Plasma chamber equipped with temperature-controlled focus...

Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of...

Reexamination Certificate

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C438S636000, C438S582000, C438S738000

Reexamination Certificate

active

06767844

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to a semiconductor processing equipment and a method for using the equipment, more particularly, relates to a plasma chamber that is equipped with a temperature-controlled focus ring and a method of operating the chamber.
BACKGROUND OF THE INVENTION
In the fabrication of modern integrated circuit devices, one of the key requirements is the ability to construct plugs or interconnects in reduced dimensions such that they may be used in a multi-level metalization structure. The numerous processing steps involved require the formation of via holes for the plug or interconnect in a dimension of 0.5 &mgr;m or less for high-density logic devices. For instance, in forming tungsten plugs by a chemical vapor deposition method, via holes in such small dimensions must be formed by etching through layers of oxide and spin-on-glass materials at a high etch rate. A high-density plasma etching process utilizing a fluorine chemistry is thus used for such via formation process.
The via hole formation process can be enhanced by improving the etch directionality by a mechanism known as sidewall passivation to improve the anisotropy of the etching process. By utilizing a suitable etchant gas and suitable reactor parameters, an etch-inhibiting film of a polymeric nature can be formed on vertical sidewalls. The etch-inhibiting film slows down or completely stops any possible lateral etching of horizontal surfaces in the via hole. For instance, when a fluorine-containing etchant gas such as CFH
3
is used, a fluorine-type polymeric film is formed on the sidewalls. Many photoresist materials may also contribute to the formation of polymeric films on the sidewalls. After the sidewall is coated with a polymeric film, it is protected by the inhibitor film to preserve the line width or via hole diameter control.
In a modern etch chamber, an electrostatic chuck (or E-chuck), is frequently used in which the chuck electrostatically attracts and holds a wafer that is positioned on top. The use of E-chuck is highly desirable in the vacuum handling and processing of wafers. In contrast to a conventional method of holding wafers by mechanical clamping means where only slow movement is allowed during wafer handling, an E-chuck can hold and move wafers with a force equivalent to several tens of Torr pressure. Another advantage for the E-chuck is that no particle generation or contamination problem can occur since there are no moving parts acting on the wafer. Moreover, the electrostatic force utilized on an E-chuck is sufficient in preventing bowing of a wafer which normally occurs in mechanical clamping and thus promotes uniform heat transfer over the entire wafer surface.
In an etch chamber equipped with a plasma generating device and an E-chuck, a shadow ring may be utilized as a seal around the peripheral edge of the wafer. The shadow ring, also known as a focus ring, is utilized for achieving a more uniform plasma distribution over the entire surface of the wafer and for restricting the distribution of the plasma cloud to only the wafer surface area, i.e. and thus the name of focus ring. The uniform distribution function may be further enhanced by a RF bias voltage applied on the wafer during a plasma etching process. Another function served by the shadow ring is sealing at the wafer level the upper compartment of the etch chamber which contains the plasma from the lower compartment of the etch chamber which contains various mechanical components for controlling the E-chuck. This is important since it prevents the plasma from attacking the hardware components contained in the lower compartment of the etch chamber. In order to survive high temperature and hostile environments, a shadow ring is frequently constructed of a ceramic material such as quartz.
In an etch chamber equipped with a high density plasma and an E-chuck, problems sometimes arise in the operation of the E-chuck. High density gas plasma formed has a short debye length and consequently vary small sheaths are formed at boundaries of objects that are present in the gas plasma. In order to prevent the plasma from affecting the voltage on the electrode of the E-chuck, the electrode positioned in a plasma chamber must be sufficiently isolated from the plasma. In a typical E-chuck positioned in a high density plasma, the electrode has a voltage applied to it with respect to a ground reference point. The wafer is referenced back to the same ground reference by the plasma. The effective voltage for the electrostatic clamping of the wafer is then the voltage which appears across the E-chuck dielectric layer between the isolated electrode and the wafer. The voltage applied to the isolated electrode may be positive or negative with respect to the chamber ground. However, the electrostatic force depends on the algebraic difference between the wafer and the isolated electrode.
When the gaps around an E-chuck exceed several debye lengths, plasma may either be generated in the gaps or may be extracted into the gaps. When the plasma contacts the electrostatic chuck which has an imperfect dielectric layer or the E-chuck electrode, a current may flow between the E-chuck and the plasma. The voltage at the E-chuck electrode is therefore affected. Typically, the magnitude of the E-chuck voltage is reduced when a current flows between the chuck and the plasma which leads to a reduction in the electrostatic force. The efficiency of the E-chuck for holding a wafer is therefore affected. Ideally, the solution to the problem is to shield the E-chuck from the high density plasma by limiting gaps between the E-chuck and a shadow ring around the E-chuck to less than several debye lengths. In such an ideal situation, plasma can be prevented from being generated in the gaps or being extracted into the gaps. Since the ideal equipment conditions cannot be achieved in a manufacturing environment, the generation of plasma in the gaps or the extraction of plasma into the gaps and therefore attacking a shadow ring which is normally fabricated of quartz cannot be avoided. In a normal fabrication environment, it has been found that a quartz shadow ring would only survive about one preventive maintenance cycle or about 2,000 wafers. The corrosion occurred on the surface of the quartz shadow ring is usually severe enough that it must be replaced during a preventive maintenance procedure.
Referring initially to
FIG. 1
, wherein a conventional etch chamber
10
equipped with a shadow ring
12
around an electrostatic chuck
16
is shown. The etch chamber
10
is equipped with a coil antenna
14
as a plasma source in a reaction chamber
20
formed by a silicon ceiling block
22
, a dome-shaped sidewall
24
, a chamber wall liner
26
and the electrostatic chuck
16
. The dome-shaped sidewall
24
and the chamber wall liner
26
are normally fabricated of quartz. The chamber wall liner
26
may be equipped with an opening for the passage of a wafer paddle in loading and unloading wafers. It may be removed from the vacuum chamber
10
for cleaning.
The shadow ring
12
is positioned inside the plasma reaction chamber
20
which can be lifted up to a process position by positioning pins
32
. The positioning pins
32
lift the shadow ring
12
away from the wafer when a wafer is being loaded or unloaded. A multiplicity of cooling gas channels
34
is provided inside the electrostatic chuck
16
at near its top surface
36
. A high heat conductivity gas such as helium can be circulated through the cooling gas channels
34
to provide a suitable gas pressure on the bottom side of wafer
30
for transferring heat away from the wafer to the water-cooled E-chuck
16
during an etch process. The supply lines for the cooling gas to channel
34
are not shown. The electrostatic chuck
16
is aligned by an electrostatic chuck collar
38
. The etching gas is fed into chamber
20
through gas inlet
28
. A thermal coupler
42
is mounted in the silicon ceiling block
22
for controlling temperature.
The shadow ring, or focus ring
12
,

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