Phase Shift Masks - EAPSM
Embedded Attenuated Phase Shift Masks (EAPSM), at 248nm and 193nm wavelengths
EAPSM utilizes a wavelength-tuned, 6% transmission MoSiON absorber to produce a 180 degree phase shift. This improves resolution and depth of focus at the wafer lithography tool.
Leading-edge e-beam or laser patterning tools are used to define the top chrome layer. Once defined, the chrome layer serves as the pattern for the MoSiON below it by means of an inductively coupled plasma (ICP) dry etch process.
The mask is recoated with resist, and a "second-level" exposure performed using a laser patterning tool, to define the active phase-shift pattern area, while the mask fiducials, barcode and titles are left in high-contrast chrome.
Critical defects are repaired using precision beam or AFM tools, and verified using aerial image metrology (AIMS).
Proprietary cleaning and treatment processes minimize the risk of exposure-dependent haze defects developing, even after prolonged exposure in the wafer fab.