Auto tilt stage

Details Auto tilt stage Auto tilt stage

2000-09-29

2002-06-18

Mack, Ricky (Department: 2873)

Optical: systems and elements

Optical modulator

Light wave temporal modulation

Reexamination Certificate

active

06407850

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of semiconductor integrated circuit (IC) manufacturing, and more specifically, to an apparatus for automatically tilting a sample to a desired angle for processing, measurement, or inspection.
2. Discussion of Related Art
During semiconductor IC manufacturing, failure analysis (FA) of a product is often performed at various stages of processing to locate failures and identify causes. The FA may include physical or chemical techniques. A common type of physical FA is to cross-section a Silicon wafer containing the product for analysis in a transmission electron microscope (TEM). A TEM can resolve structural details in the devices that are on the order of 2 Angstroms.
TEM samples may be prepared with various orientations to reveal different parts of the device structure. Examples are shown in FIG.
1
(
a
) and FIG.
1
(
b
). A TEM sample
130
has a length
110
of about 3 millimeters, a height
112
of about 1 millimeter, and a depth
114
of about 20 micrometers. The TEM sample
130
has a device layer
103
formed on a substrate
105
. A platinum cap
107
is deposited over a region of interest
116
. Ion milling is used to remove material from one side
133
of the Platinum cap
107
. Then ion milling is used to remove material from the other side
136
of the Platinum cap
107
. As a result, an area of interest
116
in the sample
130
is reduced to a thickness
118
of about 1000 Angstroms so electrons can penetrate to form an image. The platinum cap
107
is subsequently removed.
In a dual-beam focused ion beam (FIB) tool from FEI corporation, as shown in FIG.
2
(
a
), an ion beam
220
is used to sputter away material from the sample
230
while, at the same time, an electron beam
225
is used to monitor the progress. The electron beam
225
points downwards vertically while the ion beam
220
points downwards with an angle
265
from the vertical. In the XL820 model of the tool, the angle
265
is fixed at 52 degrees.
FIG.
2
(
a
) shows a sample
230
that is clamped in a vice
240
attached to a stage
260
. The sample
230
should be parallel to the ion beam
220
in order to be thinned down properly from the top down. In order to align the sample
230
with the ion beam
220
, a stage
260
on which the sample
230
rests must be tilted at an angle
275
. If the sample
230
is mounted perpendicularly relative to the stage
260
, as is desired, then the tilt angle
275
will be equal to a sample rotation angle
270
.
The sample
230
may be inadvertently misaligned in a vice
240
by an angle
280
from the vertical, as shown in FIG.
2
(
b
). In such a case, the sample
230
would not be mounted perpendicularly relative to the stage
260
.
One problematic consequence of sample misalignment is that the ion beam
220
may not be able to mill one side
233
of the sample
230
straight down since the tilt angle
275
of the XL820 stage
260
cannot go beyond 52 degrees. Another problem is that the electron beam
225
may not be able to monitor the progress of the ion milling if the side
233
being ion milled is not directly in the line of sight of the electron beam
225
. Milling “blindly” may result in poor control of depth and symmetry.
A similar problem may arise with misalignment of a sample
230
that is being converted from analysis with a scanning electron microscope (SEM) to analysis with a TEM. In a TEM sample, a deposited platinum cap
107
protects the top surface directly over a region of interest
116
, as shown in FIG.
1
(
a
) and FIG.
1
(
b
). However, a sample previously analyzed with a SEM will have platinum covering the face (not shown), as well as the top surface, of the region of interest
116
. As a result, the additional platinum protecting the face of the region of interest
116
cannot be milled of symmetrically since the stage
260
of the XL820 is unable to tilt to an angle
275
that exceeds 52 degrees.
A possible solution for handling a misaligned sample
230
is to modify the stage
260
to tilt at an angle
275
that is beyond the mill angle
265
of 52 degrees. However, such a modification would be costly and difficult to implement.
Thus, what is needed is an apparatus for automatically tilting a sample to a desired angle for processing, measurement, or inspection.


REFERENCES:
patent: 6335224 (2002-01-01), Peterson et al.
patent: 6337027 (2002-01-01), Humphrey

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