Materials in use or under consideration for many applications in new and emerging technologies are often available only in small quantities and many times in the form of thin films, wafers and sheets. Such size and form limitations present a number of challenges to those wishing to evaluate thermal performance characteristics. This has resulted in a need to develop totally new transient or modify current transient and steady state techniques significantly. Various new or modified techniques to measure thermophysical properties are described. Illustrations of, applications to and results on semiconductors, superconductors, diamonds, polymers, composites and layered structures will be discussed.

Calculations of thermoelastic internal stresses for different systems comprised of one or several films deposited on a substrate are presented. The calculated stresses are compared to stresses directly determined by deflection measurements. The film(s)/substrate systems were submitted to cyclic bending tests in order to analyse the evolution of their internal stresses. When a significant relaxation of the stresses is detected, it is discussed with respect to the activation of irreversible deformation mechanisms, which will depend on the nature of the phases constituting the system.

Growing use of thin films in encapsulated integrated circuits(IC's) necessitated new developments in measurement of their mechanical properties in-situ. This can be done by a hybrid analytical experimental approach. The films are approximated by orthotropic membranes and the substrate is assumed to be an elastic continuum. It can be shown that power of stress singularity is a function of geometry and film/substrate material properties. By loading the sample and measuring actual displacement field in the close proximity to the crack or edge, one can evaluate the needed properties.

The technique used to measure full field displacements is enhanced moire' interferometry. It is based on the formation of fringes by the coexistence of light wave fronts diffracted from a specimen grating of high frequency. These specimen gratings are created on the specimen surface using a replication technique from a specially prepared mold. Two beams of coherent laser light illuminate the specimen grating obliquely to create a virtual reference grating in front of the specimen. The frequency f of this grating is chosen to be 2400 lines/ mm, this corresponds to a sensitivity of 0.417 µk per fringe order. When the specimen is deformed the interference pattern (moire' fringes) is formed and collected by a video camera connected to a PC-based digital image processor. Analysis of the moire pattern results in full field displacement.

Impedance spectroscopy (IS) was used as a nondestructive technique to measure the interphase processes of encapsulated microelectronic substrates exposed to high relative humidity. The advantages of IS include: sensitivity of IS to chemical kinetics, ability of in-situ testing of encapsulated packages and non-destructive nature.

Samples undergoing contamination under high relative humidity, produce frequency responses resembling those found for electrochemical cells. This suggests that the presence of hygroscopic residues induce surface water uptake resulting in the formation of surface electrochemical cells and decreased interphase impedance.

Samples undergoing a process of “supercleaning” using argon plasma and exposed to high relative humidity, produce frequency responses that more closely approach responses characteristic of dry samples than do conventionally cleaned or contaminated samples.

An overview of ceramic packaging as it evolved over the last two decades from dual-in-line packages to state-of-the-art multilayer multichip packages ispresented. IBM's 69 layer glass-ceramic/copper multilayer multichip substrate with dielectric constant of 5.0, thermal expansion exactly matching silicon and exceptional dimensional control is summarized.

High Performance Integrated Circuits form the basic building blocks of modern electronic systems that are designed to process ever larger numbers of electrical signals at greater signal velocity and fidelity. In such applications, each circuit must be packaged in order to provide it with necessary mechanical support, environmental protection, electrical interconnection and thermal cooling. The package, however, can also impose certain constraints on the chip. It can degrade electrical performance, add size and weight, introduce reliability problems and increase cost. Thus, packaging can be viewed as a complex balance between the provision of desired functions and the reduction of associated constraints.

The ability to strike a proper balance has become increasingly difficult in recent years due to the relentless march of integrated circuits toward higher levels of complexity, size, speed, heat flux and customization. It is anticipated that the continuing evolution of high performance circuits and systems will soon be limited by the package designs and materials-of-construction, rather than by the devices on the semiconductor chip.

The intent of this talk is to provide a brief overview of high performance packaging and the related materials issues. The approach is to (a) present the forecasted trends in relevant circuit performance characteristics, (b) discuss the impact of these characteristics on current chip and board level packaging methods, and (c) present new package and materials concepts that might furnish potential solutions to the developing circuit-package performance gap.

In the next generation of semiconductor devices, minimum dimensions will be smaller, aspect ratios (height to width) of devices features will be larger, and BPSG dielectrics will be challenged to deal with these changes. A new process, which integrates deposition, flow, and anneal of BPSG films, and allows void-free filling of high-aspect-ratio trenches with excellent surface planarization, is presented in this paper. Scanning electron micrographs are used to show the extent of film coverage and planarization. Additional characterization includes ion chromatography, ellipsometry, stress measurements, and breakdown field measurements.

