Saw chipping improvement to achieve defect free bare die products

In the recent years, there is increasing trend of utilizing bare die (without packaging) in many applications. For semiconductors provider, this type of business requires totally new quality expectations, because there is nothing covering the die. The die sawing process becomes very critical, as not only rejects are not allowed, but the die physical quality and appearance are also easily visible to the customers. The die saw chipping become one of the most critical issue, as its appearance can create all kind of customer concerns and complaints. One of the effective containment actions is rejecting all defective die and even those cosmetic rejects. However, this action consumes a lot of yield loss without providing real benefits to both providers and customers. In order to go for real improvements, conventional methods were verified again, follows by utilization of more comprehensive methods. One interesting finding was slower table speed did not provide better saw cutting quality, but instead much worse chipping was observed. Therefore, a new comprehensive method was required and expected analysis need to be performed with a lot of fundamental verifications. These verifications required to be performed on the material properties, blade behaviours, cutting characteristics and process parameters. From initial verification, current process window had repeatedly showing high yield loss of around 10%. With screening tests of various process parameters did not provide any significant statistical model, indicating there were more significant factors. Therefore, a new process need to be established from fundamental level, started from material properties. Due to chipping occurrence happens at the backmetal layer, the understanding of its metallization scheme was important. From previous process experience, blade cutting requirements are unique per respective metal scheme. There were several blade properties selected for evaluations, together with pre-conditioning performa- ce (dressing & pre-cut). Surprisingly, the blade pre-conditioning played much critical role. The pre-conditioning is required to remove the blade bonding material and exposing uniform diamond grit. Only when the blade achieved ready condition, new blade features could be effective. The optimum blade features utilized balancing of grit size and concentration base on considerations of blade entry and exit from wafer. With optimum blade, several rounds of process window optimization proved that some conventional perceptions might not work well in actual process. When the optimized window was ready, robustness tests managed to confirm its performance. The last step of process development was executing effective and optimum process control to make sure successful noise prevention. When optimum process implemented in production, saw chipping was eliminated, saving yield loss of 10%. More importantly, customer quality risk was improved to zero, resulted in multi folding effect of their confidence level to the maximum level.