Radiation imagery chemistry: process – composition – or product th – Registration or layout process other than color proofing
Reexamination Certificate
2002-07-08
2004-12-07
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Registration or layout process other than color proofing
C430S311000
Reexamination Certificate
active
06828071
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a method of to aligning a wafer and masks. In particular, the present invention relates to a method of aligning a wafer mask wherein alignment marks are deposited in each die area.
2. Description of the Related Art
Forming an integrated circuit on a substrate (wafer) requires a series of process steps. These process steps include the deposition and patterning of material layers such as insulating layers, polysilicon layers and metal layers. The layers are typically patterned using a photoresist layer that is patterned over the material layer by exposing the photoresist through a photomask or a reticle. The photoresist is then developed to provide the pattern. Typically, the photomask or the reticle has alignment marks that are aligned to alignment marks formed on the substrate in a previous process step. However, as the integrated circuit feature size continues to decrease to obtain increased circuit density, it has become difficult to register or align one masking level to the previous level.
As shown in
FIG. 1
, generally, two global alignment marks
142
and
144
are deposited on the mask
140
in the conventional alignment method, and then the alignment marks
102
and
104
are aligned with the two global alignment marks
142
and
144
by a He—Ne Laser of an exposure system
160
. Next, all the fields, for example chip areas or die areas, on the wafer
100
are exposed in a step-and-repeat mariner using an optical stepper. Consequently, the wafer
100
usually has a plurality of fields (dies) divided by the scribe lines. A desired pattern
146
in the mask
140
is transferred to each corresponding field in the wafer by exposing through the lens
120
, step-and-repeat.
In the above method, the global alignment marks
142
and
144
are formed on the mask
140
for aligning with the marks
102
and
104
. Further, a plurality of alignment marks
148
are deposited on the intersection of scribe lines for intra-field alignment. Therefore, different patterns on each mask can be transferred to the fields in the wafer by global alignment and the intra-field alignment.
As shown in
FIG. 2
, the alignment marks
1031
are complete when the exposure field
103
, for example a shot, is complete. Therefore, the field on the wafer can align with the masks accurately by the exposure system and then the optical stepper can transfer the pattern from the mask to each field
105
accurately. However, the alignment marks
148
on the scribe lines may be unclear or disappear entirely incomplete exposure fields at the wafer's edge regions, even if the fields form complete squares. Therefore, the fields at the wafer edge regions cannot align with the masks accurately. In this case, the optical stepper cannot transfer the pattern from the mask to each field
105
accurately. This situation is illation in
FIG. 2
, where all the
106
A,
106
B,
106
C~
106
G at the wafer edge region may not align with the masks accurately because the alignment mark is incomplete or missing.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of aligning a wafer and masks. In the present invention, alignment marks are deposited at the corner of each field. Consequently, the exposure system can align the mask with each field accurately for exposure process. Furthermore, after the fields are detached by a wafer saw, the alignment marks at the corner of each field also can be used for alignment in subsequent processes, for example, bonding wire in the packing process.
In the present invention, a wafer having a surface with a plurality of fields and scribe lines is provided. An initial mask and a subsequent mask having a first pattern and a second pattern respectively corresponding to the fields are provided. The initial mask and the subsequent mask further have a plurality of original alignment marks respectively at the corners thereof corresponding to the fields. Next, the first pattern is transferred to each field and a plurality of secondary alignment marks corresponding to the original alignment marks are formed by the initial mask. Then intra-field alignment is performed by aligning the original alignment masks of the subsequent mask with the secondary alignment marks at the corner of the field to form the second pattern on each field.
REFERENCES:
patent: 6638671 (2003-10-01), Ausschnitt et al.
Nanya Technology Corporation
Young Christopher G.
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