In-line Raman spectroscopy for gate-all-around nanosheet device manufacturing

Daniel Schmidt,Jacob Ofek,Daniel Fishman,Noga Meir,Lior Neeman,Juntao Li,Nicolas Loubet,Yonatan Oren,Aron Cepler,Curtis Durfee

doi:10.1117/1.jmm.21.2.021203

Abstract

In-line Raman spectroscopy for compositional and strain metrology throughout front-end-of-line (FEOL) manufacturing of next-generation gate-all-around nanosheet field-effect transistors is presented. Thin and alternating layers of fully strained pseudomorphic Si(1 − x)Gex and Si were grown epitaxially on a Si substrate and subsequently patterned. Intentional strain variations were introduced by changing the Ge content (x = 0.25, 0.35, 0.50). Polarization-dependent in-line Raman spectroscopy was employed to characterize and quantify the strain evolution of Si and Si(1 − x)Gex nanosheets throughout FEOL processing by focusing on the analysis of Si-Si and Si-Ge optical phonon modes. To evaluate the accuracy of the Raman metrology results, strain reference data were acquired by non-destructive high-resolution x-ray diffraction and from destructive lattice deformation maps using precession electron diffraction. It was found that the germanium-alloy composition as well as Si and Si(1 − x)Gex strain obtained by Raman spectroscopy are in very good agreement with reference metrology and follow trends of previously published simulations.

Highlights

Nanosheet gate-all-around (GAA) field effect-transistors (FETs) will be the next-generation device architecture replacing finFET technology either year or in 2023.1 The new transistor type is an evolutionary step from finFETs with better performance due to superior electrostatics and short channel control, for example.[2]
A nanosheet GAAFET may be viewed, in a simplistic manner, as a finFET rotated on its side, where the fin is a horizontal nanosheet with a gate wrapped around the entire perimeter
The maps confirm that all samples are fully strained as evidenced by the fact that the diffraction peaks from the substrate and the Sið1−xÞGex layers line up in the horizontal direction

Summary

Introduction

Nanosheet gate-all-around (GAA) field effect-transistors (FETs) will be the next-generation device architecture replacing finFET technology either year or in 2023.1 The new transistor type is an evolutionary step from finFETs with better performance due to superior electrostatics and short channel control, for example.[2]. A perfect crystal quality is critical to achieve defect free, biaxially strained Sið1−xÞGex, and strain-free Si single crystalline layers This multilayer stack is patterned in both in-plane orientations to define channel length and width. Schmidt et al.: In-line Raman spectroscopy for gate-all-around nanosheet device manufacturing materials create many unconstrained free surfaces throughout the patterning process, leading to natural relaxation. Overcoming these challenges requires either complex and costly manufacturing schemes or innovative strain engineering approaches.[3,4]. No matter which integration scheme is pursued, the complex manufacturing process, related to the channels and their immediate environment, requires tight specification limits and additional, more advanced, and novel in-line metrology capabilities compared to previous transistor architectures. The determined strain is compared to reference metrology and discussed with respect to recently published simulation results.[5,6]

Experimental Details

Raman Spectroscopy

Comparison to Reference Metrology

Raman Strain Monitoring

Strain Tracking Through FEOL Patterning

Conclusions and Outlook