cleaning of silicon-silicon ---containing carbon...

Cleaning ofCleaning ofCleaning ofCleaning ofSiliconSiliconSiliconSilicon----Containing Carbon ContaminationContaining Carbon ContaminationContaining Carbon ContaminationContaining Carbon Contamination

Toshihisa Anazawa, Noriaki Takagi,Osamu Suga, Iwao Nishiyama

MIRAI-Semiconductor Leading Edge Technologies, Inc.

Koichi Yamawaki, Hirotsugu Yano, Akira Izumi

Kyushu Institute of Technology

Toshinori Miura, Mitsuru Kekura

MEIDENSHA CORPORATION

RC-P04

EUVL Symposium 2010EUVL Symposium 2010EUVL Symposium 2010EUVL Symposium 2010 2222

Contamination and CleaningContamination and CleaningContamination and CleaningContamination and Cleaning

�EUV masks and mirrors arecontaminated by EUV irradiationin an usual vacuum condition.

40 nm

unirradiated

irradiated (R~13%↓)

200 µµµµm

40 nm

0 5 10 15 20Depth (nm)

0

20

40

60

80

100

Ratio (atomic %)

Si

OH

CCCCC

SubstrateSurface

1 k 800600400200 0

Binding Energy (eV)

Intensity

Mg Ka

C1s

Si2sSi2p

O1s

Mo 3d

O KLL

C KLL

�Contaminationmainly consistsof carbonand hydrogen.

�Contamination deteriorateslithographic performance.→ It must be cleaned.

These XPS are measured by Canon.

0.5

0.6

0.7

0.8

0.9

1

0 5 10 15 20

Film Thickness (nm)

Reflectivity

/Threshold

/EDarea Reflectivity

Threshold

ED Area

hp22nm(x5) Iso //


Reported Cleaning StudiesReported Cleaning StudiesReported Cleaning StudiesReported Cleaning Studies

Selete-MEIDENSHA [EUVL Symp. 2009]•Extremely high speed90 nm/minPure O3

Hydrogen Plasma

TNO [EUVL Symp. 2009]•Damageless

•Low speed0.19 nm/min

LASTI [MNC2003]•Easy to apply

•Low speed0.24 nm/minEUV + O2

SNL [SPIE,4688,431(2002)]•Low speed

•Reflectivity down<0.1 nm/min

Oxygen Plasma

TNO [EUVL Symp. 2008]•Modest speed

•Sputter damage5 nm/min

Shielded Plasma

ASET-Kyutech [JJAP, 46, L633 (2007)]Selete-Kyutech [EIPBN2008]

LASTI [JVSTB, 23, 247 (2005)]

Institution [Reference]

•Recovery from Ru oxidation

•Heat load

•readily available

•Difficulty in UV Irradiation

Advanttages

Problems

~1 nm/min

~1 nm/min

Rate

Hydrogen Radical(Hot Filament)

UV/O3

Technique


Our Previous StudiesOur Previous StudiesOur Previous StudiesOur Previous Studies�Hydrogen radical cleaning

H2

Sample

Shower head

Hot W wireIR pyrometer

Thermal Shield

Sample Stage(Water-Cooled)

to Power Supply

HHHHHHHHHHHH

HHHHHHHH

HHHH

HHHH HHHH

Vac. Gauge

HHHH2222 HHHH2222

to TMP

View Port

•Simple hot W filament efficiently decomposes hydrogen molecule to hydrogen radical.

•Not only carbon contamination but also oxidation of Ru-capping layer can be recovered.

•Carbon removal rate ~ 1 nm/min.

�Pure ozone cleaning (alkene-gas assisted)

Exhaust

Pure O3

～100 %

Ethylene

condensationevaporation

generation

MEIDEN Pure Ozone Generator

•Pure ozone is activated by the alkene assist gas.

•It needs no heating nor irradiation of any light (UV or EUV, etc.) and the removal rate is extremely high.

