# [Semiconductor x English Part 5] What is Deposition? Explained with a "Mille-Feuille" Analogy
**Meta Description:** A gentle explanation of "What is deposition?" for beginners. We introduce the mechanism of layering thin films on a wafer, using a "mille-feuille" analogy, and explain it in a way that is "easy for anyone to understand" along with English expressions.
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Hello! Welcome to the 5th installment of "Semiconductor x English" 🦍💙
Last time, we learned about "**etching**," which is the process of removing unnecessary parts.
(If you haven't already, please be sure to check out parts 1 through 4!)
> 🦍💬 **Gorilabo-sensei**
> "Last time, we learned up to the point of carving out patterns to create circuit shapes. But a semiconductor isn't finished with just that. Today, let's look at the process of 'layering films'!"
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## Is a circuit not finished after drawing it once?
In the series so far, we have learned the following flow:
- Part 3: "**Photolithography**" to transfer patterns with light
- Part 4: "**Etching**" to remove unnecessary parts
But in reality, semiconductor circuits are not completed with just these two.
**Layering a new film, drawing the pattern again, and then etching again**—
By repeating this many times, complex circuits are created.
That "layering films" process is today's theme: "**Deposition**."
> Figure: Before deposition, there are only the substrate and circuit irregularities, but after deposition, a thin film is layered on top.
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## 1. What is deposition?
**Deposition** is:
**The process of creating a new thin film on the surface of a wafer.**
In English, it is called "**deposition**."
> **Deposition = The work of layering thin films on top of a wafer**
While photolithography and etching are about "removing to create a shape," deposition is imagined as a process of "**adding new materials.**"
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## 2. What does deposition do?
The general flow is something like this:
1. Set the wafer inside the equipment.
2. Send **gases or particles** that serve as materials into the equipment.
3. The material **gradually accumulates** on the surface of the wafer.
4. Continue until the accumulated material reaches the target thickness.
5. A thin film is completed.
The thickness of the accumulated film can sometimes be as thin as **1/1000th of a human hair**.
It is a very precise process.
> 🦍💬 **Gorilabo-sensei's note**
> "It's close to the image of snow falling and piling up quietly. However, it piles up much thinner and more uniformly than snow."
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## 3. An easy-to-understand analogy: Layering like a mille-feuille
To make deposition easier to visualize, let's use this analogy:
> **Deposition = The work of layering thin layers many times like a mille-feuille**
- A mille-feuille is made by layering many sheets of pie crust and cream.
- Semiconductor circuits are also made by repeatedly alternating between "circuit layers" and "deposited layers."
- Every time a layer is added, the circuit becomes more complex and higher-performing.
> Figure: An image of circuit layers and deposited layers being stacked alternately on a substrate.
> 🦍💬 **Gorilabo-sensei's note**
> "In cutting-edge semiconductors, these layers can sometimes exceed 100. Just imagining it makes me hungry, but it's actually a very precise world."
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## 4. Let's look at it in English: Breaking down the word 'deposition'
Let's break down the word **Deposition** a little bit.
| English Word (Etymology) | Meaning |
|---|---|
| **De-** | Down (prefix) |
| **Posit** | To place (from Latin) |
| **-ion** | The act of (suffix that makes it a noun) |
When you put them together,
**Deposition = Placing down = Accumulating by layering**
That is the image.
### English phrases used on-site
In semiconductor factories, this kind of English is often used.
1. **"This process deposits a thin film on the wafer."**
→ This process deposits a thin film on the wafer.
2. **"The film thickness is carefully controlled."**
→ The film thickness is carefully controlled.
3. **"Deposition and etching are repeated many times."**
→ Deposition and etching are repeated many times.
As in the third sentence, deposition and etching have a relationship where they are **repeated as a set**.
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## 5. Are there different types of deposition methods?
There are several methods for deposition. Here are two representative ones.
- **CVD (Chemical Vapor Deposition)**
→ A method of creating a film by causing a chemical reaction with gas.
- **PVD (Physical Vapor Deposition)**
→ A method of creating a film by physically propelling the material.
Both have in common that they use "vapor" to create a film, but the difference is whether they use "chemical reactions" or "physical force."
> 🦍💬 **Gorilabo-sensei's note**
> "CVD is like 'coating with a chemical reaction,' and PVD is like 'evaporating and sticking the material on.' Both are methods that are very active in semiconductor factories."
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## 6. Where is deposition used?
Deposition is performed in an area of the semiconductor factory called the "**deposition process**."
The representative equipment used is "**deposition equipment**."
And in this deposition process, the "**MFC**" introduced in Part 1 is also active.
It is the MFC that accurately controls the amount of raw material gas used in CVD.
- Drawing patterns with photolithography (Part 3)
- Removing with etching (Part 4)
- Layering new layers with deposition (Part 5)
- Drawing patterns again, removing, and layering...
By repeating this many times, the complex semiconductor chips inside the smartphones and computers we use are completed.
> Figure: The overall picture of the cycle: Photolithography → Etching → Deposition → Repeat.
> 🦍💬 **Gorilabo-sensei's note**
> "Everything we learned in parts 3, 4, and 5 connects to this cycle. Semiconductor manufacturing is made up of these steady repetitions."
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## 7. Summary
Let's look back at the points from this time.
- **Deposition = The process of layering thin films on a wafer**
- It is called "deposition" in English
- The image is "layering layers like a mille-feuille"
- Methods include "CVD" and "PVD"
- In the deposition process, the "**MFC**" learned in Part 1 also adjusts the gas amount
- The circuit is completed by repeating the cycle of photolithography → etching → deposition
"Drawing," "removing," "layering"—only when these three processes are combined is a complex semiconductor chip born.
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## Semiconductor x English Word Box 📘
I have summarized the English words you want to remember today.
| English | Japanese |
|---|---|
| Deposition | Deposition/Accumulation |
| Thin film | Thin film |
| Thickness | Thickness |
| CVD (Chemical Vapor Deposition) | Chemical Vapor Deposition |
| PVD (Physical Vapor Deposition) | Physical Vapor Deposition |
| Repeat | Repeat |
| Layer | Layer |
| Control | Control |
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How was it?
This time, I explained "what is deposition" while incorporating the mille-feuille analogy.
Photolithography, etching, deposition—by repeating these three, the complex circuits of a semiconductor are completed little by little.
> 🦍💬 **Gorilabo-sensei**
> "Now you've learned the basic cycle of semiconductor manufacturing! Next time, I'll talk about 'inspection,' where we check if the circuits made this way are working correctly. Look forward to it!"
Let's continue to learn semiconductor terms little by little with Gorilabo-sensei 🦍
**Semiconductor x English**
**Easy for anyone to understand!**