Silicon Wafers with SiO2 or Si3N4
Thermal Oxidation of Silicon
Fields of Application
The electronic (resistivity 1014 ... 1016 Ohm cm, breakthrough field 106 ... 107 V/cm, barrier for electrons and holes from crystalline Si > 3 eV), mechanical (melting point approx. 1700°C) and optical (transparent in the visible as well as near infrared and ultraviolet spectral range) properties of SiO2 make it a suitable material for the dielectric film in transistors, capacitors (DRAM) or flash-memories; and as a hard mask for diffusion, implantation, wet or dry chemical etching; and generally as an isolator between integrated devices, or as an antireflection layer on e. g. solar cells.
Required SiO2 film thicknesses range from a few nm (gate-oxide of state-of-the-art CMOS transistors) up to several μm for electrical insulation. Compared to sputtered or CVD SiO2, thermal SiO2 reveals a better and more reproducible electrical insulation.
Compared to (crystalline) quartz, native (= few nm grown at room temperature in air) and thermal (growth temperature 800 - 1200°C) silicon dioxide (schema of an oxidation furnace right) is amorphous (= without longterm atomic lattice order). The silicon in native or thermally grown SiO2 evolves from the Si substrate, which is partially consumed during SiO2 growth: 100 nm SiO2 requires approx. 46 nm Si, while the wafer thickness simultaneously increases by approx. 54 nm.
Dry and Wet SiO2
One has to distinguish between dry oxide (Si + O2 -> SiO2), and – with H2O as process gas – wet oxide (Si + 2 H2O -> SiO2 + 2 H2). At the same process parameters, due to the higher growth rate, wet oxide reveals a higher porosity and HF etch rate.
Oxidation Rate and Attainable SiO2 Film Thickness
At the beginning of thermal SiO2 growth, the chemical reactions on the surface/interface limit the film thickness which increases linearly with time. With the SiO2 thickness increasing, the more and more dominating oxygen diffusion through the already-grown film towards the Si/SiO2-interface limits the growth rate. The SiO2 thickness now increases with the square-root of growth time.
Besides the process gas composition (O2/H2O), their partial pressure as well as the substrate temperature (activation energy of oxygen diffusion and chemical reaction at the Si/SiO2-interface), the SiO2 growth rate also depends on the Si substrate crystal orientation, mechanical strain of the substrate (e. g. in case of already processed device layers), as well as on substrate doping (e. g. faster oxide growth on phosphorous doped silicon).
Our Wafers with Thermal SiO2
We supply silicon wafers with dry (thin SiO2 films up to approx. 200 - 300 nm) or dry/wet/dry thermal oxide. The possible SiO2 thickness ranges from approx. 50 nm to 3 µm.
Silicon Nitride Coating
Fields of Application for Silicon Nitride
In the field of tool-making, stoichiometric trisilicon tetranitride (Si3N4) with its very high mechanical and thermal stability is used for tools such as roller bearings used under harsh conditions.
For semiconductor devices, the chemical, electrical and optical properties of amorphous hydrogenated silicon nitride (SiNx) make this material well-suited for different applications, such as for
- passivation or insulating layers in integrated circuits
- masking or etch stop material in wet and plasma etching processes due to its high chemical stability
- masking material in silicon oxidation processes due to the very low oxygen diffusion coefficient in SiNx
- anti-reflective coating in photovoltaics due to its adjustable refractive index
PECVD and LPCVD Silicon Nitride
SiNx layers realized by the plasma enhanced chemical vapour deposition (PECVD) technique from SiH4 and NH3 typically – depending on the deposition temperature and gas composition – contain 5 - 20 atom% hydrogen which saturates dangling bonds and thus chemically and mechanically stabilizes the SiNx lattice.
SiNx layers realized by the low pressure chemical vapour deposition (LPCVD) technique typically shows a lower H-content and higher stability against HF.
SiNx can be etched via photoresist masks either with buffered or unbuffered HF or (selectively to SiO2) with concentrated phosphoric acid. The HF etch rate of SiNx depends on the SiNx deposition temperature and its refractive index. A hydrogen-rich SiNx film deposited at 100°C with a refractive index of n = 1.9 shows an etch rate of several 100 nm/min in buffered HF (12.5 % HF). The etch rate drops to less than 10 nm/min for SiNx films deposited at 400°C with a refractive index of n = 2.
Properties of Amorphous SiO2 and SiNx Films
The table below lists “typical” values for selected amorphous SiO2 and SiNx film properties. Dependant on the deposition conditions, measured values can deviate from these values.
Our Wafers with PECDV or LPCVD Si3N4 / SiNx
We supply silicon wafers with silicon nitride films on either one side (PECVD) or both sides (LPCVD) with various Si3N4 thicknesses.:
- Available 4 inch Si + Si3N4 wafers: Our 4 inch Si+Si3N4 wafer stock list