Tantalum powder for semiconductor sputtering targets
With the rapid development of semiconductor technology, the demand for tantalum used as sputtering film is gradually increasing. In integrated circuits, tantalum is used as a diffusion barrier. It is placed between silicon and copper conductors. Commonly used targets are generally made of tantalum ingots, but in some special cases, such as nb-silicon alloy targets, the I/M method cannot be used due to the different melting points of nb and silicon and the low toughness of silicon compounds.Only powder metallurgy can be used as targets.
The performance of the target directly affects the performance of the sputtered film. In the formation of the film, no substances that pollute the semiconductor device can exist.
When the sputtering film is formed, if there are impurities in the tantalum (alloy, compound) target, impurities will be introduced into the sputtering chamber, causing coarse particles to attach to the substrate and short-circuit the film circuit.
At the same time, impurities will also become the reason for the increase of protrusion particles in the film. Therefore, there are high requirements for the quality of lithium powder and tantalum targets.Although the performance of metal tantalum is relatively stable, metal tantalum powder with finer particle size is more active and reacts with oxygen, nitrogen, etc. at room temperature, which increases the content of impurities such as oxygen and nitrogen in tantalum powder.
Although the purity of some metal tantalum products such as commercially available tantalum ingots can reach 99.995% or even higher, the finer the tantalum powder, the higher the corresponding activity, and the ability to adsorb oxygen, nitrogen, hydrogen, and carbon also increases accordingly. Therefore, it has always been considered quite difficult and difficult to increase the purity of tantalum powder to more than 99.99%.
However, reducing the particle size of tantalum powder is very necessary to improve the quality of tantalum powder and tantalum targets. The target material field hopes to obtain high-purity tantalum powder with an average particle size D50<25 μm.
At present, the production process of conventional metallurgical grade tantalum powder adopts the method of simultaneous dehydrogenation and oxygen reduction. Due to different usage directions, the requirements for purity and particle size of ordinary metallurgical grade tantalum powder are not high. The process of simultaneous dehydrogenation and oxygen reduction can effectively save costs.
The dehydrogenation is to heat and decompose tantalum hydride to remove the adsorbed hydrogen. The decomposition temperature of tantalum hydride is 600°C, but the speed is extremely slow.
As the temperature rises, the decomposition speed increases. A large amount of hydrogen begins to be released above 800°C. In order to fully release hydrogen, the temperature must be higher than 800°C. The higher the temperature, the more thorough the dehydrogenation.
