TiSiN sputtered films as Copper diffusion barriers

The thermal stability of thin Ru single layer and Ru/TaN bilayers grown on bare Si by plasma enhanced atomic layer deposition (PEALD) have been studied with Cu/Ru, Cu/Ru/TaN structures as a function of annealing temperature. To investigate the characteristics as a copper diffusion barrier, a 50 nm thick Cu film was sputtered on Ru and Ru/TaN layers and each samples subjected to thermal annealing under N2 ambient with varied temperature 300, 400, and 500 degrees C, respectively. It was found that the single 5 nm thick ALD Ru layer acted as an effective Cu diffusion barrier up to 400 degrees C. On the other hand ALD Ru (5 nm)/TaN (3.2 nm) showed the improved diffusion barrier characteristics even though the annealing temperature increased up to 500 degrees C. Based on the experimental results, the failure mechanism of diffusion barrier would be related to the crystallization of amorphous Ru thin film as temperature raised which implies the crystallized Ru grain boundary served as the diffusion path of Cu atoms. The combination of ALD Ru incorporated with TaN layer would be a promising barrier structure in Cu metallization.

Stability of Cu/Ir/Si trilayer structure to moderate annealing

Ultra low dielectric constant (κ) material is needed as the inter-metal dielectrics to reduce RC delay when device dimension is scaled to sub-100nm. Porous dielectric films have been considered as good candidates for the application as inter-metal dielectrics due to their ultra low-k properties. Identifying proper dielectric copper diffusion barrier on the porous low-k films is critical for the low-k/Cu damascene fabrication process. In this study, we have evaluated the compatibility of plasma-deposited amorphous Boron Nitride film as a dielectrics copper diffusion barrier on a MSQ-based porous low-k LKD5109 film (from JSR). Both microwave plasma enhanced CVD (2.45 GHz) and radio-frequency plasma enhanced CVD (13.56 MHz) were applied for the BN deposition in order to evaluate the compatibility of the two plasma processes with the porous film. Growth parameters were optimized to minimize the boron diffusion and carbon depletion in the porous low-k films, which were found to have deleterious effects on the dielectric properties of the low-k films. FTIR and micro-Raman were employed for analyzing the changes in chemical structure of the low-k films after BN growth. Capacitance-voltage measurement was used to characterize the dielectric constants of BN film on Si and the BN-deposited porous low-k film. SIMS characterization was carried out to evaluate the performance of the BN film against copper diffusion.

Atomic layer deposition for high aspect ratio through silicon vias

Diffusion barrier property of MnSixOy layer formed by chemical vapor deposition for Cu advanced interconnect application

NiSi as a conductive diffusion barrier to silicon has been studied. We demonstrate that the NiSi films formed using the single step annealing process are as good as the two step process using XRD and Raman. Quality of NiSi films formed using e-beam Ni and electroless Ni process has been compared. Incomplete surface coverage and presence of constituents other than Ni are the main challenges with electroless Ni. We also demonstrate that Cu reduces the thermal stability of NiSi films. The detection of Cu has proven to be difficult due to temperature limitations.

Ta-Si-C film was prepared by magnetron sputtering, and the thermal stability of the plasma-treated film as a copper diffusion barrier was evaluated. The barrier properties and failure behaviors of the studied films were elucidated using a four-point probe, x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The as-deposited Ta-Si-C film had an amorphous structure, and the structure remained stable at an elevated temperature, allowing the film to be adopted as a barrier to inhibit Cu diffusion. The Cu/Ta26Si41C32/Si stacked structure had a failure temperature of 750°C/1 min when the 5-nm-thick Ta26Si41C32 film was treated by exposure to Ar/H2 plasma mixture, while the stacked film failed at 800°C/1 min when treated by exposure to Ar/N2 plasma mixture. Using the Ar/N2 plasma treatment favorably enhanced the thermal stability of the Ta26Si41C32 thin film as a barrier for Cu interconnections. When the Ta-Si-C film thickness was further reduced to 2 nm, the film retained the barrier effect at 650°C, 700°C, and 750°C for Ta34Si47C18, Ta30Si44C25, and Ta26Si41C32 compositions, respectively.

The purpose is to show that TDDB reliability of damascene structures has to be assessed as a system composed of a dielectric, copper diffusion barrier and copper. This becomes mandatory when porous low-k materials are considered, since barrier integrity is a key contributor in TDDB behavior. Solely addressing the dielectric properties is not adequate. When a not fully dense barrier is considered the apparent dielectric properties are degraded due to copper migration into the dielectric.

Alchimer develops alternative wet solutions based on electrografting (eG™) and chemical grafting (cG™) proprietary technologies. eG is based on surface chemistry formulations and processes. It is applied to conductive and semiconductive surfaces, and enables self-oriented growth of thin coatings of various materials, especially polymer and metals, initiated by in-situ chemical reactions between specific precursor molecules and the surface. Due to outstanding thermal, mechanical and electrical properties, electrografted polymer layers are an efficient insulation layer for TSV applications. In this paper, we fill focus on the copper diffusion barrier properties of this eG polymer layer and the associated Cost of Ownership (CoO) reduction for TSV metallization.

