Cleaning of Silicon-Containing Carbon Contamination

Transcription

1 RC-P4 Cleaning of Silicon-Containing 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

2 Contamination and Cleaning EUV masks and mirrors are contaminated by EUV irradiation in an usual vacuum condition. Contamination mainly consists of carbon and hydrogen. Intensity These XPS are measured by Canon. Mg Ka O KLL O1s C KLL 1 k Binding Energy (ev) Contamination deteriorates lithographic performance. It must be cleaned. Mo 3d Si 2s Si 2p C1s unirradiated 2 µm irradiated Reflectivity /Threshold /EDarea Ratio (atomic %) (R~13% ) 4 nm 4 nm Depth (nm) EUVL Symposium 21 2 C hp22nm(x5) Iso // H Film Thickness (nm) Si O Substrate Surface Reflectivity Threshold ED Area

3 Reported Cleaning Studies Technique Rate Advanttages Problems Institution [Reference] Oxygen Plasma Hydrogen Plasma <.1 nm/min Low speed Reflectivity down SNL [SPIE,4688,431(22)] EUV + O 2.24 nm/min Easy to apply Low speed LASTI [MNC23] UV/O 3 ~1 nm/min readily available Difficulty in UV Irradiation LASTI [JVSTB, 23, 247 (25)] Hydrogen Radical (Hot Filament) ~1 nm/min Recovery from Ru oxidation Heat load ASET-Kyutech [JJAP, 46, L633 (27)] Selete-Kyutech [EIPBN28] Shielded Plasma 5 nm/min.19 nm/min Modest speed Sputter damage Damageless Low speed TNO [EUVL Symp. 28] TNO [EUVL Symp. 29] Pure O 3 9 nm/min Extremely high speed Selete-MEIDENSHA [EUVL Symp. 29] EUVL Symposium 21 3

4 Hydrogen radical cleaning Shower head IR pyrometer View Port Vac. Gauge H 2 H 2 H 2 H H H H H H H H Sample Stage (Water-Cooled) Our Previous Studies to Power Supply Hot W wire Thermal Shield Sample to TMP 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) MEIDEN Pure Ozone Generator generation Ethylene Pure O 3 ~1 % condensation evaporation Exhaust 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 ~ 9 nm/min. EUVL Symposium 21 4

5 Problem Caused by Contained Si Using the pure O 3 cleaning, the reflectivity degradation of SR* contaminated multilayer mask brank is almost recovered. However, the reflectivity recovery of strongly contaminated or multiple contaminated sample is not good enough. We investigated the cleaning residue. The cause of accumulating degradation is cleaning residue SiO 2. *Synchrotron Radiation % Note that Si capping layer is stable to pure O 3 cleaning. Reflectivity Reflectivity 7% 6% 5% 4% 3% 2% 1% 7% 6% 5% 4% 3% 2% 1% % Atomic % After 1st cleaning After 2nd cleaning 1. Initial 2. Contami 3. O Wavelength (nm) 3. O 3 4. Re-Contami 5. 2nd O Wavelength (nm) Chemical states of surface Si (XPS) SiO 2 SiOx EUVL Symposium Si 58 27

6 Where Does Si Come from? Almost all carboneous contamination we investigated (SR, DPP, LPP) contains several parcents of Si species. Other groups also reported Si in contaminations. Intel MET N1 mirror: C : O : Si ~7 % : 2 % : 1 % G1, G2 mirror: C : O : Si ~ 85 % : 1 % : 5 % Albany MET G2: C : O : Si : P : N = 74 : 2 : 2 : 2 : 1 The origin of Si was unclear. So we deposited contamination on sapphier (Al 2 O 3 ) substrates. Clean Contami After O 3 Al 2 O 3 Al 2 O 3 Al 2 O 3 The result clearly shows that Si comes from vacuum. Intensity (arb. units) 32 In addition, this Si species seem hard to remove by oxidative cleaning. Manish Chandhok, IEUVI Optics Contamination / Lifetime TWG (1st Mar. 27) Andrea Wüest et al., IEUVI Optics Contamination / Lifetime TWG (1st Nov. 27) No Si species has been detected by QMS or GC-M. C 1s Clean Contami after O 3 2 Si 2s 16 Al 2s 12 Binding Energy (ev) Al Kα XPS Si 2p Al 2p EUVL Symposium

7 Cleanablity Studies of Si:C Experimental flow: Si doped C (Si:C) sputter-deposited film Characterization Cleaning processing (Pure O 3, H-radical) Characterization (XPS, HFS/RBS) Cleaning process condition: Pure O 3 assist gas = ethylene ~1 Pa room temperature H radical gas pressure ~1-2 Pa filament temperature ~178 o C Characterization: Si concentration dependence of film removal rate. Process time dependence of Si distribution. XPS: Xray Photoelectron Spectroscopy HFS: Hydrogen Forward Schattering spectrometry RBS: Rutherford Back Scattering spectrometry 1. Si concentration 2.area densities of C and Si etc. (natural oxide) 3. Si and O distributions Si substrate Si:C EUVL Symposium 21 7

