Active solid-state devices (e.g. – transistors – solid-state diode – Test or calibration structure
Reexamination Certificate
2000-03-21
2002-01-15
Wilson, Allan R. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Test or calibration structure
C257S215000, C257S235000, C257S239000
Reexamination Certificate
active
06339229
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a test structure for reliability evaluation of an insulation film such as a gate insulating film.
2. Description of the Background Art
Generally, a technique called “Time Depend Dielectric Breakdown (TDDB)” is used for reliability evaluation of an insulation film such as a gate insulating film.
FIG. 28
is a cross-sectional view of a conventional test structure for insulation-film evaluation used in the TDDB test. A gate insulating film
102
to be evaluated is formed across the surface of a substrate
101
and a gate electrode
103
is formed across the surface of the gate insulating film
102
. The TDDB test is conducted using an evaluation pattern such as a pattern including the edge of the active region (field edge), a pattern including the gate edge, and a flat pattern consisting only of surface components, thereby evaluating process damage to the gate insulating film with respect to each component. For instance, the TDDB test using a gate edge pattern evaluates how the gate insulating film receives damage from etching in forming a gate electrode.
The TDDB test for a certain period of time causes a dielectric breakdown in the gate insulating film at any rate. The reliability of the gate insulating film is evaluated by means of statistical processing of such a fault-time distribution. To clarify the physical cause of failures, however, failure analysis is absolutely necessary.
According to a failure analysis technique using the conventional test structure for insulation-film evaluation, failure analysis is performed in the following two steps: (1) finding the physical location of a failure using an emission analyzer or an electron beam tester, for example; and (2) observing the failure using a scanning electron microscopy (SEM), for example. This technique has a problem that especially the former step is complicated.
SUMMARY OF THE INVENTION
A first aspect of the present invention is directed to a test structure for insulation-film evaluation comprising: a substrate; an insulation film to be evaluated which is formed on a main surface of the substrate; an electrode array formed on the insulation film and consisting of a plurality of electrodes arranged in spaced manner, a plurality of wires for applying a voltage to the plurality of electrodes, the voltage including a voltage for applying evaluation stress to the insulation film and a voltage for sequentially transferring charge generated in breakdown part of the insulation film along the electrode array to detect the presence or absence of breakdown in the insulation film due to the application of the evaluation stress; and a read circuit for sequentially reading the presence or absence of the transfer of the charge.
According to a second aspect of the present invention, in the test structure of the first aspect, adjacent three of the electrodes in the electrode array are connected to different ones of the wires.
According to a third aspect of the present invention, in the test structure of the first aspect, the electrode array consists of the electrodes under which an impurity region is formed in the main surface of the substrate and the electrodes under which the impurity region is not formed in the main surface of the substrate, which are aligned alternately.
According to a fourth aspect of the present invention, in the test structure of the first aspect, the electrode array consists of the electrodes doped with impurities and the electrodes not doped with the impurities, which are aligned alternately.
According to a fifth aspect of the present invention, in the test structure of the first aspect, adjacent four of the electrodes in the electrode array are connected to different ones of the wires.
According to a sixth aspect of the present invention, in the test structure of the first aspect, the electrode array consists of first electrodes and second electrodes which are aligned alternately, the first electrodes formed on a thin-film portion of the insulation film having a first thickness, the second electrodes formed on a thick-film portion of the insulation film having a second thickness larger than the first thickness; and adjacent four of the electrodes in the electrode array are connected to different ones of the wires.
According to a seventh aspect of the present invention, in the test structure of the sixth aspect, the second electrodes extend over the end portions of the first electrodes.
According to an eighth aspect of the present invention, in the test structure of the first aspect, a plurality of impurity regions with different impurity concentrations are adjacently formed in the main surface of the substrate under each of the electrodes.
According to a ninth aspect of the present invention, the test structure of either of the first to eighth aspects further comprises: a drawn region formed along the electrode array in the main surface of the substrate, for drawing charge flowing out of a potential well under breakdown part of the insulation film caused by the application of the evaluation stress.
According to a tenth aspect of the present invention, in the test structure of either of the first to ninth aspects, the substrate includes an element isolation region where an clement isolation insulation film is formed, and an active region defined by the element isolation insulation film; and the end portions of the electrodes are within the active region.
According to an eleventh aspect of the present invention, in the test structure of either of the first to ninth aspects, the substrate includes an element isolation region where an element isolation insulation film is formed, and an active region defined by the element isolation insulation film; and the electrodes extend over a boundary between the element isolation region and the active region.
According to a twelfth aspect of the present invention, in the test structure of either of the first to eleventh aspects, cells including the electrodes are arranged in the form of a matrix, all of the cells being electrically connected to each other by an active region of the substrate.
According to a thirteenth aspect of the present invention, in the test structure of either of the first to eleventh aspects, cells including the electrodes are arranged in the form of a matrix, a plurality of the cells being divided into a plurality of groups by an element isolation region of the substrate; and the read circuit is provided for each of the groups.
A fourteenth aspect of the present invention is directed to a test structure for insulation-film evaluation, comprising: a substrate; an insulation film to be evaluated which is formed on a main surface of the substrate; an electrode matrix consisting of a plurality of electrodes formed in the form of a matrix on the insulation film; a stress applying circuit for applying evaluation stress to the insulation film; a first shift register capable of applying a voltage to the plurality of electrodes for each column of the electrode matrix; and a second shift register which is electrically connected to the substrate for each row of the electrode matrix and capable of detecting whether or not the application of the voltage by the first register causes current flow to the substrate through the insulation film.
According to a fifteenth aspect of the present invention, in the test structure of the fourteenth aspect, the electrode matrix includes at least two rows having the insulation film of different thicknesses.
According to a sixteenth aspect of the present invention, in the test structure of either of the first to fifteenth aspects, cells including the electrodes are arranged in the form of a matrix; and a mark is provided at predetermined blocks on the substrate.
The test structure for insulation-film evaluation of the first aspect adopts the CCD structure, wherein the charge supplied into the substrate due to a breakdown of the insulation film is sequentially transferred so that the read circuit can locate a failure. This structure simplifi
Murata Naofumi
Shiga Katsuya
Mitsubishi Denki & Kabushiki Kaisha
Wilson Allan R.
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