Plasma etch control by means of physical plasma parameter measurement with HERCULES A. Steinbach F. Bell D. Knobloch S. Wurm Ch. Koelbl D. Köhler -1-
Contents - Introduction - Motivation - Plasma monitoring tool HERCULES - Al etch on LAM TCP 96 SE - Contact etch on Applied Materials Centura MxP+ - Summary -2-
Our way of plasma processing today an effective way? Process parameters power pressure B field gas flow... Black Box called plasma processing Process results etch rate uniformity selectivity particles... - Experience and statistical methods in process development - Process Monitoring and Tool control by test wafers -3-
Measuring Techniques for real time Plasma Monitoring rf probe rf voltage rf current power Process parameters external power pressure B field gas flow body temp. Ion flux probe j+ (wall) Process parameter rf voltage (wafer) rf current bias voltage effective power Chamber parameters surface temp. polymer e.g. gas ad / desorption depending on ion current We begin to measure! Plasma excitation Power balance and potential distribution electron collision rate, electron energy distribution electron density plasma potential bulk power Hercules ion density ion temperature neutral densities neutral temp. excitations Wafer Surface ion energy ion current radiation neutral flows (radicals) surface temp. layer thickness OES k*i(λ ) Process Results external measured etch rate uniformity selectivity particles Interferometry Reflectence spectroscopy layer thickness ne, ν e, PBulk Species in the volume -4-
Basic HERCULES Model High Frequency Electron Resonance Current Low Pressure Spectroscopy -5-
Principle and experimental setup rf current rf voltage FFT Algorithm Model SEERS Electron collision rate Electron density Bulk power DC bias voltage - Passive electrical method, no influence on the plasma - Integral measurement -6-
SEERS provides reciprocally averaged parameters Self Excited Electron Resonance Spectroscopy --
HERCULES Sensor Types Surface: anodized aluminum, similar to chamber wall -8-
TCP: Al etch - trend analysis main etch - Cl2 - MFC failure - Cleans Al etching - trend analysis main etch - LAM TCP 96 8.19 14 3.5.1 1 8 6 4.2.19 6.4.19. 9 5.6 1 3.1 2.5.1 quick clean Cl2-MFC error 2.1 main clean 4.8.19 1.5.1 4.19 3.2.19 364 1 31 38 385 Lot No. 392 399 collsion rate [1/s] optical emission (EP) *3 etch time [s] 12 electron density [1/cm3] Cl2-MFC drift/error 5.16 46 Joint project Siemens - ASI - Lam -9-
TCP: Al etch - trend analysis barrier etch - Cl2 - MFC failure - Cleans etch time [s] 3 2 1 electron density [1/cm3] 4 8.19 2.4.1.2.19 2.1.1 main clean 6.4.19 5.6.19 Quick clean 1.5.1 Cl2-MFC drift/error. 1.8.1 Cl2-MFC error 9 1.2.1 4.8 1 4.19 3.2.19 364 9.16 31 38 385 Lot No. 392 399 collsion rate [1/s] optical emission (EP) *5 Al etching - trend analysis barrier etch - LAM TCP 96 6.16 46 Joint project Siemens - ASI - Lam - 1 -
TCP: Al etch in Cl - first wafer effect Al etching in Cl - first wafer effect2- LAM TCP 96 2 Product wafer - resist mask on Al (appr. 5%) electron density [1/cm 3 ] 8.19 main etch.19 first wafer. 9 6 1 5.19 second 4.19 third wafer First wafer effect in main etch Longer etch time 3.19 4 8 process time [s] 12 16-11 -
TCP: Al etch - with / without barrier (TiN,Ti) Al etching - with/without barrier (TiN, Ti) - LAM TCP 96 Ti layer detected each curve averaged from five testwafers 5.1 break through (Al2O3) collision rate [1/s] 4.1 3.1 Ti layer 2.1 8 nm AlSiCu 1 SiO2 with TiN (1 nm), Ti (15 nm) 2 4 6 8 process time [s] Joint project Siemens - ASI - Lam - 12-1 12
Electron Collision Rate vs. Pressure Bulk Power vs. rf Power -1 3 Coll. Rate [1s ] 25 11 B. Power [mw / cm²] MxP+: CT etch: Plasma parameters dependíng on process parameters BPSG Structure 2 15 1 6 8 9 1 9 BPSG Structure 5 12 RF Power [W] 14 16 18 2 Pressure [mtorr] Electron Collision Rate vs. CF4 flow -1 Coll. Rate [1 s ] 9.8 Change of process chemistry strong nonlinear correlation BPSG.6 Structure 9.6.2 6.8 9.4 1 2 3 4 CF4 flow [sccm] - 13 -
MxP+: CT etch - Etch rate BPSG (blanket) depending on plasma parameters Etch Rate and Uniformity BPSG vs. Bulk Power Etch Rate BPSG vs. Electron Collision Rate 3 5 Etch Rate [nm / min] 6 Uniformity [%] Etch Rate [nm / min] 4 68 66 64 Pressure increasing RF Power increasing 4 2 12 14 16 18 62 6 2 8 9-1 Electron Collision Rate [1 s ] Bulk Power [mw / cm ²] Etch Rate vs. Electron Density Obvious correlations between etch rate and Etch Rate [nm / min] 6 65 63 CF4 flow decreasing 61 1.2 1. Electron Density [1 11.2 8 electron collision rate electron density bulk power / cm ³] - 14 -
