Influence of underlying interlevel dielectric films on extrusion formationin aluminum interconnects

Knowledge of the mechanical properties of interlevel dielectric films and t heir impact on submicron interconnect reliability is becoming more and more important as critical dimensions in ultralarge scale integrated circuits a re scaled down. For example, lateral aluminum (Al) extrusions into spaces b etween metal lines, which become more of a concern as the pitches shrink, a ppear to depend partially on properties of SiO2 underlayers. In this articl e nanoindentation, wafer curvature, and infrared absorbance techniques have been used to study the mechanical propel-ties of several common interlevel dielectric SiO2 films such as undoped silica glass using a silane (SiH4) p recursor, undoped silica glass using a tetraethylorthosilicate precursor, p hosphosilicate glass deposited by plasma-enhanced chemical vapor deposition and borophosphosilicate glass (BPSG) deposited by subatmosphere chemical v apor deposition. The elastic modulus E and hardness H of the as-deposited a nd densified SiO2 layers are measured by nanoindentation. The coefficients of thermal expansion (CTE) of the densified layers are estimated by tempera ture-dependent wafer curvature measurements. Fourier transform infrared spe ctroscopy is used to obtain the chemical structures of all SiO2 layers. Amo ng the four common interlevel layers, BPSG exhibits the smallest modulus/ h ardness and a relatively small amount of moisture loss during anneal. The B PSG shows the highest CTE, which generates the smallest thermal stress due to a closer match in the CTE between Al and SiO2. BPSG again has the lowest as-deposited compressive stress and the lowest local Si-O-Si strain before annealing. The center frequency of the Si-O bond stretching vibration exhi bits a linear dependence on total film stress. The shifts of Si-O peaks for all the SiO2 layers also correlate well with the stress hysteresis obtaine d from wafer curvature measurements. Stress interactions between the variou s SiO2 underlayers and the Al metal film are also investigated. The impact of dielectric elastic properties on interconnect reliability during thermal cycles is proposed. (C) 2000 American Vacuum Society. [S0734-211X(00)04206 -2].