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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

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Research Objectives 1. Verify process rates of standard recipes on deposition and etching tools. The tools utilized for deposition were: Unaxis PECVD, Plasma Therm PECVD (left chamber SiN, right chamber SiO 2 ), 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. 2. Evaluate deposition uniformity of the Plasma Therm PECVD. 3. Comparing deposition samples before and after maintenance on the Unaxis PECVD.

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Research Procedure for Verifying Deposition Rates of Standard SiO 2 and SiN Recipes 1. 10 minute cleaning process of each deposition tool prior to use. 2. 1 minute seasoning of standard recipe on a miscellaneous wafer to create the desired environment in the chamber. 3. Place wafer in the center of the chamber and run the standard recipe for SiO 2 or SiN x using the appropriate tool. 4. 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. 5. Spin coat each wafer with HMDS and photoresist 1827 and then bake for 10 minutes at 110°C on a hotplate.

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Research Procedure cont. 6. Expose the mask pattern to each wafer using the MA6. 7. Develop each exposed wafer using developer MF319. 8. Evaluate sufficient development of each wafer by checking its profile using the P15 profilometer or Alpha Step 500.

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Research Procedure for Verifying Etch Rates of Standard SiO 2 and SiN Recipes 1. 10 minute cleaning process of each etching tool prior to use. 2. 1 minute seasoning of standard recipe on a miscellaneous wafer to create the desired environment in the chamber. 3. 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. 4. 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 Remover and use the data obtained to determine the etch rate for each process.

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Research Procedure for Uniformity Evaluation Using the Plasma Therm PECVD 1. 10 minute cleaning process of Plasma Therm PECVD prior to use. 2. Run a 1 minute seasoning deposition on a miscellaneous wafer to create the desired environment in the chamber. 3. Place wafers in the chamber, making note of each wafers position. 4. Run the standard silicon dioxide deposition recipe for 20 minutes on the wafers. 5. 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.

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Process Recipes 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 SiH 4 1k 400 sccm N 2 O 2k 900 sccm Power 0 W Step 3 – SiO 2 deposition 900 mTorr SiH 4 1k 400 sccm N 2 O 2k 900 sccm Power 25W

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Process Recipes Deposition STS PECVD lfsinO2a.set ( standard low frequency silicon dioxide) a) N 2 O 1420 (actual 1413 – 1427) b) 2% SiH 4 /N 2 2% SiH 4 400 sccm c) Process pressure 550 mTorr d) APC Angle 0 (actual 67.4) e) Process temp. 300°C f) Aux. Temp. 250°C (actual 241°C) g) Power @ 380 kHz 60W (actual 49- 53) h) Load position 10.0% (actual 24.4%) i) Tune position 62.0% (actual 59.8%) Deposition STS PECVD lfsina.set (standard low frequency silicon nitride) a) NH3 20 sccm b) 2% SiH 4 /N 2 2% SiH 4 2000 sccm c) Process pressure 550 mTorr d) Process temp. 300°C (actual 298°C) e) Aux temp. 250°C (actual 240 °C) f) Power @ 380 kHz 60W (actual 53- 58) g) Load position 3% (actual 14.7%) h) Tune position 65% (actual 61.2% – 61.4%)

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Process Recipes Deposition PT PECVD STDOX.PRC (standard silicon dioxide right chamber)250°C Step 4 – Gas stabilization 700 mTorr SiH 4 400 sccm N 2 O 900 sccm Power 0 W Step 5 – Deposition 700 mTorr for SiO 2 (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 SiH 4 200 sccm N 2 900 sccm NH 3 5.00 sccm Power0 W Step 5 – Deposition 900 mTorr SiH 4 200 sccm N 2 900 sccm NH 3 5.00 sccm Power 30 W

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Process Recipes Measuring Film Thickness Woollam Ellipsometer Thin oxide recipe for SiO 2 projected thickness less than 2500 Å. Thick oxide recipe for SiO 2 projected thickness greater than 2500 Å. Thin nitride recipe for SiN projected thickness less than 2500 Å. Thick nitride recipe for SiN projected 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

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Process Recipes 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

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

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DEPOSITION AND ETCH MAPPING FOR WAFERS 1 - 12 Unaxis PECVD STS PECVD PT PECVD PT RIE (right chamber) 1, 2, 195,69,10 Adv. Vac RIE 3,47,811,12, 15, 16, 17, 18

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

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UNIFORMITY AND DEPOSITION RATE RESULTS

