A Hydrogen Plasma Treatment for Soft and Selective Silicon Nitride Etching

Abstract

In this paper, the development of a soft and selective method to increase the etching rate and control accurately the etched thickness of Si3N4 material is reported. This technique combines the low damage characteristics of wet etching with the anisotropy of plasma etching which is compatible with the requirements of many surface sensitive electronic devices such as MOS transistors. This consists on a local modification of the Si3N4 layer using hydrogen‐based plasma followed by wet chemical etching in buffered oxide etch solution. The plasma conditions are optimized and a relatively high etch rate is demonstrated. FTIR analyses show clear evidence that the formation of N–H and Si–H species in the hydrogenated Si3N4 layer contributes effectively to the increase of the etching rate. Finally, a chemical etching model is proposed to explain the higher etch rate of hydrogenated Si3N4.

In Situ Monitoring of Surface Reactions during Atomic Layer Etching of Silicon Nitride Using Hydrogen Plasma and Fluorine Radicals

“…The less intense peak at 1530 cm –1 is ascribed to −NH 2 groups. These results are in agreement with data reported by Bouchilaoun, who observed increases in the intensities of peaks related to Si–H and N–H bonds using ex situ transmittance FTIR. Our results confirm that the concentration of N–H bonds initially increased and then plateaued at ∼15 s, while the Si–H bond concentration also increased over time but stabilized after 60 s. Additionally, as the hydrogen exposure time was increased, the bands related to −NH x groups and Si–H bonds shifted toward lower wavenumbers.…”

“…This indicates that the Si–N bond can be substituted to the N–H bond by hydrogen ions. Thus, chemical changes such as the production of N–H and Si–H bonds can increase the hydrogen content in SiN films subjected to a hydrogen plasma …”

“…Thus, chemical changes such as the production of N−H and Si−H bonds can increase the hydrogen content in SiN films subjected to a hydrogen plasma. 32 3.3. In Situ Analyses of Chemical Bonds during SiN Modification.…”

Effects of hydrogen content in films on the etching of LPCVD and PECVD SiN films using CF4/H2 plasma at different substrate temperatures

“…[ 22 ] Hydrogen ion was found to exhibit a higher reactivity with nitrogen than Si to form N–H bonds or outfluxes in the SiN films. [ 18,21,48 ] The hydrogen and its surface reaction caused the ER decrease at a lower temperature for the PE‐SiN films because of the formation of N–H x layer (around 400 eV) on the surface of the samples, as confirmed by Figure 9a,b, the N 1s XPS spectra with a TOA of 15° (more surface sensitive) for T s = 20°C and –20°C. On the contrary, for the LP‐SiN films, we learned that the T s only had a minor effect on ER because the films exhibited the almost identical surface structure regardless of T s , as shown in Figure 9c,d, the N 1s spectra with a TOA of 20°.…”

“…The influences of hydrogen content in the SiN films on their wet etching behaviors have been investigated. [ 18,19 ] In dry process etching, the comparative studies on the etching behaviors of the PE‐ and LP‐SiN have been investigated by CF 4 /H 2 and CF 4 /O 2 plasmas. [ 12,20 ] It has been shown that the etch behavior of the two kinds of SiN was very similar by using CF 4 /H 2 plasma with different hydrogen additions.…”