•Carbon removal rate ~ 90 nm/min.


Problem Caused by Contained SiProblem Caused by Contained SiProblem Caused by Contained SiProblem Caused by Contained Si

Using the pure O3 cleaning,the reflectivity degradation ofSR* contaminated multilayermask brank is almost recovered.

However, the reflectivity recoveryof strongly contaminated ormultiple contaminated sampleis not good enough.

We investigated the cleaning residue.

The cause of accumulatingdegradation iscleaning residue SiO2.

0

4

SiOx

2773After 2nd cleaning

58

Si0

38

SiO2

After 1st cleaning

Atomic %

*Synchrotron Radiation 0%

10%

20%

30%

40%

50%

60%

70%

13 13.5 14

Wavelength (nm)

Reflectivity

0%

10%

20%

30%

40%

50%

60%

70%

13 13.5 14

Wavelength (nm)

Reflectivity

1. Initial2. Contami3. O3

3. O3

4. Re-Contami5. 2nd O3

Chemical states of surface Si (XPS)

Note that Si capping layer is stable to pure O3 cleaning.


Where Does Si Come from ?Where Does Si Come from ?Where Does Si Come from ?Where Does Si Come from ?

4080120160200240280320

Binding Energy (eV)

Intensity (arb. units)

C1s

Si2s

Al2s

Si2p

Al2p

Al Kα XPSCleanContamiafter O3

Other groups also reported Si in contaminations.Intel METN1 mirror: C : O : C : O : C : O : C : O : SiSiSiSi ~70 % : 20 % : 70 % : 20 % : 70 % : 20 % : 70 % : 20 % : 10 %10 %10 %10 %G1, G2 mirror: C : O : C : O : C : O : C : O : SiSiSiSi ~ 85 % : 10 % : 85 % : 10 % : 85 % : 10 % : 85 % : 10 % : 5 5 5 5 %%%%

Albany METG2: C : O : C : O : C : O : C : O : SiSiSiSi : P : N: P : N: P : N: P : N = 74 : 20 : 74 : 20 : 74 : 20 : 74 : 20 : 2222 : 2 : : 2 : : 2 : : 2 : 1111

Manish Chandhok,IEUVI Optics Contamination /Lifetime TWG (1st Mar. 2007)

Andrea Wüest et al.,IEUVI Optics Contamination /Lifetime TWG (1st Nov. 2007)

The origin of Si was unclear.So we deposited contaminationon sapphier (Al2O3) substrates.

In addition, this Si species seemhard to remove by oxidative cleaning.

The result clearly shows thatSi comes from vacuum.

Almost all carboneous contamination we investigated(SR, DPP, LPP) contains several parcents of Si species.

No Si species has been detected by QMS or GC-M.

Contami After O3

Al2O3 Al2O3 Al2O3

Clean


Cleanablity Studies of Si:CCleanablity Studies of Si:CCleanablity Studies of Si:CCleanablity Studies of Si:CExperimental flow:Si doped C (Si:C) sputter-deposited film → Characterization

↓Cleaning processing (Pure O3, H-radical)

↓Characterization (XPS, HFS/RBS)

Characterization:Si concentration dependence offilm removal rate.Process time dependence ofSi distribution.

XPS: Xray Photoelectron SpectroscopyHFS: Hydrogen Forward Schattering spectrometryRBS: Rutherford Back Scattering spectrometry

Cleaning process condition:Pure O3— assist gas = ethylene ~100 Pa

room temperatureH radical — gas pressure ~10-2 Pa

filament temperature ~1780 oC

Si substrate(natural oxide)

Si:C

1. Si concentration

2.area densities of C and Si etc.

