For Nickel Silicide Sub-0.1¦Ìmcmos Device Technology,

As CMOS IC fabrication technology continuously progresses toward sub-0.1μm nodes, the self-aligned silicide (SALICIDE) material and technology also require corresponding innovations. Due to the limitation of narrow line effect, TiSi₂ is replaced by CoSi₂ in SALICIDE technology at 0.25/0.18μm node. Recent studies show that the sheet resistance (Rs) of CoSi₂ formed on poly-Si line with physical line width less than 40nm will dramatically increase. The silicon consumption for CoSi₂ formation is also much larger than NiSi, which conflicts with the shallow junction application. Besides, it is difficult for Co film to form low resistivity compound with SiGe material. With the development of nanometer scale CMOS technologies, NiSi has been considered as the most promising silicide for next generation SALICIDE technology.Because the formation temperature of NiSi is low enough and Ni atoms are always the dominating diffusion species during Ni/Si reaction, a single-step rapid thermal process (RTP) is accepted as one of its advantages in early studies. Recent investigation, however, has shown that NiSi formation by a single-step RTP may result in excess silicidation at the edges of patterned Si regions, which significantly degrades the device characteristics. A novel process technology, i.e., a two-step RTP is introduced to form NiSi, in which only partial as-deposited Ni film will be consumed and the high resistivity Ni₂Si phase will generally form during the first step RTP (RTP1) with an anneal temperature as low as 300℃, the unreacted Ni will then be removed by a wet etch, a second step RTP (RTP2) with a higher temperature is followed to form the low resistivity NiSi phase. So it is interesting to investigate the nickel silicidation in low temperature range and the two-step RTP NiSi SALICIDE technology. The main content and results of this thesis are summarized as follows.1. The solid state reaction of ultra-thin nickel film on both n+/p and p+/n junction substrates has been investigated in low temperature range. The film composition, structure and properties of the formed nickel silicide are characterized.- The experimental results demonstrate that the optimized process windows for RTP1 and RTP2 have been found for silicidation on both n+/p and p+/n junction substrates for CMOS fabrication.- The experimental results show that the Rs value of Ni-silicide formed on p+/n junction substrate is much higher than that on n+/p junction substrate after low temperature RTP1 anneal. With various material characterizations and analysis, it is revealed that the observed difference in Rs between Ni-silicide films should be attributed to the difference between the formed grain sizes. It is revealed that the dopant (As and B) will significantly redistribute after silicidation in the low temperature range, such as 300°C or 450°C. SIMS analysis shows that there is a dopant accumulation peak near the silicide/Si interface, which is caused by segregation and helpful to lower the contact resistance. In the meanwhile, the study reveals another dopant accumulation peak just several nm beneath the silicide surface. Further analysis shows that it is related to the void layer formed by the Kirkendall voiding effect usually observed in thin film reaction. According to the location of the void layer, the study demonstrates that although Ni atoms are the dominating diffusion species during Ni/Si reaction, Si atoms are not immobile, on the contrary they also diffuse into the Ni film and react with Ni there.2. To better control Ni/Si solid state reaction during RTP1, the formation kinetics of Ni2Si thin film is investigated. The kinetics model for Ni2Si formation is proposed, in which the linear-parabolic thin film growth kinetics is discussed. The study demonstrates that NiiSi thin film is more stable on n+/p junction substrate than on p+/n junction substrate. In the anneal temperature range between 262²77°C, the experimental results reveal that the growth of N12S1 thin film linearly depends on reaction time. It means that the film growth is dominated by Ni/Si interface reaction. The study shows that the activation energy for Ni2Si thin film growth in low temperature range is 1.35eV. This activation energy is successfully applied to explain different Rs-T curves.3. The NiSi SALICIDE technology with different RTP schemes has been studied by means of NiSi/Si Schottky contacts."" The experimental results demonstrate that the area-contact characteristics of NiSi/Si Schottky diodes by a two-step RTP are significantly improved comparing with a single-step RTP, i.e., the diode leakage is suppressed when a two-step RTP is applied. The study successfully investigates the dependence of the Schottky barrier height (SBH) distribution inhomogeneity of the NiSi/Si contacts on different RTP schemes by means of temperature dependent I-V technique (I-V-T), which demonstrates that the two-step RTP NiSi SALICIDE technology is superior to the single-step RTP case in the view of the SBH inhomogeneity.