Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Reexamination Certificate
2001-03-27
2003-05-13
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
C324S229000, C324S238000, C324S240000
Reexamination Certificate
active
06563308
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application claims benefit of priority under 35USC §119 to Japanese patent applications No. 2000-089356, filed on Mar. 28, 2000 and No. 2001-028187, filed on Feb. 5, 2001, the contents of which are incorporated by reference herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a system for measuring the thickness of a film. More specifically, the invention relates to an eddy current loss measuring sensor for measuring an eddy current loss due to an eddy current which is excited in a conductive film on the surface of a wafer by magnetizing a high frequency magnetic field, in a process for fabricating a semiconductor integrated circuit device, a thickness measuring system and method for non-contact-measuring the thickness of the conductive film on the basis of the measured eddy current loss, and a computer readable recorded medium in which a program for executing the method has been recorded.
2. Description of the Prior Art
A method for measuring the thickness of a conductive film using an eddy current is effective in a non-contact, non-destructive thickness measuring technique.
In a thickness measuring method using an eddy current, the distance between a coil (sensor) for generating a magnetic field and a conductive film has a great influence on the quantity of an eddy current loss in the conductive film. Therefore, it is important to precisely control the distance between the sensor and the conductive film.
FIG. 23
shows a data in an example of an experiment in which the quantity of an eddy current loss was measured as the variations in inductance and resistance of a sensor. It can also be understood from this figure that the inductance and resistance of the sensor vary in accordance with the distance between the sensor and the conductive film.
In order to reduce measurement errors due to such dependency on distance to improve measurement precision, the following techniques are proposed.
For example, as a first method, as shown in
FIG. 23
, there is a method for previously obtaining a correlation between the distance between a sensor and a conductive film and a measured value and for carrying out measurement at a plurality of points while varying the distance between the sensor and the conductive film, to carry out correction at the respective points of measurement using the above described correlation.
As a second method, as shown in
FIG. 24
, there is a method for measuring inductance Q by means of an impedance analyzer, when coils
103
a
and
103
b
for exciting an eddy current are provided on both sides of a conductive film serving as an object to be measured, so as to face each other via the conductive film, and connected in series.
However, according to the above described second measuring method, there is a disadvantage in that the system is complicated and large-scale.
In the first method for carrying out measurement at the plurality of points while varying the distance, the sensor or stage must be operated times of measurement, and a data processing must be every one of the points of measurement, so that it takes very much time to carry out the measurement. Therefore, there is a problem in that this method is of no practical use since it is unsuitable for a high-speed measurement, which is required in a mass production line, and for a real-time measurement in a thickness forming process.
On the other hand, as an attempt to localize a magnetic field, which is generated by a coil, at a point in order to enable to carry out a localized thickness measurement to improve measurement precision, there is only a method for inserting a core
110
of ferrite or a magnetic material into a coil
108
as shown in
FIG. 25
, in addition to a method for decreasing the diameter of the coil to enhance resolution.
As a sensor for measuring a displacement of a metal conductor, a sensor for localizing a magnetic field on a conductor is proposed. Referring to
FIGS. 26A through 26D
, an example thereof will be described below.
As shown in
FIG. 26A
, a displacement sensor comprises a receiving coil
112
wound onto a ferrite core
111
, a high frequency exciting coil
113
wound onto the outside of the receiving coil
112
, and an outer screening plate
114
of copper which is provided so as to cover the ferrite core
111
and the coils
112
and
113
, and the top of which is open.
The high frequency exciting coil
113
is designed to receive a high frequency current to generate a magnetic field to excite an eddy current to a metal conductor C serving as an object to be measured. The receiving coil
112
is designed to receive a magnetic field having a magnetic flux density which is reduced by the eddy current produced by the metal conductor C.
The outer screening plate
114
comprises semi-cylindrical portions
114
a
and
114
b
which are arranged so as to face each other. Typically as shown in
FIG. 26B
, the semi-cylindrical portions have semi-circular bottom plate half-portions
114
c
and
114
d,
respectively. The right and left semi-cylindrical portions
114
a
and
114
b
are arranged so as to face each other via a minute clearance to form a radially extending insulating slit
115
between the bottom plate half-portions
114
c
and
114
d
as shown in the bottom drawing of FIG.
26
C. Thus, the outer screening plate
114
comprises the right and left semi-cylindrical portions which are separated from each other by the insulating slit
115
to be insulated from each other. While the linear insulating slit has been described in this embodiment, a cross insulating slit may be formed.
If a high frequency exciting current is passed through the high frequency exciting coil
113
, a high frequency magnetic field is produced to induce an eddy current in the right and left bottom plate half-portions
114
c
and
114
d
of the outer screening plate
114
. Since this eddy current is generated in a direction in which the magnetic field is interrupted, a synthetic magnetic field of the magnetic field due to the exciting coil
113
and the magnetic field due to the eddy current in the respective bottom plate half-portions
114
c
and
114
d
has a small magnetic flux density in the respective bottom plate half-portions
114
c
and
114
d,
and a large magnetic flux density in the insulating slit
115
. For that reason, as shown in
FIG. 25D
, an uneven high frequency magnetic field having a magnetic flux density of a maximum value Bmax in an insulating slit portion S
0
is formed in a sensor head. Therefore, when the sensor head is arranged above the metal conductor C of a copper wire or the like as shown in
FIG. 26A
, if the conductor C is arranged directly below the insulating slit
115
of the outer screening plate
114
, the electric flux density in a space occupied by the conductor C is maximum, and the screening effect of the outer screening plate
114
is weakest with respect to the alternating magnetic field induced by the eddy current of the conductor C. At this time, the influence of the conductor C on impedance of the receiving coil
112
of the sensor head is maximum.
Thus, the structure in which the linear or cross slit causes the magnetic flux to extend into the longitudinal region is effective in the examination of the displacement of an elongated body of a metal conductor or the like. However, this structure is insufficient for a localized thickness measurement since it is required to form a magnetic field serving as a stop.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to eliminate the aforementioned problems and to provide an eddy current loss measuring sensor capable of carrying out a localized thickness measurement, a thickness measuring system and method for rapidly and precisely measuring the thickness of a film, and a computer readable recorded medium in which a program for executing the method has been recorded.
According to a first aspect of the present invention, there is provided an eddy current loss measuring sensor comprising: an exciti
Kaneko Hisashi
Matsuda Tetsuo
Miyoshi Motosuke
Nagano Osamu
Yamazaki Yuichiro
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Kinder Darrell
Lefkowitz Edward
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