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Pattern Transfer Presentation Transcript
1.Pattern Transfer
2.Course Contents: UNIT
1: Introduction to technologies UNIT
2: Diffusion and Ion Implantation UNIT
3: Chemical Vapor Deposition and Layer Growth UNIT
4: Pattern Transfer UNIT
5: VLSI Process Integration
3.References: Stephen A. Campbell, The Science and Engineering of Microelectronic Fabrication, Oxford University Press, 1996. Garima Mathur and Rahul Mundra, Introduction to IC Technology, Ashirwad Publications, Jaipur, 2007 S. M. Sze, VLSI Technology, McGRAW-HILL, 1988. Hong Xiao, Introduction to Semiconductor Manufacturing, Prentice Hall, 2001. SK Gandhi, VLSI fabrication principles, John Wiley 1983. D. Nagchoudhuri, Principles Of Microelectronic Technology, Wheeler Publishing, 1998.
4.Maximum Marks and The Teaching Plan This Course has Maximum Marks 100 80 for final exam 20 for internal assessment
5.Teaching Plan
6.: Pattern Transfer Processes: Photolithography Etching
7.What is Lithography? Lithography (from Greek – lithos = 'stone' + graph? = 'to write') is a method for printing using a stone or a metal plate with a completely smooth surface. Lithography uses oil or fat and gum arabic to divide the smooth surface into hydrophobic regions which accept the ink, and hydrophilic regions which reject it and thus become the background. Invented by Bavarian author Alois Senefelder in 1796, lithography can be used to print text or artwork onto paper or another suitable material.
8.Lithography Process Lithography uses simple chemical processes to create an image. The positive part of an image would be a hydrophobic, or "water hating" chemical, while the negative image would be hydrophilic or "water loving". When a compatible printing ink and water mixture is applied to the plate, the ink will adhere to the positive image and the water will clean the negative image. This allows a flat print plate to be used, enabling much longer and more detailed print runs than the older physical methods of printing (e.g., intaglio printing, Letterpress printing).
9.Photolithography The word "lithography" also refers to photolithography, a microfabrication technique used to make integrated circuits and MEMS. Photolithographic techniques have more in common with etching than with lithography.
10.Objective of lithography: To transfer the designed pattern from the mask or reticle to the photoresist on the wafer surface.
11.Mechanism Some materials undergo chemical changes when exposed to light of a particular wavelength. (Photo-chemicals) Their solubility in some solvents (developers) is reversed. Their resistance to other chemicals (Etchants) also gets changed. When photo-chemicals are exposed through a patterned mask, developed and underlying layer etched, the designed pattern is transferred to the etched layer.
12.How it is done?
13.Photolithography
14.Photolithography (continued)
15.Basic Experimental Setup
16.Steps of Photolithography Process Vapor Prime Dehydration Bake Adhesion Promoter Application Spin Coat - Resist Application by spin coating Soft bake Alignment and Exposure Post Exposure Bake (PEB) Development Cycle Hard bake and Resist Stabilization Inspect Development
17.Step No. 1: Wafer Cleaning Purpose: To clean and dry the surface of the wafer Equipment: Chemical Bath, Water rinser, Spin dryer, Oven Method: Dip the wafers in solvent, Rinse in Deionized water to remove solvent, spin dry
18.Step 1b:Primer Coating
19.Step No. 3: Soft Bake Purpose – To remove solvent from PR Equipment – Hot Plate or Conventional Oven or Microwave Oven Method – Heat the wafer ~ 150 C for ~ 15 minutes
20.Step 4: 21.Step No. 5: PEB – Post Exposure Bake Purpose: to increase the inertness of the resist on the substrate to subsequent chemical, plasma or ion beam attack Equipment: Conventional Oven Method: Heat the wafer at ~ 200 C for ~ 20 minutes 22.Step No. 6: Pattern Development Purpose: to develop the desired pattern in the Photo-resist Equipment: Baths for developing and cleaning chemicals and spin dryer Method: Dip the wafer in the developing and rinsing chemicals for desired times and then spin dry.
23.Step No. 7: Hard Bake Purpose: to remove water and any other liquid and to harden the photoresist present on the wafer. Equipment: Oven Method: Heat at ~ 200 C for about 20 minutes
24.Step No. 8: Develop Inspect Optical Inspection under microscope (100X) is done to check for Line Resolution Line Width Resolution Particles and Defects .
25.Growth of Silicon dioxide by thermal oxidation .
26.Applications Fabrication of : VLSI devices MMIC devices Thin film hybrid microcircuits Thick film hybrid microcircuits MEMS devices LTCC Microsystems Micro-machining
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