characterization of organic contaminants outgassed · pdf file3/25/03 p. sun/c. ayre, ca...

3/25/03 P. Sun/C. Ayre, CA MATTEC, Intel 1

Characterization of Organic Contaminants Outgassed from Materials Used in Semiconductor Fabs/Processing

Peng Sun and Caroline Ayre California Materials Technology

Intel Corporation


Outline

• Introduction• Analytical Methods for Materials’ Outgassing

Measurements• Characterization of Outgassed Organic Contaminants

Using Thermal Desorption-Gas Chromatography-Mass Spectrometry (TD-GC-MS)

• Ammonia/Amines’ Outgassing• Summary


Introduction: Airborne Molecular Contamination (AMC)Airborne contaminants that:– Are smaller than particles, << 0.01 um or 100 Å, typically: 2-50 Å. – Are in the form of molecular vapor. – Pass through HEPA/ULPA filters.

• Note: Most cleanrooms are clean for particles, but contaminated with AMC.HEPA/UPLA filtration systems can be AMC sources.

Airborne contamination

Molecules(vapor)

Particles

Special filters needed

Std HEPA/ULPA filters sufficient


Introduction: Airborne Molecular Contamination (AMC)

• AMC Classification (SEMI F21-95):– Acids: HCl, HF, HNO3, H2SO4– Bases: NH3, amines, NMP– Condensables: organics with boiling point (bp) > 150 oC– Dopants: P, B, As compounds

• Material outgassing is one of the major sources of AMC.

• Notes:1. Some compounds belong to more than one class.2. Some compounds are not covered by this classification.3. NMP: N-methyl-pyrrolidinone, photoresist stripper or polyimide solvent.


Introduction: Molecular Condensables (MC)• Known Problematic Organic Contaminants:

– Flame retardants, e.g. organophosphorus – Siloxanes– Polymer/plastic additives, e.g. plasticizers, antioxidants– Amines/amides (such as NMP) – Decomposition compounds

• Effects of Organic Contamination:– Surface properties (e.g. hydrophobicity)– Lower breakdown voltage – Unintentional doping– Haze degradation– Oxide growth rate and quality – Post-CVD defects– Delamination– Optic and mask hazing


Introduction: Effects of Organic Contamination -Unintentional Doping Due to Outgassing

• Unintentional doping on Si device wafers during furnace operation was observed.• Witness wafer test showed that phosphorus contamination on witness wafers was roughly linear

with exposure time.• TD-GCMS analysis of various components of HEPA filters identified that the contaminant as Fyro

PCF flame retardant outgassed from the HEPA polyurethane potting material.

Reference: J.A. Lebens, et al., “Unintentional doping of wafers due to organophosphates in the cleanroom ambient”, J. Electrochem. Soc., 143(9), 2906-2909 (1996).

Sheet resistance map of a contaminated waferPhosphorus contamination vs. exposure time of witness wafer to cleanroom contaminated by Fyrol


Introduction: Effects of Organic Contamination -Breakdown Voltage Reduction

• Notes: 1. Organic contamination on the first SiO2 surface causes degradation in the polysilicon layer, resulting in breakdown field strength reduction. 2. Storage time in cassettes prior to the first polysilicon deposition can affect breakdown field strength.

Reference: M. Tamaoki, et al., “The effect of airborne contaminants in the cleanroom for ULSI manufacturing process”, 1995 IEEE/SEMI Advance Semiconductor Manufacturing Conference, 322-326 (1995).

Wafers exposed to cleanroom w/o chemical filters

Wafers exposed to cleanroom with chemical filters

Device structure used to measure breakdown strength of inter-polysilicon SiO2


Introduction: Sources of Organic Outgassing Contamination

– sealants – adhesives – paints – lubricants – plastics– HEPA/ULPA filtration systems – floor tiles – wafer carriers – cleanroom consumables: gloves, garments, tapes, cleaners… – process chemicals– people …


Introduction: ITRS Roadmap for Wafer Surface Organics

Wafer surface organic contamination: Carbon atoms/cm2:

2001 2002 2003 2004 2005 2006 2007Technology (nm): 130 90 65

‘99 edition: 6.6x1013 5.3x1013 4.9x1013 4.5x1013 4.1x1013 2.1x1013 (2008)

‘02 edition: 2.6x1014 2.1x1013 1.8x1013 1.5x1013 1.3x1013 1.1x1013 1.0x1013

• Trend: Tighter wafer surface organic contamination requirements due to increasing sensitivity to organic condensables’ contamination.


