• PDF / 456,495 Bytes
• 6 Pages / 612 x 792 pts (letter) Page_size
• 96 Downloads / 227 Views

DOWNLOAD

REPORT

---

0991-C05-04

Influence of Microstructure on Aggressive Chemical Mechanical Planarization Processes for Thick Copper Films Patrick J. Andersen, and Megan Frary Materials Science and Engineering, Boise State University, 1910 University Drive, Boise, ID, 83725

ABSTRACT Novel die-stacking schema using through-wafer vias may require thick electrodeposited copper and aggressive first-step chemical mechanical planarization (CMP). However, the effect of microstructural parameters, including surface orientation and grain size, on the CMP behavior of thick electrodeposited copper is not well understood. Here we explore the relationship between the surface orientation of copper grains and local CMP removal parameters using electron backscatter diffraction and topography correlation techniques. In the present work, solid copper disks are studied which are annealed to produce samples with differing grain sizes. In addition, aggressive CMP is performed on copper films (30 µm) electrodeposited on silicon. At the bulk level, the slurry composition is found to have the greatest effect on the removal rate and surface roughness. At the microstructural level, the nature of the grain boundaries (e.g. coincidence site lattice (CSL) vs. non-CSL boundaries) is shown to impact the depth of grooving at the grain boundaries. A relationship between surface orientation and local removal rate is found. INTRODUCTION Thick copper films may be required to fill large or irregular features on a patterned silicon wafer. For instance, a thick copper film is required to fill large through-wafer vias when stacking die in a technique called 3-D integration [1]. To shorten processing time, a two-step process may be used which starts with an aggressive slurry composition to remove the bulk, and is followed by conventional chemical mechanical planarization (CMP) to polish [2]. Aggressive CMP slurries typically have a strong chemically-active component with varying quantities and sizes of abrasive. Slurries with low-abrasive components have different localized removal mechanisms than do slurries with highly-abrasive components. Therefore, the microstructure of the copper film should affect how these removal mechanisms occur because of differences in grain size, grain orientation and surface energy. For example, a grain with the close-packed (111) plane at the surface will be more resistant to chemical and mechanical attack than one oriented less favorably. Additionally, other properties of the film including hardness could impact CMP output parameters. The effect that the microstructure of copper thin films has on conventional CMP processes has been established, but there has been little work on thick films. For example, Ni et al. [3] studied post-CMP surface roughness in samples with twinned or equiaxed grains. They found that the highly-twinned sample had significantly greater roughness than the equiaxed sample because of the alternating grain orientations. The higher surface energy of the less favorably oriented twin grain resulted in greater local copper