In semiconductor chip manufacturing, dedicated metrology targets are used for measuring overlay (OVL) between layers after the lithographic process step. Until recently, overlay targets have had typical dimensions of 20x20 microns, but have been reduced in size to allow for more critical product real estate. Reducing metrology target size, however, increases optical crosstalk and diffractions from the target’s edges which can introduce significant errors in the reported OVL values. In this work, we will evaluate the following parameters: 1. The beam spot shape on the metrology target 2. The best target design under size/wavelength constraints 3. Improved OVL extraction algorithm We will present the hardware and software optimizations for experimental measurements taken over a cascade of targets. While decreasing the target’s size, we quantified the OVL measurement performance via dynamic precision, tool-induced shift (TIS), and results through focus (Z position). We will demonstrate how these optimizations enable the measurement of targets as small as 6x6 microns without compromising throughput or measurement quality.
Scribe line width reduction and high-order scanner correctibles are driving overlay (OVL) target size reduction. Shrinking imaging-based overlay (IBO) target size for standard target types, such as AIM® or BiB, is not possible without a performance impact. In this paper, new target layouts and supporting OVL tool setup methods will be explored to enable small OVL targets to meet performance, accuracy, and robustness requirements. Two approaches have been explored: (1) measuring smaller grating pitches utilizing oblique illumination, and (2) measuring targets not obeying 180° rotational symmetry requirement (half-targets). Each of these approaches allows shrinking conventional imaging OVL target area by a factor of two. Evaluation results are reviewed in this paper and further target size reduction is presented.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.