Question

Method used for obtaining highly pure silicon used as a semiconductor material, is: (a) electrochemical (b) oxidation (c) zone refining (d) crystallization

Short answer

Zone refining is used to obtain highly pure silicon for semiconductors.

Step-by-step solution

Understand the Requirement for Purity

Silicon used in semiconductors needs to be extremely pure. This means that even the smallest amount of impurities can affect the performance of silicon in electronic components.

Recognize the Purpose of Zone Refining

Zone refining is a technique specifically used to increase the purity of a material. It involves melting a small region of a solid material and then moving this melted 'zone' across the material to separate impurities.

Compare Options for Purity Efficiency

(a) Electrochemical methods are usually not sufficient for the extreme purity needed for semiconductors. (b) Oxidation is a process used to add oxygen but does not remove impurities from silicon. (c) Zone refining is specifically designed to purify materials like silicon to the high levels needed for semiconductors. (d) Crystallization can purify but not to the level needed for semiconductors.

Identify the Best Method

Evaluate all options and conclude that zone refining (option c) is the method used for obtaining the high purity silicon required for semiconductors.

Key concepts

Semiconductor Material

Semiconductors are materials that have electrical conductivity between that of a conductor and an insulator. Silicon is a prime example of a semiconductor material, largely due to its abundance and excellent semiconductor properties. These materials are essential for the fabrication of electronic components like transistors and diodes, which are the building blocks of modern electronics.

• They can conduct electricity under certain conditions, making them versatile for electronic devices.
• Semiconductors are crucial in devices like computers, smartphones, and solar cells.

The unique property that enables them to function in electronic circuits is their ability to change from a conductor to an insulator through doping. This tuning of electrical properties is vital, as it allows precise control over the flow of electrical current, thereby enabling the creation of complex electronic circuits.

High Purity Silicon

To use silicon effectively as a semiconductor, it must be extremely pure. Even trace impurities can drastically alter its electrical properties, impacting the performance of semiconductor devices.

• High purity silicon is also known as "electronic grade silicon" and is essential for reliable, high-performance electronics.
• This purity ensures consistent electrical characteristics and reduces defects in semiconductor wafers.

Achieving high purity silicon involves removing contaminants that could cause unwanted electrical charges or weaken the crystal structure. As a result, various techniques are employed to refine silicon, aiming for a purity of 99.9999999%, often referred to as "nine nines" or "9N" purity.

Impurity Removal Methods

When refining silicon for semiconductor applications, removing impurities is critical. Various methods are employed to purify silicon, but the one particularly suited for achieving the highest levels of purity is zone refining.

• Zone refining works by melting a narrow region of silicon and moving this melted zone slowly along the silicon rod.
• The process relies on the principle that impurities often concentrate in the molten zone, thus being separated from the solid portion.

As the molten zone moves, impurities are carried to one end of the rod, effectively concentrating them and leaving behind high-purity silicon. This method is preferred because it can achieve the extraordinarily high purity levels required for semiconductor-grade silicon, unlike other methods which may leave residual impurities. Zone refining is a precise and efficient way to ensure that silicon used in electronics meets the stringent purity standards necessary for high-performance and reliable electronic devices.