Post on 20-May-2020
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.