Abrading – Abrading process
Reexamination Certificate
2003-05-30
2004-07-20
Hail, III, Joseph J. (Department: 3723)
Abrading
Abrading process
C451S364000, C451S365000, C451S367000, C451S369000, C451S380000, C451S177000
Reexamination Certificate
active
06764383
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to methods and apparatuses for processing microfeature workpiece samples.
BACKGROUND
During the development and production of microfeature workpieces, such as wafers, engineers periodically conduct destructive tests of selected workpieces to evaluate the efficacy of new and/or existing processes. One technique for carrying out such tests includes cutting a sample section from the microelectronic wafer, then grinding the sample to expose a feature of interest. The feature of interest is then examined with a transmission electron microscope (TEM). If necessary, the processes performed on subsequent wafers can be adjusted to correct any defects identified during the TEM examination.
FIG. 1
is partially schematic illustration of an apparatus
10
for performing the foregoing process. Such an apparatus is available from South Bay Technology of San Clemente, Calif. The apparatus
10
includes a body
11
into which two micrometer legs
20
a
,
20
b
are threadably inserted. The apparatus
10
can optionally include a third micrometer leg
20
c
. A sample holder
30
is fixedly attached to the body
11
and supports a sample
40
, which is cut from a wafer. The apparatus
10
is then positioned adjacent to a grinding surface
51
of a grinding wheel
50
. While the grinding wheel
50
rotates (as indicated by arrow R), an edge
39
of the sample
40
protruding from the sample holder
30
contacts the grinding surface
51
, as do contact surfaces
21
of the micrometer legs
20
a
,
20
b
. Accordingly, the micrometer legs
20
a
,
20
b
can support the sample
40
in a fixed orientation relative to the grinding surface
51
while the sample
40
is ground down to expose the feature of interest.
FIG. 2
illustrates details of a sample
40
configured in accordance with the prior art. The sample
40
can have a plurality of active areas
43
, each of which includes features of interest. Typical features of interest include container-shaped capacitors
44
that are electrically coupled to contacts
45
and are separated from an intermediate contact
47
by gate runners
46
. It is typically desirable to grind the sample
40
down to a cleavage plane
48
to expose adjacent features within at least one of the active areas
43
. Because the cleavage plane
48
is generally parallel to significant, readily visible features of the sample
40
(such as an array edge
41
or a metal runner
42
), and because these features are typically aligned with a crystal plane of the wafer from which the sample
40
is extracted (as indicated by parallel axis X), it is relatively straightforward to precisely grind the sample
40
down to the cleavage plane
48
and expose the features of interest for TEM examination. For example, the sample
40
can be cut from its wafer by eye (i.e., without using a precise, machine-guided alignment process) so that the edge
39
of the sample
40
is at least approximately parallel to the cleavage plane
48
. The operator can then iteratively: (a) adjust one of the micrometer legs
20
a
or
20
b
(
FIG. 1
) relative to the other; (b) grind the sample
40
; and then (c) examine the edge of the sample
40
with reference to the array edge
41
, the metal runner
42
, or another easily visible feature parallel to the cleavage plane
48
. Accordingly, the operator can orient the edge
39
of the sample
40
to be parallel with the cleavage plane
48
. Once this orientation is obtained, the sample
40
can be ground down, as discussed above, until the features of interest at the cleavage plane
48
are exposed.
As the semiconductor industry moves to fit more active areas
43
into each wafer, some wafers have active areas
43
oriented such that the desired cleavage plane
48
exposed during destructive testing is no longer aligned with either the crystal plane (e.g., the X axis) or the easily visible features (e.g., the array edge
41
and/or the metal runner
42
) of the sample
40
. As a result, the initial cut that forms the edge
39
of the sample
40
is made at a significant angle relative to the X direction and the easily visible features. This operation can produce an initial cut that is misaligned by several degrees relative to the desired cleavage plane
48
. Such a large misalignment is not easily corrected by the iterative method described above. For example, if the micrometer legs
20
a
,
20
b
, are adjusted to have significantly different lengths (to account for the initially misaligned cut), the corresponding contact surfaces
21
become highly faceted rather than flat (as indicated in an exaggerated fashion by phantom lines in FIG.
1
). When the faceted micrometer legs
20
a
,
20
b
are subsequently rotated for further adjustment, the relative offset between the legs becomes unpredictable because the contact surfaces
21
are faceted rather than flat. This in turn can cause the sample
40
to be misoriented. If the sample
40
is not properly oriented, the desired features of interest will not be exposed during grinding, defeating the purpose for forming the sample.
REFERENCES:
patent: 3835590 (1974-09-01), Hoffman
patent: 5882156 (1999-03-01), Hetzler
Chandler Phillip L.
Fiechter Mark J.
Green Colin A.
Hail III Joseph J.
McDonald Shantese
Micro)n Technology, Inc.
Perkins Coie LLP
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