Challenges in spacer process development for leading‐edge high‐k metal gate technology

Abstract

Transistor performance is a key enabler for state‐of‐the‐art electronic devices. Besides fast switching performance, low power consumption is a critical parameter for mobile products. The implementation of HfO2 as a gate dielectric with a high permittivity reduces leakage current and power consumption drastically. Metal gates and work function materials are required to adjust Fermi levels and are essential for device performance. In addition to these key elements of high‐k metal gate (HKMG) technology, encapsulation liners and spacers are found to have a significant impact. We show that the performance of HKMG transistors has a strong dependency on the film quality and growth conditions of the SiN spacers. A good conformality and excellent step coverage at low deposition temperature is achieved with an atomic layer deposition (ALD) process using dichlorosilane and ionized radicals of ammonia. This ALD process is superior to standard LPCVD and PECVD processes with regards to thickness control, within‐wafer‐uniformity and matching of the thickness values between dense and isolated transistors. ALD SiN is applied as a spacer to define the implant profiles. The impact of the ALD SiN spacers on transistor universal curve, miller capacitance and Vt is demonstrated. Further application is a hard mask for selective epitaxy of SiGe. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Review—Silicon Nitride and Silicon Nitride-Rich Thin Film Technologies: Trends in Deposition Techniques and Related Applications

“…These geometries include highly complex topographical structures, such as extremely high aspect ratio or exceedingly narrow channels, vias, and trenches in IC applications. 92,93 For nitrogen, the majority of the work described the use of NH 3 or N 2 . One report suggested the additional use of hydrazine (N 2 H 4 ), 101 which is quite undesirable given its elevated toxicity and high instability, while another proposed the utilization of t-butylhydrazine (C 4 H 12 N 2 ).…”

Correlation of film density and wet etch rate in hydrofluoric acid of plasma enhanced atomic layer deposited silicon nitride

“…The need for SiN x as a hydrofluoric (HF) etch resistant, insulating spacer for modern transistor processes in particular introduces a need for films which are pinhole free at very thin dimensions and highly conformal. [1][2][3] Additionally, the film should be a low k material to minimize frequency losses, which is again is met by SiN x . Further, the processing requirements of modern logic at the smallest technology nodes additionally have a stringent thermal budget such that depositions should be performed at as low of a temperature as possible and at least below 450 • C. More than a decade ago, early work in SiN x thermal ALD and PEALD were shown with various chlorosilanes and nitridation reactants such as ammonia or hydrazine.…”

Atomic Layer Deposition of Silicon Nitride Thin Films: A Review of Recent Progress, Challenges, and Outlooks

“…Gate spacers with a low wet etch rate (i.e., good etch resistance) are required to keep the encapsulated HKMG stacks still intact after the subsequent cleaning and etching steps [43]. …”

“…In addition, a low process temperature after implantation is beneficial in preventing the diffusion of dopant atoms [2,43]. …”