•What is SSL?

SSL is an advanced abrasive suspension carrier based on PEG-200.  It provides long-term stability to abrasive slurries, preventing the hard settling of suspended particles over time and use.  Such abrasive slurries are widely used in wire saws for ingot slicing and for lapping applied to wafer manufacturing.  SSL can be provided as a suspension carrier or as a pre-manufactured abrasive slurry to meet customer specifications.  SSL carrier is unique because of the advanced package of components that is added to the Polyethylene Glycol 200 base carrier.  SSL slurry comprises the SSL carrier and suspended abrasive at a solids loading level that meets customer needs and specifications.  Nearly all abrasive materials are compatible and are stabilized in SSL carrier.   

1. •What is the appearance of SSL carrier?
   

SSL carrier appearance differs from the standard PEG.  SSL carrier is a cloudy suspension that is translucent cream to light yellow in color.

1. •How is SSL different than PEG-based slurries?
   

•SSL provides long-term stable abrasive slurry, and prevents hard-cake formation during storage or use.  Abrasive slurry from SSL carrier is stable for months at a time, and can be reformed into the original virgin slurry with simple mixing,

•SSL remains as a uniform suspension throughout the ingot cut, and results in no solids agglomeration anywhere in the wire saw.

•SSL tends to cover the wire more evenly and produces a more uniform kerf slot during the wire saw slicing run. 

•The relative abrasive content in the slurry does not change due to agglomeration during the slicing run as it does with typical glycol or oil based slurries, which are unstable by nature, and result in rapid solids agglomeration and hard settling. 

•What are the benefits that PPT customers have observed using SSL?

The typical improvements / benefit achieved using SSL include the following:

•increased wafer yield,

•improved process consistency with more uniform surface parameters and less variation,

•reduced kerf / improved wafer thickness,

•reduced slurry usage,

•reduced  slurry abrasive loading,

•reduced slurry preparation / mixing time,

•easier saw cleans, and

•reduced wire drag and wire saw energy usage measured as drive motor power requirement. 

•How do I know that SSL will work in my wire saw operation, and that significant cost savings will be realized?

Like with any new carrier or slurry system, it is necessary to run slicing tests under normal wire saw conditions and with typical ingots to optimize SSL for that specific set of saw conditions, and to demonstrate the improvements for each customer.  However, PPT has collected data from large numbers of our customers in continuous production runs, over several years and within two different industries: Solar and Semiconductor.  This production performance data has clearly demonstrated a consistent trend of improved wafer quality resulting in improved wafer yields, ease of slurry handling, more efficient slurry usage rates and overall lower cost of manufacture for wafering with multi-wire saws.

SSL additives enable the independent adjustment of viscosity in a single product using the industry standard PEG 200 at a constant abrasive loading.  This allows the SSL slurry product to be optimized on different types of wire saws; whether high production load with low table speeds or lower production loads at higher table speeds.  Once an optimized process is established, the SSL system will provide significant cost improvements that are consistent and sustainable over the long term.

•How should SSL carrier be stored?

SSL needs to be stored in a dry place at 15°C - 35°C.  The product should remain in a sealed container until use.  As with standard PEG slurries, it is recommended that SSL be stored in a manner that avoids prolonged exposure to humid air.

•How does SSL slurry preparation and slurry mixing differ from standard glycol slurries?

SSL mixes faster and easier with abrasive than straight PEG based carriers.  Further, SSL slurries re-mixes more easily after prolonged storage.  Straight PEG slurries, after only a few days, form a hard settled cake of solids at the bottom of the container which cannot readily be remixed back into a uniform slurry. 

For SSL, best mixing is achieved by using a dual blade mixer at the bottom and center of the shaft.  PPT can make further recommendations for mixer types and configurations for a given mixing vessel.

For slurry preparation using SSL carrier, it is important that the abrasive is added at a slow and regular pace to the stirring carrier, and NEAR the center vortex where dispersion within the stirring carrier is maximized. 

•Will the additives in the SSL slurry rinse properly when used in wafer rinse stations?

Yes.  SSL additives dissolve completely in water with no residue.  This includes high pH rinse water with detergents.  PPT has extensive experience with water rinsing for wafer manufacturing, and has found that the SSL slurry rinses more easily than standard PEG slurries.

•Can SSL be used to cut Si bricks into ingots?

Typically, bricks are cut into ingots by using a diamond blade or I.D. saw rather than using silicon-carbide abrasive slurry.  In the case that abrasive slurry is used for this type of cutting, SSL can be used even if a low grade abrasive with higher particle size is used.  

•What is the conductivity of SSL?

The conductivity of SSL is somewhat higher than that of PEG and changes slightly with the additive level.  Depending on wire fault settings of the wire saw, you may need to adjust the level of detection.   If your wire fault system of the saw is based on voltage, all that is needed is to slightly lessen the voltage drop sensitivity.  A similar reduction in sensitivity might have to be made for a fault system based on wire current.  It is best to load the saw with the SSL slurry and run it normally.  If a detection signal light occurs, then the operator can reduce the wire fault detection setting by 20% at that time.