- A microchip is a set of electronic circuits on a small flat piece of silicon. On the chip, transistors act as miniature electrical switches that can turn a current on or off. The pattern of tiny switches is created on the silicon wafer by adding and removing materials to form a multilayered lattice of interconnected shapes.
- A modern day microchip contains billions of transistors, measured in nanometers. Most advanced microchips contains features
- Moore's Law: Gordon Moore (co-founder of Intel) observed in 1975 that the number of transistors on a microchip would double in every two years. Thus, exponentially increasing computing power while decreasing the cost of chips.
Flavors of Chips
Based on functionality microchips are categorised into following categories:
- Logic chips: They are brains of electronic devices as they process information to complete a task. Examples of Logic chips:
- Central Processing Units (CPUs): Generalised microchip that handles main processing functions of a computing device.
- Processors designed for specific functionality such as:
- Graphical Processing Units: Optimised for visual display.
- Neural Processing Units: Designed for deep and machine learning applications.
- Memory chips: They store information. There are two types of memory chips:
- Volatile memory chips: They are the working memory chips that save data only while the device's power is turned on. Ex. DRAM (Dynamic Random Access Memory) helps to run programs on your device. DRAM are fast to read and write data.
- Non-Volatile Memory chips: They save data even after the device is turned off. Ex. NAND Flash stores data. NAND is slow to read and write data.
- ASICs: They are simple, single-purpose chips used for performing repetitive processing routines such as scanning barcode.
- SoCs: They are essentially integrator chips. They are a relatively new type of chip that combines many chips and circuits in a single chip and circuits in a single chip and may integrate things such as graphics, audio, camera, video and Wi-Fi.
Manufacturing of microchips
- Microchips are made by building up complex patterns of transistors, layer by layer, on a silicon wafer.
- The process used make chips is known as lithography (or 'photolithography').
- Lithography is a process by which is light is projected through a blueprint of the pattern that will printed (known as a 'mask' or 'reticle').
- Modern chips have up 100 layers. All these layers need to align on top of each other with nanometer precision (called 'overlay').
- The cleanrooms of the chipmakers' fabs (fabrication facilities), air quality and temperature are tightly controlled as if even the smallest speck of dust ends on the wafer, it can ruin the microchip. Most chipmakers have 'ISO Class 1' cleanrooms that are 'zero dust' that are more than 10,000 times cleaner than ambient air.
- Rayleigh criterion equation: This equation dictates the basic science behind lithography and determines how small the features on a chip can be printed.
- CD (Critical Dimension) is the smallest possible feature which can be engraved using light.
- λ (Wavelength) is the wavelength of the light used for lithography.
- NA (Numerical Aperture) measures how much light they can collect.
- k1 factor is a coefficient that depends on many factors related to the chip manufacturing process. The physical limit lithography is k1 = 0.25.
- Thus, to reduce critical dimension, there is a need for shorter wavelength of light, more powerful lenses etc.
Semiconductor Lithography
Definition: Semiconductor Lithography is a process used in the fabrication of semiconductor devices, such as integrated circuits (ICs) and microchips. It involves transferring a pattern from a photomask to a light-sensitive chemical photoresist on the substrate.
Importance: Lithography is a critical step in semiconductor manufacturing as it determines the size and shape of the components on the chip, which in turn affects the performance, power consumption, and cost of the final product.
Types of Lithography:
- Optical Lithography: Uses light to transfer the pattern from the mask to the wafer. It is the most common type of lithography used in mass production.
- Extreme Ultraviolet (EUV) Lithography: Utilizes extremely short wavelength light (13.5 nm) to enable the fabrication of even smaller features.
- Electron Beam Lithography: Uses a focused electron beam to directly write the pattern onto the wafer without the need for a mask. It is used for low-volume production and research purposes.
