Design of the Manufacturing Facility (Manufacturing Machinery)

Below is a list of the equipment that will be used for semiconductor fabrication on the space station. As previously mentioned, the environment of space requires (or encourages) some equipment modifications. These will be listed in the equipment descriptions. The chart below is a brief list of the machinery involved in the semiconductor fabrication process. It includes the price, mass, volume, and energy consumption of each piece of equipment. The company/model column lists the information for comparable equipment used on earth. I should mention that this is how all of these figures were obtained. Earth equipment information was used (since no space equipment exists, or not to my knowledge, anyway) and modified to reflect any changes that were made. The choices in what equipment to use (and most of the pictures) were obtained by viewing the lab equipment lists for the Integrated Circuit Laboratory at MIT (website - see bibliography).

Manufacturing Equipment

Note: values in blue are approximate costs. All volumes and masses are estimated by visual means or expert advice (Bill Woods)

The following is a list of the function of each set of equipment and ways in which it should be modified:

Lithography Equipment

Wafer Stepper	The lithography equipment is used in the imaging process to imprint certain patterns onto either the wafer surface or another layer grown on the wafer. First, the Photoresist Coater is used to deposit a layer of photoresist on the wafer. This process will have to be modified from the current process which relies on gravity, but the adjustment will be minimal. The Bake Oven is used to harden the photoresist. Then, the photoresist is exposed to light using the Wafer Stepper . The exposed resist is removed using the Developer , revealing the surface below, and then the remaining photoresist is again baked in the bake oven to prepare for the etching process (see below). After etching, the photoresist is removed using the Photoresist Stripper . The accuracy of the imaged pattern is examined using the Linewidth Measurer .
Photoresist coater	Photo resist Stripper
The bake oven

The Nitrogen Compartment

Attached to one of the modular docking ports of the utility compartment is a pressurized compartment of nitrogen which is required for the photoresist coating. Nitrogen was chosen because it is extremely cheap and common compared to other gases. The system is a single atmosphere system and is thus much easier to purify. At the end of the compartment facing the robotical track is intake for the container of wafers. This is then fed into a miniature airlock where it is pressurized and loaded into the automated photoresist equipment.

The Furnace

Many of the processes (depositing oxide layers, CVD) in semiconductor fabrication involve extreme temperatures in the order of 1100 degrees Celsius. This could be generated conventionally with electricity however this would warrant high current power cables and extremely large solar collectors with efficiencies in the order of ~15%. However, if solar collection was used directly to heat the furnace chamber the efficiency of the system would be greatly improved. This led to this design.

This design would use the focusing of the sun's light (solar luminosity of the sun ~1400j/sm ² )to heat the chamber. A hemispheric solar collector made of aluminum would reflect approximately 90% of the light into the center of the hemisphere where the furnace chamber is. The furnace chamber is made of carbon black because of the high temperatures it can withstand and the fact that it absorbs a very large amount of the heat exposed to it. The boom holding the furnace chamber in place is adjustable so the it can be moved in and out of the focus of the light. (once extremely high temperatures are reached the heat will not dissipate very well). Inside the chamber there are electrical heating elements to regulate the heat to a specific temperature. The whole apparatus is attached to a boom which juts of the end of the manufacturing platform. At the point of attachment there is a pivot as to allow the collector to track the sun. Along the boom runs a secondary robot shielded with heat resistant materials. This robot carries the containers extremely slowly down the boom as not to create an extreme temperature difference and destroy the wafer. They are then loaded into the furnace chamber by means of a robotical gripper.

Oxidation and Chemical Vapor Deposition (CVD)

Ion Implantation

Ion Implanter

The ion implantation equipment is used to introduce dopants to the wafer. The Ion Implanter drives ions into the wafer surface. The ion implanter pictured here is quite large because it includes a vacuum system. The space version will not require the vacuum, which drastically reduces price, mass, volume, and wattage. The Rapid Thermal Annealer is used to repair crystal damage that the ion implantation causes as the ions penetrate the wafer.

Metal Deposition Equipment

Sputtering System

The Sputtering System is a vacuum process that deposits a layer of metal on a wafer by shooting charged particles at the target metal. The particles from the target metal "sputter" off and land on the wafer surface. This is a vacuum process, so it will be modified to operate in a vacuum environment. The Residual Gas Analyzer is used, as it’s name implies, to analyze the gases used in the sputtering process.

Etching Equipment

Polysilicon and Nitride Etcher

Etching is performed after the photoresist is developed and baked during lithography. The exposed surface is etched using the appropriate etcher; that is Polysilicon and Nitride Etcher for polysilicon and nitride surfaces, Oxide Etcher for silicon dioxide surfaces, and Metal Etcher for metal surfaces. These are plasma (dry) etchers, as opposed to chemical(wet) etchers. Plasma etching uses gases instead of chemicals to etch the surface, a fact which is important when considering launch costs (weight of chemicals is greater than weight of gasses). All etchers require a vacuum, so, again the weights and volumes etc. will be considerably smaller when they are modified for space. The Toxic Gas Monitor monitors the gases used in the process for any leakage. Leakage isn’t that dangerous in space, but it is wasteful.

Inspection and Test Equipment

Electron Microscope	All of the equipment below is used for wafer quality control. This is important equipment, for it allows detection of mistakes before they can be reproduced in mass quantities. The equipment consists of the CV Plotter, Ellipsometer, Spreading Resistance Probe, Automatic Four-Point Probe, Junction Sectioner, Surface Profiler, Inspection Microscope, Scanning Electron Microscope, Electrical Measurements (Measurer), and Probers. They are responsible for inspecting the wafer surface, measuring the thickness of deposited films, electrical testing, etc. The Scanning Electron Microscope also uses a vacuum and is modified to operate in the natural vacuum of space.
Ellipsometer	CV plotter
4 point probe	Surface Profiler
Inspection Microscope	Probers

Heat Disposal of the Equipment

Heat is very hard to dispose of in space because there is no conduction to an atmosphere therefor heat disposal is strictly done by radiation. Therefore, to dispose of the heat generated by all the machines onboard the platform, a water cooling system is run through every machine and then pumped to a large radiator fin. From there the heat will be radiated into space. The heat in this case would be in the order of 50-60 degrees