Abstract:

This paper describes a recently-developed technique capable of simultaneous measurement of particulate and dissolved residue concentrations in colloidal suspensions. In this technique, the suspension undergoing analysis is dispersed into air as small, uniformly-sized droplets. The liquid is then evaporated from the droplets and the size distribution of the resulting particles measured. The droplets formed are such that each contains either one or no particles prior to evaporation. Hence the droplets dry to either the particle that was originally in the droplet or to a “dissolved residue particle” whose size is determined by the concentration of dissolved material initially in the droplet.

The particle size distribution is measured using a scanning mobility particle sizer (SMPS) that can size and count particles from 2.5 nm to 500 nm in diameter and has 64 size channels per decade of size (e.g. 64 channels between 10 and 100 nm). In most cases the dissolved residue particle diameters are smaller than 10 nm and the technique is capable of measuring the size distribution of particulates in the suspension from 10 to 500 nm.

The instrumentation used can be calibrated such that the airborne concentrations of the particulates (originally present in the colloidal suspension) can be converted to liquidborne concentrations and the size of the dissolved residue particles can be used to determine the mass concentration of dissolved residue.

The paper shows use of the technique for measurement of particulate and dissolved residue concentrations in suspensions of uniformly sized particles, chemical planarization (CMP) slurries, and polishing slurries. An example of a trimodal particle size distribution measured in a polishing slurry is shown in Figure 1.