Method for preventing contamination in a plasma process chamber

Details Method for preventing contamination in a plasma process chamber Method for preventing contamination in a plasma process chamber

2001-04-18

2002-11-19

Mills, Gregory (Department: 1763)

Etching a substrate: processes

Gas phase etching of substrate

Application of energy to the gaseous etchant or to the...

C438S710000

Reexamination Certificate

active

06482331

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to a plasma process and a chamber for conducting such process and more particularly, relates to a method for preventing particle contamination in a plasma process chamber and an apparatus for carrying out such method.
BACKGROUND OF THE INVENTION
In the fabrication of semiconductor integrated circuit (IC) devices, various device features such as insulation layers, metallization layers, passivation layers, etc., are formed on a semi-conducting substrate. It is known that the quality of an IC device fabricated is a function of the processes in which these features are formed. The yield of an IC fabrication process is in turn a function of the quality of the device fabricated and a function of the cleanliness of the manufacturing environment in which the IC device is processed.
The ever increasing trend of miniaturization of semiconductor IC devices occurring in recent years requires more stringent control of the cleanliness in the fabrication process or in the processing chamber where the process is conducted. This leads to a more stringent control of the maximum amount of impurities and contaminants that are allowed in a process chamber. When the dimension of a miniaturized device approaches the sub-half-micron level, even a minutest amount of contaminants can significantly reduce the yield of the IC manufacturing process. For instance, the yield of the process can be drastically reduced by the presence of contaminating particles during deposition or etching of films which leads to the formation of voids, dislocations or short-circuits resulting in performance and reliability problems in the IC devices fabricated.
In recent years, contamination caused by particles or films has been reduced by the improvements made in the quality of clean rooms and by the increasing utilization of automated equipment which are designed to minimize exposure to human operators. However, even though contaminants from external sources have been reduced, various contaminating particles and films are still generated inside the process chamber during the processing of semiconductor wafers. Some possible sources of contamination that have been identified include the process gases and liquids, the interior walls of the process chambers and the mechanical wear of the wafer handling equipment. The chances of generating contaminating particles are also increased in process chambers that are equipped with plasma enhancement. Various chemically reacted fragments are generated from the processing gases which include ions, electrons and radicals. These fragments can combine and form negatively charged particles which may ultimately contaminate a substrate that is being processed in the chamber. Various other materials such as polymeric films may also be coated on the process chamber walls during plasma processing. The films may dislodge and fall from the process chamber walls when subjected to mechanical and thermal stresses such that they fall onto the wafers that are being processed.
An example for illustrating chamber wall contamination is the etcher
10
shown in FIG.
1
. Etcher
10
is a plasma chamber that is equipped with magnetic field enhancement generated by an upper rotating magnet
12
and a lower rotating magnet
14
. The plasma etcher
10
includes a housing
16
that is typically made of a non-magnetic material such as aluminum which defines a chamber
20
. A substrate holder
22
which is also a cathode is connected to a RF generator
24
which is in turn connected to a gas inlet (or showerhead)
26
. The showerhead
26
also acts as an anode. A process gas
28
is supplied to chamber
20
through the gas inlet
26
. A semi-conducting substrate
30
to be processed is positioned on the substrate holder or cathode
22
.
The semi-conducting substrate
30
is normally held against the substrate holder
22
by a clamp ring
32
. During a plasma etching process, a semi-conducting wafer
30
heats up significantly during the process and must be cooled by a cooling gas from a cooling gas supply (not shown) such that heat can be transferred to a water cooled wafer holder
36
. The function of the clamp ring
32
is also to hold the substrate
30
down against the pressure generated by the cooling gas. An exhaust port
34
which is connected to a vacuum pump (not shown) evacuates the chamber. During an etching process, the upper rotating magnet
12
and the lower rotating magnet
14
function together to provide a magnetic field inside the process chamber
20
.
In a conventional cleaning process for the plasma etch chamber
10
, a cleaning gas supply is first flown through the gas inlet port
26
into the chamber
20
and then, the RF generator
24
is turned on. The cleaning procedure is conducted after a predetermined number, i.e. between 100-500 of wafers have been processed in chamber
20
. A plasma of the cleaning gas ions is formed in the space between the showerhead
26
and the wafer holder
32
to loosen the contaminating particles and films from the chamber walls and the showerhead
26
(i.e. the upper electrode).
In an etching process for polysilicon or metal, a chlorine etching gas is frequently used. On the other hand, the etching gas used for oxide or nitride is frequently a fluorine gas. During a plasma etching process, the reactive plasma ions have a high energy level and therefore can easily combine with any available chemical fragments or elements in the chamber to form contaminating particles or films. For instance, in a metal etching process, the elements frequently seen in the etch chamber includes C, H, N, O, Al, Ti, TiN and Si. Different elements such as C, N, O, Br, Si and W are seen in a polysilicon etch chamber. The contaminating particles or films formed by often volatile chemical fragments or elements during an etching process float or suspend in the chamber due to the interaction with high energy plasma ion particles when the RF power is turned on. The phenomenon of the floating or suspended particles can be explained by the fact that the particles have higher energy and temperature while suspended in a plasma cloud. However, at the end of a conventional etching process, the RF power is switched off which leads to the sudden loss of energy in the suspended contaminating particles and causing them to fall or stick to the chamber walls or the upper electrode. This is shown in
FIGS. 2A and 2B
.
FIG. 2A
shows a simplified etch chamber
40
equipped with a chamber cavity
42
defined by chamber walls
44
. A process gas inlet
46
is used to flow a process gas into the chamber cavity
42
. An upper electrode
48
and a lower electrode/wafer holder
50
are used to supply RF power to the chamber and to produce plasma ions. A gas outlet
54
is used to evacuate the process gas from the chamber cavity
42
at the end of the etching process. During the etching process, contaminating particles
52
formed as etch byproducts are buoyant and are suspended in the chamber cavity
42
. A wafer
56
is supported by the wafer holder
50
for processing.
After a conventional etching process is conducted, the RF power and the heating lamps are turned off. The suspended, contaminating byproducts or particles
52
are easily deposited on chamber walls
58
, upper electrode
48
and wafer
50
. These contaminating particles (or films) are frequently formed of a carbon or chlorine containing polymeric material and when adhered to the chamber wall
58
, are very difficult to remove. Conventionally, a wet cleaning process must be conducted after approximately 2,000-4,000 wafers have been processed in the etch chamber
40
. The wet cleaning process is carried out by suing cleaning solvent such as IPA, deionized water, combination IPA/deionized water or the more volatile acetone. The wet cleaning process causes a downtime of the etcher as long as one full day.
It has been discovered that a major chamber contamination source is the polymeric material that adhered to the chamber wall during the etching process when the chamber wall is heat

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