Abstract
Scatterometry, the analysis of light scaattered by diffraction from periodic structures, is shown to be a versatile metrology technique applicable to a number of processes involved in microelectronic manufacturing. Contemporary inspection technologies such as scanning force microscopy (SFM) and scanning electron microscopy (SEM), apart from being slow and possibly destructive, in general cannot be used in-situ. Scatterometry, on the other hand, is rapid, nondestructive, inexpensive, and has the potential for use in-situ. In the production of a sub-micron microelectronic device, a typical series of process steps could involve the deposition of a poly-Si layer on oxide, followed by the application of an anti-reflection coating (ARC) and resist layer. After the resist is exposed and developed there are four dimensions which will affect further wafer processing: the linewidth of the resist, the resist thickness, and the ARC and poly-Si thicknesses. By varying the angle of incidence and continuously monitoring the diffracted power in any diffraction order, a scatter 'signature' may be obtained. We have demonstrated that there is sufficient information in one signature to determine all these dimensions at once, even when the linewidth dimensions are as small as 0.25 micrometers and the poly-Si thickness is on the order to 2500 angstrom. Results from determining these dimensions on a 25 wafer study show excellent agreement between the scatterometry measurements and measurements made with other metrology instruments (SEM and ellipsometer). For example, there is a 22.6 nm average difference between SEM and scatterometry measurements of 0.25 micrometers nominal linewidths. In addition, the repeatability (1(sigma) ) of this technique is shown to be sub-nanometer for all of the parameters measured (linewidth, resist height, ARC thickness, and poly thickness).
