Physical Vapor Deposition - Sputtering
-- Sputtering process is widely used in semicondcutor industry. Mainly for metal film to creat or modify eletrical characteristics.
In optics Insustry, dielectric material film is ususally required. Sputtering method is not popular and narrow down in certain
products like ITO, STN.LCD...
Plasma Sputtering is also an important branch in PVD technology. In 1852, Grove founded the sputtering deposition method. This method is well developed and applied to industry during 200 years and lasting to morden time.
The main principle is to build a vaccum chamber and fill with Argon. By adding a high voltage, the argon will arc to plasma state. The argon ion (Ar+) will toward to cathode with high speed and sputter the target material (use target as cathode). The target atom or molecular will be hit to substrate surface and condense as a film.
Instead of heat melting in evaporation method, the plasma Ar+ ion hit and sputter the target is the main mechanism in plasma sputtering method. The target atom is knocked out by Ar+ ion, the knock force is so big and can accelerate target atom a high speed. With such velocity, the target atom can hit and attach to substrate surface deeply. The film density is good than evaporation.
DC Sputtering (Planar Diode Sputtering) :
Using target as cahode and substrate as anode, pump the vaccum to 10-3Pa, fill argon gas, apply 1000~V Voltage. The ion in plamsa will be accelerated toward cathode, hit the target and transfer the energy sputtering the target to substrate surface. DC supttering use target as a cathode. It must be a conductive material (metal). It can't sputter dielectric material target. It is oldest sputtering method.
RF Sputtering Deposition:
in DC systems, positive charge will accumlate on the cathode (target) and need 1012 volts to sputter insulators. But such high voltage will easy make arcing and harm the target source and produced film. It was improved by Wehner in 1955. An alternative voltage current in Radio Frequency 13.5MHz was applied in DC system. With alternative characteristic, the positive charge will stay in plasma zone and not to accumlate to cathode. The cathode can sustain a high voltage difference and continue the sputtering work.
Dual Cathodes Sputtering Deposition:
For improving the speed of deposition rate, a dual cathodes is used. Apply a 40 KHz frequence alternative volatage current to daul cathodes( It will steady change the positive and negative pole in on cathode; the alternative current voltage in much lower than anode voltage). The alternative current will neutralize the accumlated charges in target source. The sputtering will steady work without interference of electric charges.
Triode Sputtering Deposition:
If add a electron beam which is gererated by heat in Dual Cathodes Supttering System, It can increae the quantity of Ar+ ion to hit target and quickly make the film. It can effectively increase the sputtering rate. Film quality is better than Dual Cathode Sputtring.
Magnetron Sputtering Deposition:
By adding a megnetic field in the system, the electron will move in spiral following the megnetic lineation. This will hugely increase the ionization density of argon gas and opportunity of collision. The density will be 1010 ion/cm3 and increase to 1013 ion/cm3. Therefore, the deposition rate can be increased. This system also can be applied to DC, RF, Dual cathode Sputtering methods. It also can be applied to some substrates which can't stand for high working temperature. Most important of all, It can join into continuous production line.
Continuous prodcution Megentron Sputtering Deposition Line
Magnetron Sputtering Deposition can't apply to high magnetic target. It will make a concave consumption and not equally eliminate the thickness of target block. This will harm the film quality and uniformity.
Ion Beam Sputtering Deposition, IBSD:
This method is newest developed and may be most important in high class optical filters. It installed a isolated Ion Source in high vacuum chamber. Use ion particle knock out the atom of target and let target atom through the vacuum space and deposite on substrate surface. As said in evaporation page, the ion particle is havy compare to target atom. This knock will be a powerful method and can transfer a good kinematic energy to target atom particle. The high density and amorphous film is with low scattering characteristic. It can make high class laser mirror and filters used in Gyro and Laser Interferometer Gravitational Wave Observatory (LIGO).