Computer-aided design and analysis of circuits and semiconductor – Nanotechnology related integrated circuit design
Reexamination Certificate
1998-08-18
2002-04-09
Smith, Matthew (Department: 2825)
Computer-aided design and analysis of circuits and semiconductor
Nanotechnology related integrated circuit design
C714S738000
Reexamination Certificate
active
06370675
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a design and evaluation system for designing and evaluating semiconductor integrated circuits such as a large scale integrated circuit (LSI), and more particularly, to a semiconductor integrated circuit design and evaluation system for evaluating, at high speed, a test pattern produced for a semiconductor test system or performing a diagnostic test on the design of the semiconductor integrated circuit, based on logic simulation data produced in a design stage of the semiconductor integrated circuit through a CAD (computer aided design) process, without using an actual semiconductor test system or semiconductor integrated circuit to be tested.
BACKGROUND OF THE INVENTION
In a process of developing semiconductor integrated circuits such as a large scale integrated circuit (LSI), almost always, a design method using a computer aided design (CAD) tool is employed. Such a design environment using a CAD tool is also refereed to as an electronic design automation (EDA) environment. In such a semiconductor development process incorporating the CAD tool, desired semiconductor circuits are created in an LSI with the use of a hardware description language such as VHDL and Verilog. Also in this process, functions of the semiconductor circuits thus designed are evaluated through a software simulator called a device logic simulator.
A device logic simulator includes an interface commonly called a testbench through which test data (vector) is applied to the device data showing the intended semiconductor circuits and the resultant response of the intended semiconductor circuits are evaluated.
After the design stage of the LSI circuit, actual LSI devices are produced and are tested by a semiconductor test system such as an LSI tester to determine whether the LSI devices perform the intended functions properly. An LSI tester supplies a test pattern (test vector) to an LSI device under test and compares the resultant outputs of the LSI device with expected data to determine pass/fail of the LSI device. For testing an LSI device with higher level of functionality and density, a test pattern to be applied to the LSI device must accordingly be complex and lengthy, resulting in significantly large work load and work hours in producing the test pattern. Therefore, it is not preferable to produce a test pattern when an LSI device under test is actually produced, especially as to LSI devices of shorter life cycles, because it causes a time delay to put the LSI devices into market.
Thus, to improve an overall test efficiency and productivity of the semiconductor integrated circuits, it is a common practice to make use of the data produced through the operation of the device logic simulator in an actual test of the semiconductor integrated circuits. The test procedure performed by the LSI tester in testing a semiconductor integrated circuit has a substantial similarity with a test procedure by the device logic simulator by the CAD process noted above in testing the design data of the semiconductor circuit. For example, test patterns and expected value patterns for an LSI tester to test the intended semiconductor integrated circuits are produced by utilizing the resultant data (dump file) produced by executing the device logic simulation. However, as of today, there is no system which is able to produce test patterns and expected data patterns to be used in an LSI tester and to evaluate the same, with high speed and low cost, based on the dump file derived from the design stage of the LSI devices.
In such logic simulation data, test patterns to be applied to a device model as well as the resultant outputs (expected value patterns) of the device model are expressed by an event base. Here, the event base data expresses the points of change (events) in a test pattern from logic “
1
” to logic “
0
” or vice versa with reference to the passage of time. Generally, such time passage is expressed by time lengths from a predetermined reference point or time length from a previous event. In contrast, in an actual LSI tester, test patterns are described by a cycle base. In the cycle base data, test patterns are defined relative to predetermined test cycles (tester rate) of the tester. In the event base, test patterns for the logic simulation can be described by a substantially simple form of data than that required in the cycle base.
As in the foregoing, test patterns for testing LSI devices actually produced are efficiently created by using the CAD data produced in the design stage of the LSI devices. However, because of various reasons, test patterns produced for an LSI tester in this manner may not always be appropriate to accurately detect failures of the LSI device under test. Thus, it is necessary to evaluate the test patterns produced through the foregoing procedure.
In the conventional technology, in evaluating the test patterns to be used in an LSI tester created with the use of the logic simulation data, there are basically two methods, one that uses an actual LSI tester and the other that dose not use an LSI tester. In the method of using an LSI tester, it is necessary to extract event base test patterns in the logic simulation data and convert the same to cycle base test patterns. Such test patterns in the cycle base run in the actual LSI tester to evaluate the correctness of the test patterns. This method is disadvantageous in that an expensive LSI tester is used only for evaluating an integrity of the test patterns.
In the method of not using an LSI tester, an LSI tester simulator is used for evaluating the test patterns. In this method as well, the LSI tester simulator debugs the test patterns that have been converted to the cycle base. For simulating the functions of the LSI device under test which receives the test pattern from the LSI tester simulator, a logic simulator is used which is created during the design process using the CAD tool. Since all of the evaluation process is performed through software processes, this method is disadvantageous in that it requires a very long time to finish the evaluation.
An example of the conventional technology without using the actual LSI tester is described in more detail below.
FIG. 1
is an example of conventional technology for evaluating test patterns with the use of a tester simulator and a logic simulator, i.e., an example in which all of the operation is performed by software.
In
FIG. 1
, an LSI simulator
11
formed of software is provided with pattern data and timing data created for an LSI tester from a pattern file
10
1
and a timing file
10
2
. The pattern data and the timing data are created, for example, by extracting pattern data and timing data from a dump file
15
resulted in performing a logic simulation in the design stage of the LSI device. An example of the logic simulator dump file is VCD (Value Change Dump) of Verilog. The data in the dump file
15
is converted to cycle base data by a conversion software
17
, resulting in the pattern data and timing data noted above stored in the pattern file
10
1
and the timing file
10
2
, respectively.
The LSI tester simulator
11
is to debug test patterns to test the intended LSI device or function of the LSI device without using an LSI tester hardware. The LSI tester simulator
11
generates a test pattern having pattern information and timing information and applies the test pattern to the logic simulator of the LSI device to be tested. The LSI tester simulator
11
compares the resultant output signals from the logic simulator with the expected data to determine the correctness of the test pattern or performances of the LSI device.
The LSI tester simulator
11
provides the test pattern to a format converter
12
as input data. The format converter
12
converts the input data from the LSI tester simulator
11
to a format to be accepted by a device logic simulator
13
. Generally, the device logic simulator
13
includes an interface called PLI (Programming Language Interface). Thus, in such a case, the format converter
12
converts th
Matsumura Hidenobu
Takahashi Koji
Yamoto Hiroaki
Advantest Corp.
Do Thuan
Muramatsu & Associates
Smith Matthew
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