Transfer optimized dry development process of sub-32nm HSQ/AR3 BLR resist pillar from low-K etcher to metal etcher

Abstract

The optimized dry development condition of low-k etcher obtained before is transferred to and optimized in DPSII metal etcher in this study to avoid resist pillar collapse, etch residual magnification, process continuity and tool simplicity. Three key process parameters of oxygen flow rate, bottom power and e-chuck temperature are studied for vertical pillars with various pattern densities. HSQ pillar patterning is transferred from diluted Fox-12 to commercialized XR1541-002 where the film thickness and patterned CD are matched. LTN hard mask (HM) of 100 nm thick above RRAM film stack is deposited for reducing proximity effect of XR1541-002 and improving etch resistance. Experimental results are summarized below. Highest AR of ~3.9 for HSQ/AR3 BLR semi-dense L/S=1/3 pillar with vertical profile is obtained with optimized dry develop condition of O2, N2, flow rates, chamber pressure and temperature, top and bottom power of 8, 5, sccm, 3 mTorr, 80oC, 200 and 100 watts respectively. AR is lower for looser pattern density. Oxygen flow rate and bottom power are the most critical process parameters for obtaining high AR BLR pillar and most vertical profile of pillar, just like the case of low-k etcher. E-chuck temperature is critical in profile control. Etch residual is magnified to broaden LTN pillar CD and degrade CD uniformity (CDU) if its etch process is not immediately continued after dry development process.