Transfer of Ultra-Thin Semi-Conductor Films onto Flexible Substrates

Abstract

Applying tensile strain on an undirect band gap semiconductor crystal is a very promising way to tune it into a direct band gap [1] , [2] . This basic feature can be an outstanding progress for the use of classical semiconductor as silicon or germanium in interesting optoelectronic applications [3] . One way to apply a tensile strain is to transfer an ultra-thin of semiconductor onto a flexible substrate [4] (erg: an organic polymer). The goal of this paper is to propose a simple way to obtain an ultra-thin silicon film (<200 nm) onto an expendable polymer. It consists in transferring an Unibond™ SOI silicon thin film onto a classical tape maintain by a dicing frame. This process is mainly based on classical temporary bonding process. As shown on figure, a first process is carried out onto 200 mm wafer with a SOI silicon film of 200nm and a buried oxide box of 400nm. No default is observed on the full stack after the grinding and etching steps used to remove the SOI backside substrate. No SiO2trace is also observed after the last dioxide etching. The thin silicon film is then characterized and no crack is observed. The stack is then laminated onto a frame with a Furukawa SP-537T-230 adhesive tape. The demounting of the carrier is easy and no default appears on the silicon film. The last process consists in removing the glue from the silicon. We obtain a 200 nm silicon film bonded onto the tape. Nevertheless, this glue removal leads to the appearance of some cracks ono the silicon thin film. A second process will then be presented in order to avoid the last glue removal steps and improving the final thin film quality. XRR characterizations of the transfered thin film will be presented as well as potential amount of tensile stress achievable with this unique structure. [1] Ju Li et al., MRS Bulletin, 39, pp 108-114, 2014 [2] Feng Zhang et al., Phys. Rev. Lett. 102, 2009 [3] Diode Lasers and Photonic Integrated Circuits, Second Edition, 2012 John Wiley & Sons, chap 4 [4]& Salvatore Giovanni A.et al., ACS NANO Volume 7, Issue: 10, P8809-8815, 2013 Figure 1