|
GENERAL PROCESS - REF. #GP012 | View PDF
INTRODUCTION
This application relates to the chemical vapor deposition of a diamond-like nanocomposite material, sometimes referred to as DLC (Diamond-Like Coating). The coating has low friction properties combined with improved hardness and wear resistance. The film is deposited in a modified plasma-assisted chemical vapor deposition (PACVD) process in a vacuum.
Diamond-like materials display a great combination of high hardness and elasticity, high wear resistance and a low coefficient of friction. Because of their chemical inertness, low surface energy and smoothness, these films are used in industrial applications such as hard, self-lubricating films for wear resistant release coatings in molds, sliding parts in motors and racing engines, punches and dies, space applications, optical components, and more.
A liquid precursor in this application is an organosilane compound called Siloxane. A typical vaporizer consists of a heated 1/2” round copper frit, fed by a liquid flow controller through a non-contacting capillary tube. The operating temperature is typically < 300 deg C. The frit clogs frequently due to decomposition of the liquid precursor.
An electron source is used to ionize both Argon gas and precursor vapor to form the active species for deposition. Regulated RF bias voltage is applied to the substrate to attract reactive ions formed in the plasma. One interesting point is that the Argon ions bombarding the surface of the substrate harden the coating during deposition. In order to achieve the proper hardness, the deposition rate must be very slow, so the liquid flow rates were very low, less than 8 grams per hour. A Titanium transition material is also being sputtered during this process.
THE CHALLENGE
The system described above delivers lower than expected yield. Many coatings are rejected due to unacceptable mechanical properties. Rejected parts are reworked in a lengthy and expensive process of plasma stripping and cleaning before recoating.
Vaporizer pressure fluctuations cause the chamber pressure to fluctuate, which causes the sputter rate of the metal dopant to decrease. These pressure spikes cause sputtering yields to decrease due to poisoning of the target material. Data suggests that the vaporizer pressure fluctuations are due to incomplete vaporization (spitting liquid into the chamber). The un-vaporized liquid rapidly expands when entering the chamber, causing pressure spikes. It is also evident that the substrate bias fluctuations causes variations in the attraction of reactive ions, thereby causing variations in the film structure. Chamber pressure and bias charts are shown in Figure 1.
 THE BROOKS SOLUTION
The objective is to improve yield by eliminating chamber pressure and bias fluctuations caused by incomplete vaporization of the liquid (flat lines in chamber pressure and bias readings). A Brooks®/MSP Model 2800 Turbo-Vaporizer™ system is installed in place of the old vaporizer. A QUANTIM Model QMBC Coriolis mass flow controller, a Model 5850E MFC, the vaporizer, and heater PID controller make up the assembly. Once the system is installed and vacuum purged, the QUANTIM is filled with liquid. The vaporizer temperature is set to 200º C. The system configuration is shown in Figure 2.
Sample parts are loaded into the reactor and deposition started. Charts of chamber pressure and bias are shown in Figure 3. Both charts are essentially a flat line. The disturbance seen in chamber pressure was caused by an intentional manual pressure adjustment during the run.
 CONCLUSION
The coatings produced using the Brooks/MSP Turbo-Vaporizer system are uniform and mechanically repeatable. The chamber pressure and substrate bias stability are significantly improved, with a corresponding improvement in coating deposition. Moreover, because the Brooks/MSP Turbo-Vaporizer provides complete vaporization, less precursor liquid is required for a given layer thickness leading to improved tool utilization, less rework, and minimized chemical use. |
|
|
