Microstructures of Tungsten Suicide Films Deposited by CVD and by Sputtering
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ABSTRACT Microstructure changes, after annealing, of tungsten silicide (WSix) films formed on the polysilicon films by CVD (chemical vapor deposition) and by sputtering were compared. For both CVD and sputtered WSix films, microstructural evolutions during annealing were caused by three mechanisms; crystallization from amorphous phase, stoichiometrical change, and grain growth. The microstructures and the electrical resistances of WSix films after annealing were depended on the deposition method. The movement of excess Si in WSix film to poly-silicon during annealing was faster in case of sputtering than in case of CVD. At annealing temperature below 850 0 C, CVD films showed higher resistivity and smaller grain size than sputtered films. On the other hand, at anneal temperature above 8500C, the grain growth rate of the CVD film was higher than that of the sputtered film, and the CVD film resulted in lower resistivity than the sputtered film. The retardation of grain growth for the sputter-WSix film is thought to be caused by impurity contamination such as argon added into the film during sputtering.
INTRODUCTION Among silicide materials, technologies based on WSix polycide gate and interconnect are well established in metal oxide semiconductor (MOS) device applications due to its excellent thermal stability and VLSI (or ULSI) process compatibility. The WSix film can be deposited via all the conventional methods used in the integrated circuit processing, i.e. sputtering [1-3] and chemical vapor deposition (CVD) [4-6]. Therefore, the deposition and the characterization of the WSix film has been the subject of a number of investigation. As a result, CVD-WSix is becoming widely used because the film has low resistivity, less contamination of oxygen, and good step coverage [5]. However, with the use of the WSix film deposited by the CVD method as a gate electrode, problems occur with adhesion of the silicide material on phosphorus-doped polysilicon and degradation of the electrical breakdown of the gate SiO 2 film. Many fluorine and hydrogen atoms are included in the CVD-WSix when depositing [7,8]. The diffusion of fluorine included in the CVD-WSix film is one of the causes in degradation of electrical breakdown of the Si0 2 film when the CVD-WSix film was used as a gate electrode in MOS integrated circuits [9-11]. Sputtered WSix film also has been studied to determine their compatibility with integrated circuit fabrication processes. Although many experimental results about characterization of the WSix film has been published, there is few report about direct comparison between different deposition methods of the WSix film. In application of the WSix film in ULSI devices, which deposition method between CVD and sputtering is more effective in process integration is important because degradation by fluorine diffusion into gate oxide below 10 nm will be more severe. In this study, microstructure changes, after annealing, of WSix films with 150 nm thickness formed on the poly-silicon films by CVD and by sputtering were
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