A high performance interconnection network on a chip is essential to match the ever improving performance of the semiconductor devices they interconnect. This issue reviews the need, some fundamental background justifying the need, approaches one can take in trying to satisfy the need, and associated issues related to the concept of multilevel interconnection (MLI) technology for the ULSI/GSI era of the silicon integrated circuits, with emphasis on materials and the processes that will lead to an acceptable MLI scheme. Thus besides discussing the MLI concepts and implementation issues, properties of metals and their alloys (especially those of Cu and Al), diffusion barrier/adhesion promoter, interlayer dielectrics, deposition and etching of mateials, planarization issues, reliability issues, and new materials concepts are presented. Emphasis is obviously placed on the presently focused research on replacing aluminum with copper based interconnections. The author's viewpoint on gradual changes in replacing current materials with newer mateials as they become available is also presented. A synergism between the materials sets for on-chip and off-chip interconnections has been pointed out.

Multilevel interconnections for ULSI and GSI era

The investigation of copper for use as an interconnection metal in the ultra large-scale integration (ULSI) era of silicon integrated circuits has accelerated in the past several years. The obvious advantages for using copper to replace currently used Al are related to its lower resistivity (1.7 μΩ-cm vs. 2.7 μω-cm for Al) and its higher electromigration resistance (several orders of magnitude higher compared with Al). The goal of this review is to examine the properties of copper and its applicability as the interconnection metal. A comparison of electromigration behavior of various possible interconnection metal in standard “bulk” state is made. This is followed by a review of the calculations made comparing (a) the RC (resistance × capacitance) time constants of various material systems and (b) the joule heating of the interconnection materials. A comparative study of various metal systems for the application as the interconnect metal is then made. These discussions will clearly establish the ...

Copper metallization for ULSL and beyond

We quantified the drift of Cu ions into various PECVD dielectrics by measuring shifts in capacitance-voltage behavior after subjecting Cu-gate MOS capacitors to bias-temperature stress. At a field of 1.0 MV/cm and temperature of 100/spl deg/C, Cu ions drift readily into PECVD oxide with a projected accumulation of 2.7/spl times/10/sup 13/ ions/cm/sup 2/ after 10 years. However, in PECVD oxynitride, the projected accumulation under the same conditions is only 2.3/spl times/10/sup 10/ ions/cm/sup 2/. These findings demonstrate the necessity of integrating drift barriers, such as PECVD oxynitride layers, in Cu interconnection systems to ensure threshold stability of parasitic field n-MOS devices.

Kinetics of copper drift in PECVD dielectrics

The segregation of Al at the surface of pure Cu and Cu-5 atom % Al alloy thin film bilayers was investigated as a function of the Al content, anneal temperature and time, and annealing ambient. Rutherford backscattering spectrometry was used to follow Al movement through the thickness of the film. Al appears to segregate on the surface as an oxide. The amount of Al segregating on the surface of the samples annealed at temperatures ≤ 400°C increases to about 14 × 10 15 atoms/cm 2 . At the same time, a small amount of Al is retained in the overlying Cu through which Al is diffusing to the surface. The Al at surface is equivalent to ∼3 nm Al 2 O 3 . The formation of this oxide was self-limiting at temperatures less than the crystalline transformation temperature of Al 2 O 3 and has structure similar to the surface oxide on pure Al, grown at similar temperatures. At higher temperatures (500 and 600°C) the oxide apparently crystallizes, allowing migration of Al and O 2 , thus leading to continued growth of the oxide. It is hypothesized that the residual oxygen (or other oxidizing species like water) reacts with Al arriving on the surface, providing the thermodynamically favored driving force to migrate Al from the alloy film through the overlying pure Cu film to the surface leading to both the homogenization of the Al content in the hilayer and oxide formation on the surface.

Surface Segregation of Al of the Bilayers of Pure Cu and Cu-Al Alloy Films

Amorphous hydrogenated silicon carbide (a-SiC:H) films were deposited from a mixture of silane and methane gases using the plasma-enhanced chemical vapor deposition (PECVD) process. The properties of the film, following ammonia plasma treatment, are reported. A lower silane flow rate reduces the refractive index, but increases the carbon content and the optical band gap. Increasing the carbon concentration of the a-SiC:H films reduces the dielectric constant. The films were treated with ammonia plasma for various treatment periods. The original film has a smooth surface with a roughness of 0.231 nm, but increasing the ammonia plasma treatment period gradually roughens the surface. The chemical bonding nature of the a-SiC:H films with higher silicon content was investigated by X-ray photoelectron spectroscopy. Various nitrogen ionization species reacted with Si to promote the formation of silicon nitride. As a result, although the dielectric constant of the a-SiC:H films increased slightly, the leakage current density declined as the ammonia plasma treatment time increased.

https://ir.nctu.edu.tw:443/bitstream/11536/28536/1/000180071900054.pdf

Effects of Ammonia Plasma Treatment on the Electrical Properties of Plasma-Enhanced Chemical Vapor Deposition Amorphous Hydrogenated Silicon Carbide Films

An investigation of the stability and electrical characteristics of Aluminum-Copper bilayer films on SiO2 has been carried out. In this investigation, a thin layer of sputtered aluminum is used as a diffusion barrier/adhesion promoter between the copper and SiO2. The electrical performance of these structures when subjected to thermal cycles and applied biases is determined. The interactions and diffusion of copper through aluminum into SiO2 was investigated using both blanket films and MOS capacitors. Results are compared with those obtained from structures of Al and Cu metallization on SiO2. Samples were annealed at various temperatures in the range of 200°C to 500°C. Analysis using four-point probe resistivity measurements, X-ray diffraction, and Rutherford Back Scattering were carried out. MOS capacitors are used to establish performance under applied bias. Capacitance-Voltage characteristics of formed alloys are discussed. These results will be presented and discussed in view of the applicability of aluminum as the adhesion promoter for copper interconnections on SiO2.

Stability of Sputter Deposited Al-Cu Bilayers on SiO2.

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Stability of Sputter Deposited Al-Cu Bilayers on SiO2.