Chapter 2.2
Dummy
Wafer Preparation and Rework
for
Tystar LPCVD
Furnaces and Lam Etchers
1.0
Title
Dummy Wafer
Preparation and Rework for Tystar LPCVD Furnaces and
Lam Etchers
2.0
Purpose
To provide
the detailed procedures of the dummy wafer preparation and rework for Tystar LPCVD furnaces and Lam etchers
3.0
Scope
This document includes the dummy wafer preparation and rework
procedures for:
Tystar9, 10, 11, 12, 14, 16, 17, 19, and 20;
Lam1, 2, 3, 4, and 5.
4.0
Applicable
Documents
4.1
Microlab Online Manual Chapter 2.6 –
Sink6 Operation
4.2
Microlab Online Manual Chapter 2.7 –
Sink7 Operation
4.3
Microlab Online Manual Chapter 2.8 –
Sink8 Operation
4.4
Microlab Online Manual Chapter 5.2 –
Tystar2 Oxidation Furnace Operation
4.5
Microlab Online Manual Chapters 5.3/5.4 –
Tystar3/4 Oxidation Furnace Operation
4.6
Microlab Online Manual Chapter 5.16
– Tystar16 Poly-Si LPCVD Furnace Operation
4.7
Microlab Online Manual Chapter 5.17
– Tystar17 Nitride LPCVD Furnace Operation
5.0
Definitions
and Process Terminology
N/A
6.0
Safety
6.1
Wear protective face shield, apron, and chemical resistant gloves when
working at a sink. Follow all the safety guidelines listed in the Sink6 - 8
online manuals.
6.2
General Microlab safety procedures should be followed.
7.0
Statistical/Process
Data
N/A
8.0
Available
Processes, Chemical, Process Notes
8.1
Hydrofluoric Acid (HF): Used to remove silicon oxide. Concentrated HF
(49%) can also be used to remove silicon nitride.
8.2
Buffered Oxide Etchant (BOE) or Buffered
HF (BHF): Used to remove silicon oxide. It contains ammonia fluoride that will decompose
to make up to fluoric ion consumed during etch process.
8.3
Phosphoric Acid: Used to remove silicon nitride film. The etch
temperature is 160°C.
8.4
Silicon Etchant: A premixed solution, of nitric acid, HF, and DI water,
used to etch poly-silicon. To increase the etch rate, the process temperature
can be increased to 50°C.
9.0
Dummy
Wafer Preparation and Rework Procedures
9.1
Dummy
Wafer Type And Identification
All dummy
wafers are test grade wafers. They should be properly scribed, on the backside
near the flat, with the equipment name they are intended to be used. This
identification is to prevent mixing up of different dummy wafers during rework
procedures. Because all the dummy wafers will be processed in a Tystar furnace, mix up of MOS and non-MOS wafers will
create a major contamination in the MOS clean furnaces.
Tystar9, 10, 11, and 19 are MOS clean furnaces and Tystar12, 14, 16,
17, and 20 are non-MOS. All the LAM etcher dummy wafers are considered non-MOS.
9.2
Tystar9
– MOS Silicon Nitride and High Temperature
Oxide LPCVD furnace
Dummy Wafer Preparation
9.2.1
Wafer Type: Test Grade Bare silicon wafers.
Quantity: 4”/25X; 6”/12X.
9.2.2
Clean the
wafers in Sink6 (Piranha and HF dip).
Dummy Wafer
Rework
9.2.3
In Sink7, etch the rework dummy wafers in concentrated HF (49%) until all
the film is removed and the wafer surface de-wet. It may take hours, even
over-night, depends on the film thickness. Increase the acid bath temperature,
but not higher than 50°C, can increase the etch rate.
9.2.4
Quick Dump Rinse (QDR) the wafers, then Spin Rinse Dry (SRD).
9.2.5
Follow Section 9.2.2 for final cleaning.
Note: Pure
silicon nitride film can be stripped using hot phosphoric acid with excellent
selectivity to the silicon substrate. However, Tystar9 all deposits high temperature
oxide (HTO), which cannot be stripped by, hot phosphoric acid.
9.3
Tystar10
– MOS Polycrystalline and Amorphous Silicon LPCVD Furnace
Dummy Wafer
Preparation
9.3.1
Wafer Type: Test Grade silicon wafer with 3kÅ of
silicon oxide.
Quantity: 4”/30X; 6”/15X.
9.3.2
Clean the bare wafers in Sink6 (Piranha and HF dip).
