Yms Micron

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Presentation foils delivered at KLA-Tencor YMS 2002. Data and foils development with project partner - MICRON.

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  • This is a representation of the locations in the silicon dioxide where the nitrogen will reside. This picture is not a true representation of the lattice structure, but merely a diagram of where nitrogen is located in the oxide. Hydrogen will also take places in the oxide near the interface and act as fixed charge or will also occupy locations in the interface. The size of nitrogen is much larger then oxygen and will stack at the interface like boulders next to marbles. There are spatial effects, the position of the nitrogen influences the electrical parameters, if N2 in the bulk then no charge just changes the dielectric constant at the interface changes. Hydrogen passivates the bonds. Luckily for us when N2 goes into the film it messes up the interface - we exploit that leads to COS or electrical characterization.
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  • Yms Micron

    1. 1. IN-LINE MONITORING OF NITRIDED GATE DIELECTRIC FILMS James Chapman Sr. Engineer, Fab Parametrics Micron Technology, Inc. Boise, ID Kwame N. Eason Key Accounts Technologist KLA-Tencor Inc. San Jose, CA
    2. 2. Outline <ul><li>Introduction </li></ul><ul><li>Gate Nitridation: Basics </li></ul><ul><li>Gate Nitridation: Monitoring Strategy </li></ul><ul><li>Sensitivity of In-line Monitoring </li></ul><ul><li>Results & Conclusions </li></ul>
    3. 3. Gate Oxide History <ul><li>CMOS scaling requires increased gate oxide capacitance per unit area </li></ul><ul><ul><li>Thinning of gate dielectric </li></ul></ul><ul><ul><li>Increase in ε r </li></ul></ul>
    4. 4. Gate Oxide Materials Challenges <ul><li>Problems With Ultra-Thin SiO 2 </li></ul><ul><ul><li>I g – Gate Leakage Current </li></ul></ul><ul><ul><li>Oxide Non-Uniformity </li></ul></ul><ul><ul><li>Surface Roughness </li></ul></ul><ul><ul><li>Boron Penetration </li></ul></ul>
    5. 5. Mechanics of Boron Penetration <ul><li>For PMOS – Boron diffuses from the doped poly through the gate dielectric with subsequent  C </li></ul><ul><ul><li>Results in counter-doping of Si, shift in V T </li></ul></ul><ul><ul><li>Nitrogen reduces this effect </li></ul></ul><ul><li>Boron enters Si substrate: </li></ul><ul><li>During implant (S/D and gate electrode) </li></ul><ul><li>By diffusion from the p-doped poly gate </li></ul> B penetration  N content  V T  channel doping Silicon Substrate - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Field Oxide
    6. 6. <ul><li>Increases ε r </li></ul><ul><li>Prevents Boron Penetration </li></ul><ul><li>How do you control and monitor this process? </li></ul>Advantages of Gate Nitridation 1 Gate Polysilicon Poly Si Si Poly Si SiON Si SiO 2 Si Oxidation (BASE OX) SiO 2 Si Gate Oxidation (BASE OX) SiON Si SiON Si Nitridation
    7. 7. Long Channel V T is Sensitive to Boron Penetration <ul><li>Gate length and the effects of Boron Penetration </li></ul><ul><ul><li>Nominal and sub-nominal devices are increasingly affected by gate length (CD) </li></ul></ul>Poly Gate Si Substrate Sub-nom Channel Drain Controlled S D V DD
    8. 8. Long Channel V T is Sensitive to Boron Penetration <ul><li>Gate length and the effects of Boron Penetration </li></ul><ul><ul><li>Nominal and sub-nominal devices are increasingly affected by gate length (CD) </li></ul></ul><ul><ul><li>Long channel V T is primarily affected by channel doping </li></ul></ul>Poly Gate Si Substrate Sub-nom Channel Drain Controlled S D V DD Long Channel Gate Controlled S D V DD
    9. 9. Threshold Voltage as a Monitor <ul><li>Pros of Using V T as a Monitor </li></ul><ul><ul><li>Exact indication of device performance </li></ul></ul><ul><ul><li>Clearly shows boron penetration excursion </li></ul></ul><ul><li>Cons of Using V T as a Monitor </li></ul><ul><ul><li>Elapsed time between gate nitridation and formation of a measurable transistor </li></ul></ul><ul><ul><li>Quantity of potential scrap is increased! </li></ul></ul>Need an in-line electrical V T monitor
    10. 10. In-Line Nitridation Monitoring with Quantox <ul><li>In-line monitoring approach: </li></ul><ul><ul><li>Use Quantox to monitor N content </li></ul></ul><ul><ul><li>Monitor Quantox GateTox, V tunnel , and Q tot </li></ul></ul><ul><li>Implementation requires: </li></ul><ul><ul><li>Demonstrated process sensitivity </li></ul></ul><ul><ul><li>Correlation to long channel V T </li></ul></ul> B penetration  N content  V T  channel doping