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Uniformity (Measured by the Woollam Ellipsometer) and Deposition Rates (Determined by dividing the thickness of the deposition by the time of deposition) WaferToolMaterial and Time Deposited UniformityProjected Deposition Actual Deposition 1UnaxisSiO 2 5 min 45.424%600 Å/ min439 Å/ min 2UnaxisSiO 2 20 min 1.7554%600 Å/ min573 Å/ min 3Unaxis Before maintenance SiN 20 min 1.2248%100 Å/ min 88 Å/ min 19Unaxis After maintenance SiN 20 min 2.1816%100 Å/ min 93 Å/ min 4UnaxisSiN 40 min1.7464%100 Å/ min90 Å/ min

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Cont. Uniformity and Deposition Rate WaferTool Material and Time Deposited Uniformity Projected Deposition Actual Deposition 5STSSiO 2 5 min3.9952%720 Å/ min710 Å/ min 6STS SiO 2 20 min1.1929%720 Å/ min721 Å/ min 7STSSiN 20 min1.5113%460 Å/ min377 Å/ min 8STSSiN 40 min1.4945%460 Å/ min473 Å/ min 9PTSiO 2 5 min3.1974%400 Å/ min517 Å/ min 10PTSiO 2 20 min3.4404%400 Å/ min527 Å/ min 11PTSiN 20 min1.6205%100 Å/ min154 Å/ min 12PTSiN 40 min1.1027%100 Å/ min142 Å/ min

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

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

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ETCH RATE RESULTS

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Step Height and Etch Rate Data Wafer and Material Etched Etching Tool and Time Step height measurement without photoresist Projected Etch Rate Actual Etch Rate 1 SiO 2 PT RIE 5 min1950 Å 400-500 Å/min390 Å/min 2 SiO 2 PT RIE 5 min2125 Å 400-500 Å/min425 Å/min 3 SiN Adv. Vac 2 min (SiO 2 recipe) 250 Å???125 Å/min

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Step height and etch rate data using the Alpha Step 500 Wafer and Material Etched Etching Tool and Time Step height measurement without photoresist Projected Etch Rate Actual Etch Rate 10 SiO 2 PT RIE 5 min 2100 Å 400-500 Å/min 420 Å/min 15 SiO 2 back right PT RIE 5 min 2175 Å 400-500 Å/min 435 Å/min 16 SiO 2 front right PT RIE 5 min 2100 Å 400-500 Å/min 420 Å/min 17 SiO 2 front left PT RIE 5 min 2000 Å 400-500 Å/min 400 Å/min 18 SiO 2 back left PT RIE 5 min 2125 Å 400-500 Å/min 425 Å/min

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Step height and etch rate data using the Alpha Step 500 Wafer and Material Etched Etching Tool and Time Step height measurement without photoresist Projected Etch Rate Actual Etch Rate 4 SiN Adv. Vac 2 min (SiO 2 recipe) 200 Å??? 100 Å/min 5 SiO 2 PT RIE 5 min2000Å 400-500 Å/min 400 Å/min 6 SiO 2 PT RIE5 min 1800 Å 400-500 Å/min 360 Å/min 7 SiN Adv. Vac 5 min (SiO 2 recipe) 425 Å ??? 85 Å/min 9 SiO 2 PT RIE 5 min3800 Å 400-500 Å/min 760 Å/min

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And thickness variations

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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

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5 minute Silicon Dioxide Unaxis PECVD Thickness variation is 65.1% Lowest thickness area Highest thickness area

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

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

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

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5 minute Silicon Dioxide STS PECVD Thickness variation is 9.2% Lowest thickness area Highest thickness area

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

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20 minute Silicon Nitride STS PECVD Thickness variation is 3.7% Lowest thickness area Highest thickness area

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40 minute Silicon Nitride STS PECVD Thickness variation is 4.9% Lowest thickness areas Highest thickness area

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5 minute Silicon Dioxide Plasma Therm PECVD lThickness variation is 7.3% Lowest thickness area Highest thickness area

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20 minute Silicon Dioxide Plasma Therm PECVD Thickness variation is 8.5% Lowest thickness area Highest thickness area

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20 minute Silicon Nitride Plasma Therm PECVD Thickness variation is 3.8% Highest thickness area Lowest thickness area

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40 minute Silicon Nitride Plasma Therm PECVD Thickness variation is 2.6% Lowest thickness area Highest thickness area

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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% Thickness variation is 8.7% Thickness variation is 7.9% Lowest thickness area Highest thickness areaHighest thickness area Lowest thickness area Lowest thickness areas Highest thickness area Lowest thickness areas Highest thickness area

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Bar Graph Representations of Deposition Rates

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Bar Graph Representations of Etch Rates

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

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

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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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