U.S. patent application number 10/499416 was filed with the patent office on 2005-03-17 for reduction of electric-field-induced damage in field-sensitive articles.
Invention is credited to Durben, Joseph A., Lindsley, Robert K., Rider, Gavin Charles.
Application Number | 20050056441 10/499416 |
Document ID | / |
Family ID | 32072926 |
Filed Date | 2005-03-17 |
United States Patent
Application |
20050056441 |
Kind Code |
A1 |
Rider, Gavin Charles ; et
al. |
March 17, 2005 |
Reduction of electric-field-induced damage in field-sensitive
articles
Abstract
A continuously electrically-conductive container (104) contains
an electrically-insulating support (110) for holding an
electric-field-sensitive article (112), such as a reticle, so that
the article is shielded from external electric fields and is not in
electrical contact with a conductive container wall (106). A SMIF
pod (302, 510) comprises an electrically conductive container for
holding an electric-field-sensitive article. A system (502) has
boundary walls (504) that form a chamber (506) for a controlled
environment. The system includes a load port (508) for receiving a
SMIF pod and an end effector (522) made of insulating material for
moving a field-sensitive article (516) within the chamber to and
from the SMIF pod. An ionizer (542) neutralizes electric charges on
the field-sensitive article.
Inventors: |
Rider, Gavin Charles; (Avon,
GB) ; Durben, Joseph A.; (Woodland Park, CO) ;
Lindsley, Robert K.; (Colorado Springs, CO) |
Correspondence
Address: |
PATTON BOGGS
1660 LINCOLN ST
SUITE 2050
DENVER
CO
80264
US
|
Family ID: |
32072926 |
Appl. No.: |
10/499416 |
Filed: |
November 1, 2004 |
PCT Filed: |
October 1, 2003 |
PCT NO: |
PCT/US03/30991 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60319585 |
Oct 1, 2002 |
|
|
|
60319665 |
Nov 2, 2002 |
|
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Current U.S.
Class: |
174/387 ;
174/388 |
Current CPC
Class: |
H01L 21/67778 20130101;
H01L 21/67359 20130101; H01L 21/67383 20130101; H01L 21/67396
20130101; H01L 21/67763 20130101; H01L 21/67386 20130101; H01L
21/67353 20130101 |
Class at
Publication: |
174/035.00R |
International
Class: |
H05K 009/00 |
Claims
1. An apparatus for holding a field-sensitive article comprising: a
conductive container having an electrically-conductive container
wall said container wall defining an enclosure; and an
electrically-insulating support located within said enclosure, said
electrically-insulating support configured for supporting a
field-sensitive article within said enclosure without electrically
contacting said electrically-conductive container wall; there being
no significant source of microwave energy within said
enclosure.
2. An apparatus as in claim 1 wherein said electrically-conductive
container wall comprises substantially only conductive
material.
3. An apparatus as in claim 1 wherein said electrically-conductive
container wall comprises substantially only metal.
4. An apparatus as in claim 1 wherein said electrically-conductive
container wall comprises substantially stainless steel.
5. An apparatus as in claim 1 wherein said electrically-insulating
support comprises substantially only insulative material.
6. An apparatus as in claim 1 wherein said electrically-insulating
support comprises ceramic material.
7. An apparatus as in claim 1 wherein said electrically-insulating
support comprises polymer plastic.
8. An apparatus as in claim 1 wherein a controlled electrical
potential is connected to said conductive container.
9. An apparatus as in claim 1 wherein an electrical connector
connects said conductive container to a controlled electrical
potential.
10. An apparatus as in claim 9 wherein said electrical connector
comprises one from a group consisting of an electrical conductor
and a static dissipative material.
11. An apparatus as in claim 1 wherein said conductive container
comprises a portion of a SMIF pod.
12. An apparatus as in claim 11 wherein said
electrically-insulating support is configured for supporting a
reticle.
13. An apparatus as in claim 11 wherein an ionizer is located
external to said enclosure for neutralizing an electric charge.
14. An apparatus as in claim 11 wherein a portion of said
electrically-conductive container wall is substantially
transparent.
15. A system for handling a field-sensitive article, said system
having boundary walls, a chamber defined by said boundary walls, a
load port for holding and operating a SMIF pod, a SMIF pod, and an
effector for moving an article within said chamber to or from an
open SMIF pod, wherein: said SMIF pod a conductive container and an
electrically-insulating support located within said conductive
container, said electrically-insulating support configured for
supporting a field-sensitive article without electrical contact to
said conductive container; and said effector being an
electrically-insulating effector configured for moving a
field-sensitive article.
16. A system as in claim 15 wherein said electrically-insulating
chamber-internal support is configured for supporting a
field-sensitive article within said chamber without electrical
contact to said boundary walls.
17. A system as in claim 16 wherein said electrically-insulating
chamber-internal support comprises substantially only insulative
material.
18. A system as in claim 15 having an internal panel located within
said chamber wherein said internal panel is an
electrically-insulating internal panel.
19. A system as in claim 18 wherein said electrically-insulating
internal panel comprises substantially only insulative
material.
20. A system as in claim 15 wherein said boundary walls are
substantially electrically conductive.
21. A system as in claim 15 wherein said boundary walls comprise
substantially only electrically conductive material.
22. A system as in claim 15 wherein said boundary walls comprise
static dissipative material.
23. A system as in claim 15 wherein said boundary walls are
connected to a controlled electrical potential.
24. A system as in claim 15 wherein said electrically-insulating
support is configured for supporting a reticle and said effector is
configured for moving a reticle.
25. A system as in claim 15 wherein an ionizer is located within
said chamber for neutralizing an electric charge.
26. A system as in claim 15 wherein a portion of said boundary
walls is substantially transparent.