9.3.3
In Tystar2, grow 3kÅ of silicon oxide using 2WETOXA
recipe. Oxidation temperature is 1000°C and time is 45 minutes.
Dummy Wafer Rework
9.3.4
Check out 3 gallons of pre-mixed “silicon Etchant” from Room 432C. Or
mix the solution using the following formula:
4500 ml DI water
4500 ml Nitric Acid
200 ml HF (49%)
9.3.5
In Sink7, carefully pour the solution into the heated bath on the left
hand inside corner. Set the bath temperature to 50°C. There
is no need to wait for the temperature to stabilize to start etching the rework
dummy wafers.
9.3.6
Check the etch process every five
minutes. Since the poly-silicon film thickness on the dummy wafers vary
significantly, some wafers may finished etching much sooner than the others.
The Silicon Etchant will etch underlayer silicon
oxide, though slowly. When the silicon oxide is consumed, it will start etching
and destroy the silicon wafers.
9.3.7
When the poly-silicon film is
etched away, the wafer shows the purple-blue color of the underlying oxide.
After the poly-silicon film on some wafers are stripped off, QDR the whole
cassette. Remove those wafers, and then put the cassette back to the Silicon
Etchant solution. Repeat the process until all the wafers are done.
9.3.8
Follow Sections
9.3.1 to 9.3.3 to prepare the reworked wafers.
9.4
Tystar11
– MOS Low Temperature Oxide (LTO/PSG) LPCVD Furnace
Dummy Wafer
Preparation
9.4.1
Wafer Type: Test Grade Bare silicon wafers.
Quantity: 4”/30X; 6”/15X.
9.4.2
Clean the wafers in Sink6 (Piranha and HF dip).
Dummy Wafer
Rework
9.4.3
Check the surface of the used dummy wafers. If the film on the surface
is peeling off, discard the wafers.
9.4.4
Etch the dummy wafers in the BHF tank on Sink8 until all wafers de-wet.
9.4.5
Follow Section 9.4.2 for final cleaning.
9.5
Tystar12
– Non-MOS Low Temperature Oxide (LTO/PSG) LPCVD Furnace
The
procedures are the same as Tystar11 (Section 9.4). Dummy
wafers from Tsytar11 and Tystar 12 furnaces can be
reworked together. Make sure not to mix them up when loading into the furnaces.
9.6
Tystar14
– Boron Doping Atmospheric Furnace
Dummy Wafer
Preparation
9.6.1
Wafer Type: Test Grade Bare silicon wafers.
Quantity: 4”/28X; 6”/14X.
9.6.2
Clean the wafers in Sink6 (Piranha and HF dip).
Dummy Wafer
Rework
9.6.3
Oxidize the used dummy wafers in Tystar3/4 using 3WETOXA/4WETOXA recipe
– temperature: 1000ºC, time: 1 hour.
9.6.4
Etch the oxidized dummy wafers in the BHF tank on Sink8 until all
wafers de-wet.
9.7
Tystar16
– Non-MOS Polycrystalline and Amorphous Silicon LPCVD Furnace
The
procedures are the same as Tystar10 (Section 9.3). Dummy
wafers from two different furnaces can be reworked together. Make sure not to
mix up MOS and N0n-MOS dummy wafers when loading into the furnaces.
9.8
Tystar17
– Non-MOS Low Stress Nitride (LSN) LPCVD Furnace
Dummy Wafer
Preparation
9.8.1
Wafer Type: Test Grade Bare silicon wafers.
Quantity: 4”/37X; 6”/12X.
9.8.2
Clean the wafers in Sink6 (Piranha and HF dip).
Dummy Wafer
Rework
9.8.3
Used dummy wafers can be reworked following Section
9.2.3 – 9.2.5, if the deposition is less than 10 microns. If the film looks
rough and non-transparent, discard the wafers.
9.9
Tystar19
– MOS Silicon/Germanium LPCVD Furnace
The procedures
are the same as Tystar10 (Section 9.3). The etch rate on
the film varies due to various Germanium content. Check frequently during the
etch process.
9.10
Tystar20
The
procedures are the same as Tystar19 (Section 9.9). Dummy
wafers from two different furnaces can be reworked together. But do not mix up
MOS and N0n-MOS dummy wafers when loading into the furnaces.
9.11
Lam1
Dummy Wafer
Preparation
9.11.1 Wafer Type: Test Grade
silicon wafer with 2kÅ of silicon nitride on 3kÅ of silicon oxide.
