Lithography Challenge

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This page provides a sample module for the Lithography Challenge. Extensions, modifications, and other implementation options can be found at: Lithography Extensions.

Contents

Background

Lithography, in the general sense, is a process used to create patterns on a substrate by exposure to electromagnetic waves. The substrate is often silicon or another semiconductor, while the wave source is usually UV light. By coating the substrate in specific photosensitive chemicals called resists, covering parts of the combination with a light impenetrable mask, and then exposing the entire setup to the wave source, it is possible to create very precise etched patterns on the substrate. This process is often used in the semiconductor industry to create the conductive patterns that make up the cores of most microchips.

There are a number of specific types of lithography, each with its own uses and benefits. The most commonly used process, known as photolithography, is fairly fast and capable of resolving patterns down to roughly one micron. It requires the use of resists and a mask. The masked substrate is exposed to intense levels of UV light which causes the exposed resist to chemically alter. The alterations, depending on the specific resist used, allow either the exposed or non-exposed parts of the substrate to be washed away using a 'rinse' chemical. This processing method is most often used in microprocessor fabrication.

For processes which require a finer resolution then photolithography, electron beam lithography is available. E-beam lithography, as the name implies, uses a beam of electrons to etch its patterns. Since electrons have a shorter wavelength than light they can be used to resolve smaller elements. In the case of current e-beam tools, it is possible to draw patterns smaller then 10nm across. The drawback to e-beam lithography is the fact that the narrow beam of electrons must be scanned over every point of the substrate that the user wishes to etch. This is in contrast to photolithography, which can expose the entire substrate at one time. This line-by-line scan causes the process to be significantly slower than photolithography. For this reason it is not often used by chip manufacturers except in the making of the masks for use in photolithography.

Applications in Nanotechnology

Lithography can be used in nanoscience for the patterning of substrates for growing such substances as nanowires or quantum dots. Lithography techniques are also used to fabricate such devices as nanogrippers (tiny tweezer-like devices used to manipulate nanoscale objects) and nearly all MEMS/NEMS (Micro/Nano Electro-Mechanical Systems) devices. Pursuit of advances in lithography can be a nanoscience topic in its own right as features can presently be resolved at the nanometer scale by e-beam techniques. Any advances made in the speed or accuracy of such techniques leads directly to a jump in the speed and/or power in the semiconductor and communications industries.

The Challenge

Your goal is to implement a simplified model of the electron beam lithography technology. In this mock-up the substrate will be replaced with thermally sensitive paper. The electron beam will be replaced with a heat source (a resistor). You will build and program an extension to the gantry used in the MFM challenge which will allow you to carry out the lithography operation. Your overall goal will be to produce increasingly complex patterns in a repeatable manner.

Materials

  • Power supply capable of delivering 10V at 0.5A (If you do not have a regulated power supply available you can likely adapt and use an AC adapter from any number of small electronics e.g. cell phone, Game Boy)
  • LEGO NXT kit and assorted bricks/plates.
  • 10 Ohm 5 watt resistor; wirewound (Please note that wirewound resistors are not the 'standard' color band resistors. They are larger and more durable to dissipate the excess heat. The ones you will need are coated in ceramic and cement. You can order them from Digikey P/N: 10W-5-ND , Mouser P/N: 280-CR5-10-RC, or most other major electronics distributors.)
  • Thermal paper (Cash register paper works well, look in office supply stores.)
  • Soldering iron and solder
  • Vice or vice grips

Construction

Simple resistor mount
Simple resistor mount

Instructions are provided for building a workable (though not perfect) movable sample table for use with the Lithography device you are to design. It can serve as a starting point for your designs. We also describe how to remove the 5 watt resistor from its casing and demonstrate the construction of a simple mount for it.

  • Instructions for building the sample table base can be found here, you need only pay attention to steps 2-41 & 58-63.
  • Opening the resistor

Goals and Grading

Your goal in the lithography challenge is to produce a device which is capable of drawing some basic patterns on the substrate in a repeatable manner. You can use the base on this page as a starting point, although you will need to modify it somewhat to create a design which is truly repeatable. You do not need to use the provided table design. The grading breakdown is out of 100 points and is as follows:

  1. Construction and documentation of changes to design base - 50 Points
  2. Repeatably able to draw a recognizable rectangle - 20 Points
  3. Repeatably able to draw a recognizable triangle - 15 Points
  4. Repeatably able to draw a recognizable circle - 15 Points

Repeatability for our purposes will constitute the ability to produce what is roughly the same shape two times. Partial Credit will be awarded.

Documentation

You will need to provide documentation of any device you create or any modifications you make to the base design. CAD drawings are recommended, although photographs of building steps are also acceptable. You should also fully document the rationales for your design decisions.

We highly recommend the use of the LDraw suite of utilities for LEGO CAD work. Instructions for installing the suite can be found on the LDraw community's getting started page. You may also want to look into the 'unofficial files' section on their web site, as many of the technic parts used in the NXT kit are still held only in this archive. You should be aware that the package has a somewhat steep learning curve, but has many similarities to professional CAD packages. Give yourself time to learn to use it properly and you will be able to create useful instruction sets like the sample MFM package.

Example

For the sake of inspiration we provide a few pictures of a device we created to test the concept. The first is a photo of the entire setup and the second is an array of samples we created during the development process. There is also a video of the device's operation available.

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