Polishing

Dry Polishing (Stress Relief)

In recent years, the demand for ultra-thin die for use in mobile phones, stacked packages, and a myriad of other applications has been increasing. But a decrease in die thickness has also resulted in decreased die strength and increased die warpage. Stress relief improves die strength for greater viability while reducing die warpage for greater usability in stacks and thin packages. The chart below outlines the four main types of stress relief, including dry polishing, a proprietary DISCO process.

DBG & Dry Etching

When the dry etcher is combined with the DBG process, it can improve die strength even further than when processing with common grinding, because the etcher can remove the die side surface damage from blade dicing. Also, with this process, there is no mechanical damage due to dicing, because the stress relief process is performed after die separation has taken place. As a result, this process shows promise in reliability improvement of those devices that undergo external stress after packaging, such as IC cards.

Wet Polishing (CMP etc.)

With the reduction in height and size of IC packages, there is increased demand for thinner built-in die in silicon devices. Therefore, the stress relief process is carried out to improve die strength after wafer backgrinding. Furthermore, a polishing process is also required after backgrinding to improve performance for devices such as high luminance sapphire (Al2O3) substrate for LEDs, lithium tantalate (LiTaO3) / lithium niobate (LiNbO3) substrate for high-speed communication device SAW filters, and silicon carbide (SiC) substrate for power devices. Typical CMP equipment places the wafer above and the polishing pad below. In contrast, DISCO equipment possess a feed axis and places the polishing pad above and the wafer below. This structure is called “in-feed polishing” and is used for both dry polishing and wet polishing (polishing technique using chemicals, among which the most well-known process is CMP). DISCO’s wet polishing, introduced here, realizes scratch reduction, mirror surface finish, and improvements to cleanliness. Furthermore, depending on the material, an Epi Ready* finish can be achieved.