Slide 1: Intro to Photolithography
Intro to Photolithography Reviewed 2025 © 2009-2025 Micron Technology, Inc. All rights reserved. Information, products, and/or specifications are subject to change without notice. All information is provided on an “AS IS” basis without warranties of any kind. Statements regarding products, including
Slide 2: Copyright guidelines
Copyright guidelines By using any content provided by the Micron Educator Hub, you acknowledge that Micron Technology, Inc. (“Micron”) is the sole owner of the content and agree that any use of the content provided by the Micron Educator Hub must comply with applicable laws and require strict compli
Slide 3: How to cite sources from the Micron Educator Hub
How to cite sources from the Micron Educator Hub • Micron is committed to collaborate with Use case How to cite sources educators to make semiconductor memory Whole slide deck or whole No additional citation required education resources available through the document Micron Educator Hub Description:
Slide 4: Table of Contents
Table of Contents 1 Purpose of Photolithography - Align and Expose - Post-exposure bake 2 Photolithography in the overall process flow - Develop 3 Photolithography process basics 6 Equipment used in Photolithography - Resolution, wavelength, Numerical Aperture - Immersion lithography 7 Primary Measu
Slide 5: Intro to Photolithography – goal and objectives
Intro to Photolithography – goal and objectives Goal Objectives • Provide a foundational understanding of • State the purpose of the Photolithography process Photolithography in the semiconductor memory and how it fits into the overall semiconductor industry and the role of the Photolithography memo
Slide 6: Target Audience
Target Audience • This Intro to Photolithography module covers the basics of Pro tip semiconductor photolithography process. Everyone interviewing at Micron • NCGs (New College Grads), and new employees in technical can use this presentation to roles need to understand these concepts prepare for the
Slide 7: Purpose of Photolithography
Purpose of Photolithography 7
Slide 8: Purpose of Photolithography
oxide 1 Purpose of Photolithography Areas where oxide needs to be removed silicon Example to explain the purpose of the Photolithography process in semiconductor memory fabrication resist 2 1. A silicon wafer has a layer of silicon dioxide (a.k.a. Photolithography oxide process oxide) and the silico
Slide 9: Purpose of Photolithography (cont’)
Purpose of Photolithography (cont’) Another example to explain the purpose of the Region of silicon where higher conductivity needed 1 Photolithography process in semiconductor memory silicon fabrication resist 1. A region of the silicon wafer needs to have higher Photolithography 2 conductivity whe
Slide 10: Photolithography basics
Photolithography basics A house floorplan A DRAM memory die floorplan • Photolithography establishes the “floorplan” for the wafers – Sets down temporary layers – These layers guide other process areas like Etch and Implant in building the structures needed on wafer to create the different component
Slide 11: Interesting Facts About Photolithography
Interesting Facts About Photolithography • The word photolithography literally means in Greek: – Using light (photo) – On stone (litho) – To print or write (graphy) • At Micron, the words “Photolithography” and “Photo” are used interchangeably • The words “photoresist” and “resist” are also used int
Slide 12: Photolithography in the Overall Process Flow
Photolithography in the Overall Process Flow 12
Slide 13: Wafer Processing Areas – Five Basic Actions
Wafer Processing Areas – Five Basic Actions Add Material Remove/Etch Create Patterns Change Electrical Measure/Inspect Material Properties Dopants Resist Resist Oxide Oxide Oxide Oxide Oxide Silicon Silicon Silicon Silicon Silicon • Diffusion • Dry Etch • Photolithography • Implant • Metrology • CVD
Slide 14: Simplified Wafer Processing Flow
Simplified Wafer Processing Flow Wafer Start Wet Process Probe Testing Beginning of Fabrication End of Fabrication Clean CVD, Diffusion, PVD Ion Wet Process Wet Process CMP Film Deposition, Implant Clean Oxidation, Clean Planarization Metallization, Anneal, or Plating Photo Patterning Wet Process Dr
Slide 15: Wafer Process Traveler and Recipes
This Traveler step takes place Wafer Process Traveler and Recipes in the Photolithography area. Step # Traveler Step Fab Area At Micron, the sequential list of every step needed to make a memory chip is called a Traveler. Other 161 TG - GATE HARDMASK DEPOSITION CVD semiconductor companies may call i
Slide 16: Breakout of Traveler Steps by Functional Area