27. A system for handling a field-sensitive article, said system
having boundary walls, a chamber defined by said boundary walls,
and a container within said chamber for holding a field-sensitive
article, wherein: said container comprises an
electrically-conductive container wall, said container wall
defining an enclosure; an electrically-insulating support located
within said enclosure, said electrically-insulating support
configured for supporting a field-sensitive article within said
enclosure without electrically contacting said
electrically-conductive container wall; and an ionizer for
providing charge-neutralizing ions in said chamber.
28. An electrically-insulating support for a reticle, said support
having an insulating member wherein there is no conducting or
static dissipative material close enough to said reticule to cause
a concentration of electrical field lines sufficient to cause
field-induced damage.
29. An electrically-insulating support as in claim 28 wherein there
is no conducting or static dissipative material within 2 microns of
said reticule.
30. An electrically-insulating support as in claim 28 wherein there
is no conducting or static dissipative material within 2 mm of said
reticule.
31. An electrically-insulating support as in claim 28 wherein there
is no conducting or static dissipative material within 10 mm of
said reticule.
32. A method of avoiding field-induced damage of a field-sensitive
article by holding said field-sensitive article with an
electrically-insulating support located within an enclosure defined
by an electrically-conductive container wall of a conductive
container so that said field-sensitive article does not
electrically contact said electrically-conductive container wall
and is not exposed to any significant source of microwave
radiation.
33. A method as in claim 32 of: locating said conductive container
in a chamber having a controlled environment; generating ions in
said controlled environment in said chamber; and opening said
conductive container in said controlled environment.
34. A method as in claim 32 of: locating said conductive container
in a chamber having a controlled environment; opening said
conductive container in said controlled environment; and moving
said field-sensitive article out of said conductive container into
said controlled environment using an electrically-insulating
effector.
35. A method of protecting a field-sensitive reticule from
electric-field induced damage, by keeping all conductive or static
dissipative material far enough away from said reticule to prevent
a concentration of electrical field lines sufficient to cause
field-induced damage to said reticle.
36. A method as in claim 35 wherein said protecting is keeping said
conducting or static dissipative material at least 2 microns away
from said reticule.
37. A method as in claim 35 wherein said protecting is keeping said
conducting or static dissipative material at least 2 mm away from
said reticule.
38. A method as in claim 35 wherein said protecting is keeping said
conducting or static dissipative material at least 10 mm away from
said reticule.
Description
FIELD OF THE INVENTION
[0001] This invention relates to the field of controlling and
reducing electric-field-induced damage during integrated circuit
fabrication and, in particular, to protection against
electric-field-induced damage in reticles.
BACKGROUND OF THE INVENTION
[0002] Statement of the Problem
[0003] Certain objects in semiconductor manufacturing, such as
packaged devices, silicon wafers and reticles are prone to damage
by field-induced potentials. A reticle is an optically clear
ceramic substrate (typically quartz) having a thin metal (e.g.,
chromium) coating in which a pattern has been formed. Field-induced
damage can occur even without any electrical contact being made
with the sensitive object. The mechanism of damage has been widely
identified as resulting from electrostatic discharge (ESD), a
mechanism that occurs when the voltage between electrically
isolated parts within a device or object is raised by field
induction to a point at which a discharge occurs between them.
There is a threshold for the occurrence of such discharge, below
which the risk of damage is considered to be small. The various
thresholds for discharge in different types of object have been
estimated and "safe" levels for electric field around them have
been prescribed in several places, such as the International
Technology Roadmap for Semiconductors.
[0004] Much of the information available about static control was
developed for spark avoidance where there is an explosion risk,
such as in the handling of flammable liquids and vapors. Spark
avoidance has also been a priority in semiconductor manufacturing
since the radio emissions from spark events can cause data
corruption in the electronics used to control process
equipment.
[0005] To minimize the risk of ESD, it is common practice to
control static charge levels in the environments where
field-sensitive objects are handled. The guidance given by bodies
such as the ESD Association of America for the control of ESD
includes the avoidance of all insulators that are not necessary for
the process, the use of static dissipative materials wherever the
use of metal is inappropriate (e.g., for transparency or chemical
inertness), and electrical grounding of all conductive or
dissipative parts of the equipment through a common ground point.
It is common practice to control static charge levels in handling
environments. For example, grounded static dissipative materials
are used in semiconductor manufacturing facilities (herein "fabs")
to minimize tribocharging of reticle pods and other handling
equipment.
[0006] Electrostatic buildup on and discharge from reticles can
damage or destroy the reticles, and concern about electrostatic
damage has been increasing in recent years as device geometries get
finer and the requirements for reliability become more
stringent.
[0007] It is known to store and transfer workpieces, such as
semiconductor wafers and reticles, using a standard mechanical
interface, or SMIF, system. In conventional SMIF pods, it is known
to have conductive contacts on the reticle support in the pod door
to dissipate electrostatic charge from the bottom surface of the
reticle. The charge is then grounded through the pod door.
Similarly, conductive contacts are provided on the reticle retainer
in the pod shell to dissipate electrostatic charge from the top
surface of the reticle. The charge from the top surface is then
grounded through the pod shell. The pod shell, therefore, typically
includes static dissipative materials to provide a path to ground
for the static charge from the top surface of the reticle. Another
type of reticle container provides a conductive path between the
reticle retainer and the reticle supports, as disclosed in U.S.
Pat. No. 6,513,654, issued Feb. 4, 2003, to Smith et al. This
allows electrostatic charge to be dissipated from the top surface
of the reticle without the use of static dissipative materials in
the pod shell.
