Nano-graphoepitaxy of semiconductors for 3D integration
The advantages of integrating semiconductor devices at more than one level (3D integration) are now recognized. Key to achieving monolithic 3DICs is the ability to form single crystal semiconductor islands at the upper level without unduly heating the lower level structures. In prior work a surface relief grating of 3.8?m pitch in the substrate was used to mediate single crystal formation while continuous wave (CW) heating a thin film of amorphous silicon; the term graphoepitaxy was coined. CW heating is not possible in our case because it would overheat the lower layers. Moreover the area of the crystallites need only be about 100nm to accommodate todays transistors. Thus we have chosen a substrate grating pitch of 190nm (hence the term nano-graphoepitaxy) and a modulated CW laser to reduce the heating time to several ?s. Preliminary results indicate the substrate grating lines can indeed determine the position of the crystallite boundaries when the film thickness is 100nm; the effect is much less pronounced in 500nm thick films.
graphoepitaxy crystallization nanoimprint transient heating