Second-generation polishers

Sequential processing tools also increase the risk of multiple wafer damage. If a stray particle appears on one of the three pads, all wafers will be damaged by this particle and all three pads must be replaced. Also, in the event of a defective pad, it may be very difficult to identify quickly which pad needs to be replaced so all three pads may have to be changed. Tool utilization is also limited by tool inflexibility for example, should a failure occur to any one component in this sequential tool, the entire system must be stopped while repairs are done. 

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Raw throughput is higher (second- and third-generation polishers produce 25 to 60 wfr/hr in production). 

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. 

Emphasis in CMP technology in 1998-1999 has evolved from a nearly exclusive focus on traditional polish systems to the use in manufacturing of advanced second- and third-generation polishers. This advance in technology has translated into standard CMP processes for oxide, polysilicon, and tungsten CMP, and expanded interest in aluminum CMP, copper CMP,... 

Second, friction during CMP generates heat that can affect the reaction kinetics as well as soften the polish pad. On most tools, heat transfer away... 

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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