Capillary type underfill is still the mainstream underfill for mass production flip chip applications. Flip chip packages are migrating to ultra low-k, Pb-free, 3D and fine pitch packages. Underfill selection is becoming more critical. This paper discusses the performance and potential of underfills using a novel organic-inorganic hybrid polymer technology.

Compared to eutectic and high lead solder, tin-silver-copper solder has lower C.T.E., higher elasticity and greater brittleness. In light of these properties, it is generally better to select high Tg and lower CTE underfill in order to prevent bump fatigue during reliability testing. Given the brittleness of low-k dielectric layers of flip chips, the destruction of low-k layers by stress inside the flip chip packages has become a major issue. Underfills for low-k packages should have low stress, and the warpage should be small. It is expected that as the low-k trend expands, the underfill is required to provide less stress. Low Tg underfill shows lower warpage. New chemical technologies have been developed to address the needs of underfills for low-k/Pb-free flip chip packages, specifically organic-inorganic hybrid polymer compounds. The organic-inorganic hybrid polymer provides excellent cure properties which enable a balanced combination of low stress and good bump protection. The material properties of the underfill were characterized using Differential Scanning Calorimetry (DSC), Thermo-Mechanical Analysis (TMA), and Dynamic Mechanical Analysis (DMA). A daisy-chained test vehicle was used for reliability testing. A detailed study is presented on the underfill properties, reliability data, as well as finite element modeling results.

The challenges associated with meeting 20nm technology requirements for better Cu CMP process uniformity and lower defectivity have been studied. Required improvements in uniformity were obtained through platen process optimization along with evaluation & selection of specific Cu slurries and pads and their performance reported. The principal factors influencing defect formation, including Cu barrier metallurgy, interconnect pattern density and process queue times were studied. Specific new post CMP clean chemistries were evaluated to assess their capability to suppress defect formation and their performance reported. The trade off between uniformity and defect suppression as a function slurry, pad and post Cu CMP clean chemistry is described.

A process-oriented stress modeling methodology is developed to investigate the stress evolution during the silicon interposer packaging process. An FEM based 3D TCAD simulator is used to perform the process steps to construct the silicon interposer stack in sequential order. These steps include TSV fabrication for passive silicon interposer, micro-bumping and reflow process for integrating active dies and passive interposer, C4-bumping and reflow for interposer BT-substrate stacking, and epoxy mold curing for interposer encapsulation. Stress simulations are carried out for each process step to obtain accurate stress evolution history. To resolve micron features within millimeter structures, the modeling strategy employs symmetry conditions, and equivalent materials for regions away from structure features of interest. The detailed structure includes 3x3 arrays of microbumps, TSV arrays, and C4-bumps with multiple material layers at the stack corner. Important design parameters include interposer thickness and edge clearance. For different silicon interposer configurations critical stresses in the outmost microbump and C4-bump are analyzed and compared. The reliability implications are discussed.

Recently there have been a number of reports indicating concern relating to the effect of porosity, pore size distribution, and pore interconnectivity on the integration of highly porous ultra low-k organosilicate glasses (OSGs) as back-end-of-line (BEOL) interconnect dielectrics. In an effort to address these concerns a number of options to control the skeleton and pore structure of OSGs have been proposed, from adding alternative OSG precursors to alternative porogen precursors. In all these options there is a need to balance pore structure modification with critical film properties such as dielectric constant and mechanical strength. In this context, this paper examines porosity and its impact on film properties for highly porous ultra low dielectric constant films. A series of PDEMS® porous OSG films were deposited by plasma enchanced chemical vapor deposition (PECVD) from DEMS® precursor (diethoxymethylsilane) and porogen ATRP (alpha-terpenine). The percent porosity and pore interconnectivity of these films relative to the dielectric constant were measured by ellipsometric porosimetry (EP) and positron annihilation spectroscopy (PALS) respectively. Porosity and pore-size distribution for films deposited using several different species (structure former or porogen precursors) were examined using EP in an effort to understand the impact of the chemical nature of the precursor on pore morphology. Results from these depositions show that it is possible to deposit films with smaller pores using alternative structure formers (ASFs) with bulky organic groups, although there are tradeoffs with respect to other film characteristics. The addition of a separate porogen (ATRP) to the ASF lowered the dielectric constant and the addition of DEMS® precursor to the ASF/ATRP mix gave the films added structural integrity and mechanical strength. Such a fundamental understanding of structure-property relationships will help support successful integration of these porous OSG films.

