J. Palleau

Copper Photocorrosion Phenomenon during Post CMP Cleaning

During post‐chemical mechanical polishing (CMP) cleaning of copper Damascene structures by diluted hydrofluoric acid , a corrosion phenomenon has been shown on patterned wafers, leaving a copper deposit and an associated copper etching. Methods are developed to eliminate the phenomenon by use of benzotriazole or crotonic acid in the diluted solutions. At the same time,the presence of these inhibitors does not change the cleaning efficiency of the diluted solutions. Also, the elimination of light during the cleaning step eliminates the corrosion. A theoretical explanation is given. ©2000 The Electrochemical Society

Ultra thin diffusion barriers for Cu interconnections at the gigabit generation and beyond

Abstract The reliability of copper interconnection depends on the barrier effectiveness of conductive or non-conductive layers to block any copper motion. The conductive barrier materials currently used in Al-based interconnections — Ti, TiN, W and nitrided W — have been investigated as barrier against copper diffusion. The barrier thickness must be as thin as possible to achieve negligible barrier contribution to the total line resistance. Electrical tests C-V on MOS capacitors were performed to assess the rate of electrically active copper impurities transported through the barrier layer. The stability of a copper/barrier/oxide/silicon structure was studied under thermal stress with or without bias. For back-end process annealing performed under vacuum, the copper diffusion was shown to be limited, and very thin barrier films were shown to be effective in preventing copper diffusion.

Film texture evolution in plasma treated TiN thin films

In semiconductor technology, TiN thin film elements can be used as diffusion barrier between a metallic layer and a silicon oxide dielectric. Plasma application during the growth of TiN thin films modifies the microstructure of these films and consequently alters their physical properties. But details of the effect of plasma application on the evolution of the film microstructure and correlations between this evolution and the physical properties are still unclear. To clarify the correlations, the microstructure of a series of TiN thin films, deposited using an organometallic chemical vapor deposition technique combined with plasma treatments has been analyzed by transmission electron microscopy (TEM). The films were obtained by repeated fabrication sequences consisting of limited film growth followed by the application of a N2/H2 gaseous plasma with various powers and duration times and are actually stackings of plasma-treated elementary layers. TEM analysis shows that these films are made of nanocrystallites and that whereas crystallites are randomly oriented when no plasma is applied, short-time plasma treatments induce a tendency to 〈200〉 texture and longer treatments progressively rotate the direction of texture to 〈220〉.In semiconductor technology, TiN thin film elements can be used as diffusion barrier between a metallic layer and a silicon oxide dielectric. Plasma application during the growth of TiN thin films modifies the microstructure of these films and consequently alters their physical properties. But details of the effect of plasma application on the evolution of the film microstructure and correlations between this evolution and the physical properties are still unclear. To clarify the correlations, the microstructure of a series of TiN thin films, deposited using an organometallic chemical vapor deposition technique combined with plasma treatments has been analyzed by transmission electron microscopy (TEM). The films were obtained by repeated fabrication sequences consisting of limited film growth followed by the application of a N2/H2 gaseous plasma with various powers and duration times and are actually stackings of plasma-treated elementary layers. TEM analysis shows that these films are made of nanocrystal...

TiN-CVD process optimization for integration with Cu-CVD

Abstract Integration of Cu-CVD as metallization for on-chip interconnect requires an efficient barrier to avoid any Cu diffusion in the insulating material. These barriers must also promote adhesion of Cu to the inter- and intra-metal level material, and have low resistivity to minimize level to level contact resistance. This paper discusses about the performance of Cu-CVD via integrated with TiN-CVD barrier in Cu/SiO 2 interconnection structures. After a review of the TiN-CVD performance as a diffusion barrier, Cu-CVD adhesion properties will be evaluated as a function of both TiN and Cu deposition process and TiN surface treatments. In addition to the standard tape test method, wettability after annealing of a thin Cu-CVD film deposited on the TiN barrier was studied to characterize adhesion of Cu-CVD to the barrier under evaluation. The presence of fluorine and fluorinated compounds were observed at the Cu/TiN interface, due to Cu-CVD deposition process based on Cupraselect. The major impact of such contamination on adhesion and TiN barrier resistivity will be evidenced. Finally, electrical results are given for two-level Cu interconnections performed in a dual damascene architecture. Very low via chain resistances are obtained after optimization of the TiN-CVD/Cu-CVD process integration.

Ti-diffusion barrier in Cu-based metallization

Abstract Reliability investigations, with or without a barrier layer, have been performed to study the penetration of copper into thermal oxide as a function of temperature and applied electric field. No copper diffusion was detected without a barrier into 100 nm thick oxide for temperature stress as high as 450°C for one hour and for bias temperature stress (BTS) as high as 300°C for 8 h at 1 MV/cm. This absence of diffusion was observed when thermal annealing was performed under vacuum. A 20 nm thick titanium layer was used as a diffusion barrier/adhesion promoter between the copper and the oxide. The devices using this barrier were not affected by a temperature stress of 600°C for 10 h and by BTS even at 450°C for 2 h at 1 MV/cm.

