Semiconductor structures and manufacturing methods

Details Semiconductor structures and manufacturing methods Semiconductor structures and manufacturing methods

2000-12-08

2003-03-25

Thomas, Tom (Department: 2811)

Semiconductor device manufacturing: process

With measuring or testing

Optical characteristic sensed

C438S014000, C438S401000, C438S462000, C257S797000, C257S798000, C250S548000, C250S557000, C356S401000

Reexamination Certificate

active

06537836

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates generally to semiconductor structures and manufacturing methods and more particularly to alignment techniques used therein.
As is known in the art, semiconductor integrated circuits are manufactured using a series of process steps which require proper alignment of the semiconductor wafer. Many alignment systems use reflected light from profile patterns formed on the surface of the semiconductor wafer to determine the location of the wafer. Such an arrangement is shown in FIG.
1
. An alignment illumination
10
, here a cross, is focused onto the surface
12
of the semiconductor wafer
14
using an optical system
16
. A portion of the light is reflected from the surface of the semiconductor wafer is directed by the optical system
16
to a detector arrangement
20
. The wafer
14
has formed along one portion thereof an alignment mark
22
, here shown diagrammatically as a series of grooves
24
etched into the surface
12
of the wafer
14
. As the wafer
14
is scanned horizontally, the detector arrangement
20
produces waveforms which enable detection of the alignment of the wafer
14
relative to the optical system
16
.
More particularly, and referring also to
FIG. 2
, there are shown four sites, i.e., site
1
, site
2
, site
3
and site
4
of alignment marks on each of both the upper and lower peripheral portions of a semiconductor wafer
14
. Each one of the sites includes two sets of lines
13
, one at +45 degrees with respect to the vertical, or Y axis, and the other set of lines
15
being at −45 degrees with respect to the Y axis. The alignment illumination projected by the optical system (
FIG. 1
) onto the surface of the wafer is a cross, such as used in the MICRASCAN equipment manufactured by Silicon Valley Group (SVG), San Jose, Calif. A “standard” alignment mark, in one half of a site, for the MICRASCAN III equipment is shown in FIG.
3
and consists of wide stripes at a 45 degree angle separated by variable spacing. Another version is shown in FIG.
4
and is made up of lines at the locations where the “standard” mark has the edges of its stripes. The size of both versions is 60×60 micrometers. The alignment marks etched into the surface of the wafer are shown in
FIG. 2
as a pair orthogonal sets of a series of parallel lines, only one of the two sets being shown in
FIGS. 3 and 4
.
Referring again to
FIG. 1
, the alignment illumination, a cross is projected onto the surface
12
of wafer
14
with the pair of intersecting arms of the cross being disposed nominally orthogonal to the lines in each of the sites. The cross-shaped light (i.e., the alignment illumination) is projected by the optical system
16
onto, and scanned across the site (
FIG. 2
) along the X direction indicated on the surface
12
of the wafer
14
. The optical system
16
includes a prism (
FIG. 1
) which directs a portion of the light reflected surface
12
of the wafer
14
onto a detector arrangement
20
shown diagrammatically in FIG.
1
. Thus, as indicated, there are four detectors
22
1
,
22
2
,
22
3
, and
22
4
; one pair
22
1
and
22
2
being disposed along an axis +45 degrees with respect to the Y axis and one pair
22
3
and
22
4
being disposed along an axis −45 degrees with respect to the Y axis. The pair of detectors
22
1
, (i.e., “Left +45”) and
22
2
(i.e., “Right +45”) is used for detection of light reflected by lines
13
at +45 degrees with respect to the Y axis and the pair of detectors
22
3
(i.e., “Left −45”) and
22
4
(i.e., “Right −45”) are used to detect light reflected by lines
15
at −45 degrees with respect to the Y axis.
More particularly, to determine the location of an alignment site, two marks
13
,
15
(FIG.
1
); one oriented at +45 degrees and one at −45 degrees with respect to the Y axis, are required. The alignment marks
13
,
15
are scanned by the optical system with an X shaped illumination, as described above. The light reflected from the surface of the wafer and the alignment lines is detected in the dark field mode, i.e., only light scattered from the marks at an angle is analyzed. Two detectors
22
1
and
22
2
record simultaneously the reflected light; one detector
22
2
located to the right side and one detector
22
1
to the left side of the mark's edge. When scanning the +45 degree lines
13
, the set of detectors
22
1
and
22
2
is activated and when the −45 degree lines
15
are scanned, the set of detectors
22
3
,
22
4
are activated. More particularly, referring to
FIG. 1
, when the alignment illumination is over the +45 degree lines
13
of site
1
, the “Left +45” and “Right +45” detectors
22
1
and
22
2
are activated and the “Left −45” and “Right −45” detectors
22
3
and
22
4
, are deactivated. When the alignment illumination moves over the −45 degree lines
15
of site
1
, the “Left −45” and “Right −45” detectors
22
3
and
22
4
are activated and the “Left +45” and “Right +45” detectors
22
1
and
22
2
are deactivated. It is noted that with such an arrangement, each alignment site is made up of a pair of spatially separated sets
13
,
15
of parallel orthogonal lines with two sets in the site being sequentially activated/deactivated detectors. Such spatial separation increases the area required for an alignment site.
SUMMARY OF THE INVENTION
In accordance with the present invention, a semiconductor body is provided having an alignment mark comprising a pair of sets of parallel lines disposed on the semiconductor body, the parallel lines in one of the sets being disposed orthogonal to the parallel lines in the other one of the set, the two sets of parallel lines being in an overlaying relationship.
With such structure, the same amount of wafer surface area enables twice as many alignment sites. Thus, the arrangement allows the alignment system to acquire twice the amount of metrology information during the same alignment scanning process to thereby increase the alignment quality. Further, there is no loss of through-put because the same time is used for scanning the sites as in the system described above.
In accordance with another embodiment, a method is provided for detecting an alignment mark on a semiconductor body. The method includes providing the alignment mark on the semiconductor body, such alignment mark comprising a pair of sets of parallel lines disposed on the semiconductor body, the parallel lines in one of the sets being disposed orthogonal to the parallel lines in the other one of the set, the two sets of parallel lines being in an overlaying relationship. The alignment illumination comprising a pair of orthogonal, lines of impinging light is scanned over the surface of the alignment mark, one of such pair of impinging light lines being orthogonal to, and laterally displaced from, the other one of such pair of impinging light lines, impinging light being reflected by the alignment lines in the surface of the semiconductor when such impinging light is over to provide a pair of laterally displaced beams of reflected light. The method includes detecting in each one of a pair of laterally spaced detectors a corresponding one of the laterally displaced beams of reflected light.
In accordance with another embodiment of the invention, apparatus is provided for detecting an alignment mark on a semiconductor body, such alignment mark. The alignment mark comprises a pair of sets of parallel lines disposed on the semiconductor body, the parallel lines in one of the sets being disposed orthogonal to the parallel lines in the other one of the set, the two sets of parallel lines being in an overlaying relationship. The apparatus includes an optical system for scanning an alignment illumination comprising a pair of orthogonal, lines of impinging light over the surface of the alignment mark, one of such pair of impinging light lines being orthogonal to, and laterally displaced from, the other one of such p

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