Bucknell C. Webb

Three-dimensional silicon integration

Three-dimensional (3D) silicon integration of active devices with through-silicon vias (TSVs), thinned silicon, and silicon-to-silicon fine-pitch interconnections offers many product benefits. Advantages of these emerging 3D silicon integration technologies can include the following: power efficiency, performance enhancements, significant product miniaturization, cost reduction, and modular design for improved time to market. IBM research activities are aimed at providing design rules, structures, and processes that make 3D technology manufacturable for chips used in actual products on the basis of data from test-vehicle (i.e., prototype) design, fabrication, and characterization demonstrations. Three-dimensional integration can be applied to a wide range of interconnection densities (<10/cm2 to 108/cm2), requiring new architectures for product optimization and multiple options for fabrication. Demonstration test structures, which are designed, fabricated, and characterized, are used to generate experimental data, establish models and design guidelines, and help define processes for future product consideration. This paper 1) reviews technology integration from a historical perspective, 2) describes industry-wide progress in 3D technology with examples of TSV and silicon-silicon interconnection advancement over the last 10 years, 3) highlights 3D technology from IBM, including demonstration test vehicles used to develop ground rules, collect data, and evaluate reliability, and 4) provides examples of 3D emerging industry product applications that could create marketable systems.

3D chip-stacking technology with through-silicon vias and low-volume lead-free interconnections

Three-dimensional (3D) integration using through-silicon vias (TSVs) and low-volume lead-free solder interconnects allows the formation of high signal bandwidth, fine pitch, and short-distance interconnections in stacked dies. There are several approaches for 3D chip stacking including chip to chip, chip to wafer, and wafer to wafer. Chip-to-chip integration and chip-to-wafer integration offer the ability to stack known good dies, which can lead to higher yields without integrated redundancy. In the future, with structure and process optimization, wafer-to-wafer integration may provide an ultimate solution for the highest manufacturing throughput assuming a high yield and minimal loss of good dies and wafers. In the near term, chip-to-chip and chip-to-wafer integration may offer high yield, high flexibility, and high performance with added time-to-market advantages. In this work, results are reported for 3D integration after using a chip-to-wafer assembly process using 3D chip-stacking technology and fine-pitch interconnects with lead-free solder. Stacks of up to six dies were assembled and characterized using lead-free solder interconnections that were less than 6 µm in height. The average resistance of the TSV including the lead-free solder interconnect was as low as 21 mΩ.

A 2.5D Integrated Voltage Regulator Using Coupled-Magnetic-Core Inductors on Silicon Interposer

An integrated voltage regulator (IVR) is presented that uses custom fabricated thin-film magnetic power inductors. The inductors are fabricated on a silicon interposer and integrated with a multi-phase buck converter IC by 2.5D chip stacking. Several inductor design variations have been fabricated and tested. The best performance has been achieved with a set of eight coupled inductors that each occupies 0.245 mm2 and provides 12.5 nH with 270 mΩ DC. With early inductor prototypes, the IVR efficiency for a 1.8 V:1.0 V conversion ratio peaks at 71% with FEOL current density of 10.8 A/mm2 and inductor current density of 1.53 A/mm2. At maximum load current, 69% conversion efficiency and 1.8 V:1.2 V conversion ratio the FEOL current density reaches 22.6 A/mm2 and inductor current density reaches 3.21 A/mm2.

High‐frequency permeability of laminated and unlaminated, narrow, thin‐film magnetic stripes (invited)

The permeability of the magnetic material in a thin‐film magnetic head is an important, but hard to characterize, parameter since the magnetic permeability depends on the head domain structure, the drive frequency, and the shape and size of the head. We have measured the high‐frequency permeability from 1 MHz to 300 MHz, hysteresis loops, and domain structure of unlaminated and multilayer magnetic thin‐films as a function of stripe width for arrays of long narrow stripes. Monolithic permalloy films and permalloy films laminated with SiO2 have been photolithographically patterned and ion‐milled to create 3 to 1000 μm wide rectangles, 1 cm long, with the hard axis oriented along the long axis of the rectangles. The high‐frequency permeability of each array of a given width is measured by the signal detected by a nonresonant butterfly‐coil pickup loop when the film is driven by a uniform radio‐frequency magnetic field generated by a strip‐line waveguide. The changes in domain pattern as the film structure an...