3. Si and O distributions


Sample Characterization of Si:CSample Characterization of Si:CSample Characterization of Si:CSample Characterization of Si:C

Converted from area density with bulk densities:

C (amorphous) = 9.02~10.53×1022 atoms/cm3

SiO2 (amorphous) = 6.62×1022 atoms/cm3

Si = 5.00×1022 atoms/cm3

128

138

153

161

146

Film Thickness(nm)

1282

1361

1532

1607

1435

Initial Area Density(1015atom/cm2)

15.2 %

11.1 %

6.2 %

4.2 %

0 %

Si

C and Si are co-sputter-deposited on Si wafers.Doping rate is controlled by area of Si pieces placed on C target.

83.3

73.8

69

66.3

61.9

6.2

11.1

15.2

12.2

15.3

16.7

14.1

13.8

5.2

6.8

7.1

7.7

4.2

0% 20% 40% 60% 80% 100%

0

4.2

6.2

11.1

15.2

Si Dope (%)

Atomic Ratio

C

Si

H

O

Ar

Fe

RBS/HFS

XPS

~70 % of C is C-C or C-H; π-π* satellite is also observed.Si mainly exists as SiOx (x<2); Si-C is not observed.


0

50

100

150

200

250

0 5 10 15 20

Initial Si Ratio (%)

Normalized Removal Rate

SiSiSiSi----Ratio Dependence for Pure ORatio Dependence for Pure ORatio Dependence for Pure ORatio Dependence for Pure O3333

~50 nm/minSputter-deposited carbon is harder to remove than CVD deposited carbon.

~10 nm/min

~30 nm/min

Contained Si is also removed at initial stage.C removal rate decreses with Si concentration.

Data at initial 30 sec

*Decresed amountpar timepar ratio of element

*RBS Result

CSi


Change by Processing Time of Pure OChange by Processing Time of Pure OChange by Processing Time of Pure OChange by Processing Time of Pure O3333

0

200

400

600

800

1000

1200

1400

0 1 2 3 4 5 6 7 8 9 10

Time (min)

C Area Density (cm-2)

0

20

40

60

80

100

120

140

Si/O Area Density (cm-2)

Thickness (nm)

0

20

40

60

80

100

120

140

160

180

0 10020 40 60 80At. Ratio (%)

0 10020 40 60 80At. Ratio (%)

0 10020 40 60 80At. Ratio (%)

0 10020 40 60 80At. Ratio (%)

0 10020 40 60 80At. Ratio (%)

0 10020 40 60 80At. Ratio (%)

Initial 30 s 1 min 2 min 5 min 10 min

CarbonCarbonCarbonCarbonHydrogenHydrogenHydrogenHydrogenSiliconSiliconSiliconSiliconOxygenOxygenOxygenOxygen

We observed time dependence of depth profile of Si 4.2 % sample.

C decreses with time but removalrate gradually slow down.Si also decreses but forms condensed layer at surface region.O increases and final ratio Si:O=1:2.


0

100

200

300

400

500

600

0 5 10 15 20

Initial Si Ratio (%)

Normalized Removal Rate

SiSiSiSi----Ratio Dependence for HRatio Dependence for HRatio Dependence for HRatio Dependence for H----radicalradicalradicalradical

~1.2 nm/min

~0.3 nm/min

Rate decrease with Si seems smaller than O3.Si removal rate seems higher than O3.

Data at initial 30 min

*Decresed amountpar timepar ratio of element

*RBS Result

CSi


0

200

400

600

800

1000

1200

1400

0 30 60 90 120

Time (min)

C Area Density (cm-2)

0

20

40

60

80

100

120

140

Si/O Area Density (cm-2)

Change by Processing Time of HChange by Processing Time of HChange by Processing Time of HChange by Processing Time of H----radicalradicalradicalradical

CarbonCarbonCarbonCarbonHydrogenHydrogenHydrogenHydrogenSiliconSiliconSiliconSiliconOxygenOxygenOxygenOxygen

Thickness (nm)

0

20

40

60

80

100

120

140

160

180

0 10020 40 60 80At. Ratio (%)

0 10020 40 60 80At. Ratio (%)

0 10020 40 60 80At. Ratio (%)

Initial 30 min 120 min

We observed time dependence of depth profile of Si 4.2 % sample.