[0008] Field-sensitive objects often carry electrical charge. An
object can acquire a charge through tribocharging during handling,
through normal processing such as rinsing with deionized water,
through ionizer malfunction and by other events. Not all such
situations can be avoided, particularly when charging is an
unfortunate by-product of the process itself (such as washing). It
is known to provide air ionizers to neutralize electric charges on
objects.
SUMMARY OF THE INVENTION
[0009] The present invention helps to the problems outlined above
by providing apparati, systems and methods for avoiding
electric-field-induced damage to field-sensitive articles.
[0010] A first basic embodiment of an apparatus in accordance with
the invention for holding a field-sensitive article comprises a
conductive container having an electrically-conductive container
wall that defines an enclosure. A conductive container functions as
a Faraday cage by substantially preventing an external electric
field from passing through the conductive container wall. As a
result, the external electric field has no influence in the
enclosure within the conductive container or in any objects within
the container. Typically, the electrically-conductive container
wall comprises substantially only conductive material, but the
conductive container wall can also be made from non-conducting
material that is coated or embedded with conductive material to
make the wall electrically conducting. Another important element of
an apparatus in accordance with the invention is an
electrically-insulating support located within the enclosure. The
electrically-insulating support is configured for supporting a
field-sensitive article within the enclosure so that the
field-sensitive article is not in electrical contact with the
electrically-conductive container wall or with other conductive or
static dissipative objects. By keeping the field-sensitive article
electrically isolated and distant from the conductive wall of the
container (Faraday cage), an apparatus in accordance with the
invention further protects a field-sensitive article, such as a
reticle, that is possibly carrying an electric charge before it is
moved into the conductive container against the risk posed by a
charged object being in close proximity to a fixed-potential
surface. Conventional systems of the prior art typically support
the reticle on static dissipative supports. Preferably, an
electrically-insulating support in accordance with the invention
comprises substantially only insulative material; such as
insulative ceramic or polymer plastic material.
[0011] A conductive container in accordance with the invention
usually is connected to a controlled potential, preferably a fixed
potential, such as electrical ground. Certain embodiments include a
distinct controlled electrical potential connected to the
conductive container. Accordingly, certain embodiments comprise an
electrical connector, such as an electrical conductor or a static
dissipative connector, connecting the conductive container to a
controlled electrical potential.
[0012] In some embodiments, a conductive container is a portion of
a SMIF pod. In some embodiments, the electrically-insulating
support within the enclosure of the container is configured for
supporting a reticle. An apparatus in accordance with the invention
optionally includes an ionizer located external to the enclosure
for neutralizing an electric charge. It is located within the
chamber to neutralize charges that might be on a field-sensitive
article before or after it is placed in the enclosure of the
container, as well as neutralize charges that might be on
insulative internal structures in the chamber or within the
conductive container. In some embodiments, a portion of the
electrically-conductive container wall is substantially
transparent.
[0013] Another basic embodiment comprises a system for handling a
field-sensitive article. The system includes boundary walls, a
chamber defined by the boundary walls, a load port for holding and
operating a SMIF pod, a SMIF pod, and an effector for moving an
article within the chamber to or from an open SMIF pod. In
accordance with the invention, the SMIF pod comprises a conductive
container and an electrically-insulating support located within the
conductive container. The electrically-insulating support is
configured for supporting a field-sensitive article without
electrical contact to the conductive container. The effector is an
electrically-insulating effector configured for moving a
field-sensitive article. Some embodiments further include an
electrically-insulating chamber-internal support configured for
supporting a field-sensitive article within the chamber without
electrical contact to the boundary walls. In preferred embodiments,
electrically-insulating structures located within the chamber
boundary walls, such as the electrically-insulating
chamber-internal support, comprise substantially only insulative
material. Some embodiments further comprise an
electrically-insulating internal panel located within the chamber.
Preferably, the electrically-insulating internal panel comprises
substantially only insulative material. In some embodiments, the
boundary walls are substantially electrically conductive, often
being made from electrically conductive material. In other
embodiments, the boundary walls are mainly static dissipative. In
preferred embodiments of the system, the boundary walls are
connected to a controlled electrical potential or to electrical
ground. In some embodiments, the electrically-insulating support is
configured for supporting a reticle and the effector is configured
for moving a reticle. Some systems in accordance with the invention
further an ionizer located within the chamber for neutralizing a
electric charges. To provide visibility into the system, some
embodiments include at least a portion of the boundary walls that
is substantially transparent.
[0014] Still another basic embodiment for handling a
field-sensitive includes boundary walls, a chamber defined by the
boundary walls, and a container within the chamber for holding a
field-sensitive article. The container comprises an
electrically-conductive container wall in accordance with the
invention that defines an enclosure. The system also includes an
electrically-insulating support located within the enclosure and
configured for supporting a field-sensitive article within the
enclosure so that the field-sensitive article is not come into
electrical contact with the electrically-conductive container wall
or with other conductive or static dissipative objects. The system
further includes an ionizer for providing charge-neutralizing ions
in the chamber.
[0015] A method of avoiding field-induced damage of a
field-sensitive article includes holding the field-sensitive
article with an electrically-insulating support located within an
enclosure defined by an electrically-conductive container wall of a
conductive container so that the field-sensitive article does not
electrically contact the electrically-conductive container wall.
Some methods in accordance with the invention further include
locating the conductive container in a chamber having a controlled
environment, generating ions in the controlled environment in the
chamber, and opening the conductive container in the controlled
environment. Some embodiments in accordance with the invention
include locating the conductive container in a chamber having a
controlled environment, then opening the conductive container in
the controlled environment, and then moving the field-sensitive
article out of the conductive container into the controlled
environment using an electrically-insulating effector.
