Wacker Siltronic AG

Semicon 2002 / Ehmann / 17.04.20021

Determination of Organic Contaminants

on Silicon Wafer Surfaces

Determination of Organic Contaminants

on Silicon Wafer Surfaces

Th. Ehmann, L. Fabry, L. Kotz, S. Pahlke, C. Mantler

Wacker Siltronic AG, Research and Development InternationalPOB 1140 84479 Burghausen, Germany

thomas.ehmann@wacker.com

Wacker Siltronic AG

Semicon 2002 / Ehmann / 17.04.20022

Impact of Organic ContaminantsImpact of Organic Contaminants

• Time Dependent Haze - TDH

• Inadvertent surface etching

• Enhanced metal adsorption

• Disturbance of surface sensitive processese.g. photolithography, silicon on glass, plasma TEOS

• Organics undergo degradation, graphitization, carbonization and formation of SiC during thermal treatment

Wacker Siltronic AG

Semicon 2002 / Ehmann / 17.04.20023

OrganicsOrganicsApprox. 7.5 Mio Organic Compounds according to Beilstein Handbook of Organic Chemistry

Wacker Siltronic AG

Semicon 2002 / Ehmann / 17.04.20024

Techniques used at Wacker Siltronic for Monitoring Organic ContaminantsTechniques used at Wacker Siltronic for Monitoring Organic Contaminants

• IC Ion Chromatography

• CE Capillary Electrophoresis

• TD-GC/MS Thermodesorption Gas Chromatography / Mass Spectrometry

• GC-TOFMS Gas Chromatography / Time-of-Flight Mass Spectrometry

• TOFSIMS Time-of-Flight Secondary Ion Mass Spectrometry

• SR-TXRF Synchrotron Total Reflection X-ray Fluorescence Spectrometry

Wacker Siltronic AG

Semicon 2002 / Ehmann / 17.04.20025

Interaction of Organic with Wafer SurfaceInteraction of Organic with Wafer Surfacehydrophobic hydrophilic

O O

RR

R R

n

Wacker Siltronic AG

Semicon 2002 / Ehmann / 17.04.20026

Wafer Surface Water Extraction MethodWSWEMWafer Surface Water Extraction MethodWSWEM

wetting extraction sampling

• extraction of a 300 mm wafer with 4 mL UPW containing internal standards

• extraction volume adjusted to wafer diameter• LOQ of 2 x 1011 ions / cm2 or approx. 16 pg / cm2

Wacker Siltronic AG

Semicon 2002 / Ehmann / 17.04.20027

Anions due to WSWEMAnions due to WSWEM

12 3

45

6

7 8

9

10

11

1213

1 chloride, 2 nitrate, 3 sulfate, 4 perchlorate = internal standard, 5 fluoride, 6 formate, 7 unknown, 8 phosphate,9 carbonate, 10 methanesulfonate, 11 acetate, 12 propionate, 13 butanesulfonate

Wacker Siltronic AG

Semicon 2002 / Ehmann / 17.04.20028

Cations due to WSWEMCations due to WSWEM

1

2 3 4 5

Internal Standard

Internal Standard

1 ammonium, 2 potassium, 3 sodium, 4 calcium, 5 trimethylammonium

Wacker Siltronic AG

Semicon 2002 / Ehmann / 17.04.20029

Wafer Surface Preparation by VPDVapor Phase DecompositionWafer Surface Preparation by VPDVapor Phase Decomposition

6 HF + SiO2 H2SiF6 + 2 H2O

• native oxide layer SiO2

• dissolving the native oxide layer

• soluble contaminants in fluorosilic acid

• integral wafer contamination can be collected in one droplet

• LOQ of 5 x 1010 ions / cm2 or approx. 4 pg / cm2 for 300 mm wafer

Wacker Siltronic AG

Semicon 2002 / Ehmann / 17.04.200210

Anions due to VPDAnions due to VPD1

23

4

5

1 nitrate, 2 sulfate, 3 perchlorate = internal standard, 4 oxalate, 5 fluoride (from VPD preparation)

Wacker Siltronic AG

Semicon 2002 / Ehmann / 17.04.200211

Assumed Binding of OxalateAssumed Binding of Oxalate

Si Si Si Si Si Si

OH OH OH OH OHOC

O COOHSO4

2- Cl-aqueous film

native oxide

silicon substrate

Wacker Siltronic AG

Semicon 2002 / Ehmann / 17.04.200212

Adsorption of Dicarboxylic Acid and subsequent Chemical Reaction on Si SurfaceAdsorption of Dicarboxylic Acid and subsequent Chemical Reaction on Si Surface

M. Mitsuya, N. Sugita, Chemisorption of Dicarboxylic Acids on an Si(111) Surface and Subsequent Chemical Reactions at the Surface of Adsorbed Molecular Layers. Langmuir 1997, 13, 7075 - 7079.

F3C

F3CF2CO O

O O

F3C

Cl O

O O

F3C

OH O

O O

Si Si SiSi

F F

fluorine terminatedSi surface

as-deposited layerof 2-(trifluoromethyl)terephthalic acid

after chlorination withthionyl chloride / hexa-methylphosphoramide

after esterification with2-(perfluorohexyl)ethanol

Wacker Siltronic AG

Semicon 2002 / Ehmann / 17.04.200213

Ozonolysis in Organic SynthesisOzonolysis in Organic SynthesisR1

R2

R3

R4

O-

O+ O

R2 R3R1 R4

O OO

R4R3

O+

O-

+R2R1

O

R4R3

O+

O-R2R1

OO

O O

R1

R2

R3

R4

+ H2O

- H2O2

R1

R2 O O R3

R4

+

R1

H O+ H2O2

R1

OH OH2O+

1,2,3-trioxolanemolozonide

ozonide

Wacker Siltronic AG

Semicon 2002 / Ehmann / 17.04.200214

Volatile Organic Compounds - VOCVolatile Organic Compounds - VOC

• Standards: ASTM F 1982-99 and SEMI E108-0301

• Silicon Wafer Analyzer SWA 256 from GL Sciencesheat furnace for complete wafer up to 300 mm

• Thermal Desorption of VOC’s from Wafer Surface at 400°C

• Adsorption of VOC’s on Sampling Tube (Tenax)

• Determination of VOC’s by TD-GC/MS

Wacker Siltronic AG

Semicon 2002 / Ehmann / 17.04.200215

Surface Wafer Analyzer 256 M - GL ScienceSurface Wafer Analyzer 256 M - GL Science

Wacker Siltronic AG

Semicon 2002 / Ehmann / 17.04.200216

SWA 256 - TD-GC/MSSWA 256 - TD-GC/MS

Silicon Wafer Analyzer - SWA 256 thermal desorption gas chromatographycoupled to mass spectrometry

wafer

adsorption sample tubeTenax

Wacker Siltronic AG

Semicon 2002 / Ehmann / 17.04.200217

VOC’s on a Test Wafer exposed toCleanroom Air for 72 h VOC’s on a Test Wafer exposed toCleanroom Air for 72 h

Wacker Siltronic AG

Semicon 2002 / Ehmann / 17.04.200218

SummarySummary

• No single technique for monitoring organic

• Origin of organic contaminants very often ambiguous

• Effect of special molecule unclear

Much more R&D is necessary for an understanding of organics

comparable to the knowledge of metal contamination.