---
title: "Define photolithography and its types"
subject: "Embedded System"
chapter: 8
key: "semester_6/embedded_system:photolithography-types"
source: https://www.bctengineer.com/q/semester_6/embedded_system/photolithography-types
site: BCT Engineering
---

# Define photolithography and its types

Embedded System · Chapter 8: IC Technology

- Asked in: 2079 Asoj, 3 marks; 2078 Baisakh, 3 marks (asked 2 times)
- Video: [Photolithography: Step by step](https://www.youtube.com/watch?v=oBKhN4n-EGI) — Jae-Hwang Lee
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/embedded_system/photolithography-types
- Whole chapter: https://www.bctengineer.com/md/semester_6/embedded_system/chapter-8

## Question

Define photolithography and its types.

## Short answer

Photolithography transfers a mask pattern onto photoresist. Types: positive resist (exposed dissolvesol) vs negative (exposed hardens); exposure: contact, proximity, projection printing; radiation sources include UV, DUV, EUV, e-beam.

## Answer

#### Photolithography

Photolithography is the process of transferring a circuit pattern from a photomask to a layer of photoresist on a wafer using light, so that the pattern can then be etched or doped into the wafer. It is the basic patterning step in IC fabrication.

#### Types

1. **By resist type**
   - *Positive:* exposed resist becomes soluble and is removed, so the pattern equals the mask.
   - *Negative:* exposed resist hardens, unexposed part is removed, so the pattern is the inverse of the mask.
2. **By exposure method**
   - *Contact printing:* mask touches the wafer; good resolution but damages mask and wafer.
   - *Proximity printing:* a small gap (10-25 µm) separates them; no damage but diffraction limits resolution.
   - *Projection printing:* a lens projects the mask image (steppers and scanners, 4x-5x reduction); the standard in modern fabs.
3. **By radiation source**
   - *Optical (UV, DUV, EUV):* i-line 365 nm, KrF 248 nm, ArF 193 nm, EUV 13.5 nm.
   - *Electron-beam (direct write)* for masks and research; *X-ray* and *ion-beam* lithography for very fine features.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Negative resist?
   A. Exposed dissolves
   B. Exposed resist hardens; pattern is inverse of mask
   C. Same as mask
   D. No resist
   Answer: B. Opposite of positive. (Key point: Negative)

2. Proximity printing?
   A. Small gap; no damage but diffraction limits resolution
   B. Contact; damages
   C. Projection lens
   D. E-beam
   Answer: A. 10-25 um gap. (Key point: Proximity)

3. Standard in modern fabs?
   A. Contact
   B. Proximity
   C. X-ray
   D. Projection printing (steppers/scanners)
   Answer: D. 4x-5x reduction. (Key point: Modern)