Methods of inspecting integrated circuit substrates using...

Details Methods of inspecting integrated circuit substrates using... Methods of inspecting integrated circuit substrates using...

1999-08-27

2003-02-25

Nguyen, Kiet T. (Department: 2881)

Radiant energy

Inspection of solids or liquids by charged particles

Electron probe type

C250S307000

Reexamination Certificate

active

06525318

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to methods of inspecting integrated circuit substrate, and more particularly to methods of inspecting integrated circuit substrates at intermediate stages of fabrication.
BACKGROUND OF THE INVENTION
As a design rule gets smaller in fabricating semiconductor devices, it becomes very difficult to form a contact hole which opens a predetermined portion of a semiconductor substrate. Accordingly, it is important to monitor whether or not a contact hole is formed properly on a semiconductor substrate. In particular, by effectively monitoring in-line the state, open or not-open, of a contact hole during fabrication of a semiconductor device, the time required for fabricating the semiconductor device can be reduced and the yield can be greatly enhanced.
However, conventional in-line monitoring of an open or not-open state of a contact hole has been performed manually by an operator using a general image measurement apparatus. In this case, a monitoring error may result from the manual operation and thus unreliable results may be obtained.
Also, in order to monitor the open or not-open state of a contact hole using the general image measurement apparatus, a high voltage of about 20 KV must be used. However, if a high voltage such as about 20 KV is used, it is not possible to precisely monitor the state, open or not-open, of a contact hole.
FIG. 1
is a schematic diagram illustrating a conventional electron beam inspection apparatus, and
FIG. 2
illustrates a semiconductor substrate used for determining whether a contact hole is in an open or not-open state. In detail, the electron beam inspection apparatus shown in
FIG. 1
includes an electron-beam gun
1
for supplying electron beams. The electron beams are emitted from the electron-beam gun
1
and are accelerated before passing through a gun aperture
3
. The electron beam inspection apparatus includes electron beam receiving means which allows an electron beam to move properly toward a sample, e.g., the surface of a semiconductor substrate, for scanning the semiconductor substrate. Here, a condenser lens
5
collimates the diverging electron beam
2
and the collimated electron beam
2
passes through an electrostatic octapole
7
for astigmatism correction and alignment. Then, the electron beam
2
having passed through the electrostatic octapole
7
passes through a beam adjusting aperture
9
and an icosapole deflector
11
. The electron beam
2
having passed through the beam adjusting aperture
9
and the icosapole deflector
11
passes through an objective lens
13
to then be incident on a sample
15
shown in FIG.
2
. Either a positive voltage or a negative voltage may be applied to the sample
15
in the electron beam inspection apparatus. An x-y stage (not shown) capable of moving in x and y axes directions and supporting the sample
15
is provided under the sample
15
.
In the electron beam inspection apparatus, secondary electrons emitted from the sample
15
after passing through the objective lens
13
are detected by a secondary electron detector
21
via an extraction electrode
17
and a Wien filter
19
. A positive voltage is applied to the extraction electrode
17
and a negative voltage is applied to the sample
15
so that the secondary electrons move to the secondary electron detector
21
via the Wien filter
19
to then be detected. The Wien filter
19
comprised of an electrostatic octapole and a 60° magnetic field deflector, removes opposed electric and magnetic deflections for the electron beam
2
. The sample
15
may be in the form of a semiconductor substrate
31
shown in
FIG. 2
, or a mask substrate (not shown). If the sample
15
is a mask substrate having an electron beam transmission area, the electron beam
2
is received by a transmitted electron detector
25
via an electrostatic transmission lens
23
to then be detected.
The possibility of determining in-line the state, open or not-open, of a contact hole will now be evaluated in the case of testing the sample semiconductor substrate shown in
FIG. 2
with the electron beam inspection apparatus shown in FIG.
1
. First, the sample semiconductor substrate shown in
FIG. 2
tested with the electron beam inspection apparatus shown in
FIG. 1
will be described. In detail, a gate oxide layer (not shown), a gate electrode consisting of a polysilicon layer
33
and a tungsten silicide layer
35
, and an insulation layer
37
for insulating the gate electrode are sequentially formed on a p-type silicon substrate
31
having an n-type impurity region
32
to be a source and a drain. Spacers
39
are formed at both side walls of the stacked structure of the gate electrode and the insulation layer
37
. A contact hole
41
which exposes the silicon substrate
31
between the spacers
39
is formed. Next, in-line monitoring of whether a contact hole formed in the semiconductor substrate shown in
FIG. 2
is in an open or not-open state is performed using the electron beam inspection apparatus shown in FIG.
1
. Here, if an unetched material layer
43
shown in
FIG. 2
(e.g., an oxide or nitride layer) is present in the contact hole, primary electrons (represented by reference numeral
45
in
FIG. 2
) do not flow properly to the silicon substrate
31
so that electrons accumulate on the surface of the unetched material layer
43
. Then, a large amount of secondary electrons (represented by reference numeral
47
in
FIG. 2
) are emitted from the surface of the silicon substrate
31
due to repulsive force of electrons. Depending on a difference in secondary electron yields, a brighter (white) or darker (black) image is displayed for a portion where a large amount of secondary electrons
47
are emitted, that is, a portion where the unetched material layer
43
is present, compared to portions where the unetched material layer
43
is not present.
Notwithstanding this method of performing in-line inspection, it may still be difficult to reliably detect the presence of unetched material. For example,
FIG. 3
illustrates movement of primary and secondary electrons when performing in-line monitoring of a contact hole using the electron beam inspection apparatus shown in FIG.
1
. In
FIG. 3
, the same reference numerals as those of
FIG. 2
denote the same elements. In detail, the primary electrons
45
incident on the substrate
31
are activated within the unetched material layer
43
in the contact hole and in the substrate
31
and then move toward the lower portion of the substrate
31
. Then, since the difference in secondary electron yields between a portion with the unetched material layer
43
and a neighboring portion without the unetched material layer
43
is not large, the bright and dark sections of the image are not as distinguishable. Thus, it may be difficult to inspect the state, open or not-open, of the contact holes shown in
FIGS. 2 and 3
, by using the electron beam inspection apparatus shown in FIG.
1
.
FIGS. 4 through 6
illustrate images of contact holes observed by a high-voltage electron beam inspection apparatus in the case when the unetched material layer shown in
FIG. 3
is an oxide layer. In detail,
FIGS. 4A through 4C
show that the unetched material layer
43
shown in
FIG. 3
(i.e., an oxide layer) is removed by etching. Specifically, in view of a flat zone of a semiconductor wafer,
FIG. 4A
shows a cell portion present on the top of the semiconductor wafer,
FIG. 4B
shows a cell portion in the center thereof, and
FIG. 4C
shows a cell portion at the bottom thereof. In these cases, the oxide layer on the edge portion of the cell is not completely etched, thus preventing the contact hole from being opened, so that a bright image is displayed. The oxide layer of the interior portion of the cell is completely etched, so that a dark image is displayed.
FIGS. 5A through 5C
show cases where the thickness of the unetched material layer
43
is 300 Å. Here, like in
FIGS. 4A through 4C
, in view of a flat zone of a semiconductor wafer,
FIG. 5A
shows a cel

Affiliated with

Also associated with

Rating

Methods of inspecting integrated circuit substrates using... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Methods of inspecting integrated circuit substrates using..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Methods of inspecting integrated circuit substrates using... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3126115