Motivation 

NASA Goddard Space Flight Center has observed material 

degradation issues in their superconducting microelectronic devices, 

including material discoloration, dissolution, and surface structure 

modification. To mitigate these issues, the NESC surveyed recent 

device anomalies in terms of handling, chemical and environmental 

exposures, operation and test histories, and full details of failure 

indications. Following this survey, an in-depth investigation 

was conducted into the issues surrounding a superconducting 

microelectronic device that was fabricated through physical vapor 

deposition, reactive ion etching, and wet chemistry on a silicon wafer. 

This device experienced a discoloration of the layered molybdenum / 

niobium / molybdenum (Mo/Nb/Mo) leads that worsened over time.

Analytical Procedures

Detailed imaging and compositional analyses of the device was 

undertaken using the following techniques: scanning and transmission 

electron microscopy (SEM/TEM), atomic force microscopy, x-ray 

photoelectron spectroscopy (XPS), Fourier transform infrared 

spectroscopy, inductively coupled plasma spectroscopy, two-wire 

resistance measurements, and electroanalysis. 

Technical Findings

• Electroanalytical experiments and XPS studies of the processing fluids, including solvents, revealed no concerns of galvanic 

corrosion at dissimilar metal interfaces. 

• Electron microscopy revealed the presence of metal oxides, 

including molybdenum oxide (MoOx) and aluminum oxide 

(AlOx) in the discolored regions. For example, a 7-layered 

structure on the leads was discovered when a 3-layered 

structure was Expected (Figure 1.) Studies to determine origin 

of oxidation and unexpected metals (i.e. Al) revealed three 

possible sources: (1) prolonged oxygen plasma exposure, 

(2) residual materials in fabrication chamber from previous 

users, and (3) exposure to deionized water (DIW). For Mo thinfilms, microscopy and resistance measurements revealed that 

DIW caused a discoloration and an increase in the electrical 

resistance of the devices. Extended exposure to DIW led to 

Mo dissolution.

• Materials and processes were implemented in the creation 

of recent devices without a full understanding of the material 

interactions and impacts. In addition, inadequate process 

controls, including quality control measures, were present.

Process Improvement Recommendations

1. Monitor effect of common use chemicals on microelectronic device fabrication. Conduct a full materials investigation before incorporating new materials into fabrication processes. If possible, 

understand long-term stability and interactions of materials used.

2. Ensure integrity of etching and deposition chambers. Conduct 

dummy deposition runs to ensure unwanted contaminants from 

prior runs are removed and to verify desired surface chemistry 

is achieved. Develop requirements for chamber cleanliness.

3. Avoid long exposures to oxygen plasma and understand effects 

of various exposure conditions to the surface chemistries of the 

microelectronic device. 

4. Avoid using DIW on certain substrates and initiate hermetic 

sealing, if necessary, to avoid long-term degradation of the 

microelectronic devices.

Organizational Process Recommendations

1. Re-verify fabrication processes after any process change or 

off-nominal result.

2. Introduce inspection test points to collect objectively verifiable 

data to ensure process conformity.

3. Collaborate outside of sphere of influence to determine and set 

verifiable requirements at onset of work.

References

1. Parker, D.; Beamesderfer, M.; Brown, A. Assessment of Degradation in Microfabricated Detectors and MEMS Devices. 

NESC-RP-21-01640.

NASA Engineering and Safety Center Technical Bulletin No. 23-07

National Aeronautics and Space Administration

Best Practices for Fabrication of Microelectronic Devices

Material degradation during the fabrication of microelectronic devices has plagued the space industry for many years owing to the 

layering of many dissimilar metals to create these devices. Often, commonly used materials and systems are overlooked as potential 

sources of material degradation. This technical bulletin highlights extensive research to isolate probable causes of this degradation. 

www.nasa.gov For more information, Donald S. Parker donald.s.parker@nasa.gov 10/31/23 DOC ID: 20230015509 

Figure 1. (left) Expected material layer stack of the superconducting leads of a detector. (center) Actual layer stack as 

determined through TEM cross-sectional analysis (right).

Expected Layer Stack Actual Layer Stack

Mo (20 nm)

Mo (70 nm)

Nb (70 nm)

AIOx (5 nm)

MoOx (30.2 nm)

Mo (12.2 nm)

Mo (21.8 nm)

Mo (46.1 nm)

Nb (58.2 nm)

MoOx (4.5 nm)

In TEM: Discolored area showing

several layers with platinum (Pt) on top. Credit: JHU

Layered Lead Composition