Outline






Analytical Methods for Outgassing Measurements

• Most widely used methods in semiconductor industry:– Direct Outgassing

• Weight loss method– for total outgassing assessment

• TD-GC-MS method– for outgassing compound identification and quantification

– Indirect Outgassing Measurement Using Witness Wafers• TD-GC-MS analysis of witness wafers

– full wafer analysis• Time-of-flight Secondary Ion Mass Spectrometry (TOF-SIMS)

analysis of witness wafers– spot analysis


Analytical Methods for Outgassing Measurements

• Industry Standards:– ASTM F1227-89, “Standard Test Method for Total Mass Loss of

Materials and Condensation of Outgassed Volatiles on Microelectronics-Related Substrates”

– IEST WG-CC031 Recommended Practice: “Method for Characterizing Outgassed Organic Compounds from Cleanroom Materials and Components” (to be published in 2003)

– SEMI Environmental Contamination Control (ECC) WG: SEMI E108-0301: “Test Method for The Assessment of Outgassing Organic Contamination from Minienvironments Using Gas Chromatography/Mass Spectroscopy”

– ASTM F1982-99: “Standard Test Methods for Analyzing Organic Contaminants on Silicon Wafer Surfaces by Thermal Desorption Gas Chromatography”


Outline






Characterization of Outgassed Organic Contaminants Using TD-GC-MS

• Schematic Diagram of TD-GC-MS Technique:


Detection of Outgassed Polycyclodimethyl-siloxanes from a Cleanroom Sealant

• TD-GC-MS Analysis Results:

Total outgassing: 680 ug/g

Siloxanes: 290 ug/g

Total organics: 7.6 ng/cm2

Siloxanes: 6 ng/cm2

Direct outgassing of a sealant

Surface analysis of a witness wafer exposed to the sealant:

Siloxane: 2.5E14 Carbon atoms/cm2, 10x > ITRS requirement (1.8E13)

ug = microgram, ng = nanogramRetention Time (min)


Detection of Outgassing Poly-Cyclodimethylsiloxanes

• Identification of Dodecamethyl-cyclohexasiloxane: Unknown spectrum

Dodecamethyl-cyclohexasiloxane standard spectrum

40 60 80 1001201401601802002202402602803003203403603804004204400

1000

2000

3000

4000

5000

6000

7000

8000

9000

m/z-->

Abundance

Scan 1815 (10.891 min): 10300202.D341

73

429

147

20745 251 311117 179 39728122591 367

40 60 80 1001201401601802002202402602803003203403603804004204400

1000

2000

3000

4000

5000

6000

7000

8000

9000

m/z-->

Abundance

#27931: Cyclohexasiloxane, dodecamethyl-73

341

429

147

20745 311267117 397


Detection of Triethyl Phosphate (TEP) Outgassed from a Cleanroom Sealant

Triethyl phosphate: 49 ug/g

Triethyl phosphate: 5.8 ng/cm2

5.00 10.00 15.00 20.00 25.00 30.00 35.00

1000000

2000000

3000000

4000000

5000000

6000000

7000000

8000000

9000000

1e+07

1.1e+07

1.2e+07

1.3e+07

1.4e+07

Time-->

Abundance

TIC: 12160202.D

5.00 10.00 15.00 20.00 25.00 30.00 35.00

500000

1000000

1500000

2000000

2500000

3000000

3500000

4000000

4500000

5000000

5500000

6000000

6500000

7000000

7500000

8000000

8500000

9000000

9500000

Time-->

Abundance

TIC: 12060206.D

Direct outgassing of a cleanroom sealant

Surface analysis of witness wafer exposed to the same sealant

~2E13 P atoms/cm2, >> critical level: 1E12

Retention Time (min)


Detection of Triethyl Phosphate (TEP) Outgassed from a Cleanroom Sealant

• Identification of Triethyl phosphate (TEP):

