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Evaluating Baseline Deposition and Etch Recipes for Silicon Dioxide and Silicon Nitride using PECVD and RIE Tools

Evaluating Baseline Deposition and Etch Recipes for Silicon Dioxide and Silicon Nitride using PECVD and RIE Tools. Presented by Ayesha K. Denny NNIN RET GIFT Fellow Ga Tech MiRC Summer 2007. Research Objectives.

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Evaluating Baseline Deposition and Etch Recipes for Silicon Dioxide and Silicon Nitride using PECVD and RIE Tools

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  1. Evaluating Baseline Deposition and Etch Recipes for Silicon Dioxide and Silicon Nitride using PECVD and RIE Tools Presented by Ayesha K. Denny NNIN RET GIFT Fellow Ga Tech MiRC Summer 2007

  2. Research Objectives • Verify process rates of standard recipes on deposition and etching tools. The tools utilized for deposition were: Unaxis PECVD, Plasma Therm PECVD(leftchamber SiN, right chamber SiO2), and STS PECVD. Etching tools used were Plasma Therm RIE (right chamber) and the Vision Oxide(Advance Vac). Substances deposited and etched were silicon dioxide and silicon nitride. • Evaluate deposition uniformity of the Plasma Therm PECVD. • Comparing deposition samples before and after maintenance on the Unaxis PECVD.

  3. Research Procedure for Verifying Deposition Rates of Standard SiO2 and SiN Recipes • 10 minute cleaning process of each deposition tool prior to use. • 1 minute seasoning of standard recipe on a “miscellaneous wafer” to create the desired environment in the chamber. • Place wafer in the center of the chamber and run the standard recipe for SiO2 or SiNx using the appropriate tool. • Measure film thickness of each wafer by completing a 5 point scan using the Woollam Ellipsometer and then determining the deposition rate and uniformity using the data obtained. • Spin coat each wafer with HMDS and photoresist 1827 and then bake for 10 minutes at 110°C on a hotplate.

  4. Research Procedure con’t. • Expose the mask pattern to each wafer using the MA6. • Develop each exposed wafer using developerMF319. • Evaluate sufficient development of each wafer by checking its profile using the P15 profilometer or Alpha Step500.

  5. Research Procedure for Verifying Etch Rates of Standard SiO2 and SiN Recipes • 10 minute cleaning process of each etching tool prior to use. • 1 minute seasoning of standard recipe on a “miscellaneous wafer” to create the desired environment in the chamber. • Place the wafer in the center of the chamber for the Adv. Vac or the front right position of the PT RIE (for consistency purposes only), and run the standard etching recipe for the specified time using the appropriate etching tool. • Obtain a post-etch profile of each wafer using P15 Profilometer or the Alpha Step 500 after stripping the sample of its photoresist using 1165 Removerand use the data obtained to determine the etch rate for each process.

  6. Research Procedure for Uniformity Evaluation Using the Plasma Therm PECVD • 10 minute cleaning process of Plasma Therm PECVD prior to use. • Run a 1 minute seasoning deposition on a “miscellaneous wafer” to create the desired environment in the chamber. • Place wafers in the chamber, making note of each wafer’s position. • Run the standard silicon dioxide deposition recipe for 20 minutes on the wafers. • Measure film thickness of each wafer by completing a 5 point scan using the Woollam Ellipsometer and then determining the deposition and uniformity rate using the data obtained.

  7. Cleaning Chamber (10 minutes) Unaxis PECVD CLN_250.PRC STS PECVD quickcln.set PT PECVD CLEANR.PRC At 250C Adv. Vac CleanO2 PT RIE CLNLOVAC.PRC Depositions Unaxis PECVD STD_OX Step 1 – Initial  250°C Step 2 – Gas Stabilization 900mTorr SiH4 1k 400 sccm N2O 2k 900 sccm Power 0 W Step 3 – SiO2 deposition 900 mTorr SiH4 1k 400 sccm N2O 2k 900 sccm Power 25W Process Recipes

