Title of Invention	AN AUTOMATIC GAS DELIVERY SYSTEM FOR DIFFUSION OF DOPANT IN SILISON USING A LIQUID DOPANT SOURCE SUCH AS PHOSPHOROUS OXYCHLORIDE (POCI3)
Abstract	This invention relates to an automatic gas delivery system for dopant diffusion in semiconductors using a liquid diffusion source. It works on the basis of a PLC based controller module (1.1), a display cum keyboard panel (1.6), a relay card (1.2) and a manifold of electro-pneumatic solenoid valves (1.3) actuating a set of corresponding pneumatic valves in a combination of sequences allowing a flow of carrier gas (N2) through a bubbler containing liquid dopant source, reactant gas (O2) and dilution gas (N2) through different routes of gas manifold for mixing inside the diffusion furnace for the purpose of dopant diffusion in semiconductors.

Title of Invention

AN AUTOMATIC GAS DELIVERY SYSTEM FOR DIFFUSION OF DOPANT IN SILISON USING A LIQUID DOPANT SOURCE SUCH AS PHOSPHOROUS OXYCHLORIDE (POCI3)

Abstract

This invention relates to an automatic gas delivery system for dopant diffusion in semiconductors using a liquid diffusion source. It works on the basis of a PLC based controller module (1.1), a display cum keyboard panel (1.6), a relay card (1.2) and a manifold of electro-pneumatic solenoid valves (1.3) actuating a set of corresponding pneumatic valves in a combination of sequences allowing a flow of carrier gas (N2) through a bubbler containing liquid dopant source, reactant gas (O2) and dilution gas (N2) through different routes of gas manifold for mixing inside the diffusion furnace for the purpose of dopant diffusion in semiconductors.

