Active solid-state devices (e.g. – transistors – solid-state diode – Alignment marks
Reexamination Certificate
1999-03-18
2002-11-12
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Alignment marks
Reexamination Certificate
active
06479904
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a registration accuracy measurement mark, and particularly to a registration accuracy measurement mark used for measuring overlay accuracy in the lithography process in the manufacturing process of semiconductor devices.
2. Description of the Background Art
According to a conventional method for measuring the overlay accuracy relative to two lithography steps in a manufacturing process of a semiconductor device, a pattern of a registration accuracy measurement mark is formed simultaneously with a master pattern (referring to a pattern to be actually produced) using the same mask in each lithography step, in order to measure the overlay accuracy of the master pattern by the overlay accuracy of the registration accuracy measurement mark pattern. A conventional registration accuracy measurement mark is hereinafter described referring to
FIGS. 10-15
.
Referring to
FIG. 10
, the conventional registration accuracy measurement mark is arranged in a scribe line region
112
adjacent to a circuit region
111
where a master pattern
101
is to be formed. Referring to
FIG. 11
, a master pattern
105
a
of the first layer and a registration accuracy measurement mark pattern
105
b
of the first layer are partitioned by a lowered region generated by a groove
110
of scribe line region
112
. Master pattern
101
of the second layer is placed on the first layer master pattern
105
a
and a registration accuracy measurement mark pattern
102
of the second layer is placed on the first layer registration accuracy measurement mark pattern
105
b
as a line located along the four sides of a rectangle to have its part parallel to the second layer master pattern
101
.
In the case of such a registration accuracy measurement mark, since the width of the second layer registration accuracy measurement mark pattern
102
is determined independently of the width of the second layer master pattern
101
, the amount of offset (amount of displacement) due to aberration, (i.e., the difference between the position of an optical from by a lens and ideal optical image) is different between the master pattern and the registration accuracy measurement mark pattern both at the second layer when the patterns are generated. A phenomenon thus observed upon generation of the second layer registration accuracy measurement mark pattern
102
and master pattern
101
is that the relative positions of those patterns at the second layer are different from those of the respective patterns on a mask pattern. This phenomenon is described below.
The light passing through a mask usually advances with a prescribed diffraction angle according to the size of each opening of the mask, after transmitting through the opening. Each pattern thus generated by the mask is displaced by the diffraction angle of the transmitted light, resulting in a phenomenon where offset due to the aberration is observed.
The diffraction angle of the light transmitted through the opening formed as a wider line on the mask is different from that of the light transmitted through the opening formed as a narrower line. Therefore, if the width of the master pattern is different from that of the registration accuracy measurement mark pattern, the amount of offset attributable to the aberration would be different. The difference in the amount of offset due to aberration causes the difference between the master pattern and the registration accuracy measurement mark pattern in the amount of offset in registration (alignment). The difference in the amount of offset due to aberration thus influences registration.
In order to avoid this influence of the difference in the amount of offset due to aberration, a master pattern formed as lines and a registration accuracy measurement mark pattern formed as lines are produced to have the same width as shown in
FIGS. 12 and 13
. In this case, the same width of the second layer registration accuracy measurement mark pattern
102
and the second layer master pattern
101
allows the amount of offset due to aberration to be the same, so that the second layer registration accuracy measurement mark pattern
102
and the second layer master pattern
101
are generated to have the relative spacing between their lines which is the same as that of the opening pattern formed on the mask.
In the above-described case shown in
FIGS. 12 and 13
, it is unnecessary to consider the depth of focus since the height of the surface of the first layer registration accuracy measurement mark pattern
105
b
on which the second layer registration accuracy measurement mark pattern
102
is formed coincides with that of the first layer master pattern
105
a
on which the second layer master pattern
101
is formed.
On the contrary, referring to
FIGS. 14 and 15
, if the first layer registration accuracy measurement mark pattern
105
b
on which the second layer registration accuracy measurement mark pattern
102
is formed and the first layer master pattern
105
a
on which the second layer master pattern
101
is formed are produced to have different heights, the depth of focus that compensates for the difference in height cannot be secured. As a result, the second layer registration accuracy measurement mark pattern
102
cannot be produced accurately due to the out of focus state.
According to a design usually employed, the difference in height between the surface of the first layer registration accuracy measurement mark pattern
105
b
on which the second layer registration accuracy measurement mark pattern
101
is formed and that of the first layer master pattern
105
a
on which the second layer master pattern
101
is formed is approximately 0.6 &mgr;m at maximum in both cases where the first layer registration accuracy measurement mark pattern is higher than the first layer master pattern and vice versa. Accordingly, if the depth of focus of more than approximately 1.2 &mgr;m is ensured, the pattern generation is possible in the focused state even if there is a difference in height between the surface of the first layer registration accuracy measurement mark pattern
105
b
and that of the first layer master pattern
105
a.
In order to increase the depth of focus, the width of the second layer registration accuracy measurement mark pattern
102
is made larger than that of the second layer master pattern
101
. According to this method, an opening width of a mask for generating the second layer registration accuracy measurement mark pattern
102
is made larger than that for generating the second layer master pattern
101
, so that the diffraction angle of the light transmitted through the opening of the mask for generating the second layer registration accuracy measurement mark pattern
102
is reduced. Consequently, the angle of light incident on the surface of the substrate is closer to the right angle relative to the surface to achieve increase in the depth of focus.
However, if the second layer registration accuracy measurement mark pattern
102
is made too wider than the second layer master pattern
101
for securing the increased depth of focus, the influence of the difference in the amount of displacement due to aberration also increases. Accordingly, the width of the second layer registration accuracy measurement mark pattern
102
should be made larger than that of the second layer master pattern
101
such that it allows measurement in the overlay inspection to be within the range of an allowable measurement error and allows the registration accuracy measurement mark pattern to be formed with sufficient depth of focus ensured, even if there is a formation error of patterns due to the difference in the amount of offset induced by aberration.
The allowable measurement error in the amount of offset in registration is now described. Usually, if the line-like master pattern with its dimension of approximately 0.2 &mgr;m to 1.0 &mgr;m is used, the numerical standard of the allowable measurement error in the amount of offset in registration
Chaudhuri Olik
Mitsubishi Denki & Kabushiki Kaisha
Wille Douglas A.
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