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-14-- 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 E F G

• 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

Overview of the Gas Flow

G H I

G—Exhaust H—Fan on roofI—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

• DCS-- .2 SL • NH3-- .05SL

– P doped SiO2 • PH3 (15%)/SiH4-- .05 SL • SiH4-- .1 SL• O2 -- .2 SL• N2– 3 SL

– SiO2• SiH4-- .05 SL• O2-- .2 SL• N2-- .5 SL

– Poly Silicon• 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)        

GasSpecific 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

15% PH3/SiH4 1.1305 1200 16.36 41.19 349.87 547.38 1207.62

 

    Pressures

RFO / Flow Rate in SLPM (Minimum)      

GasSpecific 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 2.39 5.28 0.2

NH3 0.593 110 2.07 5.21 44.28 69.28 152.84 0.05

DCS is shipped as a liquefied gas under its own vapor pressure (9 psig @ 70°F) for that reason, a RFO is not recommenced

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 DCS NH3 PH3 (15%-SiH4) O2

Nitride 450 3.0 1.0

PSG 450 2.1 0.9 4.1

LTO 450 1.3 5.7

Poly 450 1.4

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

Gas TLV (ppm)

.5 TLV

Concentration (ppm)

Reading (Silane Sensor) (ppm)

Minimum Detectable

concentration (ppm)

Reading for .5 TLV (ppm)

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