Dielectric Picture Fabrication
How to Make Your Own Dielectric pictures are easy, just follow the step by step instructions.
Faculty Contact: Aaron Hawkins || Student Contact: Joshua Beutler
Color displays are typically made using ink or paint dyes. These dyes appear as certain colors because each color of dye absorbs different portions of the incident light. Because dyes absorb light, they decay over time, and consequently, pictures made using them eventually fade. Pictures made from thin dielectric films on a reflective surface will never fade, even when constantly exposed to light. With dielectric pictures, the colors in an image are created through optical interference rather than absorbtion. The following tutorial steps through the process of making a RGB pixelated color picture in silicon dioxide grown on a silicon wafer. Going through the process of making a dielectric picture is an excellent way to teach the basics of photolithography and illustrates the color properties of different film thicknesses of silicon dioxide.
Choosing a Picture
When choosing a picture, first consider picture size. Choose a picture that is X pixels long by X pixels wide. This will be compatible with the software and fit on the wafer. Second, consider your color scheme. Since it is very difficult to obtain a true red color with silicon dioxide, we recommend that you choose a picture that has a minimal amount of red in it. This will render a more accurate reproduction. Since green and blue dielectric layers are quite brilliant and vivid in silicon dioxide, choose a picture that maximizes a color scheme of blue and green.
Pixelating a Picture Don't forget Alignment Marks
Once the picture is pixelated and in Skill, add alignment marks and whatever else you desire. The layout consists of three dark field layers that will need to be converted to clear field layers (more on dark and clear field farther down). Be sure to design your alignment marks appropiately.
Converting a Skill file to eps or Post Script
Using Cadence, or another CAD program that uses Skill, export your document to a GDSII format. GDSII is a good file format to use since it is accepted by many layout programs. Next, open the GDSII file in a program that can convert it and save each layer of the file in a .eps or post script file. Here at BYU, we use CleWin to convert a GDSII file into a post script file, but other programs exist that can do the same thing.
Making a Transparency
We recommend that making your transparency on a high resolution printer that prints at 3600 dpi. Any commercial grade printing company should be able to do this. Have the transparencies made clear field rather than dark field, i.e. the transparencies will have dark features and a transparent background. A dark field has transparent features and a dark background.
Making a Photomask
We strongly recommend that you use your transparency for the sole purpose of a template that enables you to convert to a photomask. Using a photomask over a transparency is advantageous because it allows easy alignment and multiple uses. Remember the following guidelines:
1. Handle all transparencies with gloves so oils from hands do not contaminate them.
2. Make sure that the transparency is placed flipped left to right on the resist side of the mask. This will ensure that the picture and writing on the mask are in the correct direction.
3. Be sure to secure the transparency flush with the plate. We recommend placing a completely clear piece of photomask glass over the transparency.
4. Exposure can easily be done under an aligner.
In a thermal oxidation furnace, grow 5200 angstroms of silicon dioxide on the wafers. This will give you a green color--the first of your basis. Using basic photolithography, use the green mask and positive photoresist to etch the down to a suitable blue color. Use the blue mask and positive photoresist to etch down to a suitable red color. Then, use the red mask and negative photoresist to etch down to a red (more pink). After exposing and developing, set the wafer with the negative photoresist on a hot plate at 400°C for at least 10 minutes. This will blacken the resist and help to give a black background to the picture so that the colors are more vivid.
References on the fabrication of color pictures:
Aaron Hawkins, R. Wang, G. Sanber, J. Beutler, and S. Schultz, "Color Pictures Using Dielectric Films," Color Res. and Appl., (accepted).
J. Kvavle, C. Bell, J. Henrie, S. Schultz, and A. Hawkins, "Improvement to reflective dielectric film color pictures," Opt. Expr., vol. 12, p. 5789-5794, Nov. 2004. Link to article
Reference on the determination of colors:
J. Henrie, S. Kellis, S. Schultz, and A. Hawkins, "Electronic color charts for dielectric films on silicon," Opt. Exp., vol. 12, pp. 1464-1469, Apr. 2004. Link to article