Chip processing techniques

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Chip processing techniques


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Semiconductor Wafer Processing:

Semiconductor Wafer Processing 1 From Crystal to Integrated Circuit

Learning Resources:

Learning Resources S. Mahajan & K.S.S. Harsha (1999) Principles of Growth and Processing of Semiconductor, WCB McGraw-Hill, 512pp. EE-527 Microfabrication , Photolitholgraphy , R. B. Darling. Mark. A. McCord, M. J. Rooks, SPIE HANDBOOK OF MICROLITHOGRAPHY, MICROMACHINING AND MICROFABRICATION. – INFRASTRUCTURE is primarily an electronic publication and research resource devoted to provide information about the Semiconductor, Semiconductor Equipment and Flat Panel Display Industries 2

Background Knowledge:

Background Knowledge To study this course effectively, students are expected to have relevant basic knowledge on: Materials Science Solid State Physics Fundamentals Physics 3


Terminologies Crystal Growth Epitaxy Oxidation Lithography Masking Local Doping Ion Implantation Etching Wafer Cleaning Diffusion Metallization Electrode Packaging Testing 4

Learning Outcomes:

Learning Outcomes Student should have the ability to: Elaborate the basics process in growing the crystal Describe the important steps in wafer fabrication such as epitaxy , oxidation, diffusion, lithography, photolithography, etching etc. Explain the final stage in wafer fabrication i.e. metallization, electrode, pacakaging and testing 5


Introduction To convert the semiconductor crystal into a device requires several fabrication steps. These steps include oxidation, diffusion, ion implantation, metallization, lithography, and etching. The following section gives the brief steps of semiconductor fabrication process. Details of each process which applicable are available elsewhere   6

The Chip MakingProcess:

The Chip MakingProcess 7

Making the Wafer:

Making the Wafer 8

Wafer Preparation :

Wafer Preparation The first stage of the fabrication process is to turn the single crystal of semiconductor material into many thinly sliced wafers. T he boule of semiconductor has a non-uniform diameter. In commercial wafer processing, high yields depend on the uniformity of the wafers. T he semiconductor crystal is machined on a lathe into a cylinder. The orientation of the crystal planes is fixed by the seed crystal, usually {100}, for many semiconductors including InP . The orientation within the plane must be fixed by x-ray diffraction. 9

Wafer Preparation :

Wafer Preparation Once the geometry of the cylinder is established, a flat is ground along the its length. The cylinder is sliced into thin wafers using a diamond annular saw. The cut wafers have some saw marks that must be removed. This is achieved using a combination of mechanical polishing and chemical etching until the surface of the wafer is optically flat. 10

The Mask Making Process:

The Mask Making Process 11


Epitaxy 12

Photolithography Process:

Photolithography Process 13

Mask and Lithography :

Mask and Lithography Masks are created to define areas that will be protected or removed during the lithography stage. Photoresist is spin-coated onto the semiconductor wafer. A photoresist is a light-sensitive material that on exposure to ultra-violet light causes it to undergo a chemical reaction. This is similar to the action of light on a photographic film. The photoresist is developed creating a negative Image of the mask. An etchant will selectively etch away the material not protected by the photoresist . There are two types of photoresist that react in differently on exposure to ultra-violet light. If the photo-resist hardens on exposure to the light, when the excess resist is removed a negative copy of the mask is left behind and hence it is known as a negative photo-resist. Positive resists are designed to degrade on exposure to light. When developed, the resist is deposited in those areas where the light did not expose the resist, resulting in a positive copy of the mask. As more components are packed onto a single chip, this demands the use of techniques such as electron-beam lithography or x-ray lithography. 14

Photolithography Processes:

Photolithography Processes 15

Oxidation and Exposure:

Oxidation and Exposure 16

Etching and Stripping:

Etching and Stripping 17


Etching Etching may be required in the fabrication of wafers, for example to create the mesa structure or in creating areas for re-growth for current blocking layers. The most common method of etching material is chemical etching. 18

Diffusion and Implantation:

Diffusion and Implantation 19


Diffusion 20

Thermal diffusion:

Thermal diffusion Thermal diffusion is a high temperature process where the dopant atoms are deposited on to or near the surface of the wafer from the gas phase. Wafers can be batch-processed in furnaces similar to those used for oxidation The impurity profile or distribution is determined mainly by the diffusion temperature and time, and decreases monotonically from the surface. The maximum concentration of a particular diffusing impurity is always found at the surface. 21

Thermal Diffusion:

Thermal Diffusion Furnace for diffusing impurities (e.g. phosphorus) into silicon . 22


Implantation The ability to modify the properties of a semiconductor through the addition of controlled amounts of impurity atoms is an important aspect of silicon device and IC manufacture. In the following sections, the two principal methods which are used to introduce impurities into silicon, thermal diffusion and ion implantation , will be discussed and the basic equations describing the impurity profiles below the surface of the wafer will be analysed . 23

Ion Implantation:

Ion Implantation Its consists of five main components; ( i ) the ion source where appropriate ion species are generated; (ii) the anal yser magnet which removes or filters out unwanted ions; (iii) the ion beam accelerator column which gives the selected ion species its energy; (iv) the horizontal and vertical scanning electtrodes which deflect the ion beam electrostatically and allow it to be scanned, or rastered , across the wafer; (v) the target which holds the wafer. The whole unit is housed inside a large vacuum chamber and wafers are transferred into and from the implanter one at a time. 24

Ion Implantation:

Ion Implantation 25


Deposition 26


Oxidation 27

Inter connection:

Inter connection 28


Metallization 29

Metalization :

Metalization There are three techniques that are commonly used to create contacts: thin-film vacuum evaporation sputtering electroplating 30

Chemical Mechanical Planarization:

Chemical Mechanical Planarization 31

Inter connect - Layers:

Inter connect - Layers 32

Inspection & Measurement:

Inspection & Measurement 33


Inspection 34

Test, Assembly and Packaging:

Test, Assembly and Packaging 35

Wafer Probe or Test:

Wafer Probe or Test 36

Memory Repair:

Memory Repair 37

Assembly and Packaging:

Assembly and Packaging 38

Package Test:

Package Test 39

Group Work Assignment:

Group Work Assignment Crystal Growth Techniques Epitaxy ; LPE, VPE, MBE Dry and Wet Oxidation Masking Lithography and Photolithography Local Doping Diffusion Ion Implantation Chemical Etching Wafer Cleaning Wafer Testing Dice Separation Metallization Electrode Packaging Testing Elaborate the integrated circuit (chip) making techniques . The discussion must include the following processes. Prepare also a poster with A0 size). 40