6.3 Precursors for chemical vapor deposition of copper  (Page 2/5)

Applications of metal cvd

There are a number of potential microelectronic applications for metal CVD, including gate metallization (deposit on semiconductor), contact metallization (deposit on semiconductor), diffusion barrier metallization (deposit on semiconductor), interconnect metallization (deposit on insulator and conductor or semiconductor). Most of the relevant features of metal CVD are found in the interconnect and via fill applications, which we briefly describe here. There are basically two types of metal CVD processes that may occur:

1. Blanket or nonselective deposition, in which deposition proceeds uniformly over a variety of surfaces.
2. Selective deposition in which deposition only occurs on certain types of surfaces (usually semiconductors or conductors, but not insulators).

A primary application of blanket metal CVD is for interconnects. The conformal nature of the CVD process is one of the key advantages of CVD over PVD and is a driving force for its research and development. The degree of conformality is usually described as the “step coverage”, which is normally defined as the ratio of the deposit thickness on the step sidewall to the deposit thickness on the top surface. Another application for blanket metal CVD is via hole filling to planarize each level for subsequent processing, This is achieved by depositing a conformal film and etching back to the insulator surface, leaving the metal “plug” intact. Another unique aspect of CVD is its potential to deposit films selectively, which would eliminate several processing steps required to perform the same task. The primary application for selective metal CVD would be for via hole filling. Ideally, deposition only occurs on exposed conductor or semiconductor surfaces, so filling of the via hole is achieved in a single step.

Copper cvd

The chemical vapor deposition of copper originally suffered from a lack of readily available copper compounds with the requisite properties to serve as CVD precursors. The successful development of a technologically useful copper CVD process requires first and foremost the design and synthesis of a copper precursor which is volatile, i.e., possesses an appreciable vapor pressure and vaporization rate to allow ease in transportation to the reaction zone and deposition at high growth rates. Its decomposition mechanism(s) should preferably be straightforward and lead to the formation of pure copper and volatile by-products that are nonreactive and can be cleanly removed from the reaction zone to prevent film, substrate, and reactor contamination. Gaseous or liquid sources are preferred to solid sources to avoid undesirable variations in vaporization rates because of surface-area changes during evaporation of solid sources and to permit high levels of reproducibility and control in source delivery. Other desirable features in precursor selection include chemical and thermal stability to allow extended shelf life and ease in transport and handling, relative safety to minimize the industrial and environmental impact of processing and disposal, and low synthesis and production costs to ensure an economically viable process.