Full Silicidation of Silicon Gate Electrodes Using Nickel-Terbium Alloy for MOSFET Applications

Abstract

The full silicidation of silicon gate electrodes using Ni-Tb alloy was investigated for metal oxide semiconductor field effect transistor ͑MOSFET͒ applications. Results showed that a dual-layer silicide gate consisting of a top NiTb silicide layer and a bottom NiSi layer was formed. Full silicidation using Ni 0.8 Tb 0.2 resulted in a gate work function of 4.41 eV. This is lower than a work function of 4.68 eV obtained from full Ni silicidation. The work function lowering was linked to structural changes in the underlying NiSi layer. No physical or electrical degradation was observed after forming gas annealing at 420°C for 30 min. NiTb-silicided gate electrodes have work functions suitable for application in advanced transistor structures.Due to aggressive scaling of complementary metal-oxidesemiconductor ͑CMOS͒ devices, metal gates electrodes are required for replacing conventional poly-Si gates to overcome polydepletion and dopant penetration problems. 1 However, in selecting suitable metal gate materials, their work functions must be considered to control the transistor's threshold voltage ͑V TH ͒. 2,3 To obtain low and symmetrical V TH for optimal device performance, the gate work function must be close to the conduction and valence bands for nand p-channel bulk CMOS transistors, respectively, or about 0.2 eV above and below the intrinsic Si Fermi level for advanced transistor structures ͑surround-gate or double-gate transistors͒. 2 In recent years, fully-silicided ͑FUSI͒ NiSi has become an attractive metal electrode candidate because of its compatibility with the current CMOS process and its tunable work function. 4-8 It was demonstrated that a wide work function range ͑4.29-4.99 eV͒ for NiSi can be obtained by the total silicidation of doped poly-Si gates using various dopants ͑e.g., As, P, and B͒. 8 Alternatively, the formation of a FUSI ternary silicide with Ni and a second metal is another attractive work function tuning method. For example, Co x Ni 1−x Si 2 was reported by Sim and co-workers to show a linear work function tunability from the intrinsic Si Fermi level to ϳ0.2 eV above it. 9 In addition, it was also proven that by incorporating a large concentration of Pt ͑ϳ33%͒ into a ternary silicide with Ni, a suitable p-MOS metal gate work function can be obtained. 10 Still, the prospect of forming ternary silicides using a Ni-rare earth metal alloy for lower work function modulation has not been explored. Terbium ͑Tb͒, which is one of the rare-earth ͑or lanthanide͒ group of elements, has been reported to possess a low work function ͑ϳ3.0 eV͒. 11 In this study we investigated the effect of alloying Ni with Tb for FUSI metal gate applications. Experimentalp-Type Si͑100͒ substrates were used for FUSI MOS capacitor fabrication. After standard pregate cleaning, a SiO 2 gate dielectric ͑10 nm͒ was thermally grown and etched to obtain different thicknesses for work function extraction. Undoped amorphous Si ͑60 nm͒ was deposited by low-pressure chemical vapor deposition. The Si gate was then patterned and Ni ...

Pre-doping effects on Ni fully silicided metal gate on SiO2 dielectric

“…3 shows Raman spectrum of a Ni silicide film after silicidation and SE. The prominent peaks at 215 and 197 cm À1 agree well with the characteristic Raman peaks of NiSi, indicating the formation of crystalline NiSi [9]. Three weak peaks at about 164, 253, and 309 cm À1 may be due to Ni 3 Si 2 , and the second order transverse acoustic mode of Si and the by-product modes [13].…”

“…Ni-based FUSI metal gate for dual-gate CMOS applications has been investigated extensively due to its excellent compatibility with the conventional CMOS field effect transistor fabrication process [4][5][6][7][8][9][10][11]. The NiSi electrode has a mid-gap work function (WF) [6], but threshold voltage (V th ) design requires band edge WFs of gate electrodes (close to conduction band for n-channel metal-oxide-semiconductor (MOS), and close to valence band for p-channel MOS) [6].…”

“…The NiSi electrode has a mid-gap work function (WF) [6], but threshold voltage (V th ) design requires band edge WFs of gate electrodes (close to conduction band for n-channel metal-oxide-semiconductor (MOS), and close to valence band for p-channel MOS) [6]. Several methods to tune WF were demonstrated such as phase control (NiSi for NMOS, Ni-rich silicide for PMOS), dopant implantation (B, P, As, Sb, Al), and alloying, which allow to reach adequate WF and V th values [4][5][6][7][8][9][10]. This paper investigates Ni FUSI gate process on SiO 2 dielectric, and the predoping effects on the WF of Ni FUSI gate and FUSI gated SiO 2 / Si(1 0 0) interface traps before/after forming gas anneal (FGA).…”

Impact of interfacial dipole on effective work function of nickel fully silicided gate electrodes formed on rare-earth-based dielectric interlayers

“…[3][4][5][6][7][8][9] Recent significant progress was made through interface engineering using an ultrathin rare-earth ͑RE͒ incorporated dielectric layer beneath the NiSi gate, achieving ⌽ m values close to the Si conduction band edge. RE-O-Si bonding in these ultrathin ͑ϳ1 nm͒ interlayers induces highly polarized RE-O bonds at the gate/dielectric interface.…”

Demonstration of Low $V_{t}$ Ni-FUSI N-MOSFETs With SiON Dielectrics by Using a $\hbox{Dy}_{2}\hbox{O}_{3}$ Cap Layer

“…To meet the work-function (WF) requirements for Ni-FUSI electrode, numerous approaches have been studied, such as by the impurity doping technologies (P, As, B, Al, etc.) [4], [5], by controlling the Ni silicide phase formation (i.e., Ni-rich silicide versus Ni monosilicide) [6], or by using Ni-based alloys (such as Ni-Yb, Ni-Tb, and Ni-Pt) for FUSI formation [1], [7]. Despite of these efforts, low V t n-MOSFETs using Ni-FUSI electrode is still not readily viable for high-performance applications.…”