Wafer Size: 6”.
9.11.2 Clean the bare wafers
in Sink6 (Piranha and HF dip).
9.11.3
In Tystar3/4, grow 3kÅ of silicon oxide using
3WETOXA/4WETOXA recipe. Oxidation temperature is 1000°C and time is 45 minutes.
9.11.4
In Tystar17, grown 2kÅ of silicon oxide using
STDNITA.017 recipe. Deposition time is 1 hour.
Dummy Wafer
Rework
9.11.5
Dummy wafers should be used on
both sides until the deep purple-bluish color of underlying silicon oxide shows
up.
9.11.6
In Sink7, etch the rework dummy wafers in concentrated HF (49%) until
all the film is removed and the wafer surface de-wet.
9.11.7
Follow Section 9.11.2 – 9.11.4 to prepare the
reworked dummy wafers.
9.12
Lam2
Dummy Wafer
Preparation
9.12.1 Wafer Type: Test Grade
silicon wafer with 6kÅ of silicon oxide.
Wafer Size: 6”.
9.12.2 Clean the bare wafers
in Sink6 (Piranha and HF dip).
9.12.3
In Tystar3/4, grow 6kÅ of silicon oxide using
3WETOXA/4WETOXA recipe. Oxidation temperature is 1000°C and time is 2 hours.
Dummy Wafer
Rework
9.12.4
Dummy wafers should be used on
both sides until the silver color of underlying silicon shows up.
9.12.5
In Sink8, etch the rework dummy wafers in 5:1 BHF tank until all the
film is removed and the wafer surface de-wet.
9.12.6
Follow Section 9.12.2 – 9.12.3 to prepare the
reworked dummy wafers.
9.13
Lam3
Dummy Wafer
Preparation
9.13.1 Wafer Type: Test Grade
silicon wafer with 6kÅ of aluminum film on 3kÅ of silicon oxide.
Wafer Size: 4”.
9.13.2 Clean the bare wafers
in Sink6 (Piranha and HF dip).
9.13.3
In Tystar3/4, grow 6kÅ of silicon oxide using
3WETOXA/4WETOXA recipe. Oxidation temperature is 1000°C and time is 45 minutes.
9.13.4
In CPA, deposit aluminum film
using the following process parameters: 4.0 kW, 6 mtorr,
and 20-cm/min speed, double runs.
Dummy Wafer
Rework
9.13.5
Dummy wafers should be used until
the deep purple-bluish color of underlying silicon oxide shows up.
9.13.6
In Sink8, etch the rework dummy wafers in Aluminum Etch tank until all
the aluminum film is removed and the wafer shows the deep
purple-bluish color of underlying silicon oxide completely.
9.13.7
QDR the dummy wafers, then etch them in 5:1 BHF tank until all the
oxide film is removed and the wafer surface de-wet.
9.13.8
Follow Section 9.13.2 – 9.13.4 to prepare the
reworked dummy wafers.
9.14
Lam4
Dummy Wafer
Preparation
9.14.1 Wafer Type: Test Grade
silicon wafer with 6kÅ of undoped-poly-silicon
film on 3kÅ of
silicon oxide.
Wafer Size: 4”.
9.14.2 Clean the bare wafers
in Sink6 (Piranha and HF dip).
9.14.3
In Tystar3/4, grow 3 kÅ of silicon oxide using 3WETOXA/4WETOXA recipe.
Oxidation temperature is 1000°C and
time is 45 minutes.
9.14.4
In Tystar16, deposit undoped-poly-silicon film using16SUPLYA recipe. Deposition
time is 1 hour.
Dummy Wafer
Rework
9.14.5
Dummy wafers should be used until
the deep purple-bluish color of underlying silicon oxide shows up.
9.14.6
In Sink7, etch the rework dummy wafers in silicon etch solution (see Section 9.3.4) until all the poly-silicon film is removed
and the wafer shows the deep purple-bluish color of
underlying silicon oxide completely.
9.14.7
QDR the dummy wafers, then etch them in 5:1 BHF tank of Sink8 until all
the oxide film is removed and the wafer surface de-wet.
9.14.8
Follow Section 9.14.2 – 9.14.4 to prepare the reworked dummy wafers.
9.15
Lam5
The
procedures are the same as Lam4, except the wafer used is 6”.
10.0
Troubleshooting
Guidelines
N/A
11.0
Figures & Schematics
N/A
N/A