Microfabrication

Our facilities for fabricating integrated circuits are essential to nearly all of the work in the Group. We maintain a research-class facility specialized in the fabrication of complex super-conducting circuits, nanoscale electronics and MEMS structures. Beginning with computer-aided design, we use electron-beam and optical lithography to make structures smaller than 50 nm and complex circuits containing as many as 32,000 Josephson junctions. Our tools are housed in 200 m2 of “class 100” cleanroom space, which was improved greatly in 1999. We have recently added tools for fabricating MEMS that are essential for the creation of many of our ultra-sensitive instruments, and for micromachined ion traps for future clocks.

Maggie Crews inspects mask
Maggie Crews inspects a mask generated in our new Optical Pattern Generator.
Our facilities are available as an “open-shop” operation. After appropriate training, all of our staff can personally use them to fabricate the devices needed for their research. We keep the facility and the processes flexible and under the control of each individual user to avoid con-straining research and to allow maximum creativity. Our past accomplishments are testimony to the success of our approach.

In the past year we have upgraded our optical pattern generator (shown above) to a modern instrument capable of making masks with feature sizes of 1.5 micrometers. Having an in-house mask-making facility allows very rapid turn-around, which improves productivity and encourages creativity. For patterning at the 1 µm scale, we use optical lithography in an I-line stepper and a deep-UV contact aligner. Electron-beam lithography enables patterning at less than 50 nm. Our capability in electron beam lithography is currently being expanded with the addition of a second scanning electron microscope with wafer-scale stages and load lock.

Our thin-film deposition and etching tools are similar to those found in a semiconductor fabrication facility, but they have been optimized for normal and superconducting metal fabrication. We have general purpose and dedicated sputtering and e-beam systems to deposit multilayers of metals. We use electron cyclotron resonance (ECR) plasma-enhanced chemical vapor deposition (CVD) of SiO2 for circuit insulation. Dry etching is performed in standard RIE and plasma etching tools.

Leila Vale
Leila Vale examines a 76 mm Nb/Al2O3/Nb trilayer wafer that will be used for Josephson junction circuit fabrication
We have recently installed the tools necessary to fabricate MEMS structures. We use a set of research-scale tube furnace reactors (5" capable), for wet and dry silicon oxidation, solid-source diffusion of boron, low-stress silicon nitride/polysilicon low-pressure chemical vapor deposition (LPCVD), and LPCVD of low-temperature oxide. We have added two silicon dry-etch tools for micromachining of Si. We use xenon difluoride gas to rapidly and isotropically etch silicon. This year we have also acquired a deep silicon reactive ion etch system to allow highly anisotropic etching of Si.