212th ECS Meeting, Abstract #1148, © The Electrochemical Society STRUCTURAL AND MORPHOLOGICAL PROPERTIES OF NITROGEN DOPED POLYSILICON FOR ADVANCED GATE MATERIAL

Polysilicon (poly-Si) is mainly used as gate material for metal-oxide-semiconductor (MOS) based devices. As the dimensions of the MOS based devices keep shrinking, their performance depends critically on the film properties such as surface morphology and grain size distribution. Especially, it is strongly required that poly-Si gate has a uniform grain size distribution through the entire film stack to keep endurance and reliability of the devices [1]. In this work, improvement of the grain size distribution and morphology of poly-Si was investigated using nitrogen doped poly-Si. Nitrogen doped poly-Si was deposited by low pressure chemical vapor deposition (LPCVD) from silane (SiH4) and ammonia (NH3). The temperature and NH3/SiH4 ratio were varied, and their effects on deposition rate, nitrogen concentration, surface roughness, and grain size were discussed. The deposition rate of nitrogen doped poly-Si decreased with increasing NH3/SiH4 ratio (Figure 1). It was because the pyrolysis of SiH4 was inhibited by the presence of NH3. NH3 reacts with SiH4 to increase H2 concentration in the gas phase [2], resulting in a decrease in the deposition rate. The surface roughness of nitrogen doped poly-Si also decreased with increasing NH3/SiH4 ratio (Figure 2). Therefore, it can be said that the roughness of nitrogen doped poly-Si is related to deposition kinetics rather than to microstructure