Thin Nitride Measurement Example GOAL: Get the most information from your data and analyze it properly to make the right decisions! Look at the data in multiple ways to understand your process better. The old saying is Let the Data or parts talk to you. 1
Thin Nitride Measurement Example Definition of Thin Nitride : sub 1000A thickness Film to measure: PECVD Silicon Nitride deposited on Silicon_ A nominal 450A nitride film thickness was deposited on fifteen silicon wafers using a Novellus Thickness and R.I. (refractive index n) was measured on an Optiprobe Model DUV and a Tencor Model tool Measurement data from the two measurement tools was then compared. 2
Thin Nitride Measurement works on the dispersion principle ( refractive index is a function of wavelength) and uses wavelength to determine thickness and refractive index. The Refractive index on is quoted at the 632 nm wavelength! A recipe was optimized to measure Thin Silicon Nitride thickness (400-500A) and refractive index. Summary of Tencor measurement data: Goodness GOF values of 0.994 were obtained. Thickness range: 414-447A (sample dependent) Refractive Index range: 1.97-2.07 ( inter wafer dependent) (632 nm) 3
Optiprobe Thin Nitride Measurement Optiprobe uses ellipsometry and BPR to determine thickness and refractive index. A recipe was optimized to measure Thin Silicon Nitride thickness (400-500A) and refractive index. Summary of Optiprobe measurement data: Thickness range: 442-470A (sample dependent) Refractive Index range: 1.93-1.96 ( inter wafer dependent) 4
Recipe PCVD/Nitride/Thin Nitride - 5PT Validation and comparison to Optiprobe 15 wafer test Thickness Comparsion EXCEL FORMATED DATA Setup Wafer # Center UV 1050 Top Left Bottom Right Center Top Left Bottom Right 1 427 428 425 438 428 456 446 450 458 452 2 427 427 424 437 426 451 453 450 454 451 3 421 423 422 430 422 451 450 450 452 448 4 421 424 420 428 421 446 448 445 447 445 5 419 422 421 428 420 448 450 446 448 448 6 420 420 421 428 423 449 448 448 448 447 7 417 417 420 428 419 444 445 447 446 442 8 419 419 419.9 427 420 445 445 447 446 445 9 418 421 417 428 421 445 446 444 447 444 10 421 426 422 430 423 450 452 447 449 448 11 427 424 423 435 426 453 451 448 452 448 12 429 431 429 441 431 459 452 451 458 450 13 442.2 445 441 446 442 467 469 463 467 465 14 446 446 443 447 442 470 465 466 466 462 15 417 415 414 414 416 449 446 442 446 442 5
Recipe PCVD/Nitride/Thin Nitride - 5PT Validation and comparison to Optiprobe 15 wafer test Refractive Index Comparsion EXCEL FORMATED DATA Setup Wafer # RI CEN RI TOP RI LEFT RI BOT RI RIGHT RI CEN RI TOP RI LEFT RI BOT RI RIGHT 1 2.0543 2.045 2.045 1.9832 2.0402 1.946 1.9583 1.968 1.9471 1.9452 2 2.0622 2.0381 2.0426 2.0252 2.0382 1.9517 1.9418 1.944 1.9418 1.9417 3 2.0651 2.0454 2.0454 2.026 2.0415 1.9465 1.9398 1.9394 1.9381 1.9438 4 2.0687 2.0403 2.0469 2.0254 2.0445 1.955 1.9446 1.9447 1.9447 1.9441 5 2.036 2.0344 2.0483 2.0256 