High power electrostatic chuck contact

In a vacuum processing chamber, an exemplary electrical contact assembly between an electrostatic chuck and a voltage source comprises a flexible wire connected at one end to the underside of the electrostatic chuck and at the other end to a conductive socket fixed in the electrode cap. An electrical contacting member which is connected to the voltage source is removably received into the socket so that the electrode cap can be replaced by lifting the electrode cap and socket off of the contacting member which is fixed in the electrode base.

FIELD OF THE INVENTION 
The present invention relates generally to an electrostatic chuck for 
holding a substrate in a vacuum processing chamber, and more particularly 
to an electrical contact for supplying power to an electrostatic chuck 
which allows the electrostatic chuck to be removed. 
BACKGROUND OF THE INVENTION 
Vacuum processing chambers are generally used for etching and chemical 
vapor deposition (CVD) of materials on substrates by supplying an etching 
or deposition gas to the vacuum chamber and application of an RF field to 
the gas. Examples of parallel plate, transformer coupled plasma (TCP), and 
electron-cyclotron resonance (ECR) reactors are disclosed in commonly 
owned U.S. Pat. Nos. 4,340,462; 4,948,458; and 5,200,232. The substrates 
are held in place within the vacuum chamber during processing by substrate 
holders. Conventional substrate holders include mechanical clamps and 
electrostatic chucks (ESC). Examples of mechanical clamps and ESC 
substrate holders are provided in commonly owned U.S. Pat. No. 5,262,029 
and commonly owned U.S. application Ser. No. 08/401,524 filed on Mar. 10, 
1995. Substrate holders in the form of an electrode can supply radio 
frequency (RF) power into the chamber, as disclosed in U.S. Pat. No. 
4,579,618. 
Mechanical clamps generally employ a clamp ring which surrounds the 
substrate and presses down on the top surface of the substrate around its 
periphery. Further examples of mechanical clamping rings are disclosed in 
U.S. Pat. Nos. 4,615,755; 5,013,400; and 5,326,725. Due to the fact that 
these known mechanical clamps cover the edge portions of the substrate, 
mechanical clamps reduce the area of the substrate which is able to be 
processed. Some additional drawbacks of mechanical clamps are that the 
clamp ring may cause damage to the edge of the substrate or may cause 
particles to become dislodged and contaminate the substrate in the 
chamber. In addition, although mechanical clamps are suitable for use in 
many applications with small substrates, when large substrates such as 
flat panel displays are processed using mechanical clamps, the panels may 
have a tendency to become bowed due to the supply of pressurized gas used 
for increasing thermal conduction between the substrate and the water 
cooled substrate holder. 
Electrostatic chucks are used for holding substrates (e.g., semiconductor 
wafers, flat panel display substrates, etc.) in place in a vacuum chamber 
in situations where it is desirable to avoid a clamping ring which extends 
over a portion of the substrate upper surface. Rather than mechanically 
clamping an article to the chuck, electrostatic chucks employ the 
attractive coulomb force between oppositely charged surfaces to clamp the 
article to the chuck. Electrostatic chucks of the monopolar type utilize a 
single electrode. The single electrode, separated from the wafer by a 
dielectric material, is biased with an AC or DC power supply. The article 
to be clamped acts as a second electrode and, together with the 
intervening dielectric and the first electrode, forms a parallel plate 
capacitor. The electrostatic force between the article and the chuck is 
proportional to the square of the voltage between them, proportional to 
the dielectric constant of the dielectric medium separating them, and 
inversely proportional to the square of the distance between them. U.S. 
Pat. No. 4,665,463 discloses an example of a monopolar electrostatic 
chuck. 
FIG. 1 shows the operation of a typical bipolar electrostatic chuck. 
Electrostatic chucks of the bipolar type utilize mutual attraction between 
polarized electrodes which are separated by a dielectric layer. For 
instance, see U.S. Pat. Nos. 4,692,836 and 5,055,964. As shown in FIG. 1, 
a series of interdigitated electrodes 42 and 44 are disposed within an 
encapsulating layer 32 of dielectric material. The electrodes 42 and 44 
rest on a base dielectric layer 30. By application of a voltage between 
the electrodes 42 and 44, e.g., applying voltages of opposite polarities 
to the two electrodes, electric fields 48 are created which intercept the 
wafer 14. In a bipolar electrostatic chuck, the attractive force is 
produced between polarized charges, i.e., the charge induced on the 
material to be chucked and the charge on the electrodes, to 
electrostatically clamp the wafer 14 to the dielectric material 32 by the 
Johnsen-Rahbek effect. 
