"Z2" - Upgraded Homemade Silicon Chips

Sam Zeloof

13 Aug 202105:46

Summary

TLDRThe video describes the creation of a homemade silicon chip with 100 transistors, made using a polysilicon gate process. The chip operates at lower voltages, improving performance and efficiency. The creator outlines their fabrication process, including steps like photolithography, doping, and etching. They also compare their new chip to Intel's first processor, which had only 2,000 transistors, highlighting the progress. The chip's applications include LED flashers and guitar pedals, and the creator details the precise tools and techniques used. The video invites viewers to support future semiconductor experiments.

Takeaways

🔬 The speaker created a homemade silicon chip in their garage and recently developed version 2 with 100 transistors, improving on the older version.
💡 The new chip uses a polysilicon gate process, enabling it to work at lower voltages (threshold voltage of about 1V), reducing power consumption.
📉 The older chips required higher voltage, necessitating 9V batteries, but the new version can run on 3.3V and 5V logic levels.
🧪 The fabrication process involves using photoresist and photolithography with homemade tools like a spin coater and maskless stepper.
🎥 The speaker uses a DLP projector setup to project patterns onto the wafer, reducing the image to the appropriate size for exposure.
🔍 A potassium hydroxide solution is used to etch away exposed photoresist in the photolithography process, allowing further development of the chip.
🔥 The source and drain of the MOSFETs are created by doping with phosphorus, followed by high-temperature baking at over 1000°C.
🔧 Layers such as the gate and contact are etched using reactive ion etching and hydrofluoric acid, with metal layers added via vacuum evaporation.
📏 Detailed inspection follows to measure parameters like gate dimensions and layer thicknesses, ensuring quality control.
📊 The final chip is tested using a probe station, comparing the ID vs VDS curve of the MOSFETs to industry standards, yielding promising results.

Q & A

What is significant about the silicon chip described in the transcript?
-The silicon chip described is homemade and is the second version of the creator's design, featuring 100 transistors that are smaller, faster, and better than the previous version. This chip represents a significant improvement in complexity, approaching the level of early commercial chips like Intel’s first processor, which had only 2,000 transistors.
What advantage does the new version of the chip have over the previous one?
-The new version operates at much lower voltages, with a threshold voltage of about 1 volt, allowing it to be powered by 3.3V and 5V logic levels. This results in lower power consumption, a higher density of transistors in a smaller area, and better overall performance.
How did the creator design the chip layout?
-The creator used Photoshop to design the layout, as it’s simpler to use for a project with only four layers. More complex software wasn’t necessary for this simple chip design process.
What materials and tools are used to fabricate the silicon chip?
-The creator starts with 200mm silicon wafers, dices them into smaller bits using a diamond scribe, and then uses a homemade spin coater for depositing photoresist. Other materials and tools include phosphorus solution for doping, polysilicon for the gate layer, and aluminum for the metal layer. The chip is processed in steps involving photolithography, spin coating, etching, and baking.
What is the purpose of using a spin coater in the process?
-The spin coater is used to evenly apply a thin layer of photoresist onto the wafer. The wafer is spun at high speeds (4,000 rpm) for 30 seconds, which ensures a uniform and consistent layer across the entire surface.
How does the photolithography process work in this project?
-Photolithography involves projecting an image of the design from a laptop onto the wafer using a DLP projector and optics. The wafer is then exposed to light, which hardens certain areas of the photoresist. The unexposed areas are later dissolved away during development, leaving the desired pattern on the wafer.
What is the purpose of doping, and how is it done?
-Doping introduces impurities into specific regions of the silicon to create the source and drain areas of the MOSFETs. In this process, a phosphorus solution is spun onto the wafer and then baked at over 1,000°C for 45 minutes to drive the phosphorus atoms into the predefined areas.
What steps are involved in forming the metal contacts on the chip?
-After defining the gate and contact layers, the chip undergoes a process to remove the insulating silicon dioxide layer. Metal contacts are then deposited by evaporating aluminum onto the wafer, followed by photolithography to define the metal layer. Finally, residual aluminum is etched off to form the contact points.
How are the transistors tested once the chip is complete?
-The transistors are tested using a probe station, where small tungsten needles are used to make electrical connections with the chip’s transistors. The creator uses test equipment and programming to define the tests, such as measuring current versus voltage (ID vs VDS), and then analyzes the results.
What are the potential applications of the chip created in the transcript?
-The creator has already made projects like an LED flasher and a guitar distortion pedal using the first version of the chip. With the improved version, the creator expects to build even more complex circuits and applications, thanks to the increased transistor count and lower power consumption.

Outlines

00:00

🔧 Homemade Silicon Chip Version 2: An Impressive Leap

The creator describes their second iteration of a homemade silicon chip, which now contains 100 transistors that are smaller, faster, and more efficient compared to their earlier version. They produced an array of 12 of these chips, totaling 1,200 transistors. With Intel’s first processor having just 2,000 transistors, they highlight that they are nearing a significant level of complexity. Previous projects, such as a guitar distortion pedal and LED flasher, were successful but required high voltages, an issue improved in this new design with low-voltage polysilicon gate technology.

05:01

💡 Chip Fabrication with Polysilicon Gates: The Detailed Process

This paragraph delves into the detailed steps of creating the new silicon chip. It starts with designing in Photoshop due to the simplicity of working with only four layers. The creator dices 200mm wafers into smaller sections and begins the process by applying photoresist to the wafer with a homemade spin coater. After drying the photoresist, they use a maskless photolithography stepper to project the design onto the wafer. The development process removes exposed areas of the photoresist, followed by an etching procedure to form the chip's structure.

