Stress and Microstructure Evolution in Mo Thin Films without or with Cover Layers during Thermal-Cycling

Abstract

The intrinsic stress behavior and microstructure evolution of Molybdenum thin films were investigated to evaluate their applicability as a metallization in high temperature microelectronic devices. For this purpose, 100 nm thick Mo films were sputter-deposited without or with an AlN or SiO2 cover layer on thermally oxidized Si substrates. The samples were subjected to thermal cycling up to 900 °C in ultrahigh vacuum; meanwhile, the in-situ stress behavior was monitored by a laser based Multi-beam Optical Sensor (MOS) system. After preannealing at 900 °C for 24 h, the uncovered films showed a high residual stress at room temperature and a plastic behavior at high temperatures, while the covered Mo films showed an almost entirely elastic deformation during the thermal cycling between room temperature and 900 °C with hardly any plastic deformation, and a constant stress value during isothermal annealing without a notable creep. Furthermore, after thermal cycling, the Mo films without as well as with a cover layer showed low electrical resistivity (≤ 10 μΩ·cm).

Thermomechanical and Creep Behaviors of Multilayered Metallization Systems Developed for High‐Temperature Surface Acoustic Wave Sensors

“…More descriptions about the reasons for the selection of such barrier and cover layers systems are available in the previous studies. [1,2,5,8,12,26] The schematic views of the metallization systems used in this study are shown in Figure 1. It is worth mentioning that the Si substrate is not used in the real application and the reason for using it as a substrate in this study is the isotropic behavior of the Si [100] in the wafer plane (cubic anisotropy) which is more convenient for the strain-stress and creep calculations compared to an anisotropic piezoelectric material which is required to fabricate SAW sensors.…”

“…Thin films consisting of pure molybdenum (Mo), molybdenumlanthanum oxide (MoLa), and ruthenium-aluminum (RuAl) are suggested metal films for electrodes of high-temperature (HT) surface acoustic wave (SAW) sensors based on our recent extensive researches on different multilayered thin film systems. [1][2][3][4][5][6][7][8][9][10] Despite the high performance temperature of the metallization systems made of these metals, they have characteristics such as low electrical resistivity and corrosion resistance, which make them a suitable choice for SAW sensor electrodes. [2,11,12] DOI: 10.1002/admt.202201979 HT-SAW sensors can be used for wireless sensing of temperature, pressure, and detection of gases, in turbine rotors, furnaces, ovens, etc., without any batteries or high sources of energy.…”

“…[1][2][3][4][5][6][7][8][9][10] Despite the high performance temperature of the metallization systems made of these metals, they have characteristics such as low electrical resistivity and corrosion resistance, which make them a suitable choice for SAW sensor electrodes. [2,11,12] DOI: 10.1002/admt.202201979 HT-SAW sensors can be used for wireless sensing of temperature, pressure, and detection of gases, in turbine rotors, furnaces, ovens, etc., without any batteries or high sources of energy. A very high reliable sensing operation at different high temperatures between 300 °C to 900 °C is expected for a HT-SAW sensor, which depends on the stability and durability of the electrodes (such as interdigital transducers (IDTs)) and the substrate materials.…”

“…Most studies on the metal films with HT applications have only focused on the material aspects for the development of a stable metallization system at high temperatures, such as the investigation of functional cover and barrier layers, tailoring a multilayer metal film for special applications, deposition, and stabilization process. [2,[10][11][12]17] So far, very little attention has been paid to the intrinsic stress due to the deposition process, as well as the thermomechanical and creep behaviors of these films. [2] Moreover, the comparison of the metallization systems' behaviors with each other would give some significant insights into the effectiveness of each film.…”

“…[2,[10][11][12]17] So far, very little attention has been paid to the intrinsic stress due to the deposition process, as well as the thermomechanical and creep behaviors of these films. [2] Moreover, the comparison of the metallization systems' behaviors with each other would give some significant insights into the effectiveness of each film.…”