Andrew J. McKerrow

MEASUREMENT OF ELASTIC MODULUS, POISSON RATIO, AND COEFFICIENT OF THERMAL EXPANSION OF ON-WAFER SUBMICRON FILMS

A bending beam method has been developed to measure the elastic modulus E, the coefficient of thermal expansion (CTE) and the Poisson ratio ν for on-wafer dielectric films with thicknesses in the submicron range. The method was demonstrated for 0.5 μm thick silicon dioxide films made from tetraethylorthosilane (TEOS). First, the biaxial elastic modulus E/(1-ν) and CTE were measured on blanket TEOS on Si and GaAs substrates and found to be 77 GPa and 1.0 ppm/°C, respectively. The Poisson ratio ν was determined by combining the finite element calculation and the experimental result of the thermal stresses of TEOS fine lines on the Si substrate. The Poisson ratio of TEOS was determined to be 0.24 and, as a consequence, the Young’s modulus was 59 GPa. Fourier transform infrared spectra were obtained for TEOS films on the Si and GaAs substrates to ensure that the chemical structure of the film is independent of the substrate.

Thermomechanical properties and moisture uptake characteristics of hydrogen silsesquioxane submicron films

This letter describes measurement of the biaxial modulus, coefficient of thermal expansion (CTE), and moisture uptake characteristics of hydrogen silsesquioxane (HSQ) thin films. The biaxial modulus and CTE were determined using a bending beam method, and moisture uptake was studied using a quartz crystal microbalance method. The biaxial modulus and CTE of a 0.5 μm HSQ film were measured on Si and Ge substrates and found to be 7.07 GPa and 20.5 ppm/°C, respectively. The value determined for the diffusion constant of water in a 0.7-μm-thick HSQ films is 3.61×10−10 cm2/s at room temperature.

On-wafer characterization of thermomechanical properties of dielectric thin films by a bending beam technique

A bending beam technique has been developed for on-wafer characterization of thermomechanical properties of dielectric thin films including Young’s modulus (E), the coefficient of thermal expansion (CTE), and the Poisson ratio (ν). The biaxial modulus E/(1−ν) and CTE were determined by measuring the thermal stresses of the dielectric film as a function of temperature on two different substrates. The Poisson ratio and Young’s modulus were determined by measuring the temperature dependence of the thermal stress of periodic line structures of the dielectric film. Three dielectric thin films were selected for this study, consisting of silica made from tetraethylorthosilane (TEOS), hydrogen silsesquioxane (HSQ), and biphenyltetracarboxylic dianhydride-p-phenylene diamine (BPDA-PDA). The deduced biaxial modulus and CTE are 77 GPa and 1.0 ppm/°C for TEOS, 7.07 GPa and 20.5 ppm/°C for HSQ, and 11.1 GPa and 3.4 ppm/°C for BPDA-PDA. The Poisson ratio is determined to be 0.24 and Young’s modulus is 59 GPa for the TE...

Overview Of Process Integration Issues For Low K Dielectrics

The era of silicon Ultra-Large-Scale-Integration (ULSI) has spurred an everincreasing level of functional integration on-chip, driving a need for greater circuit density and higher performance. While traditional transistor scaling has thus far met this challenge, interconnect scaling has become the performance-limiting factor for new designs. Both interconnect resistance and capacitance play key roles in overall performance, but modeling simulations have highlighted the importance of reducing parasitic capacitance to manage crosstalk, power dissipation and RC delay. New dielectric materials with lower permittivity (k) are needed to meet this challenge. This paper summarizes the process integration and reliability issues associated with the use of novel low k materials in multilevel interconnects.

Measuring the elastic modulus and ultimate strength of low-k dielectric materials by means of the bulge test

The mechanical properties of organosilicate glass (OSG) thin films were measured for the first time using bulge testing of OSG / silicon nitride (SiN/sub x/) freestanding membranes. Evaluation of two different OSG films revealed significant differences in Youngs modulus and residual stress between the two dielectric films. Youngs modulus of both types of OSGs was independently measured using nanoindentation and found to be at least 8.5-17% greater than that measured using the bulge test. It is well known, and demonstrated herein, that modulus data obtained from nanoindentation is influenced by mechanical properties of the substrate. Operating without this constraint, it is believed that data obtained using the bulge test more accurately represents the intrinsic mechanical properties of OSG thin films.