[0016] Thus, a field-sensitive article is protected from the
effects of externally generated electric fields and also from the
effects of being electrically charged, which might occur during
handling.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] A more complete understanding of the invention may be
obtained by reference to the drawings, in which:
[0018] FIG. 1 schematically depicts a cross-sectional view of a
generalized basic embodiment of an apparatus in accordance with the
invention for holding a field-sensitive article;
[0019] FIG. 2 depicts schematically an enlarged portion of FIG. 1
showing field contours in the vicinity of an electric charge on a
reticle;
[0020] FIG. 3 depicts schematically field contours in the vicinity
of an electric charge on a reticle supported by a conventional
conductive or dissipative support of the prior art;
[0021] FIG. 4 depicts a perspective view of a SMIF pod for holding
a field-sensitive reticle in accordance with the invention;
[0022] FIG. 5 depicts a cross-sectional view of a SMIF pod in a
closed position holding a field-sensitive reticle;
[0023] FIG. 6A depicts a perspective view of a cassette portion of
a multi-reticle SMIF pod;
[0024] FIG. 6B depicts a perspective view of a cover portion of a
multi-reticle SMIF pod;
[0025] FIG. 7 depicts schematically a cross-sectional view of a
system in accordance with the invention containing a SMIF pod, a
load port and a controlled environment;
[0026] FIG. 8 shows a schematic view of the system of FIG. 7 in
which the SMIF pod is in an open position within the controlled
environment;
[0027] FIG. 9 depicts field lines of an electric field between an
electric charge on an article and boundary walls at a different
electrical potential, such field lines being largely unperturbed by
the insulative effector and insulative internal panels in
accordance with the invention;
[0028] FIG. 10 depicts a system in accordance with the invention
comprising an ionizer for neutralizing electrical charges on a
field-sensitive article and on insulative panels and other internal
structures;
[0029] FIG. 11 depicts a conventional system of the prior art that
includes an effector made from conductive or static dissipative
material, not in accordance with the invention; and
[0030] FIG. 12 depicts a conventional system of the prior art that
includes internal panels comprising conductive or static
dissipative material, not in accordance with the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0031] The invention is described herein with reference to FIGS.
1-12. It should be understood that the structures and systems
depicted in schematic form in FIGS. 1, 2, and 4-10 are used to
explain the invention and are not precise depictions of actual
structures and systems in accordance with the invention.
Furthermore, processes are described in the specification with
reference to FIGS. 1, 2, 4-10; nevertheless, it is clear that
methods in accordance with the invention can be practiced using
apparati very different from those depicted in FIGS. 1, 2, 4-10.
The preferred embodiments described herein are exemplary and are
not intended to limit the scope of the invention, which is defined
in the claims below.
[0032] Embodiments in accordance with the invention are described
herein mainly with reference to the handling of reticles. Is
understood, however, that the invention is useful for protecting a
wide variety of field-sensitive articles, particularly in
semiconductor manufacturing facilities.
[0033] Field-induced damage in reticles was previously attributed
in the art to multiple low-level ESD events, with voltages being
around 150 volts for micron-sized gaps, lower than the minimum of
approximately 350 volts predicted by Paschen's Law for inner
discharge and atmospheric pressure. Analysis of field-induced
damage indicates that in addition to ESD, there are separate and
more subtle damage mechanisms, which occur simultaneously as a
result of field penetration into the mask image area. These damage
mechanisms involve electric field-induced migration ("EFM") of
metal (typically chrome) onto the surface of a reticle substrate
(typically quartz) between lines. These damage mechanisms take
place at lower potential differences in the reticle than those that
cause ESD events. Field-sensitive articles have different
sensitivity to field-induced potentials. For example, the
sensitivity of a reticle depends upon the length, spacing and
density of the chrome lines in the image area. The induced-voltage
range that results in EFM damage is believed to begin at about 5 V
for reticle line gaps of about 1 micron. As integrated-circuit
feature dimensions become smaller, the sensitivity of reticles to
ESD and EFM increases. EFM is a gradually operating cumulative
damage mechanism, so reticle degradation progresses continually
over time rather than occurring as a discrete event.
[0034] When a field sensitive object such as a reticle is
transported within a fab, it passes through many electrostatic
hazards. Shielding from externally generated electric fields is a
necessary part of the protection of such an object. Shielding from
electric fields is provided by placing a fully conductive enclosure
around the object. As has been explained, however, bringing a
fixed-potential object (such as a grounded container wall or a
grounded effector) close to a charged field-sensitive article
results in a strong electric field. Embodiments in accordance with
the invention help to reduce such risks.
[0035] FIG. 1 schematically depicts a cross-sectional view 100 of a
generalized basic embodiment of an apparatus 102 in accordance with
the invention for holding a field-sensitive article. Apparatus 102
includes a conductive container 104 having electrically-conductive
container wall 106. Container wall 106 defines an enclosure 108.
Apparatus 102 further includes an electrically-insulating support
110 configured for supporting a field-sensitive article 112 within
enclosure 108 in such a manner that field-sensitive article 112
does not come in contact with electrically-conducted container wall
106.
[0036] Ideally, container wall 106 provides a continuous, integral
conductive container enclosing the space of enclosure 108, thereby
enclosing a field-sensitive article 112 in a so-called Faraday
cage. A container wall that is not a continuous, integral
conductive wall still provides protection in the enclosure against
electric fields external to the container, but the degree of
protection decreases as a container wall becomes less integrally
conductive. The material of container wall 106 may comprise
substantially only electrically conductive material. Alternatively
or in combination with a substantially conductive material,
container wall 106 may comprise insulative or static dissipative
material that functions as a support for a coating of conductive
material, or insulative or static dissipative material embedded
with conductive material, such as graphite or other conductive
particles, or with an embedded metal mesh. Preferably, the
conductive material is a conductive metal, such as
stainless-steel-304 or aluminum-6061. Typically, container wall 106
comprises substantially only a conductive metal, such as stainless
steel 304. Stainless-steel-304 and other types of stainless steel
are commonly used in clean-room environments of integrated-circuit
fabrication facilities ("fabs"). When container wall 106 comprises
insulative or static dissipative material coated with a conductive
material, these materials should be selected to minimize outgassing
into enclosure 108.
