As the most aggressive features in advanced memory designs continue to shrink, so does the overlay budget. The number of layer stacks also creates unwanted topography, and the alignment robustness of lithography tools becomes much more important for on-product overly. Canon developed a through-the-mask moiré alignment system for the FPA-1200NZ2C nanoimprint lithography (NIL) system allowing high-speed measurement of several alignment marks within each imprint field and alignment compensation to be completed during the imprinting sequence. To provide increased process flexibility and overlay accuracy while maintaining high-productivity, we have developed a new low-noise and high-resolution moiré diffraction alignment system based on spatial phase interferometry. In this paper, we report on the TTM detection system used in FPA-1200NZ2C. In particular, the principle of moiré detection and the improvement of the detection method will be described. The measurement error of moiré is analyzed by a simplified model calculation and we confirmed the relationship between process change and alignment error. Results of analyses proved that selection of the wavelength are key factors for optimizing alignment accuracy. Based on these results we applied the following improvement items: 1) Dual Dipole illumination, 2) Optimization of the alignment wavelength. We evaluated the new alignment system measurement error by comparing the moiré measurement value with the measured overlay values for 24 wafers and confirmed that new TTM alignment system can reduce to the measurement error more than 40%. The data shows that our moiré measurement system can provide process robustness and can support mass-production of leading-edge memory products.
Imprint lithography has been shown to be a promising technique for replication of nano-scale features. Jet and Flash Imprint Lithography* (J-FIL*) involves the field-by-field deposition and exposure of a low viscosity resist deposited by jetting technology onto the substrate. The patterned mask is lowered into the fluid which then quickly flows into the relief patterns in the mask by capillary action. Following this filling step, the resist is crosslinked under UV radiation, and then the mask is removed, leaving a patterned resist on the substrate.
There are many criteria that determine whether a particular technology is ready for wafer manufacturing. Included on the list are overlay, throughput and defectivity. The most demanding devices now require overlay of better than 4nm, 3 sigma. Throughput for an imprint tool is generally targeted at 80 wafers per hour. Defectivity and mask life play a significant role relative to meeting the cost of ownership (CoO) requirements in the production of semiconductor devices.
The purpose of this paper is to report the status of throughput and defectivity work and to describe the progress made in addressing overlay for advanced devices. In order to address high order corrections, a high order distortion correction (HODC) system is introduced. The combination of applying magnification actuation to the mask, and temperature correction to the wafer is described in detail and examples are presented for the correction of K7, K11 and K17 distortions as well as distortions on actual device wafers.
The rapid advancement in lithography and continuing shrink in feature dimensions demand tighter overlay tolerances for
fabrication of memory circuits with higher yields (Refer to table 1 for ITRS overlay requirements). To meet tight overlay
tolerances, sources of alignment errors need to be identified and corrected accurately. Alignment errors can be
contributed by 3 factors; wafer induced shift (WIS), tool induced shift (TIS) and WIS-TIS interaction. WIS is introduced
by wafer processing while TIS is introduced by the alignment tool (i.e. scanner or metrology).
This paper introduces methods for improvement of alignment performance at layers that experience WIS. A study on
mark reflectivity was done. A number of various alignment mark designs were evaluated. The most robust mark to
Tungsten Chemical Mechanical Polishing (WCMP) process, based on experimental results, will be illustrated. The
concept of the 'Alignment Parameter Optimizer' to select the best alignment illumination mode for each mark and the
best sample shots for alignment within the wafer, taking throughput into consideration, will be discussed. A new
alignment algorithm that is able to compensate for asymmetric alignment marks will also be presented in this paper.
Finally, production data from a Dynamic Random Access Memory (DRAM) manufacturer with the implementation of
the above-mentioned concepts will be illustrated.
The 65nm and the subsequent 45nm node lithography require very stringent CD control. To realize high-accuracy CD
control on an exposure tool, it is essential to reduce wavefront aberrations induced by projection optics design and
manufacturing errors and then stabilize the aberrations while the exposure tool is in operation. We have developed two
types of new hyper-NA ArF projection optics to integrate into our new platform exposure tool: a dry system and a
catadioptric system for immersion application. In this paper, aberration measurement results of these projection
systems are shown, demonstrating that ultra-low aberration is realized. In addition, a new projection optical system has
been developed which incorporates high degree-of-freedom Aberration Controllers and automatic aberration measuring
sensors. These controllers and sensors are linked together through Aberration Solver, a software program to determine
optimal target values for aberration correction, thereby allowing the projection optics to maintain its best optical
properties. The system offers excellent performance in correcting aberrations that come from lens heating, and makes it
possible to guarantee extremely low aberrations during operation of the exposure tool.
As the most critical semiconductor device geometries shrink down to the quarter micron order, requirements for overlay accuracy also become increasingly critical in the actual semiconductor manufacturing process. Factors in overlay error (especially, alignment error) originate in the interaction of process and tool. It is therefore necessary to improve alignment accuracy from both the process and the tool sides. In an effort to solve this as a tool supplier, we at Canon must minimize tool factors to reduce alignment errors caused by the interaction of process and tool factors. We though that we needed some evaluation criteria with such interaction take into account, and redefined the concepts of tool induced shift and wafer induced shift as a criterion. This paper introduces these new concepts and discusses validity of the criteria showing experimental results of alignment accuracy implementing the idea in the real process.
The frequency of an AlGaAs laser diode (LD) was controlled by using a photothermal effect. If intensity-modulated light from a heating LD is focused on the active domain of another LD, a heat spot changes the effective cavity length of the LD and thus modulates the lasting frequency. For frequency stabilization, frequency shift is detected by a Fabry-Pérot etalon, and it is compensated for by controlling the intensity of the heating LD via a proportional-integral-derivative controller. The highest stability obtained is 2.6x 10-11 (π = 10 s), which is an improvement of 2 to 3 orders of magnitude over the free-running state. In this method, the concurrent intensity modulation is much smaller than in the current modulation method.
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