To supply power to the electrodes of the electrostatic chuck, typically 
wires or cables are run from the electrodes through the electrode cap to 
the voltage source which supplies the voltage. FIG. 2, for example, shows 
an electrode cap 50 having an electrostatic chuck 52 sandwiched between 
two dielectric layers 54 and 56. A multi stranded wire 58 is connected to 
the electrostatic chuck 52 with a solder joint 60. The wire 58 passes 
through the electrode cap 50 and may be insulated from the conductive 
electrode cap 50 with a suitable insulator 62. The other end of the wire 
58 is connected to the voltage source. 
While the system shown in FIG. 2 operates adequately to supply power from a 
remote source to the electrostatic chuck 52, if any problems with the 
electrostatic chuck 52 arise or if a different electrostatic chuck is 
desired for a particular application, it is costly and difficult to 
replace the electrostatic chuck 52 which is sandwiched between two 
dielectric layers in the electrode cap and hard-wired to the voltage 
source. Such replacement typically encompasses a teardown of the system 
resulting in significant down-time. In addition, the arrangement shown in 
FIG. 2 utilizes a relatively long wire 58 to supply power to the 
electrostatic chuck 52 which limits the amount of power which may be 
supplied to the electrostatic chuck 52. 
SUMMARY OF THE INVENTION 
According to an exemplary embodiment of the present invention, a high power 
electrostatic chuck contact is provided. The contact may be housed within 
the electrode cap of a vacuum processing chamber and may include a socket 
which is electrically connected to an electrode of the electrostatic chuck 
with flexible wire which extends from the electrostatic chuck to the 
socket. The wire and the socket may be electrically insulated from the 
electrode cap. A contacting member is provided on the electrode base of 
the vacuum processing chamber to supply power to the electrostatic chuck 
via the socket. The contacting member may thus be connected at one end to 
a DC and/or an RF power source. The other end of the contacting member is 
received in the socket of the electrode cap. Because the contacting member 
is easily removed from the socket, the electrode cap, which houses the 
electrostatic chuck, is easily removed from the electrode base. 
According to another aspect of the present invention, the socket can be 
made to have a relatively large surface area for receiving the contacting 
member, the wire connecting the socket and the electrostatic chuck may 
contact the socket over a large surface area, and the wire connecting the 
socket and the electrostatic chuck may have a relatively short length. 
This configuration provides the additional advantage that RF energy can be 
coupled to a plasma, for example, through the electrostatic chuck, rather 
than through the electrode cap, which allows a lesser RF power to be used 
since the RF power is closer to the plasma and does not pass through a 
thick dielectric layer. 
An exemplary electrostatic chuck for a vacuum chamber thus comprises an 
electrode for clamping an article to the electrostatic chuck, a wire 
having a first end connected to the electrode, and a conductive socket 
connected to a second end of the wire, the conductive socket adapted to 
receive power through a removable electrical contacting member. 
An exemplary method of assembling an electrostatic chuck used to support 
substrates in a vacuum processing chamber comprises the steps of slidably 
attaching a removable cap including an electrostatic chuck and a first 
electrical contacting member to a support member including a second 
electrical contacting member such that the first and second contacting 
members are electrically connected together, and securing the cap to the 
support member with at least one fastening member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 3a-3c show an electrical contact assembly 100 according to an 
exemplary embodiment of the invention. The contact assembly 100 generally 
comprises a wire or cable 102 which is connected between an electrostatic 
chuck 104 and an electrical socket 106. The contact assembly 100 may be 
housed within the electrode cap 110 of a vacuum processing chamber. 
The electrostatic chuck 104 is preferably of the monopolar or bipolar 
variety and may include one or more electrodes which produce a coulomb 
attractive force on a substrate to be supported within the vacuum chamber. 
The electrodes may be sandwiched between an upper dielectric layer 112 and 
a lower dielectric layer 114 which insulate the electrodes from the 
electrode cap 110 and from the substrate to be supported. A thin silicone 
RTV layer 116 may be formed below the lower dielectric layer 114 to bond 
the lower dielectric layer to the electrode cap 110. 
As shown in FIG. 3c, a first end 108 of the wire 102 is connected to an 
electrode of the electrostatic chuck 104. In a bipolar electrostatic 
chuck, a first contact assembly 100 may be provided for one of the 
electrodes (e.g., the positive electrode) and a second contact assembly 
100 may be provided for the opposite electrode (e.g., the negative 
electrode). In addition, it is possible to use more than two contact 
assemblies 100 to supply power to the electrodes of the electrostatic 
chuck. To provide access to the electrodes, a recess 118 is formed in the 
bottom dielectric layer 114 and silicone RTV layer 116 where the 
connection is to be made. The wire 102 can then be electrically connected 
to the electrode by any suitable method, for example with a solder joint 
120. 
