1. Field of the Invention
This invention relates to test structures and methods used in semiconductor device fabrication.
2. Description of the Related Art
Damascene refers to a process for making interconnect lines in a semiconductor device. In a damascene structure 100 shown in FIG. 1A, damascene trenches 101 and 105 are formed using conventional patterning (e.g. lithography and etching) techniques. A diffusion barrier 102 is deposited on the trenches to prevent leakage of subsequently deposited metal 103 into a dielectric layer 104. In this particular example, metal 103 is copper while dielectric layer 104 is a low dielectric constant (xe2x80x9clow-kxe2x80x9d) dielectric material such as TEOS.
Chemical mechanical planarization (xe2x80x9cCMPxe2x80x9d) is used to remove portions of metal 103 which are outside the trenches and to obtain a flat surface for subsequent formation of overlying layers. CMP removes material from the semiconductor wafer by pressing the device side of the wafer against a rotating polishing pad in the presence of a slurry. FIG. 1B depicts structure 100 after a CMP process. A post-CMP clean is performed on the wafer containing structure 100 immediately after the CMP process to remove contaminants, residual slurry, and loose metal particles that were introduced during polishing.
As shown in FIG. 1B, a poor post-CMP clean can leave metal atoms 107 in field area 108,thereby causing a line-to-line short between trenches 101 and 105. Line-to-line shorts can lead to device unreliability if not catastrophic failure. Thus, the amount of metal atoms left in the area between the trenches (the field area) must be periodically determined and analyzed to ensure that metal atoms are adequately removed by the post-CMP clean process. Common methods for measuring metal concentrations in field areas include Secondary Ion Mass Spectroscopy (xe2x80x9cSIMSxe2x80x9d), Auger mapping, and Electron Energy Loss Spectroscopy (xe2x80x9cEELSxe2x80x9d). These methods, however, require expensive equipment and long setup time.
Thus, it is highly desirable to have a fast, sensitive, and simple technique for measuring metal concentrations in a field area.
In an embodiment of the invention, a voltage is applied on a first trench structure while a second trench structure is grounded. The resultant current is measured and used as an indicator of metal concentration in the field area between the trench structures.