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Semiconductor CMP Slurries

An important problem in today’s advanced semiconductor manufacturing occurs in the planarization of semiconductor wafers. Polishing slurries, known as chemical mechanical planarization (CMP) slurries, are used as an abrasive to polish the wafer to the extremely high specifications for planarization required for the manufacturing of semiconductors. CMP slurries are made up of nanoparticles that are much smaller than xSight’s detection threshold of 500 nm, making the nanoparticles themselves invisible to xSight.

Uniformity of the slurry nanoparticles is critical to achieve the tight tolerances for flatness required for semiconductor microchips.

Array of semiconductor wafers
close up of a single semiconductor wafer

The occasional large particle, or agglomerates formed when many of the nanoparticles cluster together creating larger particles, can wreak havoc in manufacturing. Single larger particles, often called LPCs (large particle contaminants) can create scratches in the surface of a wafer rendering it scrap material. Estimates place the value of scrap in the semiconductor industry as a result of damaged wafers at $1 billion annually.

Holographic Characterization of CMP Slurry Agglomerates

2 vials of turbid CMP slurries

The size of problematic larger particles falls in the ideal range for theTotal Holographic Characterization® performed by xSight, 500 nm – 10 microns. The turbidity of CMP slurries is a challenge for optical techniques because the turbidity creates too much opacity to detect a signal from the LPCs. The unique Total Holographic Characterization® signature of an LPC is a hologram, which is detected even in the presence of the sea of smaller particles in the background.

data from 2 CMP slurries

Above is a plot of nanoparticle agglomerates as a function of their index of refraction vs. size. Each point in the plot represents a single agglomerate. The nanoparticles are not detected with xSight (see inset labeled “Good”). When agglomerates form, xSight detects their holograms (see inset labeled “Reject).

Monitoring Slurries Under Different Environmental Conditions

CMP slurries are sensitive to different environmental conditions. The propensity of slurries to agglomerate can depend upon environmental properties such as pH and ionic strength. As seen below, Spheryx’s xSight reveals CMP slurry agglomeration under different conditions. In Panel (a) below, agglomerate concentrations were measured over a range of pH from 2 to 11. In Panel (b), ionic strength was varied by changing salt concentration from 0.3 to 90 mM. Understanding agglomeration behavior as a function of environmental parameters is critical when designing CMP slurry formulations. xSight delivers results for a variety of different CMP slurry materials including silica, ceria, alumina, diamond and others.

xSight data from a study of silica slurries at different pH and at different ionic strength

Contact us for more information on how Spheryx can help with your slurries.

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