Gaseous Impurities in Co Silicidation: Impact and Solutions

Abstract

With the application of a Co salicide process in deep submicrometer integrated circuits manufacturing, the potential benefit of its linewidth independent sheet resistance could be hindered due to the interaction of traces of gaseous impurities from different sources with silicide formation. In this work, we first analyze in situ the thermal desorption behavior of various dielectric and metal layers encountered in Co salicide process, by using the rapid thermal processing tool-atmospheric pressure ionization mass spectrometry. Based on these results as well as information from the literature, the detrimental impact of gaseous impurities ͑mainly O 2 and H 2 O͒ has been analyzed. The key facts are that Si has a stronger chemical affinity to O than Co, and the interaction of Co and Si oxide occurs only with great difficulty. We also argue that impurities from thermal desorption can have a stronger impact to the silicidation ͑edge thinning effect͒ compared to the impurities already in the processing ambient, due to its strong and direct interaction to the adjacent Co/Si interface. The fundamental principle of a technical solution is that the process should prevent O from coming into the Co/Si interface, and/or should be capable of removing the Si oxide already there. A few solutions reported in literature, including depositing Co at elevated temperatures, Co with reactive or nonreactive capping, and the use of Co͑Ti͒ alloys, are analyzed.

Monitoring and purging dynamics of trace gaseous impurity in atmospheric pressure rapid thermal process

“…However, if the prepurging time or flow rate was not enough, the discoloration was always observed on part of the Ti film that was close to the door exhaust. 5 Light brown discoloration at the rear edge extends to a large area. 2͒.…”

“…[1][2][3][4][5] The sources of trace gaseous impurities in atmospheric pressure process chamber are from: ͑1͒ Clean room ambient gases streaming into the chamber during wafer loading or backdiffusion from the vent lines, ͑2͒ air leaks when the pressure in the chamber is lower than the ambient pressure, such as 759 to 760 Torr, ͑3͒ thermal desorption during wafer heating, and ͑4͒ gaseous impurities hidden in traps ͑deep gaps, holes, etc.͒ in the chamber. The residual gaseous impurities in these equipment are becoming an important factor in device failure thereby threatening production yield in the submicron ultralarge scale integrated industry.…”

“…13 Oxygen monitoring was successfully performed on a commercial RTP system by using a zirconiaoxygen sensor. 5,13 Ti-coated wafers are widely used for trace O 2 monitoring in the RTP industry. Recently, atmospheric ionization mass spectrometry ͑APIMS͒ has been used as a very sensitive technique to detect trace impurities a͒ Electronic mail: yaozhi.hu@mattson.com at atmospheric pressure in some research laboratories.…”

Quantitative Evaluation of Cobalt Disilicide/Si Interfacial Roughness

“…This purification is needed because the CoSi 2 formation process is highly sensitive to traces of oxygen-containing impurities in the annealing ambient. 16 Extremely low levels of these impurities are essential for smooth CoSi 2 formation. 12 Indeed, attempts to form CoSi 2 from Co x N by ex-situ RTA were unsuccessful owing to the sample contamination during the exposure to the air and the annealing ambient (our ex-situ RTA tool does not use purified gas for annealing).…”

Effect of CoSi2Formation Process on CMOS Transistor Electrical Properties for Sub-100-nm Memory Applications

“…[9][10][11] For this reason, extensive studies have been done to minimize annoying silicide spikes or avoid strange penetration into bulk Si. Despite the necessity for a clean surface, oxide insertion into the Co/Si interface tends to be employed to mitigate the drastic Co-Si reaction.…”