1. Field of the Invention
The present invention relates to a method of forming trench isolation, and more particularly, to a method of forming both shallow trench isolation and deep trench isolation of a semiconductor device.
2. Description of the Prior Art
Semiconductor manufacturing process involves a series of processes for forming and configuring structures of electronic elements in and on a semiconductor substrate. Each of these electronic elements, such as MOS transistors, must be electrically isolated from the others in order to avoid shorting the circuits.
A variety of techniques have been developed to prevent these electronic elements from interfering with each other. Among these techniques, trench isolation has been most commonly used in semiconductor manufacturing. Typically, different depths of the trench isolation are required according to the properties of the isolated electronic elements. For example, shallow trench isolation (STI) is capable of isolating the MOS transistors in a peripheral area or logic area. On the other hand, deep trench isolation (DTI) is required for high voltage elements or sensing elements. Thus, shallow trenches and deep trenches are often required to be formed in a semiconductor device.
Trench isolation structures are typically formed by steps of mask patterning, trench etching, trench filling, and planarization. As for the trench isolation structures with different depths, a conventional method is simply separating the formation of STI structures and DTI structures into two sequential processes. In other words, the aforementioned steps repeat twice to form the STI and DTI respectively, leading to a lengthy and inefficient fabrication process. Accordingly, there is a strong need in the art for alternate methods of forming both STI and DTI of a semiconductor device.