Semiconductor Wafers: Types and Uses

Semiconductor Wafers: Types and Uses

When we look around us, we will find many things and objects around which is an application of silicon or other semiconductor devices in a way or another. It is there on televisions, laptops, mobile phones, smart gadgets and other circuitries that are available. Silicon is the second most common element on Earth, after the oxygen at first place, and seventh most available element in the universe. It has high stability and mobility at higher and even at standard room temperatures. Due to the availability of holes or electrons, according to the type of doping the semiconductor has gone through, it becomes easier to conduct electric current through the material.

A wafer is a thin slice from the crystal of the semiconductor that possess almost the same physical and electrical properties as its mother crystalline semiconductor substance, but act as a substratum for different electrical, electronic and microelectronic devices and gadgets. It may not be wrong to say that all the development in the technology these days especially in the field of electrical, electronics and microelectronics are due to the semiconductors. They are used in the manufacturing of solar cells and panels, which are the most widely used green way to produce and generate electric energy. All the advancement in the electrical and electronics field is due to smaller sizes of the previous giants-like components that includes diode, rectifiers, ICs (Integrated Circuits), etc. are all applications and possible due to the use of mainly silicon or other semiconductor materials.

Wafers

A semiconductor wafer is usually referred to as a slice, made up of semiconductor materials such as c-Si (Crystalline Silicon). Semiconductor wafers are synthesized from crystalline materials of high purity (99.9999999% or higher) with no defect in it. The formation of the semiconductor is carried out on a single piece, crystal form of semiconductor material. Depending upon the size of their diameter, semiconductor wafers are available in wide range of sizes to select according to the requirements. The silicon made semiconductor wafers are synthesized and available in sizes ranging from 25.4 mm (1 inch) to 300 mm (11.8 inches). The increase in the diameter of the silicon wafers reduces the cost of the semiconductor wafers and increases the throughput in the targeted purpose. No silicon wafer of diameter above 300 mm or 11.8 inches, is available right now as serious hurdles are being faced in its formation. However, researches are being carried out by Intel, TSMC and Samsung separately, for the feasibility and availability of the wafer slice in 450 mm diameter.

The diameters for the semiconductor wafers synthesized from materials other than Silicon varies from the diameters of the semiconductor wafers made from silicon. The diameter for the slice depends on the mechanical strength of the material. The thickness and the diameter of the final wafers must be in accordance with the mechanical strength and other physical properties of the material, of which the wafer is to be synthesize. The final product must be strong enough to handle its own weight without cracking during the handling in the production of various applications. The increase in the thickness or diameter also result in the increase in the weight of the wafer as more material is added in the synthesis of the slice. The diameter can not be increased when enough weight has been added as it compromises the strength of the slice. A comparatively low pressure will be enough to break down the wafer for a larger diameter if weight is not accordingly set.

As the semiconductor wafers are synthesized from the crystal material, they also possess crystalline, diamond-cube structure. When the crystal form of semiconductor materials is cut into wafers, they align their surface into one of the crystal orientations, described by Miller Index. The orientation may be important as the electrical and structural properties of a single crystal are anisotropic i.e. it depends on the orientation of the crystals and has different properties for different orientations of crystals.

Types of semiconductor wafers:

Mainly, there are two types of semiconductor wafers:

1. Undoped semiconductor wafers

2. Doped semiconductor wafers

1. Undoped semiconductor wafers

The undoped semiconductor wafers are the slice made from purely crystalline of silicon or any other semiconductor material. They are an ideal semiconductor wafer, which are also known as ‘intrinsic semiconductor wafer’.

2. Doped semiconductor wafers

Silicon semiconductor wafers, in general, are never a 100% silicon or of pure semiconductor material. Rather, they are made with an impurity factor of doping, which is carried out during the formation of the semiconductor material, with the concentration of doping in between 1013 to 1016 atoms of doping element in a cm3 of the semiconductor material to be doped. But this added impurity still does not compromise on the overall purity, which sustain a purity level of 99.9999999% or more percent of the semiconductor material. The doping of the silicon or other semiconductor materials enables us to change and control the physical and electrical properties of the wafers as compared to the physical and electrical properties of the undoped semiconductor material. Depending on the elements, the semiconductor materials are doped with, the semiconductor wafers are further divided into two types:

a. N-type semiconductor wafers

b. P-type semiconductor wafers

a. N-type semiconductor wafers

When during the formation of the silicon or other semiconductor materials wafer, the atoms of phosphorus, arsenic or antimony are added to the semiconductor material, which results in the formation of the N-type semiconductor wafers. The N-type semiconductor wafers are enriched in negatively charged ions or electrons, which are responsible to allow the passage of the electric current from one side of the doped material to the other side of the material.

b. P-type semiconductor wafers

If atoms of Boron are added to the semiconductor as dopant during the formation of the semiconductor materials wafer, it results in the formation of the P-type semiconductor wafers. The P-type semiconductor are enriched in positively charged holes and holes are responsible to allow the passage of the electric current from one side of the doped material to the other side of the material.

The semiconductor wafers are also categorized into two types depending on the level of the doped atoms:

i. Extrinsic semiconductor wafers

ii. Degenerated semiconductor wafers

i. Extrinsic semiconductor wafers

Those doped semiconductor wafers, which have tiny to the moderate percent of the dopant or have comparatively lower numbers of atoms of dopant in the crystal of silicon or other semiconductor materials, are known as ‘extrinsic semiconductor wafers’.

ii. Degenerated semiconductor wafers

Those doped semiconductor wafers, which have high percentages of the dopant or have comparatively greater numbers of atoms of dopant in the crystal of silicon or other semiconductor materials, are known as ‘degenerated semiconductor wafers’.

Other types of semiconductor wafers include polished (they are polished on both sides of the wafer slice), epitaxial and SOI (Silicon on Insulator).

Uses of semiconductor wafers

The semiconductor wafers find their application in many fields of modern technology. They are widely used in photovoltaics, in the manufacturing of solar cells and in the fabrication of ASIC or simply IC (Integrated Circuit). Not only this, the wafers act as a substrate for different microelectronic devices that are built-in or upon the wafer itself. Other details are given below as:

Silicon is referred as the best semiconductor due its high mobility at high or even the standard room temperature. That’s why it allows the passage of electric current at higher rates as compared to other materials. For the said reason, it is deployed in different electrical devices, despite of the fact that metallic substances can get the job done as well but have their own limitation.

They are deployed in the development of the chips and microchips that are later used in the electrical gadgets. For their current conducting properties, they are used in the manufacturing and creation of integrated circuits or ICs, which commands actions in electrical and electronics devices. They find their application in the laptop, computers, smartphones, digital and electrical gadgets, appliance and others a lot to name them. Silicon is the main used element, its wafer is just a thin layer, that acts like substratum.

Apart from these, they are used in the manufacturing of the calibration instrument due to their stability, applications of high power, detectors, sensors, fabrication of MEMS, diodes, rectifiers, transistors and optoelectronic components.

Silicon or other semiconductor materials are the most widely used materials these days in the field of technology. They not only provide a better option in contrast to other metallics substance out there but also widely available on the Earth. It is due to the development and researches on silicon and semiconductor materials that the advancement in technology is possible at this huge level. Further researches are being made for the increment of the size and controlling the properties by the mean of doping of semiconductor wafers. 

11th Dec 2019

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