[0037] The term "conductive material" and related terms as used in
this specification generally mean a material having a surface
resistivity not exceeding approximately 1.times.10.sup.3 ohms per
square and a volume resistivity not exceeding approximately
1.times.10.sup.3 ohm-cm. The terms "insulative material",
"insulating material" and related terms are used in this
specification generally mean material having a surface resistivity
not less than about 1.times.10.sup.12 ohms per square and a volume
resistivity not less than about 1.times.10.sup.11 ohm-cm. The term
"static dissipative material", "dissipative material" and related
terms as used in this specification generally mean a material
having a surface resistivity in a range of about from
1.times.10.sup.3 to 1.times.10.sup.12 ohms per square and a volume
resistivity in a range of about from 1.times.10.sup.3 to
1.times.10.sup.11 ohm-cm. The term "nonconductive material" and
related terms in this specification generally means a material
showing no significant conductive properties, that is, an
insulative material.
[0038] The term "electrically conductive" and related terms are
used broadly in this specification to refer to a material or to a
structure that is, for example, electrically conductive as defined
above, or is coated with a conductive material.
[0039] The term "electrically insulating" and related terms are
used broadly in this specification to refer to a material or to
structure that is, for example, electrically insulating as defined
above, or is coated with an insulating material.
[0040] An electrically-conductive container in accordance with the
invention functions as a Faraday cage, effectively shielding the
enclosure within a container from electric fields external to the
container. An external electric field can arise in a variety of
ways, for example, from an electric charge or from alternating
current.
[0041] A general objective of embodiments in accordance with the
invention is to maintain a field-sensitive article 112 in enclosure
108 as far away as possible from surfaces or conductive objects
having a ground or other electrical potential. For this reason,
electrically-insulating support 110 preferably is made only from
insulative material. Practically, an electrically-insulating
support 110 in accordance with the invention is physically
connected directly or indirectly with conductive container wall
106. Nevertheless, as much as possible of any
electrically-insulating support 110 proximate to a field-sensitive
article 112 is made from electrically insulative material. As
depicted in FIG. 1, apparatus 102 typically includes
electrically-insulating internal panels 114. In the embodiment of
apparatus 102, internal panels 114 function as insulating side
retainers or article-alignment retainers. Ideally, all internal
structures, such as electrically-insulating support 110 and
internal panels 114, that are located within enclosure 108 are made
only from insulative material. When manufacturing or operational
constraints do not practically allow an internal structure within
enclosure 108 to be made from insulative material, then portions of
such a structure that are in the close vicinity of a
field-sensitive article 112 while it is supported on support 110 or
being moved in or out of enclosure 108 should be made from
insulative material. An electrically-insulating support and other
structures located within the enclosure function in accordance with
the invention even when they comprise conductive material so long
as a field-sensitive article only comes into contact with
electrically-insulating (insulative) material, for example, with an
electrical-insulator coating on the support or other internal
structure. Nevertheless, the protection of a field-sensitive
article is not as good as when the support or other internal
structure comprises only insulative material.
[0042] Ideally, a field-sensitive article 112 does not come into
close proximity with other conductive surfaces. Therefore,
external-electric-field-free enclosure 108 is designed to be as
large as possible within manufacturing and operational constraints.
The design and locations of support 110, internal panel 114 and
other structures in enclosure 108, and container openings (not
shown) for moving an article into or out of enclosure 108 are
implemented to minimize electric field effects on a field-sensitive
article 112.
[0043] When an electric charge, such as a static electric charge,
exists on a field-sensitive article 112, then an electric field
exists between the charge on the article and the internal
conductive features of the container and any conductive structures
within enclosure 108. The field gradient depends on the distance
between the charged article and conductive container wall 106 and
any conductive or static dissipative features that are in
electrical contact with container wall 106. Furthermore, the
intensity of the electric field depends on the charge distribution
and the topography of both the field-sensitive article and the
internal conductive or dissipative surfaces of container 104. Any
protrusions or sharp features on the internal conductive or static
dissipative surfaces of the container that might concentrate the
field emanating from the charged article increase the risk of
field-induced damage, such as ESD and EFM. For this reason,
internal structures 110, 114 preferably are made only from
insulative material, and conductive container walls 106 preferably
are smooth, without sharp protrusions and corners. Conductive
container wall 106 depicted in FIG. 1 has a smooth elliptical
shape. It is understood that conductive container wall 106 in
accordance with the invention can have various shapes. It is also
clear that conductive wall 106 can be housed in a structure having
a shape different from container wall 106. Also, container wall 106
may comprise one or a plurality of sections that fit together to
make a continuous, integral electrically-conductive container in
accordance with the invention.
[0044] Holding a field-sensitive article 112, such as a reticle, in
an external-field-free enclosure 108 of a conductive container 106
on insulating supports 110 does not increase the risk to the
article beyond the risk already posed by a) electrically charging
it in the first place, and b) modifying the field pattern around
the object by placing it within a grounded conductive or static
dissipative container to allow the object to be stored or
transported in a stable environment to a place where the charge
that has been placed on the object can be safely neutralized or
dissipated.
[0045] A preferred embodiment of the invention includes a fully
electrically conductive container (Faraday cage), but the principle
of protection against field-induced damage of a charged article
through electrical isolation also applies to a static dissipative
container.
