Intro

Congratulations! If you reached this page via the QR code, then you are holding what is most likely the smallest book in the world!

In particular, you are holding a version of Moby Dick by Herman Melville that has been shrunk to a minute size and defined by our state of the art Electron Beam Lithography system onto a silicon wafer. Despite a length of roughly 1.300.000 characters (about 650 pages) this version of the book covers an area of just 0.046 mm^2. At this scale it can fit more than 9000 times on one face of a 1 euro coin! It is not a super convenient format for reading since this would require an expensive Scanning Electron Microscope but it demonstrates the scale of modern day semiconductor fabrication techniques.

Final chip with DTU logo and the Moby Dick book placed in the center of the circle. The circle is 2000 µm in diameter.

How it was made

The process consists of a few steps

1) Generate the pattern from a text file

2) Expose the pattern onto a wafer with an Electron Beam Lithography system

3) Etch the pattern into the wafer using a plasma based etching system

4) Image the result in a Scanning Electron Microscope

Let us look at the steps one by one.

Pattern generation

Converting this amount of text is not easily done through any regular mask layout tool. Thus, a custom python script was developed which can take a simple text file and convert it to a GDS layout. The resulting GDS file can be downloaded here and viewed in any GDS editor. For the actual exposure a scale of 0.6 was applied to the pattern resulting in a pattern size of 192 x 240 µm^2. The target linewidth of the letters at this scale is just about 30 nm.

The pattern generated with the text assembled in a fairly condensed format of 14 columns.

Exposure

For this exposure we coated a 100 mm Si wafer with 70 nm ZEP 520A resist. To hit the relatively small feature size it is essential to work with a thin resist layer.

The exposure was done on our state of the art JEOL 9500 FSZ exposure system. If you are interested in seeing the system in operation consider this video on our Youtube channel. Exposure was done at a low beam current of only 0.22 nA and a voltage of 100 keV. The DTU logo on the chip was however exposed at a much higher beam current.

Our JEOL 9500 FSZ system in the DTU Nanolab cleanroom.

Etching

The pattern was etched in an SF6 plasma using an SPTS Pegasus system. The etched depth is about 30 nm.

The resulting pattern after etching and resist stripping.

Imaging

SEM imaging was done on both a Zeiss Gemini and a Raith eLine Plus system. The latter is a fully automated system that was used to acquire 295 images to fully image the entire book.

SEM image of a small fraction of the book. Letter line width is 31 nm and letter height is about 116 nm.