2.0359 1.9484 1.9389 1.9451 1.9424 1.94 6 2.0637 2.0413 2.0446 2.0296 2.0381 1.9487 1.9388 1.9385 1.9407 1.943 7 2.0546 2.0345 2.038 2.0212 2.0403 1.9508 1.9398 1.9394 1.9433 1.9454 8 2.0574 2.0327 2.0358 2.0199 2.032 1.9494 1.9389 1.9412 1.941 1.941 9 2.0523 2.0297 2.0346 2.0205 2.0368 1.9508 1.9398 1.9394 1.9433 1.9454 10 2.038 2.0272 2.032 2.009 2.0309 1.9445 1.9345 1.9372 1.9361 1.938 11 2.0355 2.0229 2.0231 1.9679 2.025 1.9457 1.9372 1.9409 1.939 1.9432 12 2.039 2.0254 2.0079 2.0164 2.0227 1.946 1.9399 1.9384 1.9393 1.9424 13 2.0355 2.0062 2.0047 2.0158 2.016 1.9481 1.9395 1.9413 1.9411 1.9414 14 2.0622 2.0415 2.0337 2.0467 2.0424 1.9488 1.9437 1.9404 1.9432 1.9437 15 1.9458 1.936 1.9411 1.9358 1.9409 6
comparison to Optiprobe 15 wafer test Thickness Comparsion Always look at data graphically first: EXCEL Plot Thickness A 480 470 460 450 440 430 Silicon Nitride Thickness measurements Vs Optiprobe Center UV 1050 Top Left Bottom Right Center Top Left Bottom Right 420 410 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Wafer # What can we say about this data? 7
comparison to Optiprobe 15 wafer test Thickness Comparsion Always look at data graphically first: EXCEL Plot Thickness A 2.08 2.06 2.04 2.02 2 1.98 1.96 1.94 1.92 Silicon Nitride Refractive Index measurements Vs Optiprobe 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Wafer # RI CEN RI TOP RI LEFT RI BOT RI RIGHT RI CEN RI TOP RI LEFT RI BOT RI RIGHT What can we say about this data? 8
Recipe PCVD/Nitride/Thin Nitride - 5PT Validation and comparison to Optiprobe 15 wafer test Thickness Comparsion EXCEL Data Analysis 9
Recipe PCVD/Nitride/Thin Nitride - 5PT Validation and comparison to Optiprobe 15 wafer test Thickness Comparsion EXCEL Descriptive Statistics 10
Recipe PCVD/Nitride/Thin Nitride - 5PT Validation and comparison to Optiprobe 15 wafer test Thickness Comparsion EXCEL Descriptive Statistics Statistic Center UV 1050 Top Left Bottom Right Center Top Left Bottom Right Mean 424.75 425.87 424.13 432.33 425.33 452.20 451.07 449.60 452.27 449.13 Standard Error 2.27 2.33 2.07 2.19 2.00 2.014707825 1.816502832 1.689744979 1.819122412 1.692748305 Median 421 424 422 430 423 450 450 448 449 448 Mode 427 424 422 428 426 451 446 450 446 448 Std Dev 8.81 9.01 8.02 8.48 7.74 7.80 7.04 6.54 7.05 6.56 Sample Variance 77.56 81.12 64.33 71.95 59.95 60.89 49.50 42.83 49.64 42.98 Kurtosis 1.8894897 1.63175426 2.1459123 0.5599923 1.339804911 1.051828528 2.779915121 2.801025593 0.325151756 2.0216176 Skewness 1.5862297 1.42082751 1.5886698-0.011463 1.396416849 1.311750606 1.79513239 1.764434256 1.166492983 1.502582425 Range 29.00 31.00 29.00 33.00 26.00 26.00 24.00 24.00 21.00 23.00 Minimum 417 415 414 414 416 444 445 442 446 442 Maximum 446 446 443 447 442 470 469 466 467 465 Sum 6371.2 6388 6361.9 6485 6380 6783 6766 6744 6784 6737 Count 15 15 15 15 15 15 15 15 15 15 11