The combined thickness of the electrostatic chuck 104 and upper dielectric 
layer 112 can be as small as 0.15 millimeter, which makes the structure 
very fragile. To reduce the likelihood of damaging the electrostatic chuck 
104 and upper dielectric layer 112, it is preferable that the wire 102 be 
relatively flexible. A flexible wire reduces the amount of stress that may 
be applied to the electrostatic chuck 104 by the wire through handling, 
thermal cycling, etc. 
A second end 122 of the wire 102 is electrically connected to the socket 
106. The socket 106, which is shown in greater detail in FIG. 4, may 
include parallel flanges 124 which extend outward from the socket 106. The 
flanges 124 define an area 126 between them in which the cable 102 is 
connected. The cable 102 may thus be wrapped around the socket 106 in the 
connection area 126 which provides an electrical connection adequate for 
powering the electrostatic chuck 102 to clamp an article. 
According to a preferred embodiment, the socket 106 has a relatively large 
surface area and the cable 102 contacts the socket over a relatively large 
surface area. In addition, the cable 102 preferably has a relatively short 
length, e.g., 1.5 inches and a relatively large diameter, e.g., 0.09 
inches. This exemplary configuration allows high power RF energy to be 
coupled to the plasma through the electrostatic chuck rather than through 
the electrode cap 110 and provides the advantage that a reduced RF power 
can be used because there is significantly less dielectric material 
between the electrostatic chuck and the article than between the electrode 
cap 110 and the article. Therefore, less RF power is required because it 
is not necessary to power the RF energy from the electrode cap through a 
significant amount of dielectric material. According to one embodiment of 
the invention, the RF energy coupled through the electrostatic chuck is RF 
bias energy which controls, for example, the ion energy in the plasma. The 
plasma density may be controlled independently with a separate RF source. 
The end 108 of the cable 102 which is connected to the electrostatic chuck 
104 is preferably offset from a longitudinal axis 107 of the socket 106 
according to an exemplary embodiment of the invention. A top view of the 
electrode cap 110 which shows this configuration is illustrated in FIG. 5. 
In FIG. 5, two contact assemblies 100 are shown from above in which the 
location of the connection of the wire to the electrostatic chuck 104 is 
offset from the central axis 107 of the socket 106. 
The socket 106, which may be made of brass or any other suitable conductor, 
is fitted securely within a cup 128 shown in greater detail in FIGS. 6a 
and 6b. The cup 128 provides a cavity to receive the socket 106 and is 
preferably formed of an insulative material to insulate the socket 106 
from the electrode cap 110. For example, the cup 128 may be formed of 
TORLON, a 30% glass filed polyamideamide according to an exemplary 
embodiment of the invention. To receive the cable 102, the cup 128 may 
have an opening 130 which is adjacent to the connection area 126 of the 
socket 106. The interior diameter of the cup 128 may be enlarged at a 
lower portion 132 to accommodate the flanges 124 and connection area 126 
of the socket 106. When the cable 102 is connected to the socket 106, the 
cable is disposed within an annular space defined on the outside by the 
cup 128 and on the inside by the connection area 126 between the two 
flanges 124. 
The cup 128 and the socket 106 may be secured in the electrode cap 110 by 
means of a socket nut 134. As shown in greater detail in FIGS. 7a and 7b, 
the socket nut 134 provides a first abutting surface 136 which maintains 
the socket 106 within the cup 128 as well as a second abutting surface 138 
which retains the cup 128 in the electrode cap 110. The socket nut 134 can 
have outer threads 140 so that it can be screwed into corresponding inner 
threads in the electrode cap 110. The socket nut 134 thus provides a 
secure attachment of the socket 106 and insulating cup 128 in the 
electrode cap 110. The socket nut 134 is preferably formed of an insulator 
such as TORLON. 
To maintain the position of the wire 102 with respect to the electrostatic 
chuck 104 and to insulate the wire 102, the electrode cap 110 may include 
a cavity 142 filled with an insulator 144 such as epoxy, as shown in FIG. 
3a. The insulator 144 encapsulates the wire 102 which fixes the position 
of the wire 102 with respect to the electrostatic chuck 104, thus 
preventing the wire 102 from exerting any stress on the electrostatic 
chuck 104. To further insulate the wire 102, an insulating sheath 146 can 
be formed around the wire 102. The insulating sheath 146 preferably has a 
high breakdown voltage to prevent a discharge to the electrode cap 110, 
for example. 
