Pattern-density step height

Figure 6.7 Diagrams illustrating the relationship between removal rate and step height (Xie, 2007) (a) pattern density (PD) CMP model (h) pattern-density step height (PDSH) CMP model.

Figure 6.13 Neighboring pattern density (pad long-range bending) effects of the CMP process (Fan, 2012) (a) monitor sites at left, center, and right in a 50% pattern density STEP array of the MIT standard layout (h) up area thickness evolution (c) step height evolution.

What gives rise to streaks in a RHEED pattern from a real surface For integral-order beams, die explanation is atomic steps. Atomic steps will be present on nearly all crystalline surfaces. At the very least a step density sufficient to account for any misorientation of the sample from perfeedy flat must be included. Diffraction is sensitive to atomic steps. They will show up in the RHEED pattern as streaking or as splitdng of the diffracted beam at certain diffraction conditions that depend on the path difference of a wave scattered from atomic planes displaced by an atomic step height. If the path difference is an odd muldple of A./2, the waves scattered... 

The model by Grillaert et al. addresses step height dependencies and includes a density dependence. Smith et al. [48] integrated the effective pattern density model described earlier with the time and step-height dependent model of Grillaert et al. to accurately predict both up and down area polishing. The resulting analytic expression for the up area amount removed (AR) is... 

FIGURE 7.23 The overall average overburden copper thickness and step height of 100 pm copper in the 50 % metal density region on a SEMATECH 854 patterned wafer (from Ref. 109). 

In the present study, we propose a new equation to predict the planarity after STI CMP process by erosion modeling which incorporates active pattern density, initial step height, selectivity between oxide and silicon nitride and over CMP amounts. 

The values for the erosion is zero and H(initial step height) when effective oxide density of the patterned area is I and zero, respectively. The erosion increases with increasing initial step height and decreasing effective oxide pattern density during the first step. The effective oxide density of second step becomes one because the local oxide step height in patterned area was fully eliminated during the first step ... 

From eqns.(6)-(9), the following relation is obtained for the third step of STI CMP as a function of initial step height, oxide effective density, active pattern density, P, and selectivity of slurry, S ... 

The final expression to predict the erosion during STI CMP becomes the function of initial step height, effective oxide density, over CMP amount, active pattern density and selectivity between oxide and nitride. 

Figure 5. The effect of initial step height on the erosion at various active pattern densities. (5=200A, S=4.3, Pe=p)...

In this section, three example applications intimately related to the pattern dependent behavior of CMP are briefly discussed. First, we note the relative importance of die-level effects with respect to typical wafer-scale nonuniformity. Second, we describe recent application of the integrated density and step height model to the run by run control of ILD CMP. Finally, we summarize issues in the application of density models to prediction of shallow trench isolation. 

The ability to accurately model die pattern evolution as discussed in this paper provides a solution applicable to the ran by run control of multi-product patterned wafers [13]. As shown in Fig. 10, a feedback control loop incorporating the integrated density and step-height pattern dependent model was developed. For each device type, an appropriate set of model parameters (including effective blanket rate BR and planarization length) were determined. The model for the effective blanket rate includes a term Delta(n) that is updated on each run n to track the tool drift in rate over time due to pad and consumable wear ... 

The proposed copper model framework described above captures three key effects step height (or dishing height) dependencies, effective density dependencies, and selectivity between removal in multiple material polish systems. The parameters shown in the removal rate diagrams also need to be extended to account for two additional important pattern dependent effects, as shown in Fig. 14. 

The change of surface profile during chemical-mechanical planarization (CMP) is monitored continuously in this study. The influences fiom pattern dependency and substrate effects are discussed. Step height reduction rate is a function of pattern density and down force. The rate decreases with time until planarization is achieved. As the polish approaches the patterns underneath, the interaction between substrate effects and pattern dependency results in the resurgence of step height. The implication of this newly found phenomenon is discussed. 

In this work, we perform a series of CMP experiments on wafers with different pattern densities and width. The evolution of step height reduction is monitored continuously. The interaction between pattern dependency and substrate effects is observed, and the impacts of these effects on CMP process control are discussed. 

Careful examination over the measured data over different patterns reveals that the step height reduction rate is higher for smaller patterns and larger spacings, both of which indicate that local removal rate is higher for lower pattern densities over the range investigated. The results above are similar to previous studies. 

In this study, we examined evolution of surface profiles during CMP, and the pattern dependency and substrate effects associated with it. Step height reduction rate decreases with polish time or remaining step height, and is also a function of pattern density. After planarization has been achieved, the film is thinned down continuously and step height reappears as the polish approaches the interface between the blanket oxide and the nitride patterns underneath. This phenomenon may result from the interaction between substrate effects and pattern dependency and it may be the origin of dishing effects. 

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