In low-dielectric-constant (low-k) materials, the dielectric constant is reduced through a reduction in electronic polarization or through the introduction of porosity. For ultra-low-k (k value less than 2.4) materials, introduction of porosity is a common method. However, this reduces the mechanical strength of the materials. In this work, two types (carbon-based and silica-based) of spin-on porous ultra-low-k materials are studied. The mechanical properties, including hardness, Young's modulus, stress, stress hysteresis, and adhesion properties of the films are investigated. Compared with the dense low-k materials, the hardness and Young's modulus of the ultra-low-k films are low. The residual stress for the ultra-low-k films on bare Si wafer at room temperature is less than 100 MPa. The stress decreases from tensile to compressive with the increasing temperature up to 430 degreesC, and returns to the initial value as temperature decreasing to room temperature. Scotch tape test, Stud pull test, and chemical mechanical polishing (CMP) check are used for adhesion characterization. No peeling is found between the ultra-low-k materials and the underlying layer SiC after Scotch tape test. (C) 2004 Elsevier B.V. All rights reserved.