Process Technology

Magnetron Sputtering Process

Magnetron sputtering is a vapor deposition process wherein target surface material is removed primarily in atomic form because of argon ion bombardment from the argon plasma and deposition of this material on substrate. The process is basically momentum transfer phenomenon. As these Ar ions collide with the target surface, atoms or occasionally entire molecules of the target material are ejected. The resulting coatings are compact and highly adherent in view of continuous bombardment of Ar ions which removes loosely bonded material from substrate surface. Many a times reactive gas such as nitrogen, oxygen etc. is mixed with argon which combines with ejected target material to deposit layers which show interesting properties.
 
Sputtering has proved to be a successful method of coating a variety of substrates with thin films of electrically conductive or nonconductive materials. One of the most striking characteristics of sputtering is its universality. Since the coating material is passed into vapor phase by a mechanical rather than a chemical or thermal process, virtually any material can be deposited. Pure DC or Pulsed DC power supplies are used to sputter electrically conductive materials, while radio frequency power supplies are used for nonconductive dielectric materials.

Plasma Ion Nitriding

Plasma Nitriding, also called glow discharge nitriding or ion nitriding, is a well-known technology for many years. Plasma Nitriding can be adequately described as plasma treatment of metal substrate surface. Main gases used for plasma are hydrogen, argon, nitrogen C2H2, CH4 and oxygen Ion bombardment from the plasma undertakes conversion of substrate surface material into very hard nitrides of parent surface. Plasma nitriding has been very successful in surface treatment for iron, steel, and cast iron for industrial applications. The Plasma nitriding process produces a hard outer skin on the material being nitrided. The hardness achieved on the surface decreases with depth until the core hardness is reached.  Thickness of the top hard material thus created is call “Case Depth”. The nitride forming elements in the steel’s composition are the primary factors controlling the hardness and the case depth. The low alloy steel will provide a deeper case depth but a lower overall hardness. The high alloy content of the stainless steel creates a high surface hardness and a sharp transition zone between the nitrided surface and the core material. Topmost portion of the case depth is called compound layer or white layer which is hardest. The hardness values achieved in plasma nitriding are dependent of the metallurgy of the job. Plasma Nitriding offers minimal job distortions, excellent process control with accurate plasma chemistry and is quite environment friendly as compared to competing techniques.
 
The nitrogen in this gas mixture is ionized by an applied voltage. The nitrogen ions are then accelerated toward the work surface. Molecular nitrogen is inert and no metallurgical reaction takes place on those surfaces not reached by the    ionized nitrogen. The high velocity ionized nitrogen first sputter cleans the     work surface by dislodging impurity atoms and then joins with the metal to form the desired metal nitrides on the surface of the work. The    superior pre-cleaning technique of sputtering permits reduction in processing time with an significant reduction in gas and utility usage.

The driving potential for plasma nitriding is a voltage drop that is perpendicular to the work surface, called the cathode fall voltage. Since the cathode fall voltage must everywhere be equal, this nitriding potential is everywhere equal and complex shape can be uniformly treated. Because there is a finite small dimension that cannot be penetrated by the glow discharge, it is practical to apply reusable metal masks to work surface areas where nitriding is not desired.

Precise gas mixture control permits the nature of the compound and diffusion zones to be completely controlled. Work can be nitrided with no measurable white layer or compound zone for some applications.     Either a wear-resistant epsilon layer or a gamma prime layer with high fatigue strength can be deposited for other applications. But, in every     case, the compound zone can be made free from the brittle mixed phases. The diffusion zone can contain nitrides or carbo-nitrides with no observable grain boundary networks.

Corona Poling

Corona discharge is a partial breakdown of air, usually at atmospheric pressure, and is initiated by an intense electric field between Tungsten Pin Assembly and sample surface. This causes the shower of ionized air towards sample surface wherein the excess charge may reside on the surface or penetrate it. The residing charge on the surface of sample generates very high electric field across the sample thickness. The substrate holder assembly is provided with a heater assembly to carry out poling at higher temperatures of 250°C in order to increase the molecular mobility of the molecules. Unlike in Oil Poling Equipment, this technique does not require deposition of electrically conducting electrodes on the sample surface. Corona discharge has been used to pole films of ferroelectric materials for applications in NEMs and MEMs, sensors, actuators etc. materials to enhance piezoelectric properties.