Proceedings Article | 23 March 2011
KEYWORDS: Overlay metrology, Scanners, Metrology, Semiconducting wafers, Critical dimension metrology, Lithography, Control systems, Diffraction, Process control, Diffraction gratings
As leading edge lithography moves to 22-nm design rules, low k1 technologies like double patterning are the new
resolution enablers, and system control and setup are the new drivers to meet remarkably tight process requirements. The
way of thinking and executing setup and control of lithography scanners is changing in four ways.
First, unusually tight process tolerances call for very dense sampling [1], which in effect means measurements at high
throughput combined with high order modeling and corrections to compensate for wafer spatial fingerprint.
Second, complex interactions between scanner and process no longer allow separation of error sources through
traditional metrology approaches, which are based on using one set of metrology tools and methods for setup and
another for scanner performance control. Moreover, setup and control of overlay is done independently from CD
uniformity, which in effect leads to independent and conflicting adjustments for the scanner.
Third, traditional CD setup and control is based on the focus and dose calculated from their CD response and not from
measurement of their effect on pattern profile, which allows a clean and orthogonal de-convolution of focus and dose
variations across the wafer.
Fourth, scanner setup and control has to take into consideration the final goal of lithography, which is the accurate
printing of a complex pattern describing a real device layout. To this end we introduce a new setup and control
metrology step: measuring-to-match scanner 1D and 2D proximity.
In this paper we will describe the strategy for setup and control of overlay, focus, CD and proximity based on the
YieldStarTM metrology tool and present the resulting performance. YieldStar-200 is a new, high throughput metrology
tool based on a high numerical aperture scatterometer concept. The tool can be used stand-alone as well as integrated in a
processing track. It is suitable for determining process offsets in X,Y and Z directions through Overlay and Focus
measurements respectively. In addition CD profile information can be measured enabling proximity matching
applications.
By using a technique [2][3][4] to de-convolve dose and focus based on the profile measurement of a well-characterized
process monitor target, we show that the dose and focus signature of a high NA 193nm immersion scanner can be
effectively measured and corrected. A similar approach was also taken to address overlay errors using the diffraction
based overlay capability [5] of the same metrology tool. We demonstrate the advantage of having a single metrology tool
solution, which enables us to reduce dose, focus and overlay variability to their minimum non-correctable signatures.
This technique makes use of the high accuracy and repeatability of the YieldStar tool and provides a common reference
of scanner setup and user process. Using ASML's YieldStar in combination with ASML scanners, and control solutions
allows for a direct link from the metrology tool to the system settings, ensuring that the appropriate system settings can
be easily and directly updated.