  8. Deposition STS PECVD lfsinO2a.set ( standard low frequency silicon dioxide) N2O 1420 (actual 1413 – 1427) 2% SiH4/N2 2% SiH4 400 sccm Process pressure 550 mTorr APC Angle 0 (actual 67.4) Process temp. 300°C Aux. Temp. 250°C (actual 241°C) Power @ 380 kHz 60W (actual 49-53) Load position 10.0% (actual 24.4%) Tune position 62.0% (actual 59.8%) Deposition STS PECVD lfsina.set (standard low frequency silicon nitride) NH3 20 sccm 2% SiH4/N2 2% SiH4 2000 sccm Process pressure 550 mTorr Process temp. 300°C (actual 298°C) Aux temp. 250°C (actual 240 °C) Power @ 380 kHz 60W (actual 53-58) Load position 3% (actual 14.7%) Tune position 65% (actual 61.2% – 61.4%) Process Recipes

  9. Deposition PT PECVD STDOX.PRC (standard silicon dioxide right chamber) 250°C Step 4 – Gas stabilization 700 mTorr SiH4 400 sccm N2O 900 sccm Power 0 W Step 5 – Deposition 700 mTorr for SiO2 (actual 723-725 mTorr) 900 mTorr for SiN (actual 920-922 mTorr) Power 25 W (actual range 22-28W) Deposition PT PECVD STDNIT.PRC (standard silicon nitride left chamber) 250°C Step 4 – Gas stabilization 900 mTorr SiH4 200 sccm N2 900 sccm NH3 5.00 sccm Power0 W Step 5 – Deposition 900 mTorr SiH4 200 sccm N2 900 sccm NH3 5.00 sccm Power 30 W Process Recipes

  10. Measuring Film Thickness Woollam Ellipsometer Thin oxide recipe for SiO2 projected thickness less than 2500 Å. Thick oxide recipe for SiO2 projected thickness greater than 2500 Å. Thin nitride recipe for SiNprojected thickness less than 2500 Å. Thick nitride recipe for SiNprojected thickness greater than 2500 Å. 4 inch, 5 point scan Spin coating using CEE 100CB Spinner HMDS 3000 rpm 1000 rpm/s 15s Photoresist 1827 3000 rpm 1000 rpm/s 30s Baking on a hotplate 110°C 10 minutes Process Recipes

  11. Exposing and Developing MA6 Channel 2 Exposure time: 30 sec Exposure type: Low Vacuum contact Wavelength : 405nm MF319 Developer Agitate exposed wafer until mask pattern is visible and “rainbow color” on wafer disappears– approx. 45 to 120 seconds. Profiling P15 Sampling rate at 50Hz Applied force of 0.5 mg Alpha Step 500 AS5 recipe Process Recipes

  12. Etching PT RIE (right chamber) STDOX.PRC (standard silicon dioxide) Step 2 – Gas stabilization 20 mTorr CHF3 22.5 sccm O2 2.5 sccm Power 0 W Step 3 – Etching 20 mTorr CHF3 22.5 sccm O2 2.5 sccm Power 300W Etching PT RIE (right chamber) STDNIT.PRC (standard silicon nitride) Step 2 – Gas stabilization 40 mTorr CHF3 45.0 sccm O2 5.0 sccm Power 0 W Step 3 – Etching 40 mTorr CHF3 45.0 sccm O2 5.0 sccm Power 200 W Process Recipes

  13. DEPOSITION AND ETCH MAPPING FOR WAFERS 1 - 12

  14. Wafer Positions on the Platen for Deposition Uniformity Evaluation of the Plasma Therm PECVD Back left Back right Front right Front left

  15. UNIFORMITY AND DEPOSITION RATE RESULTS

  16. Uniformity (Measured by the Woollam Ellipsometer)and Deposition Rates(Determined by dividing the thickness of the deposition by the time of deposition)

  17. Con’t. Uniformity and Deposition Rate

  18. Uniformity Results determined by the Woollam Ellipsometer for the 20 minute Silicon Dioxide Process – Plasma Therm PECVD 3.0724% 5.4553% 3.6400% 3.6207%

  19. Deposition Rate for the Uniformity 20 minute Silicon Dioxide Process on the Plasma Therm PECVD (400 Å/min projected) 471 Å/min 458 Å/min 486 Å/min 494 Å/min

