Bengal Engineering and Science University 2006 B.E Electronics & Tele-Communication Engineering Microelectronics - Question Paper
the ques. paper is with the attachment.
Ex/BESUS/ ETC-405/ 06
B.E. (ETC) Part-II 4th Semester Examination, 2006
Time : 2 hours Full Marks : 50
Use separate answerscriyt for each half. One mark is reserved for neatness in each half.
FIRST HALF
(Answer Q.No.l and ONE_from the rest.)
1. What do you understand by (any four) : [4x3]
i) Isolation diffusion step in fabricating a Monolithic IC chip, ii)
Edge contouring and lapping of silicon wafers, iii) Molecular Impingement rate in MBE systems, iv) Projected Range &
Projected Straggle of Ion distribution, v) Electromigration in VLSI chips.
2. a) A silicon ingot, containing 10 boron atoms/cm1 is to be grown by the
Czochralski technique. Assuming a segregation co-efficient of 0.8 for boron atoms in silicon crystal, what is the concentration of boron atoms in the melt to offer the right concentration in the ingot? If the initial load of silicon in the crucible is 50 kg, how many gms of boron (atomic weight = 10.8) should be added? (Density of molten silicon is 2.53 gm/c.c).
b) Draw only a neat & labelled sketch of the CZOCHRALSKI APPARATUS for extracting single crystal p-si wafers.
c) What is Segregation Co-efficient? Give typical values. [5+5+2]
4. a) Draw a neat and simplified block diagram illustrating the connection of different pumps with a physical vapour deposition (PVD) system. Suggest the type of pumps to be used with PVD systems for attaining vacuum of the order of (i) 10"2 Torr, (ii) 10"5 to 10~6 Torr, (iii) 10"2 to 10~3 Torr.
b) Why chilling plants are compulsory unit attached to all vacuum evaporation systems? Which type of thin film materials calls for multiple source
evaporation? Why?
|(4+3)+(3+2)j
5. a) Identify clearly all the advantages in using GaAs wafers over Silicon wafers in fabricating electronic devices.
b) Describe very briefly the preparation of single crystal GaAs by the Horizontal Bridgeman (HB) technique. Mention the advantages of this technique vis-a-vis
the LEG process of preparing GaAs wafers.
(6+(4+2)j
6. a) Draw only a neat labelled sketch of the R.F. sputtering systems for depositing
thin films. What is meant by 'thin films'?
b) How can an ohmic electrode be deposited over thin film Gr II-VI semiconductors by using ELECTRODEPOSITION technique?
Suggest very briefly how you would proceed to verify the ohmic nature of the contact. [(4+l)+4+3)
a) Draw only four to five neat cross-sectional views of a silicon wafer subjected
to photolithographic window opening sequence by using negative PR.
b) What are the advantages of using Electron beam lithography over optical lithography?
c) What is the purpose of a Mask aligner? State some of its figures of merit.
[6+2+4]
b) Halide and Hydride process of preparing GaAs
c) Ion-Implant damages & its remedies.
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Attachment: |
| Earning: Approval pending. |
