The LPCVD system for use in the
Micro/Nano Fabrication Center
Michael J. Berman, MFC Manager
Email: mberman@ece.arizona.edu
Phone: 520-626-1223
Agenda
• Tool overview
• Layout of tool and support items
• Gas
– Type
– Volume
• Safety
– Systems
– Training
• Abatement system
What is the LPCVD Tool?
The LPCVD tool is a Low-Pressure Chemical Vapor
Deposition System with 4 Process Tubes.
The Tubes (and Processes) are:
– Silicon nitride
– Polysilicon
– Low Temperature Silicon Dioxide (LTO)
– Phosphorous doped (4%) LTO (PSG)
The System
The process will:
• Have a working volume of 350mm long x 150mm
diameter
• Have a processing pressure of about 100 to 300m
Torr, and
• Use the following hazardous gases:
– SiH4 (PSG, LTO & PSG)
– PH3 (15% in SiH4) ( PSG only)
– DCS (dichlorosilane--H2SiCl2) (Nitride only)
Layout of tool
Detailed Layout of System
• G1- O2 & NH3
Cabinet
• G2- SiH4, Ph3/SiH4 &
DCS Cabinet
• G3- Gas Lines
• S1 & S2- SiH4 sensors
• E480-1- Main 480 v
Box
• E480-2- Main System
Power Cabinet
Detailed Layout 2
• E208-1-- 208 v 200
amp power for pumps
• P-14-- Pumps
• E208-2--100 amp box
• AB-1-- Abatement
system
• S-3– SiH4 sensor for
exhaust
• EX-1-- Exhaust line
Overview of the Gas Flow
(SiH4, 15% PH3 in SiH4 & DCS)
A
•
•
•
•
•
•
•
B
C
D
A -Gas Cabinets with Auto Purge Panels
B -Double contained Stainless Steel Gas Lines
C -The LPCVD System Tool
D -4” Stainless Steel Exhaust Lines
E -Vacuum Pump (one per tube)
F -Gas Abatement System
G -House Exhaust System
E
F
G
Overview of the Gas Flow
G
H
G—Exhaust
H—Fan on roof
I
I—Smoke stack
Gas flows
(in Standard Liters)
•
Process flows:
–
–
–
N2 purge (all tubes before and after process) -- 10 SL
Tube in standby -- .2 SL
Silicon Nitride
•
•
–
P doped SiO2
•
•
•
•
–
•
SiH4-- .05 SL
O2-- .2 SL
N2-.5 SL
Poly Silicon
•
•
PH3 (15%)/SiH4-- .05 SL
SiH4-- .1 SL
O2 -- .2 SL
N2–
3 SL
SiO2
•
•
•
–
DCS-- .2 SL
NH3-- .05SL
SiH4-- .06 SL
Note: About 50% of the process gases become part of the film and do not enter the
exhaust
Pump Purge
–
–
In process tube-- 20 SL
Idle tubes-7 SL
Gas Flows
• Only one tube will be in process at any time.
– Will be interlocked by the system software.
– Other 3 tubes will be in standby
• Typical Flows (SiO2 Film) will be:
–
–
–
–
–
.05 SL SiH4 (process gas)
.6 SL N2 (stand by for other 3 tubes)
20 SL N2 pump bias (the tube in process)
21 SL N2 for the other 3 pumps
Total gas going into exhaust system:
• 41.625 SL during process, with of which 41.6 is N2
• During time of no process, the each tube will have .2 SL N2
flowing at the tube and 7 SL of N2 at the pumps or a total of
28.8 SL of N2
A--The Gas Cabinet
• The Gas Cabinet is/has:
– Air Products with Gas Guard
450 Auto purge panels.
– Self closing door/ports
– Exhausted with > 200 fpm
velocity
– 12 gauge steel
– Negative Pressure (exhaust)
interlocked to shutdown flow
and give an alarm
• Gas Cabinet meets all of the
requirements of the University.
