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

# Photolithography types and pre-steps

Embedded System · Chapter 8: IC Technology

- Asked in: 2072 Magh, 8 marks
- 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-pre-steps
- Whole chapter: https://www.bctengineer.com/md/semester_6/embedded_system/chapter-8

## Question

What is photolithography and what are its types? Describe the steps that need to be performed before photolithography process.

## Answer

**Photolithography** is the process of using light to transfer a circuit pattern from a mask to a photoresist layer on the wafer, so the pattern can be etched or doped into the wafer.

#### Types

- **Positive and negative** photolithography, depending on the photoresist (exposed part removed or kept).
- **Contact, proximity and projection** printing, depending on how the mask is placed relative to the wafer.
- **Optical (UV, DUV, EUV), electron-beam, X-ray and ion-beam** lithography, depending on the radiation used.

#### Steps before photolithography

```text
 Sand --> pure Si --> Crystal --> Ingot --> Wafers
 (SiO2)   (poly)      growth      shaping    slicing
                                               |
 Resist <-- HMDS <-- Oxidation <-- Clean <-- Polish
 coating    prime     / deposition
```

1. **Raw material purification:** quartz sand (SiO2) is reduced to metallurgical silicon and purified to electronic-grade polysilicon (99.9999999 %).
2. **Crystal growth:** the Czochralski method pulls a single-crystal ingot from molten silicon, doped p-type or n-type.
3. **Ingot shaping:** the ingot is ground to a standard diameter and a flat or notch marks the orientation.
4. **Slicing:** a diamond saw cuts the ingot into wafers (about 0.5-0.8 mm thick).
5. **Lapping, etching and polishing:** removes saw damage and gives a mirror-flat surface (chemical-mechanical polishing).
6. **Cleaning:** RCA cleaning removes particles, organics and metal ions.
7. **Oxidation or film deposition:** a thin SiO2 (thermal oxidation), poly-Si or metal layer is formed, which the first lithography will pattern.
8. **Dehydration bake and priming:** HMDS improves adhesion of the photoresist, which is then spin-coated.

## Check yourself

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

1. Method for single-crystal ingot?
   A. Czochralski
   B. Sawing
   C. Etching
   D. CVD only
   Answer: A. Pulled from molten silicon. (Key point: Crystal growth)

2. Slicing uses?
   A. Laser etch
   B. Spin
   C. Photoresist
   D. Diamond saw, wafers 0.5-0.8 mm
   Answer: D. Then lap and polish. (Key point: Slicing)

3. RCA cleaning removes?
   A. Oxide only
   B. Resist
   C. Particles, organics, metal ions
   D. Silicon
   Answer: C. Before oxidation. (Key point: Cleaning)

4. Purpose of HMDS?
   A. Grows oxide
   B. Improves resist adhesion
   C. Dopes
   D. Etches
   Answer: B. Before spin-coat. (Key point: HMDS)

## Related in Embedded System

- [Steps of photolithography process](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Aphotolithography-steps) — Embedded System, chapter 8, asked 4×

## Related in other subjects

- [Need for pre-emphasis and de-emphasis in FM](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aneed-pre-de-emphasis-fm) — Communication Systems, chapter 3
- [Pre-qualification of contractors and its need](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Aprequalification-need) — Construction Management, chapter 5, asked 5×
- [Limiter-discriminator FM demodulation; need for pre-emphasis](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Alimiter-discriminator-pre-emphasis) — Communication Systems, chapter 3
- [Pre-qualification steps vs post-qualification](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Aprequalification-steps-post) — Construction Management, chapter 5