Measuring Particles in CMP Slurries
Kristi Nicholas and Rakesh Singh
BOC Edwards, Chaska, Minn.
Don Grant and Mark Litchy
CT Associates, Inc. Bloomington, Minn.
Slurry is a primary factor in the etch rate and quality of CMP processing. Although a slurry is chosen during process development, in the production environment its characteristics, or “health,” can change during shipping, handling and distribution. Reliable CMP slurry analysis can be key to consistent, quality CMP processing.
With CMP becoming increasingly important in IC manufacturing, slurry characteristics play a major role in determining process conditions. Slurries are complex suspensions that can be comprised of shear sensitive solids and reactive chemicals. Slurry particles are optimized to enhance process performance, but handling can cause shifts in size distributions or create agglomerations that form larger particles that can cause scratching on the wafer surface. By monitoring slurry “health,” engineers can proactively evaluate slurry quality to ensure the most reliable CMP processing.
Control of CMP processes has been hindered by the inability to detect slurry damage before it adversely affects product yield. For years, slurry pH, conductivity and total solids have been monitored during CMP processes. More recently, CMP slurry analyzers have been used to characterize slurry particles in terms of concentration and size distribution. This study was undertaken to determine which slurry characteristics change when slurry is circulated and which instruments can most sensitively detect the onset of change. Effective slurry monitoring depends greatly on the type of analytical instrument, its sensitivity, repeatability and resolution.
CTA publication #43: Semiconductor International, 24(8): 201-206