Deposition shield assembly for a semiconductor wafer processing system

A readily removable deposition shield assembly for processing chambers such as chemical vapor deposition (CVD), ion implantation, or physical vapor deposition (PVD) or sputtering chambers, is disclosed. The shield assembly includes a shield member which is mounted to the chamber for easy removal, such as by screws, and defines a space along the periphery of the substrate support. A shadow ring is inserted into the peripheral space and is thus mounted in removable fashion and is automatically centered about the substrate by an alignment ring. The alignment ring removably rests upon a flange extending from the outer periphery of an electrostatic chuck. The shadow ring overlaps the cylindrical shield member, the alignment ring and the peripheral edge of a substrate retained by the chuck. Collectively, these components prevent deposition on the chamber and hardware outside the processing region.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to deposition shields for processing 
chambers, including for example physical vapor deposition or sputtering 
chambers, chemical vapor deposition chambers and ion implantation 
chambers. More specifically, the invention relates to a deposition shield 
assembly for protecting an electrostatic chuck from the deposition species 
during semiconductor wafer processing. 
2. Description of the Background Art 
In deposition processes, species from a source such as a target, a gas 
inlet manifold and the like may deposit on exposed internal chamber 
surfaces, including the chamber walls and hardware. Shields are available 
which are designed to intercept such species. However, the presently 
available shields have not been successful in completely blocking unwanted 
deposition on these surfaces. Also, such shields may be difficult and/or 
time-consuming to replace, and require relatively frequent replacement. 
The use of automatic substrate exchange systems, with their attendant 
in-chamber movable components, increases the difficulty of attaining 
adequate shielding and easy replacement of these shields. 
Furthermore, recent developments in high temperature semiconductor 
processing, such as high temperature physical vapor deposition (PVD), have 
begun using substrate support and retention pedestals that contain 
electrostatic chucks. The performance of such chucks is substantially 
reduced if the chuck is exposed to the deposition species. The 
interference with chuck performance is especially pronounced when the 
deposition species is a metal such as copper. Furthermore, sustained 
exposure to the deposition species may contaminate the chuck to such an 
extent as to make the chuck inoperative. Consequently, it is imperative 
that none of the surfaces of the chuck be exposed to the deposition 
species. 
Therefore, there is a need in the art for shields that provide adequate 
shielding for an electrostatic chuck. 
SUMMARY OF THE INVENTION 
The invention is a shield assembly that circumscribes an electrostatic 
chuck within a semiconductor processing system and protects the chuck from 
exposure to deposition species within the system. The shield assembly 
comprises a removable shadow ring and an alignment ring. The alignment 
ring rests upon a circumferential flange extending from the outer edge of 
the electrostatic chuck. The support surface of the chuck, upon which a 
substrate is retained, has a diameter that is slightly smaller than the 
diameter of a substrate. Consequently, a substrate retained by the chuck 
overhangs an inner portion of the top surface of the alignment ring. The 
shadow ring circumscribes the peripheral edge of the electrostatic chuck 
and is coaxially aligned with the center axis of the chuck. The shadow 
ring rests upon an outer portion of the top surface of the alignment ring. 
The shadow ring has a roof portion that overhangs the outer peripheral 
edge of the substrate, but does not contact the substrate. The roof 
portion also defines a labyrinth gap between the shadow and alignment 
rings. The labyrinth gap ensures that the electrostatic chuck is not 
exposed to the deposition species. 
Importantly, the shield assembly is effective and easily removed from the 
pedestal for cleaning and/or replacement. In addition, other components 
operating in conjunction with the removable shield assembly, including a 
chamber shield member, define an assembly that is especially tailored to 
eliminate contact of the deposition species with the electrostatic chuck.

To facilitate understanding, identical reference numerals have been used, 
where possible, to designate identical elements that are common to the 
figures. 
DETAILED DESCRIPTION 
FIG. 1 is a simplified schematic drawing illustrating the shield assembly 
118 of the present invention incorporated in a semiconductor wafer 
processing system 100. The invention effectively shields an electrostatic 
chuck 136 from the deposition species, yet affords easy removal of the 
shield components for cleaning or replacement. The invention is generally 
applicable to deposition chambers of semiconductor wafer processing 
systems, including, for example, physical vapor deposition (PVD) or 
sputtering chambers, chemical vapor deposition (CVD) chambers, and ion 
implant chambers where an electrostatic chuck is used to retain a 
substrate within the chamber. 
By way of example, FIG. 1 schematically illustrates a PVD or sputtering 
system 100. The system 100 contains a vacuum chamber 116, an electrostatic 
chuck 136, a shield assembly 118 and an elevator system 132. The substrate 
120 (e.g., a semiconductor wafer) is positioned upon a support surface of 
the electrostatic chuck 136. In the exemplary arrangement, the 
electrostatic chuck 136 is attached, as by a plurality of screws, to a 
conventional vertically movable elevator system 132. (Please note, 
conventional hardware such as gas inlet manifolds and/or vacuum pumps are 
omitted for clarity.) 
