FIELD OF THE INVENTION

This invention relates to the prevention of the plasma damage during the
processing of amorphous silicon layers for the fabrication of passivated interface
heterojunction solar cells. More particularly, the invention relates to a method for
preventing plasma damages to surfaces of silicon wafer during plasma
deposition process in a plasma chamber
BACKGROUND OF THE INVENTION
When semiconductor devices are manufactured, various plasma processes, which
include dry etching, deposition by means of plasma CVD method and the like,
are used. The plasma contains various reactive species including high energy
ions. These reactive species or ions damage the surface of the substrates or
underlying layers when they impinge on them.
Concerning damage to the semiconductor devices, US patent no. 20040209467
A1 published in 2004, described a method for reducing plasma charging
damages on gate dielectric film. Polysilicon layer with smaller grain size is formed
over the gate dielectric film. Since the grain size is smaller, a low electric field is
developed at the grain tip at the polysilicon/dielectric film interface. Local
damages to the gate dielectric film are thus reduced.

US patent no. 20080199612 A1 published in 2008, a method and apparatus is
described for hydrogenation of a target for healing of the plasma damage, such
as a polycrystalline silicon film on a glass substrate, by using an atomic hydrogen
source. The target is subjected to intermittent exposure of the atomic hydrogen
field of the source until at least one area of the target has been subjected to the
hydrogen field for a predetermined minimum period of time. The processing area
of the source established by its atomic hydrogen field is smaller than the target,
and after the target is moved into the high temperature processing zone it is
translated within the high temperature processing zone to intermittently process.
In another prior art described in U.S. Pat. No. 6,235,642 filed in Jan 2000. A
method for collecting and grounding through trench regions is given. However,
additional processes are needed to form the conduction channels for diverging
charges to ground.
In addition to the plasma processing damage, due to potential of the devices
because of charge buildup, instant damage of the surface of the device occurs
during impingement of high energy ions at the plasma start up. The plasma that
is generated in the reaction chambers is designed to maintain a balance between
the number of the positive charges and the number of the negative charges.
However, during plasma ignition time, higher voltage is applied for plasma start
up and a large amount of current flow resulting in high energy ion impingement
on the surface of the device.

Plasma deposition of thin films on a substrate requires the substrates to be
placed on a grounded or electrically powered plateform. Usually the sample is
first placed under the electrode, and the plasma is ignited. This method creates
plasma damage to the initial layers of the deposited layers. This kind of damage
are significant and are detrimental to the devices.
OBJECT OF INVENTION
It is therefore an object of the invention to propose a method for preventing
plasma damages to surfaces of silicon wafer during plasma deposition process in
a plasma chamber.
SUMMARY OF THE INVENTION
According o the present invention, high vacuum resident zones are provided in
the chamber and the plasma ignition is initiated when the same is not under the
electrode. The deposition is carried out in a moving mode after the plasma is
stabilized thus preventing plasma ignition time damage.
According to the invention, a system is designed, where a sample is fed through
the plasma zone only after the plasma is ignited. Thus helps in avoiding the
plasma ignition damage to the sample.

BRIEF DESCRPTION OF THE ACCOMPANYING DRAWING
Figure 1 shows schematic of a plasma deposition chamber with resident zones
formed on both sides of the plasma zone.
DETAILED DESCRIPTION OF THE INVENTION
In figure 1, schematic of the plasma deposition chamber (1) is given. The
chamber consists of a stainless steel chamber, wherein at least one plasma zone
(2) and two resident zones (3) are accommodated in the chamber. The chamber
has a pumping arrangement (10) equipped with vacuum creating pumps. The
process gases (8) are fed through an electrode (9) creating glow discharge (80).
Samples (4) (silicon wafers or glass pieces) are loaded in a carrier and are
moved under the electrode using a transport arrangement (5). The chamber (1)
can be attached to other chambers though gate valves (11).
For carrying out plasma deposition process, the substrates (4) are brought in
though the gate valve 11 and parked in the chamber (1) in the resident zone (3).
The system is evacuated to a predetermined level of vacuum and the process
gases are introduced. Once parameters like gas flows, pressure, temperature etc
are stabilized, the plasma is ignited. The power is minimized to the
predetermined process requirement and the substrates (4) are moved from left
resident zone (3) to the right resident zone (3). The layers are deposited on the
substrates (4) in a moving mode as they pass through the plasma zone (2).

WE CLAIM :
1. A method for preventing plasma damages to surfaces of silicon wafer
during plasma deposition process in a plasma chamber, the plasma chamber
(1) comprising a metal chamber accommodating at least one plasma zone
(2); two vacuum resident zones (3); a plurality of vacuum creating pumps
(10); an electrode (9) receiving process gases (8) via a port created in the
chamber (1) and generating glow discharge; a transport means (5) to allow
movement of silicon wafer samples (4) under the electrode (9); and a
plurality of valves (11) enabling the chamber (1) with additional chambers,
the method comprising :
placing the samples (4) through the gate valve (11) into the chamber (1)
and parking in a proximate resident zone (3) under high vacuum;
evacuating the chamber (1) to a predetermined level of vacuum;

introducing the process gases (8) into the chamber (1) and allowing the
gas pressure, gas flow and gas temperature to be stabilized;
igniting the plasma including adjustment of the plasma to a required
power;
moving the samples (4) from the proximate resident zone (3) to a distant
resident zone (3) under the electrode (9); and
depositing layers on the samples (4) in a moving mode of the samples
when crossing the plasma zone (2).
2. The method as claimed in claim 1, wherein the chamber (1) is made of
stainless steel.