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).
Similar Questions
Match the following :
List - I List - II (a) Lift OFF (i) Etching (b) Rant's Rule (ii) Crystal Growtd (c) Hydrofluoric acid (iii) Packaging (d) Float zone (iv) Metallisation Codes :
What is the name of adhesion promoter used in case of positive photo resist ?
What is the correct sequence of the following step in the fabrication of a monolithic, bipolar junction transistor ?
1. Emitter diffusion
2. Base diffusion
3. Buried layer formation
4. Epi-layer formationSelect the correct sequence using the codes given below :
When silicon dioxide of thickness d is grown, the Silicon consumed is :
Match List - I with List - II.
List - I List - II (A) Annealing (I) Isolation (B) Sealing (II) Doping (C) Ion implantation (III) Packing density (D) Oxidation (IV) Crystal restoration Choose the correct answer from the options given below :
Arrange the following in ascending order based on their diffusivity :
(A) Boron
(B) Arsenic
(C) Antimony
(D) PhosphorusChoose the most appropriate answer from the options given below :
The idea of using diffusion techniques was disclosed in patent by Pfann in the year :
A thin layer of dopant is deposited onto silicon surface with a fixed total amount of dopants QT per unit area. If D is the diffusivity of dopants, then the surface concentration is :
Fick's second law of diffusion in one dimensional form can be expressed as :
For a diffused layer that forms a p-n junction an average sheet resistance RS is defined and related to junction depth xj, the carrier mobility μ, and impurity distribution C(x) as :
Important Questions from Semiconductor Process Flow
Which one of the following processes is preferred to form the gate dielectric (SiO2) of MOSFETs?
Arrange the following in the correct sequence of steps for MOS fabrication
A. Wafer formation
B. Photolithography
C. Oxidation
D. Gate and source/drain formation
E. Metallization
Choose the correct answer from the options given below:Which of the following statements are true for optical photoresists
A. Solubility of a photo-resist changes on exposure to light in developer solution.
B. Solubility of a photo-resist does not change on exposure to light in developer solution.
C. A negative photo-resist on exposure to light becomes less soluble in developer solution.
D. A positive photo-resist on exposure to light becomes more soluble in developer solution.
Choose the correct answer from the options given below:- In particle beam lithography, the resolution depends upon :
A. For impurity diffusion in semiconductor, concentration gradient is the only essential requirement.
B. Annealing is a mandatory step after ion-implantation.
C. Wet etching is normally anisotropic
D. High temperature is required for the growth of $SiO_2$ because oxidation reaction takes place at high temperature
E. Bird's beak formation is a characteristic of LOCOS isolation
Choose the correct answer from the options given below:
