"Z2" - Upgraded Homemade Silicon Chips

Summary

The 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.