Triethyl phosphate standard spectrum

Unknown spectrum

20 40 60 80 100 120 140 160 180 200 220 240 260 2800

2000

4000

6000

8000

m/z-->

Abundance

Scan 1929 (11.563 min): 12160202.D155

99

127

81

111 13945 18265 167 207 235 263 29133

20 40 60 80 100 120 140 160 180 200 220 240 260 2800

2000

4000

6000

8000

m/z-->

Abundance

#43455: Triethyl phosphate99

155

12781

29

45 1111396515 182167


Characterization of Outgassed Organic Contaminants Using TD-GC-MS

• Polymer materials chosen outgas organic contaminants commonly seen in semiconductor Fab cleanrooms. Organic contaminants monitored included:

• polycyclodimethylsilocxanes• Dibutyl phthalate (DBP)• Butylated hydroxytoluene (BHT)• 2-Ethyl-1-hexanol• Methylstyrene• Naphthalene

• Outgassing behaviors of selected contaminants were studied by varying the following parameters:

• outgassing time• outgassing temperature• surface area• weight


Outgassing Concentration vs. Outgassing Time: Siloxanes

• Linear relationship between outgassing concentration and outgassing time within a time range. Outgassing rate can be estimated from the slope.

• Same findings for Dibutyl phthalate (DBP) and Butylated hydroxytoluene (BHT)(not shown).

• Linear relationship was also observed at 75 oC with higher slope values, indicating higher outgassing rate at 75 oC.

Outgassing Time Dependance (at 50oC)

y = 0.0236x + 0.0744R2 = 0.9993

y = 0.0394x + 0.0609R2 = 0.9872

y = 0.0358x + 0.2154R2 = 0.9816

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 5 10 15 20 25 30 35Outgassing Time (min)

Out

gass

ing

Con

cent

ratio

n (p

pmw

, ng/

g)

Octamethyl-cyclotetrasiloxane

Decamethyl-cyclopentasiloxane

Dodecamethyl-cyclohexasiloxane


Outgassing Concentration vs. Temperature: Siloxanes and DBP

• Linear relationship between Log (Outgassing Conc.) and inverse of outgassing temperature (1/T).

• In agreement with findings reported by K. Takeda, et al., IEST 2000 ESTECH Proceedings, pp. 71-77 (2000).

• Same result was observed for Butylated hydroxytoluene (BHT) (not shown).

Outgassing vs. Temperature

y = -3.9015x + 11.825R2 = 0.9726

y = -1.724x + 5.301R2 = 0.9945

y = -1.782x + 5.4216R2 = 0.9977

y = -1.5764x + 4.6101R2 = 0.9841

-1.00

-0.50

0.00

0.50

1.00

1.50

2.00

2.50

2.50 2.60 2.70 2.80 2.90 3.00 3.10 3.20

1/T x 103 (1/K x 103)

Log

(Out

gass

ing

Con

c.)

Octamethyl-cyclotetrasiloxaneDecamethyl-cyclopentasiloxaneDodecamethyl-cyclohexasiloxaneDibutyl Phthalate (DBP)


Outgassing Quantity vs. Surface Area: Siloxanes

• Outgassing quantity ∝ surface area when sample weight is constant.

Siloxane Outgassing Dependence on Sample Surface Area (outgassing condition: 50oC, 15 min)

0

100

200

300

400

500

600

700



Tetradecamethyl-cycloheptasiloxane

Outgassing Compound

Tota

l Out

gass

ing

(ng)

1x surface area, 1x sample weight


Outgassing ∝ Surface Area

1x surface area 1x weight



Outgassing Quantity vs. Sample Surface Area

• Outgassing quantity ∝ surface area when sample weight is constant.1x surface area 1x weight


Outgassing Dependence on Sample Surface Area (outgassing condition: 50oC, 15 min)

0

100

200

300

400

500

600

2-ethyl-1-hexanol Methylstyrene Naphthalene

Outgassing Compound

Tota

l Out

gass

ing

(ng)



Outgassing ∝ Surface Area


Outgassing Quantity vs. Sample WeightOutgassing Dependence on Sample Weight (50oC, 15min)

0

100

200

300

400

500

600



Tetradecamethyl-cycloheptasiloxane

Outgassing Compound

Tota

l Out

gass

ing

(ng)

1x sample weight, 1x surface area

2x sample weight, 1x surface area

Outgassing is independent of sample weight

• Outgassing is independent of sample weight when surface area is constant.• Same results for methylstyrene, 2-ethyl-1-hexanol and naphthalene (not shown).