Magnetic and structural characterization of sputtered FeN multilayer films

The magnetic and structural properties of ferromagnetic FeN thin films, FeN/FeN (ferromagnetic/paramagnetic), and FeN/SiO2 multilayers deposited in a rotational dc magnetron sputter system were investigated. Monolithic films containing ≂2 at. % N2 had 4πMs values ≂25 kG. The Fe16N2 phase has been identified by electron microdiffraction in these films. Saturation magnetostriction (λs) has been related to N2 content and can be varied from −3×10−6 to 5×10−6 in a range of compositions where 4πMs is ≳22 kG. Lamination reduced easy and hard axis coercivity to <1 Oe and produced single domain configurations in yoke‐shaped structures. Lorentz microscopy indicated that the ferromagnetic FeN layers in the FeN/FeN films were exchanged coupled while those in the FeN/SiO2 films were magnetostatically coupled.

Integrated on-chip inductors with electroplated magnetic yokes (invited)

Thin-film ferromagnetic inductors show great potential as the energy storage element for integrated circuits containing on-chip power management. In order to achieve the high energy storage required for power management, on-chip inductors require relatively thick magnetic yoke materials (several microns or more), which can be readily deposited by electroplating through a photoresist mask as demonstrated in this paper, the yoke material of choice being Ni45Fe55, whose properties of relatively high moment and electrical resistivity make it an attractive model yoke material for inductors. Inductors were designed with a variety of yoke geometries, and included both single-turn and multi-turn coil designs, which were fabricated on 200 mm silicon wafers in a CMOS back-end-of-line (BEOL) facility. Each inductor consisted of electroplated copper coils enclosed by the electroplated Ni45Fe55 yokes; aspects of the fabrication of the inductors are discussed. Magnetic properties of the electroplated yoke materials are...

A 2.5D integrated voltage regulator using coupled-magnetic-core inductors on silicon interposer delivering 10.8A/mm 2

Energy consumption is a dominant constraint on the performance of modern microprocessors and systems-on-chip. Dynamic voltage and frequency scaling (DVFS) is a promising technique for performing “on-the-fly” energy-performance optimization in the presence of workload variability. Effective implementation of DVFS requires voltage regulators that can provide many independent power supplies and can transition power supply levels on nanosecond timescales, which is not possible with modern board-level voltage regulator modules (VRMs) [1]. Switched-inductor integrated voltage regulators (IVRs) can enable effective implementation of DVFS, eliminating the need for separate VRMs and reducing power distribution network (PDN) impedance requirements by performing dc-dc conversion close to the load while supporting high peak current densities [2–3]. The primary obstacle facing development of IVRs is integration of suitable power inductors. This work presents an early prototype switched-inductor IVR using 2.5D chip stacking for inductor integration.

Detection of the magnetization reversal of individual interacting single-domain particles within Co-Cr columnar thin-films

The fundamental Barkhausen noise generated by the magnetization reversal of individual particles within a particulate magnetic medium has been observed using the anomalous Hall effect (AHE) as a sensitive magnetization probe. This is the first time the reversal of individual interacting single or nearly single domain particles has been detected. The jumps correspond to magnetic switching volumes of approximately 3*10/sup -15/ cm/sup 3/ with moments around 10/sup -12/ emu. The magnetization in a Co-Cr thin film, a columnar perpendicular magnetic recording medium, is determined by passing a current through the film and measuring the AHE voltage induced within the sample itself. Hall samples as small as 0.6 mu and containing only a few hundred columns have been made via microlithography. For these samples, the voltage change due to the reversal of a single column can be readily detected with a system sensitivity of 4*10/sup -14/ emu. The spatial dependence of the measurement response over the surface of the Hall geometry has been determined by both calculation and experiment, so that the magnitude of magnetization changes detected by jumps in the AHE voltage can be adjusted for geometric effects. >

A self-servowrite clocking process

A high-speed process for servowriting hard-disk assemblies (HDAs) without an external clock head has been developed. This robust process achieves servo-pattern alignment accuracy comparable to or better than that achieved with conventional clock-head based servowriters at a substantially reduced capital and process cost.

Interference resonances in the permeability of laminated magnetic thin films

In high‐frequency magnetic structures (like thin‐film magnetic heads) which have been laminated to avoid eddy current loss, it is standard to assume that electromagnetic coupling across the dielectric separating the magnetic layers is small. We show that for macroscopic films with insulating interlayers, the laminated structure is better modeled by an anisotropic effective medium with a magnetic permeability of around 3000 but an insulating dielectric function perpendicular to the lamination plane, while still metallic parallel to the lamination plane. Electromagnetic waves can propagate parallel to the lamination direction but with 1/100 of the free‐space wavelength. The electromagnetic (capacitive) coupling between the layers can lead to radically altered propagation of magnetic flux and generate novel permeance resonances caused by interference effects across the width of the film. A Fourier series solution constructed with a mean‐field theory for the wave equation for laminated slab geometries predict...