Hydrogen terminated silicon surfaces play an important role in the integrated circuit (IC) industry. Ultra-pure water is extensively used for the cleaning and surface preparation of silicon surfaces. This work studies the effects of ultra-pure water on hydrogen passivated silicon surfaces in a short time frame of 120 minutes using fourier transform infrared spectroscopy – attenuated total reflection techniques. Varying conditions of ultra-pure water are used. This includes dissolved oxygen poor media after nitrogen bubbling and equilibration under nitrogen atmosphere, as well as metal contaminated solutions. Both microscopically rough and ideal monohydride terminated surfaces are examined. Hydrogen terminated silicon is also used as the sensing electrode for a potentiometric sensor for ultra-trace amounts of metal contaminants. Previous studies show the use of this potentiometric electrode sensor in hydrofluoric acid solution. This work is able to shows sensor function in ultra-pure water media without the need for further addition of hydrofluoric acid. This is considered a boon for the sensor due to the hazardous nature of hydrofluoric acid. Thin carbon films can be formed by spin coating photoresist onto silicon substrates and pyrolyzing at 1000 degrees C under reducing conditions. This work also shows that the electroless deposition of palladium and platinum may be accomplished in hydrofluoric acid solutions to attain palladium and platinum nanoparticles on a this film carbon surface for use as an electrode. Catalysis of these substrates is studied using hydrogen evolution in acidic media, cyclic voltammetry, and catalysis of formaldehyde. X-ray diffractometry (XRD) is used to ensure that there is little strain on palladium and platinum particles. Iridium is thought to be a prime candidate for investigation as a new generation copper diffusion barrier for the IC industry. Copper electrodeposition on iridium is studied to address the potential of iridium as a copper diffusion barrier. Copper electrodeposition is studied using a current-transient technique to obtain insight into the nucleation and growth mechanism. Copper on iridum was annealed up to 600 degrees C. X-ray photoelectron spectroscopy and XRD confirm that electrodeposited copper exists in a metallic state. XRD shows that copper exists in the characteristic face-centered cubic (111) form. XRD also confirms the stability of the copper-iridium interface with no new peaks after annealing, which is indicative that no interaction occurs. Scanning electron microscopy, and Scotch ® Tape peel tests confirm the uniformity and strength of copper on iridium even after annealing to 600 degrees C.

In this work, we examine deep silicon copper interconnect related failure mechanisms due to deep silicon via etching based on BOSCH process. Though it is the best candidate for performing deep and high aspect ratio silicon etching, its cyclical nature of doing series of etch and passivation process creates very rough sidewall thus impacting the electrical performance of through-wafer copper interconnection. In the present work we have designed a dedicated test vehicle to study and evaluate the deep silicon via etch induced defects such as sidewall scallops, conformality of dielectric isolation and copper diffusion barrier over the entire depth of the via. In addition, thermo-mechanical simulation has been done to identify the potential weak sites to help us to zoom into possible failures sites.

Mixed phase materials composed of refractory metal-based pairs such as Ru/TaN and Ru/WCN, grown by plasma enhanced atomic layer deposition (PEALD), can perform as directly platable Cu diffusion barriers which can be scaled to thicknesses of ~2-3nm. While such direct plate liners employ conventional barrier materials such as TaN and WCN, direct plate liner extendibility may be enhanced by employing a barrier metal with a lower intrinsic resistivity without the presence of carbide or nitride phases that are effective at preventing the diffusion of Cu. In considering suitable materials for this application, both the ability to support copper electrodeposition as well as good intrinsic copper and oxygen diffusion barrier performance are critical characteristics. Accordingly, dopant metals such as Co are selected as materials to investigate for replacement of conventional barrier materials in direct plate barriers by combining with Ru to form RuCo mixtures.

Our laboratory is developing new chemical precursors for the growth of electropositive metal and element thin films by atomic layer deposition (ALD). We are also interested in processes that exhibit area selective growth. ALD has many current applications in copper metallization, diffusion barriers, liners, and transistor fabrication. Thermal ALD is often preferred because plasmas can afford low conformal coverage due to radical recombination on the walls of deep and narrow features. There has been extensive progress in the thermal ALD of copper and noble metal films in recent years, because the positive electrochemical potentials allow relatively easy reduction of precursor ions to the metals. Thermal ALD approaches to most other metals and elements in the periodic table are not well developed, due to the negative electrochemical potentials of the ions and a current lack of ALD co-reagents that can convert the ions to the metals or elements. Herein, we will describe the thermal ALD growth of electropositive metals such as nickel, cobalt, aluminium, and others. The ALD of nickel and cobalt metal films has been achieved using precursors containing diazadienyl ligands (precursors 1 and 2). These precursors enable the deposition of cobalt and nickel metal films at temperatures below 200 °C and use alkylamines as benign co-reagents. Growth rates are high (0.60 Å/cycle for nickel, 0.98 Å/cycle for cobalt), high purity, low resistivity metal films are obtained, and the films have low rms roughnesses. The processes exhibit inherent selective growth on metal substrates such as platinum, ruthenium, and copper. By contrast, no growth is observed on insulating substrates. We will also overview a new thermal ALD process for the growth of aluminum metal films. This process entails treatment of surface-bound AlCl3 with a thermally stable, volatile aluminium hydride co-reagent. The growth rate for the aluminium metal ALD process is high, and high purity, low resistivity aluminium metal films are obtained. Prospects for the area selective growth of aluminum metal films will be presented. These examples demonstrate that ALD processes can be enabled for electropositive metals through careful design of precursors and chemistry. Moreover, many of the metal ALD processes exhibit area selective growth. Figure 1

Co-MOCVD processed seed layer for through silicon via copper metallization

We investigated diffusion barrier performance of chemical vapor deposition (CVD) TiN films prepared using tetrakis-dimethyl-amino titanium, Ti[N(CH3)2]4, to copper in the Cu/TiN/Si structure. The in situ treatment of the TiN films using N2/H2 plasma was found to significantly improve barrier performance against copper diffusion. The plasma-treated TiN films were stable up to 650 °C but as-deposited TiN films showed an evidence of copper diffusion into silicon even after annealing at 550 °C. The causes of the different effectiveness as a copper diffusion barrier of the two types of the CVD TiN films were discussed.