Question

question about semiconductor devices

1. Why is not a physical mask necessary in electron beam lithography? How does the throughput of electron beam lithography compare to UV lithography?

2. What is a plasma, and how can it be formed? What are the advantages, and potential disadvantages, with a plasma-enhanced CVD process?

3. There are three important categories/families of dry etch processes, which are those three? Which one can give the highest anisotropy?

4. Ion implantation is today used for most impurity doping in CMOS (digital electronics) --- why? What are the advantages of ion implantation compared to doping by diffusion? Explain why high temperature annealing process is normally applied after ion implantation.

thank you for answering!

Answer 1

ANSWERS :

ANS 1. The physical mask is not necessary in electron beam lithography because it is not used to pattern the surface with beam of electrons as the pattern is already being programmed so as to increase the efficiency of how the beam will travel.

The throughput of electron beam lithography is low as compared to UV lithography

ANS 2. Plasma : it is a state of matter which is made up of atoms where some are electrons and positive charge ions move freely.

In semiconductor the plasma is formed by 2 ways which are sputtering and the other one is striping, where the plasma is created by using inert gases eg. Argon.

Advantages of plasma enhanced CVD process :

* It has high purity in compred to simple CVD.

* The temperature of deposition is very low.

* The plasma enhanced CVD provides easy control of reaction parameters.

Disadvantages of plasma enhanced CVD process :

* It has high temperature because of which cooling is necessary which is a cumbersome process making it less effective and thus it's temperature is a possible disadvantage.

* It uses inorganic materials which impose threat to the environment.

* It can sometimes produce toxic substances , so the risk of toxicity is high.

ANS 3. Three important categories of dry etch process:

a) Ion Beam Etching : In this argon ions are radiated into the surface . In the chamber another gas is led which reacts with argon to form the dry etch process.

b) Plasma Etching : It is isotropic thus used to remove the entire layers of film.

c) Reactive ion etching : It is both isotropic as well as anisotropic

The highest anisotropy is provided by Ion beam itching because due to perpendicular radiation the erosion on walls is very low thus anisotropy is high.

ANS 4. Ion implantation is used for most doping in CMOS because :

* In ion implantation the process time is short.

* There is low temperature throughout the process.

* In this process multiple materials can be used for masking that can be oxides, nitrides etc.

Advantages over diffusion :

* Ion implantation has advantages over diffusion that is the ion implantation is very directional and also isotropic so the impact is very high but in diffusion their is lateral diffusion so impact is less.

* In Ion implantation the depth of the implant can be controlled so it is more preferred.

* Ion implantation has a short process time and also relatively low temperature.

High temperature annealing is applied after ion implantation because the annealing process has a huge affect on the ion implanted solar cell this is because it control the diffusion and also the activation of the ion implants.