• PDF / 630,496 Bytes
• 11 Pages / 584.957 x 782.986 pts Page_size
• 117 Downloads / 196 Views

DOWNLOAD

REPORT

---

Wei-Chao Chen and Kuei-Hsien Chen Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan

Chien-Ting Wu and Li-Chyong Chen Center for Condensed Matter Sciences, National Taiwan University, Taipei 106, Taiwan (Received 25 May 2011; accepted 28 December 2011)

The effect of direct current (dc) substrate bias on the promotion of nanocrystallization in Si network has been studied, specifically within He-diluted SiH4 plasma in radio frequency (RF)-plasma-enhanced chemical vapor deposition. In view of organizing nanocrystallinity, controlled transmission of energy to the growing surface is needed and that is obtainable from metastable helium (He*) bombardment and, in particular, ionic helium (He+) bombardment under negative substrate bias. The structural morphology has been adequately regulated to a homogeneous network restraining from an exclusive columnar structure that is coherent to low-temperature growth. Notable improvements in the film quality in terms of enhanced crystallinity with low hydrogen content as well as reduced incubation volume, bulk void, and surface roughness have been demonstrated, even at low substrate temperature and low RF power. Use of appropriate dc substrate-bias has been identified as a supplementary parameter efficiently organizing the growth, making it more device-friendly.

I. INTRODUCTION

The perpetual technological urge on the miniaturization of semiconductor devices has driven the demand for thin dielectric films that makes the surface and interface structure of multilayers crucial to the performance of devices. A rough surface of individual layer tends to have a higher interfacial trap density, and that induces inherent nonuniformity in the growth of subsequent overlayers. Rough surfaces are usually accompanied by columnar growth that leads to serious quality degradation of devices. Thus, understanding the surface roughness and columnar growth mechanisms involved in the bulk and suppressing them is of great significance, both for fundamental research and for device applications. One successful method for fabricating thin films with smooth interfaces is chemical vapor deposition (CVD) at relatively high processing temperatures. High temperature provides extensive film precursor diffusion on the surface, leading to improved crystallinity.1,2 The highly mobile precursor species are able to move about the surface, filling in voids, suppress the formation of porous microstructures that lead to surface roughness. Although

a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.4 J. Mater. Res., Vol. 27, No. 9, May 14, 2012

moderately high substrate temperatures are favorable for forming smooth film interfaces, they are also incompatible with many temperature-sensitive materials such as some optical plastics. Using Ar as a diluent to the (SiH4 + H2)plasma improved crystallinity was reported in P-doped microcrystalline (lc)-Si:H films even at a very low thickness.3 Despite this, smooth surfaces with featureless microstructure are still obt