Patent Application
20130200535
1. Field of Invention
This invention relates to an integrated circuit (IC) process, and more particularly relates to an overlay mark used for alignment accuracy measurement in an IC process.
2. Description of Related Art
As the linewidth of the IC process continuously gets narrower, the alignment accuracy between a lower layer and an upper layer becomes more and more important. Therefore, an overlay mark is generally formed on a wafer to check alignment accuracy.
A conventional overlay mark typically includes x-directional linear patterns and y-directional linear patterns of a single pre-layer, and x-directional linear patterns and y-directional linear patterns of the current layer. Overlay errors have been measured only between two adjacent layers.
However, in ICs with multiple layers, displacement between non-adjacent layers may compromise IC performance. Therefore, improving the integrity of overlay marks between multiple pre-layers is still an important issue in the field.
Accordingly, this invention provides an overlay mark used in an IC process for alignment accuracy measurement.
The overlay mark of this invention includes N (N≧2) groups of first x-directional linear patterns each defined from a different one of N pre-layers, N groups of second x-directional linear patterns of a current layer, N groups of first y-directional linear patterns each defined from a different one of the N pre-layers, and N groups of second y-directional linear patterns of the current layer. Each group of second x-directional linear patterns is disposed together with one group of first x-directional linear patterns, wherein the second x-directional linear patterns and the first x-directional linear patterns are arranged alternately. Each group of second y-directional linear patterns is disposed together with one group of first y-directional linear patterns, wherein the second y-directional linear patterns and the first y-directional linear patterns are arranged alternately.
In an embodiment, at least one pre-layer among the N pre-layers is defined by M (M≧2) exposure steps, the group of first x-directional linear patterns of the at least one pre-layer includes M sets of first x-directional linear patterns defined by the M exposure steps respectively and disposed in M first regions respectively, and the group of first y-directional linear patterns of the at least one pre-layer includes M sets of first y-directional linear patterns defined by the M exposure steps respectively and disposed in M second regions respectively.
In another embodiment, at least one pre-layer among the N pre-layers requires higher overlay accuracy than the other(s), the group of first x-directional linear patterns of the at least one pre-layer includes M sets of first x-directional linear patterns disposed in M first regions respectively, and the group of first y-directional linear patterns of the at least one pre-layer includes M sets of first y-directional linear patterns disposed in M second regions respectively.
Since the linear patterns of at least two (N≧2) pre-layers are disposed together with the linear patterns of the current layer in the overlay mark of this invention, the overlay measurement is more convenient so that the overlay measurement time is saved, and the area utilization efficiency of the overlay mark is higher than the prior art.
In order to make the aforementioned and other objects, features and advantages of the present invention comprehensible, a preferred embodiment accompanied with figures is described in detail below.
It is noted that the following embodiments of N=2 are intended to further explain this invention but not to limit its scope. For example, it is possible to include linear patterns of more than two (N>2) pre-layers in one overlay mark of this invention.
Referring to
In this embodiment, each of the two (N=2) pre-layer is defined by two (M=2) exposure steps. The group of x-directional linear patterns 102 of the first pre-layer includes two sets 102-1 and 102-2 defined by the two exposure steps respectively and disposed in two neighboring regions 121 and 123 respectively. The group of x-directional linear patterns 104 of the second pre-layer includes two sets 104-1 and 104-2 defined by the two exposure steps respectively and disposed in two neighboring regions 125 and 127 respectively. The group of y-directional linear patterns 112 of the first pre-layer includes two sets 112-1 and 112-2 defined by the two exposure steps respectively and disposed in two neighboring regions 131 and 133 respectively. The group of y-directional linear patterns 114 of the second pre-layer includes two sets 114-1 and 114-2 defined by the two exposure steps respectively and disposed in two neighboring regions 135 and 137 respectively.
In this embodiment, the region (121+123) of the group of x-directional linear patterns 102 of the first pre-layer and the region (131+133) of the group of first y-directional linear patterns 112 of the first pre-layer are arranged in the x-direction. The region (125+127) of the group of x-directional linear patterns 104 of the second pre-layer and the region (135+137) of the group of first y-directional linear patterns 114 of the second pre-layer are arranged also in the x-direction. The two regions (121+123 and 125+127) of the two groups of x-directional linear patterns 102 and 104 of the two pre-layers are arranged in the y-direction. The two regions (131+133 and 135+137) of the two groups of y-directional linear patterns 112 and 114 are arranged also in the y-direction. Nevertheless, all the above arrangement directions can be turned by 90° at the same time, depending on the shape of the area for forming the overlay mark.
The overlay mark can be used to derive overlay errors in the following manner. The x-overlay error of the first exposure step of the first pre-layer with respect to the current layer is taken as an example here. First, for each pair of a y-directional linear pattern 112-1 defined by the first exposure step to the first pre-layer and a y-directional linear pattern 116 of the current layer, the distance between the two is measured. An average distance is then calculated from the measured distance values for all the pairs of 112-1 and 116, and is compared with a predetermined value to derive the result, wherein the predetermined value corresponds to a case where no x-overlay error is present.
Referring to
In this embodiment, the second pre-layer is defined by two (M=2) exposure steps as in the precedent embodiment. Similarly, the group of x-directional linear patterns 204 for the second pre-layer includes two sets 204-1 and 204-2 defined by the two exposure steps respectively and disposed in two neighboring regions 225 and 227 respectively. The group of y-directional linear patterns 214 for the second pre-layer includes two sets 214-1 and 214-2 defined by the two exposure steps respectively and disposed in two neighboring regions 235 and 237 respectively.
On the other hand, the first pre-layer is defined by only one exposure step, but requires higher overlay accuracy than the second pre-layer. Hence, a “weight” is given to the pattern of the first pre-layer. More specifically, the group of x-directional linear patterns 202 of the first pre-layer includes two sets disposed in two neighboring regions 221 and 223 respectively, and the group of y-directional linear patterns 212 of the first pre-layer includes two sets in two neighboring regions 231 and 233 respectively.
In this embodiment, the region (221+223) of the group of x-directional linear patterns 202 of the first pre-layer and the region (231+233) of the group of first y-directional linear patterns 212 of the first pre-layer are arranged in the x-direction. The region (225+227) of the group of x-directional linear patterns 204 of the second pre-layer and the region (235+237) of the group of first y-directional linear patterns 214 of the second pre-layer are arranged also in the x-direction. The two regions (221+223 and 225+227) of the two groups of x-directional linear patterns 202 and 204 of the two pre-layers are arranged in the y-direction. The two regions (231+233 and 235+237) of the two groups of y-directional linear patterns 212 and 214 of the two pre-layers are arranged also in the y-direction. Nevertheless, all the above arrangement directions can be turned by 90° at the same time, depending on the shape of the area for forming the overlay mark.
As indicated by the above embodiments, since the linear patterns of at least two (N≧2) pre-layers are disposed together with the linear patterns of the current layer in the overlay mark of this invention, the overlay measurement is more convenient so that the overlay measurement time is saved, and the area utilization efficiency of the overlay mark is higher than the conventional overlay mark.
This invention has been disclosed above in the preferred embodiments, but is not limited to those. It is known to persons skilled in the art that some modifications and innovations may be made without departing from the spirit and scope of this invention. Hence, the scope of this invention should be defined by the following claims.
