Vac Tec Systems

Introduction

The cathodic arc plasma deposition process has been used to evaporate materials including titanium, aluminum, copper, tantalum, chrome, niobium, and others. The pure and reacted films have been analyzed for morphology, adhesion, friction, and hardness, plus undergone tests relating to specific applications. Tests to determine resistance to corrosion and the stability of thicker films have been done with selected materials. Generally, the test results have been better with the cathodic arc deposited films as compared with similar materials applied with evaporation or sputtering. The hard coatings generated with cathodic arc and a reactive gas (nitrogen) have normally provided test results superior to an uncoated substrate.

Coating uniformity tests were conducted with various cathode sizes. These tests were done to establish the capability of this process to coat uniform critical dimensions plus develop economics of large scale production vacuum coaters and substrate fixturing. The characteristics of the cathodic arc deposition process enable it to provide uniformity similar to or better than comparative processes and at competitive production costs while avoiding environmentally hazardous mater i als.

Process

The cathodic arc deposition system consists of a vacuum chamber, cathodes, arc power supplies, bias power supply, arc starter system, anodes, a control panel, and automatic computer control. The system also utilizes an infrared temperature monitor for substrate temperature control (Attachment A).

Briefly, the process consists of:

* Loading the substrates into the chamber,

* Rough and high vacuum pumpdown,

* Pre-heat of parts by bias voltage and/or separate heater,

* Arc initiation

* Reactive gas (if reactive process>,

* Coating,

* Vent chamber and remove parts.

The arc initiation is by a mechnical starter or a gas discharge ignition system. The arc is self-sustaining on the target material providing the cathode current is maintained above minimum levels. The evaporation caused by the arc spot (typically 1 to 3 |»m dia.) results in:

* A high percentage of the material is ionized <30 to 100'/.) .

* Ions existing in several charge states in the plasma (i.e.» Ti , Ti-, Ti+e and Ti-3).

* Kinetic energies are typically in the 10 to 100 eV range.

* High evaporation and deposition rates.

The arc spot randomly scans the target material and provides uniform erosion on the target and deposition on the substrate. Methods involving electro-magnets are sometimes employed to control the arc movement thus further enhancing the deposition uniformity and erosion of the target.

The microscopic melting caused by the arc spot is localized to small regions of a few micrometers in diameter. This allows the placing of cathodes at any position in the chamber for optimum coating as there is no molten pool or high temperature target material present in the chamber.

The arc current densities are in the range of 10A/m=. This causes flash evaporation of the target material and the resulting vapor consists of electrons, ions, neutral vapor atoms and micron droplets. The current on the cathodes does not radically change the emissions for the arc spot as the spots tend to split or unite as current is increased or decreased.

Use of large cathodes/targets with the confined arc design provides good coating uniformity and lends itself to large volume production vaccuum chambers. The confined arc prohibits the arc from leavng the target surface.due to the passive boundaries. Magnetically held arc spots do not allow large cathode design and cannot assure coating uniformity over large areas or on many substrates unless an array of cathodes is employed. The confined arc cathodes typically range from 5" diameter to 8" wide by 50" long (there is no apparent limiting size). Magnetically held arc sources are limited to approximately 3" d iameter.

The target to substrate distance with cathodic arc depositied coatings is typically about 8" to IV' (compared to 2" to <*" for sputter. This allows irregularly shaped substrates to be manipulated in the chamber and for various sized parts to be coated in the chamber without complex fixture changes. Source to substrate distance may be critical if the parts have low temperature requirements such as polymers or low particle pressure metals due to the heat generated by the cathodes.

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