Material removal rates

CMP of HDD substrate in four kinds of slurries, each with a different mean particle diameter of 15,30,50, and 160 nm as shown in Fig. 33, was conducted by Lei and Luo [43]. The dependences of Wa, Ra, and material removal rate on the Si02 particle size are shown in Figs. 34(a)-34(c), respec-... 

Oxidizer concentration is also one of the important factors in determining material removal rate, and it was found to increase with the oxidizer concentration [43,106]. With the increase of oxidizer concentration, both Wa and Ra decrease at first and then increase, the optimum concentration is 1 wt %, and relative low oxidizer concentration helps to get lower Wa and Ra values as shown in Figs. 36(a) and 36(b). High concentration of oxidizer may result in excessive corrosive wear, which will lead to the increasing of topographical variations. 

Fig. 34 —Effect of the particle size on (a) surface waviness Wa, (b) surface roughness Ra, and (c) material removal rate. The slurry contains 5 wt % SIO2 particles, 1.5 wt % oxidizer, and 1 wt % lubricant In Dl water at pH 1.8.

Change of material removal rate with pH value is very interesting. Neither low nor high pH value exhibits the high MRR, which may be attributed to a passivation effect on the disk surfaces under the low pH value and a slow chemical dissolution rate under the high pH value. 

In 1996, Liu et al. [129] analyzed the wear mechanism based on the rolling kinematics of abrasive particles between the pad and wafer. They summarized that the kinetics of polishing are (1) material removal rate is dependent on the real contact area between the slurry particle and the wafer surface. The real contact area is related to the applied pressure, the curvature, and Young s modulus of the slurry... 

Luo and Domfeld [110] introduced a fitting parameter H , a d5mamical" hardness value of the wafer surface to show the chemical effect and mechanical effect on the interface in their model. It reflects the influences of chemicals on the mechanical material removal. It is found that the nonlinear down pressure dependence of material removal rate is related to a probability density function of the abrasive size and the elastic deformation of the pad. 

Zhou, C. H., Shan, L., and Hight, R., "Influence of Colloidal Abrasive Size on Material Removal Rate and Surface Finish in Si02 Chemical Mechanical Polishing, Tribol. Trans., Vol. 45,2002, pp. 232-230. 

In a typical modeling approach, the material removal rate is modeled as a function of easily controlled process parameters. The most basic model is one that predicts the bulk rate of material removal in a macroscopic fashion. An empirical observation by Preston is widely used, in which the rate of material thickness reduction is proportial to the product of (a) the relative velocity between the wafer and the polish pad and (b) the pressure on the surface of the wafer ... 

Guo, Y., Tang, J., Dornfield, D. (1998). A finite element model for wafer material removal rate and non-uniformity in chemical mechanical polishing process. Proc. 3rd Int. CMP for ULSI Multilevel Interconnect. Conf, Santa Clara, pp. 113-118. 

FIGURE 2.22 Correlation among hydroxyl content on surface, material removal rates for 71, and Ti relaxation slopes measured using DMNR technique. 

The CMP output parameters include removal rate, planarization efficiency, surface finish, material removal rate selectivity, wafer-to-wafer uniformity, within-wafer uniformity, dishing and erosion, and defect levels [15]. 

What is tribometrology What are its applications during the CMP process In a fabrieation plant, one of the CMP stations encountered inconsistent material removal rate. Given that the slurry is fully functional, how would you use trihometrology to determine the source of inconsistency ... 

The chemical-mechanical polishing or planarization (CMP) process is a complex interplay between the wafer and the consumables involved. The consumables include slurry, pad, conditioner, and so on. During polishing, the pad carries the slurry and delivers it to the wafer surface. It also transmits the normal and shear forces from the polisher to the wafer. Therefore, polishing pad plays a critical role in the CMP process and influences the outcomes such as material removal rate (MRR), within-wafer nonuniformity (WIWNU), wafer-to-wafer nonuniformity (WTWNU), step height reduction efficiency (SHRE), and defect counts. 

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