Spring devices – Vehicle – Compound
Reexamination Certificate
2001-02-23
2003-02-04
Hail, III, Joseph J. (Department: 3723)
Spring devices
Vehicle
Compound
C269S266000, C269S020000, C269S903000, C451S388000
Reexamination Certificate
active
06513796
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of Invention
The present invention generally relates to the field of semiconductor wafer processing. More particularly, the present invention is directed to a wafer chuck having a removable insert.
During various steps of processing a semiconductor wafer during the manufacturing of microelectronic devices, the wafer must be held firmly in a fixed position with its processed surface as planar as possible. For example, during projection photolithography processing, the processed surface must be substantially coincident with the focal plane of the projection optics. If one or more regions of the processed surface deviate from the focal plane, the deviation must not exceed the depth of focus of the projection optics. Otherwise, the projected pattern at such regions will be distorted and the regions may be unusable.
As feature sizes of patterns are becoming increasingly smaller, so are depths of focus. This is so because smaller feature sizes require larger numerical apertures that translate into shallower depths of focus. In addition, the size of the field printed or scanned during each exposure is relatively large to increase throughput and increase productivity. These characteristics of current photolithographic practices accentuate the need for maintaining the processed surface of a wafer as planar as possible during photolithography.
Dirt particles on the backsides of wafers often present a significant obstacle in achieving the necessary planarity required for photolithographic patterning. Even with ultra-clean rooms and extensive wafer cleaning procedures, it is virtually impossible to completely rid the wafers, particularly their backsides, of dirt particles. In fact, many dirt particles that interfere with planarizing the processed surfaces of the wafer come from the wafers themselves after they have been cleaned. For example, such dirt particles are often in the form of chips from the wafer edges and flakes from films grown or deposited upon the wafers.
To minimize the impact of dirt particles on planarizing the processed surface, the wafer chucks used to hold wafers during photolithography have evolved from chucks having optically-flat surfaces for engaging the backside of a wafer to vacuum chucks having annular grooves in their optically-flat surfaces to hold the wafer firmly in place and, most recently, to pin-type, or “bed-of-nails,” vacuum chucks, which are generally represented by prior art vacuum chuck
1
0
illustrated in
FIGS. 1 and 2
.
As shown in
FIGS. 1 and 2
, prior art vacuum chuck
10
comprises a metal base
12
having an upper surface
14
and a plurality of aluminum pins
16
extending upward from the upper surface. The upper ends
18
of the plurality of pins
16
all lie within a common plane that is positioned parallel to the focal plane of the projection optics. The upper end
18
of each pin
16
has a planar surface
20
that engages a wafer
22
. If wafer
20
is warped or otherwise not planar, it may not engage one or more of pins
16
. To reduce or eliminate any out-of-planeness of wafer
22
and/or to hold the wafer firmly to chuck
10
, the chuck is connected to a vacuum source (not shown) that provides a vacuum in a vacuum region
24
located between wafer
22
and upper surface
14
of chuck vacuum
10
. Vacuum region
24
is in fluid communication with the vacuum source via vacuum ports
26
and is generally isolated from the environment surrounding vacuum chuck
10
when wafer
20
is inserted therein by a seal ring
28
.
Although pin-type vacuum chucks, such as vacuum chuck
10
described above, are a vast improvement over chucks having larger areas of contact with wafers, they are still subject to the influence of dirt particles and, therefore, must be cleaned periodically to prevent the dirt particles from affecting the lithography process. Over time, continual cleaning of vacuum chuck
10
typically causes upper ends
18
of pins
16
to be worn away, particularly at the pins proximate to the center of the chuck. Uneven wear among pins
16
causes the upper ends
18
of the pins to define a non-planar, rather than planar, surface, which reduces the accuracy of vacuum chuck
10
, and eventually causes intolerable focus error that requires the chuck to be replaced. Another disadvantage of vacuum chuck
10
is that the wafer contact area of planar surface
20
of each pin
16
is relatively large, increasing the probability that dirt particles on wafer
22
will interfere with direct contact between the wafer and one or more pins.
BRIEF SUMMARY OF THE INVENTION
In one aspect, the present invention is directed to a chuck/insert assembly for holding a workpiece. The chuck/insert assembly comprises a chuck that includes a first base having a first surface. At least one first spacer extends away from the first surface. An insert is removably engaged with the at least one first spacer so as to form a first vacuum region between the insert and the chuck. The insert includes a second base having a second surface. At least one second spacer extends away from the second surface and has a distal end located opposite the second surface. The distal end is adapted for engaging the workpiece.
In another aspect, the present invention is directed to a method of forming an insert for a vacuum chuck from a body having a surface. The method comprises the steps of patterning onto the surface of the body at least one spacer location and removing material surrounding the at least one spacer location so as to form at least one spacer.
REFERENCES:
patent: 3937579 (1976-02-01), Schmidt
patent: 4213698 (1980-07-01), Firtion et al.
patent: RE31053 (1982-10-01), Firtion
patent: 4506184 (1985-03-01), Siddall
patent: 4724222 (1988-02-01), Feldman
patent: 4845530 (1989-07-01), Matsukawa
patent: 5197089 (1993-03-01), Baker
patent: 5291239 (1994-03-01), Jackson
patent: 5382311 (1995-01-01), Ishikawa
patent: 5431737 (1995-07-01), Keller
patent: 5737063 (1998-04-01), Miyachi
patent: 5998801 (1999-12-01), Imai
patent: 6043892 (2000-03-01), Park
patent: 6073681 (2000-06-01), Getchel
patent: 6168668 (2001-01-01), Yodovsky
patent: 6182956 (2001-02-01), McMillan
Leidy Robert K.
Sonntag Paul D.
Downs Rachlin & Martin PLLC
International Business Machines - Corporation
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