SCD 050

The SCD 050 is a table top sputtering device for basic sputter-coating under rough-vacuum conditions. A water cooled sputter head makes the SCD 050 ideal for extensive thick layer sputtering processes.

Key Features

• Compact bench unit
• "Super Cool" Sputtering
• Fine grained films
• Absolute personnel safety
• Easy and safe operation
• Very simple film thickness determination
• precisely reproducible film thickness
• State of the art electronics
• Cost-effective operation
• Etching device espands application possibilites
• Variety of target materials

Detailed Description

The Sputtering Method

Argon gas is admitted through a gas dosing valve to a specimen chamber that has been evacuated by a roughing pump. Flushing the chamber several times with argon makes it easier to pump out undesired gases, particularly water vapour. After this flushing process, the atmosphere in the chamber should consist of as much pure argon as possible. A working pressure of between 0.05 and 0.1 mbar is then established in the chamber, and the sputtering process can be started.

To start the sputtering process, a high voltage is applied to the target (cathode). This produces a high voltage field between the target and the specimen table (anode). The free electrons in this field are forced into a spiral path by a magnet system where they collide with the argon atoms in the field. Each collision knocks an electron out of the outer shell of the argon atom, positively charging the otherwise neutral argon. This is a cascading process that causes a glow discharge (plasma) to ignite. The positively charged argon ions are now accelerated to the cathode (target) where they impinge, knocking off metal atoms as they hit. Collisions also occur between the metal atoms thus released and the other gas molecules in the vacuum chamber. This causes the metal atoms to scatter widely, forming a diffuse cloud. The metal atoms from this cloud impinge on the specimen from all directions and condense evenly on it. Thus even very fissured specimen surfaces are coated with an even, thin metal film that is sufficiently electrically conductive for examination in the SEM.

Because of the high surface diffusion of their atoms, gold and silver tend to form 4 islands. Thus the desired electrical conductivity is not achieved until the film is at least 10 nm thick. Platinum produces films with the finest grains. The fine grained structure of the sputtered film is a function of the target material, the working distance, the gas pressure and the sputtering current as well as of the process duration. In practical application however, the sputtering parameters must be chosen according to the heat load the particular specimen can withstand. Heat-sensitive specimens such as those of biological origin or plastic foams are thus sputter coated from as long a working distance and as low a current as possible. Here one must take into account that the process must be correspondingly longer to achieve the same desired film thickness.

Modern scanning electron microscopes have extremely high resolving powers that often require very finely grained films. These can be achieved through the correct selection of the sputtering parameters or by first coating the specimen with a carbon film (refer to the carbon-metal-carbon accessory.) Reversing the voltage supply polarity allows the specimen table instead of the target to be placed on high voltage, enabling material to be sputtered off the sample, providing an "etching" effect that cleans it. A shutter protects the target from contamination during this process. By reversing the polarity again and opening the shutter, the sample can then be sputter coated in the same cycle without breaking the vacuum.