Topic 3: Multi-Beam Full Cut Laser Dicing for Thin Si wafers

Thursday, September 06
2:30pm to 3:00pm

Presentation Abstract

Over the last years the singulation of thin (<70um) semiconductor wafers with a thick (up to 30um) top layers (ILD, metal stack) as well as back side layers (eg DAF, Metal) is a challenge in the production process of wafer singulation. The traditional blade dicing process is encountering serious yield issues. These issues can be addressed by applying hybrid dicing technologies such as DBG, SDBG or Plasma dicing. However, as the wafers are becoming thinner and have many other materials in the dicing street other than Si, these process flows are not providing the yield, cost, flexibility and productivity required.

For wafer thicknesses in the range of 100 µm up to 250 µm the laser ablation singulation process has become the process of record in many applications. For the wafer thickness regime below 100 µm it is considered to have limited capability due to a reduced die strength (related to the alternative separation technologies). Specifically, as the ratio between die size and wafer thickness is > 10:1, traditional laser ablation is not considered as a separation technology.

In previous papers presented we have reported results of an investigation on the root cause of the reduced die strength for the laser ablation process. This revealed that the re-solidification of the Si resulted in lattice defects which acts as the initiators of die crack and therefore reduced the die strength.

We have used the knowhow and experience gained to develop new laser processes which each have their own specific characteristics in terms of the wafer thickness which they can cover and the die strength level that can be achieved. 

In this paper we will reveal the results achieved for the three-different laser ablation based dicing technologies. It covers nano second UV laser based on the V-DOE process (patented), a multi beam short pulse (femto second) laser dicing process (patent pending) and a multi beam nano second UV laser based process followed by a plasma etching process (patented).

For each dicing technology we will demonstrate the results over various inspection technologies (Visual Microscope, SEM, TEM and Raman Spectroscopy). For each technology we also will provide die strength data and assembly data results achieved for various applications (memory, power).

In addition to the results we will also report the influence on process window based on a variety of process parameter studies.

The results will demonstrate that for a laser based dicing process a die strength level of over 1000MPa is achieved for wafers from 30um thickness up to 200um thickness. Wafers have been diced which include up to 30um ILD and metal stacks on the front side in the dicing street as well as 10um of Cu back side metallization.

Finally a cost comparison of the three singulation processes is done and benchmarked against other wafer separation technologies such as SDBG, Plasma dicing and laser groove + blade saw.

This paper will address the results of a study done on the impact of the dicing quality of thin Si wafers which led to the development various dicing solutions each with their specific characteristics and application area.

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