Study of Cu contamination during copper integration for subquarter micron technology

Abstract Copper contamination in several dielectric deposited on copper-CVD film was investigated. This study aims at integrating copper in a dual damascene structure interconnection for sub-quarter micron technology. A complete contamination profile into the deposited dielectric was available using SIMS, TXRF (total X-ray reflection fluorescence) and LPD–AAS (liquid phase decomposition–atomic absorption spectroscopy) as complementary characterization tools. The Cu contamination profile of the SiN/SiO2 and SiO2 structure deposited on copper was given. The PECVD process used for both process cleaning of the chamber and SiOF deposition imply plasma with fluorine and the reactivity of this species with copper was shown to be critical for dielectric contamination and copper contact surface. Eventually, a cleaning solution was investigated to lower the contamination at the surface of the dielectric, the most contaminated part.

TEM studies of the microstructure evolution in plasma treated CVD TiN thin films used as diffusion barriers

Abstract In semi-conductor technology, TiN thin films elements are used as diffusion barriers between a copper interconnect layer and a silicon oxide dielectric. Plasma treatment application, by modifying the film microstructure, can improve the film barrier properties and its electrical conductivity. But details of the plasma application effect on the film microstructure evolution and correlations of this evolution with the physical properties are still unclear. To clarify the correlations, the microstructure of a series of TiN thin films deposited using an OMCVD (organo-metallic chemical vapor deposition) technique has been analyzed by transmission electron microscopy (TEM). The films were obtained by cycling a basic synthesis sequence including first a limited film growth and then application of a N2/H2 gaseous plasma with various powers and duration times. Films are actually stackings of plasma-treated elementary layers. TEM analyses show that films are made of nanocrystallites and that whereas no texture is observed when no plasma is applied, short-time plasma treatment induces a tendency to 〈100〉 texture and if treatment is longer, the direction of texture progressively rotates to 〈110〉. A tentative interpretation of this texture evolution has been made in terms of nucleation and growth and correlations between this evolution and the effect on the physical properties have been obtained.

Thermodynamic and experimental study of Cu-LPCVD by reduction of copper chloride

Abstract Copper thin films have been deposited on (100) silicon substrates covered by a refractory metal film (W, Cr) via low pressure chemical vapor deposition (LPCVD) using Cu 3 Cl 3 as a precursor. Synthesis of the halide occures via chlorination of copper by Cl 2 . According to thermodynamic calculations, the chlorination efficiency may be controlled by the temperature of the chlorination chamber ( T 1 ) and the chlorine flow rate. For T 1 > 450°C copper chloride deposition rates in excess of 1 μm/min can be obtained. Deposition is performed “in situ” on individual 4 inch Si wafers heated by halogen lamps up to 500°C. The copper formation results from the reduction of Cu 3 Cl 3 by hydrogen and starts at temperatures as low as 250°C. The morphology, composition and properties of the deposited layers are strongly dependent on the wafer temperature and reactor total pressure. In this paper, we present a thermodynamic analysis of copper chlorination and of the chemical reactions involved in the LPCVD of copper by reduction of copper chloride together with an overall description of the results obtained so far with this new process.

Study of the thermal stability at the Cu/SiOF interface

Abstract For future interconnect technologies several material changes are required. Low-k dielectrics in combination with copper should offer the most efficient structures for interconnection. In this paper we have evaluated for the first time the compatibility of Cu and SiOF. An obvious advantage of SiOF is its similarity with SiO 2 and therefore its ability to be easily integrated into MLM architectures. Different MIS structures, Cu/Barrier layer or not/SiOF/Si substrate, were formed to study the stability of the interface as a function of the temperature and electrical field applied. Ti and TiN thin films were used as barrier layers. Electrical (C-V and G-V measurements) and analytical characterizations (SIMS) have been performed. In the absence of a barrier neither Cu diffusion within SiOF nor F diffusion into Cu was detected by electrical measurements, even after annealing at 500°C for 10 h. Moreover, positive mobile charges were not detected under a BTS stress of (3 MV/cm, 250°C). The result would indicate that Cu diffusion into SiO 2 is dramatically reduced by F dopant. In the case of Ti and TiN in contact with SiOF, SIMS profiles show clearly fluor diffusion in the barrier layer.

Influence of boron on WSi2 formation by direct reaction between tungsten and silicon

Abstract The reaction between W and Si forming tungsten silicide has been studied for boron implanted samples. It is shown that dopant implantation in the silicon layer strongly slows down the reaction. Boron diffusion towards the metal leads to a very sharp peak in the concentration in this layer. Decrease in growth rate can be justified by formation of stable tungsten boride compounds detected by X-ray diffraction. When boron is implanted in W, fast dopant redistribution through the whole metal layer occurs at low annealing temperatures. Small slowing down effects on the reaction are then observed.