The “Antenna effect” is a common name given for the effects of charge accumulation in an integrated circuit during its processing. This effect is also referred to as “Plasma Induced Damage”, “Process Induced Damage”. The antenna effect which can more specifically be called the ‘Plasma-induced gate oxide damage’ is basically an effect that can cause much yield and also reliability problems during the manufacturing of semiconductor devices. The semiconductor device manufacturing means fabricating the Semiconductor devices that are used in an integrated circuit (IC) as a chip.
Factories normally supply their own antenna rules, which must be obeyed and taken under consideration while working to avoid this problem. A violation of any such rules can be hazardous and is called an ‘Antenna violation’. Here, the word antenna has an entirely different meaning; it does not mean the device that converts electric radiations to electromagnetic fields. If you view a typical net Integrated circuit, you can easily observe that it contains a transmitter as well as a receiver. This process is the same as the process in any communication system which contains a transmitter from where the information is sent and a receiver at where the information reaches by a medium or any channel.
As per the circuitry, the receiver consists of a gate electrode having a thin Gate dielectric (this is the dielectric layer that separates the terminal of the gate from the underlying source). This Gate dielectric is very thin and hence there is a risk and big chance of it to breakdown. This can only happen if the chip acquires much more voltage than the normal operating voltage of the chip; which means that if more voltage than the normal is applied to the chip, there would be huge chances of it to stop operating and that is called breakdown.
The earlier gate dielectrics were made up of Silicon Dioxide but due to recent inventions, the old Silicon dioxide dielectric Gate has been replaced by high Potassium dielectric materials which originally may or may not be oxides but still, they perform the work with the same efficiency and also has some improved qualities.
The breakdown can also be prevented by fabricating the chip. If for once the chip is fabricated, the breakdown cannot happen; owing to the fact that every drain has an implant connected to it. The implant may be connected further by a diode (a device that allows the current to flow only in one direction. It has very negligible resistance in one direction and high in the other direction). Whenever there is an issue of the voltage, the diode breaks down in such a manner that it is not destructed fully; hence it protects the gate oxide this way.
Sometimes, there are also chances of freaky Gate oxides which are very harmful if we look around in case of power dissipation. The Gate oxide waste dissipates more power but these are good for damage from antenna effect. A leaky oxide as the name suggests dissipate power and hence protects it from accumulating at a point and therefore product from oxide breakdown. It is a very surprising fact to know that a thin gate oxide has fewer chances of getting damaged than thick gate oxide. This is because a thin oxide dissipates power more easily when compared to thick oxide.
There are some antenna rules which are very essential to be followed when one wants to run everything smoothly. There are different antenna rules for both thin and thick oxides. So, if your process has thin and thick oxides both, then there will be different rules for both of them. If charge accumulates on a node that is electrically isolated of an IC during processing, it may cause many numbers of problems, ranging from easily-detected failure to the most damaging and irresistible one and this can be less detectable problems.
IMPACT OF DAMAGE
The PID may cause big failure if the energy of the accumulated charge is dissipated on a single spot of the gate oxide. This may even cause the permanent failure of the process or the transistor. This can be the most damaging case but many times the damage is not as big as we consider, it may just be the degraded performance of the transistor. Dedicated performance may be due to many problems; it may be due to leaky gate oxides, old Gate oxide, very high voltages, frequent high changes in the voltages, hot electron effects, or an increase in noise generation.
We do not see these types of effects in digital circuits. These types of effects can only be seen in analog circuits. In order to prevent the accumulation of the charge and thus prevent the breakdown, many rules have been developed as stated above but one of the most important rules is the ‘Antenna ratio’. This ratio is defined as the ‘Area of metal’ to the ‘Area of the gate oxide’ to which the metal is attached.
Generally, antenna violations can be fixed by the router. A router is a specially designed integrated circuit. If we change the order of the layers in a router and then if the gate immediately connects to the highest metal layer, then no antenna violation will occur. This is one method of how you can prevent antenna violations by the use of a router. The Other feasible way to prevent this was the use of the diode as already explained which protects the gate oxide from destroying and is itself destroyed in a non-destructible manner.