Breakout of Traveler Steps by Functional Area Photolithography The pie chart on the right shows a typical distribution of the percentage of traveler steps by each fab area in memory manufacturing. 16
Slide 17: Photolithography Process Basics
Photolithography Process Basics 17
Slide 18: Photolithography
Photolithography Ultraviolet • The Photolithography area defines a temporary pattern that other areas (usually Dry Etch Light or Implant) use as a mask to create the structures or implants needed on the wafer. Reticle (Mask) • The temporary pattern is created on a photosensitive film called photores
Slide 19: From circuit design to photolithography
From circuit design to photolithography 4 Each reticle creates a 1 Circuit designers design 3 Each layer of the layout is written into a reticle. unique photoresist pattern at the circuits of a new memory Dozens of reticles are needed to manufacture the a specific Photolithography memory chip. Here
Slide 20: Photolithography Overview
Photolithography Overview 1. Light 1 Light • Light from an ultraviolet (UV) source. Reticle moves 2 Reticle (Mask) 2. Reticle • Also known as photomask or mask • Contains the pattern to be transferred to photoresist • In semiconductor memory manufacturing the reticle pattern is typically 4X larger t
Slide 21: Dimensions definitions
Dimensions definitions Light • CD = Critical Dimension Pitch Reticle (Mask) • CD examples: – Line Width Resist – Space Width – Diameter (for contacts) • Pitch = Line CD + Space CD Lens (optical system Pitch Half Pitch • If Line = Space – Then Half Pitch (hp) = CD Resist • In the semiconductor memory
Slide 22: The Quest for Smaller Pitches
Example: given a certain memory density (e.g. 1 Gb)… The Quest for Smaller Smaller pitch enables Pitches smaller die size Original Pitch New smaller Pitch • Pitch Size Matters! • Photolithography is usually tasked with printing the Resist smallest pitch possible – But of course, process must be manu
Slide 23: Resolution
Resolution • Resolution = how small can we print? • The Rayleigh’s equation helps answer this question Rayleigh's Equation factor that depends on process characteristics • Rayleigh’s equation indicates: k Light wavelength (lambda) R= 1) As Wavelength () Resolution NA Numerical Aperture of the im
Slide 24: Electromagnetic Radiation - Wavelength
Electromagnetic Radiation - Wavelength • Light is an Electromagnetic Wave Wavelength () • Wavelength () is the distance between the peaks of a wave • Visible light has wavelengths from about 380 nm (violet) to 700 nm Amplitude (red). With visible light, wavelength is perceived as color. • Photolit
Slide 25: Wavelengths used in the memory semiconductor industry
Wavelengths used in the memory semiconductor industry • Wavelengths used in Photolithography to expose photoresist in Semiconductor Memory manufacturing: 365 nm, 248 nm, 193 nm, 13.5 nm (EUV) k Which of the wavelengths used in R= Photolithography can resolve the smallest pitch? NA Hint: look at R
Slide 26: Numerical Aperture
k Numerical Aperture R= NA • Numerical Aperture (NA) is a value that characterizes the size of the lens and its ability to capture light from a wide range of angles. Light Reticle (Mask) • NA can be described as the “light gathering ability” of an optical system. • Higher NA systems can resolve o
Slide 27: Intro to Immersion Lithography
Intro to Immersion Lithography • The Index of refraction (nf) is the ratio between the speed of light in a air vacuum and the speed of light in another medium or material. • It is the measure of how much light slows when it travels through a water medium or material (with respect to perfect vacuum)
Slide 28: Intro to Immersion Lithography
Immersion Lithography Intro to Immersion Lithography Ultraviolet Light • Historically, the space between the lens and the wafer has been filled Reticle (Mask) with air (Dry Lithography) • Immersion Lithography was introduced to achieve the effect of increasing the numerical aperture (NA) of the syst
Slide 29: Resolutions by technology
Resolutions by technology k R= NA Resolution by Photolithography technology Technology I-Line DUV 193 nm DUV dry 193 nm DUV EUV Immersion Wavelength 365 nm 248 nm 193 nm 193 nm 13.5 nm Light source Mercury arc lamp KrF excimer ArF laser ArF laser Sn laser pulsed laser plasma Numerical NA = 0.45 t
Slide 30: Photolithography Parameters: Focus
Photolithography Parameters: Focus • Focal plane refers to the precise vertical position of the wafer where the projected image from the scanner lens is sharply formed. The wafer stage can be adjusted vertically to place the resist in the focal plane. • The typical unit used to describe focus is nm.