    11. 11. Quantox Approach <ul><li>Both film leakage and capacitance are affected by N content </li></ul><ul><li>Quantox offers INDEPENDENT measure of each property </li></ul>Capacitance: GateTox™ Leakage: V tunnel
    12. 12. Quantox Approach, Cont’d <ul><li>Q tot is sensitive to N induced fixed charge </li></ul><ul><li>N replaces O in SiO 2 lattice </li></ul><ul><ul><li>Resulting in + 1 valence (fixed charge) </li></ul></ul>Fixed Charge: Q tot
    13. 13. Sensitivity of In-line Monitoring <ul><li>Design of Experiments (DOE) evaluated over nitridation processing space </li></ul><ul><ul><li>Explored 20 % -700 % variation from the nominal </li></ul></ul><ul><ul><li>Measured Quantox GateTox, V tunnel , Q tot post nitridation and compared to long channel V T </li></ul></ul>Poly - Si RPNO Si Deposition Poly - Si SiON Si Polysilicon Deposition SiO 2 Si Oxidation (BASE OX) SiO 2 Si Gate Oxidation (BASE OX) SiON Si SiON Si Nitridation Quantox
    14. 14. Quantox Data Compared to V T <ul><li>Quantox results compared to long channel V T </li></ul><ul><li>R 2 is least squares fit to data (best fit) </li></ul><ul><li>V T variation completely dominated by N content </li></ul><ul><li>GateTox demonstrated sensitivity to N content </li></ul>Capacitance
    15. 15. Leakage and Q tot Correlation Results N content Leakage
    16. 16. Confirmation of Monitoring Strategy <ul><li>Forced Double Nitridation Excursion </li></ul><ul><ul><li>Previously nitrided film put back in monitoring loop, as noted by cartoon. </li></ul></ul><ul><li>Wafer measured after nitridation, electrical parameter (V tunnel ) picks up excursion. </li></ul>Forced Excursion Double Nitridation Nitr. Poly Ox Processing Step
    17. 17. In-line Measured After Nitridation V tunnel V tunnel identifies the excursion Forced Excursion Double Nitridation:
    18. 18. In-line Correlation to Capacitance C ox  1/ Thickness <ul><li>Inverse of GateTox compared to Capacitance </li></ul><ul><ul><li>R 2 = 97 % </li></ul></ul><ul><li>Capacitance variation direct result of nitridation DOE </li></ul><ul><li>GateTox demonstrated sensitivity to N content </li></ul>
    19. 19. Conclusion <ul><li>Quantox parameters effectively monitor nitridation: </li></ul><ul><ul><li>GateTox (capacitance), </li></ul></ul><ul><ul><li>V tunnel (leakage) </li></ul></ul><ul><ul><li>Q tot (fixed charge) </li></ul></ul><ul><li>In-line electrical parameters catch nitridation excursion </li></ul><ul><li>In-line capacitance correlates to EoL capacitance </li></ul>97% Q tot 95% V Tunnel 95% GateTox R 2 to P ch long V T Parameter
    20. 20. Acknowledgements <ul><li>Micron Technology, Inc. : </li></ul><ul><ul><li>Terry Letourneau </li></ul></ul><ul><ul><li>Kevin Emberton </li></ul></ul><ul><li>KLA-Tencor Inc.: </li></ul><ul><ul><li>Gary Rusk </li></ul></ul><ul><ul><li>Torsten Kaack </li></ul></ul><ul><ul><li>Catherine Hartford </li></ul></ul>
    21. 21. Back-Up Slides
    22. 22. Quantox Technology Overview Corona Charge Bias, Q SILICON OXIDE High Voltage Corona Ions 1. Repeat Non-Contact Voltmeter, V surf Electronics V surf 2. Surface Photovoltage, SPV - - + + SPV LIGHT Transient Detection 3.
    23. 23. Q-V Sweep Parameter Extraction Inversion Accumulation C ox : Q-V slope V tunnel
    24. 24. Q-SPV Sweep Parameter Extraction Q total = -Q (SPV = 0)
    25. 25. V T as a Monitor (cont.) <ul><li>Dielectric Parameters that Affect Boron Penetration </li></ul><ul><ul><li>Physical Thickness </li></ul></ul><ul><ul><ul><li>As thickness decreases </li></ul></ul></ul><ul><ul><ul><li>Boron counter-doping increases </li></ul></ul></ul><ul><ul><ul><li>V T Decreases </li></ul></ul></ul>Boron counter-doping will move E f closer to E i , thus reducing voltage required to reach threshold condition
    26. 26. V T as a Monitor (cont.) <ul><ul><li>Nitrogen Content </li></ul></ul><ul><ul><ul><li>As N decreases </li></ul></ul></ul><ul><ul><ul><li>Boron counter-doping increases </li></ul></ul></ul><ul><ul><ul><li>V T decreases </li></ul></ul></ul><ul><ul><li>Dielectric Quality </li></ul></ul><ul><ul><ul><li>As Quality decreases </li></ul></ul></ul><ul><ul><ul><li>Boron counter-doping increases </li></ul></ul></ul><ul><ul><ul><li>V T decreases </li></ul></ul></ul>

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