The exemplary vacuum chamber 116 includes a cylindrical chamber wall 114 
and a support ring 112 which is mounted to the top of the chamber wall, as 
by welding. The top of the chamber is closed by a target plate 106. The 
plate 106 is electrically insulated from the chamber walls 114 by an 
annular insulator 110 that rests between the target plate 106 and the 
support ring 112. Generally, to ensure the integrity of the vacuum in the 
chamber 116, O-rings (not shown) are used above and below the insulator 
110 to provide a vacuum seal. The target plate 106 may be fabricated of a 
material that will become the deposition species or it may contain a 
coating 108 of the deposition species. To facilitate the sputtering 
process, a high voltage DC power supply 102 is connected between the 
target 106 and the chamber walls 114. 
The electrostatic chuck 136 retains and supports a substrate 120 within the 
chamber 116. In the preferred embodiment of the invention, the 
electrostatic chuck 136 contains one or more electrodes 122 and 124 
imbedded within a ceramic chuck body 108. In a conventional manner, the 
electrodes are driven by a voltage from an electrode power supply 104 and, 
in response to application of the voltage, the substrate 120 is 
electrostatically clamped to the support surface of the chuck. The ceramic 
chuck body is, for example, fabricated of aluminum-nitride or 
boron-nitride. Such a relatively low resistivity material promotes the 
Johnsen-Rahbek effect during high temperature processing. Other relatively 
low resistivity ceramics also form useful high temperature chuck materials 
such as alumina doped with a titanium oxide or a chromium oxide. If the 
chuck is to be used at low temperatures only, then other ceramic and/or 
dielectric materials such as alumina are used to form the chuck body. An 
illustrative ceramic electrostatic chuck is disclosed in U.S. Pat. No. 
5,117,121 issued May 26, 1992 and U.S. patent application Ser. No. 
08/612,652 filed Mar. 8, 1996, both of which are herein incorporated by 
reference. Examples of non-ceramic electrostatic chucks are disclosed in 
U.S. Pat. No. 4,184,188 issued Jan. 15, 1980 and U.S. Pat. No. 4,384,918 
issued May 24, 1983, both of which are incorporated herein by reference. 
A wall-like cylindrical shield member 126 is mounted to the support ring 
112. That is, the cylindrical shield 126 has an inwardly (or outwardly) 
extending upper lip 142 which is attached to the bottom of the adapter 
plate 112 by a plurality of screws. The cylindrical shape of the shield 
member 126 is illustrative of a shield member that conforms to the shape 
of the chamber and/or the substrate. The shield member 126 may, of course, 
be of any shape. A flange 144 extending upward from annular bottom wall 
146 of the shield member 126 surrounds the periphery of the electrostatic 
chuck 136, leaving a space 148 between the flange 144 and the chuck 136. 
In addition to the shield member 126, the shield assembly 118 also includes 
an annular shadow ring 130 having an inner diameter which is selected so 
that the ring fits peripherally over the edge of the substrate 120 without 
contacting the substrate. The shadow ring rests upon an alignment ring 128 
and the alignment ring 128 is supported by a flange 140 that extends from 
the electrostatic chuck. 
FIG. 2 depicts a detailed cross-sectional view of the shield assembly 118 
within region 2--2 of FIG. 1. The alignment ring 128 rests upon an upper 
surface 206 of the flange 140 of the chuck 136. When in position on the 
chuck flange, an inner diameter surface 206 of the alignment ring 128 
substantially abuts the outer peripheral surface 207 of the chuck. The 
support surface 208 of the chuck has a diameter that is slightly smaller 
than the diameter of a substrate 120. As such, the peripheral edge of the 
substrate overhangs the edge of the chuck and, consequently, overhangs the 
top surface 210 of the alignment ring 128. The top surface 210 of the 
alignment ring 128 has two portions. A first portion 212 is spaced-apart 
and parallel to the backside peripheral edge surface of the substrate 120 
to form a gap 216 having a width of 0.3 mm. A second portion 214 is 
recessed from the first portion by approximately 1.0 mm. and forms a 
support surface for the shadow ring 130. The outer diameter surface 218 of 
the alignment ring 128 has a "radiused edge" structure. 
The shadow ring 130 comprises a downward extending, tapered centering 
flange 200 which fits into the opening 148 between the shield member 
flange 144 and the side edge of the chuck 136, and a second, outer flange 
202 which is generally parallel to flange 144. The shadow ring 130 is 
mounted in removable fashion at the periphery of the substrate 120 by 
seating the two flanges 200 and 202 over the mating flange 144 of the 
cylindrical shield member 126, with the tapered centering flange 200 
extending into the opening 148. Additionally, to facilitate accurate 
positioning of the shadow ring with respect to the substrate, the tapered 
centering flange 200 abuts the "radiused" surface 218 of the alignment 
ring 128 and the shadow ring repeatably aligns with the substrate and the 
chuck. The alignment tolerance is .+-.5 mils. 
