The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings:
Smaller device and dimensions and tighter process control windows have created a need for CD metrology tools having higher levels of precision and accuracy. As critical dimensions (CD) for semiconductor devices shrink to a few tens of nanometers, the line edge roughness (LER) and line width roughness (LWR) becomes a critical issue.
As previously described, LER of a patterned line is an accumulation of the roughness originating from the resist, materials and etch. At the 90-nm and below, controlling the cross-sectional profile of critical layer structures such as gate patterning is key to maximizing yield and transistor performance.
The present invention pertains to a non-destructive, optical method for measuring and characterizing line width roughness (LWR) of a printed feature such as a critical layer of resist lines, which provides chipmakers with an effective in-line process control. The non-destructive, optical method of this invention is implemented using a spectroscopic critical dimension (SCD) optical metrology technique based on spectroscopic ellipsometry (SE), which is typically used to measure film thickness and film properties. Traditional SCD metrology techniques give no indication of a measured feature's line width roughness. However, the non-destructive, optical method of this invention may use other optical technologies such as reflectometry. Known vendors include but not limited to Timbre OCD and NOVA OCD.
The wafer 1 is transferred to the spectroscopic ellipsometry based SCD measurement tool 100 that is equipped with at least a broad-band light source 20, a rotating polarizer 30, an analyzer 40, a prism 50, an array detector 60 and a computer or data processing unit 120. For example, the SCD measurement tool 100 may be SpectroCD SCD measurement system available from KLA-Tencor Corp. or any equivalent systems.
According to the preferred embodiment, for example, the gratings 11 may be 3000-4000 angstrom photoresist lines over 100-200 angstrom bottom anti-reflection coating (BARC), but not limited thereto.
According to the preferred embodiment, for example, the gratings 11 are repeating line/space features of uniform period and have a line/space ratio of 80/100 nm (180 nm pitch). The line size and period of the grating are designed to represent the in-die feature that is being controlled.
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The contact hole model is defined by the following equation:
(x2/a2)1/1−r+(y2/b2)1/1−r=1
Varying the parameter values and calculating theoretical spectra construct the library.
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According to this invention, the present invention is particularly suited for a case that the L/S is less than 1/13.
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Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.