Chemical Mechanical Polishing Model in ATHENA

A Chemical Mechanical Polish (CMP) capability that enables more complete closed loop process modeling has been added to the Elite module of ATHENA. The CMP modeling has become increasingly important as a component of aggressive back end processes. Simulation of the polishing process step gives important insight into final interconnect geometries.

The CMP module is available in version 3.0 of ATHENA. It incorporates two separate models that can be tailored to describe a variety of different polish machines. The two models are a hard polish model and a soft polish model.

The hard polish model polishes the structure at a rate that is a function of the pattern density in the structure. A number of user specifiable parameters allow the model to be calibrated for a particular piece of equipment. This calibrated model can then be used predictively.

The soft polish model incorporates the effects of the vertical and horizontal deformation of the polishing pad as it polishes the structure. Model parameters control how much the polishing pad will deform with respect to the height of the feature and the stiffness of the pad. The model parameters control the effective feature shadowing and the effect of pad compression.

Both models include the effects of isotropic chemical etch processes that are calculated simultaneously with the mechanical erosion.

Figure 1 illustrates the use of the CMP module as applied to a set of isolated lines and isolated spaces. Figure 2 shows an overlay plot of 5 micron lines after two stages of polishing. Figure 3 compares 10 micron lines under the same polish conditions.

 

 

Figure 1. Hard polish model.

 

Figure 2. Soft polish model on 5µm lines.

 

Figure 3. Softpolish model on 10µm lines.

 

References

[1.] J. Warnock, "A Two-Dimensional Process Model for Chemimechanical Polish Planarization", Jour. Electrochem. Soc., Vol. 138, No. 8, Aug, 1991.

[2.] P. Burke, "Semi-Empirical Modeling of SiO2 Chemical-Mechanical Polishing Planarization", VMIC Conference, 1991.