A Study of Dilute Cu Alloys for Dual-Damascene Interconnect ...

A Study of Dilute Cu Alloysfor Dual-Damascene Interconnect ApplicationsCara Hutchison, Anil Bhanap, Mike Pinter, Wuwen Yi,Karen Scholer, Nicole Truong, Bob Prater, Eal LeeHoneywell Electronic MaterialsNovember 19, 2003TFUG Meetingeal.lee@honeywell.comCu Alloy Evaluation Page 1Proprietary and Confidential

AFM Microstructure of PVD Cu-Seed FilmCu-Ti (Ra=1.7 nm)Cu-Sn (Ra=1.01 nm)Grain size 86 nmGrain size 57 nmTi and Sn addition produced finer grain sizes.Cu Alloy Evaluation Page 5Proprietary and Confidential

AFM Microstructure of PVD Cu-Seed FilmCu-Ag (Ra=1.05 nm)Angled View of Cu-Ag30 nm15 nmGrain size 25 nmAg addition produced the finest grain sizes.Cu Alloy Evaluation Page 6Proprietary and Confidential

AFM topography of 1200A Cu-Al deposited @2 kW and 6kW at RTCuAl @2kW/27A/s3DRa=2. 860 nm80 nm40 nmCuAl @6kW/78A/s3DRa=0.646 nm20 nm10 nmHigh power deposition produces finer grain size and smoother surface due toenhanced nucleation rate.Cu Alloy Evaluation Page 7Proprietary and Confidential

XRD characterization of Cu-0.5at.%X filmsFilm(350C/30 min)XRD Integrated Peak Intensity (%) 6N Cu-Seed100 0 0 06N Cu + ECD85.1 4.8 3.1 6.9CuSn-Seed100 0 0 0CuSn + ECD82.2 8.2 4.0 5.6CuAl-Seed100 0 0 0CuAl + ECD64.8 18.0 7.3 10.0CuAg-Seed100 0 0 0CuAg + ECD56.0 21.9 10.2 11.9CuTi-Seed100 0 0 0CuTi + ECD80.7 6.8 3.5 9.0Cu-seed showed predominantly orientation for all alloying additions, but ECD Cuorientation varied with seed composition, 69Cu seed extending orientation most.Cu Alloy Evaluation Page 8Proprietary and Confidential

SIMS Analysis Layer StructureAnnealed @ 400 o C for 1 hourCu 2kÅECD 5kÅCu 2kÅTaN/TaAlloyCuAlloyBarrierOxide layer at this interfaceremains and may suppressthe diffusion. This can causenon-symmetric SIMS profile.Oxide layer at this interfacedissolves away during ECD.Cu Alloy Evaluation Page 9Proprietary and Confidential

SIMS diffusion profile of alloying elements after 400C/1 hrCu-0.5 at.% AgCu10 8Cu-0.5 at.% Al10 8Concentration (atoms/cc)10 23 10 410 2210 2110 20Ag10 710 610 5Secondary Ion Intensity (cts/s)Concentration (atoms/cc)10 23 10 410 2210 2110 20AlCu10 710 610 5Secondary Ion Intensity (cts/s)Concentration (atoms/cc)10 1910 2210 2110 200 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Depth (micron)10 8SnCu-0.5 at.% SnCu10 710 610 5Secondary Ion INtensity (cts/s)10 1910 1910 1810 170 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Depth (micron)10 8TiCu-0.5 at.% TiCu10 710 610 510 23 10 410 20 10 410 190 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Depth (micron)10 16Ag diffuses fastest followed by Sn.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Depth (micron)Cu Alloy Evaluation Page 10Proprietary and Confidential

Film Characterization Summary•Reflectivity of Cu-seed layer varies strongly with annealing temperature,whereas that of ECD Cu shows little variation.•Alloying addition imparts little effect on the grain size and electricalresistivity of ECD copper.•Stress of seed layer is generally higher than those of ECD Cu, but impartslittle effect on the stress of ECD film.•All alloyed Cu-seed films show good adhesion to TaN/Ta barrier.•All Cu-seed showed predominantly orientation regardless ofcomposition.•SIMS analysis shows complete homogenization of Ag through ECD Cu,whereas Mg shows limited diffusion. Non-symmetric diffusion of Ti and AlSIMS indicates surface oxidation effect. Potential advantage ordisadvantage of this diffusional behavior should be evaluated.Cu Alloy Evaluation Page 11Proprietary and Confidential

Electrical Testing FlowProcess flowTest structureILD deposition: SiN\SiO 2Trench patterning:Litho, Etch, AshSnake•3Degas: 415C, 100 sBarrier dep.: TaN\TaCu seed dep.CombECP Cu (10kA)Cu Anneal200C/60minCMPE-TEST•1•Line-to-line leakage (also called comb leakage):Apply voltage between Pads (1,2 shorted) and Pad (3)•Snake resistance (also called Serpentine resistance):Apply voltage between Pad 1 and Pad 2•2Cu Alloy Evaluation Page 12Proprietary and Confidential

