A novel slurry injection system for CMP

Many CMP processes are performed on single wafer rotary polishers. The wafer is held top surface down in a rotating wafer carrier and is pressed against a rotating polymer pad on which a chemically active slurry is dispensed. The removal rates of various materials depend on the applied pressure, the kinematics, and on the chemistry and particle content of the slurry. Different materials and combinations of materials on the wafer surface require different slurries in order to achieve the desired removal rate, rate selectivity between exposed materials, and the desired uniformity, surface quality, and defect count. The material properties and surface stmcture of the pad also affect the latter three measures. Pads and slurries are therefore critical elements of the process and together constitute a large fraction of the cost of IC manufacturing (Moinpour, 2007, p. 27). 

In this chapter, we focus on slurry application. In by far the most common slurry application method, referred to here as point application (PA), the slurry is dispensed in a continuous or possibly pulsating stream onto the pad from a tube at the end of a slurry arm. This is generally done at a fixed location near the platen center. PA slurry flow rates vary but are usually on the order of 120—250 mL/min, depending on the wafer and platen size. 

the slurry stream forms a small puddle on the pad under the application point and is carried by platen rotation until it encounters the wafer carrier. At the leading edge of the carrier, the slurry creates a bow wave that may be as much as several millimeters high. Some of the slurry in the bow wave is advected under the carrier and 

Advances in Chemical Mechanical Planarization (CMP). http //dx.dd.oi l0.1016/B978-0-08-100165-3.00015-2 

Only slurry that enters the pad/wafer gap can remove material, but most of it apparently is not utilized (PhUipossian and Mitchell, 2003). Slurry that has been advected under the wafer can be carried around by the platen several times, either re-entering the gap or joining the bow wave on each pass. Within the gap, the slurry chemistry alters the surface of the wafer. However, material removal not caused directly by the chemistry is accomplished by the simultaneous action of pad asperities that contact the wafer surface and slurry or slurry particles contained in the contact area. This lubricated three-body contact (pad asperities, wafer, slurry, and slurry particles) is thought to be the dominant material removal mechanism in many processes (Wang et al., 2007 Borucki and PhUipossian, 2007). Since the contact area between the pad and the wafer is very small, typically much less than 1% of the wafer surface (Elmufdi and Muldowney, 2006 Sun et al., 2010 Jiao et al., 2012), it is likely that very little of the slurry is directly involved in material removal. 

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