Optimum biasing for 45 nm node chromeless and attenuated phase shift mask

Abstract

Resolution enhancement technology (RET) refers to a technique that extends the usable resolution of an imaging system without decreasing the wavelength of light or increasing the numerical aperture (NA) of the imaging tool. Off-axis illumination (OAI) and a phase shift mask (PSM) are essentially accompanied by optical proximity correction (OPC) for semiconductor device manufacturing nowadays. A chromeless PSM (CLM or CPL) is compared to an attenuated PSM (att.PSM) to make 45 nm dense line and space pattern. To obtain the best possible resolution, a proper OPC is required with CPL and the most common application of OPC technique is the use of space bias. The optical system with a high numerical aperture (NA), a strong OAI, and a proper polarization can decrease the k1 value well below 0.3. CPL has various advantages over alternating PSM such as no necessity of double exposure, small pattern displacement, and no CD error caused by the intensity imbalance. But CPL has some disadvantages. In the case of 100 % transmittance pure CPL, there is no shading material that is usually deposited on the line pattern for both att.PSM and alternating PSM to control the line width. Because of no shading material for CPL, the required resist critical dimension (CD) has to be obtained by using phase only and it is difficult to control the resist CD through pitch. As expected, CPL needs smaller dose than att.PSM to make the desired 45 nm CD with 0.94 NA. Our simulation results showed that 10 nm negative bias is optimum for CPL mask. We demonstrated that CPL mask and att.PSM technology can be used to make 45 nm node by the negative space bias.