The benefits of AIN as a substrate material for the electronics packaging industry appear to be limited by the deleterious effects of boundaries in the polycrystalline material. Some observations on different types of boundary in AIN using several complementary techniques are reported.

Anomalously low laser damage resistance thresholds have been observed in many thin film systems. Thermal conductivity values well below bulk have been suggested as a possible cause. A series of reactively sputtered AIN films were deposited on fused quartz and sapphire substrates. Their thermal conductivities were measured using the thermal comparator technique. Important factors contributing to the apparently large thermal resistance in the AIN films include film surfaces, small grain size, and high oxygen concentration. Preferred orientation and columnar morphology also affect film conductivity. Film microstructures were observed by transmission electron microscopy, and correlated with measured values of thermal conductivity.

The durability and oxidation behavior of polycrystalline aluminum nitride substrates have been investigated using scanning electron microscopy and x-ray diffraction.

Characteristics such as CTE close to that of silicon, high thermal conductivity, and good dielectric properties make aluminum nitride (AIN) an excellent dielectric for packaging silicon-based high density multichip interconnects. However, there remains many aspects of its behavior that have not been characterized. One such example is the behavior of the various metallizations used within a package. As with A12O3, these metallizations must contribute toward a hermetic seal separating the die from the environment. However, the chemical behavior of the metallization systems used for A12O3 may not be compatible with non-oxide ceramics such as AIN. Consequently, these chemical interactions are investigated in view of the requirements for each application within electronic packages. Hermeticity testing results are also included in the discussion.

We developed a novel negative photosensitive polyimide composition for microelectronics. It was prepared by the synthesis of polyamic acid precursor in N, N-dimethly acryl amide. The solution properties, processing conditions and film properties are compared with two conventional, ester and ion type photosensitive polyimides.

The novel composition has higher sensitivity than the other two types because the density of the photoreactive groups is much higher. And it provides wider patterning process range, better adhesion and lower final curing temperature.

We also examined the effect between three types of polyimides and epoxy molding compounds on the reliability of ICs after moisture/solder reflow process. The novel photosensitive composition has good adhesion to metals, inoranic layers and molding compound and improves the reliability of ICs by supressing the interfacial delamination.

Polyimides are considered as promising packaging materials in multi-layer interconnections and multi-chip modules because of their low dielectric constant and good planarizability. Photosensitive polyimidesiloxane (SIM2000XL) as a newly emerging polyimide is showing not only similar properties as conventional polyimides but also the advantages of process simplification and improved adhesion. Moreover, it is proposed that SIM2000XL can be an oxygen-plasma etching barrier in multi-level lithographic systems because of its high silicon content.

We characterized the photosensitivity of SIM2000XL thin films under excimer laser (193 nm) exposure. The sensitivity of SIM2000XL was found to be about 20 mJ/cm2. After the SIM2000XL thin films were exposed through a photomask in the contact mode, development gave the usual negative patterns. However, the remained film thickness after exposure reached a maximum of about 65 % of the initial film thickness and decreased with further irradiation. This can be attributed to the competing processes of polymer crosslinkage and chain-scission. This phenomenon is important for applications of polymers in DUV lithography. A detailed study of these two competing processes are presented.

Liquid crystalline epoxy networks have been prepared from glycidyl terminated polyether oligomers of varying molecular weight. These oligomers were prepared by functionalizing hydroxy terminated oligomers based on 4,4'- dihydroxy-α-methylstilbene and α,ω-dibromoalkanes with glycidyl groups. Curing of these oligomers was carried out either within their nematic mesophase or in their isotropic state. Different thermal properties were observed after curing under these two sets of conditions. Extremely low values of the coefficient of thermal expansion in the range of 15 to 60 ppm/°C were achieved. To produce aligned thermosets, orientation of the liquid crystalline phase was induced during the curing process by a magnetic field. Orientation of these networks was measured by wide angle x-ray diffraction (WAXD).

The combination of Cu and parylene (poly-p-xylylene) for metallization and insulator in integrated circuit or packaging multilayer interconnection systems gives one of the lowest resistance and capacitance values per unit length. In this paper we present a detailed study of the diffusion characteristics of Cu in parylene-n (PA-n) substrates. PA-n was vapor-deposited and Cu metallization performed at room temperature using the Partially Ionized Beam (PIB) technique. Rutherford Backscattering (RBS) technique has been used to study the diffusion of Cu in PA-n substrate after annealing the samples to elevated temperatures in vacuum. We found no sign of Cu diffusion after the Cu/PA-n sample was annealed at 300°C for 6 hours. Diffusion occurs at 350 °C. However, preannealed PA-n substrate prior to Cu deposition can prevent the diffusion even at a temperatures above 350°C. Also we found that amorphous carbon and chromium are good diffusion barriers of Cu on PA-n. The dry adhesion between PA-n deposited on Al, Cu and Ag was found to be good. The adhesion of these PIB deposited metals on PA-n in high vacuum was also very good.

