铝和铜互连线的晶粒结构及残余应力研究

采用X射线衍射仪和扫描探针显微镜,观察和测量了分别由大马士革工艺制备的Cu互连线和由反应刻蚀工艺制备的Al互连线的晶粒结构和应力状态.大马士革工艺凹槽中的Cu互连线受到机械应力的影响,使Cu互连线的晶粒尺寸(45~65 nm)小于Al互连线的晶粒尺寸(200~300 nm);Cu互连线(111)的织构强度(2.56)低于Al互连线(111)的织构强度(15.35);Cu互连线沿线宽方向的应力σ22随线宽的减小而增加,即沉积态和退火态的Cu互连线的σ22由73和254 MPa(4μm线宽)分别增加到104和301 MPa(0.5μm线宽).Cu互连线和Al互连线的流体静应力σ均为张应力.Al互连线的主应力σ11、σ22和σ33随Al膜厚度的减小而增加.退火使Al互连线的σ11、σ22和σ33降低,表明Al互连线中的残余应力主要为热应力.

Study on Grain Structures and Residual Stresses of AI and Cu Interconnects

Grain structures and stress states were observed and measured by using the x-ray diffractometer and the atomic force microscope for Cu and Al interconnect lines fabricated by damascene processing and reactive ion etching processing, respectively. Due to the influence of the mechanical stress on the Cu line in the damascene trench, the grain size of Cu lines (45～65 nm) was smaller than that of AI lines (200～300 nm) ; the strength of (111) texture of Cu lines (2.56) become weaker than that of Al lines (15.35) ; and the stress across the lines σ_(22) increased with the decrease in Cu line width, i. e. , for deposited and annealed Cu lines, σ_(22) increased from～73 and～250 MPa (4 μm-line width) to ～ 104 and 301 MPa (0. 5μm-line width), respectively. The hydrostatic stress σ was tensile for Cu and Al lines. Stresses, σ_(11)、σ_(22) andσ_(33) of Al lines increased with decrease in Al film thickness. Stresses, σ_(11)、σ_(22) and σ_(33) of Al lines decreased after annealing, indicated that thermal stress was the main contributor to residual stress in Al lines.