1. 20/03/2003 Impact of Carbon on short channel behavior in deep submicronic N MOSFET’s 4 th European Workshop on Ultimate Integration of Silicon Impact of Carbon on short channel behavior in deep submicronic N MOSFET ’s K. Romanjek 1, G. Ghibaudo 1, T. Ernst 2 1) IMEP, ENSERG, BP 257, 23 rue des Martyrs, 38016 Grenoble, cedex 16, France 2) CEA/LETI, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France

2. 20/03/2003 Impact of Carbon on short channel behavior in deep submicronic N MOSFET’s 4 th European Workshop on Ultimate Integration of Silicon Outline Introduction 1 Device fabrication and parameter extraction technique N MOSFET’s structure Y function method Impact of Carbon on electrical parameters Threshold voltage Low Field mobility Transconductance parameter Boron pockets influence Comparison between transistors with and without pockets Neutralization of Boron pockets using body bias Conclusion

3. 20/03/2003 Impact of Carbon on short channel behavior in deep submicronic N MOSFET’s 4 th European Workshop on Ultimate Integration of Silicon 2 Introduction Why Carbon incorporation in deep submicronic N MOSFET’s ? TEM picture by CEA-Leti

4. 20/03/2003 Impact of Carbon on short channel behavior in deep submicronic N MOSFET’s 4 th European Workshop on Ultimate Integration of Silicon 3 Device fabrication and parameter extraction technique N MOSFET’s structure Transistors studied : NMOSFET’s t cap = 2nm after oxidation t Si:C = 3, 6 or 10nm x = 0.6 or 1% t oxide = 2nm W = 10µm L = 10µm to 50nm fabricated by CEA-Leti

5. 20/03/2003 Impact of Carbon on short channel behavior in deep submicronic N MOSFET’s 4 th European Workshop on Ultimate Integration of Silicon Device fabrication and parameter extraction technique Y function method low V d V g >> V t 4

6. 20/03/2003 Impact of Carbon on short channel behavior in deep submicronic N MOSFET’s 4 th European Workshop on Ultimate Integration of Silicon 5 Impact of Carbon on electrical parameters Threshold voltage (1/2) Better control of the roll off : Epitaxial channel as compared to implanted one Si:C transistors compared to Si transistors Si:C C 0.6 % 10 nm C 1 % 6 nm C 1 % 10 nm Si EpitaxySi Implanted channel

7. 20/03/2003 Impact of Carbon on short channel behavior in deep submicronic N MOSFET’s 4 th European Workshop on Ultimate Integration of Silicon 6 Impact of Carbon on electrical parameters Threshold voltage (2/2) Si:C parameters : -20 -10 0 10 20 30 40 0,010,11 Channel length (µm) Threshold voltage variation (%) 40nm Si PSD /C 1 % 10 nm C 1 % 6 nm C 1 % 3 nm C 1 % 10 nm C 0.6 % 10 nm C 1 % 10 nm 3 nm Si:C layer thickness is not sufficient to limit Boron diffusion 0.6 % of Carbon is sufficient to control the rool-off 40nm PSD layer isn’t necessary to have a better control of the roll off

8. 20/03/2003 Impact of Carbon on short channel behavior in deep submicronic N MOSFET’s 4 th European Workshop on Ultimate Integration of Silicon 7 Impact of Carbon on electrical parameters Low Field mobility Even for long transistors we don’t have a clear gain due to carbon incorporation For Si:C transistor a strong decrease is noticed For ultrashort channel length there is a convergence of all curves. EpitaxySi Implanted channel Si C 0.6 % 10 nm C 1 % 6 nm C 1 % 10 nm Si:C

9. 20/03/2003 Impact of Carbon on short channel behavior in deep submicronic N MOSFET’s 4 th European Workshop on Ultimate Integration of Silicon 8 Impact of Carbon on electrical parameters Transconductance parameter Even for Si transistors we have a slight degradation may due to Boron Pockets For Si:C transistor a strong degradation is noticed The transconductance parameter is studied to account for the possible variation of difference between electrical and technological channel length 0 5 10 15 20 25 0,010,11 Channel length (µm) Gm/Gm(Lmax) Si EpitaxySi Implanted channel 1/L Si:C C 0.6 % 10 nm C 1 % 6 nm C 1 % 10 nm

10. 20/03/2003 Impact of Carbon on short channel behavior in deep submicronic N MOSFET’s 4 th European Workshop on Ultimate Integration of Silicon Comparison between transistors with and without pockets (1/2) Boron pockets influence 9 Transistors without pockets have a stronger roll off than transistors with pockets : Boron pockets contribute to the control of short channel effects. For Si:C transistors, a good control of the roll off still persists even for transistors without pockets : Carbon incorporation also controls the short channel effects.

11. 20/03/2003 Impact of Carbon on short channel behavior in deep submicronic N MOSFET’s 4 th European Workshop on Ultimate Integration of Silicon Comparison between transistors with and without pockets (2/2) Boron pockets influence 10 Transistors with pockets have a higher degradation than transistors without pockets : Boron pockets contribute to degradation of the carrier transport. For Si:C transistors, a strong degradation still persists even for transistors without pockets : Carbon incorporation also degrades the carrier transport.

12. 20/03/2003 Impact of Carbon on short channel behavior in deep submicronic N MOSFET’s 4 th European Workshop on Ultimate Integration of Silicon Neutralization of Boron pockets using body bias (1/2) Impact of Carbon on electrical parameters 11 For Si transistors : roll on due to implant pockets is totally neutralized by body bias. For Si:C transistors : a good control of the roll off still persists even when Boron pockets are neutralized.

13. 20/03/2003 Impact of Carbon on short channel behavior in deep submicronic N MOSFET’s 4 th European Workshop on Ultimate Integration of Silicon 12 For Si transistors : degradation due to implant pockets totally neutralized by body bias. For Si:C transistors : a degradation still persists even when Boron pockets are neutralized. Neutralization of Boron pockets using body bias (2/2) Impact of Carbon on electrical parameters

14. 20/03/2003 Impact of Carbon on short channel behavior in deep submicronic N MOSFET’s 4 th European Workshop on Ultimate Integration of Silicon 13 Conclusion Short channel effects : As expected, a good control of the roll off is noticed for Si:C transistors. By a method based on a body bias, we have separated the contribution due to Boron pockets and have shown that a Si:C layer contributes mainly to the control of the roll off. The most critical parameter is the Si:C layer thickness, it has to be large enough to be a good barrier for Boron diffusion in order to obtain a retrograde doping profile. Carrier transport : Unfortunately, we have observed a degradation of carrier transport in Si:C transistors may due to a high percentage of Interstitial Carbon atoms which create defects in the oxide and/or in the channel. We have shown that this degradation is partially due to Boron pockets, but the major part is due to Carbon incorporation.