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Barrier metals are thin layers of metal or ceramics placed between objects to prevent contamination. They must be conductive and inert, with the right thickness. Titanium nitride is the most common barrier metal in semiconductors, while diffusion barriers protect metal components from welding. Gold, nickel, and aluminum are common metals used for diffusion barriers.
A barrier metal is a thin layer of metal, in the form of plating or film, that is placed between two objects to prevent soft metals from contaminating other objects. For example, copper and brass components in modern chips and circuits always include a thin layer of metal plating around them to avoid corrupting the crystalline semiconductors themselves. Sometimes, barrier metals are made of ceramics such as tungsten nitride rather than real metals, but they are still considered barrier metals.
Barrier metals require specific physical properties to be useful to the semiconductor industry. Obviously the barrier metal must be sufficiently inert to avoid contaminating the surrounding materials themselves; however, semiconductor fabrication is built around the flow of electricity through the device. Therefore, the barrier metal must be conductive enough to avoid interruption of the electrical flow.
Very few metals meet both of these criteria, meaning that only a small handful of materials serve as barrier metals in semiconductors. Titanium nitride is the barrier metal most commonly found in semiconductors. Chromium, tantalum, tantalum nitride and tungsten nitride are also used.
Conductivity and hardness aren’t the only two properties taken into consideration with a barrier metal; the thickness of the barrier metal also plays a crucial role in its effectiveness. Soft metals such as copper can penetrate too thin a barrier. Any soft metal that penetrates a thin barrier could contaminate the vulnerable object on the other side. On the other hand, too thick metal plating significantly affects the flow of electricity in the circuit. Semiconductor engineers spend a lot of time in test labs trying to get the balance right.
However, not all barrier metals shield crystalline semiconductors. Soft metals corrode harder metal surfaces just as easily, and such contamination can lead to product failure in high-tech devices. A thin layer of inert metal that prevents two other metals from contacting is known as a diffusion barrier. Diffusion barriers are often found between the layers of sheet metal and protect the metal components from welding.
The metals used for a diffusion barrier are not always the same metals used to shield semiconductors, although devices that rely on the flow of electricity between their metal components might use the same barrier metals as semiconductor devices. In general, metal plate diffusion barriers require the same inert properties as semiconductor barriers, but must also be able to adhere to different metals on both sides. Gold, nickel and aluminum are three common metals used for diffusion barriers.
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