Thin wafer dicing using a high repetition rate femtosecond laser

Nitinkumar Sudani, Ryerson University

Date of Award

2009

Degree Type

Thesis

Degree Name

Master of Applied Science (MASc)

Department

Mechanical Engineering

First Advisor

K. Venkatakrishnan

Second Advisor

Bo Tan

Abstract

The demand for more compact and more efficient stable devices is driving the semiconductor industry towards the use of thin wafers with thickness less than 100μm. The stackable devices made with these thin wafers offer a greater advantage for the IC manufacturing industry in terms of circuit density, higher clock speeds and heat dissipation. Dicing, being the first step of the assembly process, plays an important role in the success of the application of thin wafers. Currently used mechanical saw dicing and conventional dicing do not satisfy the need for quality and throughput. The mechanical and thermal damage, low die strength and throughput, push towards seeking of a new dicing technique.

This thesis proposes a femtosecond laser dicing technique to overcome the limitation of the currently used techniques. A high repetition rate, high power femtosecond laser is investigated for meeting the quality and throughput requirement. A feasibility study of the proposed laser system and the analysis of control parameters, such as the number of pulses, scan speed and pulse energy, are also presented. The influence of pulsewidth and repetition rate on parameters such as the ablation threshold, kerf width, ablation depth, fluence and debris are analyzed in detail. Results of die strength and surface analysis of the dies cut using the proposed laser system show the capability of meeting the current quality and throughput requirement and hence can be considered a significant step towards commercial application of the proposed dicing technique.