The shadow ring 130 also comprises a raised, inward-extending roof portion 
220 which overhangs and protects the periphery of the substrate 120 and 
prevents deposition on the surfaces on which the shadow ring 130 rests and 
on the associated ring-surface interfaces. To facilitate such protection 
when the shadow ring 130 rests upon the alignment ring 128, a bottom 
surface of the roof portion 220 is sculpted to form a labyrinth gap 222 
between the alignment ring 128 and the shadow ring 130. The labyrinth gap 
222 extends along the top peripheral edge surface of the substrate 120 for 
a distance of approximately 24 mils at a spacing from the substrate of 
approximately 12 mils, slopes downward past the edge of the substrate 120, 
and then extends laterally along the second portion 214 of the top surface 
210 of the alignment ring 128 for a length of approximately 0.25 inches 
and a height of approximately 30 mils. To sufficiently eliminate 
deposition species penetration into the labyrinth gap 222, the ratio of 
the overhang distance of the roof portion over the substrate to the 
spacing between the overhang and the substrate surface is between 1.5 and 
2. Furthermore, to ensure that any species that do penetrate the labyrinth 
gap 222 do not cause adhesion of the shadow ring to the alignment ring, 
the gap therebetween should be approximately 30 mils. With this gap, 
deposition species should not cause the shield components to adhere to one 
another nor adhere to the substrate. Furthermore, the combination of 
shield components ensures that the deposition species will not contact the 
electrostatic chuck. 
As mentioned, the shield assembly uniquely combines full effective 
shielding of the chamber with easy removal. Specifically, effective 
shielding action is provided by the cylindrical shield member 126, the 
relatively wide electrostatic chuck 136 (that is, the chuck flange 140 
extends laterally beyond the substrate) the alignment ring 128, which 
overlaps the backside peripheral edge of the substrate and the chuck, and 
the shadow ring 130, which overlaps both the chuck and the 
inward-extending bottom section of the shield member 126. These 
overlapping components combine to isolate the processing region of the 
chamber 116 from the rest of the chamber interior and shield the rest of 
the chamber (for example, chamber walls 114 and the internal chamber 
hardware such as the chuck 136 and the movable elevator 132) from 
deposition. The shield components are easily removed, by removing the 
target and the adapter plate mounting hardware and lifting, as a unit, the 
adapter plate 112; the shield member 126, which is attached to the adapter 
plate; and the shadow ring 130, which is supported in removable fashion on 
the shield member 126. The alignment ring 128 can then lifted from the 
chamber. 
In use, the elevator system 132 vertically raises and lowers the 
electrostatic chuck 132 to enable a wafer transport robot (not shown) to 
place and retrieve the substrate from the support surface of the chuck. 
When the chuck 136 is lowered, the shadow ring 130 rests on the flange 144 
the shield member 126 and is separated from the alignment ring 128. Once 
the substrate 120 is placed upon the chuck 136, the chuck is raised to 
place the substrate into a process position within the chamber. As the 
chuck is raised, the alignment ring 128 contacts the shadow ring 130 
forming the labyrinth gap 222. Interaction of the centering flange 200 and 
the surface 118 of the alignment ring centers the shadow ring 130, e.g., 
the shadow ring becomes coaxially aligned with a central axis of the chuck 
136. Additionally, through use of the present invention, the electrostatic 
chuck 136 does not contact the shadow ring 130 and, as such, is not 
subject to being chipped or cracked by the impact with the shadow ring. In 
essence, the alignment ring 128 operates as a buffer to absorb the shock 
of contact with the shadow ring as the chuck is raised into the process 
position. This is an extremely important aspect of the invention for 
electrostatic chucks that are fabricated from ceramic materials such as 
aluminum-nitride, boron-nitride and the like. 
Useful material for the components of the shield assembly 118 must meet the 
environmental requirements of the processing system 100. As such, for high 
temperature PVD systems (e.g., deposition temperatures greater than 
500.degree. C.), the shadow and alignment rings are fabricated from 
alumina. Low temperature systems may use such materials as stainless 
steel, aluminum, titanium and copper. In these low temperature systems, 
stainless steel is a preferred material because it is relatively easy to 
clean. Aluminum or copper may be preferred when depositing materials such 
as tungsten which do not stick to stainless steel. 
Although various embodiments which incorporate the teachings of the present 
invention have been shown and described in detail herein, those skilled in 
the art can readily devise many other varied embodiments that still 
incorporate these teachings.