🔬 MOSFET Creation: Doping and Etching Explained

This section continues with the MOSFET (transistor) fabrication process. After forming the chip's structure, the photoresist mask is stripped off, and phosphorus atoms are introduced into the wells through a doping process at high temperatures. The etching steps are repeated twice more for the gate and contact layers. These steps involve etching the gate and using reactive ion etching for the contact layer to ensure good electrical connections. The chip is then placed in a vacuum chamber to apply a metal layer, typically aluminum, which completes the foundational structure.

📊 Testing the Finished Silicon Chip: A Close Inspection

The creator inspects the finished chip closely, measuring parameters like gate length and layer thickness, using a microscope to check for accuracy. They place the chip on a probe station with tiny tungsten needles to make precise electrical connections for testing the transistors. The final part of the process involves using test equipment to analyze the chip’s performance, comparing its curves to ideal MOSFET models. Encouraged by the positive results, the creator reflects on their success and considers launching a Patreon to support more semiconductor experiments.

Mindmap

Keywords

💡Silicon Chip

A silicon chip is a small piece of silicon material on which circuits are created for various electronic functions. In the video, the creator talks about making homemade silicon chips in his garage, emphasizing the innovation and complexity of personal semiconductor fabrication. His second version has 100 transistors, showing the progress he’s made from his earlier work.

💡Transistors

Transistors are semiconductor devices used to amplify or switch electronic signals and power. The creator mentions that his new chip contains 100 transistors, which are essential in creating more complex circuits. He compares this to Intel’s first processor, which had only 2,000 transistors, demonstrating that even his home projects are approaching significant levels of complexity.

💡MOSFET

MOSFET stands for Metal-Oxide-Semiconductor Field-Effect Transistor, a type of transistor commonly used in electronic circuits. The creator refers to high threshold voltages of his earlier MOSFETs, which required higher power to operate. In the new chip, the threshold voltage is lower, allowing it to function at lower power levels like 3.3 or 5 volts, enhancing efficiency.

💡Polysilicon Gate Process

A polysilicon gate process is a method in semiconductor fabrication that involves using a layer of polycrystalline silicon for the gate electrode in MOSFETs. This process allows for better control of the transistor’s performance. The creator mentions this advancement in his second chip, which significantly improves power efficiency and allows for smaller, more densely packed transistors.

💡Photoresist

Photoresist is a light-sensitive material used in the lithography process to create patterns on a substrate, such as a silicon wafer. The creator uses photoresist to define layers of his chip. After applying it on the wafer, it is exposed to light, and the exposed portions are then developed and etched, allowing for precise construction of transistor components.

💡Photolithography

Photolithography is a process used in semiconductor fabrication to transfer patterns onto a substrate using light. In the video, the creator uses a homemade photolithography stepper to project images from his laptop onto the silicon wafer, which helps define various layers of the chip. This step is crucial in defining the transistors' source, drain, and gate regions.

💡Doping

Doping in semiconductor fabrication refers to the introduction of impurities into the silicon wafer to change its electrical properties. The creator describes spinning on a phosphorus dopant solution, which is baked at over 1000 degrees Celsius to diffuse the phosphorus atoms into the silicon, forming the source and drain regions of his MOSFETs.

💡Spin Coating

Spin coating is a technique used to apply a thin, uniform layer of material onto a flat surface, often used in semiconductor fabrication. The creator uses spin coating to apply both photoresist and dopants onto the wafer. By spinning the wafer at high speeds, he ensures a smooth, even distribution of materials essential for accurate photolithography and doping.

💡Reactive Ion Etching

Reactive Ion Etching (RIE) is a technique used to etch specific patterns into the wafer using chemically reactive plasma. The creator uses RIE to remove insulating layers of silicon dioxide in his chip, allowing him to make electrical contacts to the transistor components. This step is essential for finalizing the chip’s construction.

💡Probe Station

A probe station is a device used to physically connect to very small components on a semiconductor wafer for testing and characterization. In the video, the creator uses a probe station with tungsten needles to test his transistors by making contact with them. It’s a delicate process necessary for measuring the electrical characteristics of the MOSFETs, ensuring they work correctly.

Highlights

Created the world's first homemade silicon chip in a garage fabrication lab.

Version 2 of the chip contains 100 transistors, smaller, faster, and more efficient than the first version.

Made an array of 12 chips with a total of 1,200 transistors, nearing the complexity of Intel's first processor, which had 2,000 transistors.

Earlier projects with the first chip included an LED flasher and a guitar distortion pedal, both requiring 9-volt batteries due to high MOSFET threshold voltage.

The new chip uses a polysilicon gate process, lowering the threshold voltage to 1 volt and enabling operation at 3.3 and 5 volts.

For simple designs, uses Photoshop to create the four-layer structure instead of complicated software.

Begins with 200 mm silicon wafers, diced into smaller pieces using a diamond scribe for processing.

Uses a homemade spin coater to apply photoresist for the first layer, spun at 4,000 RPM for 30 seconds and dried on a hot plate at 95°C.

A homemade maskless photolithography stepper is used for exposure, projecting designs from a laptop using a DLP projector and optics.

Positive photoresist is etched away with potassium hydroxide after exposure, revealing the underlying structure for further processing.

Dopant layer applied with phosphorus solution, then baked at over 1000°C for 45 minutes to create the source and drain regions of the MOSFETs.

Polysilicon etching and multiple rounds of photolithography create the gate and contact layers of the MOSFETs.

Uses reactive ion etching or hydrofluoric acid to remove insulating silicon dioxide before applying metal contacts.

Final metal layer applied via aluminum sputtering or thermal evaporation, followed by photolithography to define the metal contacts.

Final testing includes using a probe station with tungsten needles to measure electrical characteristics, confirming successful MOSFET performance.