As the field of superconducting quantum computing advances from the few-qubit stage to largerscale processors, qubit addressability and extensibility will necessitate the use of 3D integration and packaging. While 3D integration is well-developed for commercial electronics, relatively little work has been performed to determine its compatibility with high-coherence solid-state qubits. Of particular concern, qubit coherence times can be suppressed by the requisite processing steps and close proximity of another chip. In this work, we use a flip-chip process to bond a chip with superconducting flux qubits to another chip containing structures for qubit readout and control. We demonstrate that high qubit coherence (T1, T 2,echo > 20 µs) is maintained in a flip-chip geometry in the presence of galvanic, capacitive, and inductive coupling between the chips.

Since its introduction into integrated circuit (IC) manufacturing by IBM Corporation in the mid-1980s, chemical mechanical planarization (CMP) has become a key enabling technology in the semiconductor industry. All of the major IC manufacturers including Intel, Motorola, and IBM now incorporate CMP in the production of their chips. In addition to IC production, CMP applications have spread into other manufacturing processes including dynamic random access memory (DRAM) chips, hard drives, and modem chips.Given the magnitude of capital invested in this technology, there is a large impetus to develop a fundamental understanding of the process. Research with this goal in mind is being performed; however, an overall understanding of the process remains elusive because of the multidisciplinary nature of CMP. Researchers have focused on individual aspects of the process, such as slurry chemistry, 1-5 wafer-pad dynamics, 6-8 mechanisms, [9][10][11][12][13][14] and numerical simulations of the slurry fluid mechanics. [15][16][17] There has been, however, little experimental research regarding slurry fluid mechanics.Several researchers have commented on the importance of slurry flow and slurry distribution beneath the wafer although the importance of slurry flow has not been experimentally demonstrated. Stavreva et al. 18 discussed how the pad's ability to transport slurry could affect the polishing rate and uniformity during copper CMP. Parikh found that slurry flow rate had a large effect on the polishing uniformity on an orbital polisher. 19 Ali et al. 20 stated that the slurry composition, flow rate, and direction of slurry impingement onto the polishing pad all play important roles in interdielectric removal rates. Singer 21 reported that the manner in which slurry is transported from the outside of the wafer to its center is critically important. Sugimoto et al. 22 showed that slurry transport in grooved pads is important in reducing thermal gradients across a wafer. Since polishing rates are temperature dependent, a reduction in thermal gradients across the wafer is believed to reduce the within-wafer-nonuniformity. Ali et al. 23 postulated that the degradation in the removal rates of pads without conditioning is due to the decrease in the pad's slurry holding capacity. Liang et al. 24 postulated that Cabot's new open cell pads do not need macroscopic surface topography because of the pad's efficiency in channeling the slurry. Despite the fact that slurry flow generally is considered to be an important factor in the CMP process, there has not been an experimental study of the slurry flow or a numerical simulation sophisticated enough to examine the slurry behavior under realistic conditions. Slurry transport and mixing could influence the polishing performance in two ways: (i) transport of polished material and (ii) nonuniform slurry transport. The first mechanism was postulated by Cook in his research on glass polishing. 4 Cook suggested that polishing removal rate is influenced by the transport of polished materi...

The fluid film thickness and drag during chemical-mechanical polishing are largely dependent on the shape of the wafer polished. In this study we use dual emission laser induced fluorescence to measure the film thickness and a strain gage, mounted on the polishing table, to measure the friction force between the wafer and the pad. All measurements are taken during real polishing processes. The trends indicate that with a convex wafer in contact with the polishing pad, the slurry layer increases with increasing platen speed and decreases with increasing downforce. The drag force decreases with increasing platen speed and increases with increasing downforce. These similarities are observed for both in-situ and ex-situ conditioning. However, these trends are significantly different for the case of a concave wafer in contact with the polishing pad. During ex-situ conditioning the trends are similar as with a convex wafer. However, in-situ conditioning decreases the slurry film layer with increasing platen speed, and increases it with increasing downforce in the case of the concave wafer. The drag force increases with increasing platen speed as well as increasing downforce. Since we are continually polishing, the wafer shape does change over the course of each experiment causing a larger error in repeatability than the measurement error itself. Different wafers are used throughout the experiment and the results are consistent with the variance of the wafer shape. Local pressure measurements on the rotating wafer help explain the variances in fluid film thickness and friction during polishing.

No abstract

This article details an effort to improve the understanding and prediction of turbulent flow inside a droplet of molten metal levitated in an electromagnetic field. It is shown that the flow field in a test case, a nickel droplet levitated under microgravity conditions, is in the transitional regime between laminar and turbulent flow. Past research efforts have used laminar, enhanced viscosity, and kϪ turbulence models to describe the flow. The method highlighted in our study is the renormalization group (RNG) algorithm. We show that an accurate description of the turbulent eddy viscosity T is critical in order to obtain realistic velocity fields, and that T cannot be uniform in levitated droplets. The RNG method does not impose isotropic length or time scales on the flow field, thus allowing such nonuniform features to be captured. A number of other materials processing applications exhibit similarly complex flow characteristics, such as highly recirculating, transitional, and free surface flows, for which this modeling approach may prove useful.