Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2001-08-10
2003-11-25
Duda, Kathleen (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S311000, C250S492210
Reexamination Certificate
active
06653029
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to photomask scanning and repair in semiconductor processing, and more particularly to the use of dual-focused ion beams for such scanning and repair.
BACKGROUND OF THE INVENTION
Deposition and patterning are two of the basic steps performed in semiconductor processing. Patterning is also referred to as photolithography, masking, oxide or metal removal, and microlithography. Patterning enables the selective removal of material deposited on a semiconductor substrate, or wafer, as a result of deposition. The process of adding layers and removing selective parts of them, in conjunction with other processes, permits the fabrication of semiconductor devices.
This is shown by reference to
FIGS. 1A-1D
. In
FIG. 1A
, a layer
104
has been deposited on a semiconductor substrate
102
. A layer of photoresist
106
is over the layer
104
. A mask
108
is positioned over the photoresist
106
, and has opaque regions
110
and
112
. The base of the mask
108
is itself clear, and made out of glass. The opaque regions
110
and
112
of the mask
108
are formed out of chromium. Exposure involves the application of ultraviolet rays
114
. The parts of the photoresist
106
that are not underneath the opaque regions
110
and
112
are exposed to the ultraviolet rays
114
, and become polymerized as the photoresist
106
′. The parts of the photoresist
106
underneath the regions
110
and
112
are not exposed to the rays
114
, and remain unpolymerized.
In
FIG. 1B
, the polymerized photoresist
106
′ is developed, which removes the photoresist
106
′, leaving only the unpolymerized photoresist
106
. The unpolymerized photoresist
106
has a pattern that corresponds to the opaque regions
110
and
112
of the mask
108
of FIG.
1
A. In
FIG. 1C
, the layer
104
is etched to the substrate
102
, such that the only part of the layer
104
that remains is that which is under the unpolymerized photoresist
106
. This results in two stacks, a stack
116
and a stack
118
. Finally, in
FIG. 1D
, the remaining photoresist
106
is stripped, leaving the stacks
116
and
118
of the layer
104
on the substrate
102
.
The accuracy of the mask
108
is crucial for ensuring that the semiconductor devices formed are also accurate, and perform correctly. Defects in a photomask in particular can cause the semiconductor devices fabricated with the photomask to malfunction. Two common defects are shown in
FIGS. 2A and 2B
. In
FIG. 2A
, the mask
202
has a proper opaque region
204
, but an improper opaque spot
206
. Conversely, in
FIG. 2B
, the opaque region
210
of the mask
208
has an improper hole
212
. Other common mask defects include inclusions of opacity into a clear region, protrusions of clarity into an opaque region, clear breaks within opaque regions, and opaque bridges between one opaque region and another opaque region.
Clear or missing parts of a mask are typically repaired by “patching” them with a carbon deposit. Opaque or unwanted chrome regions are usually removed by sputtering from a focused ion beam (FIB). One type of focused ion beam is a gallium ion beam. A focused gallium ion beam is capable of milling away opaque defects and depositing carbon film for clear defects at desired locations. The gallium ion beam may be used to help form the opaque regions on a clear mask, as well as to repair opaque and clear defects on the formed mask. The gallium ion beam is a positive ion beam, since gallium ions are themselves positive ions.
FIG. 3
shows a method
300
of the overall conventional approach that uses a gallium ion beam or other focused positive ion beam. First, the mask image is scanned using the positive ion beam to form the mask (
302
). This is also generally referred to as mask imaging or image scanning. Second, any defects in the mask are repaired, also with the positive ion beam (
304
). A difficulty with the conventional approach is that using a positive ion beam to perform mask scanning causes an excess of positive charge buildup on the mask, a phenomenon also referred to as the charge or charging effect. This positive charge buildup commonly reduces the effectiveness of the positive ion beam when performing mask scanning or repair.
One common problem is poor image quality, such as a faded or vague image, that results from the intensities of secondary ions and electrons being decreased as a result of the positive charge buildup. This is shown in FIG.
4
A. The mask
402
has clear regions
404
and
406
, and opaque regions
408
and
410
. There should also be a clear spot
412
within the opaque region
408
. However, it is not present, as indicated by the dotted-line nature of the spot
412
, because the positive ion beam is not sufficiently efficient to neutralize the accumulated positive charge for isolated spots and patterns. This may require that a carbon film to be deposited to reduce the charging effect for the clear spot
412
to be properly formed.
Another common problem is that the charge buildup causes diversion of the positive ion beam during mask repair, which results in a loss of edge-placement accuracy because the ion bombardment position has shifted away from the desired location due to the diversion. This is shown in FIG.
4
B. The mask
414
has a clear region
415
in which there are opaque regions
416
and
418
. There should also be clear spots
420
in the region
416
, and clear spots
422
and
424
in the region
418
. However, because of the charge buildup, the clear spots
420
,
422
, and
424
have not been formed, as indicated by the dotted-line nature of the spots
420
,
422
, and
424
.
To repair the mask, the ion beam is positioned over the desired locations of the spots
420
,
422
, and
424
. However, the charge buildup diverts the beam. This causes the spot
420
′ to be created within a newly formed opaque region
426
, instead of the spot
420
to be created within the opaque region
416
. Similarly, beam diversion causes the spots
422
′ and
424
′ to be created within newly formed opaque regions
428
and
430
, respectively, instead of the spots
422
and
424
to be created within the opaque
418
.
Therefore, there is a need for image scanning and mask repair that does not exhibit these problems. Specifically, there is a need for image scanning that does not result in charge buildup, and that does not result in vague or faded images. There is also a need for preventing ion beam diversion during mask repair. For these and other reasons, there is a need for the present invention.
SUMMARY OF THE INVENTION
The invention relates to the use of dual-focused ion beams for semiconductor image scanning and mask repair. A mask, such as a photomask, is imaged with either a focused negative ion beam, such as a focused oxygen ion beam, or a focused positive ion beam, such as a focused gallium ion beam. Mask imaging is also referred to as image scanning. Clear or opaque defects in the mask are repaired with the other ion beam that was not used in imaging of the mask. For instance, image scanning is performed with the focused negative ion beam to neutralize potential charge buildup, and mask repair is performed with the focused positive ion beam. The negative and position ion beams may be focused by an apparatus having a negative ion mechanism supplying negative ions, a positive ion mechanism supplying positive ions, a filter to select the desired ratio of the negative to the positive ions, and an aiming mechanism to focus the ions onto the mask.
The invention provides for advantages not found within the prior art. Imaging scanning does not result in positive charge buildup, or such buildup is neutralized, when a negative ion beam is used for mask scanning. This results in an image that is not faded or vague. Furthermore, any necessary mask repair can be performed by a positive ion beam without diversion of the beam, due to the lack of positive charge buildup. When a positive ion beam is used for mask scanning, a negative ion beam is us
Chin Chih Cheng
Hung Chang-Cheng
Lin Chin Hsiang
Lin Chuan-Yuan
Duda Kathleen
Taiwan Semiconductor Manufacturing Co. Ltd.
Tung & Associates
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