120 min H-radical processingseems correspond to 2~3 min prosessing of pure O3.Si decreses faster than pure O3 but SiO2 condensed layer is also formed.


Comparison between H and Pure OComparison between H and Pure OComparison between H and Pure OComparison between H and Pure O3333

H H H H ―――― SiSiSiSi

H H H H ―――― CCCC

OOOO3333 ―――― SiSiSiSi

OOOO3333 ―――― CCCC

20151050

Si Ratio (%)

1.0

0.8

0.6

0.4

0.2

0

1.2

Rela

tive

Rem

ova

l R

ates

(arb

. units)

Both of techniques removes a little Si but SiO2 layers are formed at surface region.Absolute removal rate is several tens faster for pure O3.Rate decrease by Si containing is smaller for H-radical.


0%

10%

20%

30%

40%

50%

60%

70%

13.0 13.5 14.0

Wavelength (nm)

Reflectivity

Recovery from SiORecovery from SiORecovery from SiORecovery from SiO2222 FormationFormationFormationFormationOnce SiO2 is formed, it seems hardto remove it by mild-dry process.Thus we tried wet etching.

1.1

3.8

SiO2 (nm)

71029After wet etching

0

4

SiOx

2773After 2nd cleaning

58

Si0

38

SiO2

After 1st cleaning

Atomic %

1. Initial4. Re-Contami5. 2nd O3

6. Wet

Using wet etching process, SiO2

residue has successfully removed andreflectivity was completely recoverd.

Si0 is Si in capping layer.

Note that SiO2 removal process removes not onlycleaning residue but also natural oxide of Si cappingthen mutiple application will damage the multilayer.

Chemical states of surface Si (XPS)

45%

50%

55%

60%

65%

70%

Peak Reflectivity

Initial

Contami

O3

2nd O

32nd O

3

Re-Contami

Wet


9698100102104106108110Binding Energy (eV)


02004006008001000Binding Energy (eV)


Favorable SolutionFavorable SolutionFavorable SolutionFavorable Solution

Ta 4f

Si 2p

C

Si 2s

Ta 4dTa 4p

O 1s

O KLL

Si 2p

Clean

Contami

Difference

Contamination of EUV1

It seems no Si is containedin a contaminationon a mask of EUV1.

For such contamination,both of H radical andpure O3 can be appliedwithout wet SiO2 removal.

It's important to operatein such vacuum conditions.

Clean

Contami

Al Kαααα XPS

Al Kαααα XPS


ConclusionConclusionConclusionConclusion

� = Incompatible

�

�

(no info)

☺

Ru-cap

w/ wet

w/ wet �☺(needless)(needless)

� = Applicable☺ = Suitable

�☺☺(needless)

☺��☺☺☺Pure O3

☺��☺H

Si-capSiO2C w/SiC

For Si free contamination on Si-cap, pure O3 is the best.For Si containing contamination, pure O3 does not work well.For SiO2 containing contamination, H-radical is also no good.Residual SiO2 species can be removed and rescued by wet etching without apparent damege.

Si free vacuum condition is essential.


SummarySummarySummarySummary

SR contamination samples are preparedby H. Ikeda at SR center of Ritsumeikan University.

This work was supported by New Energy and Indastrial Technology Development Organization.

AcknowledgmentAcknowledgmentAcknowledgmentAcknowledgment

Origin of Si contained in carboneous contamination is investigated.Cleanability of pure O3 and H-radical cleaning,and behaviour of Si while cleaning is examined.Rescue process for degradation by residual SiO2

is demonstrated.In some case, contamination contains little Si.It's important to operate in such a vacuum conditions.

cleaning of silicon-silicon ---containing carbon...

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