Optics: measuring and testing – Position or displacement
Reexamination Certificate
2001-03-26
2003-05-13
Lee, Michael G. (Department: 2877)
Optics: measuring and testing
Position or displacement
C356S620000, C250S559300
Reexamination Certificate
active
06563594
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a system and a method for detecting misalignment between masks in manufacturing a semiconductor device. In more specific, the present invention relates to a system and a method for detecting a position of a misalignment measurement mark which is previously formed on a semiconductor substrate.
2. Description of the Prior Art
In manufacturing a semiconductor device with lamination layers stacked with thin films having different patterns respectively, it is greatly important to accurately align a mask (reticle) with a semiconductor substrate for forming a pattern thereon.
For such mask alignment, a commonly adapted method has steps of previously forming a misalignment measurement mark (which will hereinafter be occasionally referred as a measurement mark) in a region other than that for forming a device on a semiconductor substrate, detecting the position of the measurement mark and adjusting a mask alignment position on the basis of the detected position.
Conventional methods for detecting a position of an alignment measurement mark will hereinafter be described taking a slice level method and a correlation method for instances. In the following respective figures, the same reference numbers are given to the same portions, and the descriptions thereof are appropriately omitted.
FIG. 1
is a schematic diagram showing a conventional measurement mark position detecting system. The misalignment measurement mark position detecting system
110
shown in this figure comprises; a light source
13
, a half mirror
15
, a stage
70
, a CCD (Charge Coupled Device) sensor
33
, an A-D (Analogue to Digital) converter
35
and a control computer
110
. A Si (silicon) substrate
120
is supported on the stage
70
. The substrate
120
is previously provided with a measurement mark
20
which is an object to be measured. In this figure a cross section diagram of the measurement mark
20
is shown taken along a line in the X direction and portions of the substrate
120
other than the measurement mark
20
are omitted.
FIG. 2
is an enlarged view of the measurement mark
20
shown in FIG.
1
. As shown in
FIG. 2
, the measurement mark
20
includes a SiO
2
layer
23
formed on the Si substrate
120
, and a SiN layer
27
which on the SiO
2
layer
23
so as to protrude therefrom. The SiO
2
layer
23
and the SiN layer
27
are formed in thickness of T
1
and T
2
respectively, and each values thereof are 1 &mgr;m in this example. Two concavities C
1
and C
2
are formed on a surface of the SiO
2
layer
23
. These concavities have depth D
1
and D
2
of 0.12 &mgr;m respectively and thus constitute steps. The SiN layer
27
is arranged such that the center thereof is positioned right in the middle of concavities C
1
and C
2
in the cross section view of the FIG.
2
. That is, from the point of view of the SiN layer
27
the SiN layer
27
is arranged such that the center thereof is positioned right in the middle of outside edges E
1
, E
4
of the concavities. The measurement mark
20
thus forms a symmetry shape with respect to the centerline
11
of SiN layer
27
.
The position of the measurement mark can be detected by detecting the center point P
1
on the top surface of the SiN layer
27
. However, a typical method of detecting the point P
1
includes a step of recognizing that the center point P
1
of the SiN layer
27
coincides with the middle point of the outside edges E
1
, E
4
of concavities C
1
, C
2
.
(1) Slice Level Method
Referring
FIGS. 3B
,
4
and
6
showing waveforms and the flow-chart of
FIG. 5
, a slice level method for detecting a measurement mark will be described.
First, using the system
100
, a beam of light L
1
having a predetermined wavelength &lgr; or white light is emitted from the light source
13
to irradiate the measurement mark
20
via the half-mirror
15
(step S
101
). A reflected beam of light L
2
is generated from the measurement mark
20
. The reflected beam L
2
passes through the half-mirror
15
and is detected by a CCD sensor
33
(step S
102
). The reflected beam L
2
includes a ray from the interface between Si substrate
120
and SiO
2
layer
23
, a ray from the surface of the SiO
2
layer
23
, a ray from the interface between SiO
2
layer
23
and SiN layer
27
and a ray from the surface of the SiN layer
27
. Since above mentioned rays interfere each other, the reflected beam L
2
enters the CCD sensor
33
as the beam having various light strength dependent on each difference between the optical path lengths from these interfaces or surfaces to a pixel portion of the CCD sensor
33
.
In the CCD sensor
33
pixels are arranged in a row in the x direction. Electric charges are generated from each pixel in response to the rays of the reflected beam entering the pixel. Signals from these charges are conveyed to the control computer
110
through the A/D converter
35
.
The control computer
110
processes the signals supplied from the CCD sensor
33
to recognize a waveform in a diagram with a horizontal axis and a vertical axis. The horizontal axis denotes X coordinates of the measurement mark in the X direction and the vertical axis denotes strengths of the reflected beam from the measurement mark (step S
103
). A position coordinate of the measurement mark with respect to the substrate
120
(which will hereinafter referred to as a wafer position coordinate) is detected in a conventional way.
FIG. 3B
shows a waveform diagram obtained by the control computer
110
together with the shape of the measurement mark in a cross-sectional view. As shown in
FIG. 3B
, each position coordinate on the horizontal axis corresponds to a positional coordinate of the measurement mark respectively. For example, edges E
1
through E
6
of the convexo-concave shape correspond to X
1
through X
6
of the waveform figure respectively.
As shown in
FIG. 3B
, assuming that the light strength of the reflected beam from the concavity C
1
corresponding the position coordinates from X
1
to X
2
is rd
1
, and that the light strength of the reflected beam from the concavity C
2
corresponding to the position coordinates form X
5
to X
6
is rd
2
, and that the light strength of the reflected beam from the other surface of the SiO
2
layer
23
is r
0
, the following correlation exists between these strengths.
ro>rd
1
, rd
2
(1)
rd
1
=rd
2
(2)
Thus, the waveform of the reflected beam obtained from the measurement mark having a line symmetry shape in a cross section view has a concavity portion in shape in and near the region of the position coordinates from X
1
to X
2
and a concavity portion in and near the region of the position coordinates from X
5
to X
6
. The entire waveform has a line symmetry shape along a line
11
′ which passes the middle point X
34
of X
3
and X
4
and is perpendicular to the X-axis.
Referring now to FIG.
4
and
FIG. 5
, a method for processing a waveform in such a symmetry shape and for detecting the position of the measurement mark
20
by means of a slice level method will be described below.
First, the position XM
1
where the light strength drops most sharply in and near a region having position coordinates from X
1
to X
2
in the waveform figure is detected (step S
104
).
Similarly, the position XM
6
where the light strength rises most sharply in and near a region having position coordinates from X
5
to X
6
in the waveform figure is detected (step S
105
).
Next, the middle position XM
16
of the position XM
1
and the position XM
6
acquired at above-mentioned step is calculated (step S
106
).
Then, at steps similar to the above steps S
104
through S
0106
, the position XM
3
where the light strength drops most sharply in a portion having position coordinate of and near the X
3
, and the position XM
4
where the light strength rises most sharply in a portion having position coordinate of and near X
4
are detected respectively (steps S
107
and S
108
). Then a middle position XM
34
of the X
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Le Uyen-Chau
Lee Michael G.
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