Process and electromigration issues of the copper line over a dielectric step etched with a new plasma-based process have been studied. The N2 and CF4 additive gas effects on the line profile, undercut, and “neck” formation at the cusp area were investigated with respect to changes of the plasma phase chemistry and ion bombardment energy. The sidewall passivation layer hindered the excessive attack of the cusp region. The undercut of the photoresist pattern caused the residue formation. The lifetime of the etched copper was related to the line shape and the film topography, which directly affected the local current density and stress. With the proper control the plasma phase chemistry and ion bombardment energy, the Cu film over a topographic surface can be etched into fine lines with a long electromigration lifetime.

It was found for the first time that the control of the size of pore sealant is important to prevent diffusions of pore sealant into pores of porous low-k films and to achieve a good toluene seal property. Two pore sealants (PS-A, B) were prepared and the seal property and porous structure were studied using toluene based ellipsometric porosimetry (EP) measurements. It was revealed that small pore sealant (PS-B) diffuses into pores of porous low-k (PLK) films and did not show any seal property, while large pore sealant (PS-A) does not diffuse into pores of porous low-k films and shows a good toluene seal property. Ellipsometry shows that PS-A forms conformal layer only on the vicinity of surface of porous low-k films, but porous structure of porous low-k films at the bottom part is kept, according the fact that the refractive index did not increase.

Furthermore, we developed a new pore seal material (PS-C) to form ultra-thin conformal layer by a single pass, which shows a good toluene seal property. The dielectric constant increased from 2.10 to 2.25 by covering with PS-C. The obtained layer also shows the effect as the protect layer of porous low-k films from plasma damages.

This study presents an effort to couple a wafer removal rate profile model based on the locally relevant Preston equation to the change in pad thickness profile which reflects to post polish profile of the wafers after Chemical Mechanical Planarization. The result is a dynamic predictor of how the wafer removal rate profile shifts as the pad ages. These predictions can be used to fine tune the conditioner operating characteristics without having to carry out high cost and time consuming experiments. The accuracy of the predictions is demonstrated by individual confirmation experiments in addition to the evaluation of the defectivity performance with the varied pad conditioning profiles.

A computational model of amorphous SiCOH materials is described that will facilitate studies of SiCOH behavior under different thermal and mechanical stresses. This involved developing an atomic-scale model of an SiCOH thin film, which exhibited structural, mechanical and electrical properties in agreement with experimental studies. We developed a unique process for computationally creating the structure of SiCOH films. We created an algorithm for introducing and estimating porosity in the system, which provides detailed information about the system’s pore size distribution on multiple length scales. We used Density Functional Theory (DFT) to develop a simple correlation that calculates the dielectric constant of a large SiCOH structure based only on its atomic composition and volume. Finally, we confirmed the mechanical properties of the model using established Molecular Dynamics techniques. We verified that essential electronic and mechanical properties of the model structure reproduce experimental data for a representative SiCOH material within acceptable accuracy. We find the mechanical properties are significantly weakened by the presence of pendant carbon groups.

As critical dimensions decrease, key dimension-related dielectric etch challenges emerge, including via and trench uniformity and etch depth profile. The transition to ultra-low-k films such as BDIII (Black Diamond; k=2.55) dielectrics requires consideration of film sensitivity to compositional modification, polymer interactions at pores, and the effect of diffusion. Use of N2/O2 plasma at 60 ˚C to modify the M1 trench profile has been demonstrated to lower the RC delay by 14% as compared to traditional CO2 plasmas at 60˚C. Use of a DHF solution to clean the etching residue in the dual damascene structure results in >97% yield with a tight range of via chain resistance.

