Highly Sensitive Monitoring of Ru Etching Using Optical Emission

Abstract

During Ru etch with oxygen-based plasma, strong emission lines have been observed in the region of 340-390 nm with the most prominent peak at 373 nm. These are attributed to the emission of neutral Ru. We have shown that the emission can be used for end-point detection for Ru patterning by plasma etch as well as for highly sensitive in situ monitoring of the etch chamber cleaning after Ru processing.Continuous scaling of metal-oxide-semiconductor field effect transistors ͑MOSFETs͒ brings challenges that cannot be resolved using conventional materials. A straightforward example is the polysilicon gate that starts showing a number of limitations as the gate size goes below 100 nm. The main limitations are high gate resistance and gate depletion. Gate depletion, which arises due to insufficient dopant activation close to the poly-Si/gate dielectric interface, lowers the surface-effective field that degrades device performance. Both problems can be overcome by using metals as the gate electrode. Metals have low resistivity and high electron density that is not subjected to depletion.Ruthenium is one of the promising candidates for the metal gate electrode. It has the appropriate work function of p-MOS devices and is thermally stable in contact with dielectrics like SiO 2 or ZrO 2 . 1 Since Ru forms volatile ruthenium tetraoxide RuO 4 ͑boiling temperature Ϸ104°C͒, it is reported to be relatively easily patterned by ozone gas 2 or oxygen plasma. 3 It was found that addition of 10% Cl 2 increases the etch rate. This might be due to the fact that chlorine can increase the concentration of oxygen radicals and ions. 4 No etch products other than RuO 4 and some RuO 3 ͑such as RuF 5 ͒ were observed during etching of RuO 2 with O 2 /CF 4 plasma. Exposure of RuO 2 to Cl 2 plasma left some Cl on the surface ͑as found by X-ray photoelectron spectroscopy, XPS͒ but no Ru chloride. 4 Attempts to etch RuO 2 with SF 6 /Ar, BCl 3 /Cl 2 , SF 6 /BCl 3 /Ar were reported to be unsuccessful; no ruthenium-containing species were detected in the downstream emission by Fourier transform ion cyclotron resonance ͑FTICR͒ spectroscopy. 5 It can be concluded that no plasma other than an O 2 -containing is known to etch Ru ͑or RuO 2 ͒. The optical emission was studied during the etching of ruthenium oxide by oxygen-containing plasma. It was shown that the emission can be used for end-point detection, and it was assumed that a possible source of the emission is Ru atoms. 5 Knowledge of the emission spectra is necessary to develop etch monitoring during patterning of Ru metal gates. On the other hand, the optical emission spectroscopy of electronically excited radicals is extremely sensitive and can be used for quantitative monitoring of small amounts of Ru contaminating the etch chamber.In this paper we present experimental data on optical emission spectra, characteristic for the Ru etch process and demonstrate their utility for the end-point detection during Ru patterning and for Ru contamination monitoring in the etch chamber after processing of R...

Ru Films from Bis(ethylcyclopentadienyl)ruthenium Using Ozone as a Reactant by Atomic Layer Deposition for Capacitor Electrodes

“…It is likely that at higher concentrations, the flux of reactive oxygen species is of such magnitude that the etching of the Ru films by forming a volatile RuO 4 is dominating over the deposition. 43 Considering the effect of the ozone concentration on the phase of the deposited films, an ozone concentration of 50 g/m 3 was chosen for depositing the Ru films. Figure 1a shows the thickness per cycle and the resistivity of the ALD-Ru films deposited on ZrO 2 (5.5 nm)/SiO 2 (100 nm)/p-type Si substrate using ozone as a function of the pulse time for ozone at a deposition temperature of 275 • C. The pulse time for Ru(EtCp) 2 was fixed at 5 s. The pulse time for ozone was varied from 0.5 to 5 s at a fixed ozone concentration of 50 g/m 3 .…”

“…It is likely that at higher concentrations, the flux of reactive oxygen species is of such magnitude that the etching of the Ru films by forming a volatile RuO 4 is dominating over the deposition. 43 Considering the effect of the ozone concentration on the phase of the deposited films, an ozone concentration of 50 g/m 3 was chosen for depositing the Ru films.…”

Atomic layer deposition of Ru from CpRu(CO)2Et using O2 gas and O2 plasma

“…Therefore, a plasma power of 100 W was chosen. It is likely that at higher powers, the flux of reactive oxygen species is of such magnitude that etching of the Ru film 37 is dominating over deposition. This was also corroborated by a brief experiment in which Ru films were exposed to O 2 plasma and after few ͑Ͻ10 s͒ seconds, 0.3-0.5 nm had been etched off the films.…”