Shozo Shirai

Melting of silicon crystals and a possible origin of swirl defects

Abstract Melting and growth processes of thin crystals were investigated by in situ X-ray topographic observation. Dislocated crystals were found to melt homogeneously from their surfaces. Droplets of the silicon liquid (locally molten regions) were observed inside dislocation-free crystals, simultaneously with melting from their surfaces. After cooling from the melting process, microdefects were detected at the positions of the droplets by etching and transmission topography. Impurity hydrogen was found to suppress growth of the defects in size after solidification of the droplets. The formation process of the microdefects initiated from the droplet formation is explained by assuming some kinds of impurities which act as absorption centers for infrared radiation penetrating the crystals. As an origin of swirl defects in bulk crystals, the possibility of droplet formation near the growth interfaces during remelting periods is suggested.

Invited) Swirl Defects in Silicon Crystals

The current understanding of microdefects in a striated distribution (swirls) in dislocation-free crystals is reviewed with focusing on their formation mechanism. In float-zoned crystals, their formation is due to clustering of self-interstitials and/or impurity segregation which depend upon both growth conditions and cooling processes. A model for the origin of self-interstitials is proposed which is based on the in-situ X-ray topographic observation that liquid drops are formed inside of crystals by superheating and microdefects are generated by their solidification. A systematic presentation of the swirl formation is attempted in the basis of this model, in contrast with other models of the non-equilibrium incorporation of interstitials at the growth interface and the predominant equilibrium existence of interstitials near the melting point. For Czochralski-grown crystals, the nucleation center of oxygen precipitates is discussed in comparison with the swirl formation of float-zoned crystals.

Development of high-performance tri-layer material

As chip size and pattern size continue to shrink, the thickness of photo resist is getting thinner and thinner. One of the major reasons is to prevent the small resist features from collapse. Its very challenging to get enough etch resistance from such thin resist thickness. An approach of Si-tri-layer stack which consists of resist, Si ARC (Si contenting anti-reflection coating), organic underlayer from top to bottom has been adopted by many IC makers in the manufacturing of 45 nm node. Even higher resist etching selectivity is needed for 32 nm node. Si ARC, of Si content as high as 43%, provides good etch selectivity. At the same time, tri-layer also provides good control over reflectivity in high NA immersion lithography. However, there are several well know issues concern Si-rich ARC. Resist compatibility and shelf life are on top of the list. An aim of our development work was to overcome those issues in order to produce manufacturing-worthy Si-rich ARC. Several synthesis methods were investigated to form Si-rich ARC film with different properties. Collapse of resist patterns is used as an indicator of lithographic compatibility. Lithographic performance was checked by accelerated shelf life tests at high temperature in order to predict the shelf life at room temperature. It was found that adhesion between resist and Si-rich ARC is improved when contact angle of Si-rich ARC is increased to more than 60 degree. Certain synthesis methods improve shelf life. After optimization of film properties and synthesis methods of Si-rich ARC, SHB-A940 series have best litho compatibility and shelf life is six months at storage temperature below 10°C.