– Air flow/Exhaust will be
checked after install before
any gases are brought on site
A--Restricted Flow Orifices
Pressures
RFO / Flow
Rate in SLPM
(Peak)
Gas
Specific
Gravity
Full
0.006 "
0.010"
0.031"
0.040"
0.052"
SiH4
1.12
1200
16.44
41.39
351.51
549.94
1213.27
1.1305
1200
16.36
41.19
349.87
547.38
1207.62
15%
PH3/SiH4
Pressures
RFO / Flow
Rate in SLPM
(Minimum)
Gas
Specific
Gravity
Empty (150)
psig)
0.006 "
0.010"
0.031"
0.040"
0.052"
Desired Flow
SiH4
1.12
150
2.06
5.17
43.94
68.74
151.66
0.1
15%
PH3/SiH4
1.1305
150
2.05
5.15
43.73
68.42
150.95
0.05
DCS
3.473
9.2
0.07
0.18
1.53
NH3
0.593
110
2.07
5.21
44.28
2.39
69.28
5.28
152.84
DCS is shipped as a liquefied gas under its own vapor pressure (9 psig @ 70°F) for that reason, a RFO is not recommenced
0.2
0.05
A--Restricted Flow Orifices
•
•
•
•
SiH4—0.006” RFO
PH3 15% in SiH4—0.006” RFO
NH3—0.006” RFO
DCS—RFO not recommenced
B—Double contained Stainless
Steel gas lines
• The gas lines for the
SiH4, PH3 in SiH4 & DCS
will be:
– Double contained Stainless
Steel gas lines
– Center line is ¼ in.
– Outer line is ½ in.
• All contact with gases will
be Stainless Steel or glass
till the gas is exhausted on
the pump. There will be a
20 + liters per min N2 added
at the pump.
Gas Bottles
Gas used per 1,000 A
(in SL)
Process
N2
SiH4
Nitride
450
PSG
450
2.1
LTO
450
1.3
Poly
450
1.4
DCS
NH3
3.0
1.0
PH3 (15%-SiH4)
O2
0.9
4.1
5.7
Gas Volume
• Total Gas Volume for:
– SiH4
– DCS
– PH3 (15%- 85%-SiH4)
• Will be less than 20 Cu. Ft.
– This is based on not having the H6
• Storing Gas in Lab:
Our plans are to store no more than 3 bottles in the
lab, when a bottle is needing to be changed, a new
bottle will be brought in and the old one removed.
Safety Issues for LPCVD System
for SiH4 Gas Cabinet
• Pneumatically-controlled Gas Valves/Auto Purge
for DCS, Sih4 & SiH4 (15% PH3)
• Interlock to stop flow based on:
– Low Cabinet Exhaust
– Electrical Power Failure
– Gas Sensor
– .5 TLV inside the Gas Cabinet (for SiH4 or HCL)
– EMO/EMP (in any of the 3 locations)
– Fail-closed based on the LPCVD tool going into an
alarm mode
• Lights and horn sounds, if the .5 TLV level is crossed in the
work area or with Gas Cabinet.
Safety Systems
In the areas
• In the fab, in front of the LPCVD:
– SiH4 to monitor area for .5 TLV levels.
– Lights and horn that sound alarm in fab/chase.
– An evacuation plan of area (see diagram, next pages).
• In the chase, behind LPCVD:
– Identical SiH4 monitor in cabinet to monitor area for
.5 TLV levels.
– Lights and horn that sound/flash alarm in fab/chase
– Light in the room leading into the chase and down the
hallway in the chase (see diagram, next pages).
Evacuation of area
• Two types of Evacuation Plans:
• Scheduled
– In the course of changing a gas bottle, or
– When other PM activities may impede safety
– All persons not taking part in the PM activates will
leave both the fab and the chase.
• Unscheduled
– On gas cabinet alarms and lights
– All persons will evaluate the fab/chase based on the
lights and horns
Alarms and lights
• Lights and horn placement will be as marked on the next pages.
– Gas bottle change
• A “do not Enter” light will be at each door way to be used during gas bottle
change.
• There will also be chains to block some areas of the fab during the bottle
change.
• Light & horn will be turned on when the TLV for the gas cabinet or
the work area is greater than .5 TLV, this will cause all persons to
leave the fab and chase. There will also be lights for “Do not enter”
at the doorways.
• The colors of the safety lights and type of horn are being work with
Jose Arizpe, to match University/government standards.
• The system may at some future time be interconnect to the house
fire/smoke system.
– Based on future work this interconnection can:
• Set off the fire/smoke system
• Be set off by the fire/smoke system
Evacuation plan
Safety—The gas Sensor
• The safety monitor is a product of Zellweger Analytics also known as
Honeywell.
• The safety monitor is a Silane Low Level Sensor (SiH4), model
MIDAS-S-SHL (which works with other gases, see diagram below).
