What is polycrystalline silicon used for?
Polycrystalline silicon is the key feedstock in the crystalline silicon based photovoltaic industry and used for the production of conventional solar cells.
What are the advantages of poly silicon gate over metal gate?
The source and drain region is created using ion-implantation method, which is a very high temperature annealing process. If metal is used as gate then it would melt. The melting point of polysilicon is higher, this is also one of the reason for choosing polysilicon over metal.
Why are gate terminals made of poly silicon instead of metal What is the purpose of the gate terminal?
The thin gate oxide under the gate (polysilicon) acts as a mask for the doping process thus preventing further doping under the gate region.
Which material is used as gate metal?
These shorts are created by pyramidal-shaped spikes of silicon-aluminum alloy – pointing vertically “down” into the silicon wafer. The practical high-temperature limit for annealing aluminum on silicon is on the order of 450 °C. Polysilicon is also attractive for the easy manufacturing of self-aligned gates.
What is meant by polycrystalline material?
A polycrystalline material is comprised of many small crystallites with different crystal orientations that are separated by grain boundaries. This is the common structure of most technical materials. The blade has been cast to a near net shape, and the surface has been etched to show the individual crystallites.
What is the difference between monocrystalline and polycrystalline?
Polycrystalline solar panels have blue cells made of multiple silicon crystals, and they are less efficient but more affordable. Monocrystalline panels have black cells made of single crystals, and they offer a higher efficiency at a higher price.
What is CMOS polysilicon?
Thus, poly-crystalline silicon (polysilicon) became the modern gate material because it is the same chemical composition as the silicon channel beneath the gate oxide. In inversion, the work-function difference is close to zero, making the threshold voltage lower and ensuring the transistor can be turned on.
What is the difference between silicon and polysilicon?
In context|chemistry|lang=en terms the difference between silicon and polysilicon. is that silicon is (chemistry) a nonmetallic element (symbol si) with an atomic number of 14 and atomic weight of 280855 while polysilicon is (chemistry) containing many silicon atoms, especially when linked into chains or networks.
What materials do we use for metals on a CMOS chip?
CMOS circuits use a combination of p-type and n-type metal–oxide–semiconductor field-effect transistor (MOSFETs) to implement logic gates and other digital circuits.
What is the difference between polysilicon and silicon?
Where are polycrystalline materials used?
Many technologically useful materials are polycrystalline or amorphous in nature. They are used as primary raw materials in energy, semiconductor, solar, manufacturing and photovoltaic industries. Polycrystalline materials have a microstructure composed of single crystals and grain boundaries (GB).
Why the properties of polycrystalline materials are often isotropic?
For many polycrystalline materials the grain orientations are random before any working (deformation) of the material is done. Therefore, even if the individual grains are anisotropic, the property differences tend to average out and, overall, the material is isotropic.
Why do we use polysilicon instead of metal for gates?
One reason for the initial switch to polysilicon is that fabrication processes after the initial doping required very high temperature annealing. Metal gates would melt under such conditions whereas polysilicon would not.
Why is the VT of a polysilicon gate higher than a silicon gate?
Using metal would result in a higher Vt compared to polysilicon since a polysilicon gate would be of the same or similar material composition as the bulk silicon channel. As we reach smaller and smaller scales, the need for a higher Vt has become important again due to problems of leakage.
What is the use of polysilicon gate as an alignment mask?
In step (h) the wafer will be diffused with n+ using polysilicon gate as an alignment mask. i.e. the polysilicon aligns the source and the drain to be exactly under the gate. This approach solves the problem of random misalignment errors, which caused the speed of the device to be dramatically influenced by it.
What are the gate materials used in MOSFET IC fabrication?
In the MOSFET IC fabrication process, it is preferable to deposit the gate material prior to certain high-temperature steps in order to make better performing transistors. Unfortunately these high temperatures would melt metal gates, thus a high melting point material such as poly-crystalline silicon is preferable to metal as gate material.