CMP for Copper TSV Applications

Through-silicon via (TSV) 3-D packaging and integration present many new opportunities and challenges for metals CMP applications. For front-side TSV polishing, challenges include the removal of large amounts of copper overburden, dishing control during copper clearing steps, and removal of large amounts of barrier metal and dielectric layers while still maintaining control over topography and defectivity. Additionally, the choice of barrier material can have significant impact on polishing in terms of the mechanical reliability regarding adhesion between the barrier metal and underlying dielectric layers. This paper will address many of these challenges with an emphasis on innovative technologies for superior process and endpoint controls, such as real-time profile control for thick copper films up to 6μm or more in thickness and automatic endpoint controls for barrier removal and dielectric stopping. The paper will also discuss some salient challenges for back-side TSV polishing, including the handling and polishing of bonded wafer pairs and strategies to minimize handling and polishing damage to the potentially fragile thinned device wafer. Additionally, the development of slurries with highly tunable copper-to-dielectric selectivity will be critical for enabling a wide range of final topographies, depending on requirements for subsequent bonding steps.

MOCVD Growth of GaN on bulk AlN Substrates

In this paper, the growth of epitaxial GaN layers on c-plane and a-plane bulk AIN substrates by metalorganic vapor phase epitaxy is reported. The AlN boules were grown by the sublimationrecondensation technique. Single crystal GaN films grown on the c-plane orientation replicate the substrate orientation. However the surface of the epilayer had a high density of cross-hatch defect lines, presumably caused by mechanical polishing damage. The low temperature PL spectra of these films were dominated by exciton emission at 3.470 eV with a FWHM of 14 meV at 7 K. On the other hand, GaN grown on the a-plane orientation AlN was polycrystalline and the surface was rough with ridge-like facets. The PL from this film showed a dominate peak at 3.406 eV which may originate from defect-bound excitons. The quality of the GaN layers grown on these AIN bulk substrates appeared to be limited by the surface preparation method, which has not been optimized.

Etching And Hydrogen Incorporation In ScAlMgO4

ScAlMgO4 is a potential substrate for GaN epitaxy. We have compared three different plasma chemistries for dry patterning of ScAlMgO4, namely Cl2−, F2− or CH4/H2-based. Significant etch rates (>1000Å.min−1) were obtained only with Cl2 (and BCl3), and the rates were directly proportional to both ion energy and ion density in the plasma. Since the etching is ionassisted under all conditions, extremely anisotropic sidewalls are produced on patterned features. Of the wet chemistries investigated at 300K, only HF wet chemical solutions were found to etch ScAlMgO4, although HNO3 can be used at ≤150°C for removal of substrate polishing damage. Hydrogen as 2H has been incorporated into ScAlMgO4 by both ion implantation and by exposure to a plasma at 250°C. In the implanted material diffusion begins at ˜500°C and most of the hydrogen is lost by ≤ 750°C. This thermal stability for hydrogen retention is considerably lower than for other substrate materials for GaN epilayer growth, such as Al2O3 and SiC. There is minimal permeation of 2H from a plasma at 250°C (DH ˜5×10−16 cm2·s−1) in ScAlMgO4, and thus unintentional hydrogen incorporation into GaN overlayers should be minimal at typical growth temperatures.