Read the following passage and answer the questions that follow : Diffusion of impurity atoms in silicon is important in silicon integrated circuit processing. The idea of using diffusion techniques to alter the type of conductivity in silicon or germanium was disclosed in a patent by Pfann. Since then various ways of introducing dopants into silicon by diffusion have been studied with the goal of controlling dopant distribution, total dopant concentration, its uniformity reproducibility, and of processing a large number of device wafers in a batch to reduce the manufacturing cost. The diffusion is used to form bases, emitters and resistors in bipolar devices technology, to form source and drain regions and to dope polysilicon in MOS device technology. Dopant atoms that span a wide range of concentrations can be introduced into silicon in many ways.
The idea of using diffusion techniques was disclosed in patent by Pfann in the year :
1952
William Pfann disclosed the use of diffusion to alter the conductivity type of silicon and germanium in a patent of 1952 — option 2.
Where the date sits in the history of the technology, which is what makes it memorable rather than arbitrary:
| Year | Development |
|---|---|
| 1947 | Point-contact transistor demonstrated at Bell Labs |
| 1948 | Shockley's junction transistor conceived |
| 1952 | Pfann's diffusion patent |
| 1958 | First integrated circuit (Kilby) |
| 1960 | First planar MOSFET |
Pfann's own major contribution was zone refining, the technique of passing a molten zone repeatedly along an ingot so that impurities are swept to one end. It is what first made semiconductor-grade material pure enough to be useful, and it is the necessary complement to diffusion: one removes unwanted impurities, the other introduces wanted ones under control.
Why diffusion mattered so much. Before it, junctions were made by alloying or by grown-junction methods, in which the junction depth was poorly controlled and set by mechanical or crystal-growth conditions. Diffusion made the depth a function of temperature and time alone:
\(x_{j}\propto\sqrt{Dt}\)
— both quantities that a furnace controls precisely. Thin, reproducible base regions became possible, and with them high-frequency transistors; and because the process works on a whole wafer at once through an oxide mask, it is what made batch manufacture possible. The passage's phrase about "processing a large number of device wafers in a batch to reduce the manufacturing cost" points at exactly this.
The date's significance in one line : it falls between the invention of the transistor and the invention of the integrated circuit, and it is one of the steps that made the second possible.
Hence, the year is 1952.
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Match the following :
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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 :
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(A) Boron
(B) Arsenic
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Fick's second law of diffusion in one dimensional form can be expressed as :
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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:
