Coating apparatus – Gas or vapor deposition – With treating means
Reexamination Certificate
2000-02-17
2002-04-09
Mills, Gregory (Department: 1763)
Coating apparatus
Gas or vapor deposition
With treating means
C118S7230ME, C118S7230ER, C156S345420, C055S286000
Reexamination Certificate
active
06367412
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to plasma sources. In particular, the invention relates to liners used in inductively or microwave powered plasma sources.
BACKGROUND ART
Plasma processing is widely used in many applications in the field of fabrication of semiconductor integrated circuit. In the most common and long standing class of application, one or more wafers are inserted in a plasma reactor, and a processing gas is injected into the reactor and is excited into a plasma by coupling electrical energy into the plasma reactor. In etching applications, the processing gas typically includes a halogen-based gas, and typically RF power is applied to the pedestal electrode supporting the wafer to excite the gas into a plasma. In applications involving chemical vapor deposition, the processing gas includes chemical precursors of the material to be deposited, and typically RF power is applied to a showerhead electrode in opposition to the wafer being coated. The RF plasma activates the chemical reaction converting the precursor gas into the material coated on the wafer. In sputtering applications, typically negative DC power is applied to a target electrode comprising the material to be sputter deposited on the wafer. A working gas, such as argon, is excited into a plasma, and the positive argon ions are attracted to the negatively biased target to sputter the target material, which is then deposited on the wafer. Recently, there has been much interest in high-density plasma (HDP) reactors additionally including an RF inductive coil positioned adjacent to the plasma reactor to couple RF energy into a plasma source region.
Aside from these standard applications, plasmas have also been used for auxiliary purposes in semiconductor processing chambers. Plasmas are used to dry clean surfaces of the chamber without the need to open the chamber for operator access or even to vent the chamber to atmospheric pressure. Plasmas have also been used to clean or precondition wafer surfaces before the more standard types of processing, whether by plasma or by thermal activation.
Most typically, the plasma is generated in the processing chamber containing the substrate being processed. However, for some processes, the gas is excited into a plasma in a remote location and then transported in its excited state to the processing chamber. One such configuration is illustrated schematically in
FIG. 1. A
processing reactor
10
includes a pedestal
12
for supporting a wafer
14
to be processed. A vacuum pumping system
16
connected to the reactor
10
maintains the reactor at the relatively lower pressures associated with semiconductor processing, particularly plasma processing. These pressures are typically in the range of about 1 milliTorr to a few hundred Torr. The details of the reactor
10
are not illustrated, and the reactor may be configured for etching, CVD, sputtering, or possibly other processes. Particularly for CVD, the deposition may be performed by a thermal process while auxiliary functions may be performed by a plasma process.
A remote plasma source (RPS)
20
is connected to the reactor
10
but is distinctly separate from it. The RPS
20
receives gas from a gas source
22
, excites it into a plasma, and delivers the plasma-excited gas to the reactor
10
. A plasma usually contains some combination of ions and radicals of the excited gas. For example, a hydrogen plasma created from H
2
gas may contain positively charged H
+
ions and neutral H* radicals. Usually, the path between the remote plasma source
20
and the reactor
10
is long enough that the ions recombine before reaching the reactor and a mostly neutral stream of radicals is delivered to either process the wafer
14
or to clean the wafer
14
or the reactor chamber
10
. However, there are applications, such as metal etching, in which a remote plasma source excites the processing gas into a plasma for etching or other direct processing of the wafer without the use of a plasma source within the reactor chamber.
Remote plasma sources usually rely on a large amount of microwave or RF energy applied to a dielectric tube carrying the gas. This configuration is referred to as an applicator. The large amounts of applied power, its application in sequences lasting on the order of minutes or less, and the corrosive nature of even argon plasmas have imposed severe design constraints on the applicator.
A similar set of problems has arisen in a structurally similar application of abatement plasma chambers. Semiconductor processing often involves noxious processing gases or noxious gaseous byproducts. In the past, the standard procedure has relied upon tall smokestacks to vent the gaseous exhaust from semiconductor processing reactors to a height sufficient that the noxious exhaust presents little risk of harm at ground level. Many people will no longer accept such a solution, and such exhausts are regulated by state and federal regulations. Chlorofluorocarbons (CFCs) have been shown to deplete the ozone layer on a world-wide scale. An international treaty has attempted to reduce if not virtually eliminate the emission of CFCs into the atmosphere. Furthermore, environmental and local political groups have shown an increasing intolerance for any emission of noxious material into the atmosphere regardless of the level of risk associated with such emission.
For these reasons, clean semiconductor processing systems are greatly desired. The use of CFC precursors has in large part been eliminated. Nonetheless, the complex plasma chemistry may result in a large number of materials in the exhaust, and the variety and uncertainty have made it difficult to assure that there is no noxious material in the reactor exhaust. Therefore, one favored approach scrubs the exhaust to somehow remove or deactivate those chemicals considered to be dangerous. One generic approach is to plasma treat the exhaust from the chamber to assure that the contents of the exhaust are in a benign form. For example, they have been thoroughly oxidized. With few exceptions, oxides of almost all materials used in semiconductor processing are not considered to be particularly dangerous.
Such a plasma abatement system is schematically illustrated in FIG.
2
. It includes a dielectric plasma tube
30
positioned between the processing chamber
10
and the final stage of the vacuum pumping system
16
. Additional pumping elements may be positioned upstream of the plasma tube
30
, but the pressure within the tube
30
must be low enough to allow a plasma to be excited from the exhaust gas. An RF coil
32
is wrapped around the plasma tube and is powered from an RF source
34
to couple sufficient electrical energy into the plasma tube
30
to excite the gas within it into a plasma. A oxygen source
36
is positioned upstream of the plasma tube
32
to inject oxygen into the exhaust stream so that the plasma within the plasma tube contains not only the exhaust but also sufficient oxygen to oxidize substantially all of the oxidizable components of the exhaust whatever their source and composition. The figures fail to illustrate the valves and mass flow controllers associated with the gas sources
22
,
36
,
42
.
To provide some specificity to the example, the reactor is assumed to be a capacitively coupled oxide etch reactor in which the pedestal electrode
12
is selectively powered from an RF power source
40
to excite a perfluorocarbon etching gas supplied from a source
42
into an etching plasma. Examples of perfluorocarbons are CF
4
, C
2
F
6
, C
3
F
8
, C
4
F
8
, and C
4
F
6
. Typically, an argon diluent gas is also supplied, but argon is a chemically inactive gas considered to be harmless in the small amounts associated with plasma processing and will not be further discussed. Although the perfluorocarbon is excited into a plasma to chemically react with the oxide being etched and to a lesser extent with the chamber parts and other parts of the integrated circuit structure, a substantial fraction of unreacted perfluorocarbon gas is exh
Bhatnagar Ashish
Kaushal Tony S.
Moalem Mehran
Ramaswamy Kartik
Shamouilian Shamouil
Bach Joseph
Guenzer Charles S.
Hassanzadeh P.
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