Electricity: measuring and testing – Electrostatic field – Using modulation-type electrometer
Reexamination Certificate
2000-10-18
2002-10-08
Le, N. (Department: 2858)
Electricity: measuring and testing
Electrostatic field
Using modulation-type electrometer
C324S457000, C324S072000
Reexamination Certificate
active
06462552
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for measuring an electrostatic potential or charge and particularly to an apparatus for measuring an electrostatic charge borne on a semiconductor device.
2. Description of the Related Art
A semiconductor device is commonly produced by forming a plurality of semiconductor devices on a substrate of Si (silicon) or GaAs (gallium arsenide); sawing or machining the substrate into individual semiconductor devices (each referred to as a die) by the dicing process; mounting the die in a package and connecting electrodes formed on the die to external leads using gold wires; and finally completing the manufacturing procedure by sealing the package in resin, for example.
Quality deficiencies in semiconductor devices have been caused by failures in the processes of forming semiconductor devices on a substrate: for example, failure in the photolithography to form a pattern of a designed size; and penetration fault of a contact hole to be penetrated through an insulator layer to connect upper and lower wiring layers.
Recently, the tendency toward decreasing a size of a semiconductor device has carried about a deteriorated immunity from static electricity of a semiconductor device. As a result, quality deficiencies caused by the static electricity have increased in addition to those caused by faulty processes as described above.
In order to track the sources of the deficiencies, the present inventor et al. have disclosed an apparatus for measuring an electrostatic charge using a coulomb meter in Japanese Patent Laid-open No. H07-325119.
The measuring apparatus will be set forth with reference to the drawings below.
FIG. 1
is a schematic diagram of the apparatus described in the quoted literature. A dielectric substance
4
of a known dielectric constant surrounds a metal rod
14
. Grounded metal plate
15
covers dielectric substance
14
.
The wiring arranged between an object to be measured and dielectric substance
4
is positionally fixed with respect to dielectric substance
4
to keep the relative position unchanged, thereby preventing measured values from being varied by a deformation of the wiring. Since metal plate
15
shields metal rod
14
from an external electromagnetic wave, the measurement of the electrostatic charge is not affected by an electromagnetic induction. Furthermore, dielectric material
4
is configured so as to establish a distributed capacity along the path through which the charge to be measured moves. This configuration of dielectric substance
4
allows the distributed capacitor to act as a delay line. Thus, charging of the distributed capacitor propagates successively from the proximity to the object concerned. Consequently, voltmeter
5
is protected from being instantaneously applied with a high voltage of the object
1
. In this way, the electrostatic charge in question can be preserved from the leakage that will otherwise occur through voltmeter
5
to the ground.
FIG. 2
represents an example in which the above-described measuring apparatus is applied to the manufacturing process of an LSI.
In this example, an excess mobile electric charge is measured at a lead terminal. Such an electric charge is often generated when LSI
16
is slid on a sloped metal rail
17
and carried from the top to the bottom, as is shown in
FIG. 2
a
).
Such a carrying system has been often employed in a process step of manufacturing an LSI. The measurement is carried out by two procedures: the preliminary procedure and the measurement procedure. The preliminary procedure is performed, as is shown in
FIG. 1
, by connecting metal plate
15
arranged outermost of the measuring apparatus to the ground potential; connecting voltmeter
5
between the top end of inner metal rod
14
and the ground potential; and sufficiently discharging the capacitor made up of metal rod
14
and metal plate
15
interposed by dielectric substance
4
by short-circuiting metal rod
14
and metal plate
15
.
Next, the measurement procedure is carried out, as is shown in enlarged exploded
FIG. 2
b
), by bringing the pointed bottom tip of metal rod
14
into contact with lead terminal
18
of LSI
16
that has slid down on metal rail
17
; observing the value indicated in voltmeter
5
; and calculating excess mobile electric charge from the equation Q=CV.
Lately, the tendency toward small-sizing a semiconductor device such as an MR head (magneto-resistive head) for reading magnetic data in semiconductor ICs (a DRAM, a processor and a CCD) and a hard-disk has been rapidly advanced.
Small-sizing of semiconductor devices entails high susceptibility to an electrostatic charge created on a semiconductor device while it is manufactured, assembled and practically used. For this reason, it is an urgent need to improve a technique for measuring an electrostatic charge borne on a semiconductor device to protect the device from troubles caused by the electrostatic charge.
In electronic devices since 1997, front-end products have suffered from significant deterioration in electrostatic-charge immunity.
For example, the wiring rule of a large-scale integrated circuit is now reducing to less than 0.25 &mgr; m and will presumably reach 0.18 &mgr;m in 2000. Furthermore, in a field of a semiconductor device as well, the area of each pixel in a picture CCD has been small-sized in order to improve fineness of a picture.
A storing density of a hard disk, on the other hand, has been increased to as high as 5-15 GBit/inch
2
. This has enabled to realize a small-sized head for read and/or write.
In the field of the liquid crystal display (LCD) as well, an improvement of the resolution has been advanced through small-sizing of a display pixel. As the digital broadcast becomes full-fledged and the high-vision TV becomes widespread in the near future, the pixels in the picture display such as a plasma display will be rendered small-sized. The small-sizing entails susceptibleness to an electrostatic charge.
The minimum quantity of the static electricity that adversely affects the small-sized semiconductor device does not fall within a measurable range of the above-described traditional measuring apparatus. Thus, an improvement of the measuring apparatus is required.
In Southeast Asia where manufacture sites have shifted to as well as in Japan, U.S.A. and Europe, troubles caused by static electricity in manufacture lines and markets have been occurring in rapid succession. Thus, it is an urgent need to dissolve the troubles. For this reason, it is necessary to provide for measurement of an electrostatic charge with improved precision and simplicity.
It is an object of the present invention to provide measuring apparatuses capable of measuring an electrostatic potential of a human body and an electrostatic potential of a metal workbench, neither of which can be measured by the traditional measuring apparatus using a coulomb meter.
It is another object of the present invention to provide a measuring apparatus capable of detecting a state of the ions in the ambient air. It is a further object to obviate troubles caused by an electrostatic charge in a manufacture line comprehensively allowing for the results of the measurements by means of above-described measuring apparatuses.
SUMMARY OF THE INVENTION
In order to achieve the object of the present invention, a first electrometer of the present invention comprises an external electrical conductor, a surface electrometer, an inner electrical conductor, an amplifier circuit and a control section.
The external electrical conductor has two sections: a first section probes an electric potential of an object of interest and a second section is configured to adapt for contacting the object.
The surface electrometer detects an electric potential of the first section.
The inner electrical conductor is isolated from the external electrical conductor and serves for supporting the surface electrometer and shielding it from an external electric field.
The amplifier circuit converts the ou
Hayes & Soloway P.C.
Kerveros James
Le N.
NEC Corporation
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