FIGS. 8a and 8b show an exemplary contacting member 150 which is received 
into the socket 106 to provide power to the electrostatic chuck 104. One 
end of the contacting member 150 is connected to a DC voltage source which 
supplies power to the electrostatic chuck 104 to create the electrostatic 
clamping force. In addition, an RF bias source may be coupled to the 
contacting member so that the electrostatic chuck 104, rather than the 
electrode cap, provides at least a portion of the RF bias energy to the 
vacuum chamber. The RF bias source may be isolated from the DC voltage 
source with a conventional coupling capacitor. 
The other end of the contacting member 150 makes contact with the inside 
surface of the socket 106. According to a preferred embodiment, the 
contacting member includes contacts 154 which are flexible and which bow 
outwardly from the contacting member 150. Preferably, the contacts 154 bow 
outwardly to form a diameter which is greater than the inner diameter of 
the socket 106. In this way, the contacts 154 are forced inward when the 
contacting member 150 is inserted into the socket 106, which results in a 
good electrical connection between the contacting member 150 and the 
inside of the conductive socket 106. 
FIG. 9 shows the contact assembly 100 with the contacting member 150 
inserted into the socket 106. In this position, the contacts 154 of the 
contacting member 150 (see FIG. 8b) are forced inward by the inside 
surface of the socket 106. The contacting member 150 may be provided with 
a bushing 158, shown in greater detail in FIGS. 10a and 10b, which 
insulates a lower portion of the contacting member 150. The bushing 158 
may be formed of an insulator such as TORLON. The contacting member 150 
may be secured within the bushing 158 by means of a retaining screw 160, 
which is shown in greater detail in FIGS. 11a and 11b. The retaining screw 
160 may have outer threads 162 which are screwed into corresponding inner 
threads 164 on the bushing 158. The retaining screw 160 may be formed of 
NYLON or other suitable material. 
The bushing 158, because it is preferably formed of an insulating material, 
insulates the contacting member 150 from the base 170 of the electrode, as 
best shown in FIG. 12. FIG. 12 also shows the dividing line 174 between 
the electrode cap 110 and the electrode base 170. The electrode cap 110, 
which houses the electrostatic chuck 104, can be removed from the 
electrode base 170 because the contacting member 150 is easily removable 
from the socket 106. FIG. 9 further shows that the bushing 158 has a 
shoulder 176 which abuts the bottom of the electrode base 170 so that if 
the electrode cap 110 is removed, the shoulder 176 of the bushing 158 
retains the bushing 158 (and contacting member 150) in the electrode base 
170. The contacting member 150 then projects upward from the electrode 
base 170 to be plugged into a conductive socket on a replacement electrode 
cap. Because the electrode cap 110 and the electrostatic chuck 104 are 
removable from the electrode base 170, it is easy to replace the electrode 
cap and electrostatic chuck without the need for a system teardown. This 
provides a great advantage, for example, if the fragile electrostatic 
chuck becomes damaged or if a certain electrostatic chuck is desired for a 
particular process. In addition, because the contact arrangement between 
the electrostatic chuck and the power source is configured to allow high 
power RF energy to be coupled through the electrostatic chuck, exemplary 
embodiments of the present invention provide the additional advantage that 
the RF power can be reduced since it is closer to the plasma and does not 
pass through a significant amount of dielectric material. 
As will be readily appreciated by those skilled in the art, the electrical 
contact assembly according to exemplary embodiments of the present 
invention can provide enormous cost and time savings in the event that an 
electrostatic chuck needs to be replaced. Rather than undergoing a system 
teardown, the damaged electrostatic chuck can simply be unplugged from the 
electrode base and a replacement electrode cap plugged into the electrode 
base. Also, by utilizing a relatively flexible cable to connect the 
electrostatic chuck to the socket, the possibility of a damaging stress 
being applied to the underside of the fragile electrostatic chuck can be 
minimized. In addition, the dimensions of the contact assembly, e.g., the 
wire and socket, can be advantageously configured to allow high power RF 
energy to be coupled to a plasma, for example, through the electrostatic 
chuck rather than the electrode cap, which provides a significant savings 
in power consumption. 
The above-described exemplary embodiments are intended to be illustrative 
in all respects, rather than restrictive, of the present invention. Thus 
the present invention is capable of many variations in detailed 
implementation that can be derived from the description contained herein 
by a person skilled in the art. All such variations and modifications are 
considered to be within the scope and spirit of the present invention as 
defined by the following claims.