CONTROLLED REACTION ON INTERFACE OF Cu/Cu(Ge, Zr)/SiO2/Si MULTILAYER FILM AND ITS THERMAL STABILITY

A self-formation barrier method using CuX (X=Mn, Ti, Zr, Ru, RuN, WN, Ge, etc.) alloys with various concentration solutes has been extensively investigated to meet the requirements of low sheet resistivity, ultra-thin and high thermal stability for Cu metallization. However, intolerable reactions would take place at the interface of the Cu alloy layer and SiO2/Si layer before the processing temperature reaches high enough to drive the mass migration of alloy elements to interface. In fact, the reaction of Cu alloy layer with SiO2/Si layer is almost unavoidable due to that Cu diffuses very fast in Si substrate below 200 degrees C. Among those Cu-based alloys, CuGe alloy system has received particular attention because Cu can directly react with Ge below 150 degrees C and forms epsilon-Cu3Ge films which exhibit a remarkable resistivity (5.5 mu Omega.cm), and the Cu3Ge films also possess high oxidation resistance and interface bonding performance, so can be used as a good diffusion barrier for Cu as well. However, two major problems prevent it from being put into practice. The first is that the mutual diffusion occures between the Cu3Ge films and the Si substrates above 400 degrees C, and lead to a notable increase in resistivity. The second one is that the germanide film degrades morphologically at 350 V. Therefore, according to the deficiencies existing in these Cu-based alloys, the main objective of the present research aims at taking advantage of the selective reaction characteristic of Cu, Ge and Zr elements to achieve a controlled interface reaction behavior of Cu/Cu(Ge, Zr)/SiO2/Si multilayer. The multilayer structure was characterized by FPPT, XRD, TEM, XPS and EDS. The results showed that the reaction sequence of the atoms in Cu(Ge, Zr) films and adjacent layers affected the thermal stability of Cu/Cu(Ge, Zr)/SiO2/Si multilayer structure. Under the temperature of 200 degrees C, Ge atoms reacted selectively with Cu film and produced epsilon-Cu3Ge phase which exhibitted a remarkably low metallic resistivity, and the Cu3Ge phase could be used as a good diffusion barrier. With further increasing annealing temperature (above 450 degrees C), Zr atoms precipitated at the interface or grain boundary of Cu3Ge layer and reacted with silicon oxide further to form stable and ultra-thin amorphous ZrOx/ZrSiyOx compounds. So the Cu3Ge layer combined with the amorphous ZrOx/ZrSiyOx compounds provided superior barrier properties in reducing Cu diffusion into Si at high annealed temperature.