Hot Cathode Ionization Gauge Installation and Quartz Thin Film Deposition Thickness Monitor Repair

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IMG_9111 IMG_9110Installation of a Perkin Elmer hot cathode ionization gauge on my PVD chamber. I applied current to the filament briefly at atmospheric pressure and the filament did not burn out so it may have a yttria-coated iridium filament rather than tungsten or any other refractory element. This will be my main mid to high vacuum gauge, used in conjunction with a thermcouple gauge and a Baratron pressure traducer for backing pressure measurement. The gauge mounted up to a 2 3/4″ conflat. I have a HP 59822B ionization gauge controller which provides filament current and reads collector current and displays it in torr.

Thanks to Charles Alexanian for this additional information:

“…your assumption about your gauge is correct in that it is an iridium filament. That being said the yittria coating can be poisoned by a great many things requiring a re calibration of your system depending on which type or controller you are using. The tungsten filament versions stayed popular in chamber research because you could simply boil off anything that might condense on the filament… I have changed over my Bayard Alpert type gauges. (That is the technical term for the gauge you are showing) for inverted magnetron types, particularly the MKS903 type units because they give a analog voltage output and require no external controller. Additionally they can be easily disassembled and cleaned. The also have a higher starting pressure where I no longer need thermocouple gauges.”

The quartz thickness monitor is a Maxtek TM-100 that I picked up on ebay for under $100. The board is very corroded so after a lot of contact cleaning I was able to get it working. Displays rate in angstroms per sec and integrates to find total thickness. Surprisingly simple circuity, it’s all based around a single counter chip and of course 7 segment display drivers and such.

Semiconductor Fabrication Basics – Home Chip Lab

A brief introduction to semiconductor fabrication processes and terminology. It is not intended to be an in depth view of any single process, but rather an overview so that provides enough information for someone to get started with making diodes and transistors at home.

Tour of my home chip fab setup in early 2017. I’ve been accumulating this equipment since October of 2016.

 

 

Step by step FET fabrication

 

High vacuum basics

Switch Mode Power Supply Design + laser cut/etched PCB

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Buck/Boost converter design for a solar glider I was working on last summer, at 16v it reached 98% peak efficiency and 95% average in boost mode. Also tried to make a linear power supply board using a laser engraver to cut away the copper, it worked pretty well to replace the normal ferric chloride etch step. Continue reading Switch Mode Power Supply Design + laser cut/etched PCB

Rewound MOT for thermal evaporation – 800amps and new Lindberg 1″ tube furnace for diffusion

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Rewound a microwave oven transformer using 1 gauge welding wire. Before saturation it puts out 1.8volts ish. I plan to use it to heat up a tungsten boat for thermal evaporation deposition. I may rewind it with slightly thinner wire so I can get more turns on the secondary and a little higher voltage. Last picture is a new/old Lindberg 1″ dia. tube furnace I got, goes up to 1400c which is crazy. I use it for diffusion of N type and P type dopants into my homemade semiconductors as well as thermal oxidation. I have a large nitrogen tank which allows me to create a nitrogen atmosphere in it during diffusion and when I want to facilitate SiO2 growth I pump steam through the furnace and turn the nitrogen flow off. I have a mass flow controller for the nitrogen but haven’t hooked it up yet.

Fabrication and Characterization of N-Channel Enhancement Mode Insulated Gate Field Effect Transistors

Update 8/27/17: Developing Patterning Process for Homemade Microelectronics

Update 7/30/17: Developing Metalization Process for Homemade Microelectronics

These are my first working transistors. Specifically, they are insulated gate enhancement mode n channel field effect transistors. I also made a depletion mode FET with a conducting channel and it worked even better than the enhancement mode ones. I drew out the steps I took to make this, they’re based on Jeri Ellsworth’s work but with a few main changes. It is very important that your dielectric overlap source and drain regions on the FET, otherwise no inversion layer can be formed and the FET cannot turn on. Only a small overlap is necessary and the larger it is, the more unwanted capacitance there is. This is not normally a consideration in actual production because inherent lateral diffusion takes care of the overlap but for these large hand made devices I found you have to get very lucky with your alignment if you don’t budget extra overlap.

A huge thanks to Jeri for making her videos about home chip fabrication which got me interested in these experiments in the first place.

You can see in the center of the transistor there is a red region of silicon dioxide, this is the gate and the color indicates that it is roughly 750 angstroms thick. I would like to make the gate thinner so I can achieve lower threshold voltages, etc. but it is hard to make a truly insulating gate much thinner than that in a dirty environment because of pinholes and other impurities in the oxide layer.

A brief introduction to semiconductor fabrication processes and terminology. It is not intended to be an in depth view of any single process, but rather an overview so that provides enough information for someone to get started with making diodes and transistors at home.

Tour of my home chip fab setup in early 2017. I’ve been accumulating this equipment since October of 2016.

Step by step FET fabrication