Because of rapid advances in semiconductor technology, polymer dielectrics are finding widespread use in high-density packaging to improve performance and processability. Notable among these materials are polyimides, benzocyclobutene resins, and fluoropolymer containing composites.

Polyimides have been used extensively for chip passivation and first-level packaging. Benzocyclobutenes, processed as conventional thermosets, are being investigated as thin film dielectric for use in multichip modules. A silicon containing derivative can be used as a plasma etch stop. Polytetrafluoroethylene is used either as matrix or reinforcement in circuit boards to produce a low dielectric constant composite.

Knowledge of materials properties is crucial to ensure the reliability and function of products incorporating these polymers. In this article, a few selected characterization techniques for the determination of important materials properties such as solvent diffusion, plasma etch rate, and thermomechanical characteristics will be discussed.

The effects of curing rate and solvent content prior to curing were examined for Hitachi PIX L110 polyimide thin films. DMA, TMA, DSC, and wafer bow measurements were used to elucidate in-plane storage modulus, Z-axis CTE, heat capacity, and residual stress dependencies on processing conditions and film position across the wafer. It was found that the residual stress and storage modulus are highly dependent on the processing conditions. Additionally, the heat capacity and storage modulus showed significant dependency on wafer position as well as processing conditions. The Z-axis CTE was found to deviate significantly from values published for the in-plane (xy) direction.

Electronic packaging has been changing.rapidly to meet the often conflicting demands of higher speed and lower cost. In the multichip module (MCM), an array of semiconductor chips is mounted on a substrate and interconnected via a network of multilevel metal lines with polymer layers used as a dielectric between orthogonal metal signal paths. A potential reliability problem that must be investigated is the absorption of moisture by the dielectric in the MCM package. Moisture absorption may lead to long term problems such as loss of adhesion, corrosion of the metal interconnect and increased insulator conductivity.

Bisbenzocyclobutene (BCB) is an insulating polymer that is being used in the MCM package as a dielectric material. In this work, the moisture uptake in BCB is investigated gravimetrically using a Cahn-1000 microbalance with a resolution of I pgram. The BCB films are spincoated onto silicon substrates and cured yielding film thickness ranging from 7 to 20µm. The moisture uptake of the BCB film is monitored in situ and non destructively to reveal the performance of the film as used in an integrated circuit environment. The moisture uptake of the films was monitored at different ambient relative humidity (RIH) values between 20% and 80% at 23°C. The transient behavior of the moisture absorption in BCB films has been characterized. Moisture uptake in BCB films increases as the relative humidity is increased, and reaches a maximum of less than 0.2% by weight at 80% RH. By comparison, this moisture uptake is significantly lower than that of fully cured PMDA-ODA polyimide, which is about 2.5% by weight under similar conditions. The transient data show that the equilibration time for a 22.8 µ.m film is approximately 220 seconds, yielding a diffusion coefficient of about 4.5µm2/s.

The etch rates of BCB film in a reactive ion etcher(RIE) were measured using Ar, O2, O2+CF4, and O2+SF6 gas mixtures. Faster etch rates were obtained when CF4 and SF6 were added to oxygen, since the presence of atomic fluorine enhances the etch rate of organics, while also etching Si and SiO2 formed by exposure to oxygen gas. Surface compositional changes on the BCB film were observed by XPS after plasma modification. Pure O2 and O2+CF4 plasma oxidized the carbo-siloxane linkage (C-Si-O) of the BCB, resulting in the formation of SiO2 on the surface. The O2 +SF6 plasma, however, did not produce the surface SiO2, because of its faster Si and SiO2 etch rates. Ar ion sputtering following the plasma modification, restored the surface chemical composition to a state similar to the initial BCB surface.

Interfacial characteristics such as chemical reaction, metal diffusion, and morphology were investigated for Cr/BCB and Ti/BCB structures. Using Auger and XPS depth profiling, the formation of Ti carbide and Cr oxide was confirmed at the metal/BCB interface. Annealing at 250 °C for extended time periods resulted in diffusion of Cr and Ti into the BCB and subsequent formation of CrSi2 and Ti-Si compound precipitates. The reaction is a thermal diffusion controlled process which was dependent on time and temperature. It was also found that Ar backsputtering treatment on BCB film before metallization was found to roughen the surface resulting in metal spikes which penetrate into the BCB film.