Conclusions: Characterization of Outgassed Organic Contaminants Using TD-GC-MS

• Linear relationship between outgassing concentration and outgassing time in a certain time range.– where the slope equals the outgassing rate.

• Linear relationship between logarithm of outgassing concentration and 1/T; where ‘T’ is the absolute outgassing temperature.

• Outgassing amount ∝ sample surface area.• Outgassing is independent of sample weight when surface area

remains constant.– Suggests that outgassing is indeed a surface phenomenon.

Note: These findings are based on the limited number of contaminantstested.

– Materials’ outgassing can be far more complicated due to large number of variables in the physical and chemical properties of different materials used in cleanrooms.


Outline






Ammonia/Amines’ Outgassing• T-topping defect caused by NH3/amines’ Outgassing:

• Airborne bases outgassed from cleanroom materials can neutralize the photo-generated acid during the time delay between the exposure and post-exposure bake, generating insoluble products, which cannot be dissolved by developer solvent. A lip forms at the top of the developed resist profile, known as “T-topping”.

T-topping SEM image


Ammonia/Amines’ Outgassing• Gas Diffusion-Conductivity Detection-based

NH3/Amines’ Outgassing Method:

ppb = parts per billion

Capable of detecting 1 ng/g (ppb) of NH3/amines’ outgassed


NH3/Amines Outgassing of Two Cleanroom Sealants

Sealant A caused significant T-topping defects in E0 delay photoresist test due to its high NH3/amine outgassing.


Time Dependence of NH3/Amines’ Outgassing

Time dependent NH3/amine outgassing of a sealant: room temperature

Surface NH4+ of witness wafers exposed to same sealant: room temperature

NH3/Amine Outgassing vs. Cure Time

0100200300400500600700800

0 10 20 30 40 50 60 70 80

Cure Time (hour)

NH3/

Amin

e O

utga

ssin

g (n

g/g)

Wafer Surface NH4+ vs. Cure Time(1 hour exposure at room temperature)

0

500

1000

1500

2000

2500

3000

0 10 20 30 40 50 60 70 80Cure Time (hour)

Waf

er S

urfa

ce N

H4+

(E10

NH4

+/cm

2)

control wafer


NH3/Amines’ Outgassing vs. Wafer Surface NH4+

Wafer Exposure Test(1 hour exposure at room temperature)

0

500

1000

1500

2000

2500

3000

0 100 200 300 400 500 600 700 800NH3 Outgassing

(ng/g)

Waf

er S

urfa

ce N

H4+

(E

10 N

H4+

/cm

2)

Linear relationship between witness wafer surface NH4+ and sealant NH3/amines’ outgassing concentration


Summary• Many AMC contaminants found in semiconductor Fabs come

from outgassing of cleanroom materials. Outgassed contaminants can adversely affect many processes, resulting in yield loss, shortened tool life and reduced long-term device reliability.

• The large variety of cleanroom materials and numerous outgassing contaminants combined with the complexity of process steps makes understanding detrimental levels of specificcontaminants in particular processes very challenging.

• Screening materials for both condensable and NH3/amines’ outgassing prior to bringing them into Fabs can be used as a first-line-of-defense against molecular contaminants such asorganophosphorus, siloxanes, plasticizers and ammonia/amines.


Summary

• New microelectronic fabrication processes with decreasing device geometries are increasingly susceptible to AMC.

• As processes and chemistries change, requirements for monitoring, control and analysis of materials’ outgassing will evolve as well.

• Cooperative efforts among manufacturers of integrated circuit, materials and analytical tools are needed to better understand the impact of molecular contaminants and to properly define specifications applicable to new ULSI technologies.


Acknowledgements

• Yaacov Maoz of Intel Fab 18 for providing the “T-topping” defect SEM image.

• Zari Pourmotamed of Intel California Materials Technology for collecting time-dependent NH3/amines’ outgassing data.

• Joseph O’Sullivan of Intel Facilities Technology for providing valuable technical inputs.

characterization of organic contaminants outgassed · pdf file3/25/03 p. sun/c. ayre, ca...

Documents