CMP Slurry Metrology, Distribution, and Filtration

Abstract

Chemical-mechanical planarization (CMP) is one of the most tightly controlled, key enabling processes in integrated chip (IC) manufacturing. With the industry's transition from 90 to 65 nm and then further to 45 and 32 nm, CMP processes are becoming much more complex while demanding stringent management of CMP slurry quality during its manufacturing, blending, and distribution. Slurry distribution in IC fabs is accomplished using chemical blending and delivery systems designed on different liquid dispense technologies. Handling in these systems may cause changes in abrasive and/or chemical properties of the slurry. To maintain slurry health during its usage and replenishment, it is essential to monitor and adjust its chemical properties (e.g., oxidizer and additive levels and their replenishment needs) and the abrasive characteristics (e.g., composition, large and mean particle size distributions, weight percentage of solids (wt% solids), density or specific gravity, and settling and redispersion behavior). Bench-top and handling characterizations can provide useful insights into the slurry metrology parameters and health management challenges. Efficient CMP slurry metrology tools should be able to measure the chemical and/or oxidizer concentration(s), large particle counts (LPC), and mean particle size distribution (PSD) on a realtime basis and use this information for CMP process control.The removal of large, defect-causing particles without changing constant slurry flow and mean PSD of abrasives is critical for CMP slurry health. LPC growth in slurries is typically managed using postblending, global loop, and point-of-use (POU) filtration. Filtration can effectively remove large particles if Microelectronic Applications of Chemical Mechanical Planarization, Edited by Yuzhuo Li 563 the size of particles to be removed (e.g., >0.5 or >1.0 mm) is at least one order of magnitude larger than the mean working particles to be retained in the slurry. In slurry-handling situations involving even small increases in the mean size of the abrasives, it may be very difficult to selectively remove particles that are only slightly larger than mean size particles to restore handled slurry PSD and LPC to the fresh slurry. Tighter POU filter flow rate, pressure drop, and lifetime can be significantly affected because of mean PSD changes in extensively handled slurries. Using optimum rating filters in the global loop and POU and limiting the total number of slurry turnovers before consumption should help in slurry health maintenance, providing stable CMP performance in such cases. Current slurry manufacturing processes target 90 % and higher reduction in cumulative LPC at !0.56 or 1.01 mm. Single-pass filtration solutions using graded density, multiple thin layer, pleated depth filter media, or membranes can provide required large particle retention depending on the slurry abrasive and chemical composition. Results of particle retention, flow rate, and pressure drop from filtration tests using tighter depth filters show very diffe...

Storage Temperature Effects on the Slurry Health Parameters and SiO2 Removal Rates during Chemical Mechanical Polishing

“…While there have been several reports on slurry stability, shelflife, and performance consistency, 8,9 the effects of storage temperature on slurry health parameters, our focus here, has received less attention in the published literature. Slurry health may undergo undesirable changes caused by wide diurnal, monthly, and seasonal temperature variations during handling, storage, and transportation.…”

“…[1][2][3][4][5][6] CMP slurry characteristics, reflecting slurry health, and their quality control are critical to achieving repeatable and consistent CMP performances. [7][8][9][10] Slurry health can change during slurry preparation, packaging, shipping, handling, and storage. 8,9,11 Figure 1 shows the typical logistics of CMP slurry usage, starting from the slurry manufacturer to the end-user.…”

“…[7][8][9][10] Slurry health can change during slurry preparation, packaging, shipping, handling, and storage. 8,9,11 Figure 1 shows the typical logistics of CMP slurry usage, starting from the slurry manufacturer to the end-user. 1 All inventories/slurry containers are stored at the slurry manufacturer, 2 shipped from the manufacturer to intermediate warehouses a couple of times, and again stored before use in the semiconductor manufacturing facilities (fabs).…”

“…CMP slurry quality assessment process monitors the quality of slurries by measuring various slurry health parameters such as mean particle size, particle size distribution (PSD), zeta potential, large particle counts, pH, conductivity, viscosity, wt% solids, density or specific gravity, total dissolved solids (TDS), etc. [7][8][9] Despite careful monitoring of the quality of slurries, CMP slurries from different product batches or within batches sometimes cause variation in CMP performances in the fab. In view of this and due to the increasing complexity of CMP processes and their cost of ownership, there has been an increasing demand to detect and identify quality variations of the slurry rapidly before introducing it to the slurry blend and delivery systems.…”