25 Å gate oxide without boron penetration for 0.25 and 0.3-μm PMOSFETs

Self Cite

We have found that nitrogen incorporation in the gate-oxide, by implantation into the Si, degrades the low field inversion mobility. Although submicron transistors fabricated using nitrogen implantation have been reported to show higher drive currents compared with "pure" oxides, we have measured about 20% degradation in large area transistors for a 2e14 cm 2 nitrogen implant. These measurements were done using nMOS transistors with thin gate-oxides ( 4 nm). Thickness determination was done by simulation fit to capacitance-voltage (C-V) measurements by including quantization and tunneling effects. We furthermore, observed that the decrease in the mobility has an increased sensitivity to the channel doping concentration.

Section: Introductionmentioning

confidence: 99%

Reduced electron mobility due to nitrogen implant prior to the gate oxide growth

Kamgar¹,

Clemens²,

Ghetti³

et al. 2000

Self Cite

“…The studies also show that the N is not uniformly distributed within the 25-Å oxide, which results in a much higher N concentration toward the interface at the substrate. These additional observations might be linked to the explanation of the improved oxide thickness uniformity [5,6], the prevention of B penetration, and the improved nMOSFET noise level. Results on 0.2-m nMOSFET's and preliminary XPS data have been presented separately [7].…”

Section: Discussionmentioning

confidence: 96%

“…However, because B penetration also depends strongly on the oxide thickness, incorporating N in the NO or N O ambients might become insufficient when the oxide is thinner than 40Å [4]. Recently, our experiment has indicated that oxides grown on N-implanted Si substrates could effectively prevent boron penetration [5]. We have also reported a study on the growth rates, interface quality, and uniformities of such oxides [6].…”

Section: Introductionmentioning

confidence: 82%

“…A sacrificial oxide layer of 200Å thickness was used for the high-energy tub implants, channel-stop implants, and threshold voltage adjustment implant. In addition, N was also implanted at 25 keV with doses varying from to cm The implant peak of N was 350Å into the Si substrate beneath the sacrificial oxide, i.e., the total implant range was 550Å The sacrificial oxide was then etched away in HF solutions, and 25-40Å gate oxides were grown at 800 C. The oxide thickness depended on both the growth time and the N dose [5], [6]. For example, the oxide thickness was 34Å (52Å) from 10-min (25-min) oxidation without N implant or when the N dose was cm However, with cm N dose, 10-min (25-min) oxidation grew only 25Å (40Å) oxide.…”

Section: Device Fabricationmentioning

confidence: 99%

See 1 more Smart Citation

Preventing boron penetration through 25-/spl Aring/ gate oxides with nitrogen implant in the Si substrates

Liu¹,

Ma²,

Luftman³

et al. 1997

Self Cite

For gate oxides thinner than 40Å, conventional schemes of incorporating N in the oxides might become insufficient in stopping B penetration. By implanting N into the Si substrates with a sacrificial oxide layer, we have grown 25Å gate oxide and prevented B penetration in the presence of F after 90 min of 850 C and 10 s of 1050 C anneals. SIMS analyses surprisingly reveal a N peak formed within the thin oxide layer, while no N is left in the Si substrate beyond the oxide layer. In addition, no B is seen in the substrate, either. As a consequence, threshold voltage of pMOSFET's is shifted to a more negative value which agrees with calculations assuming no B penetration. Meanwhile, threshold voltage of nMOSFET's is not affected by the N implant, which confirms that B penetration is the only explanation for the pMOSFET data. Prevention of B peneitration also improves the short-channel effects for 0.25-m pMOSFET's, while no difference is seen in nMOSFET's with and without N implant.

“…Regardless of the approach, the fabricated thin gate oxides have always been susceptible to boron penetration, which deteriorates the p-channel transistor's performance. It is known that nitrogen incorporation in the gate oxide suppresses boron penetration [4], [5] and that the location of nitrogen in the film impacts the boron penetration and interface properties of the gate oxide [5]- [8].…”

Section: Introductionmentioning

confidence: 99%

A study of nitrogen peak location in gate oxides grown on nitrogen implanted substrates and its impact on boron penetration

Mirabedini¹,

Kamath²,

Yeh³

2003

This work investigates properties of gate oxides grown on nitrogen-implanted substrates. It was demonstrated that the location of nitrogen peak in the gate oxide, once fixed at the beginning of the oxidation step, does not change with continued oxidation. Using this property, nitrogen peak was engineered near the gate oxide interface with substrate and was shown to suppress boron penetration more effectively without any significant degradation of the channel mobility in comparison to the case where the nitrogen peak is located within the bulk of the gate oxide.