Micro-Raman spectroscopy, scanning electron microcopy, atomic force microscopy and preferential etching were used to characterize the sub-surface damage induced by the rough and fine grinding steps used to make ultra-thin silicon wafers. The roughly and ultra-finely ground silicon wafers were examined on both the machined (1 0 0) planes and the cross-sectional (1 1 0) planes. They reveal similar multi-layer damage structures, consisting of amorphous, plastically deformed and elastically stressed layers. However, the thickness of each layer in the roughly ground sample is much higher than its counterpart layers in the ultra-finely ground sample. The residual stress after rough and ultra-fine grinding is in the range of several hundreds MPa and 30 MPa, respectively. In each case, the top amorphous layer is believed to be the result of sequential phase transformations (Si-I to Si-II to amorphous Si). These phase transformations correspond to a ductile grinding mechanism, which is dominating in ultra-fine grinding. On the other hand, in rough grinding, a mixed mechanism of ductile and brittle grinding causes multi-layer damage and sub-surface cracks.

https://iopscience.iop.org/article/10.1088/0268-1242/23/7/075038/pdf

Process induced sub-surface damage in mechanically ground silicon wafers

This article reviews advanced polishing, grinding and finishing processes for challenging manufacturing applications. The topics covered are machining of advanced alloys; machining of wafers; stren...

Advanced polishing, grinding and finishing processes for various manufacturing applications: a review

A bonding technique suitable for bonding a non-metal body, such as a silicon MEMS sensor, to a metal surface, such a steel mechanical component is rapid enough to be compatible with typical manufacturing processes, and avoids any detrimental change in material properties of the metal surface arising from the bonding process. The bonding technique has many possible applications, including bonding of MEMS strain sensors to metal mechanical components. The inventive bonding technique uses inductive heating of a heat-activated bonding agent disposed between metal and non-metal objects to quickly and effectively bond the two without changing their material properties. Representative tests of silicon to steel bonding using this technique have demonstrated excellent bond strength without changing the steel's material properties. Thus, with this induction bonding approach, silicon MEMS devices can be manufacturably bonded to mechanical steel components for real time monitoring of the conditions/environment of a steel component.

Bonding a non-metal body to a metal surface using inductive heating

Investigation of chipping and wear of silicon wafer dicing

An overview and emerging challenges in mechanical dicing of silicon (Si) wafer are discussed from view point of narrow kerf, thin wafer, chip strength enhancement, Copper (Cu)/low-k wafers and dicing challenges for emerging technologies.

Overview and emerging challenges in mechanical dicing of silicon wafers

Die cracking is an annoying problem in the packaging industry. In this paper, we identified the weak regions, in terms of mechanical strength, in chips in a semiconductor wafer using the three-point bending test. The weak regions were observed in two sectors approximately 45/spl deg/ wide, axisymmetric to the wafer center. The strength of the chips within these weak regions was about 30%-35% lower than the average chip strength of the whole wafer. The existence of these weak regions was related to spiral grinding marks, which, in turn, were formed by backside mechanical grinding. The probability distributions of the chip strength and the chip fragmentary pattern confirmed this relationship. When wafers were mechanically ground until they were 50-/spl mu/m thick, chip warpage was found to be oriented to the direction of the grinding marks. Meanwhile, by slowing the mechanical grinding speed by 50%, we were able to increase the average chip strength by 56%. Either plasma etching or polishing after mechanical grinding eliminated the weak regions, and the optimal amount of mechanical grinding and the polishing depths were observed, beyond which the chip strength would not increase. On the other hand, a preprocess for blunting a new saw blade for chip dicing was found to be essential as the chip strength increased five-fold, whereas increasing the dicing speed or using dual saw instead of a single saw had only small effects on the chip strength degradation.

C.Z. Tsai

Papers

Study on the effects of wafer thinning and dicing on chip strength