– With the lowest detectable limit (LDL) at 0.18 ppm
– Minimum alarm set point at 0.24 ppm
Concent
ration
(ppm)
Reading
(Silane
Sensor)
(ppm)
Minimum
Detectable
concentration
(ppm)
Reading
for .5 TLV
(ppm)
Gas
TLV (ppm)
.5
TL
V
Silane
5
2.5
1
1
0.18
2.50
DCS
500
250
--
--
--
--
HCL
5
2.5
5.4
1
0.98
0.46
PH3 (15% in Silane)
0.3
0.15
0.7
1
0.13
0.21
Silane (85% -15% PH3)
1.7
0.85
1.0
1
0.18
0.85
Safety Training
• Gas bottle changes:
– PPE will be SCBA, flame suit (including face shield).
• SCBA training is being reviewed and planned with Julia Rosen of Risk
Management & Safety
• Basic training will be completed before any of the toxic gases are brought on
site
– The person using the PPE will be trained and approved by the ERT
Team leader based on inputs by PPE, gas vendor or outside sources.
– Each time there is a bottle change in addition to the person performing
the bottle change, a second person will be in the same PPE with the
same level of training, near by to assist if there is a problem.
•
•
•
•
All lab personal will be trained in proper knowledge & evacuation.
All current users will be trained in proper knowledge & evacuation.
All new users will be trained before they receive access
Training information will also be available through our website at
http://mfc.engr.arizona.edu.
ERT
• MFC will put into action an ERT team for the lab.
• Gregg Cure’ will assist as team leader.
– Gregg brings experience with ERT from working with other fabs
• All staff and users will receive training to learn policies and
procedures, safety and to understand ERT functions
• ERT is offered on campus through the University’s Facilities
Department, Spill Control Unit.
• Gas training (PPE, gas vendor and others, if needed)
– Bottle changes
– Leak resolution
• ERT will be defined and reviewed with RM before the gases
are brought on site
Abatement System
A Centrotherm Dry Resin canister for Gas Abatement
System will be used on the output end of the pumps.
This system will:
• React & Remove SiH4, DCS, NH3 & PH3
– All 4 gases should be at or near the TLV before going into the
exhaust
– The exhaust has a flow of about 300,000,000 sccm
• Sensor on the output of the Abatement System will be set to
about 2X TLV for SiH4 before going into exhaust.
• An alarm will be used to signal when to change a canister.
• Sensor will have a go/no-go light
• Or if there is a problem with the sensor system
Exhaust System Output
• Output is at or near TLV before going into the
Exhaust system
• The exhaust is > 300,000,000 sccm
Procurement spec for:
Silane
•
•
•
•
•
Silane Name of gas
SiH4 Chemical formula of gas
Semiconductor Grade 4N8 Purity
0 % of secondary gas
Maximum amount of gas in bottle
– 8.0 cu ft
– 365 grams weight
•
•
•
•
•
•
350 CGA fitting
Bottle size name Cylinder UF
Bottle size dimension 6” x 19” (D x H)
0.006” Restricted Flow Orifices
MSDS on file
Approved vendor list
– Matheson-Trigas
Procurement spec for:
15% PH3 in Silane
•
•
•
•
•
Name 15% PH3 in Silane
Chemical formula of gas PH3 (15%) in SiH4
Semiconductor Grade Purity
15 +- 2% of secondary gas
Maximum amount of gas in bottle
– 1.6 cu ft
– 365 grams weight
•
•
•
•
•
•
350 CGA fitting
Bottle size name Cylinder SA
Bottle size dimension 2” x 12” (D x H)
0.006” Restricted Flow Orifices
MSDS on file
Approved vendor list
– Matheson-Trigas
Procurement spec for:
DCS
•
•
•
•
•
Name Dichlorosilane (DCS)
Chemical formula H2SiCl2
Semiconductor Grade 2N Purity
0 % of secondary gas
Maximum amount of gas in bottle
– 8.4 cu ft
– 2.2 LBS. weight
•
•
•
•
•
•
678 CGA fitting
Bottle size name Cylinder JF
Bottle size dimension 4” x 13” (D x H)
Restricted Flow Orifices none (due to the low pressure)
MSDS on file
Approved vendor list
– Matheson-Trigas
Procurement spec for:
Ammonia
•
•
•
•
•
Name Ammonia
Chemical formula NH3
Semiconductor Grade 5N Purity Purity
0 % of secondary gas
Maximum amount of gas in bottle
– 50 LBS +- 10% weight
•
•
•
•
•
•
660 CGA fitting
Bottle size name Cylinder QF
Bottle size dimension 9” x 51” (D x H)
0.006” Restricted Flow Orifices
MSDS on file
Approved vendor list
– Matheson-Trigas