Photomask Etching Methods for Producing Self-Aligned Phase-Shifting Features With Multiple Phase Values (Rim Shifters and Anti-Boundary Layers)
Original Publication Date: 2009-Jul-21
Included in the Prior Art Database: 2009-Jul-21
A method and system for fabricating 3-phase masks by using a single mask patterning step in conjunction with self aligning etching techniques is disclosed. A hardmask film is placed on top of an attenuating phase shift film, which resides on top of a quartz substrate. The single mask patterning step is followed by a self aligning etching process which isotropically etches the hardmask film to decrease its size in the X-Y dimension and forms clear features on the attenuated phase shift film.
Photomask Etching Methods for Producing Self -Aligned Phase-Shifting Features With Multiple Phase Values (Rim Shifters and Anti-Boundary Layers)
Disclosed is a method and system for fabricating 3-phase masks and creating Anti-Boundary Layer (ABL) structures by using a single mask patterning step in conjunction with self-aligning etching techniques. Mask designers typically use a 2-D model known as the "thin mask approximation" (TMA) to model how a photomask pattern translates into the pattern printed on a wafer. This model has significant inaccuracies. It would be much more accurate to use a 3-D model, but the computational requirements of a 3-D model make this impractical. The use of ABLs makes the TMA much more accurate.
A hardmask film is placed on top of an attenuating phase shift film, which resides on top of a quartz substrate. The attenuating phase shift film is etched away during the single mask patterning step. The hardmask film is also etched isotropically to reduce its size in the X-Y dimension. The hardmask film is then used for defining the features for the etching process. Thereafter, the attenuating phase shift film is etched to form clear features. This ensures that no extra write steps are required and no deposition tools are needed for forming a spacer in an ABL structure. Fig. 1 displays examples of ABL structures.
Fig. 2 illustrates a first method to create spacer using an isotropic etching process. In Fig. 2, a patterned resist includes a resist layer placed on top of a Chromium (Cr) layer, which resides on a quartz layer. In this etching process, directional etching of the Cr layer is followed by etching of the quartz layer. Subsequently, the Cr layer is etched isotropically, and the resist layer is stripped. Thereafter, the quartz layer is etched and the Cr layer is stripped away. Time required for isotropic etching process determines the width of spacer and time required for directional etching of the Cr layer determines the height of spacer.
Fig. 3 illustrate...