Electrostatic chuck with improved RF power distribution

Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – With microwave gas energizing means

Reexamination Certificate

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Details

C361S234000, C279S128000, C118S728000

Reexamination Certificate

active

06267839

ABSTRACT:

BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The invention relates to semiconductor wafer processing equipment and, more particularly, the invention relates to electrostatic substrate supports having an RF bias electrode.
2. Description of the Background Art
A semiconductor wafer processing system for manufacture of integrated circuits (IC's) generally includes a vacuum chamber within which is mounted a wafer support during processing. The wafer support typically comprises a susceptor mounted to a pedestal. The pedestal is typically fabricated from a metal such as aluminum. The susceptor may be fabricated from laminated sheets of a polymer. However, for high temperature applications, the susceptor is typically fabricated from a ceramic material such as aluminum oxide or aluminum nitride. The susceptor typically contains various components which provide heating and/or cooling of the wafer. The susceptor may also include elements for clamping (chucking) a wafer to retain it in a stationary position upon the susceptor surface. Such clamping is provided by either a mechanical clamp or an electrostatic chuck. The susceptor may also include one or more electrodes for applying a bias voltage to the wafer. Such a bias voltage may be a direct current (DC) bias or a radio frequency (RF) bias. An RF bias may be used, for example, to supply or enhance power to a plasma that exists within the chamber during an etch or deposition process.
FIG. 1
depicts a wafer support
100
of the prior art. In the wafer support
100
, a pedestal
102
supports a ceramic susceptor
104
. The susceptor
104
is typically made by cold laminating several layers
106
i
(e.g. layers
106
1
,
106
2
. . .
106
5
) of “green tape” consisting of a ceramic powder of alumina or aluminum nitride with a suitable organic binder such as butadiene (synthetic rubber) or poly-methyl methacrylate. The electrode patterns
108
are screen or stencil printed onto the appropriate green tape layer using inks or pastes made with molybdenum or tungsten powders along with a suitable organic binder. Interconnections between the electrodes
108
and connections
112
to the exterior of the susceptor are made by punching holes in the green tape layers and filling them with the same or similar tungsten/molybdenum paste through screen printing masks to form vias
110
. The laminated layers are sintered at elevated temperatures to solidify the ceramic to form the monolithic susceptor
104
with thick film metal electrodes
108
embedded in the ceramic. During the sintering process, the organic binders are charred and removed as CO and CO
2
.
The metal paste and the ceramic layers
106
generally sinter at different temperatures and, thus, shrink non-uniformly during sintering. Such non-uniformity in the shrinkage, if severe enough, causes severe bowing, distortion or cracking of the laminate. To alleviate such problems, the metal inks or pastes are usually mixed with large proportions (up to 40% by volume) of ceramic powder to match the shrinkage behavior of the surrounding ceramic during sintering.
Prior art attempts to solve the problem include using thicker electrodes. However, the thickness of the electrodes
108
is limited to only 10 or 15 microns by the sintering process. If the metal electrodes are made thin and fragile they easily break and reform many times due to the shrinkage in the surrounding ceramic. Thus, strains are dissipated before they become large enough to damage the ceramic.
The resulting electrodes
108
and interconnecting vias
110
and connections
112
are, therefore, highly resistive. High resistivity is not a problem where the electrode
108
serves only as a DC electrode for chucking or DC bias. However, high resistivity presents a problem when it is desired to use the electrode
108
for RF bias.
The problem arises because, in common designs, the vias
112
connecting the electrodes
108
to the outside are located in the central area
114
of the susceptor. A thin highly resistive electrode will have a high impedance due to ohmic resistance. Consequently, a large proportion of the power delivered to the electrodes
108
will be dissipated as heat. Thus, the efficiency of RF power transferred to the plasma in the chamber is low. This is unsuitable for delivery of RF energy to the plasma at power levels of 500 to 1500 watts. Furthermore, the RF power distribution over the area of electrodes
108
is non-uniform which leads to non-uniformity of the plasma temperature across the wafer. The plasma develops “hot spots” where the plasma temperature is greater. Consequently, the etch, deposition or other plasma process will be non-uniform over the surface of the wafer. Thus, a number of the IC's on a given wafer may be rendered unusable thereby decreasing wafer yield.
Other solutions involve stacking multiple thin RF electrodes in layers separated by layers of ceramic. The RF power is then capacitively coupled from one electrode layer to the next. Although this does reduce the overall impedance of the metal structure, it also leads to power losses through the capacitive couplings. Furthermore, it does not solve the problem of non-uniform RF power distribution over the area of the electrodes.
Therefore, a need exists in the art for a susceptor for a semiconductor processing system having a low impedance electrode structure that uniformly distributes RF power over the area of the electrode and a concomitant method of manufacturing same.
SUMMARY OF THE INVENTION
The disadvantages associated with the prior art are overcome by the present invention of a susceptor having multiple parallel electrical contacts between an RF electrode and a thick, robust electrode near the bottom of the susceptor. The thick, robust electrode has a low resistance and, therefore, evenly distributes RF power over its area. The multiple parallel electrical contacts ensure that the RF power is also uniformly distributed across an area of the RF electrode. The susceptor generally comprises a ceramic support body, at least one RF electrode embedded within the body, a robust electrode disposed below the RF electrode, and a plurality of electrically conductive vias extending between the robust electrode and the RF electrode. The vias make a plurality of parallel electrical contacts between the robust electrode and a plurality of points substantially uniformly distributed over an area of the RF electrode. The robust electrode, RF electrodes and vias are typically made of a metal such as molybdenum, tungsten or copper. Generally, the robust electrode is attached to a bottom side of the support body and is aligned substantially parallel to the RF electrode. An insulator plate is attached to the bottom side of the support body for electrically isolating the robust electrode from a pedestal that supports the susceptor.
A method of fabricating a susceptor of the present invention begins with the step of forming a ceramic body. The body is formed by creating a plurality of layers of ceramic green tape and stacking the layers on top of one another. One or more electrodes are embedded within the ceramic body by screen printing one or more electrode patterns on selected ones of the layers using a paste containing a metal powder. A plurality of vias is formed by punching holes in selected layers such that the holes in adjacent layers are aligned when the layers are subsequently stacked together. After the holes are filled with a paste containing a metal powder the layers are stacked. After stacking, the layers are cured to form the ceramic body. The metal powder consolidates to form the electrodes and vias. The vias form a plurality of contacts at a plurality of points substantially uniformly distributed over an area of the RF electrode.
A robust electrode, having a low resistance, is disposed below the other electrodes at a bottom of the ceramic body. The robust electrode is joined to the exposed ends of the vias. Thus, the vias form a plurality of parallel electrical connections between the robust electrode and a plurality of points

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