1. Field of the Invention
The present invention relates to a structure of a photodiode image sensor device and a method for fabricating the same. More particularly, the present invention relates to a photodiode image sensor device having a copper interconnection and a method for fabricating the same.
2. Description of the Related Art
A photodiode image sensor converts optical information into electrical signals. There are basically two different types of solid state image sensor devices: a MOS (metal-oxide-semiconductor) type and a CCD (charge coupled device) type. Products employing photodiodes include those that employ contact image sensors (CISs) such as hand held phones (HHPs), cameras including those integrated into cellular phones, and scanners. Other products employing photodiodes include those that rely on charge coupled devices (CCDs), such as CCTV cameras, camcorders and digital cameras.
For years, aluminum has traditionally been used in the IC industry as a metal for making electrical interconnections in IC devices; however, it is generally difficult to form aluminum interconnections for a semiconductor device having a design rule or pattern thickness below 0.13 μm. But, as semiconductor devices become more highly integrated, smaller interconnection contacts are becoming increasingly necessary. Accordingly, as the demand for smaller photodiode image sensor devices increases, the pressure to make photodiode image sensors having electrical interconnections with a design rule or pattern thickness of less than 0.13 μm increases.
Copper has been suggested as an alternative to aluminum in applications where the design rule or pattern thickness is below 0.13 μm. However, copper atoms tend to diffuse into surrounding materials, such as into an interlayer dielectric layer, and can negatively impact the electrical characteristics of underlying transistors or other elements. Therefore, in order to use copper as an interconnection material in an integrated circuit device, a diffusion barrier layer is necessary to prevent diffusion of the copper into surrounding materials. Typically, such a diffusion barrier layer is formed of SiN or SiC. However, these materials are opaque, and therefore negatively impact the performance of image devices having a photodiode, which depends completely on the level of external light that it receives.