Recipe PCVD/Nitride/Thin Nitride - 5PT Validation and comparison to Optiprobe 15 wafer test Thickness Comparsion Statistic UV 1050 SiN Mean 426.48 450.85 Standard Error 1.007742448 0.80173086 Median 424 448 Mode 421 448 Standard Deviation Sample Variance 8.73 6.94 76.17 48.21 Kurtosis 0.049985321 0.983523784 Skewness 0.978771752 1.355572713 Range 33 28 Minimum 414 442 Maximum 447 470 Sum 31986.1 33814 Count 75 75 NORMSINV Normal Probability Plot - Thin Nitride Measurements 3 99.9% 2.5 99.4% 2 97.7% 1.5 93.2% 1 84.1% 0.5 69.2% 0 50% -0.5 30.9% -1 15.9% -1.5 UV 1050 SiN 6.7% -2 2.3% -2.5 0.6% -3 0.1% 410.00 420.00 430.00 440.00 450.00 460.00 470.00 480.00 Thickness A 12
Recipe PCVD/Nitride/Thin Nitride - 5PT Validation and comparison to Optiprobe Optiprobe recipe variance significantly less than recipe STATISTICAL TESTS: F- test and T-test on Thickness data REASON : Unknown UV 1050 SiN Statistic Mean 426.5 450.9 Variance 76.2 48.2 Observations 75 75 df 74 74 F 1.5799 P(F<=f) one-tail 0.0255 F Critical one-tail 1.46945 Variances are significantly different! 2.5% chance of incorrectly rejecting Null that variances are equal t-test: Two-Sample Assuming Unequal Variances Statistic UV 1050 SiN Mean 426.5 450.9 Variance 76.2 48.2 Observations 75 75 Hypothesized Mean D 0 df 141 t Stat -18.92593591 P(T<=t) one-tail 7.73673E-41 0% chance of incorrectly rejecting Null that Means are equal t Critical one-tail 1.655732831 P(T<=t) two-tail 1.54735E-40 t Critical two-tail 1.976932253 13
Recipe PCVD/Nitride/Thin Nitride - 5PT Validation and comparison to Optiprobe 15 wafer test Refractive Index Comparsion Statistic UV 1050 SiN Mean 2.03 1.94 Standard Error 0.002059678 0.000610631 Median 2.03585 1.9418 Mode 2.0622 1.9398 Standard Deviation Sample Variance 0.0172 0.0053 2.96959E-04 2.79653E-05 Kurtosis 2.959879417 6.18215699 Skewness -0.999455211 1.864596592 Range 0.1008 0.0335 Minimum 1.9679 1.9345 Maximum 2.0687 1.968 Sum 142.3886 145.7328 Count 70 75 NORMSINV Normal Probability Plot - Thin Nitride 3 99.9% 2.5 99.4% 2 97.7% 1.5 93.2% 1 84.1% 0.5 69.2% 0 50% -0.5 30.9% -1 15.9% -1.5 6.7% -2 RI 2.3% -2.5 RI 0.6% -3 0.1% 1.92 1.94 1.96 1.98 2.00 2.02 2.04 2.06 2.08 Refractive Index 14
Recipe PCVD/Nitride/Thin Nitride - 5PT Validation and comparison to Optiprobe 15 wafers STATISTICAL TESTS: F- test and T-test on Refractive Index data show improved variance with Optiprobbe Recipe as compared to REASON : Unknown F-Test Two- Sample for Variances RI RI Mean 2.034 1.943 Variance 2.970E-04 2.797E-05 Observations 70 75 t-test: Two-Sample Assuming Unequal Variances RI RI Mean 2.034 1.943 Variance 2.970E-04 2.797E-05 df 69 74 Observations 70 75 F 10.61886223 P(F<=f) one-tail 2.60228E-20 F Critical one-tail 1.477481248 Variances are significantly different! 0% chance of incorrectly rejecting Null that variances are equal Hypothesized Mean Diffe 0 df 81 t Stat 42.36807647 P(T<=t) one-tail 2.40926E-57 t Critical one-tail 1.663884177 P(T<=t) two-tail 4.81852E-57 t Critical two-tail 1.989687917 15