Full Text	FIELD OF THE INVENTION; The invention relates to the manufacture of semiconductors and solar photovoltaics in general and to a gas delivery system for diffusion of dopant in particular. PRIOR ART Dopant diffusion in silicon using a liquid dopant source is carried out for the manufacture of silicon solar cells and many other silicon based semiconductors devices. POCl3 (phosphorus oxy chloride) is the most commonly used liquid source. In the prior art, the equipment for automatic and controlled delivery of POCl3 vapours into the diffusion furnace formed a part of the diffusion furnace itself and was available at an exorbitant cost. The essential components of the gas delivery system are the gas manifold with proper design and the automatic controller. The present invention provides an automatic and simpler gas delivery system in place of the existing gas line plumbing and automatic controller of prior art. Moreover the equipment in prior art is largely imported. OBJECTS OF THE INVENTION; An object of the invention is to provide a gas delivery system, which is easier to install and maintain. Another object of the invention is to provide a gas delivery system, which is economical. A further object of the invention is to reduce dependence on foreign suppliers of such equipment. DESCRIPTION OF THE INVENTION; The automatic gas delivery system for diffusion in silicon using liquid diffusion source in accordance with the invention, works on the principle of opening and closing of a set of air-operated valves in a combination of programmed sequences to allow various gases, namely carrier nitrogen, dilution nitrogen and oxygen through different routes laid out in a gas manifold for mixing inside the diffusion furnace for the dopant diffusion in silicon. The gases are supplied in predetermined sequence and quantities to ensure optimum delivery and mixing of the gases in the diffusion furnace. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS; Fig. 1 shows a block diagram of the automatic controller. Fig. 2 shows a schematic diagram of the gas manifold according to the invention. Table 1 shows the sequence and combination of valve opening in the diffusion process. Fig. 3 is a photograph of the automatic gas delivery system for diffusion in silicon. An exemplary embodiment of the invention as depicted in the accompanying drawings will now be explained in details. However, there can be several other embodiments, all of which are deemed covered by this specification. As shown in Fig. 1, the control system comprises a programmable logic controller (PLC) (1.1), a display cum keyboard panel (1.6), a relay card (1.2) and a manifold of solenoid valves (1.3) actuating a corresponding set of pneumatic gas valves (1.4) in a gas manifold (2.0). Failure of any of these results in an audio-visual output for corrective action. Each valve position has a dedicated toggle switch and an LED to display on/off status. It enables passage of a variety of process and carrier gases through different routes for mixing inside the diffusion furnace for the purpose of dopant diffusion in silicon. The PLC based controller (1.1) as shown in Fig. 1 consists of the input port, output port and logic controller. The input port receives signal from the auto/manual selector switch (1.9) for selection of mode of operation i.e. manual or semi-auto or auto (1.9), the display cum keyboard panel (1.6) and safety interlock (1.7). The logic controller generates the output signal on the basis of preprogrammed sequence of operation and delivers to the output port. The output signals drive the relay card (1.2), which in turn switches on or off a set electro-pneumatic solenoid valves (1.3) by activating the 24 V DC supply (1.5). Accordingly, the corresponding air- operated valves (1.4) are opened or closed allowing the desired gas through the gas manifold. Each combination of valve opening is given an identity i.e. Recipe 1, Recipe 2 etc (Table —1). The safety interlocks (1.7) incorporated in the set up are 1) over pressure in liquid diffusion source bubbler as indicated by a pressure switch 2) recipe 7 not to run before recipe 9 3) recipe 8 not to run before recipe 9 4) compressed air failure 5) exhaust failure 6) nitrogen gas failure and 7) oxygen gas failure. As shown in Fig. 2, the gas manifold is also fitted with mass flow controllers (MFC-2.1) .The automation is based on PLC and the software controlling the sequence of valve operation/ actuation (AVI To AV13) together with safety interlocks are uploaded to the controller from a PC. The Controller together with gas manifold allows in a desired manner introduction of certain gases (carrier nitrogen, dilution nitrogen and oxygen) in a diffusion furnace that is maintained at a high temperature. The carrier nitrogen is made to bubble through the liquid diffusion source (2.2.) and carry its vapours inside the diffusion tube where it reacts with oxygen to form the necessary solid diffusion source. The display cum keyboard (1.6) displays the status of operation, on/off position of the valves, sequence of process, duration and elapsed time of the current process recipe, safety interlock that hold up the process. It also enables resulting of process timings as well as change of process sequence. The controller operates in three different modes i.e. manual, semi- automatic and fully automatic mode that can be selected from the auto/manual selector switch (1.9) on front panel. In the manual mode, the set of valves required for a particular process have to be manually switched on and after ensuring the correctness of the valves activated, enabled from the enable switch (3.3) on the front panel. WE CLAIM: 1. An automatic gas delivery system for diffusion of dopants in semiconductors using liquid diffusion source, consisting of a PLC based Controller (1.1), a display cum keyboard panel (1.6) a relay card (1.2), a manifold of solenoid valves (1.3) actuating a set of corresponding pneumatic valves (1.4) in a combination of sequences allowing various gases through different routes of the said gas manifold (2.0) for mixing inside the diffusion furnace and safety interlocks (1.7), characterized in that the gases are supplied in predetermined sequence and quantities to ensure optimum delivery and mixing of the gases in the diffusion furnace. 2. An automatic gas delivery system as claimed in claim 1, wherein the said gas manifold (2.0) wherein each valve position has dedicated toggle switch and LED to display on/off status, the said gas manifold being fitted with mass flow controllers (2.1). 3. An automatic gas delivery system as claimed in claim 1, wherein the PLC (1.1) controls the sequence of valve actuation together with safety interlocks. 4. A system as claimed in claim 1, wherein the safety interlocks (1.7) are for over pressure in dopant source bubbler, Recipe 7 not to run before Recipe 8, Recipe 8 not to run before receipt 9, compressed air failure, exhaust failure, nitrogen gas failure and oxygen gas failure. 5. A system as claimed in claim 4, wherein any failure of the said safety interlocks results in an audio-visual output for corrective action. 6. A system as claimed in claim 4, wherein the controller (1.1) operates in three modes of operation, namely manual, semi- automatic and fully automatic, as selected from the auto/manual selector switch on the front panel. 7. A system as claimed in claim 6, wherein for manual mode, valves are activated manually after the correctness of the valves activation is ensured, the valves being enabled from the enable switch on the said front panel. 8. A system as claimed in claim 1 and 4, wherein the safety interlocks are active in the semi-automatic and the automatic modes. This invention relates to an automatic gas delivery system for dopant diffusion in semiconductors using a liquid diffusion source. It works on the basis of a PLC based controller module (1.1), a display cum keyboard panel (1.6), a relay card (1.2) and a manifold of electro-pneumatic solenoid valves (1.3) actuating a set of corresponding pneumatic valves in a combination of sequences allowing a flow of carrier gas (N2) through a bubbler containing liquid dopant source, reactant gas (O2) and dilution gas (N2) through different routes of gas manifold for mixing inside the diffusion furnace for the purpose of dopant diffusion in semiconductors.

