Photomasks for semiconductors
Structure of binary mask is simple; it is a photomask blank covered with patterned layer of opaque material. Its transmission characteristics are either transparent or non-transparent. Binary mask is used for building a pattern in which line width being larger than the exposure wave length.
However, it is learnt that the binary mask is superior to the halftone phase shift mask used for immersion lithography for 32nm half-pitch or beyond.
Toppan and its blanks vendor have co-developed new type of binary blanks with superior workability (OMOG: Opaque MoSi on Glass). They have managed to create blanks for binary masks with better CD performance and higher resolution.
Phase Shift Masks
Phase-shifting mask (PSM) has achieved improved wafer printability with higher resolution and increased DOF (Depth of Focus), by controlling the phase shift and the transmission rate. This is a standard technology for lithography in which line width being smaller than the exposure wave length.
Most well known PSM is Halftone mask (Attenuated PSM) and Levenson mask (Alternating PSM).
Half-tone Phase Shift Mask
Half-tone mask includes chrome layer and semitransparent layer that shift the phase angle of an incoming light by 180 degree.
When light passing through materials, its speed is altered, which in turn, its phase angle is shifted. This material, a semitransparent layer is called "phase shifter".
Half-tone masks have achieved higher resolution, utilizing the interference of light created by a phase differences between with-phase shifter and without-phase shifter on the photomask blank.
EUV is a number one candidate of next generation lithography technique. EUV lithography uses EUV light (13.45nm), shorter wave length than existing DUV (ArF: 193nm), in which enabling us to fabricate smaller patterns. Unlike conventional DUV, EUV lithography requires reflective optics for wafer exposure systems and for masks, as EUV technology cannot focus light via conventional lens optics.
Toppan has built pilot line for EUV lithography and fabricated test masks to perform baseline assessment for its volume production.
Silicon stencil mask is a photomask for Electron Beam Lithography, with nanometer size apertures to fabricate nanometer scale patterns.
EB lithography has extensively studied in the semiconductor industry, exploring the replacement of optical lithography.
Toppan has been developing stencil masks as a core technology of microfabrication and establishing a supply system.
[EB writer and Stencil Masks]