Micron-Size and Submicron-Size Light-Emitting Porous Silicon Structures
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ABSTRACT We have developed three classes of techniques to produce micron-size and submicron-size lightemitting porous Si (LEPSi) patterns and to protect the rest of the wafer. In the 1st class, LEPSi lines down to 2 4m width have been made using a photoresist/silicon nitride trilayer mask, followed by anodization. PL mapping of the structures indicates that the protected regions have not been etched. Using electron beam lithography sub-0.5 micron porous Si lines have been generated. In the 2nd class, formation of porous Si is inhibited by amorphizing Si using ion implantation followed by anodization and annealing. The crystallinity and electrical properties of the implanted region have been fully characterized after annealing. Using focussed ion-beam implantation, LEPSi patterns of the order of 100 nm have been obtained. The 3rd class consists of enhancing the formation of porous Si by a low energy/low dose bombardment (ion-milling) with argon ions prior to anodization. Under appropriate conditions, we have observed a strong enhancement of the formation rate of LEPSi where bombardment took place, possibly due to the generation of a large number of defects on the wafer surface. INTRODUCTION Light-emitting porous Si (LEPSi) has shown considerable promise as an optoelectronic material which can be integrated with the state-of-the-art c-Si technology[]]. Integration of porous Si devices with conventional Si microelectronics requires the fabrication of very small porous Si regions in close proximity to Si circuitry. Previously, Barbour et al. [2] have reported formation of LEPSi patterns by the quenching of luminescence with ionirradiation. Patterns were also formed by image projection using photolithography [3,4]. Steckl et al. [5] have demonstrated 0.5 4m wide LEPSi patterns in stain-etched samples using focussed ion-beam (FIB) Ga+ implantation. Bao & Yang [61 have reported - 2 4m wide patterns of anodized porous silicon by amorphizing with Si+ implantation. In this work, we report three methods which can produce sub-micron light emitting porous silicon regions. First, we have optimized a trilayer lithographic process [1] employing crosslinked photoresist (PR) and silicon nitride (Si 3N 4 ) masks for the fabrication of - 2 4m LEPSi patterns. Smaller dimensions were realized using electron-beam lithography. Second, we have developed ion-implantation as a tool for biasing the anodization process. We have confirmed that the resultant amorphized silicon is resistant to anodization and more significantly, that it recovers its crystalline properties after post-etch annealing. We also carried out a maskless Ga+ focussed ion-beam (FIB) implant to generate LEPSi lines of the order of 100 nm. Third, we investigated the possibility of enhancing the formation of LEPSi by introduction of surface defects. Since in conventional Si processing high defect densities caused by surface damage almost always enhance the etch rate [7], we exposed c-Si samples to ion-milling and reactive ion-etching prior to anodization. It was observed that
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