  20. ETCHRATE RESULTS

  21. Step Height and Etch Rate Data

  22. Step height and etch rate data using the Alpha Step 500

  23. Step height and etch rate data using the Alpha Step 500

  24. Andthicknessvariations 3-D Graphs of Depositions

  25. Thickness variation describes the percentage difference of thickness between the lowest and highest points of the materials deposited on the wafer Step 1: Min. thickness/Max thickness = A Step 2: A x 100% = B% Step 3: 100% - B% = % of thickness variation

  26. Oxide Thickness Å Mean = 2194.4 Min = 1045.0 Max = 2996.5 Std Dev = 996.79 Uniformity = 45.424 % 2671.25 2346 2020.75 1695.5 1370.25 1045 5 minute Silicon Dioxide Unaxis PECVD Thickness variation is 65.1% Highest thickness area Lowest thickness area

  27. 20 minute Silicon Dioxide Unaxis PECVD Thickness variation is 4.5% Highest Thickness area Lowest thickness area

  28. 20 minute Silicon Nitride before and after maintenance - Unaxis PECVD Thickness variation is 3.0% Thickness variation is 5.4% Highest thickness area Lowest thickness area Highest thickness area Lowest thickness area Before manual cleaning After manual cleaning

  29. 40 minute Silicon Nitride Unaxis PECVD Thickness variation is 4.2% Highest thickness area Lowest thickness area

  30. 5 minute Silicon DioxideSTS PECVD Thickness variation is 9.2% Lowest thickness area Highest thickness area

  31. 20 minute Silicon Dioxide STS PECVD Thickness variation is 2.9% Highest thickness area Lowest thickness area

  32. 20 minute Silicon NitrideSTS PECVD Thickness variation is 3.7% Highest thickness area Lowest thickness area

  33. 40 minute Silicon NitrideSTS PECVD Thickness variation is 4.9% Highest thickness area Lowest thickness areas

  34. 5 minute Silicon DioxidePlasma Therm PECVD Thickness variation is 7.3% l Highest thickness area Lowest thickness area

  35. 20 minute Silicon DioxidePlasma Therm PECVD Thickness variation is 8.5% Lowest thickness area Highest thickness area

  36. 20 minute Silicon NitridePlasma Therm PECVD Thickness variation is 3.8% Highest thickness area Lowest thickness area

  37. 40 minute Silicon NitridePlasma Therm PECVD Thickness variation is 2.6% Lowest thickness area Highest thickness area

  38. Uniformity Evaluation for a 20 minute Standard Silicon Dioxide Deposition using the Plasma Therm PECVD Thickness variation is 7.3% Thickness variation is 13.1% Lowest thickness area Lowest thickness area Highest thickness area Highest thickness area Thickness variation is 8.7% Thickness variation is 7.9% Highest thickness area Lowest thickness areas Lowest thickness areas Highest thickness area

  39. Bar GraphRepresentations ofDeposition Rates

  40. Bar GraphRepresentations ofEtch Rates

  41. Conclusions • Silicon nitride deposition rates were more consistent than silicon dioxide depositions using the Unaxis PECVD. • Silicon dioxide deposition rates were more consistent than silicon nitride depositions using the STS PECVD. • Deposition rates for silicon dioxide and silicon nitride were more consistent using the Plasma Therm PECVD. • Depositions rates are higher in the front of the chamber for the Plasma Therm PECVD. • After maintenance (thorough cleansing) showed a 1% increase in uniformity. • Etch rates for silicon dioxide using the Plasma Therm RIE varied but fell within the projected range most of the time. • Etch rates using the Advanced Vac were inconclusive due to insufficient data (tool was down).

  42. Mentors • Dr. Nancy Healy • Janet Cobb-Sullivan • Cristina Scelsi • Dr. Kevin Martin

  43. A Special Thank you to… • Cristina Scelsi • Janet Cobb-Sullivan • Nathan Hull • Jaime Zahorian • Keri Ledford • Charlie Suh • Tran-Vinh Nguyen • Gary Spinner • Other helpful cleanroom staff • Dr. Greg Book • Rochelle Hamby and Jaclyn Murray (2007 RETs)

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