High quality laser cleaving process for mono- and polycrystalline silicon

Abstract

The cleaving process has the potential to replace the dicing of thin wafers. Its inherent advantages are no mechanical forces to the substrate, no material losses, and high edge quality. In order to determine the fundamental mechanisms leading to a reliable cleaving process the complex interaction of wavelength and temperature dependent absorption, heat transfer, material elongation and finally crack formation is theoretically described and experimentally verified. A successful process observed if sufficient thermal stress can be generated to induce a crack and if no surface deformation occurs due to overheating. Most relevant parameters determining the process window are irradiated power, cutting speed, and focus spot size. The results of these parameter variations are presented. Accuracy and reproducibility is demonstrated by cleaving stripes of different widths fulfilling the requirements of the electronic packaging industry. In the third section the influence of the crystalline orientation is investigated. As a result mono-crystalline silicon exhibits an anisotropic behaviour when changing the cutting direction whereas for polycrystalline substrates a permanent change of the crystal structure is found at the grain boundary. Finally, the obtainable edge quality is presented briefly, which leads to higher sample strengths compared to conventional laser and mechanical processes.

Die singulation technologies for advanced packaging: A critical review

“…The thermally induced stresses can lead to crack formation or cause propagation of an incipient crack at temperatures below the melting or softening temperature of the substrate. [283][284][285][286][287] In principle, cleavage separation by laser induced thermal stresses includes two phases: a "seed" crack formation and controlled propagation of the "seed" crack under laser radiation. Continuous wave CO 2 lasers emitting at $10.6 lm wavelength have been widely used from the very beginning.…”

“…But due to the temperature dependence of absorption coefficient, a nonlinear bulk volume heating of silicon takes effect. 234,286 This significantly simplifies the cleavage separation process. Tangential tensile stresses are formed around the heated zone.…”

“…234,[283][284][285][286] However, a lot of hurdles have to be tackled before it can be considered for dicing more complicated semiconductor device wafers which bear multiple stacked sensitive layers of different materials. 234,[283][284][285][286] However, a lot of hurdles have to be tackled before it can be considered for dicing more complicated semiconductor device wafers which bear multiple stacked sensitive layers of different materials.…”

“…(2) Presence of multiple different materials: With the existence of multiple different materials, such as polymeric passivation layers, low-k dielectric materials and metal layers, preparing the "seed" crack on the device side can be very challenging in terms of scribing process quality. 286,287 H. Plasma dicing Even if the laser radiation can be introduced from the backside, due to the through-thickness bulk volume absorption and heating mechanism inherent to this technology, the impact of transmitted laser photons to the sensitive device layers is yet to be known.…”

Self-Controlled Cleaving Method for Silicon DRIE Process Cross-Section Characterization

“…There are several methods for the controlled cleaving of silicon substrates, for example, preliminary micro-groove formation with subsequent thermal stress cleaving using lasers [ 46 , 47 , 48 ]. On the other hand, cleaving can be performed by etching v-groove with the sequential use of a diamond scriber [ 49 ].…”