Die singulation technologies for advanced packaging: A critical review

Abstract

Die singulation, also known as wafer dicing, is reviewed in terms of the brief history, critical challenges, characterization of singulation quality, different singulation technologies and underlying mechanisms, and post-singulation die strength enhancement. Mechanical blade dicing has been the workhorse of die separation in the semiconductor manufacturing process. It faces growing challenges due to the adoption of copper/low-k dielectric interconnect structures, thin and ultra-thin wafers, die attach films, narrow dicing streets, and complex stacked structures on the dicing streets. Key dicing quality characteristics are chipping, delamination, kerf geometry, die side wall damage, die surface contamination, and die strength degradation. Various die singulation technologies have been developed to address these challenges and quality issues, including dicing by thinning, laser based approaches, laser and mechanical hybrid method, and plasma dicing. Die strength is a critical parameter for thin and ultra-thin dies. Post-dicing die strength enhancement is becoming the complement of most dicing technologies to achieve dies with high fracture strength. Plasma dicing has the potential to achieve much higher die strengths than all the other dicing approaches.

Ultrathin Wafer Pre-Assembly and Assembly Process Technologies: A Review

“…139,140 The poor adhesion and thermomechanical properties have been identified as a major cause of metal/dielectric interfacial delamination and cracking during blade dicing of silicon wafers with low-k ILD layers. 86 The delamination and cracking driving forces can come from the CTE mismatch stresses in the low-k stack, the global CTE mismatch of the package and the external loads. 96 In addition, copper is more ductile than aluminum and will enhance the premature clogging of dicing blade, which adds additional loading to the blade to cause excessive chipping.…”

“…As the wafer thickness decreases below 100 mm, blade dicing tends to cause severe wafer damage and increased amount of chippage, cracks, delamination, and residual stress in the singulated dies ( Figure 38) and hence reducing the process yield. 60,[86][87][88]141 A wafer sawing street is inhomogeneous due to the presence of passivation layers (oxides, nitrides, and polymers), metal films, test element groups (TEGs), and polymeric materials such as die attach films (DAF) and dicing tapes at the backside of a wafer. During the dicing process, thermally softened metal and polymeric cutting debris have a tendency to fill the microscopic pores in between the abrasive grains.…”

“…The cutting mechanism of mechanical blade dicing is similar to a grinding process in which material is sheared away from a wafer by diamond abrasive grits embedded on the edge of a rotary annular blade 2,18,86 The dicing blade acts as a thin grinding wheel which is rotated at a high speed (30,000-60,000 rpm) to grind the wafer resulting in the formation of a full cut or partial cut through the wafer. The mechanism of silicon removal and surface defect formation (SSD and surface roughness) are therefore based on the same principles as wafer grinding discussed in Section 2.2.…”

“…86 A two-step blade dicing process, also known as step cutting, has become the most common blade dicing method to address various challenges, e.g., low-k ILD/copper interconnect structures, passivation layers (oxides, nitrides, and polymers), frontside and backside metal layers, TEG and lithography alignment structures, and DAF. 86,141 In the first step, a partial cut with a thicker blade is made into the wafer to minimize frontside chipping and delamination. In the second step, the remaining thickness of the wafer and part of the dicing tape are cut through using a thinner blade to minimize backside chipping (Figure 39).…”

“…85 Die strength is not only dependent on die thickness and size, but could be affected by backside and sidewall defects induced by the thinning and dicing processes. 5,14,18,[20][21][22]60,[86][87][88][89][90][91] There are two major factors affecting the die strength, namely backside surface fracture strength and sidewall fracture strength. The backside surface fracture strength is generally improved by post-grinding and stress-relief processes such as CMP, spin etching, and plasma etching.…”