8 Si Dope (%) Sample Characterization of Si:C C and Si are co-sputter-deposited on Si wafers. Doping rate is controlled by area of Si pieces placed on C target. RBS/HFS C Si H O Ar Fe Si % 4.2 % 6.2 % 11.1 % 15.2 % Initial Area Density (1 15 atom/cm 2 ) Film Thickness (nm) % 2% 4% 6% 8% 1% Atomic Ratio Converted from area density with bulk densities: C (amorphous) = 9.2~ atoms/cm 3 SiO 2 (amorphous) = atoms/cm 3 Si = atoms/cm 3 XPS ~7 % 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. EUVL Symposium 21 8

9 Normalized * Removal Rate Si-Ratio Dependence for Pure O 3 RBS Result ~3 nm/min C Si ~5 nm/min Sputter-deposited carbon is harder to remove than CVD deposited carbon. ~1 nm/min Initial Si Ratio (%) Data at initial 3 sec *Decresed amount par time par ratio of element Contained Si is also removed at initial stage. C removal rate decreses with Si concentration. EUVL Symposium 21 9

10 Change by Processing Time of Pure O 3 We observed time dependence of depth profile of Si 4.2 % sample. C decreses with time but removal rate gradually slow down. Si also decreses but forms condensed layer at surface region. O increases and final ratio Si:O=1:2. Thickness (nm) C Area Density (cm -2 ) Time (min) Initial 3 s 1 min 2 min 5 min 1 min Carbon Hydrogen Silicon Oxygen Si/O Area Density (cm -2 ) At. Ratio (%) At. Ratio (%) At. Ratio (%) At. Ratio (%) At. Ratio (%) At. Ratio (%) EUVL Symposium 21 1

11 Normalized * Removal Rate Si-Ratio Dependence for H-radical RBS Result C Si ~1.2 nm/min ~.3 nm/min Initial Si Ratio (%) Data at initial 3 min Rate decrease with Si seems smaller than O 3. Si removal rate seems higher than O 3. *Decresed amount par time par ratio of element EUVL Symposium 21 11

12 Change by Processing Time of H-radical We observed time dependence of depth profile of Si 4.2 % sample. 12 min H-radical processing seems correspond to 2~3 min prosessing of pure O 3. Si decreses faster than pure O 3 but SiO 2 condensed layer is also formed. Thickness (nm) C Area Density (cm -2 ) Initial 3 min 12 min Time (min) Carbon Hydrogen Silicon Oxygen Si/O Area Density (cm -2 ) At. Ratio (%) At. Ratio (%) At. Ratio (%) EUVL Symposium 21 12

13 Comparison between H and Pure O 3 Both of techniques removes a little Si but SiO 2 layers are formed at surface region. Absolute removal rate is several tens faster for pure O 3. Rate decrease by Si containing is smaller for H-radical. H Si Relative Removal Rates (arb. units) Si Ratio (%) H C O 3 Si O 3 C EUVL Symposium 21 13

14 Recovery from SiO Formation 2 Once SiO 2 is formed, it seems hard to remove it by mild-dry process. Thus we tried wet etching. Chemical states of surface Si (XPS) Atomic % After 1st cleaning After 2nd cleaning After wet etching SiO SiOx 4 Si SiO 2 (nm) Si is Si in capping layer. Using wet etching process, SiO 2 residue has successfully removed and reflectivity was completely recoverd. Note that SiO 2 removal process removes not only cleaning residue but also natural oxide of Si capping then mutiple application will damage the multilayer. Reflectivity Peak Reflectivity 7% 6% 5% 4% 3% 1. Initial 2% 4. Re-Contami 1% 5. 2nd O 3 6. Wet % % 65% 6% 55% 5% 45% Wavelength (nm) EUVL Symposium Initial Contami O 3 Re-Contami 2nd O 3 Wet

15 Favorable Solution Contamination of EUV1 It seems no Si is contained in a contamination on a mask of EUV1. Intensity (arb. units) Al Kα XPS O KLL Contami Clean O 1s Ta 4p C Si 2s Si 2p Ta 4f Ta 4d For such contamination, both of H radical and pure O 3 can be applied without wet SiO 2 removal. It's important to operate in such vacuum conditions. Intensity (arb. units) 1 Contami Clean Difference Binding Energy (ev) Al Kα XPS 2 Si 2p Binding Energy (ev) EUVL Symposium 21 15

16 H Conclusion w/ wet (needless) (needless) Pure O 3 w/ wet = Suitable C (needless) C w/si = Applicable SiO 2 Si-cap Ru-cap (no info) = Incompatible For Si free contamination on Si-cap, pure O 3 is the best. For Si containing contamination, pure O 3 does not work well. For SiO 2 containing contamination, H-radical is also no good. Residual SiO 2 species can be removed and rescued by wet etching without apparent damege. Si free vacuum condition is essential. EUVL Symposium 21 16

17 Summary Origin of Si contained in carboneous contamination is investigated. Cleanability of pure O 3 and H-radical cleaning, and behaviour of Si while cleaning is examined. Rescue process for degradation by residual SiO 2 is demonstrated. In some case, contamination contains little Si. It's important to operate in such a vacuum conditions. Acknowledgment SR contamination samples are prepared by H. Ikeda at SR center of Ritsumeikan University. This work was supported by New Energy and Indastrial Technology Development Organization. EUVL Symposium 21 17