Question

Q1- Explain how lithography can be considered as top-down and bottom-up method?

Q2- List the growth modes observed in epitaxial thin film growth?

Answer 1

LITHOGRAPHY

Q1)•Lithography is a process that uses focused radiant energy and chemical films that are   affected by this energy to create precise       temporary patterns in silicon wafers or other materials.

•Lithography is an important part of the top- down manufacturing process, since these    temporary patterns can be used to add or     remove material from a given area.

Lithography refers to the fabrication of one- and two-dimensional structures in which at least one of the lateral dimensions is in the nanometer range. ... However, lithography is considered a hybrid approach, because the etching process is top-down, whereas the growth of nanolayers is bottom-up.

•Lithography is one of the 4 major processes in the top-down model

–Lithography

–Etching

–Deposition

–Doping

•In order to perform the other 3 processes,   we must precisely define where to do them

•With multiple etch, deposition, and doping processes taking place in the fabrication of a device, the lithography process is               repeated many times.

•The precision and accuracy of lithography    in the manufacturing process controls, to a first degree, the success in building a         device.

A bottom-up approach is the piecing together of systems to give rise to more complex systems, thus making the original systems sub-systems of the emergent system. Bottom-up processing is a type of information processing based on incoming data from the environment to form a perception. From a cognitive psychology perspective, information enters the eyes in one direction (sensory input, or the "bottom"), and is then turned into an image by the brain that can be interpreted and recognized as a perception (output that is "built up" from processing to final cognition). In a bottom-up approach the individual base elements of the system are first specified in great detail. These elements are then linked together to form larger subsystems, which then in turn are linked, sometimes in many levels, until a complete top-level system is formed. This strategy often resembles a "seed" model, by which the beginnings are small but eventually grow in complexity and completeness. However, "organic strategies" may result in a tangle of elements and subsystems, developed in isolation and subject to local optimization as opposed to meeting a global purpose.

GROWTH MODES

Q2)

1. . Thermodynamics–Growth Modes and StructuralMismatch

2. Kinetics

3. Growth Manipulation

4. Self-organized Growth