Working process end point real time determination method

Details Working process end point real time determination method Working process end point real time determination method

2000-01-21

2002-12-03

Picard, Leo (Department: 2125)

Data processing: generic control systems or specific application

Specific application, apparatus or process

Product assembly or manufacturing

C700S033000, C700S071000, C438S005000, C438S007000, C438S691000

Reexamination Certificate

active

06490497

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a working process end point real time determination method for determining an end point of a working process on a real time basis while the working process is proceeding using a working process measurement signal which exhibits, as the working process proceeds, a great increase or decrease once while including variations and then enters steady state as the working process comes to an end.
2. Description of the Related Art
Some working process apparatus such as a semiconductor process apparatus includes a working process measuring instrument for monitoring the progress of a working process.
One of working process measurement signals obtained from a working process measuring instrument exhibits such a variation with respect to time that it exhibits a great increase or decrease once as a working process proceeds after the lapse of a fixed period of time after the working process is started, and then enters a steady state as the predetermined working process is completed. The steady state in this instance signifies a state wherein the signal exhibits little variation, and more specifically signifies a state wherein the variation amount of the signal per unit time has a very low value close to zero.
The working process measurement signal includes periodical variations because a measurement position is scanned in a fixed cycle or, although the measurement position is fixed, the working process side includes a periodical operation from such a reason that the procedure of the working process involves some irregularity depending upon the spatial position and so forth, and the progress of the working process appears on a signal variation from which the periodical variations are removed. Accordingly, the determination that the working process comes to an end determines a point at which the working process measurement signal completes entrance into a steady state from the condition wherein it includes variations.
Though not particularly shown in the accompanying drawings, in order to determine a process end point from a working process measurement signal which exhibits such a variation as described above, a method is generally used wherein the point of time at which the working process measurement signal exhibits a variation to a value equal to or lower than a predetermined value or a value equal to or higher than a predetermined value is determined as a working process end point.
More particularly, since the working process measurement signal exhibits an increase or a decrease once and then enters a steady state, the working process measurement signal is compared with a predetermined threshold value set in advance, and the point of time at which the working process measurement signal exhibits a change to a value equal to or higher than the threshold value or equal to or lower than the threshold value is determined as a working process end point. The method can be applied to working processing end point determination in a CMP process for performing chemical and mechanical polishing (CMP) of a semiconductor wafer.
FIG. 7
is a cross sectional view showing an example of a semiconductor wafer (hereinafter referred to simply as wafer) which is a working object (polishing object). Referring to
FIG. 7
, the wafer generally denoted at
1
includes a substrate
4
having a high reflection factor with respect to inspection light, an insulator layer
2
applied to the surface of the substrate
4
and having a low reflection factor with respect to the inspection light or transparent to the inspection light, and a metal layer
3
having a high reflection factor with respect to the inspection light and applied to the entire face of the insulator layer
2
in such a manner that it covers over the insulator layer
2
. In a CMP process, the metal layer
3
is polished by a CMP apparatus until the insulator layer
2
is exposed to form metal wiring lines. Accordingly, the point of time at which the metal wiring lines are formed completely is the polishing end point.
An example of an application to such a CMP process as just described is disclosed in Japanese Patent No. 2, 561, 812. The method is illustrated in a flow chart of FIG.
19
. Referring to
FIG. 19
, the working process end point real time determination method illustrated includes a first step A
1
and a second step A
2
. In the first step A
1
, an average value after each predetermined interval of time of a reflected light amount measured by a polished condition monitoring apparatus of the reflected light amount measurement type is calculated as measured light amount averaged data. Then, in the second step A
2
, the measured light amount averaged data calculated in the first step A
1
is compared with a predetermined threshold value which depends upon the reflection factor of a material formed on the wafer with respect to inspection light and the structure of the wafer such as a pattern density, and the point of time at which the measured light amount averaged data becomes a value lower then the threshold value is determined as the polishing end point.
The measured light amount averaged data calculated in the first step A
1
exhibits the following variation with respect to time. In particular, in an initial stage of polishing, since the metal layer
3
having a high reflection factor with respect to the inspection light is applied to the overall area of the uppermost layer of the wafer
1
as seen in
FIG. 7
, the measured light amount averaged data exhibits a high value. Then, as the polishing proceeds, the metal layer
3
is removed, and the insulator layer
2
having a low reflection factor with respect to the inspection light is exposed and begins to be polished. Or, where the insulator layer
2
is transparent to the inspection light, the inspection light begins to pass through the insulator layer
2
thus exposed and is reflected by the substrate
4
having a low reflection factor. Consequently, the reflected light amount gradually decreases. As the polishing further proceeds, metal wiring lines are finally formed completely. Consequently, even if the polishing thereafter proceeds, the area ratio between the insulator layer
2
and the metal layer
3
does not exhibit a variation any more, and accordingly, the measured light amount averaged data does not vary any more and exhibits a fixed value.
Accordingly, since the point of time at which the metal wiring lines are formed completely is the polishing end point, the point at which the measured light amount averaged data does not exhibit a variation any more but exhibits a fixed value indicates the polishing end point.
The measured light amount averaged data at the point of time of the end of the polishing exhibits the same value for each wafer if the reflection factor of the material formed on the wafer with respect to the inspection light and the structure of the wafer such as the pattern density are the same.
Therefore, in the second step A
2
, the measured light amount averaged data calculated in the first step A
1
is compared with a predetermined threshold value which depends upon the reflection factor of a material formed on the wafer with respect to the inspection light and the structure of the wafer such as a pattern density, and the point of time at which the measured light amount averaged data becomes a value lower then the threshold value is determined as the polishing end point.
However, the conventional method wherein a measured light amount averaged data is compared with a predetermined threshold value to determine a working process end point has a problem in that, where the working process measurement signal exhibits a great variation, the determination of the working process end point cannot be performed with a high degree of accuracy.
Where the variation of the working process measurement signal is great, the working process measurement signal cannot be smoothed sufficiently unless the time interval upon averaging of the signal is sufficiently great. In the conventional method illustr

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