Dry etching: Spacer lithography is a patterning technique to define very short feature lengths. Spacer lithography can produce features smaller than photolithographic limits. The process involves the following. A patterned sacrificial layer of height 4h' is first made. A conformal thin film is then deposited on the substrate and the sacrificial layer with thickness h' (schematic). This conformal film covers all exposed surfaces with the same thickness, as pictured below. A purely anisotropic etch of the conformal film (degree of anisotropy Af = 1) is then performed using RIE with the following parameters: The RIE process etches the conformal film at h nm/min The RIE process etches the sacrificial layer at 3xh nm/min The RIE process does not etch the substrate Conformal Film Sacrificial Layer 4h Si substrate a. Starting from the above schematic, draw the cross section after 3 minutes of RIE etching. Be sure to include relevant dimensions in terms of h. b. What is the etch selectivity for this process between the conformal film and the sacrificial layer? c. What is the etch selectivity for this process between the conformal film and the substrate? Dry etching: Spacer lithography is a patterning technique to define very short feature lengths. Spacer lithography can produce features smaller than photolithographic limits. The process involves the following. A patterned sacrificial layer of height 4h' is first made. A conformal thin film is then deposited on the substrate and the sacrificial layer with thickness h' (schematic). This conformal film covers all exposed surfaces with the same thickness, as pictured below. A purely anisotropic etch of the conformal film (degree of anisotropy Af = 1) is then performed using RIE with the following parameters: The RIE process etches the conformal film at h nm/min The RIE process etches the sacrificial layer at 3xh nm/min The RIE process does not etch the substrate Conformal Film Sacrificial Layer 4h Si substrate a. Starting from the above schematic, draw the cross section after 3 minutes of RIE etching. Be sure to include relevant dimensions in terms of h. b. What is the etch selectivity for this process between the conformal film and the sacrificial layer? c. What is the etch selectivity for this process between the conformal film and the substrate