The effect of deposition temperature, deposition pressure, or input gas ratio (SiH2Cl2:NH3) on film stress was determined for low-pressure chemical vapor deposited silicon nitride films. Wafer curvature measurements were performed for films deposited on single crystal silicon and amorphous silica wafer substrates to determine film stress σdep, biaxial modulus Ef+, and coefficient of thermal expansion αf. Apparent plane strain film modulus Ēf′ and hardness H were measured using depth-sensing indentation. Ellipsometry was used to measure film thickness tf and refractive index n. Infrared spectroscopy, x-ray photoelectron spectroscopy (XPS), forward recoil energy spectroscopy (FReS), and Rutherford backscattering spectroscopy (RBS) experiments were performed to determine film composition. Although film deposition stress varied from −135 MPa (compressive) to 235 MPa (tensile) Ef+, Ēf′, H, and αf remained nearly constant. Infrared spectroscopy resolved only Si-N species for all films, and results from FReS on three films confirmed that the hydrogen content was negligible. RBS and XPS indicated that Si/N increased with increased compressive σdep. Ellipsometry and RBS indicated that all films were silicon-rich, to a greater extent with increased compressive σdep. As RBS indicated that atomic density decreased with increased compressive deposition stress, it was concluded that the deposition conditions changed both thermal and intrinsic deposition stress for all films. In particular, intrinsic stress was tensile, and became increasingly tensile for increased Si/N and decreased atomic density. Assuming thermal stress was similar for all films examined here, the intrinsic stress must have varied from changes dependent on the deposition conditions.

Changes in structure and properties of a commercial low dielectric constant ͑low-k͒ silsesquioxane ͑SSQ͒ material are examined as a function of curing temperature ͑375-450°C͒. Curing results in a chemical reaction in which cage-like (HSiO 1.5 ) SSQ oligomers network via -O-Si-O-linkages. A direct consequence of the chemical and structural evolution is a change in electrical and mechanical properties. A correlation is made between chemical and structural changes on curing ͑quantified by infrared spectroscopy͒ and the resulting dielectric constant, film stress, hardness, and modulus. In particular, infrared spectroscopy was used to quantify the increased -O-Si-O-oligomer network formed as a result of increased curing temperature. Film modulus and hardness, determined by depth-sensing indentation, were shown to increase as a result of increased networking. Residual film stress, determined by a curvature measurement technique, was determined to be tensile with increased magnitude on increased network formation. Film dielectric constant determined by capacitance measurements of metal dot structures increased as a result of increased network formation. Capping SSQ films with thin layers of SiN x was shown to greatly improve resistance to stress-corrosion cracking for all levels of network formation.

Articles you may be interested inModeling stress development and hydrogen diffusion in plasma enhanced chemical vapor deposition silicon nitride films submitted to thermal cycles Stress development kinetics in plasma-enhanced chemical-vapor-deposited silicon nitride films J. Appl. Phys. 97, 114914 (2005); 10.1063/1.1927708 Microbridge testing of plasma-enhanced chemical-vapor deposited silicon oxide films on silicon wafers Density change and viscous flow during structural relaxation of plasma-enhanced chemical-vapor-deposited silicon oxide filmsThe mechanical response of plasma-enhanced chemical vapor deposited SiO 2 to thermal cycling is examined by substrate curvature measurement and depth-sensing indentation. Film properties of deposition stress and stress hysteresis that accompanied thermal cycling are elucidated, as well as modulus, hardness, and coefficient of thermal expansion. Thermal cycling is shown to result in major plastic deformation of the film and a switch from a compressive to a tensile state of stress; both athermal and thermal components of the net stress alter in different ways during cycling. A mechanism of hydrogen incorporation and release from as-deposited silanol groups is proposed that accounts for the change in film properties and state of stress.

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A two-parameter “area function” characterizing the depth-dependent projected area of an indenter was introduced and applied to a Berkovich tip. The two parameters have physical meaning, corresponding to the effective tip radius and effective cone angle. The indenter tip was calibrated on a commercial load-controlled Nano Indentert® XP (MTS Systems Corp., Eden Prairie, MN). All calibrations were carried out using the procedure of Oliver and Pharr [J. Mater. Res. 7, 1564 (1992)] using several homogeneous materials. Plane-strain modulus and hardness values deconvoluted from indentation load–displacement traces using the calibrated two-parameter area function compared well with the values determined using the empirical eight-parameter area function of Oliver and Pharr.