A novel mid-infrared critical dimension (IRCD) metrology has been developed on a platform suitable for fab production. Compared to traditional optical critical dimension (OCD) technology based on ultraviolet, visible, and near-IR light, the IRCD system exploits unique optical properties of common semiconductor fab materials in the mid-infrared to enable accurate measurements of high-aspect-ratio etched features. In this paper, we will show two examples of critical dry etch steps in 3D NAND channel formation module of an advanced node that require nondestructive process control: (1) channel hole active area etch and (2) amorphous carbon hardmask etch. In the first example, we take advantage of the absorption bands of silicon dioxide and silicon nitride to get accurate CD measurements at different depths, resulting in high-fidelity z-profile metrology of the channel – key to guiding process development and accelerated learning for 3D NAND device manufacturing. In the second example, the most common amorphous carbon hardmask materials for advanced 3D NAND nodes are opaque in the traditional OCD wavelength range; however, in the mid-infrared, there is light penetration and hence spectral sensitivity to dimensional parameters including sub-surface features. We show successful detection of intentional process skews and as well accurate bottom CD measurements of the hardmask.
A waveguide surface plasmon resonance (SPR) optical sensor based on wavelength modulation is presented. Strip waveguides are fabricated using MicroChem's SU-8 photoresist via UV lithography. Next, a bimetallic silver-gold film is deposited on the waveguides for exciting surface plasmon resonance. The underlying silver yields better evanescent field enhancement of the sensing surface, while the overlying gold ensures that the stability of the metallic film is not compromised. Experiments were conducted using various glucose concentrations as the analyte, and the normalized transmission output of the waveguide shows a good SPR curve for all the analytes. With a better evanescent field extension, the proposed waveguide SPR configuration extends the use of SPR, especially in bio-sensing, as longer ligands can be immobilized and bigger analytes can be monitored.