Helen L. Maynard

Enhancing tensile stress and source/drain activation with Si:C with innovations in ion implant and millisecond laser spike annealing

Strain engineering has become a workhorse in increasing charge carrier mobility to boost performance for sub-45nm CMOS logic technologies. While pFET transistors with embedded Si1−xGex layers in the S/D region have been widely employed to induce compressive strain in the silicon channel, nFET transistors have mostly depended on either tensile liners or stress memorization techniques (SMT) to introduce tensile strain. Recently, there have been reports on the use of Si:C in the nFET S/D enhancing transistor performance. In this paper we discuss results from novel ion implantation schemes employed to maximize carbon incorporation and to achieve defect free, strained Si:C layers. In addition, high activation of the dopant is maintained even in the presence of relatively high carbon incorporation. Several anneal techniques including SPE anneal, spike RTP, and laser spike anneals have been used to optimize carbon incorporation, strain and activation. Results from these different anneal techniques will be compared and discussed.

FinFET multi-Vt tuning with metal gate work function modulation by plasma doping

Multiple Vt tuning is required for SOC FinFET devices at and beyond the 22nm technology node. Traditional Vt tuning method used for planar devices is limited in terms of tuning range and sensitivity. Alternative approaches are needed to enable muti-Vt tuning needs. Previously we reported work function modulation for Vt tuning on both n-metal gate (TiAl) and p-metal gate (TiN) with beamline ion implantation in replacement metal gate and high-k last process flow. The report showed 200mV effective work function (eWF) modulation by ion implantation with fine control and no Effective Oxide Thickness (EOT) or Gate Leakage (Jg) degradation. Ion implant approach offers simplified integration flow where resist mask can be used. In this paper we are focusing on using plasma doping (PLAD) for modulating p-metal gate (TiN) work function to achieve multiple Vt with high productivity. The effect of plasma doping on eWF, EOT and Jg was studied on planar MOS Capacitor (MOSCAP) wafers. Sheet resistance (Rs) was also measured on blanket metal film stack to study the effect of doping on metal film properties such as resistance. Top-down SIMS analysis was employed for characterizing the sidewall doping on high aspect ratio silicon trench structures.

Characteristics of SiF4 Plasma Doping (PLAD)

SiF4 PLAD has been systematically characterized and optimized. The correlations between the etching, deposition, retained F dose and profile as functions of the PLAD process variables including implant voltage, RF power, pressure, pulse duty cycle, and the diluting gases have been extensively investigated. It was found that PLAD process by using pure SiF4 is in an etching or RIE regime, but can be adjusted to minimize the etching effect. It was found that diluting SiF4 with different gases can significantly impact etching and deposition characteristics. The selectivity of etching and deposition behaviors on the different substrate materials such as poly-Si, silicon oxide, and silicon nitride have been explored. With the understanding of these behaviors, SiF4 PLAD can be optimized for multiple precision doping and material modification applications.

Exploration of PLAD aluminum implants for work function adjustment

It is well known that aluminum ion implant can shift the flatband voltage (Vfb) in hafnium-oxide high-k/metal gate PMOS 3D devices [1, 2]. The current work focuses on using a high-throughput plasma doping tool for aluminum implantation into metal-oxide-semiconductor capacitor (MOSCAP) structures as a test of work-function adjustment in PMOS devices. Work was conducted in a modified Applied Materials VSE PLAD doping tool [3,4], using a 2MHz RF ICP source varying from 500W to 1,500W of power to create an approximately 1e11 cm-3 density argon plasma. This is used both for sputtering aluminum off a biased target as well as for drive-in implant, the mechanism for which has been described previously [5]. Typical Ar+ dose varied from 1e15 to 1e17 ions/cm2, and chamber argon pressure was changed from 5mT to 15mT. Optical emission data indicated the presence of aluminum in the spectrum at 309nm and 396nm. SIMS analysis on prime silicon wafers was employed to optimize the process for implant depth and retained dose. Metal oxide semiconductor capacitor (MOSCAP) structures demonstrated initial Vfb shifts of more than 400mV on the high-k metal gate (HKMG) structures. It is believed that the Ar/Al dose implanted was in excess of that required for the targeted Vfb shift, which led to oxide degradation. Future work will focus on maintaining Vfb shift by modulating the target bias and implant conditions, while reducing the accompanying increases in equivalent oxide thickness (EOT) and gate leakage current (Jg).