Resists with robust defect margins for bright field patterning are critical to high resolution lithography. In this paper, we present the application of analytical techniques to screen high resolution photoresists with reduced tendency to form side-lobe defects from diffraction in ePSM and chromeless APSM lithography. Resist candidates are compared based on a novel method to determine accurate high-contrast development etch rate curve data from diluted normality analysis combined with attenuated FTIR. The measured data is applied to determine parameters for aerial image and molecular level resist models which screen potential resists for performance in side-lobe suppression within random mask layout. Feature level prediction and experimental validation is discussed as well as general selection criteria for high resolution, low-defect liability resist materials for severe bright field ePSM and APSM lithography.
The fabrication of phase shifting masks requires precise alignment between the primary and shifter layers. The MEBESR IV electron-beam lithography system uses its SEM mode to acquire a video image of the phase shift mask (PSM) alignment mark. Digital signal- processing algorithms have been developed to accurately determine the locations of the marks. Alignment marks are acquired through various resist systems and film thicknesses. Machine control software translates and rotates the MEBES coordinate system to align it with the mask coordinate system, as determined by the location of the alignment marks. Results showing overlay accuracy between layers are presented.
Issues associated with the commercialization of phase shift masks are discussed. Design layouts incorporating multiphase transitions and voting are presented along with methods of mask fabrication. Issues associated with mask inspection and repair are discussed, along with data on actual reticles produced using the prescribed method of manufacture. Cost of reticles in relation to potential wafer processing gains are compared along with problems associated with the increased complexity of the mask making process.
Phase-shifted patterns (alternating, 90-degree, and chromeless) have been incorporated into a reticle layout, fabricated with a MEBESR III system, and evaluated experimentally at 365 nm using steppers with numerical aperture (NA) ranging from 0.4 to 0.48 and partial coherence ranging from 0.38 to 0.62. Test circuit layouts simulate actual circuit designs with critical dimensions ranging from 0.2 micrometers to 1.2 micrometers . These results, combined with experimental measurement of layer to layer registration and aerial image simulations, provide a first-order assessment of e-beam lithography requirements to support phase-shift mask technology.
Proximity effect correction is necessary to fabricate masks with 0.25 micron design rules using electron beam lithography. The GHOST technique of proximity correction has the advantage of no pattern preprocessing and is easily implemented on a raster scan system such as MEBES. Recent results show proximity corrected features at 0.3 micron. To minimize constraints on the resist characteristics, such as the Srg ratio, global sizing of patterns has been investigated and found to provide an additional degree of freedom to control sensitivities and process latitude. Simulation and experimental results will be presented to demonstrate the use of GHOST and sizing for 1X mask making, including discussion of some of the relevant issues and tradeoffs.