Full Text

FIELD OF THE INVENTION;
The invention relates to the manufacture of semiconductors and solar
photovoltaics in general and to a gas delivery system for diffusion of
dopant in particular.
PRIOR ART
Dopant diffusion in silicon using a liquid dopant source is carried out for
the manufacture of silicon solar cells and many other silicon based
semiconductors devices. POCl3 (phosphorus oxy chloride) is the most
commonly used liquid source. In the prior art, the equipment for
automatic and controlled delivery of POCl3 vapours into the diffusion
furnace formed a part of the diffusion furnace itself and was available at
an exorbitant cost. The essential components of the gas delivery system
are the gas manifold with proper design and the automatic controller.
The present invention provides an automatic and simpler gas delivery
system in place of the existing gas line plumbing and automatic
controller of prior art. Moreover the equipment in prior art is largely
imported.
OBJECTS OF THE INVENTION;
An object of the invention is to provide a gas delivery system, which is
easier to install and maintain.
Another object of the invention is to provide a gas delivery system, which
is economical.

A further object of the invention is to reduce dependence on foreign
suppliers of such equipment.
DESCRIPTION OF THE INVENTION;
The automatic gas delivery system for diffusion in silicon using liquid
diffusion source in accordance with the invention, works on the principle
of opening and closing of a set of air-operated valves in a combination of
programmed sequences to allow various gases, namely carrier nitrogen,
dilution nitrogen and oxygen through different routes laid out in a gas
manifold for mixing inside the diffusion furnace for the dopant diffusion
in silicon. The gases are supplied in predetermined sequence and
quantities to ensure optimum delivery and mixing of the gases in the
diffusion furnace.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS;
Fig. 1 shows a block diagram of the automatic controller.
Fig. 2 shows a schematic diagram of the gas manifold according to the
invention.
Table 1 shows the sequence and combination of valve opening in the
diffusion process.
Fig. 3 is a photograph of the automatic gas delivery system for diffusion
in silicon.

An exemplary embodiment of the invention as depicted in the
accompanying drawings will now be explained in details. However, there
can be several other embodiments, all of which are deemed covered by
this specification.
As shown in Fig. 1, the control system comprises a programmable logic
controller (PLC) (1.1), a display cum keyboard panel (1.6), a relay card
(1.2) and a manifold of solenoid valves (1.3) actuating a corresponding
set of pneumatic gas valves (1.4) in a gas manifold (2.0). Failure of any of
these results in an audio-visual output for corrective action. Each valve
position has a dedicated toggle switch and an LED to display on/off
status. It enables passage of a variety of process and carrier gases
through different routes for mixing inside the diffusion furnace for the
purpose of dopant diffusion in silicon.
The PLC based controller (1.1) as shown in Fig. 1 consists of the input
port, output port and logic controller. The input port receives signal from
the auto/manual selector switch (1.9) for selection of mode of operation
i.e. manual or semi-auto or auto (1.9), the display cum keyboard panel
(1.6) and safety interlock (1.7). The logic controller generates the output
signal on the basis of preprogrammed sequence of operation and delivers
to the output port. The output signals drive the relay card (1.2), which in
turn switches on or off a set electro-pneumatic solenoid valves (1.3) by
activating the 24 V DC supply (1.5). Accordingly, the corresponding air-
operated valves (1.4) are opened or closed allowing the desired gas
through the gas manifold. Each combination of valve opening is given an
identity i.e. Recipe 1, Recipe 2 etc (Table —1).

The safety interlocks (1.7) incorporated in the set up are
1) over pressure in liquid diffusion source bubbler as indicated by
a pressure switch
2) recipe 7 not to run before recipe 9
3) recipe 8 not to run before recipe 9
4) compressed air failure
5) exhaust failure
6) nitrogen gas failure and
7) oxygen gas failure.
As shown in Fig. 2, the gas manifold is also fitted with mass flow
controllers (MFC-2.1) .The automation is based on PLC and the software
controlling the sequence of valve operation/ actuation (AVI To AV13)
together with safety interlocks are uploaded to the controller from a PC.
The Controller together with gas manifold allows in a desired manner
introduction of certain gases (carrier nitrogen, dilution nitrogen and
oxygen) in a diffusion furnace that is maintained at a high temperature.
The carrier nitrogen is made to bubble through the liquid diffusion
source (2.2.) and carry its vapours inside the diffusion tube where it
reacts with oxygen to form the necessary solid diffusion source.
The display cum keyboard (1.6) displays the status of operation, on/off
position of the valves, sequence of process, duration and elapsed time of
the current process recipe, safety interlock that hold up the process. It
also enables resulting of process timings as well as change of process
sequence.

The controller operates in three different modes i.e. manual, semi-
automatic and fully automatic mode that can be selected from the
auto/manual selector switch (1.9) on front panel. In the manual mode,
the set of valves required for a particular process have to be manually
switched on and after ensuring the correctness of the valves activated,
enabled from the enable switch (3.3) on the front panel.