Subcritical Delamination of Dielectric and Metal Films from Low-k Organosilicate Glass (OSG) Thin Films in Buffered pH Solutions

Understanding subcritical fracture of low-k dielectric materials and barrier thin films in buffered solutions of different pH value is of both technical and scientific importance. Subcritical delamination of dielectric and metal barrier films from low-k organosilicate glass (OSG) films in pH buffer solutions was studied in this work. Crack path and subcritical fracture behavior of OSG depends on the choice of barrier layers. For the OSG/TaN system, fracture takes place in the OSG layer near the interface, while in OSG/SiNx system, delamination occurs at the interface. Delamination behavior of both systems is well described by a hyperbolic sine model that had been developed previously based on a chemical reaction controlled fracture process at the crack tip. The threshold toughness of both systems decreases linearly with increasing pH value. The slopes of the reaction-controlled regime of the crack velocity curves for both systems are independent of pH as predicted by the model. Near transport-controlled regime behavior was observed in OSG/TaN system.

The effects of passivation layer and film thickness on the mechanical behavior of freestanding electroplated Cu thin films with constant microstructure

The goal of this paper is to investigate the effects of film thickness and the presence of a passivation layer on the mechanical behavior of electroplated Cu thin films. In order to study the effect of passivating layers, freestanding Cu membranes were prepared using standard silicon micromachining techniques. Some of these Cu membranes were passivated by sputter depositing thin Ti films with thicknesses ranging from 20 nm to 50 nm on both sides of the membrane. The effect of film thickness was evaluated by preparing freestanding films with varying thickness but constant microstructure. To that effect, coatings of a given thickness were first vacuum annealed at elevated temperature to stabilize the microstructure. The annealed films were subsequently thinned to various thicknesses by means of chemical mechanical planarization (CMP) and freestanding membranes were prepared both with and without Ti passivation. The stress-strain curves of the freestanding Cu films were evaluated using the bulge test technique. The residual stress and elastic modulus of the film are not affected significantly by the passivation layer. The elastic modulus does not change with film thickness if the microstructure keeps constant. The yield stress increases if the film is passivated. For passivated films, yield stress is proportional to the inverse of the film thickness, which is consistent with the formation of a boundary layer of high dislocation density near the interfaces.

Effects of silicon carbide composition on dielectric barrier Voltage Ramp and TDDB reliability performance

Silicon carbide films containing either nitrogen or oxygen were integrated within a dual-level metal copper interconnect and characterized using Voltage Ramp and TDDB testing. Oxygen containing silicon carbide films were characterized by poor dielectric breakdown properties, but their performance improved with a short soak in ambient at elevated temperatures. This data suggests that oxygen containing silicon carbide films have poor moisture barrier properties. Similar evaluation of nitrogen containing silicon carbide films revealed materials properties that were more similar to those of silicon nitride. TDDB comparison of all three dielectric films is consistent with conclusions from the Voltage Ramp study.

Direct seed electroplating of copper on ruthenium liners

The ruthenium (Ru) liner based metallization scheme depends on the ability to electrodeposit Cu onto thin, resistive Ru substrates with substantially high Cu nuclei density. In the present paper, a novel electrochemical bath that utilizes Cu-complexing agents to improve the nucleation of plated Cu films on Ru is presented. Such chemistries can generate Cu nucleation density on Ru greater than 1012 nuclei/cm2, thereby enabling robust gap-fill in aggressive (CD∼30nm) dual damascene structures. Complexed-Cu plating chemistries thus provide great potential for extending Cu metallization to future technology nodes.

Low resistance wiring and 2Xnm void free fill with CVD Ruthenium liner and DirectSeed TM copper

Chemical vapor deposited (CVD) Ruthenium liners and DirectSeedTM (DS) copper were used with advanced Electrofill processes to provide lower resistance wiring compared to results using CVD Ru and conventional physical vapor deposited (PVD) Cu seed for back end of line (BEOL) structures. Different annealing temperatures and simulated BEOL thermal stress builds were used to show the difference in resistance. The grain size was also compared to show that the Ru/DS process had larger grains than the Ru/flash-Cu (F-Cu) seed. To further show the advantage of the Ru/DS seed process as a solution for future generations, 2X nm trenches were shown to have complete gap fill and thereby eliminating the need for conventional PVD Cu seed.