What is an IC ? [integrated circuit]

1. What is an IC ? [integrated circuit]

2. A IC consists of many functional blocks depending on its functionality. Every block again have its own functionality with sub blocks in it

3. If we express the same in technical terms Every block according to its functionality have an internal circuit Ex # like an op amp With in every block there will be sub-blocks performing some functions Ex # like a gate This sub block even have individual components connected in such a way to achieve a specific function Ex # transistor

4. Once a circuit is designed according to its functionality then we go for the physical implementation. If the circuit is small and if consists of a few transistors we can even implement it with hand But these days every functional circuit consists of a hundreds of thousands of transistors which is not possible to lay them out with hand and interconnecting them So we use a very large scale integrated circuit (VLSI) technology

5. This physical implementation of a circuit using VlSI technology can be classified in to three categories 1) CUSTOM VLSI DESIGN 2) SEMI CUSTOM VLSI DESIGN 3)PROGRAMABLE LOGIC DESIGN

6. CUSTOM VLSI DESIGN In CUSTOM VLSI design each and every component of the circuit will be placed and routed according to the functionality of the circuit. This make this design very complex and time consuming resulting in a very high NRE costs But the main advantage of this design is maximum optimization of the circuit which results in less power consumption and faster speed of functionality

7. SEMI-CUSTOM VLSI DESIGN In Semi Custom VLSI design we use already built standard cells or gate arrays That is the common logic functional blocks which were already built will be interconnected and used This results in reducing the design time and layout time considerably .But the disadvantage of these kind of design is that maximum optimization of the circuit is not possible which results in high power consumption and less speed in performing the function

8. PROGRAMABLE LOGIC DEVICE In this method we have already built blocks called programmable logic Device (PLD) In this method every PLD is connected to each and every gate present in the block programming of these kind of IC is done by using a nonvolatile or volatile memory technology,or by using antifuse technology The main disadvantage of this method is that there will be many unwanted elements which consumes more power resulting in bad functioning of the circuit

9. Now we will look at the way how an IC is laid out by using different technologies EX# 0.18u technology,0.25u,0.35u….etc

10. What is a technology ? Technology is a set of rules which the designer follows for laying out a design This gives all the set of rules which we should Follow in order to get desiered functionality This specifies the distance that is to be maintained Between two layers or two components in a chip

11. mask Mask layout mask Structural design mask Layering on silicon mask Layout design mask Wafer resting mask Chip cutout/ packaging

12. chip ingot Silicon wafer

19. Etching of oxide: Wet etching • It employs a liquid solution that dissolves oxide only. • Mostly buffered Hydrofluoric acid is used. • The wafer is immersed in plastic tank containing HF. • It produces sloping sidewalls under photoresist, because of isotropic etching by HF acid.

20. Nitride Pad Oxide Nitride Window Thick Oxide Bird’s Beak Local oxidation of silicon (LOCOS) • It allows selective growth of thick oxide layers. • A thin pad oxide is grown for protection from mechanical stresses. • A nitride film is produced on pad by chemical vapor deposition. • The nitride is patterned to expose the regions to be selectively oxidized. • Then it is oxidized. • The nitride layer is then stripped off.

21. Oxide Depression Before Oxidation After Oxidation Oxide Step • It is the surface discontinuity produced due to difference in oxide thickness and in the depths of the silicon surfaces. • The reason being repeated oxidation and etching to form masking layers.

22. N-type dopant source Oxide Window Oxide Step 2: Deposit dopant Step 1: Oxide removal Step 3: Drive in dopant P-type silicon N-type diffusion Fabrication of diode (planar process) • Oxide film is grown and photo lithographically patterned and etched. • A dopant source is spun onto the wafer to touch the silicon • Wafers are heated in furnace to drive dopant into silicon, which forms shallow counterdoped regions. • The finished wafer is diced to form hundreds of diodes.

23. Poly Oxide Platinum Silicon Silicide Silicidation (Cont…) • Immediately after the contacts are opened, a thin film of platinum is deposited across the entire wafer. • Wafer is heated to cause portions of platinum in contact with silicon react to form platinum silicide. • The unreacted platinum is removed using a mixture of acids called aqua regia. • It silicides both contact openings and any exposed polysilicon.

24. Before we go for a Mask layout of any tool.We simulate verify and Check the design by using Electronic Design Automation(EDA)tools

25. Tools for Custom Layout • VIRTUOSO • Lasi • L-Edit • Magic

26. Schematic representation of an element using virtuoso

27. Layout of an Element using Virtuoso

28. Tools for SemiCustom Layout • Ambit • Physically Knowledgeable synthesis (PKS) • Silicon Ensemble