ABSTRACT
Surface preparation and cleaning is one of the most critical steps in semiconductor manufacturing [1]. For all wafer cleaning tools, routine qualification is necessary to ensure that no particle contamination is introduced by the wafer cleaning equipment [2]. The broad category of wafer cleaning tools includes the poly(vinyl alcohol) (PVA) brush scrubbing tool [3]. The brush scrubber has been increasingly utilized [4] in semiconductor fabrication as a preferred technique for particle removal after CMP. Because of the high particle removal performance required of post-CMP cleaning tools, it is critical to monitor and maintain the performance of such tools [5]. The most direct measure of tool performance is inline inspection of actual product wafers [6]. While inline defect analysis is invaluable, it may require a time lag of hours or even days between wafer cleaning and discovery of high wafer defectivity. In a high-volume manufacturing environment, this delay can lead to hundreds of product wafers with possible contamination. For this reason, inline inspection of product wafers is supplemented by regular tool qualification using less expensive particle monitor (PMON) wafers. This PMON qualification should provide an accurate measure of the tool performance with the quickest possible turnaround time. For post-CMP cleaning tool qualification, it is neces-
sary to use prepared PMON wafers with contamination analogous to that found on polished product wafers. There are several methods for preparing these contaminated monitor wafers. One way is to use polished monitor wafers [7]. In this method, test wafers can be selected which represent the surface chemistry of product wafers without the expense of underlying circuitry. The test wafer surface can be homogeneous or heterogeneous, depending on the process being qualified. These test wafers can be polished under the same CMP conditions as product wafers. This method requires the same resources as inline product inspection, therefore providing an accurate measure of post-CMP tool performance but not necessarily decreasing the turnaround time. Another common method is the slurry dip [8, 9], where monitor wafers are dipped in a wet process tank of diluted slurry. Again, monitor wafers can be selected to represent the surface chemistry of product wafers. The diluted slurry can be selected to simulate the CMP chemistry. This method has the advantage of providing contaminated monitor wafers without the time or expense of using a CMP tool. Also, it is possible to deposit dry particles using an aerosol deposition technique [10]. While it is claimed that this method is more controllable and repeatable than aqueous slurry immersion, these dry particles may not represent polishing residue as accurately as a CMP slurry. Here we describe an extremely simple contamination technique - direct pipette deposition of a small volume of undiluted slurry onto a monitor wafer.
