First-generation polishers

Early generation tools kept wafers sitting in water until the cassettes were completed and the whole boat of wafers could be placed in a batch post-CMP wafer cleaner. Keeping the wafers wet until they can be cleaned is critical to achieving the expected post-CMP defectivity and related yield improvements. 

The removal rate on first-generation polishers can be improved by simply increasing the rotation rate. However, nonuniformity can suffer if the platen run-out is not controlled. Platen run-out is a measure of the wobble a platen undergoes during rotation and must be kept to a minimum to ensure good performance. 

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The first CMP tools, based on rotational platen silicon wafer polishing tools, had low throughput values (10 to 18 wfr/hr). Since the implementation of these first-generation tools for polishing, CMP tool design has... 

Fig. 6. Diameter scan of thickness (minus the mean) of a wafer that was polished using a first-generation rotational polisher. (Courtesy of SpeedFam-IPEC.)...

The platens on which wafers are polished have also evolved over time. Traditional polishing, as is done on first- and second-generation CMP tools, is done on a hard platen. The reason for a hard platen, of course, is to present as close to absolutely flat a surface as possible against which the wafer is pressed. Ideally, platens rotate perfectly. In practice, however, there is a small amount of run-out, or wobble, which limits the ability of the tool to polish films uniformly, especially at high rotation speeds. 

The first step will be dust removal. The influx of dust and other desert debris is a natural consequence of increased access to the tomb. Furthermore, the tomb floor is a reservoir of dust. We have examined the role of dust in the deterioration of mural surfaces (17-21), After the removal of dust, a dust-free, preformed cement, or better still, granite floor should be installed. Parts of the tombs in which paintings are already irretrievably lost must be covered with polished granite slabs to prevent dust generation from these obvious dust sources. Structural consolidation, cleaning of paint layers, and protection can then follow. 

For simplicity and to understand the STI mechanism, we introduce the following assumptions. First, the planarization length is zero, that is, there is no interaction between removal rates of patterned and blanket areas, and second, there is no dishing or recess at field oxide between active silicon nitrides in feature size level. On the basis of the above assumptions, STI CMP procedures can be divided into four steps as showm in Fig.2. The first step is defined as the period in which initial step heights of patterned area are perfectly eliminated. At this stage then erosion is generated due to the difference of removal rate between patterned and blanket area as showm in Fig.2(b). The second step is defined as the period in which the fully planarized oxide surface of patterned area is polished to expose the silicon nitride top surface. 

In this period, there is no newly generated erosion because of the same removal rates in both areas as shown in Fig.2(c). During the third step, oxide layer that remains after the second step is polished in blanket area, whereas mixture of oxide and nitride is polished in the patterned area. Because the removal rate of the oxide/nitride mixed area is smaller than that of oxide, the erosion that is generated in first step decreases with polishing time during the third step. The final step is defined as the period in which erosion is generated due to the difference of removal rate between the mixed area and the nitride area as shown in Fig,2(d). In order to quantify and elucidate the STI CMP as explained above, some simple relations which can predict the post STI CMP erosion were derived. 

Some tricks have been reported to avoid multiplication of nuclei, such as a low temperature electrolysis, a low concentration of the solutions, aspects of the nature and preparation of the electrode surface. The fewer defects on the electrode surface, the fewer are the nucleation sites.26,27 As a first step, the electrodes are mechanically polished using abrasive paper. In a second step, the surface is electrochemically polished by successively generating hydrogen and oxygen on the electrode while immersed in a sulfuric acid bath. Electrodes intended for use as anodes are cathodically polarized in a final step. They are then washed and dried before use. The more commonly used electrodes are Pt wires (typically 1 cm long and 1 mm diameter). Other types have been studied.28... 

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