Trench isolation, also known as Box Isolation Technique, is an integrated circuit feature which prevents electrical current leakage between adjacent semiconductor device components. Trench isolation is generally used on CMOS process technology nodes of 250 nanometers and smaller. Semiconductor devices requiring performances to avoid electrical current leakage between adjacent components or also known as electrical signal cross talk would possess trench isolation structure, which includes shallow trench isolation (STI) and/or deep trench isolation (DTI).
For example, semiconductor image sensors are used for sensing light. Complementary metal-oxide-semiconductor (CMOS) image sensors (CIS) and charge-coupled device (CCD) sensors are widely used in various applications such as digital still camera or mobile phone camera applications. These devices utilize an array of pixels in a substrate, including photodiodes and transistors that can absorb radiation projected toward the substrate and convert the sensed radiation into electrical signals.
A back side illuminated (BSI) image sensor device is one type of image sensor device. As transistor device size shrinks with each technology generation, existing BSI image sensor devices may begin to suffer from issues related to cross-talk and blooming. It has been found that as image sensor pixel size decreases, the amount of cross-talk between adjacent pixels becomes more of an important issue. In general, cross-talk can be generated from two different sources: (1) optical cross-talk which refers to the ability to optically focus incident light over a pixel through its micro lens and onto the appropriate photosensitive element; and (2) electrical cross-talk which refers to the ability to collect the generated photo carriers in the photosensitive element where they are originally generated.