Effect of ion implantation energy for the synthesis of Ge nanocrystals in SiN films with HfO2/SiO2 stack tunnel dielectrics for memory application

Bhabani Shankar Sahu,Dominique Muller,Florence Gloux,Marzia Carrada,Caroline Bonafos,Jesse Groenen,Sandrine Lhostis,Abdelilah Slaoui

doi:10.1186/1556-276x-6-177

Abstract

Ge nanocrystals (Ge-NCs) embedded in SiN dielectrics with HfO2/SiO2 stack tunnel dielectrics were synthesized by utilizing low-energy (≤5 keV) ion implantation method followed by conventional thermal annealing at 800°C, the key variable being Ge+ ion implantation energy. Two different energies (3 and 5 keV) have been chosen for the evolution of Ge-NCs, which have been found to possess significant changes in structural and chemical properties of the Ge+-implanted dielectric films, and well reflected in the charge storage properties of the Al/SiN/Ge-NC + SiN/HfO2/SiO2/Si metal-insulator-semiconductor (MIS) memory structures. No Ge-NC was detected with a lower implantation energy of 3 keV at a dose of 1.5 × 1016 cm-2, whereas a well-defined 2D-array of nearly spherical and well-separated Ge-NCs within the SiN matrix was observed for the higher-energy-implanted (5 keV) sample for the same implanted dose. The MIS memory structures implanted with 5 keV exhibits better charge storage and retention characteristics compared to the low-energy-implanted sample, indicating that the charge storage is predominantly in Ge-NCs in the memory capacitor. A significant memory window of 3.95 V has been observed under the low operating voltage of ± 6 V with good retention properties, indicating the feasibility of these stack structures for low operating voltage, non-volatile memory devices.

Highlights

During the last decade, non-volatile memory (NVM) structures consisting of semiconductor nanocrystals (NCs), in particular, Si and Ge nanocrystals (Ge-NCs), embedded in a dielectric matrix have drawn considerable attraction because of their high endurance, low operating voltage, reduced lateral discharge path, low power consumption, larger retention, and faster operation [1,2,3,4,5]
There is no significant increase of the HfO2 thickness while the interfacial SiO2 (IL) layer increases from 1.2 to 1.9 nm as a result of implantation and annealing
In summary, we have conducted a comparative investigation of Ge+ ion implantation energy-dependent memory effects in SiN dielectric layers with HfO2/SiO2 asymmetric well-isolated Ge-NCs with an average size of 3.5 nm were self-assembled within the top Si3N4 layer at a distance of 5.6 nm from SiN/HfO2 interface

Summary

Introduction

Non-volatile memory (NVM) structures consisting of semiconductor nanocrystals (NCs), in particular, Si and Ge-NCs, embedded in a dielectric matrix have drawn considerable attraction because of their high endurance, low operating voltage, reduced lateral discharge path, low power consumption, larger retention, and faster operation [1,2,3,4,5]. Lu [16] have implemented stacked HfO2/SiO2 tunnel layers and successfully fabricated uniform Ge-NCS with improved charge storage effect using electronbeam evaporation method. The top SiN layer with a thickness of about 12 nm was deposited with electron cyclotron resonance plasmaenhanced chemical vapor deposition method under a flow of SiH4 and N2 (instead of NH3) to minimize the H content in the films Ion implantation in these stack layers were carried out with 74Ge+ ions using GeH4 gas source for the extraction of Ge. The Ge+ ion implantation was carried out at two different energies of 3 and 5 keV, while the dose was kept constant at 1.5 × 1016 cm-2. Measurements were carried out using HP4192A impdance analyzer through a LABVIEW interface

Results and discussion

Conclusions

14. Likharev KK