Trace Hurd

Diffusion studies of copper on ruthenium thin film a plateable copper diffusion barrier

Diffusion studies were carried out on physical vapor deposited Cu/Ru(∼20 nm)/Si samples using secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM). Back side SIMS depth profiling revealed well-defined interfaces and showed that Cu interdiffusion was impeded by Ru thin film up to 450°C vacuum annealing. TEM showed a 20-22 nm Ru barrier layer with a columnar microstructure oriented vertically with respect to Si substrate. TEM results corroborate with SIMS data to indicate stability of the Ru film barrier for annealing temperatures up to 450°C. Direct Cu electroplating on ultrathin Ru barrier layers (<20 nm) was investigated in sulfuric acid. The electroplated Cu film is shiny, smooth, and without agglomeration under scanning electron microscopy. Excellent adhesion between interfacial layers was confirmed by the scribe-peel test. The interfacial characterization results indicate that Ru thin film is a promising candidate as a directly plateable Cu diffusion barrier.

Impact of Fe and Cu contamination on the minority carrier lifetime of silicon substrates

The effects of trace amounts of Fe and Cu in p- and n-type silicon were investigated with microwave photoconductance decay and surface photovoltage. The wafers received controlled amounts of surface contamination of Fe and Cu that are relevant for ultralarge scale integrated technologies. The substrate doping type has a strong impact on the effect of the metallic impurities. Fe, as expected, strongly degrades the minority carrier li etime of p-type substrates. On the other hand, the impact of Fe on n-type silicon is at least one order of magnitude lower than on p-type. In contrast, Cu is highly detrimental to n-type material, but has no significant impact on the minority carrier properties of p-type silicon for the contamination levels studied.

H2O2 Decomposition and Its Impact on Silicon Surface Roughening and Gate Oxide Integrity.

In this study the impact of temperature and metal contamination on the stability of hydrogen peroxide in the two most common wet chemical cleaning mixtures for wafer process operations has been investigated. The stability of the caustic mixture ( NH4OH/H2O2/H2O) was found to be very sensitive to certain metallic contaminations in the sub-ppb range, while the stability of the acid mixture ( HCl/H2O2/H2O) is mainly influenced by non metallic, anionic components of the solution itself. We observed also a strong oscillating behaviour of the rate of the oxygen gas evolution caused by the decomposition of H2O2. Furthermore it was found, that the oxygen gas bubbles, formed by the decomposition of hydrogen peroxide cause a certain kind of micro-roughness on the silicon surface through a micro masking mechanism. In a series of experiments we could prove that this kind of surface roughness has a significant impact on the integrity of thin gate oxides.

Interfacial Diffusion Studies of Cu ∕ ( 5 nm Ru ) ∕ Si Structures Physical Vapor Deposited vs Electrochemically Deposited Cu

In contrast to physical vapor deposition (PVD), the electrochemical deposition (ECD) process is dependent upon substrate resistivity. ECD of Cu on ultrathin Ru diffusion barriers remains a technological challenge due to large resistivity increase over a wide plating area. Results are presented from the comparative investigation of interfacial stability and Cu diffusion processes in PVD and ECD Cu/(5 nm Ru)/Si structures. Cu can be conformally electroplated onto (5 nm Ru)/Si surfaces (ca. 1 cm 2 ) with over 94% efficiency. However, lesser uniformity and conformality of ECD Cu are observed on (5 nm Ru)/Si samples with larger surface areas. The transmission electron microscopy (TEM) reveals that ECD Cu film is less densely packed (ca. 70 nm) than PVD Cu. HRTEM studies in conjunction with surface analyses using optical microscopy and four-point probe resistivity measurements show that 5 nm Ru can successfully impede Cu diffusion up to 300°C for 10 min, but fails at 450°C. Interfacial profiling data obtained from back side secondary-ion mass spectrometry (SIMS) analysis agree with TEM results. X-ray photoelectron spectroscopy (XPS) investigation on nitric acid-etched PVD and ECD Cu/(5 and 20 nm Ru)/Si samples shows the presence of residual ECD Cu after annealing, suggesting that ECD Cu diffuses further into Ru than PVD Cu.

Reducing Time Dependent Line to Line Leakage Following Post CMP Clean

A systematic approach was taken to identify methods to prevent post CMP corrosion of copper in 22nm interconnect structures. Line to line current leakage measurements (at various times post CMP) were used as a means to quantify the extent and time-dependence of copper corrosion. Interruption of the corrosion mechanism by the use of passivating agents in post-CMP clean chemistries is explored. A broad-based screening was conducted to identify aqueous formulations of passivating agents for protection of copper which do not have deleterious effects on line resistance and overall defectivity. A formulation was identified which was effective in preventing corrosion when applied during post CMP brush clean.

Outplating of metallic contaminants on silicon wafers from diluted acid solutions

The outplating behaviour of Fe and Cu was investigated for diluted solutions of HCl and HNO 3 . The deposition of the metallic contaminants was found to be strongly dependent on the type of surface that is exposed to the contaminated solution. Cu deposits heavily on bare silicon surfaces, whereas only low levels of Fe deposition are observed. On the other hand, on thermal oxide surfaces, the levels of deposited Fe are consistently higher than the Cu ones. The acid used appears to have no major impact on the deposition process. The pH of the solutions has a major effect on the Cu deposition and a minor effect on the Fe case.