Question

The SiO\(_2\) is grown by exposing the epitaxial layer to an oxygen atmosphere while being heated to about 1000\(^\circ\)C, because Silicon dioxide has the fundamental property of

• A. Preventing the diffusion of impurities
• B. Electrical isolation between different circuit components
• C. Prevent the depletion region of the reverse biased isolation to substrate junction
• D. Sidewall capacitance reduction

Hint:

SiO\(_2\) is a cornerstone material in silicon IC technology.
Its key properties are: excellent electrical insulator, effective diffusion mask for common dopants, good surface passivation.
Thermal oxidation of silicon is a common method to grow high-quality SiO\(_2\) layers.

Answer 1

The Correct Option is A

Silicon dioxide (SiO\(_2\)) grown or deposited on silicon wafers plays several crucial roles in integrated circuit (IC) fabrication. The process described (heating in an oxygen atmosphere) is thermal oxidation, a common way to grow high-quality SiO\(_2\) layers. Key properties and uses of SiO\(_2\) in ICs:
Diffusion Mask/Barrier: SiO\(_2\) is an excellent barrier against the diffusion of many common dopant impurities (like boron, phosphorus, arsenic) into the silicon substrate at high temperatures used during diffusion or ion implantation steps. This allows for selective doping of specific regions of the wafer by patterning the SiO\(_2\) layer (opening windows where doping is desired). This is a fundamental property used in planar technology.
Electrical Insulator/Dielectric: SiO\(_2\) is a very good electrical insulator. It is used as the gate dielectric in MOSFETs, for isolation between metal interconnect layers (interlayer dielectric - ILD), and for surface passivation.
Surface Passivation: An SiO\(_2\) layer protects the silicon surface from contamination and provides electrical stability by reducing surface states. Let's analyze the options: (a) "Preventing the diffusion of impurities": This is a primary and fundamental property of SiO\(_2\) used extensively in IC manufacturing as a mask for selective doping. (b) "Electrical isolation between different circuit components": While SiO\(_2\) is an excellent insulator and is used for isolation (e.g., LOCOS, STI, interlayer dielectric), the statement in the question about growing it on an "epitaxial layer" and its "fundamental property" points more directly to its role as a diffusion barrier during processing steps that often follow epitaxy or occur on the wafer surface. (c) "Prevent the depletion region of the reverse biased isolation to substrate junction": This is more related to specific isolation techniques (like junction isolation) rather than a fundamental property of SiO\(_2\) itself in the context of general impurity diffusion. SiO\(_2\) might be part of an isolation structure, but its role as a diffusion barrier is more direct. (d) "Sidewall capacitance reduction": While dielectrics are involved in capacitance, this is a very specific application and not the most "fundamental property" being leveraged by growing SiO\(_2\) for processing. Low-k dielectrics are specifically chosen for this, SiO\(_2\)'s k is ~3.9. Considering the fundamental properties, its role as a diffusion barrier (mask) is extremely critical and widely utilized in forming doped regions. This aligns well with "preventing the diffusion of impurities." \[ \boxed{\text{Preventing the diffusion of impurities}} \]