Czochralski (Cz) method is used instead of using float zone technique to grow Si crystal because it produces :
large diameter crystal
Czochralski growth wins on one thing above all — diameter — option 2.
Why the two methods differ so sharply. In the float-zone method there is no crucible at all: a molten zone is held between two solid ends of the rod by surface tension alone, and moved slowly along. That is what limits the diameter, because the weight of a wider molten zone eventually exceeds what surface tension can support and the melt simply collapses. Float-zone ingots are therefore restricted to roughly 150 mm.
In the Czochralski method the melt sits in a quartz crucible and a seed crystal is dipped in and slowly withdrawn while rotating. The crucible carries the weight, so the diameter is limited only by the size of the furnace — and 300 mm wafers, with 450 mm demonstrated, are routine.
| Czochralski | Float zone | |
|---|---|---|
| Diameter | Up to 300 mm and beyond | Limited to ~150 mm |
| Crucible | Quartz — adds oxygen | None |
| Oxygen content | 1018 cm−3 | Very low |
| Purity, resistivity uniformity | Good | Better |
| Cost | Lower | Higher |
Why options 1 and 3 are wrong — they describe float zone's advantages, not Czochralski's. Because float-zone silicon never touches a crucible it picks up no oxygen or crucible impurities, so it is the purer and more uniform material, and it is the one used for high-power thyristors and detectors where a very high, uniform resistivity is essential. Czochralski silicon dissolves oxygen from its quartz crucible, and that oxygen is a defect source.
But the oxygen is not entirely unwelcome, which is worth knowing: dissolved oxygen strengthens the wafer mechanically against warping during thermal cycling, and precipitated oxygen deep inside the wafer acts as an intrinsic getter, trapping metallic contaminants away from the active surface layer. Czochralski material is therefore preferred for integrated circuits despite being less pure.
Why option 4 inverts the point. Producing a small diameter is no advantage at all — wafer area is what determines how many die each process run yields, which is why the industry has pushed diameters upward for fifty years.
Hence, Czochralski is chosen because it produces a large diameter crystal.
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 system of crystal growth is a
The thermal oxidation of silicon single crystal producer stacking faults lying on the plane.
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 :
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:
