Improved resolution of an i-line stepper using a phase-shifting mask

Abstract

Improved resolution of an available i-line (365 nm) stepper using a phase-shifting mask is discussed. The resolution investigated here is not only for periodic lines but also for isolated spaces and hole patterns. To reduce the sizes of isolated space images for printing fine single spaces on a wafer, two additional line apertures with widths smaller than the critical dimension of the stepper lens are placed on each side of the main aperture of the mask. The optical phase of light passing through the main aperture and those through additional apertures are opposite. The additional apertures play a role in reducing the bright feature size to less than the line spread function of the lens. Similarly, printing a fine hole is accomplished by using a main aperture surrounded by four additional apertures. The intensity distribution on the wafer surface is simulated by comparing the images obtained with a phase-shifting mask and those obtained with a conventional transmission mask. Printing fine patterns are performed using an i-line stepper with a numerical aperture (NA) of 0.42. A pattern of 0.3 μm lines and spaces, 0.3 μm isolated spaces, and 0.4 μm hole patterns are resolved using the phase-shifting mask. The process latitudes and the effects of variations in the optical phase of the additional apertures are also investigated. The image simulations and experimental results suggest that the phase-shifting mask improve not only resolution but also exposure latitude and focus latitude. Furthermore, it is found that it is possible to control the position of the best focal plane by changing the optical phases of the additional apertures.

Computer-aided phase-shift mask design with reduced complexity

“…0.42 numerical aperture and 0.3 degrees of partial coherence. There are several advantages to our mask as compared to the one in [8,9]. There are several advantages to our mask as compared to the one in [8,9].…”

“…For comparison purposes, we have applied our algorithm to design a O.4jm contact hole for the same optical parameters used in [8,9], i.e. 0.42 numerical aperture and 0.3 degrees of partial coherence.…”

“Mask Enhancer” Technology on ArF Immersion Tool for 45-nm-Node Complementary Metal Oxide Semiconductor with 0.249 µm2 Static Random Access Memory Contact Layer Fabrication

“…This is one of the most notable advantages of the Mask Enhancer to achieve sufficient lithographic performance through pitch. Figure 2 shows several concepts of the typical phaseshifting masks for contact hole printing, such as the attenuated phase-shifting mask (Att-PSM), 5) the rim phaseshifting mask (rim-PSM), 6) and the outrigger phase-shifting mask (outrigger-PSM), 7) compared with the Mask Enhancer. All techniques except for the Mask Enhancer have basically the same principle of image enhancement even though the mask structures of these techniques are different.…”

<title>Phase plates in the object plane for microlithography</title>

“…The RIE process generally leaves a rough surface, which reduces the transmission of the phase-shifted apertures on such a "subtractive" mask . Fhe wet etch process leaves broad phase-shift steps, unacceptably undercutting the chrome 5 The successful mask makers guard their technology jealously, and charge premium prices for their output. While the high cost of a phase-shifting mask can easily be borne by a commodity product such as a semiconductor memory chip, the U.S. semiconductor industry makes its profits on application-specific integrated circuits (ASIC's) and microprocessors.…”