WE CLAIM:
1. An automatic gas delivery system for diffusion of dopants in
semiconductors using liquid diffusion source, consisting of a
PLC based Controller (1.1), a display cum keyboard panel (1.6)
a relay card (1.2), a manifold of solenoid valves (1.3) actuating a
set of corresponding pneumatic valves (1.4) in a combination of
sequences allowing various gases through different routes of the
said gas manifold (2.0) for mixing inside the diffusion furnace
and safety interlocks (1.7), characterized in that the gases are
supplied in predetermined sequence and quantities to ensure
optimum delivery and mixing of the gases in the diffusion
furnace.
2. An automatic gas delivery system as claimed in claim 1,
wherein the said gas manifold (2.0) wherein each valve position
has dedicated toggle switch and LED to display on/off status,
the said gas manifold being fitted with mass flow controllers
(2.1).
3. An automatic gas delivery system as claimed in claim 1,
wherein the PLC (1.1) controls the sequence of valve actuation
together with safety interlocks.
4. A system as claimed in claim 1, wherein the safety interlocks
(1.7) are for over pressure in dopant source bubbler, Recipe 7
not to run before Recipe 8, Recipe 8 not to run before receipt 9,
compressed air failure, exhaust failure, nitrogen gas failure and
oxygen gas failure.

5. A system as claimed in claim 4, wherein any failure of the said
safety interlocks results in an audio-visual output for corrective
action.
6. A system as claimed in claim 4, wherein the controller (1.1)
operates in three modes of operation, namely manual, semi-
automatic and fully automatic, as selected from the
auto/manual selector switch on the front panel.
7. A system as claimed in claim 6, wherein for manual mode,
valves are activated manually after the correctness of the valves
activation is ensured, the valves being enabled from the enable
switch on the said front panel.
8. A system as claimed in claim 1 and 4, wherein the safety
interlocks are active in the semi-automatic and the automatic
modes.

This invention relates to an automatic gas delivery system for dopant diffusion in semiconductors using a liquid diffusion source. It works on the basis of a PLC based controller module (1.1), a display cum keyboard
panel (1.6), a relay card (1.2) and a manifold of electro-pneumatic solenoid valves (1.3) actuating a set of corresponding pneumatic valves in a combination of sequences allowing a flow of carrier gas (N2) through a bubbler containing liquid dopant source, reactant gas (O2) and dilution gas (N2) through different routes of gas manifold for mixing inside the
diffusion furnace for the purpose of dopant diffusion in semiconductors.

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Patent Number

255500

Indian Patent Application Number

1345/KOL/2008

PG Journal Number

09/2013

Publication Date

01-Mar-2013

Grant Date

27-Feb-2013

Date of Filing

08-Aug-2008

Name of Patentee

BHARAT HEAVY ELECTRICALS LIMITED

Applicant Address

REGIONAL OPERATIONS DIVISION (ROD), PLOT NO : 9/1, DJ BLOCK 3RD FLOOR, KARUNAMOYEE, SALT LAKE CITY, KOLKATA - 700091, HAVING ITS REGISTERED OFFICE AT BHEL HOUSE, SIRI FORT, NEW DELHI – 110049

Inventors:

#	Inventor's Name	Inventor's Address
1	SANGALA RAGHUNATH REDDY	C/O BHARAT HEAVY ELECTRICALS LIMITED, REGIONAL OPERATIONS DIVISION (ROD), PLOT NO : 9/1, DJ BLOCK 3RD FLOOR, KARUNAMOYEE, SALT LAKE CITY, KOLKATA - 700091, HAVING ITS REGISTERED OFFICE AT BHEL HOUSE, SIRI FORT, NEW DELHI – 110049
2	SUDIP BHATTACHARYA	C/O BHARAT HEAVY ELECTRICALS LIMITED, REGIONAL OPERATIONS DIVISION (ROD), PLOT NO : 9/1, DJ BLOCK 3RD FLOOR, KARUNAMOYEE, SALT LAKE CITY, KOLKATA - 700091, HAVING ITS REGISTERED OFFICE AT BHEL HOUSE, SIRI FORT, NEW DELHI – 110049
3	BANSHI LAL BEDI	C/O BHARAT HEAVY ELECTRICALS LIMITED, REGIONAL OPERATIONS DIVISION (ROD), PLOT NO : 9/1, DJ BLOCK 3RD FLOOR, KARUNAMOYEE, SALT LAKE CITY, KOLKATA - 700091, HAVING ITS REGISTERED OFFICE AT BHEL HOUSE, SIRI FORT, NEW DELHI – 110049

PCT International Classification Number

H01L21/425

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA