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The stress state of low-pressure chemical vapor deposition (LPCVD) silicon dioxide (SiO2) films fluctuates upon aging due to the ambientmoisture. The related variation of the SiO2 films is a key factor of device reliability. In this study, ion implantation is introduced to improve film stress stability. The stress state modified by ion implantation is discussed in detail and an analytical model is presented. The evolution of the stress in as-deposited and P+-, As+-,and B+-implanted LPCVD SiO2 films upon aging is investigated, and the bonding nature of the films is also studied to provide insight into the physical mechanisms involved. It is demonstrated that low implantation energy slightly modifies the stress in films. In addition, P+ ion is the most appropriate impurity ion to improve film stress stability, and the stress in P+-implanted LPCVD SiO2 filmcan be stabilizedwith a lowtensile stress of 67MPawhen the film is implanted at 15 keV with a dose of 1 × 1015 cm?2.

Low-pressure chemical vapor deposition (LPCVD) is a basic thin film deposition technology. Silicon dioxide (SiO2) films grown by LPCVD are widely used in integrated circuits (ICs) and microelectromechanical systems (MEMS). They are commonly employed as the passivation layer, mask layer or sacrificial layer. Due to their good mechanical and insulating properties, LPCVD Silicon dioxide films can also be used as the structural layer of MEMS devices, such as the membrane of vibrating resonators, the dielectric of micro-scanning mirrors, and the cantilever of infrared (IR) imaging detectors.

Stress is inherent in LPCVD Silicon dioxide films due to deposition processes, and it has a significant influence on the performance of devices. Stress in LPCVD SiO2 films is known to be prone to drift with time in the ambient atmosphere, which would cause structural deformation and functional degradation. This is an important issue related to the device reliability. A lot of researchers have studied the stress evolution of SiO2 stored in the ambient atmosphere. Haque and Guan et al. showed that the stress continues to decrease progressively with increasing aging time. Park et al. pointed out that the evolution of stress is due to both structural changes in Si―O network and water molecules absorbed on walls of the pores. Bakos et al. reported that the most stable form of water in SiO2 is the interstitialmolecule, and vicinal silanol groups may form at a low-energy cost with a barrier of 1.5 eV.


 

 

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