Simulate Microchip Clean Room Contamination with Crayon Leaf Rubbings

Abstract

Have you ever made a leaf rubbing or imprint using paper and crayons? What do you think would happen if you got dirt or sand on the leaf? Would it mess up the result? In this project you will find out and learn about how this is related to the process of making the microchips that run our phones, computers, and other electronic devices. Check out this page for more science projects related to this process.

Summary

Areas of Science

Physics
Materials Science

Difficulty

Method

Scientific Method

Time Required

Short (2-5 days)

Prerequisites

None

Material Availability

This project requires fresh leaves.

Cost

Very Low (under $20)

Safety

No issues

Credits

Ben Finio, PhD, Science Buddies

Science Buddies is committed to creating content authored by scientists and educators. Learn more about our process and how we use AI.

https://www.youtube.com/watch?v=QYs4oUJEmAA

Objective

Simulate dust contamination in a clean room by adding dirt or sand to crayon leaf rubbings.

Introduction

Look around you. How many electronic devices do you see? You are probably reading this text on one right now—a phone, tablet, or computer—but there may be more in the room. Nearly all modern electronic devices depend on semiconductors, special materials that can act as both conductors and insulators. Sometimes they conduct electricity, and sometimes they do not.

Semiconductors allow us to make transistors, tiny electrical "switches" that can turn on and off. Improvements in technology have allowed engineers to make smaller and smaller transistors over the years, cramming billions of them into microchips that are barely the size of your thumbnail! That is why today's smartphones have more computing power than early computers that took up an entire room.

Watch this video for an overview of how computers and other devices have gotten smaller and smaller over the years. (Dr. Ben Finio, the author of this project, worked on the Robobee shown around the one-minute mark in the video for his Ph.D. thesis!)

https://www.youtube.com/watch?v=gfOD-Qpl6eg

You may have noticed toward the end of the video that some of the devices are even smaller than things like human hairs, red blood cells, or even bacteria. Some are literally smaller than a speck of dust! At that scale, contamination by an actual speck of dust can ruin a microchip (Figure 1). This means that the process of making microchips must be done in an extremely clean environment called a clean room (Figure 2). Clean rooms have powerful air purification systems to help prevent dust contamination, and workers must go through a very careful cleaning and preparation process before they can even enter the room.

Watch the video after Figure 2 to learn more about clean rooms.

Image Credit: onsemi
Figure 1. Dirt on a silicon wafer. Contamination like this can ruin an entire batch of chips. Image used with permission from onsemi.

Image Credit: NASA / Public domain
Figure 2. A clean room with workers wearing protective clothing to help prevent contamination.

https://www.youtube.com/watch?v=vSS_uJlrvvk

You might be thinking, "OK, but what does all of this have to do with the leaf rubbings mentioned at the beginning of this project?" Watch the following video about the semiconductor manufacturing process. As you watch, think about what would happen if a speck of dust got on top of one of the layers on the silicon wafer. What could happen to the manufacturing process?

https://www.youtube.com/watch?v=g8Qav3vIv9s

Since you probably do not have access to a real clean room for your experiment, in this project you will use a model instead. A model is something scientists and engineers can use to simulate another process using different (and usually cheaper) materials. You will make leaf rubbings using crayons and paper to represent the semiconductor manufacturing process. Grains of sand or dirt will represent dust contamination. How do you think the contamination will affect your leaf rubbings? Try the project to find out!

Terms and Concepts

• Semiconductor
• Conductor
• Insulator
• Transistor
• Microchip
• Clean room
• Silicon wafer
• Model

Questions

• How are microchips made?
• How small are transistors?
• How could dust or other contaminants affect the semiconductor manufacturing process?

Materials and Equipment

• Fresh leaves (at least 3). Larger leaves will generally work better. Make sure they are not dry or rotten.
• Printer paper
• Crayons
• Marker, pen, or pencil
• Sand or dirt
• Lab notebook

This project follows the Scientific Method. Review the steps before you begin.

1. Peel the wrapper off a crayon.
2. Place one of your leaves on top of a piece of paper with the veins facing up (Figure 3).
   
   
   Image Credit: Ben Finio, Science Buddies / Science Buddies
   Figure 3. Preparation for the leaf rubbing.
3. Place another piece of paper on top of the leaf.
4. Firmly hold the top piece of paper in place with one hand so it does not slide around. If you need help, ask another person to hold it.
5. Using the side of your crayon (not the tip), rub back and forth over the leaf to make an imprint (Figure 4).
   
   
   Image Credit: Ben Finio, Science Buddies / Science Buddies
   Figure 4. A crayon leaf rubbing.
6. Remove the top piece of paper from the leaf.
7. Using a pen, pencil, or marker (not a crayon), carefully try to trace all the veins that appear in the imprint.
8. Count the number of breaks or gaps—areas where the vein failed to trace completely. Record this number in a data table like Table 1.

	Number of gaps
Leaf number	No sand	Sand
1
2
3

Table 1. Example data table.

9. Sprinkle a small pinch of sand or dirt on top of the leaf (Figure 5). Try to distribute the sand or dirt evenly instead of dumping it all in the middle. Spread it around with your finger if needed.
   
   Image Credit: Ben Finio, Science Buddies / Science Buddies
   Figure 5. Sand sprinkled on a leaf.
10. Repeat steps 3–8 with a new piece of paper. What does your leaf rubbing look like this time?
11. Repeat steps 2–10 with at least two more leaves, for a total of at least three trials.
12. Analyze your results. How does the number of gaps compare in your leaf rubbings with and without contamination? How is this related to dust contamination in the semiconductor manufacturing process?

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Global Goals

The United Nations Sustainable Development Goals (UNSDGs) are a blueprint to achieve a better and more sustainable future for all.

This project explores topics key to Industry, Innovation and Infrastructure: Build resilient infrastructure, promote sustainable industrialization and foster innovation.

Variations

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