Chromeless Phase Lithography (CPL) is discussed as interesting option for the 65nm node and beyond offering high resolution and small Mask Error Enhancement Factor. However, it was shown recently that at high NA CPL masks can exhibit large polarization and also phase effects. A well known phase effect occurring for CPL semi dense lines are through focus Bossung tilts.
However, another manifestation of phase effects for dense lines and spaces is a reduced contrast for a symmetrical off-axis illumination due to phase errors between 0th and 1st diffraction order. In this paper it is shown that these phase effects can lead to a significant contrast loss for dense features smaller than 60nm half pitch. While also present for trench structures, the contrast reduction is more pronounced for mesa style structures. It is shown that for mesa structures an adjustment of etch depth can not recover an effective pi-phase shift. Furthermore, significant polarization effects are observed. As an example, the optimum mesa structure for TE polarization is shifted to small lines.
For an experimental validation, a CPL mask containing dense lines and spaces was fabricated. Their imaging performance was characterized with an AIMS 45i offering NA's greater than 1 and linearly polarized illumination as well as by wafer printing. Gratings with pitches down to 100 nm with varying duty cycles were measured with TE, TM and unpolarized dipole illumination. Very good agreement between measurement and simulation results confirmed the validity of theoretical predictions.
The Cr-less Phase Shift Mask (CLPSM) has been considered as one of the most practical resolution enhancement techniques (RET) solution providing low Mask Error Enhancement Factor (MEEF) for low k1 geometries for memory and logic semiconductor devices. There are several papers that show the advantages of the CLPSM compared to the other types of RET. Also the required design changes have been widely studied.
Manufacturing of CLPSM requires quartz etching additionally to the COG mask process. Contrary to CLPSM, the required characteristics of the quartz etching process for altPSM are well specified. However, the required quality of the etching process for the CLPSM has not been sufficiently evaluated yet.
In this paper, the impact of imperfections of the mask manufacturing process, like the effect of quartz sidewall profile, etch depth deviation and quartz trenching during quartz dry etching on mask imaging performance is investigated. Simulations were performed using Solid-CTM to investigate these effects for both mesa and trench type CLPSM for different pitches. A CLPSM mask was manufactured at AMTC to confirm the validity of the simulation through comparing the contrast deviation on various mesa and trench sizes. AIMS measurements have been performed for this purpose.
Laser lithography tools have been a staple in the photomask industry for second level printing for several years. This paper explores the overlay capabilities of the Alta4300D Deep UV (DUV) lithography system. The tool is manufactured by ETEC Systems, a part of the Mask Business Group of Applied Materials. The tool demonstrates good overlay performance, and an improved data path ensures the ability to handle large file sizes without an adverse impact on writing time. In addition to actual performance data on product masks, a simple analysis of the maximum total edge placement error of a hypothetical two level alt-PSM process is presented. The results show the tool is capable for many advanced phase shift overlay applications.
A chrome-less phase-shift mask for the 70nm technology was designed and manufactured. The mask contains “lines and spaces” including programmed defects. Each defect was characterized with respect to the critical dimension (CD) variation on wafer, defect size, aerial image deviation, as well as inspection capture rate. It was found that defects with an AIMS intensity deviation of above 9 % are to be considered critical. The corresponding critical defect size is dependent on the defect type. All lithographically significant mask defects were found reliably using a KLA 576 inspection tool.