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Themechanism of stress evolution in Silicon Dioxide(SiO2) has been gradually understood. However, there is still lack of an effective way to stabilize the film stress in the ambient atmosphere. In thiswork, ion implantation is used to stabilize the stress in LPCVD SiO2 films. Ion implantation is an attractive method since the implantation dose and energy can be accurately controlled and the implanted ions can precisely affect the Si―O network. The stress state of LPCVD SiO2 films implanted at different energies is studied, and an analytical model is developed to describe the stress modification. Then the effects of implantation ion types and doses on the stress evolution upon aging are systematically investigated, and a physical mechanism is proposed and discussed.

The experimental procedure startswith 4-in. siliconwafers. 300nm thick Silicon Dioxide(SiO2) films are prepared by a Thermco LPCVD furnace using tetraethylorthosilicate (TEOS) as the source material. The deposition temperature is 730 °C, and the total deposition pressure is 0.5 Torr. The back-side  Silicon Dioxide(SiO2) films are removed by buffered oxide etch (BOE), while the front-side films are protected by MEGAPOSIT S9920 photoresist. Next, the photoresist is removed by acetone, and the front-side SiO2. films are rinsed by de-ionizedwater. Annealing at 800 °C for 120min in a nitrogen (N2) filled furnace is then taken to make the front-side SiO2 film densification. After that, one sample is used as a reference, and others are separately implanted with phosphorus (P), arsenic (As) or boron difluoride (BF2) by a ULVAC IM-200Mimplanter. P, As and BF2 are chosen because they are commonly used as impurities in ICs and MEMS. BF2 is used instead of boron (B) for ultra-shallow B+ ion implantation, B+ and F+ ions are dissociated in the process of implantation, and F+ ion outdiffuses and leaves the films after annealing.

The Silicon Dioxide(SiO2) film thickness ismeasured using a Nanometrics NanoSpec AFT 4000 by analyzing the interference spectra when light passes through the film. Film stress is measured with the wafer curvature measurement technique by a KLA Tencor FLX 2320S. The effects of ion implantation on the stress evolution are studied by a Thermo Scientific Nicolet 6700 Fourier transform infrared spectroscopy (FTIR) Spectrometerwith optic resolution of 0.09 cm?1 in themid-IR range (400–4000 cm?1). A bare silicon wafer is firstly scanned to obtain the reference spectrum. Thus, the influence of substrate on the films can be eliminated by differential spectrum technology. Film surface morphology is analyzed using a dimension icon atomic force microscopy (AFM) (Bruker Dimension Icon?). The silicon (Si) tip is used in tapping mode with a scan area of 5 × 5 μm2. The surface roughness (Rq) is measured by using the root mean square (RMS) method.


 

 

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