Slide 31: Depth of Focus (DOF)
Depth of Focus (DOF) • Large DOF • Depth of Focus is the range of focus positions that • The items at the front of the yields an acceptable image, i.e., the range in which image and the ones in the the image is in focus and clearly resolved. back have similar “sharpness” (in focus) • Large DOF is de
Slide 32: Numerical Aperture and Depth of Focus
Numerical Aperture and Depth of Focus • A higher NA lens system captures a larger diffraction angle of light k Higher NA is capable of resolving smaller pitches (higher resolution), BUT . . . R= NA Higher NA reduces Depth of Focus (DOF) proportional to 1/NA2 • DOF is the range in which the image
Slide 33: Photolithography Parameters: Dose
Photolithography Parameters: Dose • Dose: is the amount of light energy that reaches the photoresist. • Dose has units of energy per unit area – The typical unit used to describe dose is mJ/cm2 (milli Joules per square centimeters). • Dose must be adjusted within a narrow range to achieve the desire
Slide 34: k1 – Rayleigh’s Process Coefficient
k1 – Rayleigh’s Process Coefficient • k1 is a process coefficient in the Rayleigh equation • k1 is a complex factor based on several lithography variables such as: – Quality/type of photoresist – Resolution enhancement techniques utilized 𝑘1 × 𝜆 - PSM - Phase Shift Masks 𝑅= 𝑁𝐴 - OAI - Off-Axis…
Slide 35: Intro to Reticles
” 2 a] Intro to Ret micron
Slide 36: Reticles
Reticles • Reticles, also called Masks or Photomasks, are used in Photolithography to expose Light a temporary pattern on the photoresist Quartz Reticle (Mask) • Micron uses different types of reticles. The reticle type described here is the Binary Chrome reticle (quartz + chrome). Other types of re
Slide 37: Reticles
Reticles Binary Reticle • The reticles are delivered to the wafer fab where Quartz (transparent) they are used in the Photolithography tools • In the Photolithography tool light passes through the quartz, but not through the chrome Chrome (opaque) • Photolithography involves projecting the reticle i
Slide 38: Types of Processes in Photolithography
Types of Processes in Photolithography 38 38
Slide 39: Photolithography Steps – Simplified flow
Photolithography Steps – Simplified flow Track Step* Track Track Track Scanner Step** Track 1) BARC*** Edge Bead UV light 2) Resist Removal Mask HMDS 1. Vapor prime 2. Spin coat 3. EBR 4. Bake 5. Align and expose 6. Post-exposure bake Spin coat BARC → Bake BARC → Spin coat Resist → Bake Resist Metro
Slide 40: Surface Preparation (HMDS Vapor Prime)
Surface Preparation (HMDS Vapor Prime) HMDS 1. Vapor prime • Purpose: eliminate water molecules from the wafer surface to improve contact angle between the resist and the wafer which improves resist adhesion HMDS • Dehydration bake in enclosed chamber with exhaust • Clean and dry wafer surface (hydr
Slide 41: Spin Coat Film - Bottom Anti-reflective Coating
Spin Coat Film - Bottom Anti-reflective Coating • BARC is a film that is spun onto the wafer Resist 2. Spin coat BARC immediately prior to application of Photoresist for BARC some processes Film to be patterned Before Exposure • Not every process requires BARC. Example: several DUV layers require BA
Slide 42: BARC - Planarity
BARC - Planarity • Planarity: 2. Spin coat BARC – Many of the wafer fabrication processes leave an uneven wafer surface with some topography. – This uneven wafer surface causes the DUV light exposure to be absorbed by the thin films at different rates, depending on the resist thickness. – The result
Slide 43: BARC – Reflectivity Control
BARC – Reflectivity Control Resist • Light reflected from a flat surface underneath the resist creates an interference pattern when combined with the incident light. 2. Spin coat BARC • The result is a wavy resist sidewall (see picture) that can lead to poorly defined features in dry etch. Standing
Slide 44: BARC – Footing reduction
BARC – Footing reduction • Photoresist patterned directly on top of some films yields a “footed” profile (see pictures on the left) • BARC helps prevent footing and achieve a more vertical profile 2. Spin coat BARC Footed Profiles - no BARC Better Profile - with BARC Resist Resist Resist Resist BARC
Slide 45: Spin Coat Film - Photoresist Application
