Insights into tungsten chemical mechanical planarization: Part I. Surface micro-texture evolution during pad break-in

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.