THIS SITE

Information for

New Electron Beam Lithography equipment at Quantum NanoFab

The Quantum NanoFab is used by many researchers at the Institute for Quantum Computing (IQC) to build new quantum structures for study in their labs. It is a cleanroom laboratory that uses technologies from the microelectronics industry in order to enable the fabrication of a variety of experimental quantum devices. As the Quantum NanoFab’s resident process engineer I would like to talk briefly about electron beam lithography in general and our new JEOL JBX-6300FS electron beam lithography tool in particular. I promise, there will be no math in this article, but I will make reference to the size of what can be written with various technologies.  A handy (and approximate) contextual guide is below:

Characteristic size

Object of that size

100 microns

Width of a human hair

1 micron

Size of a bacterial cell

100 nanometres (nm)

Size of a virus

10 nanometres

Smallest part of a modern transistor

1 nanometre

Width of a DNA strand

0.1 nanometres

Diameter of an atom

What is lithography and why do I care?

Lithography comes from two greek words lithos meaning “stone” and grapheos meaning “to write. Lithography is the process where a pattern is defined on a sample, so this pattern may be transferred into a material of interest. The maturation of lithography technology has been fundamental to enabling the explosion in density of integrated circuits over the past 50 years, better known as Moore’s Law. So to me, lithography is a very important subject!

In lithography we typically care about three things: 

  1. What is the minimum feature size that I can write?
  2. How accurately can my lithography steps be aligned to each other?
  3. How quickly can I write?

Traditional Integrated Circuit (IC) Fabs use a process called photolithography to write their tiny circuits. The process of photolithography relies on using ultraviolet light to define a pattern on the sample. The ultraviolet (UV) light passes through a glass plate (photomask), which itself has an image of the circuit drawn on it, and hits a photosensitive film on the sample. The sample and photosensitive film are immersed in a chemical developer and a reproduction of the photomask image is realized. This technology is great for writing many samples at once! You can realize many, rather small (hundreds of nanometers) size structures on a sample quite quickly. But this technology isn’t ideal when it comes to realizing much smaller structures because of the problem of diffraction. To achieve smaller device sizes, most research and development fabrication labs have to make use of Electron Beam Lithography.

Fundamentally, Electron Beam Lithography (EBL) relies on the same technologies that are used in an electron microscope. In Electron Beam Lithography first we coat our sample with an electron sensitive film. We then take the sample and mount it in the EBL system. The EBL system generates electrons in a filament, accelerates them with tens of thousands of volts and focuses them down to a spot smaller than 10 nm is size. Using electrostatic force we can make the beam move across our sample, drawing the pattern we wish to realize in the electron sensitive film. We subsequently develop this film and use the film as a template to grow or etch a layer on our sample. With this technology we can achieve sub 10 nanometre size structures, but because the small electron beam can only be in one place at a time (classically speaking) the process can be very slow.

Since electron beam lithography technology is related to electron microscope technology, a common approach to making an EBL system is simply to convert an existing electron microscope. This is a very cost effective solution, but writing small things comes with a host of problems that just aren’t accounted for in tools designed to image small things. To write a device with EBL you must have nanometer level control of the mechanical position of the sample and the position of the electron beam (beam stability). Positional control of the sample also entails extreme control of sample’s temperature, for example a 100mm Silicon wafer (our standard size in the Quantum NanoFab) will expand by 260nm if it is heated by 1°C. In a game of nanometers, keeping a consistent temperature becomes very important! In an electron microscope temperature, mechanical position and beam position may need to be stable on a timescale of seconds, but in electron beam lithography they need to be stable on the timescale of hours.

The reason we need such precise control over these parameters (sample location, beam location, temperature) is that the electron beam can’t be deflected electrostatically to hit all parts of a given sample chip. Electron lenses tend to suffer from aberrations and non-linarites much more readily than optical lenses, as a result the electron beam can’t be directed very far away from the centre of the electron column. This means that the electron beam can only hit a very small area on the sample before the beam is distorted. In order to write an area large enough to be useful we have to join together a number of writing “fields” by moving the sample mechanically with enough precision that each field boundary makes perfect contact with neighbouring fields.

JBX-6300FS Electron Beam Lithography system

JBX-6300FS Electron Beam Lithography system as installed in the Quantum NanoFab

The Quantum NanoFab’s new JEOL JBX-6300FS is different from most EBL systems you’d find in an academic Fab in that it is designed from the ground-up as an electron beam lithography tool, and is not a converted scanning electron microscope design. Our JEOL system is one of only three 100kV EBL systems in academic fabs in Canada, so we’re very lucky to have access to such an advanced tool. These purpose built systems are typically capable of higher resolution work due to higher column accelerating voltages, better quality “stitching” (joining together of adjacent writing fields), and faster operation (low inductance deflection coils and high speed pattern generators).

This spring, as part of the installation process the JEOL system was put through its paces and the results were world class:

  1. Using the JBX-6300FS’ unique “nanolithography” mode, JEOL engineers were able to write 8 nm wide lines at a pitch (line spacing) of 40 nm.
  2. Using the “high speed” mode, JEOL engineers were able to write a pattern with less than 9 nm of “stitching” misalignment between adjacent writing fields.
  3. Using the “direct write” mode, JEOL engineers were able to read alignment markers on a previously patterned wafer and align a test pattern to the pre-existing markers with better than 10 nm accuracy.

electron micrograph

An electron micrograph of a test pattern written on our JBX-6300FS Electron Beam Lithography system.  Electron micrograph captured by our Raith150-TWO Electron Beam Lithography / metrology tool.

The resolution that was achieved during this testing was quite impressive, but even more impressive were the stitching and overlay results. Stitching and overlay tests actually exceeded the manufacturer specification by over 50% and blew away the results achieved in factory testing. All of this tells me that the system was installed carefully and that the EBL room in the Quantum NanoFab is exceptionally stable acoustically electromagnetically and thermally.

Having been an electron beam lithography user for over 11 years, it’s hard to overstate how impressive this new tool is. Once the Quantum NanoFab staff and lab members are up to speed in the operation of this system, cutting edge fabrication work will be made dramatically easier. The horizon of what is possible in the Quantum NanoFab is about to be pushed a lot farther.

Comments

The increasing demand for semiconductor devices in several industries such as automotive, consumer electronics, and telecommunication among many others impacts the photolithography market positively. The EUV photolithography equipment is the fastest-growing segment in the photolithography market.

Know More | Sample Pages- http://www.marketsandmarkets.com/requestsample.asp?id=145860852

Blog topics

  1. 2016 (21)
    1. November (1)
    2. October (1)
    3. September (2)
    4. August (3)
    5. July (2)
    6. June (2)
    7. May (2)
    8. April (2)
    9. March (3)
    10. February (2)
    11. January (1)
  2. 2015 (16)
    1. December (1)
    2. November (2)
    3. October (2)
    4. September (2)
    5. August (2)
    6. July (2)
    7. June (3)
    8. May (2)

Educational programs

QKD - Quantum Key Distribution Summer School

USEQIP - Undergraduate School on Experimental Quantum Information Processing

QCSYS - Quantum Cryptography School for Young Students

Quantum Innovators logo