Match the following : Codes :List - I List - II (a) Lift - off (i) Fick's Equation (b) Dry Etching (ii) PMMA (Poly Methyl Methacrylate) (c) Lithography (iii) Bombardment of Plasma (d) Diffusion (iv) Structures of Target Material on the Surface of Substrate
(a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)
Each entry in List-II names the one thing that uniquely identifies its process. Take them one at a time.
(a) Lift-off → (iv) structures of target material on the surface of the substrate. Lift-off is a patterning technique rather than an etching one. A sacrificial resist layer is patterned first, the target material (metal, typically) is deposited over the whole wafer, and the resist is then dissolved — carrying away the unwanted metal and leaving the deposited material only where the resist was absent. The end product is exactly what List-II describes: islands of the target material standing on the substrate surface. It is the standard route for metals such as gold or lift-off-friendly alloys that are hard to etch cleanly.
(b) Dry etching → (iii) bombardment of plasma. "Dry" means no liquid etchant. Instead a gas is excited into a plasma and the resulting reactive species and energetic ions bombard the wafer, removing material chemically, physically (sputtering) or both, as in RIE. The defining feature is the plasma itself, and the practical payoff is anisotropy — vertical sidewalls, because the ions arrive vertically. Wet etching, by contrast, is isotropic and undercuts the mask.
(c) Lithography → (ii) PMMA. PMMA is the classic high-resolution resist, the workhorse positive resist of electron-beam lithography. Since a resist exists only to record a pattern from light or an electron beam, naming PMMA is naming lithography.
(d) Diffusion → (i) Fick's equation. Dopant diffusion into silicon is governed by Fick's laws:
\(J=-D\dfrac{\partial C}{\partial x}\qquad\text{and}\qquad \dfrac{\partial C}{\partial t}=D\dfrac{\partial^{2}C}{\partial x^{2}}\)
with \(D=D_{0}\exp\!\left(-\dfrac{E_{a}}{kT}\right)\), which is why diffusion depth scales as \(\sqrt{Dt}\) and why furnace temperature control is so critical.
| Process | Signature | Code |
|---|---|---|
| Lift-off | Deposited islands after resist removal | (iv) |
| Dry etching | Plasma bombardment | (iii) |
| Lithography | PMMA resist | (ii) |
| Diffusion | Fick's equation | (i) |
The pattern (iv), (iii), (ii), (i) is option 1. Note that even one certain link decides the question: diffusion with Fick's equation appears as (d)-(i) only in options 1 and 2, and dry etching is unmistakably plasma, which eliminates option 2.
Hence, the correct match is (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i).
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