Overview

Samples and tools are categorized into 4 classifications of material and process compatibility:

• Metallic Contamination

• Outgassing Contamination

• Elevated Temperature

• Backside Cleanliness

In each category, higher numbers (e.g 4) are more stringent and controlled than lower numbers (e.g. 1).

Going into a tool with a higher number classification may require specific cleaning of a sample, or it may not be allowed at all. In general, it is good practice to start with a new sample on the most stringently rated tool, and work to less stringently rated tools and processes.

Matrix

Metallic Contamination

Level 4 - RCA Clean

Wafers must have been cleaned at the RCA Cleaning Hood.

Level 3 - Metal Ion Free / Low Diffusion Metal Films

Sample must be thoroughly cleaned in UPW to remove any metal ion residual. The only metallic films that may be present on the sample are those which have low diffusion probability into silicon and other common substrates.

Level 2 - Volatile Etch Products

Sample must not form any involatile etch products during the process which may be sputtered off and contaminate the chamber. For plasma etch systems, a very general primer on determining etch byproduct boiling points can be found here: Tutorial on Etching#General-Willitetch (reproduced below). Be sure to consult with BNC staff for any materials and etch products you have questions about, especially etch byproducts with a boiling point > 185 C. Note that "dec" stands for "decomposition". In general, this means the compound explodes into other compounds and that listed compound would not be removed from the chamber.

Level 1 - Standard Semiconductor Concern

Sample should have been with semiconductor grade solvents or UPW prior to use in the tool.

Outgassing Contamination

Level 4 - High Vacuum (<10^-5 Torr)

Substrates:

• Silicon

• Glass (Quartz, Fused Silica, Pyrex)

• GaAs

• Sapphire

Deposited films:

• Inorganic oxides/compounds

• Metals, except:

  • Arsenic

  • Beryllium

  • Cadmium

  • Gallium

  • Indium

  • Magnesium

  • Mercury

  • Phosphorus

  • Tin

  • Gd

Photoresists:

EBL Resists:

Level 3 - High Vacuum, Limited flex (<10^-5 Torr)

Everything permitted in Level 4, as well as:

Substrates:

• Polycarbonate

• PEEK

• ABS plastic

Properly outgassed thin films of

Level 2 - Low Vacuum (<Atmosphere to 10^-3 Torr/1 mTorr/1 Pa)

At pressures down to 10^-3 Torr/1 mTorr/1 Pa and the substrate temperature during the process, substrate and any deposited materials must be stable solids, and should not pose a risk of outgassing contamination to the tool for the process you intend to run.

Level 1 - Atmosphere

At atmospheric pressure and the substrate temperature during the process, substrate and any deposited materials must be stable solids, and should not pose a risk of outgassing contamination to the tool for the process you intend to run.