Match List - I with List - II. Choose the correct answer from the options given below :List - I List - II (A) Annealing (I) Isolation (B) Sealing (II) Doping (C) Ion implantation (III) Packing density (D) Oxidation (IV) Crystal restoration
(A)-(IV), (B)-(III), (C)-(II), (D)-(I)
Two of the pairings are the heart of the question, and they are consecutive steps of the same process: ion implantation dopes, and annealing repairs the damage it causes. The code is (A)-(IV), (B)-(III), (C)-(II), (D)-(I) — option 4.
(C) Ion implantation and doping. Dopant ions are accelerated to tens or hundreds of keV and fired into the wafer. Compared with thermal diffusion it offers precise control of the dose, since the implanted charge is simply the integrated beam current, and of the depth, set by the accelerating energy. It is also anisotropic, so the dopant goes where the mask allows and not sideways.
(A) Annealing and crystal restoration — and why the two steps belong together. An implanted ion arrives with enormous energy and knocks silicon atoms off their lattice sites as it comes to rest, leaving a badly damaged and sometimes amorphous layer. Worse, the implanted atoms sit wherever they stopped, mostly in interstitial positions where they contribute no carriers at all. Annealing at 900–1000 °C does two things at once: it restores the crystal order, and it moves the dopants onto substitutional lattice sites so that they become electrically active. Without it, an implant would leave the wafer damaged and undoped in effect.
(D) Oxidation and isolation. A grown SiO2 layer has a band gap of about 9 eV and is an excellent insulator, so a thick field oxide grown between devices — the LOCOS process — keeps neighbouring transistors from interacting. Oxide also serves as the gate dielectric and as a diffusion mask, but among the four options offered, isolation is its match.
(B) Sealing and packing density. This is the pairing left by elimination, and it makes sense in terms of the final passivation and encapsulation of the die: how compactly devices and their interconnect can be sealed together governs how many fit in a given area.
| Step | Purpose |
|---|---|
| Ion implantation | Introduce dopants precisely |
| Annealing | Repair lattice, activate dopants |
| Oxidation | Insulate and isolate |
| Sealing | Protect the finished die |
Hence, the correct code is (A)-(IV), (B)-(III), (C)-(II), (D)-(I).
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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 :
Arrange the following in ascending order based on their diffusivity :
(A) Boron
(B) Arsenic
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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 :
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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:
