics of the element, which are dependent on the shape and impurity distribution of the element. To measure the electric characteristics of a semiconductor element, it is usual to make experimental pieces of the element. Preparing such experimental pieces needs a lot of time and labor, and therefore, deteriorates the developing efficiency of semiconductor elements. Semiconductor elements are very fine, and therefore, evaluating experimental pieces by manpower is substantially impossible.
To solve these problems, there is a technique of sampling the shape of a semiconductor element by scanning-electron microscope, preparing shape data from the sample according to image processing technology, and using the shape data on a computer to evaluate semiconductor elements. There is another technique that employs a computer to manipulate the shapes of semiconductor elements from the beginning. These techniques are used to simulate, evaluate, and analyze semiconductor elements and element manufacturing processes.
S. M. Sze has disclosed a process simulation technique in “VLSI Technology” McGraw-Hill, 1993. This technique defines a two-dimensional calculation window on a semiconductor element. The window is divided into a material region where solid material is present and a vacuum region where a vacuum or gas is present. The process simulation takes place on each of these regions.
FIG. 2
is a cross sectional view showing a simulation result of a transistor formed on a semiconductor substrate. The substrate shows impurity distributions. The transistor is a MOS transistor whose gate
1
is formed on the substrate. The gate
1
is covered with an insulation film
2
, on which a metal wire
3
of, for example, aluminum is formed.
A technique that simulates changes in the shape of a material region defined in a calculation window is called a shape simulation. Among shape simulation techniques, a technique that carries out a simulation based on a string model defined along a boundary between the material and vacuum regions of a calculation window is a two-dimensional shape simulation.
FIG. 3
shows an example of a string model. A string
501
consists of a series of segments Si each of which extends between adjacent points (Pi-1, Pi). The string
501
defines a two-dimensional material shape
502
. Data necessary for expressing the string
501
are sequential point numbers or sequential segment numbers, the coordinates of points, and an array number. The origin of the array may be any one of the points on the string
501
, and therefore, the handling of the string
501
is easy.
FIG. 4A
is a cross sectional view showing an intermediate part between gates of MOS transistors. A square
1501
is sampled to prepare a string model of
FIG. 4B. A
material region
1503
and a vacuum region
1502
are each represented with a series of points and/or segments.
When simulating surface changes during a deposition or etching process, a surface string
1504
of
FIG. 4C
between the vacuum region
1502
and the material region
1503
is defined. This is because the deposition or etching process affects only the surface of a semiconductor substrate. A sequence of points on the string
1504
usually follows a sequence of points of the vacuum region
1502
. This is to make the handling of the string
1504
simpler when several material regions are facing the surface. Once a sequence of points along the vacuum region
1502
is determined as shown in
FIG. 4C
, a boundary point that is in contact with the calculation window
1501
, vacuum region
1502
, and material region
1503
is searched for from a border point A at the upper right corner of the calculation window
1501
toward the boundary of the vacuum region
1502
. This easily and quickly finds an origin of the string
1504
between the regions
1502
and
1503
.
The shape simulation carried out on the string
1504
simulates, for example, changes to occur along the string
1504
during a deposition process that deposits metal such as aluminum on the material region
1503
in a vacuum due to physical adsorption. During the simulation, every point on the string
1504
has a different effective angle (incident angle) within which particles may fly toward the point. Accordingly, a depth angle calculation must be carried out on every point Pi on the string
1504
. FIG.
5
explains a depth angle at a point Pi on a given string between a vacuum region and a material region.
FIG. 6
shows the definition of the depth angle. A depth angle at a point Pi on a given string is defined around a reference line that extends vertically from the point Pi. The reference line is orthogonal to a horizontal line as shown in the right part of FIG.
6
. The depth angle is the sum of absolute values of a minimum angle &thgr;min and a maximum angle &thgr;max. In this specification, the sign of an angle is positive in a counterclockwise direction from a reference line and negative in a clockwise direction from the reference line.
FIG. 7
is a block diagram showing a shape simulation apparatus. The apparatus has a data reader
201
, a process controller
202
, and a result output unit
203
. The data reader
201
reads a semiconductor process flow and converts it into data to be handled by the process controller
202
. The process controller
202
repeatedly operates simulators according to a sequence of manufacturing processes. The manufacturing processes include a lithography process to be simulated by a lithography simulator
204
, a CMP process to be simulated by a CMP simulator
205
, an etching process to be simulated by an etching simulator
206
, and a deposition process to be simulated by a deposition simulator
207
. Simulation results and intermediate results are output to a display or a printer through the result output unit
203
.
FIG. 8
shows the structure of the deposition simulator
207
of FIG.
7
. The deposition simulator
207
has a controller
301
. The controller
301
receives data from the process controller
202
, transfers data among parts controlled by the controller
301
, and updates time counters. Among the parts controlled by the controller
301
, a surface string extractor
302
extracts a surfaces string between a vacuum region and a material region according to the technique mentioned above. A depth angle calculator
303
calculates a depth angle at each point on the surface string according to calculation methods to be explained later. A shift calculator
304
calculates a shift of each boundary point according to the calculations made by the depth angle c
Foley & Lardner
Kabushiki Kaisha Toshiba
Teska Kevin J.
Thomson William
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