The CNF aims to enable all research areas possible without compromising the fabrication capabilities of the existing tool set and processes. Maintaining the process capability of the CNF tool set while serving a wide range of research goals requires a system in place to prevent the possibility of chamber/tool contamination and process degradation that may come with incompatible materials.
This approach is accomplished at the tool level by designating each tool with a Number code that corresponds to the type of materials (substrates and films) allowed in that specific tool.
This policy does not cover all possibilities. If you do not see your material listed, or have a question regarding it– do not assume it is safe to process without getting clearance from the CNF staff member in charge of the tool. Assume a material is not allowed if not specifically listed!
Some tools may have additional restrictions and requirements. Researchers should check the tool webpage, check the Equipment Information Sheet, and should be aware of the individual tool requirements.
Please direct questions regarding the use of CNF equipment with samples containing biomolecules to Xinwei Wu, wu (at) cnf.cornell.edu.
Tool Categories:
Tool Categories are divided into 6 groups, Category 1, 1E, 2, 3, 4 and 5, with Category 1 being the most restrictive in allowed materials and Category 5 having the least amount of restrictions. Substrates and samples are required to be assessed by the researchers and CNF staff prior to utilizing the tool.
All samples in a more restrictive category are compatible with a lower restricted category (i.e. a sample that meets Category 1 requirements is ok to put into Category 3 or 4 tools)
Some tools may restrict samples that have been previously processed in instruments that fall in a less restricted tool category. This upward movement of samples from a less restricted tool category to a more restricted one does not apply to all tools and it is up to the researcher to verify if upward category movement is allowed for the tools in question. Just because a tool is in a category 5 class, does not mean samples will get contaminated with material residue from prior usage.
Additional Restrictions and Requirements:
Some tool categories may require additional steps prior to operation. ( i.e Furnaces require a RCA or similarly approved clean prior to running.) This is a tool by tool add-on requirement and Researches should be aware of the individual tool requirements.
Implementation
- CNF staff will evaluate new projects and process flows, highlighting possible conflicts with materials and tool usages.
- CNF tool managers will communicate the required sample characteristics during training on the equipment.
- Researches are obliged to follow the stated guidelines and should consult the tool managers if there is any uncertainty to the categorization of the sample.
Substrate, Thin Film, and Sample Classifications
Many processes in the CNF are highly sensitive to metallic contamination, particularly Alkali and Alkaline elements and some organics compounds that have been fixed with alkali buffer solutions. Those elements are outlined as Class A and Class B Metals
Additionally, a majority of tools operate at elevated temperatures in medium to high vacuum environments with plasma exposure. Materials with a high vapor pressure can contaminate these chambers impacting subsequent process runs, and need to be restricted. Films and substrates with high vapor pressure components may be restricted from a number of tools.
List of Tool Categories:
See the tables below the descriptions for details of allowed and restricted materials and for a listing of tools in each category.
Tool Category 1/1E
The 1 and 1E Category tools are restricted to silicon based substrates and films only. Silicon based films need to be deposited in chambers where the risk of metallic cross contamination is minimal. The 1 category restricts samples to limited tool exposure and no CNF ALD films, 1E allows greater tool exposure, deep etched samples, silicon based ALD and approved select ALD films to be processes.
Tool Category 2
The Category 2 tool group stays restricted to just silicon based substrates, but do allow a limited set of metal films, ALD dielectric films, and cured organics. The set of metals is defined as “CNF Refractory Metals Group” and consists of common refractory metals plus a few metals typically used in basic CMOS process steps.
Tool Category 3
The Category 3 tool group includes the materials allowed in 1, 1E, and 2, plus allows Compound Semiconductors materials and cured organic/baked photoresist materials. These tools still restrict Glass materials and any metals from the Metal Classes A and B from being processed. High vapor pressure materials are prohibited.
Tool Category 4
The Category 4 tool group allows 1, 1E, 2 and 3, tool materials, plus allows glass substrates to be processed. Films from the Class B Metal Group can be present but must be covered/buried during processing- Staff Approval required. A material that is selective to the gas chemistry being used must cover the buried Class B Metal. In addition it must contain a pattern overlap to avoid sidewall and pattern misalignment exposure. Stopping an etch process on a Group B metal is prohibited.
Samples containing Class B metals are limited to process steps under 400C.
High vapor pressure materials are prohibited as well as thin films of materials from Class A Metals.
Tool Category 5
The Category 5 tool group is the least restrictive of the tool categories. The tools typically fall in the wet chemistry, metrology, low temperature, non-vacuum, and lithography category.