Continuous decrease of the feature size of transistors in modern integrated circuits (ICs) constrains thickness of auxiliary dielectric layers in interconnects because of their relatively high dielectric constant, which reduces the efficiency of low-k material integration. Dielectric materials used today as barrier or etch-stop layers are usually SiN (k ∼ 7.0) and SiCN (k ∼ 4.8), which k-value significantly exceeds that of recent ultra low-k materials (k < 2.2). In our work we have investigated thin films of rigid-chain polyimide (PI) with a k-value of about 3.2-3.3. This film was deposited using a Langmuir-Blodgett (LB) technique and can be as thin as several monolayers. The intermolecular interaction of densely packed precursor macromolecules within a monolayer formed at the water-air interface makes it possible to avoid penetration of precursor material inside the pores. The latter peculiarity of the deposition process results in a pore sealing effect using a 4 nm PI film.

In this work a new generation of periodic mesoporous organosilica (PMO) low-k dielectrics with targeted k-values 2.0 and 1.8 is evaluated. In addition, impact of two different curing processes on properties of the mesoporous material is analyzed. It is shown that removal of templating organics with thermal annealing leads to formation of mechanically robust and chemically very stable material, while application of UV-assisted curing with broadband lamp (λ > 200 nm) causes pronounced decrease of film ability to sustain in diluted HF solution. The explanation of that phenomenon is given in terms of silica-ring structures formed within organosilica skeleton.

Understanding electromigration effects in monocrystalline metal becomes of increasing interest with decreasing width and thickness of interconnects. Using a three-dimensional, atomistic model based on the Kinetic Monte Carlo method, we investigate voids in monocrystalline silver. Subject to electromigration, voids begin to drift. We show that the drift velocity not only depends on the void size, but also on the electromigration force direction, with respect to the crystallographic orientation.

The fibDAC stress analysis method, a new tool for local stress measurement, has been applied to patterned BEoL structures after being validated at complete films by established industrial methods like wafer bow measurement. The new tool uses focused ion beam (FIB) to mill a narrow trench of down to 30 nm width into the surface of the structure under investigation to trigger stress relief in its vicinity. Capturing the corresponding deformation by high resolution SEM micrographs and local digital image correlation, the original stress can be determined by simulating the stress relief process by automated finite element analyses. Simultaneously, the extraction of key material parameters of the film like Young’s modulus and Poisson’s ratio is possible.

The spatial resolution of the fibDAC stress analysis method is 1 μm and better. It has been demonstrated at arrays of BEoL interconnects. The magnitude of the local stresses inside the metal traces has been shown to be substantially different to those occurring in the dielectrics between the lines. Such a spatial resolution clearly outperforms all established industrial methods.

Chemical Mechanical Planarization (CMP) is widely used to ensure planarity of metal and dielectric surfaces to enable photolithography and hence multilevel metallization in microelectronics manufacturing. The aim of this study is to establish a fundamental understanding on the dynamic growth of nano-scale protective oxide thin films during CMP to enable the selection of proper oxidizer concentrations for slurry formulations. Tungsten was selected as the model metal film to study the formation of these metal oxide films in various oxidizers and Atomic Force Microscope (AFM) was used to measure the surface roughness of the samples conditioned in the oxidizer environment before and after the CMP was conducted. The affect of surface roughness on wettability of the surfaces were also studied through contact angle measurements on the treated tungsten films. Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance FTIR/ATR technique in combination with the X-Ray Reflectivity (XRR) were utilized to determine the thicknesses of the oxidized nano films on the tungsten surface. The results were evaluated through the material removal responses reported in the literature for the W-CMP in addition to the comparison of the Pilling-Bedworth ratios of the oxidized nano films to determine the ability of the created oxide film as a self-protective oxide.