With the objective to ramp-up 65 nm CMOS production in early 2005, preliminary works have to start today to develop the basic technological in order to be correctly prepared. In the absence of commercial advanced 193 nm scanners compatible with these aggressive design rules, electron beam technology was employed for the realization of a first 6-T SRAM cell of a size of 0.69 μm2. This paper highlights the work performed to integrate E-beam lithography in this first 65 nm CMOS process flow.
Quality of exposures on Step&Scan systems highly depends on stages synchronization. While scanning, wafer and reticle stages must have same relative speed (4x ratio) and directions. In this paper, we investigate the tolerance to lateral vibrations of 0.18micrometers and 0.12micrometers gate patterning respectively on an ASML PAS5500/750E scanner (KrF) and a PAS5500/900 scanner (ArF) exposure tools. Results should be given both on the MA impact on overlay and the MSD effect on CD control. But, as no adapted experimental method has been found to correlate overlay degradation to induced MA and then confirm the theory that 1nm of MA induces 1nm of translation, only results on CD control will be discussed, including lateral MSD impact on nominal CD variations, process latitudes degradations and intrafield CD dispersion. In particular, we will show that MSD effect on CD strongly differs from 248nm imaging process to 193nm one.
Flare is known to be responsible for a contrast lost and a process latitude reduction. Another undesirable effect is the flare variation, which induces linewidth variation. For a stepper, this is mainly an intrafield effect. In the same way, the main contribution of flare variation comes also from the across field flare variation (AFFV). In comparison the contribution to across wafer flare variation is weak. Using a scanner, AFFV and flare mean for an isolated field has been reduced by a factor of two. Unfortunately, stray light variation across the wafer has increased, but AWFV and flare mean with adjacent field has not dropped significantly. In this paper, the averaged flare, AFFV and AWFV will be compared on a 248 nm stepper ASM/300, a scanner ASM/500 and 193 nm scanner ASM/900. Different parameters such as field size, bottom anti reflective coating, adjacent field and exposure at the edge of the wafer will be analyzed on mean flare value, AFFV and AWFV. An averaged flare for isolate field and AFFV improvement has been observed for the scanner. However, flare impact needs to be carefully considered because AWFV and flare mean with adjacent field is still not negligible. Flare value seems also to drop significantly with the wavelength change, but more experiments need to be done on this non mature technology.
The aim of this paper is to investigate the intrafield flare distribution and its link with the intrafield CD variation for various ASML lithographic tools. Flare is measured as the required dose to clear a 100micrometers -large positive resist pattern and comparing it with dose-to-clear Eo. The reticle layout used is compared of a repetitive cell which allows for 77 measurements within a single 22 X 22 mm2 field. Experimental results show that in the field of a stepper, flare decreases almost linearly form center to edge. In the field of a scanner, the flare distribution result from the distribution inside the illumination slit which is ellipsoidal. Comparing the intrafield flare distribution to the intrafield CD uniformity , it appears that flare is responsible for a part of the across field CD variation. We will see in this paper how it is possible, using a method based on statistical considerations, to decorrelate both the contributions of mask CD errors and flare variation to the intrafield CD dispersion for dense lines and 1/3 for isolated lines. The intrafield flare variation is also found to contribute a lot to the signature of the CD uniformity and to the 3 sigma dispersion.