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significantly for extracting the critical areas of an IC with many duplicates of single cells. Following the<br />

design hierarchy, it can be used to predict and characterize yields of future products in order to decide<br />

about improvements in the corresponding layout cells that enable the desired yield.<br />

47.4 Yield Forecast<br />

By making use of the yield distribution model (see subsection “Yield Distribution Model”) and the software<br />

system TRACIF/EXACCA/GRAPH (see subsection “Implementation and Performance”), yields associated<br />

with each defect type can be calculated and a sophisticated selection of IC types can be undertaken.<br />

Yield Calculations<br />

An example of the characterization of IC production process is given in Table 47.3 (for point defects)<br />

and Table 47.4 (for lithographic defects). The critical processes listed in these tables were assumed to<br />

be responsible for the yield loss in double metal CMOS production process and were accompanied by<br />

in-line yield measurements made on the corresponding test structures, and the consequent yield analysis.<br />

The critical areas of test structures are in mm 2 .<br />

TRACIF/EXACCA/GRAPH system ensures, for the yield model, the critical area of IC (for given defect<br />

type) as a union of all local critical areas. Here, the simulated results for the IC chip, which was designed<br />

using double metal CMOS process, will be presented. The critical areas for five cells of this IC called<br />

inpad, ota, buffer, selector, and exor are shown in Tables 47.5 and 47.6. The numbers in parentheses denote<br />

how many times the corresponding cell appears in the circuit layout. As can be seen from Table 47.5, the<br />

critical areas for point defects (in mm 2 ) are defined as overlap areas of the corresponding mask layers.<br />

The first three are for defects of silicon crystal lattice in the depletion region of p-n junction and the<br />

second three are for pinholes in thin and CVD oxides.<br />

© 2002 by CRC Press LLC<br />

TABLE 47.3 Yield Measurements for<br />

Point Defects<br />

Critical<br />

Process A ti Y ti1 Y ti2<br />

NWI .4265 .9754 .9861<br />

PPI .0072 .9960 .9980<br />

NPI .0072 .9980 .9980<br />

TOX 1 .9613 .8547<br />

CVD1 1 .9821 .9654<br />

CVD2 1 .9574 .9203<br />

TABLE 47.4 Yield Measurements for Lithographic<br />

Defects<br />

Critical Level A ti Y ti1 Y ti2<br />

SPPI .0042 .8940 .9168<br />

OPPI .0042 .8531 .9328<br />

SNPI .0042 .9630 .9842<br />

ONPI .0042 .9462 .9750<br />

SCON .0021 .9351 .9184<br />

OCON .0021 .9544 .9076<br />

SPOL .0042 .8677 .8559<br />

OPOL .0042 .9770 .9642<br />

SME1 .0042 .8884 .8520<br />

OME1 .0042 .9540 .9397<br />

SME2 .0042 .7985 .8220<br />

OME2 .0042 .8796 .9081

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