Why use silicon in wafer fabrication?

Question

Why use silicon in wafer fabrication?

Answer 1

Abundant, possess the desired semi-conducting properties.

Answer 2

Silicon is prevalent in wafer manufacturing because of its abundance and low cost as an unprocessed material, trading off a not entirely ideal semiconductor property (but still very good) for these qualities.  Another heavily used semiconductor wafer is gallium arsenide, particularly for its optical properties as a semiconductor.  It is the semiconducting material used for LEDs, microwave frequency integrated circuits (ie, MMICs for switching speeds > 250GHz), laser diodes and solar cells, but it is also much less prevalent in nature and thus more expensive.

Answer 3

The reason is that it is the cheapest material to use for integrated circuits. A number of features support this requirement, including processability and especially oxide formation, high density (small junctions), high yields, compatability with interconnects (Al and polysilicon), adequate electrical, mechanical and thermal performance. GaAs has low density, high defect rate, poor adhesion with metals, and I don't think it has any good oxides. Very brittle and hard to work with for folks used to silicon.

It is a semiconductor with adequate performance. The processability means it is relatively inexpensive to grow the necessary large single crystals. The crystals are relatively perfect, leading to small numbers of defects in the IC's. This is critical for yield. Also, well suited for very small junctions, which is key for density. Adequate properties to make huge wafers, supporting low cost mass production.

Compatible with many dopants of varying concentrations, and with high gradients, of both n-type and p-type. High concentrations can yield high voltage devices, while lower dopant concentrations with high gradients are ideal for small Gold and certain other metals can be used as dopants to make Schottky diodes, a very nifty device.

It easily forms a tight insulating oxide. The oxide can be easily removed with certain acids. It nicely supports  photolithography, a basic technology that makes mass production of IC's feasible. Oxide isolation trenches allow highly radiation resistant IC's.

It is compatible with and bonds metallurgically with an appropriate metal (Al) for interconnects. Copper interconnects are less compatible, but also being occaisionally used, and appear nearly ready for mass use.

It has adequate strength to readily bond wires ultrasonically or thermosonically to metal pads, unlike GaAs. It is also compatible with polysilicon interconnects.

Adequate properties to minimize chipping when dicing (cutting wafers into individual dies). Good thermal conductivity, modest thermal expansion.

Relatively inert material not seriously attacked by most chemicals.

On the down side, the energy levels are poorly suited to LED's, I don't think it is used for them anymore. Forward voltage drop is somewhat high, though Schottky diodes are much lower, especially at temp. Resistance is a little high, but you can go with high concentrations of dopants and more junction area. It's a brittle material that is difficult to handle, requiring considerable care. Very subject to ionic contamination. Over the years, a variety of techniques have been developed to sucessfully work around silicon limitations.