[0046] A reticle used for the production of semiconductor devices
is an example of a field-sensitive article suitable for protecting
in accordance with the invention. A reticle is typically made of
quartz or glass, and typically has a size of about 15 cm by 15 cm
height and width and a thickness of about 6 mm. A reticle is coated
on one side with a discontinuous light-absorbing metallic film,
typically chromium, surrounded by a continuous border of the metal,
called the guard ring. Thus, a reticle comprises both insulating
and conducting regions, the bulk of the reticle being
insulative.
[0047] FIG. 2 depicts schematically an enlarged portion of "window"
120 of FIG. 1. Window 120 in FIG. 2 shows conductive container wall
106, electrically-insulating support 110, field-sensitive reticle
112 located on support 110, and aligning side-retainer 114.
Electrically-insulating support 110 and side-retainer 114 comprise
only electrically insulative material in accordance with preferred
embodiments of the invention. As depicted in FIG. 2, a static
electrical charge 122 is located on a surface of field-sensitive
reticle 112. As a result, an electric field represented by
electric-field contours 124 exists between charge 122 on reticle
112 and conductive wall 106, which is at ground potential. Because
support 110 and side-retainer 114 comprise substantially only
insulative material, they do not significantly influence the
electric field present in enclosure 108.
[0048] FIG. 3 depicts a window 220 that shows a portion of a
conventional apparatus in the prior art having a grounded
conductive or dissipative container wall 206 that defines an
enclosure 208, a grounded conductive or dissipative support 210,
and a grounded conductive or dissipative side-retainer 214. An
electric charge 222 is located on a reticle 212, causing an
electric field represented by electric-field lines 224. Grounded
support 210 and grounded side-retainer 214 cause field-sensitive
reticle 212 to be at ground potential at contact point 230 at the
conductive chromium guard ring of reticle 212. As a result, the
voltage contours represented by field contours 224 in FIG. 3 are
more compressed compared to the voltage contours in FIG. 2. This
causes a higher voltage gradient within field-sensitive reticle 212
than in reticle 112 of FIG. 2 under otherwise similar
conditions.
[0049] In accordance with the invention, an electrically-conductive
container 104 for holding a field-sensitive article 112 with an
electrically-insulating support 110 within the container is
typically located in a controlled environment within a chamber 130
defined by boundary walls 132, as depicted in FIG. 1. When a
container 104 is open to move a field-sensitive article into or out
of container 104, typically an ionizer 140 is utilized to
neutralize electric charges located within chamber 130 and
enclosure 108. The term "chamber" is used broadly to mean a defined
space having finite boundaries that make it possible for the
environment within the space to be controlled to some desired
degree. Typically, boundaries and other structures of a controlled
environment of chamber 130 are maintained at a constant electrical
potential, as indicated by ground connector 142 in FIG. 1. In some
embodiments, electrically-conductive container 104 becomes a part
of boundary walls 132, for example, when a SMIF pod is located in a
load port. Then, when the pod opened, the exterior surface of the
pod remains outside chamber 130, but electrically-conductive
container 104 can open within environmentally-controlled chamber
130.
[0050] FIG. 4 depicts a perspective view 300 of a SMIF pod 302 for
holding a field-sensitive reticle in accordance with the invention.
FIG. 4 shows pod 302 in an open position. FIG. 5 depicts a
cross-sectional view 306 of pod 302 in a closed position holding
field-sensitive reticle 304. Pod 302 includes pod bottom 310 and
pod top 312. Pod bottom 310 comprises electrically-conductive lower
container wall 314. Pod top 312 includes electrically-conductive
upper container wall 316. In a closed position as depicted in FIG.
5, upper container wall 316 and lower container wall 314 form a
continuously electrically-conductive container 320 and define
enclosure 322. In its closed position, continuous
electrically-conductive container 320 functions as a Faraday cage,
effectively preventing any electric fields external to container
320 from penetrating into enclosure 322. Pod 302 further includes
compliant gasket 324 located between pod bottom 310 and pod top 312
to form a pressure seal when the pod is in a closed position.
Suitable compliant materials for gasket 324 are known in the art;
for example, vulcanized rubber, Viton, Chemraz or similar
materials. Locks 326A, 326B help to establish continuous electrical
contact between pod bottom 310 and pod top 312 in a closed
position, as well as to establish a pressure seal with compliant
gasket 324. Typically, electrically-conductive lower container wall
314 and electrically-conductive upper container wall 316 are made
only from conductive metal material, such as stainless steel 304.
Alternatively, container walls 314, 316 comprise insulative or
static dissipative material that are coated with or are embedded
with conductive materials to make container walls 314, 316
sufficiently conductive. Portion 328 of pod top 306 external to
container wall 316 typically comprises hard polymer plastic
material to minimize weight. Portion 328 of pod top 306 optionally
includes an automation flange 329 (see FIG. 4) and manual handles
331. In accordance with the invention, SMIF pod 302 further
comprises electrically-insulating supports, or rails, 330 made
completely from insulative material. Electrically-insulating
supports 330 support field-sensitive reticle 304 in such manner
that reticle 304 does not come into electrical contact with
electrically-conductive container walls 314, 316, which are
typically connected to a constant electrical potential, such as
electrical ground. Pod 302 further comprises
electrically-insulating side retainers 332 and
electrically-insulating vertical retainers 334, which are made
completely from insulative material. Supports 330 and retainers
332, 334 are preferably made from insulative materials that will
not abrade or chip the reticle 304, for example a soft polymer
plastic, such as nylon or delrin. Acetron GP, an acetyl polymer
available from GE Polymer, is a suitable insulative plastic
typically used for making supports 330 and retainers 332, 334.
