IC Fabrication - An Introduction

IC Fabr Fabrica icatio tion n ² An Intr Introdu oducti ction on  Jau-Wen Lin, Ph. D.

Integrated circuit showing memory blocks, logic and input/output pads around the periphery

Integrated circuit showing memory blocks, logic and input/output pads around the periphery

Six

Level of Interconnection

IC device 

  

drain

 



Silicon chip

Tin/lead plated copper  leadframe

High lead solder die attach

Semiconductor Applications

 3C : Computer--- /Communication / Consumables  Personal Computer--- Desktop Computer (DT) / Notebook (NB)

 Communication--ADSL / Cable Modem / IEEE802.11X / Bluetooth / VoIP

 Consumables--Game / DVD / Digital Camera

 3C merge--- Digital Home

Types of Chips  Dynamic Random Access Memory chips (DRAMs) - serve as the primary memory for computers

 Microprocessors (MPUs) - act as the brains of computers.

 Application Specific Integrated Circuits (A SICs)

- are custom semiconductors designed for very specific functions

 Digital Signal Processors (DSPs) - process signals, such as image and sound signals or radar pulses.

 Programmable memory chips (EPROMs, EEPROMs, and Flash) - are used to perform

functions that require programming on the chip.

Semiconductor

Fabrication

Processes  Front-End Processing (Wafer fabrication)  Back-End Processing (Assembly and Testing)

Logic Circuit Design / Layout Design A logic circuit diagram is drawn to determine the electronic circuit required for the requested function. Once the logic circuit diagram is complete, simulations are performed multiple times to test the circuit·s operation.

Photomask Creation  The photomask is a copy of the circuit pattern, drawn on a glass plate coated with a metallic film.  The glass plate lets light pass, but the metallic film does not.  Due to increasingly high integration and miniaturization of the pattern, the size of the photomask is usually magnified four to ten times the actual size.

The photomask of a RF IC Chip

Wafer Fabrication  A high-purity, single-crystal silicon called "99.999999999% (eleven-nine)" is grown from a seed to an ingot.  The wafers are generally available in diameters of 150 mm, 200 mm, or 300 mm, and are mirrorpolished and rinsed before shipment from the wafer manufacturer.

Deposition  the wafer is placed in a high-temperature furnace to make the silicon react with oxygen or water vapor, and to develop oxide films on the wafer surface (thermal oxidation).  To develop nitride films and polysilicon films, the chemical vapor deposition (CVD) method is used, in which a gaseous reactant is introduced to the silicon substrate, and chemical reaction produce the deposited layer material.  The metallic layers used in the wiring of the circuit are also formed by CVD, spattering (PVD: physical vapor deposition)

Photoresist Coating  A resin called "photoresist" is coated over the entire wafer. (~1m thick coating.)  Photoresist is a special resin similar in behavior to photography films that changes properties when exposed to light.

Masking/Exposure  Placed over the photoresist-coated wafer, which is then irradiated to have the circuit diagram transcribed onto it.  An irradiation device called the "stepper" is used to irradiate the wafer through the mask with ultraviolet (UV) light.

Lithography area in clean room

Patterning: Development  The photoresist chemically reacts and dissolves in the developing solution, only on the parts that were not masked during exposure (positive method).  Development is performed with an alkaline developing solution.  After the development, photoresist is left on the wafer surface in the shape of the mask pattern.

Etching  "Etching" refers to the physical or chemical etching of oxide films and metallic films using the resist pattern as a mask.  Etching with liquid chemicals is called "wet etching" and etching with gas is called "dry etching".

Photoresist Stripping  The photoresist remaining on the wafer surface is no longer necessary after etching is complete. Ashing by oxygen plasma or the likes is performed to remove the residual photoresist.

Device Insulation Layer (FieldOxide Film) Formation  After the oxide film and nitride film are developed, a resist pattern is formed on the regions that will become the device insulation layer.  Ion implantation is performed on the wafer, forming a p-type diffusion layer.  Next, the oxide film and nitride film on the diffusion layer are etched.  Using the nitride film pattern as the mask, the oxide film that will become the device insulation layer is developed.

Transistor Formation  A transistor is a semiconductor device with a switching function and three terminals: source, drain, and gate.  An insulation layer called "gate oxide" is first formed on the wafer surface.  A polysilicon film is deposited onto the gate oxide, and a polysilicon gate for controlling the flow of electrons between the source region and the drain region is formed by lithography and etching.  After the polysilicon gate is formed, an ntype diffusion layer consisting of both the source and the drain regions is formed by implantation of impurities

Polysilicon Gate Cross-Section Image

Metallization  Interconnecting the devices, such as transistors, formed on the silicon wafer completes the circuit.  the wafer is first covered with a thick and flat interlayer insulation film (oxide film). Next, contact holes are drilled by lithograph and etching, through the interlayer insulation film, above the devices to be connected.

Nine-layer Copper Interconnect Architecture

Wafer Inspection  Each IC on the completed wafer is electronically tested by the tester.  After this inspection, the front-end processing is complete.

Dicing  In back end processing, a wafer completed in front end processing is cut into individual IC chips and encapsulated into packages.

Mounting  After the IC chips are cut apart, they are sealed into packages. The IC chips must first be attached to a platform called the "lead frame´.

Wire bonding  The mounted IC chips are connected to the lead frames.

Encapsulation  The IC chips and the lead frame islands are encapsulated with molding resin for protection.

Characteristic Selection  The packaged IC chips are tested and selected.