Filters

The AccuSizer® liquid particle counter is used to test a wide range of filters. This may involve using two sensors upstream and downstream of the filter in order to calculate the efficiency at given size ranges. A common calculation used for filter testing is the beta ratio:



Liquid Filtration Testing

Filtration is the process of separating solids from fluids. The goal of liquid filtration testing is to remove solid particles from a liquid.

Since filtration is the process of removing particles from a fluid, particle counters are a tool frequently used to test the functioning of the filter. The feed (original fluid) and the filtrate (fluid that passes through the filter) are measured with a liquid particle counter such as our AccuSizer SPOS system. Since the feed is typically at much higher concentration than the filtrate, dilution is typically necessary, but an accurate concentration value is required to calculate the filter efficiency. The AccuSizer system is available in several configurations to meet the needs of the size of the particles to be analyzed and the extent of dilution required.

AccuSizer A2000 APS system test results before (blue) and after passing through a 5 µm (red) and 2 µm (green) filter are shown in Figure A.



Figure A

The tabular results from this experiment are shown in Figure B.



Figure B

An aqueous sample was analyzed on the AccuSizer APS system before and after a 2 µm filter. The results are shown in Figure C.



Figure C

CMP Slurry Filter Testing

In an effort to reduce the number of oversize particles in CMP slurries, filter testing has been performed.

Using an AccuSizer APS system, particles were analyzed in a ceria CMP slurry before and after it was passed through a Planargard® NMB01 and NMB03 filters. Entegris applications labs use both the AccuSizer APS and the AccuSizer FX-Nano to test retention profiles for our CMP filters. The AccuSizer FX-Nano system uses focused extinction wherein the view volume through which particles pass through the sensor is drastically reduced. This reduction provides much higher sensitivity and particle coincidence limit. Therefore, the minimum particle size limit is lowered and the coincidence limit is increased. This system is ideal for an online application where predilution is not feasible.

The ceria filtration results shown in the Figure indicate a small, but discernable LPC difference up to 20 µm. After 2 µm, essentially all the LPC counts have been removed. The ability to size and count aggregates in CMP slurries gives the user invaluable knowledge that can save time and money. With the AccuSizer FX-Nano system, conventional SPOS technology is taken to a higher level and provides the sensitivity and reliability needed for online processes.