Spin Coat Film - Photoresist Application Photoresist Dispenser • Photoresist (or resist) – photosensitive polymer used to create a temporary pattern 2. Spin coat Resist • Wafer held onto vacuum chuck • Recipe example: – Dispense several ml of photoresist – Ramp up spin speed (thousands of rpms) to d
Slide 46: Photoresist Tone
Light Source Photoresist Tone Reticle • Resists can be categorized as positive or negative tone • For a positive develop process, here is a description of the effect Chrome of resist tone: – Positive tone resist photo process Resist - Removes regions of resist exposed to light Unexposed Resist - Lea
Slide 47: Photoresist thickness for Etch process
Photoresist thickness for Etch process • Resist patterns are typically used by an Etch process or by an Ion Implant process Resist • Resist is consumed during the Etch process. Film stack • As the schematic on the right shows, at the end of the Etch process typically there should still be some remai
Slide 48: Photoresist thickness for Ion Implant process
Photoresist thickness for Ion Implant process • Resist patterns are typically used by an Etch process or by an Ion Implant process. Resist • Resist is used during the Ion Implant process to protect certain regions of the wafer from receiving implants. Silicon • As the schematic on the right shows, i
Slide 49: Edge Bead Removal (EBR)
Edge Bead Removal Edge Bead Removal (EBR) • Photoresist solvent evaporates more quickly at the edge of the wafer than any other place on the wafer because the wafer’s radial velocity is greatest there. EBR • This is a result of both axial and radial airflow dynamics influencing the rate at which sol
Slide 50: Soft Bake
Soft Bake 3. Bake • Soft bake evaporates excess solvents from the resist and solidifies/hardens the spun-on film. • Sets the resist in preparation for exposure • Soft bake improves resist adhesion and reduces out-gassing during exposure • The soft bake key recipe parameters are time (a few minutes)
Slide 51: Alignment and Exposure
Alignment and Exposure UV Light Alignment: • Aligns current pattern to previously existing pattern Reticle • Special structures are created on wafer which are used to align the wafer Clear region Opaque region (ex. Cr) Exposure • Exposes resist film with UV light passed through a patterned reticle •
Slide 52: Post-Exposure Bake (PEB)
Post-Exposure Bake (PEB) Post-exposure bake (PEB) – Positive resist example UV Light UV Light H+: Photoacid • Completes chemical reactions that are initiated during exposure Feature edge after generated during short PEB exposure • Positive tone resist line (CD) shrinks with PEB driven acid diffusion
Slide 53: Develop
Develop • Soluble areas of photoresist are dissolved by developer solution 6. Develop – TMAH: tetra methyl ammonium hydroxide in water - Used for positive and negative tone resist (case 1-2 in next slide) Developer Dispenser – nBA: n-butyl acetate - Negative tone developer for positive resist (case
Slide 54: Resist Tone / Develop
Resist Tone/ Expose UV Light Develop Etch & Strip Develop Mask Case 1 Positive Resist Positive Develop Film to be Final Image Unexposed Resist Si same as Mask Exposed Resist Film to be patterned patterned Image UV Light Mask Case 2 Negative Resist Positive Develop Film to be Final Image Unexposed Re
Slide 55: Inspect
Inspect • Inspect 7. Inspect – Inspect the wafer for pattern integrity and defects – Measure critical dimensions (CDs) – Check overlay accuracy • Pass inspection: Wafer continues to next area for further processing (Etch, Ion Implant, etc.) • Fail inspection: Wafer is reworked – Wafer goes to Resist
Slide 56: Patterning Process Flow – High Level Overview
Patterning Process Flow – High Level Overview Resist (Unexposed) Film to be patterned BARC BARC Silicon Film to be patterned Film to be patterned Silicon Wafer with Film to be Patterned 1: BARC Coat 2: Resist Coat (one film or a film stack) (used is some processes) UV Light Mask Cr Unexposed Resist
Slide 57: Photo Processes – Summary
Photo Processes – Summary Process Chemical(s) Used Tool Purpose Vapor Prime HMDS Track Remove moisture from the wafer surface to promote adhesion of resist. BARC coat BARC Track Deposit a layer of antireflective coating at a target thickness before depositing resist (for some processes). Helps with
