Optics: measuring and testing – By light interference – For dimensional measurement
Reexamination Certificate
1998-06-04
2001-05-08
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By light interference
For dimensional measurement
C356S401000
Reexamination Certificate
active
06229618
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of improving registration accuracy and to a method of forming patterns on a substrate using the method. More specifically, the present invention relates to a method of improving registration accuracy in a step of exposure during manufacturing of a semiconductor device, and to a method of forming patterns on a substrate using the method.
2. Description of the Background Art
Conventionally, measurement of positional offset of a registration accuracy measurement mark has been utilized as a method of measuring an amount of offset in registration during the steps of manufacturing a semiconductor device. In the measurement of offset of the registration accuracy measurement mark, first, a registration accuracy measurement mark is formed, and a position of a step of the measurement mark is found. Based on the position of the step, the position of the measurement mark is found. Further, based on the position of the measurement mark, an amount of offset in registration is measured. As to a specific method of finding the position of the step, a method has been known in which light beams are directed to the step and intensity of reflected light beams is found. In this method of finding the position of the step in accordance with the intensity of reflected light beams, the position of the step is detected utilizing the phenomenon that light beams are reflected irregularly at the step so that intensity of the reflected light beams is lower at the step than other portions. That is, a portion where intensity of reflected light beams is lower is found.
The conventional method of improving registration accuracy will be described with reference to
FIGS. 10
to
13
.
In the conventional method of improving registration accuracy, referring to
FIG. 10
, positions of registration accuracy measurement marks are measured at measurement points on selected ones of a plurality of chips
102
formed on a wafer
101
. In each measurement point, first and second registration accuracy measurement marks
201
and
202
are formed simultaneously with patterning of interconnections and the like. First registration accuracy measurement mark
201
is formed on the substrate, and second registration accuracy measurement mark
202
is formed on first registration accuracy measurement mark
201
.
FIGS. 11 and 12
are plan view and cross sectional view, respectively, of the first and second registration accuracy measurement marks
201
and
202
of this example.
At the time of inspection, referring to
FIG. 12
, light beams
204
are directed to first and second registration accuracy measurement marks
201
and
202
. Of the light beams
204
, a beam incident on an upper surface of second registration accuracy measurement mark
202
will be referred to as incident light beam
204
a
, and a beam reflected at the upper surface of second registration accuracy measurement mark
202
will be referred to as reflected light beam
204
b
. A beam incident on an upper surface of first registration accuracy measurement mark
201
will be referred to as incident light beam
204
c
, and a beam reflected on the upper surface of first registration accuracy measurement mark
201
will be referred to as reflected light beam
204
d
. A beam incident on an upper surface of the chip will be referred to as incident light beam
204
i
, and a beam reflected on the upper surface of the chip will be referred to as reflected light beam
204
j
. At this time, intensities of reflected light beams
204
b
,
204
d
and
204
j
are measured as shown in FIG.
13
. Intensity of a light beam is higher when the light beam is reflected from a closer point. Intensities corresponding to reflected light beams
204
b
,
204
d
and
204
j
are represented by light intensities
219
,
220
, and
223
, respectively. In order to detect the step by referring to the intensities, a step between light intensities such as observed at a boundary
224
or
227
is detected. Thus, the position of the edge of the registration accuracy measurement mark is found, and hence amount of offset in registration is found.
However, recently, degree of integration of semiconductor devices such as ICs and LSIs has been ever increasing, and the buses have been rapidly miniaturized. Accordingly, in the method of improving registration accuracy, measurement with the precision of 0.1 &mgr;m to 0.05 &mgr;m has come to be required.
The process for manufacturing devices includes repetition of patterning of interconnections.elements, deposition of an insulating film and patterning of interconnections. Here, when an interconnection of an upper layer is to be formed while unevenness of the underlying layer is not sufficiently made planar, focusing fails in the step of lithography for patterning the interconnection, resulting in formation of a dull or blurred interconnection pattern.
Widths of interconnection of VLSIs has been narrower and narrower as the devices have been miniaturized to high degree, and accordingly, margin of depth of focus (D.O.F) in lithography has been decreasing. In other words, tolerable range in focusing at the time of lithography becomes smaller. Therefore, unless the device surface is almost perfectly planarized over wide range, satisfactory patterning of interconnections cannot be ensured.
As the margin of the depth of focus decreases, the step of the registration accuracy measurement mark is reduced by rapid strides, from the order of several hundreds to several tens A. As a result, the conventional method of finding a step in accordance with light intensities described above can no longer catch up to ensure sufficient accuracy. More specifically, when a step is very small, light intensities
220
and
223
are as shown in
FIG. 13
, making it difficult to clearly identify the boarder
227
. Difficulty in identifying the step leads to difficulty in measurement or inspection of registration accuracy.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of improving registration accuracy which allows easy detection of an amount of offset in registration even when a registration accuracy measurement mark has a small step.
Another object of the present invention is to provide a method of improving registration accuracy allowing, even when a registration accuracy measurement mark has a small step, easy detection of the step.
In accordance with an aspect of the present invention, the method of improving registration accuracy in a step of exposure during manufacturing of a semiconductor device includes the following steps. First, a registration accuracy measurement mark is formed on a semiconductor substrate. Thereafter, a first resist film covering at least an edge portion of the registration accuracy measurement mark is formed. Position of the edge portion of the registration accuracy measurement mark is detected by an optical system utilizing interference. As the edge portion of the registration accuracy measurement mark is covered by the first resist, optical distance (actual step of the measurement mark×refractive index) is increased because of the refractive index (1.5
~
1.8) of the first resist higher than that of air, even when the registration accuracy measurement mark has a small step. Therefore, when interference of reflected light beams are detected in the method of detecting a step by an interference optical system, the step in terms of the detected data is seemingly enlarged. Therefore, even if the step is small, identification of the position of the edge portion is facilitated. As a result, the position of the registration accuracy measurement mark can readily be detected, facilitating calculation of the amount of offset in registration. This enables improved registration accuracy in the manufacturing process of the semiconductor devices.
Further, the registration accuracy measurement mark may include a first registration accuracy measurement mark formed of a first layer. A second registration accuracy measurement mark fo
Font Frank G.
Lee Andrew H.
McDermott & Will & Emery
Mitsubishi Denki & Kabushiki Kaisha
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