Insights into Tungsten Chemical Mechanical Planarization: Part I. Surface Micro-Texture Evolution during Pad Break-In

Abstract

The effect of conditioner types and downforces during pad break-in on pad surface micro-texture evolution is investigated. Two substantially different discs are employed (i.e. conventional vs CVD-coated), each at two different downforces. Pad samples are extracted throughout the break-in process and their surface micro-topography and pad-wafer contact characteristics are analyzed using confocal microscopy. The two conditioning discs result in different evolution paths during break-in. In general, the conventional disc produces more pad “fragments” that get counted as taller “artificial” asperities as compared to the CVD-coated disc. In contrast, the gentle shaving action of the CVD-coated disc promotes eventual flattening of the asperity tips. Regardless of the disc type, the mean summit heights decrease and reach stable values as break-in progresses. Compared to the CVD-coated disc, the conventional disc results in higher mean summit curvature indicating sharper asperities. This work underscores the need for optimum conditioner design for attaining a steady pad surface micro-texture at a given downforce and within a reasonable break-in time.

Tribological, Thermal, Kinetic, and Pad Micro-Textural Studies Using Polyphenylene Sulfide Retaining Rings in Interlayer Dielectric Chemical Mechanical Planarization

“…For better visualization, high and low areas of all images have been accentuated through a transformation that involves taking the inverse hyperbolic sine of the height data. 16,17,[37][38][39][40][41][42] The scale bar is also kept the same for all images to allow for visual comparisons. Red indicates the highest parts of the pad surface and is, therefore, representative of asperities.…”

“…Red indicates the highest parts of the pad surface and is, therefore, representative of asperities. 16,17,[37][38][39][40][41][42] Color changes from red to yellow, and then to green, indicate decreasing heights, with a certain shade of green representing the mean surface height, indicative of interpore land areas. 16,17,[37][38][39][40][41][42] Color shifts to light blue, and then to dark blue, represent gradually decreasing heights all the way to the bottom of the pores.…”

“…16,17,[37][38][39][40][41][42] Color changes from red to yellow, and then to green, indicate decreasing heights, with a certain shade of green representing the mean surface height, indicative of interpore land areas. 16,17,[37][38][39][40][41][42] Color shifts to light blue, and then to dark blue, represent gradually decreasing heights all the way to the bottom of the pores. The images can be quantified by constructing summit height probability density function (PDF) plots as shown in Fig.…”

“…3. 16,17,[37][38][39][40][41][42] Each PDF plot is normalized such that the area under the curve is equal to unity. Therefore, the area under the surface height PDF in a chosen height range gives the probability of finding a point on the surface within that range.…”

“…A more detailed description of the methods used by our group for pad topography analysis can be found elsewhere. 16,17,[37][38][39][40][41][42]…”