Optics: measuring and testing – Surface roughness
Reexamination Certificate
1999-12-01
2001-11-27
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
Surface roughness
C356S512000
Reexamination Certificate
active
06323952
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of the following priority application is herein incorporated by reference:
Japanese Patent Application No. 11-280908 filed Oct. 1, 1999.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a flatness measuring apparatus.
2. Description of the Related Art
As LSI patterns have been becoming increasingly fine in recent years, a reduction in the focal depth of optical exposure apparatuses (optical aligners) has been observed. Namely, while the wavelength must be reduced to transcribe (expose) a fine pattern, the shorter wavelength results in a reduction in the focal depth in the optical exposure apparatus since the focal depth is in proportion to the wavelength. For this reason, the quality of transcribing is determined by whether or not indentations and projections at the surface of the semiconductor wafer are contained within the focal depth, and the requirements imposed with respect to the flatness of the semiconductor wafer upon which the pattern is transcribed (exposed) are becoming increasingly rigorous. For instance, if the surface of a semiconductor wafer has undulations and the magnitude of the undulation exceeds the focal depth there will be a loss of clarity in transcribing.
In the prior art, in order to measure the flatness of a semiconductor wafer, a sensor is positioned facing opposite the two surfaces of the semiconductor wafer by holding a portion of the semiconductor wafer and the distances to the individual measuring points of the wafer are measured by scanning with the sensor. For instance, the data collection by the sensor is made to correspond to a 1 mm pitch in the transcribing area, the height distribution at the semiconductor wafer surface is measured over this 1 mm pitch and, based upon the results of the measurement, the flatness of the semiconductor water is measured.
FIG. 4
illustrates transcribing areas at a semiconductor wafer. The surface of the semiconductor wafer
20
is divided into a plurality of transcribing areas (
20
-
1
~
20
-N) (N is a positive integer) as illustrated in
FIG. 4
, for instance, and the flatness of the semiconductor wafer is measured in the individual transcribing areas.
FIG. 5
illustrates measuring points in a flatness measuring method in the prior art, in
FIG. 5
, which is an enlargement of one of the transcribing areas (e.g.,
20
-n) (n is a positive integer) in
FIG. 4
, a plurality of measuring points are set over for instance, 1 mm pitch in the transcribing area. The surface height of the semiconductor wafer
20
is measured at all the measuring points (
20
-n−1~
20
-n−M) (M is a positive integer).
FIG. 6
illustrates a reference flat plane used in the flatness measuring method in the prior art. Using the measurement data indicating the heights at the individual measuring points, a reference flat plane R
1
that represents the transcribing area (
20
-n) is calculated through a method of least squares or the like. The measurement of flatness is implemented using quantities of displacement of the individual measuring points (
20
-n−1~
20
-1−M) relative to the reference flat plane R
1
.
An optical exposure apparatus transcribes by detecting an optimal focal plane in each of the transcribing areas (
20
-
1
~
20
-N) with a focus sensor (e.g., a stepper AF sensor) or the like to transcribe with the focus adjusted to the focal plane.
FIG. 7
illustrates measuring points used during the transcribing operation performed by the optical exposure apparatus. During the transcribing operation, the heights at a plurality (4 in
FIG. 7
) of specific measuring points (
20
-n−f
1
~
20
-n−f
4
) within a transcribing area are measured by the focus sensor while the semiconductor wafer
20
is held in a wafer holder.
FIG. 8
illustrates the relationship between the reference flat plane R
1
in the flatness measuring method of the prior art and a transcribing reference flat plane R
2
used by the optical exposure apparatus for the transcribing operation. Using the measurement data indicating the heights at the individual measuring points, the transcribing reference flat plane R
2
that represents this particular transcribing area is calculated through the method of least squares or the like. Then the transcribing is performed with the focus adjusted to the transcribing reference flat plane R
2
.
However, since the number of measuring points at which the height is measured during the flatness measurement is not the same as the number of measuring points at which the height is measured during the transcribing operation, there is a problem in that the reference flat piano used for the measurement of the flatness of the semiconductor wafer
20
does not always match the reference flat plane (focal plane) used during the transcribing operation. As a result, the focusing state on the semiconductor wafer
20
during the transcribing operation cannot be assured with a high degree of accuracy.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a flatness measuring apparatus that measures the flatness that corresponds to the focusing conditions during transcription.
In order to attain the above object, a flatness measuring apparatus according to the present invention that measures flatness of a substrate on which a specific pattern is to be formed by adjusting focus to a forming reference flat plane obtained based upon height data corresponding to specific measuring points of the substrate, comprises: an arithmetic operation device that obtains height data at predetermined measuring points of the substrate, determines a flatness judging criterion flat plane based upon height data at measuring points located at positions at which the specific measuring points are located through an arithmetic operation, determines quantities of displacement at the predetermined measuring points relative to the flatness judging criterion flat plane through an arithmetic operation, and measures the flatness of the substrate based upon the quantities of displacement.
This flatness measuring apparatus preferably further comprises a decision-making device that determines the substrate to be acceptable if the flatness of the substrate measured by the arithmetic operation device satisfies a specific flatness standard value set for the substrate and determines the substrate to be unacceptable otherwise.
In the flatness measuring apparatus, preferably, at least four specific measuring points are set in a forming area over which the specific pattern is formed.
Also in the flatness measuring apparatus, preferably, the specific flatness standard value set for the substrate is determined based upon a focal depth of an apparatus that forms the specific pattern on the substrate.
Also, the flatness measuring apparatus preferably further comprises a Fizeau's interferometer that obtains the height data at the predetermined measuring points of the substrate.
Also, the flatness measuring apparatus preferably further comprises a distance sensor that obtains the height data at the predetermined measuring points of the substrate.
Another flatness measuring apparatus according to the present invention that measures flatness of a substrate on which a specific pattern is to be formed by adjusting focus to a forming reference flat plane obtained based upon height data corresponding to specific measuring points of the substrate, comprises: an arithmetic operation device that determines a reference flat plane based upon heights of all measuring points in a forming area of the substrate over which the specific pattern is to be formed through an arithmetic operation, determines quantities of displacement at all the measuring points relative to the reference flat plane through an arithmetic operation, measures the flatness of the substrate based upon the quantities of displacement relative to the reference flat plane, determines a flatness judging criterion flat plane based upon height data at measuring points located at positions at which the specific measu
Matsukawa Eiji
Nakahira Hosei
Sakuta Hironobu
Yomoto Masahiko
Nikon Corporation
Oliff & Berridg,e PLC
Pham Hoa Q.
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