Slide 58: Equipment used in Photolithography
Equipment used in Photolithography 58
Slide 59: Track Modules and Scanner
Track Modules and Scanner • Track and scanner typically linked (see picture) to meet critical timing between steps and to minimize contamination – This is known as a linked system or cluster • Tracks and scanners manufactured by different vendors Track Step Track Step Track Step Track Step 1) BARC E
Slide 60: Track
Track • Tracks perform the following operations: – Application of chemicals to the wafer (resist, developer, etc.) – Heating and cooling of the wafer • Track typically linked to scanner, but in some cases it can be stand-alone for certain coat-only processes or develop processes • Some modules of th
Slide 61: Track FOUP Load
AMHS vehicle Track FOUP Load FOUP being picked up by the AMHS system • Picture shows the side of the Track where FOUP FOUP boxes are loaded into the tool. FOUP: Front storage FOUPs with wafers Opening Unified Pod. • A FOUP is a rigid, sealed plastic pod designed to: – Protect wafers from contaminati
Slide 62: Scanners
Scanners • The Reticles are loaded into the scanner • Scanners perform the align step, map the wafer surface and adjusts the wafer stage vertically to keep image in focus, and perform the exposure step • Reticle and wafer stage move to expose every die on the wafer Engineer loading reticles in scann
Slide 63: Stepper versus Scanner
Stepper versus Scanner • Stepper Technology – Stepper projects the whole reticle field at STEPPER once SCANNER Light source: Light source: – A light source (such as a mercury i-line lamp 365, 248nm wavelength 248 or 193nm wavelength or a KrF laser) projects light through a condenser lens and a retic
Slide 64: Stepper illustration
Stepper illustration Shot 4 Shot 3 Shot 2 Shot 1 Reticle Lens system Wafer stage moves Wafer stage moves Wafer with resist Wafer stage moves 100+ shots may be needed to cover the whole wafer Efficiency opportunity: fit in a reticle as many die as possible to minimize number of shots 64
Slide 65: Primary Measurements in Photolithography
Primary Measurements in Photolithography 65
Slide 66: Photolithography Measurements
Photolithography Measurements Metrology is key to ensure the resist pattern is on target Resist Thickness: After resist is spun on the wafer, its thickness is measured to ensure the pattern will form correctly. Particle Monitor: measure defectivity on resist coat on wafer to ensure resist meets qual
Slide 67: Resist Thickness
Resist Thickness • Resist Thickness can be measured periodically What is ellipsometry? – Resist is spun on bare silicon wafer and cured (soft baked) – Several measurements are taken per wafer using a spectroscopic This technique measures the intensity of reflected light at different wavelengths to e
Slide 68: Particle Monitor Measurement
Particle Monitor Measurement • Goal: measure particles/defectivity on resist coat on wafer to ensure resist meets quality requirements. • This measurement provides information about particles and surface defects. For example: – Number of defects Normal laser beam Oblique laser beam – Location of def
Slide 69: CD Measurements
CD Measurements • Critical Dimensions (CDs) are measured on resist features to verify the scanners are printing the desired dimensions and the process is in control • If the CDs are out of spec the wafer can be reworked (resist is stripped/removed and Photo process can be done again) • Typical CD me
Slide 70: CD SEM Theory
Electron Gun CD SEM Theory Secondary electrons • Wafer is loaded in a CD SEM tool and wafer is transferred to a high Detector and Monitor vacuum chamber • The Pattern Recognition software is programmed to find a VERY Wafer specific site on a specific die location on the wafer • A very tightly focuse
Slide 71: Overlay
Overlay example: Good overlay Overlay • Photolithography layers: Structures like active areas, transistor gates, contacts and interconnects are built layer by layer, with each layer patterned using photolithography • In semiconductor manufacturing, precise stacking of structures is critical. The pla
Slide 72: Registration
