Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2000-03-14
2002-01-01
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C250S492210
Reexamination Certificate
active
06335129
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for repairing a pattern defect on a photo mask, the photo mask repaired by the repairing method, and a manufacturing method of semiconductor devices employing the repaired photo mask. The photo mask may include a phase shift mask.
2. Description of the Related Art
In the manufacturing method of the semiconductor devices such as large scale integrations (LSls), very large scale integrations (VLSIs), ultra large scale integrations (ULSIs), and giga scale integrations (GSIs), a set of photo masks or reticles is required for photolithography steps. Each of the photo masks is composed of predetermined patterns made of a light-shielding layer or phase shift layer arranged on a transparent mask substrate, such as a quartz substrate. During the fabrication process of the photo masks, miscellaneous microscopic defects
6
a
,
6
b
,
6
c
may be created on the mask substrate as shown in
FIGS. 1A
,
1
B and
1
C, for example. In each of
FIGS. 1A
to
1
C, three lines
3
a
,
3
b
, and
3
c
made of the light-shielding layer are shown, sandwiching spaces
4
and
4
between them. In
FIG. 1A
, a defect
6
a
protruding from the left edge of line
3
b
is shown. In
FIG. 1B
, an isolated defect
6
b
is shown, but very close to the left edge of line
3
b
. And in
FIG. 1C
, an isolated defect
6
c
is shown disposed midway between lines
3
a
and
3
b
. The defects
6
a
,
6
b
,
6
c
can be commonly evaporated and eliminated when exposed to a laser beam. As a result of the exposure to a laser beam, the left edge of line pattern
3
b
may develop “a mouse-nip” or “a rat-bite” as shown in FIG.
2
A. Or, although not shown, the left edge of line pattern
3
b
may develop a peeling. Or, an edge-roughness may be created on the left edge of line
3
b
as shown in
FIG. 2B
, which fails to finish in a desired normal line shape. As the feature size of such a photo mask pattern becomes significantly finer and finer, its repairing process at a high accuracy will be very difficult with a laser beam scanning precisely along the edge of the line pattern. Also, since the focusing of the laser beam is limited, the pattern defect repairing at higher accuracy, which may require a laser beam diameter finer than 0.5 &mgr;m, will thus be a troublesome task.
Also, mask repairing for removing defects may be carried out by a sputtering method using a focused ion beam (FIB). It is known that when the ion beam is directed to an irradiation area on the mask substrate made of quartz, its gallium (Ga) ions from an ion source are implanted into the quartz substrate, which generates gallium stains and hence decreases the transparency of the substrate. Moreover, the diffused FIB and the beam expansion of the FIB may result in excessive etching around the perimeter of the microscopic defect that needs to be eliminated. The excessive etching generally produces V-shaped grooves around the periphery of the microscopic defect, which are also known as “riverbeds.”
For solving the above problems, etching a chromium (Cr) film by “a gas assisted FIB etching process” is proposed as the pattern defect repairing method for removing the microscopic defect generated on a chromium mask. (K. Aita et al., SPIE, vol. 2512, p. 412 (1995), and J. David Casey, Jr. et al., SPIE, vol. 3096, pp. 322-332 (1997)). Here, the chromium mask has the light-shielding layer of a chromium (Cr) film or a chromium compound film such as chromium oxide (CrO
x
) film for delineating the required pattern on the quartz substrate. By the gas assisted FIB etching process, the gallium stains or riverbeds are reported to have been eliminated. It is reported that a mask pattern repaired by the above-mentioned pattern defect repairing method could produce an acceptable image level projected with an i-line at a wavelength of 365 nm. In the gas assisted FIB etching process, an etching gas is employed with a high selectivity of etching rates between the mask substrate and the chromium film or the chromium oxide film.
However, it was found that, in finer masks used for exposure by Deep UV (DUV) rays or further shorter wavelength rays, the chromium film repaired by the gas assisted FIB etching process still has noticeable damages to the mask substrate, attributable to the gallium stains or the riverbed.
FIG. 3
is a plan view of a repaired photo mask corresponding to
FIG. 1A
, which has been repaired by the gas assisted FIB etching process. The chromium mask
1
has an etching burn
5
a
generated at the aperture
4
, very closely disposed to the left edge of line
3
b
, from removing the microscopic defect
6
a
with the gas assisted FIB etching process.
FIG. 4
is a diagram showing the image intensity profile taken along the line III—III of
FIG. 3
on a wafer on which an image of the repaired mask pattern is projected. The ordinate in
FIG. 4
represents the intensity of the projected image and the abscissa represents locations on the wafer (along a predetermined axis, such as the X axis). In
FIG. 4
, “S” represents the position of the repaired space between lines
3
a
and
3
b
, and “L” represents the position of line
3
b
. It is assumed that the exposure conditions in a stepper loading the chromium mask (reticle) are as follows:
[007]
the exposure wavelength
&lgr; = 248 nm;
[008]
the aperture number
NA = 0.6; and
[009]
the coherence factor
&ggr; = 0.75.
As apparent from
FIG. 4
, the intensity at the etching burn
5
a
in the aperture of the repaired mask is decreased by more than 20% from that of a non-defect region of the mask. In this way, the unrequired etching burn
5
a
was unfavorably transferred onto the wafer.
The gas assisted FIB etching process may rarely be effective for repairing microscopic defect on a phase shift mask when it is made of a silicon based material such as molybdenum silicide (MoSi, or MoSi
x
) and used as the film material for producing the light-shielding pattern or the phase shifter pattern. In a step of imaging with the FIB, the phase shifter film may easily be charged up thus interrupting the projection of an image at a higher signal to noise (S/N) ratio and rendering the end point of the etching process hardly detectable with a higher accuracy.
SUMMARY OF THE INVENTION
The present invention has been achieved with a view of the foregoing features and its object is to provide a method for repairing a pattern defect, in which the damage against the transparent substrate of a mask is minimized.
Another object of the present invention is to provide a method for repairing a pattern defect, in which the etching of the surface of the transparent substrate of a mask is minimized.
It is still another object of the present invention to provide a method for repairing a pattern defect, suppressing a change in the image intensity through the mask, thereby having a favorable level of the wafer process margin.
It is still another object of the present invention to provide a photo mask having fine pattern and a high transmissivity, having uniform image intensity profiles.
It is still another object of the present invention to provide a method for manufacturing semiconductor devices having miniaturized feature sizes, with a favorable level of the process margin in the lithography process.
A first feature of the present invention involves a method for repairing a defect generated on a mask substrate. The defect may be isolated from normal patterns, or continuous excess patterns protruding from the edge of the normal pattern. More particularly, the method for repairing the pattern defect according to the first feature of the present invention comprises the steps of: (a) determining the irradiation area of an ion beam directed towards a defect by narrowing the irradiation area by a predetermined distance inwardly from the edge of defect; (b) focusing the ion beam onto its irradiation area to remove a part of the defect from its surface so as to leave a thin layer of the defect on the mask substrate;
Asano Mitsuyo
Kanamitsu Shingo
Finnegan, Henderson Farabow, Garrett and Dunner L.L.P.
Rosasco S.
LandOfFree
Method for repairing pattern defect, photo mask using the... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for repairing pattern defect, photo mask using the..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for repairing pattern defect, photo mask using the... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2836893