Insulative ceramic materials, such as quartz, are also suitable for
making supports 330 and retainers 332, 334. Alternatively, when it
is not practically feasible to make supports 330, retainers 332,
334 and other structures within enclosure 322 completely from
insulating material, these enclosure-internal structures can be
made partially from conductive or static dissipative material, as
long as only insulative surfaces of the structures are in contact
with conductive regions of reticle 304. As explained above,
protection of a reticle 304 or of some other field-sensitive
article increases as the amount and proximity of conductive or
dissipative material in enclosure 322 decrease.
[0051] Electrically-insulating support 330 preferably comprises
substantially insulative material. When support 330 also comprises
conductive or static dissipative material covered by insulating
material at the contact surfaces with a reticle, then the
insulating covering or coating is typically at least about 2
microns thick. To minimize the compression of electric field lines
if an electric field exists in the environment of the reticle,
there is preferably no conducting or static dissipative material
within 2 mm of said reticule, and more preferably not within 10 mm
of said reticule.
[0052] Similarly, when locating or moving a reticle within a
conductive container or within a controlled environment in
accordance with the invention, conducting or static dissipative
material should be kept at least 2 micron away from said reticule,
preferably 2 mm, and more preferably at least 10 millimeters
away.
[0053] FIG. 6A depicts a perspective view of a cassette portion
402A of a multi-reticle SMIF pod 402 (not completely shown). FIG.
6B depicts a perspective view of a cover portion 402B of
multi-reticle SMIF pod 402 (not completely shown). Cassette portion
402A includes pod bottom 410. Pod bottom 410 comprises
electrically-conductive container lower wall 414. Cassette portion
402A further includes electrically-conductive container sidewalls
416, electrically-conductive container back wall 418, and
electrically-conductive container upper wall 420. As depicted in
FIG. 6B, cover portion 402B comprises movable
electrically-conductive front container wall 422 and
electrically-conductive rear panel-walls 424. When cassette portion
402A and cover portion 402B are locked together in their closed
position, electrically-conductive walls 414, 416, 418, 420, 422,
and 424 form a continuous, integral conductive container wall that
defines an enclosure 426 (indicated in FIG. 6A), which corresponds
to the space in which field-sensitive reticles 430,
electrically-insulating supports 432, and electrically-insulating
side retainers 434 are enclosed. Supports 432 and retainers 434 are
fastened to insulative stanchions 436, which are integrally
connected to insulative mounting strips 437. Mounting strips 437
are attached, typically with screws, to the inside surfaces of
conductive container sidewalls 416. Cassette portion 402A further
includes compliant gasket 440 located along the outer edge of lower
container wall 414. Gasket 440 helps to form a pressure seal
between cassette portion 402A and cover portion 402B when pod 402
is in a closed position. Locks 446A, 446B help to establish
continuous electrical contact between cassette portion 402A and
cover portion 402B when pod 402 is in a closed position, as well as
to establish a pressure seal with gasket 440. Typically,
electrically-conductive container walls 414, 416, 418, 420, 422,
and 424 are made only from conductive metal material, such as
stainless steel 304. In certain preferred embodiments, one or more
of the conductive walls, particularly movable front wall 422 and
rear panel-walls 424, are made from transparent insulative glass or
plastic, which are coated with a transparent conductive metal
oxide. Alternatively, the insulative glass or plastic contains an
embedded metal mesh that does not significantly reduce the optical
transparency. Pod top 450 of cover portion 402B typically comprises
hard polymer plastic material to minimize weight. Pod top 450
optionally includes an automation flange and manual handles.
[0054] In accordance with the invention, electrically-insulating
supports 432 and side retainers 434 of cassette portion 402A, as
well as their supporting structures 436, 437, which fasten
structures 430,432 to electrically-conductive sidewalls 416, are
made completely from insulative material, typically from an
insulative plastic, such as Acetron GP. In certain embodiments,
supports, retainers, and other supporting structures are made with
an insulative ceramic, such quartz. Optionally, the surfaces of
ceramic supports 432 and retainers 434 that come into contact with
reticles 430 are coated with a thin film of insulative plastic to
provide a soft smooth surface.
[0055] Pod 402 includes an advancing retainer mechanism comprising
advancing retainer 460, depicted in FIG. 6B. When pod cover portion
402B is in a closed and locked position covering cassette portion
402A, electrically-insulating advancing retainer 460 is advanced
toward front edge 462 and comes to rest substantially in contact
with forward edges 464 of reticles 430. Preferably, advancing
retainer 460 is made substantially from only insulating material.
Advancing retainer 460 is aligned so that the advancing surface of
retainer 460 that comes to rest against the edges 464 of reticles
protrudes from the plane of conductive container wall 422. As
depicted in FIG. 6B, conductive front wall 422 comprises a
transparent conductive wall portion, namely, conductive transparent
window 468. Thus, movable front wall 422 includes conductive
conductive transparent window 468 and conductive sheet 470. Cover
portion 402B includes transparent front panel 472, typically
comprising transparent plastic, which does not advance and is not a
part of the Faraday cage. Advancing retainer 460 typically
comprises insulative plastic, such as Acetron GP. Conductive sheet
470 typically comprises a sheet of conductive metal, such as
stainless-steel-304 or aluminum-6061, that is clamped or otherwise
fastened to advancing retainer 460 using conventional techniques.
Movable conductive front wall 422 does not come into physical or
electrical contact with field-sensitive reticles 430 when pod cover
portion 402 is in its closed position with advancing retainer 460
typically being in physical contact with field-sensitive reticles
430. Preferably, movable conductive front wall 422 comes into close
proximity with conductive edges 462 and with conductive lower wall
414, but preferably does not make physical contact (to avoid
creating particles). When a surface of conductive front wall 422
that comes at least within 10 mm of a corresponding opposing
surface of edge 462 or lower wall 414, then this proximity
typically provides a sufficiently continuous integral portion of a
conductive container. To achieve a close fit of front wall 422 to
adjoining conductive surfaces at edges 462 or container bottom 414,
sheet edges 484 typically are curved inwards.