Comb Leakage Current and Serpentine ResistanceComb Leakage currentL/S = 0.32/0.32 µSerpentine resistance% Probability999590807060504030201051CuCuAgCuAlCuSnCuTi%probability999590807060504030201051CuCuAgCuAlCuSnCuTi-13-12-11-10log(A/mm)-9-8-7-6100200300Ohm/mm400500SiO2 (3500A)SiN (500A)Si Substrate•Cu alloy composition did not significantly affect comb leakage current•Cu-Ag and Cu-Al show 10-15% higher serpentine resistance than 69Cu•Cu-Ti and Cu-Sn show % higher serpentine resistance than 69CuCu Alloy Evaluation Page 13Proprietary and Confidential

Resistance vs. Line Width for Copper Alloys600Median resistance (Ohm/mm)500400300200100CuCuAgCuAlCuSnCuTi00.2 0.22 0.24 0.26 0.28 0.3 0.32 0.34 0.36 0.38 0.4Line Width (micron)Serpentine resistance in the 0.24 – 0.38 micron line width range:Line resistance decreases with line width because of reduced liner contributionAlloying Effect: 69Cu < Cu-Al ~ Cu-Ag < Cu-Ti ~ Cu-SnCu Alloy Evaluation Page 14Proprietary and Confidential

Water Box Corrosion TestProcess flowSi waferOxide ILD depositionM1 trench patterningDegas/Barrier/Cu Seed depCu platingAnneal: 200C, 1 hrM1 CMPOptical inspectionETESTAlloys69CuCu-AlCu-AgCu-SnCu-TiCu-MgAt serpentine-combstructures from 9 diesnear wafer centerOptical inspectionWater box exposureETESTStore in sealed wafer box with DIwater at bottom. Room Temp. 24 hrCu Alloy Evaluation Page 15Proprietary and Confidential

Optical Inspection of 69CuCorrosionCu Alloy Evaluation Page 16Proprietary and Confidential

Optical Inspection of Cu-AgCorrosionCu Alloy Evaluation Page 18Proprietary and Confidential

Optical Inspection of Cu-SnCorrosionCu Alloy Evaluation Page 19Proprietary and Confidential

Optical Inspection of Cu-TiNo CorrosionCu Alloy Evaluation Page 20Proprietary and Confidential

Optical Inspection of Cu-MgProfuse CorrosionCu Alloy Evaluation Page 21Proprietary and Confidential

Summary of Optical Inspection•Significant corrosion was seen after water box test incase of seed layer formed by 69Cu, Cu-Ag, Cu-Sn, andCu-Mg alloys•Very little corrosion was observed in case of Cu-Al,whereas Cu-Ti seed layer showed no corrosion.•Preferred corrosion sites are edges and corners of Cufeatures, especially those adjacent to large fieldregions.Cu Alloy Evaluation Page 22Proprietary and Confidential

Serpentine Resistance before and after exposure to water vaporL/S = 0.32/0.32 µmBefore water-box exposureAfter water-box exposure9 99 58 07 06 05 04 03 02 01 05CuCuAgCuAlCuSnCuTi9999959580 8070 7060506040504030 3020 2010 105 51110500001000000050000100000Water box exposure caused the highest increase in serpentineresistance for 69Cu and Cu-Ag, followed by Cu-Sn.No change in serpentine resistance was noticed in case of Cu-Al andCu-Ti seed layers.Cu Alloy Evaluation Page 23Proprietary and Confidential

Summary of E-TestE• ECD Cu with 69Cu seed rendered the lowest line resistance andthe highest with CuTi seed.• Alloying elements imparted no significant impact on line leakagecurrent.• Excellent corrosion resistance was seen in single level metalstructures formed using Cu-Al and Cu-Ti alloys as seed layer.This is likely due to a possible formation of a protective oxide filmon Cu surface (e.g., Al 2 O 3 , TiO 2 ).•While Ag and Sn diffuse easily throughout Cu during annealing,it doesn’t seem to form a protective layer•Cu-Sn alloy needs to be studied further. While the opticalimages showed significant corrosion, the serpentine resistancewas affected less than in case of 69Cu and Cu-Ag.Cu Alloy Evaluation Page 24Proprietary and Confidential

Final Remarks•Ag is considered to be the best candidate for improvingelectromigration resistance in consideration of its fasthomogenization, low electrical resistivity, and highatomic mass. However, actual EM data is still needed.•Ti shows the best corrosion resistance but increaseselectrical resistivity in both seed and ECD Cu.•Al shows excellent corrosion resistance and producesnegligible increase in electrical resistivity for ECD Cu.•Sn is the highest atomic mass element tested andconsidered to be good for electromigration resistance.Cu Alloy Evaluation Page 25Proprietary and Confidential