Ultra Thin SiO 2 Mask Layer for Nano-Scale Selective-Area Pecvd of Si
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ABSTRACT We discuss the applicability of ultrathin SiO 2 layers as a mask for low-temperature selectivearea deposition of Si. Thin oxide layers with estimated thickness ranging from 4 to 20 A were formed by oxidizing H-terminated Si(100) surfaces by a remote plasma exposure at room temperature. Low-temperature selective-area deposition was carried out using two different techniques: flow-modulated plasma-enhanced chemical vapor deposition (FM-PECVD) using SiH 4 and H 2, and very low pressure CVD (VLPCVD) using Si 2H 4. We show that the ultra-thin plasma oxide layers exhibit good properties for a use as a passivating mask layer, and that the oxide layer can be patterned directly by E-beam irradiation. These results open up a possibility to realize Sinanostructures formation by selective-area processing. Degradation of the oxide layer by plasma processing is also discussed.
INTRODUCTION There is an increasing number of proposals and trials to realize novel devices incorporating three-dimensional and nano-scale structures. Future semiconductor processing to fabricate such advanced structures with an ultimate precision will require the technology for selective-area deposition and etching at a nanometer scale. Among the prerequisites to realize the selective deposition at reduced lateral dimensions are (i) formation and patterning of an ultrathin (< nm) mask and (ii) deposition chemistry compatible with the thin mask as well as with the reduced dimension. One important consideration in developing these techniques is the thermal budget: if the processing can be performed at low temperatures, it may be applied at later stages in a deviceprocessing flow when doping profiles and other constituents in the device have been already completed. In this paper, we investigated the applicability of ultra-thin SiO 2 layers as a mask for selectivearea deposition of Si. The oxide layer was formed by remote-plasma oxidation of a Hterminated Si(100) surface at a room temperature. We show that the ultrathin oxide layers thus prepared are compatible with two different chemistries for selective deposition: flowmodulated plasma-enhanced chemical vapor deposition (FM-PECVD) at 473 K, and very low pressure CVD (VLPCVD) using Si 2H6 at 823 K. We will also report an initial result of E-beam patterning of the ultra-thin mask layers.
271 Mat. Res. Soc. Symp. Proc. Vol. 448 01997 Materials Research Society
EXPERIMENTAL Figure 1 shows a schematic illustration of the multi-chamber CVD system constructed for this study. It is equipped with Auger electron microscope(AES), scanning electron microscope(SEM), and scanning tunneling microscope(STM) for in-line characterization of the processed samples. The substrates used in this study were p-type, boron doped, Si(100) wafers. The samples were first RCA-cleaned and were thermally oxidized to form a sacrificial oxide layer. Prior to each experiment, a H-terminated surface was prepared by etching off the sacrificial oxide in a 30:1 HF solution. A thin SiO2 mask layer was formed by exposing the H-termina
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