[0056] FIG. 7 depicts schematically a cross-sectional view 500 of a
system 502 in accordance with the invention. System 502 includes
boundary walls 504 that define a chamber 506 having a controlled
environment. An electrical connector 507 connects boundary walls
504 to electrical ground or some other fixed potential. Boundary
walls 504 often include a transparent portion. The controlled
environment of system 502 may be any one of a variety of controlled
environments in a fab; for example, a chamber in a manufacturing
processing tool or simply a controlled environment between load
ports of two SMIF pods. System 502 further includes a load port 508
for holding and operating a SMIF pod and a SMIF pod 510. SMIF pod
510 is depicted in closed position in FIG. 7. When pod 510 is
located in load port 508, it is electrically connected by
electrical connector 509 to boundary walls 504 and thereby to
electrical ground (or some other fixed potential) through connector
507. Preferably, electrical connector 509 is resistive to prevent a
rapid electrical discharge in case pod 510 is charged before it is
loaded into load port 508. In accordance with the invention, SMIF
pod 510 comprises conductive container 512 and
electrically-insulating supports 514 for supporting a
field-sensitive article 516 so that article 516 does not come into
electrical contact with electrically conductive container 512. SMIF
pod 510 also comprises electrically-insulating aligners 517 and
electrically-insulating vertical retainers 518. Typically, system
502 includes one or more internal panels 519 within chamber 506. In
accordance with the invention, internal panels 519 and the
ancillary stanchions and other structures supporting them within
chamber 506 preferably are made substantially completely from
insulative material. The term "internal panel" is used in a general
sense to mean any one or several of a variety of structures present
in controlled environments of fabs. The meaning of "internal panel"
includes, for example: a support rail for supporting a
field-sensitive or other article within chamber 506; structures for
segregating areas for contamination control; panels for controlling
fluid flow within chamber 506; and panels for directing the flow of
ions to target locations in chamber 506. FIG. 8 shows a schematic
view 520 of system 502 in which SMIF pod 510 is in an open position
within the controlled environment of chamber 506. As depicted in
FIG. 8, system 502 further comprises an effector 522 for moving a
field-sensitive article within chamber 506 to or from opened SMIF
pod 510. Effector 522 preferably is made completely from insulative
material. In certain embodiments, effect of 522 is made from
insulative ceramic material, and is optionally coated with an
insulative plastic coating to minimize abrasion. Effector 522 is
typically an end effector of a robot arm or a manually operated
effector. It is depicted beneath reticle 516 and supporting it
under gravity, but it could equally well grip a reticle from the
sides or hold a reticle by vacuum applied to the reticle's top
surface. As depicted in view 520 of FIG. 8, field-sensitive article
516, such as a reticle, is located in chamber 506 on effector 522,
which has removed the article from supports 514. Alternatively,
insulative structure 522 is a chamber-internal support for
field-sensitive article 516. It is possible for a field-sensitive
article 516 to be carrying an electrical charge. FIG. 9 shows a
view 530 depicting field lines 532 of an electric field in a system
502 between an electric charge 531 on article 516 and boundary
walls 504 when the boundary walls are at a different electrical
potential, for example, at electrical ground. Because effector 522
and internal panels 519 are made from insulative material in
accordance with the invention, the electric field is not compressed
within chamber 506, as indicated by the long field lines 532. In
preferred embodiments in accordance with the invention, as depicted
in view 540 of FIG. 10, a system 502 comprises an ionizer 542 for
neutralizing electrical charges within chamber 506, in particular,
static electrical charges on a field-sensitive article 516 and on
insulative panels 519 and other internal structures, including the
insulative structures within the container 510 when it is
opened.
[0057] FIG. 11 depicts a cross-sectional view 600 of a conventional
system 602 of the prior art that includes an effector 622 that is
not in accordance with the invention. Effector 622 comprises
conductive or static dissipative material that is at a controlled
potential, such as ground potential. As a result, an electric field
exists between the electric charge on article 616 and effector 622.
The dense electric field, indicated by short field lines 624, has a
high field strength that is hazardous to a field-sensitive article
616.
[0058] FIG. 12 depicts a cross-sectional view 700 of a conventional
system 702 of the prior art that includes internal panels 719 that
are not in accordance with the invention. Internal panels 719
comprise conductive or static dissipative material that is at a
controlled potential, such as ground potential. As a result, an
electric field exists between the electric charge on article 716
and panels 719. The dense electric field, indicated by short field
lines 724, has a high field strength that is hazardous to a
field-sensitive article 716.
[0059] The particular systems, designs, methods and compositions
described herein are intended to illustrate the functionality and
versitility of the invention, but should not be construed to be
limited to those particular embodiments. Systems and methods in
accordance with the invention are useful in a wide variety of
circumstances and applications to control and reduce
electric-field-induced damage to field-sensitive articles,
especially in semiconductor fabs. It is evident that those skilled
in the art may now make numerous uses and modifications of the
specific embodiments described, without departing from the
inventive concepts. It is also evident that the steps recited may,
in some instances, be performed in a different order; or equivalent
structures and processes may be substituted for the structures and
processes described. Since certain changes may be made in the above
systems and methods without departing from the scope of the
invention, it is intended that all subject matter contained in the
above description or shown in the accompanying drawing be
interpreted as illustrative and not in a limiting sense.
Consequently, the invention is to be construed as embracing each
and every novel feature and novel combination of features present
in or inherently possessed by the systems, methods and compositions
described in the claims below and by their equivalents.
* * * * *