Registration Registration is the measurement of how well structures are placed relative Registration Measurement: to each other. Different types of registration marks and measurement Compare positions of center of gravity (CG) techniques are used. Here is the description of the box-in-box marks. of
Slide 73: Registration Errors
Registration Errors • X-shift translation Black: prior etched layer Blue dashed: new resist pattern 73
Slide 74: Registration Errors
Registration Errors • Y-shift translation Black: prior etched layer Red dashed: new resist pattern 74
Slide 75: Registration Errors
Registration Errors • Field Magnification Black: prior etched layer (Shot expansion) Brown dashed: new resist pattern 75
Slide 76: Registration Errors
Registration Errors • Field Rotation Black: prior etched layer Yellow dashed: new resist pattern 76
Slide 77: Registration Errors
Registration Errors • Wafer Rotation Black: prior etched layer Green dashed: new resist pattern 77
Slide 78: Registration Errors
Registration Errors • Wafer Magnification Black: prior etched layer Purple dashed: new resist pattern 78
Slide 79: Statistical Process Control (SPC)
Statistical Process Control (SPC) Critical Dimension CD1 [nm] • Metrology measurements (e.g., resist thickness, CD 48 measurements, etc.) are sent to an SPC chart 47 46 • SPC charts may be set up to collect raw data (individual 45 measurements) or aggregate data (e.g., mean average chart, 44 standar
Slide 80: Photo process control loop example
Photo process control loop example 1 2 CD SEM Measurements SPC Chart: Critical Dimension CD1 [nm] CD1 – Line CD 46 45 44 43 Concerning trend! 42 UCL 41 LCL 40 Target 39 38 100350 100351 100352 100353 100354 100355 100356 100357 100358 100359 100360 100361 100362 100363 100364 100365 100366 100367 3
Slide 81: Examples of Common Defects in Photolithography
Examples of Common Defects in Photolithography 81
Slide 82: Focus Spot
Focus spot map examples Focus Spot • Description – Very specific high spots on wafer – Parts of the wafer surface tilt/elevate slightly closer to the scanner lens, resulting in out-of-focus features during photo exposure in the elevated area. • Possible Cause No focus spots – This is typically a par
Slide 83: Resist Toppling
Resist Toppling Aspect Ratio (AR) = height/width • Description height – Resist lines that topple (collapse). This issue can cause a blocked etch in the subsequent dry etch process. width • Possible Cause – Capillary forces during the Develop process - Surfactants may be added in the Develop process
Slide 84: FM (Foreign Material)
Foreign Material defect examples FM (Foreign Material) Comet tail • Description – Seen as a foreign material or particle with a trailing streak Particle Center of wafer commonly referred to as a “comet tail” – This defect results in non-uniform resist thickness – The comet tail forms during the spin
Slide 85: Key Terminology Glossary
Key Terminology . Glossary micron
Slide 86: Glossary
Glossary Term or acronym Definition/description CD Critical Dimension. The measurement of a patterned feature like a line width, the space between lines, or a diameter. CD SEM Critical Dimension Scanning Electron Microscope. Tool that precisely measures critical dimensions. The process in photo wher
Slide 87: Glossary
Glossary Term or acronym Definition/description Photosensitive Chemicals that undergo chemical reactions in response to exposure to light. nf Refractive Index. A quantity that indicates how much light slows down as it passes through a medium. Registration Measurement of the offset between the new re
Slide 88: Resources
Resources _ amie
Slide 89: Outside References for Further Learning
Outside References for Further Learning 1. Chris Mack, Lithoguru - Lithography Training - Chris Mack 2. ASML Technology Overview - ASML technology | Supplying the semiconductor industry 3. SPIE Advanced Lithography - SPIE Advanced Lithography + Patterning 4. NNCI is an NSF funded initiative across m
Slide 90: © 2009-2025 Micron Technology, Inc. All rights reserved. Information, products, and/or specifications are subject
© 2009-2025 Micron Technology, Inc. All rights reserved. Information, products, and/or specifications are subject to change without notice. All information is provided on an “AS IS” basis without warranties of any kind. Statements regarding products, including statements regarding product features,