MxP+: CT etch - Contact angle depending on plasma parameters Contact Angle vs. Electron Collision Rate Cont. Angle vs. Electron Density 9 CF4 flow decreasing Angle [ ] Angle [ ] 9 88 86 84 1.2 89 88 8 Pressure increasing 86 1.4 1.6 1.8 Electron Density [1 11. 8 11.2 8 / cm ³] 9 1 11 Electron Collision Rate [1 12-1 s ] Cont. Angle vs. Electron Density Change of process chemistry no obvious correlation between electron density and contact angle Angle[ ] 89 88 8 CHF3 flow decreasing 86 1.5 1.6 1. Electron Density [1 1.8 8 / cm ³] - 15 -
MxP+: Chamber monitoring of contact etch processes on product wafers Process mix in Applied Materials Centura MxP+ chamber: Oxide and Nitride etch with CF4 / CHF3 / Ar / O2 chemistry Process 1 Process 3 Process 2 Descum N2 / O2 --- --- Step 1 BPSG BPSG Oxide Step 2 --Nitride -- - 16 -
MxP+: CT etch - Chamber monitoring of product wafers: electron collision rate Electron Collision Rate vs. RF Hour Electron collision rate Collision Rate [1 s -1] 12, 11, - decreases with rf hours - very sensitive to etch chemistry Pr1 Pr2! Pr1 BPSG Pr2 BPSG Pr2 Nitride Pr3 Oxide 1, 9, 8, 2 4 6 8 1 RF Hour [h] - 1-12 One point one wafer
MxP+: CT etch - Chamber monitoring on product wafers: electron density Electron Density vs. RF Hour Electron Density [1 8 cm-3] 12,5 Pr1 BPSG Pr2 BPSG Pr2 Nitride Pr3 Oxide 11,5 Electron density - decreases with rf hours slightly - sensitive to etch chemistry 1,5 9,5 8,5,5 2 4 6 8 1 RF Hour [h] - 18-12 One point one wafer
MxP+: CT etch - Chamber monitoring on product wafers: bulk power Bulk power Bulk Power vs. RF Hour Pr1 BPSG Pr2 BPSG Pr2 Nitride Pr3 Oxide Bulk Power [mw/cm 2] 3 35 33 31 29 2 25 23 2 4 6 8 1 RF Hour [h] - 19-12 - decreases with rf hours - very sensitive to power input - nearly not sensitive to etch chemistry One point one wafer
MxP+: CT etch - Chamber monitoring on blanket BPSG wafers Uniformity vs. Electron Collision Rate Electron Collision Rate vs. RF Hours Uniformity [%] -1 Collision Rate [1 s ] 9 9 8 ER BPSG Kond PARPL 6 2 6 5 4 5.2 4 6 8 1 Uniformity vs. rf hours 5. 6.2 6. -1 Electron Collision Rate [1 s ] 12 RF Hour [h] - Electron collision rate correlates with uniformity. 9 Uniformity [ ] 3 5 8 8 6 - Electron density and bulk power too 5 4 3 2 4 6 8 1 12 rf hours [h] - 2 -
MxP+: Conditioning after wet clean Bulk Power vs. rf hours 2 B. Power [mw/cm ] Coll. Rate [1-1 s ] Electron Collision Rate vs. rf hours 9 8 Resist REM SS5 6 11 111 112 24 22 Resist 2 REM SS5 18 16 11 111 rf hours [h] 112 rf hours [h] Electron Density vs. rf hours 1.5 Density [1 8 / cm³] Wetclean 9.5 Resist ER BPSG Stable chamber conditions after about 1 wafers. 8.5 11 111 rf hours [h] 112-21 -
MxP+: CT etch - short term chamber drift depending on idle time Electrical failure counts at Contact etch Electron Collision Rate vs. Wafer Number min 45 min 5h Bad chamber 9,9 9, 9,5 4 8 12 16 2 24 Wafer stnuoc eruliaf Collision Rate [1 s -1] Idle time 1,1 Wafer - Collision rate shows dependence on chamber idle time. - Constant chamber conditions after about 4 min. - Change in electron collision rate corresponds to change in electrical failure counts. - 22 -
MxP+: CT etch - short term chamber drift Electrical failure counts at Contact etch Electron Density vs. Wafer stnuoc eruliaf 8 Electron Density [1 / cm³] 12,4 12,2 12, 11,8 11,6 Wafer 5 1 15 Wafer 2 25 - Electron density and failure counts increase by wafer number. - One of four chambers causes high failure counts. - 23 -
emxp+: Arcing detection Electron collision rate vs. time Electron collision rate (mean) -1 s ] 3 Wafer 9 25 6 2.8 collision rate [1 collision rate [1 s -1 ] 3. 2.6 2.4 2.2 2 15 1 5 2. 2 4 6 8 1 12 wafer 2 4 6 8 1 12 14 time [s] Arcing between e - chuck and wafer - 24 -
Summary - Al etch in LAM TCP 96 SE, oxide and nitride etch in Applied Materials Centura MxP+ have been monitored with HERCULES. - The measured parameters depend significantly on chamber conditions and etch results. - The measured parameters are absolute values. - No difficult modeling by the user is necessary, results are immediate. - 25 -
Applications of the tool - Development and optimizing processes Long and short term tool stability Tool matching Control of chamber cleaning Control of power coupling into plasma Endpoint detection Layer resolution Spatial resolution Reduction of test- and monitor wafers Detection of tool failure Arcing detection - 26 - yes yes yes yes yes possible possible no yes yes yes