The desired properties of metallization for integrated circuits are A. low resistivity. B. low conductivity. C. easy to etch for pattern generation. D. tough to etch for pattern generation. E. no contamination with device or wafers. Choose the correct answer from the options given below :
A, C and E only
Context. Metallization is the step that deposits and patterns the metal layers forming the on-chip interconnects and the contacts to the devices. The requirements follow directly from what those interconnects have to do — carry signals with minimum loss, be shaped into fine lines, and not poison the silicon underneath.
A — low resistivity. DESIRED. Interconnect resistance causes IR drop on power rails and RC delay on signal lines:
\(R=\rho\dfrac{L}{A}, \qquad t_{delay}\propto RC\)
Lower ρ means faster, lower-loss wiring — which is exactly why the industry moved from aluminium (ρ ≈ 2.7 µΩ·cm) to copper (ρ ≈ 1.7 µΩ·cm).
B — low conductivity. NOT DESIRED. Conductivity is the reciprocal of resistivity, \(\sigma = 1/\rho\), so demanding low resistivity and low conductivity is self-contradictory. What is wanted is high conductivity.
C — easy to etch for pattern generation. DESIRED. The metal film must be selectively removed by photolithography and etching to leave fine, accurately defined tracks. A metal that etches cleanly and anisotropically gives sharp line edges and good dimensional control.
D — tough to etch. NOT DESIRED. This is simply the negation of C: a hard-to-etch metal causes residues, ragged edges and shorts between adjacent lines. (Copper is a real example — it does not form volatile etch products, which is why it is patterned by the damascene process, depositing into pre-etched trenches instead of etching the metal itself.)
E — no contamination of device or wafer. DESIRED. Metal atoms that diffuse into silicon act as deep-level generation–recombination centres, raising junction leakage and destroying minority-carrier lifetime; gold and copper are notorious for this. That is why barrier/adhesion layers such as Ti/TiN or Ta/TaN are inserted between copper and silicon.
Other properties worth knowing (not listed here): good adhesion to SiO2, the ability to form a low-resistance ohmic contact to silicon, resistance to electromigration at high current density, and a thermal-expansion coefficient close to that of silicon.
Collecting the desired properties gives A, C and E.
Hence, the correct answer is A, C and E only.
Similar Questions
The evaporation rate from a clean surface is related to the equilibrium vapour pressure Pe of the evaporating species of molecular weight M by an expression :
Czochralski (Cz) method is used instead of using float zone technique to grow Si crystal because it produces :
Czochralski system of crystal growth is a
The thermal oxidation of silicon single crystal producer stacking faults lying on the plane.
The major processing steps of BJT IC fabrication in VLSI technology are
A. Oxidation
B. Diffusion
C. Crystal growth
D. Photolithography
E. Epitaxial layer formation
Choose the correct ascending order from the options given below :
MEMS devices are within the size range of
Given below are two statements :
Statement I : Concentration of acceptor atoms in the region between isolation islands in a monolythic integrated circuit will be much higher then in a p-type substrate.
Statement II : The higher density is provided to prevent the depletion region of the reverse biased isolation to substrate junction from extending into the p+ type material.
In the light of the above statements, choose the most appropriate answer from the options given below :
Arrange the following fabrication steps in order needed to fabricate the IC :
(a) Oxidation (b) Etching (c) Metallization (d) Epitaxial growth
Codes :
Assertion (A) : In a bipolar IC fabrication, the diode isolation is used to isolate one device from the other.
Reason (R) : P+n diode used as isolation diode in IC fabrication.
Select your answer using the codes given below.
Assertion (A) : The epitaxial layer growth possesses the same crystal structure to that of the substrate on which it is grown.
Reason (R) : It can only be of similar conductivity type but possesses different value of resistivity to that of the substrate.
Select your answer using the codes given below.
Important Questions from Device Technology
- In the process of fabricating monolithic integrated circuits:
Maximum component density for a given PCB size can be obtained by
In MOSFET fabrication, the channel length is defined during the process of
The desired property of gate and interconnection metallization is
In a silicon oxidation model, \(\rm \frac{B}{A}\) is the linear rate constant and τ accounts for the shift in the time coordinate to account for the presence of the initial oxide layer, then the linear law is represented as:
