Suppression of Nitridation-Induced Interface Traps and Hole Mobility Degradation by Nitrogen Plasma Nitridation

Abstract

The impact of nitrogen plasma nitridation on the interfacial quality of ultrathin oxides ͑1.8 and 2.6 nm͒ have been investigated and compared with NO nitridation. It is found that plasma-nitrided oxides are more immune to nitridation-induced degradation of channel hole mobility, and have lower intrinsic interface-trap density as compared to NO-nitrided oxides. In addition, plasmanitrided oxides can further suppress hole mobility degradation induced by boron penetration. The superior performance of nitrogen plasma nitridation is attributed to its capability of incorporating a high level of nitrogen at the top oxide surface, while keeping the Si-SiO 2 interface intact.Introducing nitrogen into thin silicon dioxide films using NO nitridation has been widely employed in complementary metaloxide-semiconductor ͑CMOS͒ technology to suppress impurity penetration and enhance resistance to hot-carrier aging. 1-3 However, it has been widely recognized that nitrided oxides generally suffer significant degradation of channel hole mobility across all electric fields as compared to pure SiO 2 . 1,4-7 On the other hand, nitrogen plasma nitridation has recently attracted considerable interest over NO nitridation for sub-0.13 m CMOS technology because of its superior efficiency in tailoring a higher amount of nitrogen near the polysilicon/SiO 2 interface. This nitrogen-rich layer not only increases the dielectric constant of an oxynitride which can be used for reducing tunneling leakage current, but also acts as an excellent barrier to suppress impurity penetration. [8][9][10][11] However, the impact of plasma nitridation on channel hole mobility has not been assessed so far. In this paper, we have studied the effects of the plasma nitridation process on the channel hole mobility and interface-trap density of ultrathin gate oxides. We found that plasma-nitrided oxides exhibit improved immunity to the degradation of channel hole mobility induced by nitridation as compared to NO-nitrided oxides, also retard the boron-induced mobility degradation. Additionally, we show a close association between the degradation of channel hole mobility and the interface traps induced by nitridation and boron penetration. ExperimentalDevices were fabricated using 0.13 m dual-gate CMOS technology. After shallow trench isolation and twin-well formation, base oxides with optical thickness of 1.8 and 2.6 nm were grown by rapid thermal oxidation. The plasma-nitrided oxides were prepared by exposing the base oxides to an ex situ high-density decoupled nitrogen plasma source at room temperature. These oxides are referred to as decoupled plasma-nitrided oxide ͑DPNO͒ hereafter for brevity. On the other hand, rapid thermal nitrided oxides ͑RTNO͒ were formed by subjecting the base oxides to in situ rapid thermal nitridation in a NO ambient. Upon nitridation, both DPNO and RTNO received identical postnitridation annealing. Subsequently, 160 nm undoped polysilicon was deposited and patterned. p ϩ -Poly gate and p ϩ -source/drain were formed simultaneously by B im...

Charge transition levels of nitrogen dangling bonds atSi/SiO2interfaces: A first-principles study

“…7 Furthermore, nitrogen also improves the dielectric properties of the oxide layer. However, the incorporation of nitrogen at the interface is known to increase the densities of interface traps, 8 causing performance degradations and reliability problems. [9][10][11] In particular, N has been seen to amplify the negative bias temperature instability ͑NBTI͒, a critical reliability issue in integrated circuits that continues to be a problem in devices with highgate dielectrics.…”

Experimental and theoretical studies of negative bias temperature instability in ultra-thin gate dielectrics

“…The concept of a surface field-effect transistor, predecessor of the modern MOSFET, was first proposed as early as the 1930s [1]. It was until the 60's that the silicon technology became mature enough to realize MOS gate stacks based on the thermal Si02-Si framework.…”

“…1: Comparison of NBTI-induced interface trap and positive oxide charge density for nitrided oxide with and without PMA.The as-grown interface trap density D it as a function of N im is shown in Fig. 4.2.One can clearly see that the as-grown D it values before PMA are in the order of 10 11 cm" 2 eV"1 . Being in good agreement with as-grown D it values reported in[118].…”

“…This result is disturbing because oxynitride is added with the aim of increasing the thermal186 Based on the results, we propose two methods to suppress NBTI in high-k gate dielectric and at the same time maintaining the improvement in terms of thermal stability and lowering the fixed-charge induced mobility degradation. First method is to employ laminated high-k method[1] with H1D2 being deposited prior to AI2O3 deposition since HfCh has higher NBTI immunity than that of AI2O3. Second method is employ Hf-rich interfacial layer to increase the coordination number of O at the interface[222] to minimize the NBTI reaction sites.…”

“…Therefore, relaxation of the strained-layer is a requisite issue to improve reliability and realize the aggressive scaling.Nitrogen-worsen NBTI effect cannot be simply explained by a single or double factor. As demonstrated, nitrogen at Si/SiO x N y has multiple negative effects:(1) it creates more NBTI precursors (that is more N and Si-H bond); (2) it lowers the NBTI reaction energy; (3) it slightly weaken the Si-H bond strength and finally, (4) it increases the susceptibility against strain-enhanced NBTI effect. The lowering of NBTI reaction energy can be understood from the fact the nitrogen is less electronegativity than oxygen and larger negative charge at nitrogen provides a more effective Coulombic attraction center for trapping of positive charge like H + .…”