Wafer stepper method utilizing a multi-segment global alignment mark

A multi-segment alignment mark useful for a variety of processes is described. The multi-segment alignment mark comprises a plurality of segments wherein each of the segments comprises a series of sub-segments wherein each of the sub-segments comprises a series of spaces and lines, each sub-segment having the same width but having a different number of spaces and lines within the width depending on the relative width of the spaces and lines. A wafer stepper detects signals from each of the sub-segments and uses the best signal to achieve alignment.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to the fabrication of integrated circuit devices, and 
more particularly, to a multi-segment alignment mark that can be used for 
a variety of lithography masking processes in the fabrication of 
integrated circuits. 
2. Description of the Prior Art 
In the fabrication of integrated circuit devices, multiple layers of 
conductors and insulators are deposited and patterned to construct the 
integrated circuit. It is critical to align each subsequent layer with the 
previous layer with precision. This is typically accomplished by using 
alignment marks. A wafer stepper tool uses the alignment marks on a wafer 
as a reference point for adjusting a reticle over the wafer. The reticle 
contains the pattern to be generated within the layer. The reticle must be 
precisely aligned to the previous layer. A wafer stepper uses one of at 
least three methods to detect the alignment marks; these are light 
interference, bright field contrast, or dark field polarization effect. 
For example, wafer alignment on an ASML stepper uses zero marks. For oxide 
chemical mechanical polishing (CMP) processes, zero marks are distorted at 
the metal layers due to oxide residue left on the marks. Target repairs at 
via layers are necessary to ensure that the zero marks are completely 
clean and can continue to be used. ASML's scribeline primary marks (SPM) 
have been developed to replace zero marks. The segmentation of the SPM 
marks determines signal strength and so is an important criteria for good 
alignment. For a foundry using this alignment scheme, different 
segmentations must be tested to find an optimized segmentation for each of 
the different processes. This testing requires laborious effort. 
U.S. Pat. No. 5,627,624 to Yim et al shows a test reticle and alignment 
mark optimization method. U.S. Pat. No. 5,496,777 to Moriyama teaches 
forming alignment marks in enlarged portions of scribe lines. U.S. Pat. 
No. 5,401,691 to Caldwell discloses an inverse open frame alignment mark. 
U.S. Pat. No. 5,369,050 to Kawai discloses an alignment mark having a 
groove around it. U.S. Pat. No. 5,648,854 to McCoy et al discloses an 
alignment system using global alignment marks. 
SUMMARY OF THE INVENTION 
Accordingly, it is a principal object of the present invention to provide 
an effective and very manufacturable method of generating alignment marks 
in the manufacture of an integrated circuit device. 
A further object of the invention is to provide a method of generating 
alignment marks useful for a variety of lithography processes. 
A still further object is to provide a multi-segment alignment mark useful 
for a variety of lithography processes. 
Another object of the invention is to provide a method of generating 
alignment marks useful for a variety of lithography processes by using a 
multi-segment alignment mark incorporating different segmentations into 
the size of a single mark. 
Yet another object is to provide a multi-segment alignment mark 
incorporating different segmentations into the size of a single mark. 
In accordance with the objects of this invention a multi-segment alignment 
mark useful for a variety of lithography processes is achieved. The 
multi-segment alignment mark comprises a plurality of segments wherein 
each of the segments comprises a series of sub-segments wherein each of 
the sub-segments comprises a series of spaces and lines, each sub-segment 
having the same width but having a different number of spaces and lines 
within the width depending on the relative width of the spaces and lines. 
A wafer stepper detects signals from each of the sub-segments and uses the 
best signal to achieve alignment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention is a multi-segment alignment mark which incorporates 
different segmentations into the size of a single mark. This is suitable 
for the foundry industry because many different lithography processes may 
need a different mark type. The multi-segment mark of the present 
invention contains these different segmentations for different lithography 
processes. 
The multi-segment mark allows the wafer stepper to pick up the best signal 
from a broad spectrum of segmentations. Thus, it is more capable of 
tolerating process variations than conventional segmented alignment marks. 
The robustness in design of the multi-segment mark of the present 
invention will reduce the probability of misalignment. 
Using the multi-segment mark of the present invention also saves space on 
the reticle because the scribe line no longer needs a different 
segmentation mark. In the prior art, many different alignment mark types 
are printed on a layer for backup purposes in case the primary segmented 
mark fails. This is especially true in the development phase as there is a 
range of process conditions and many alignment mark must be printed for 
the purpose of aligning the subsequent layer. The multi-segment mark of 
the present invention eliminates the need for printing many different mark 
types, thus saving space allocation for alignment purposes. 
Referring now more particularly to FIG. 1, there is shown a top view 
illustration of a multi-segment global alignment mark 10 of the present 
invention. The alignment mark is made up of segments 20. Visual cross 
hairs at 16 at the center of the alignment mark are used as a reference to 
align the reticle to form the alignment mark. It should be understood that 
the multi-segment alignment mark illustrated in FIG. 1 is an example only. 
Many different combinations of lines and spaces may comprise the alignment 
mark of the present invention. 
As illustrated by way of example in FIG. 1, each segment 20 is typically 
7.0 microns wide and 90 microns long. FIG. 2 illustrates typical alignment 
mark segments of the prior art. Chrome areas 34 alternate with clear areas 
30. 
FIG. 3 is a magnification of a single segment 20 of the multi-segment 
global alignment mark of the present invention. The single segment is in 
turn segmented. For example, it may be segmented as shown in FIG. 3. 
Segment 42 has lines 34 of width 1.0 .mu. and spaces 30 of width 0.6 .mu.. 
Segment 44 has lines 34 of width 1.4 .mu. and spaces 30 of width 0.7 .mu.. 
Segment 46 has lines 34 of width 2.2 .mu. and spaces 30 of width 1.6 .mu.. 
Segment 48 has lines 34 of width 3.0 .mu. and a space 30 of width 2.0 
.mu.. Segment 50 has a line 34 of width 7.0 .mu.. That is, the reticle 
segment 20 has chrome lines 34 and clear spaces 30. 
FIG. 4 illustrates the cross-section of a substrate 10. The substrate may 
comprise any film including metal, oxide, polysilicon, and so on. A resist 
layer 14 has been coated over the film 10 to be patterned. For example, 
segment 46 of the multi-segment alignment mark 20 has been chosen to 
pattern the film 10. The resist 14 underlying the chrome lines 34 will be 
etched away while the resist underlying the spaces 30 will remain, 
resulting in the resist pattern illustrated in FIG. 4. 
A single segment of the global alignment mark of the present invention may 
be segmented further in a variety of designs, including, but not limited 
to the design illustrated in FIG. 3. Each segment 20 may be identically 
segmented within an alignment mark. However, it is possible that each 
segment 20 may be segmented differently. Any number of sub-segments from 2 
to 5 or more may be implemented in each segment 20. 
The process of the invention provides a very manufacturable method of 
generating alignment marks that can be used in a variety of lithography 
processes. The multi-segment global alignment mark of the present 
invention allows the stepper to pick up the best signal from a broad 
spectrum of segmentation. 
The process of the present invention can be used with steppers using any 
one of the three methods to detect alignment marks: light interference, 
bright field contrast, or dark field polarization effect. 
While the invention has been particularly shown and described with 
reference to the preferred embodiments thereof, it will be understood by 
those skilled in the art that various changes in form and details may be 
made without departing from the spirit and scope of the invention.