The application of SMASH alignment system for 65-55-nm logic devices

Abstract

65-55nmLogic-Devices require high performance of not only the resolution, of but also the overlay accuracy (Mean+3sigmas < 20-30nm). Thus, here, overlay performance of several layers in our advanced devices is investigated with using Immersion-exposure-tool. We used the new alignment system called SMASH TM which has the phase grating alignment sensor newly installed in our immersion-exposure-tool (XT1400Ei). SMASH supports flexible mark design in terms of size and pitch of the grating so that it can comply for our design requirement. SMASH has much smaller alignment beam size of ~ 40um for it.New mark design for our 65-55nm process will be investigated so as to obtain higher alignment accuracy than that of current marks. The alignment performance becomes more accurate proportionally to data density of the mark and it depends on the diffraction angle and efficiency from the mark. Thus, to obtain acceptable alignment accuracy with smaller mark, it should be designed such as diffraction efficiency is maximized within the required boundary condition in the pitch [diffraction angle] and segmentation of the mark.In this paper, several new marks are designed and evaluated. The evaluation shows that comparable performance could be obtained in the new design mark as in ASML's conventional marks. Finally, we select one from the new smaller marks and apply it to our 65-55nm process, especially, to the five process modules , and performance within 20nm (Mean+3sigmas) are typically obtained. The overlay accuracy needed for our 65-55nm Logic-Devices is successfully achieved with immersion-exposure-tool. SMASH* (SMart Alignment Sensor Hybrid) : the name of alignment system using with phase grating alignment sensor.

Evaluation of double-patterning techniques for advanced logic nodes

“…For the 32 nm half-pitch, the 2009 ITRS roadmap 19 calls for 2.2 nm and 3.2 nm for line and space CDU respectively, and 2.6 nm overlay (3sigma). Wafer alignment in the scanner correlates with overlay performance, and therefore any improvement to the alignment marks 20 , sampling procedure, and modeling, can lead to better overlay. By applying high-order wafer alignment together with an optimized sampling has been reported to reduce uncorrectable overlay residual by 30-40% and significantly improve wafer-to-wafer overlay variation 21 .…”

Analytic Design of Segmented Phase Grating for Optical Sensing in High-Precision Alignment System

“…Furthermore, tuning parameters numerically is a lengthy and costly process that requires a high-powered processor to deal with multiple variables simultaneously. The simulation complexity will be further increased and hence the design efficiency drops dramatically when multi-wavelength illumination is implemented to improve the physical signal robustness and to reduce the impact of asymmetric grating distortion, e.g., in some alignment systems using 532 nm and 633 nm wavelengths [5], some using 532 nm, 633 nm, 780 nm, and 852 nm wavelengths [10], and some even using a white light source [25]. A lot of research has been done on phase gratings based on scalar diffraction theory [26][27][28], especially in the field of Dammann grating [29,30].…”

“…The principle of PGA is that incident light irradiates uniformly at the grating surface and produces diffraction light with different orders. The targeted position can be extracted by the phases of the diffraction signals [ 9 , 10 ].…”

“…In general, the PGA sensors can detect nine diffraction orders of phase grating [ 9 , 10 ]. The diffraction light of the odd orders (DLO) is useful to calculate the measurement positions.…”

“…However, the diffraction light of the zeroth and the even orders (DLZE) is the main contributor of stray light which greatly deteriorates the signal quality. The diffraction light of the lower odd orders (L-DLO), such as the 1st and the 3rd, are often used to determine the measurement range, while the diffraction light of the higher odd orders (H-DLO), such as the 5th, the 7th, and the 9th, are often used to improve measurement accuracy [ 10 ]. In practice, the intensity of H-DLO is usually very low [ 11 , 12 ].…”