General lithography

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General lithography
Technology Details
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General lithography (%@@@@@%) is all of the support equipment that is required to achieve good lithography.

See Reactive ion etching and Plasma etching for an example.

Method of operation

Describe how the technology works.

Applications

How is this technology used in nanofabrication and what types of devices/research areas is it useful in?

Parameters

Here we describe what parameters are of importance in this technology (e.g. power, temperature...). May not be relevant to some technologies.

Parameter 1

Main article: Parameter 1

You may want to make a separate sub-page or article specifically for a parameter if this is longer than, say a paragraph or two. If not, get rid of the {{main|xyz}} below the heading.

Subtechnology 1

Main article: Subtechnology 1

Describe any sub-technologies of this technology.

Materials

Optional description of materials that can be processed by technology. I think the best example of where this comes in handy would be with LPCVD describing the difference between HTO and LTO.

Equipment

Automated batch equipment

Sample preparation

Sample cleaning

Main article: Sample cleaning

For good photoresist adhesion, wafers should be clean and dry. While a simple process such as rinsing with Acetone and IPA and blowing dry with an N2 gun may suffice for clean wafers, typically a more aggressive clean should be used particularly after multiple processing steps. Suggested processes and equipment is listed below.

Processes

Piranha etch and Nanostrip are good organic cleans for removing residue on the surface of a wafer prior to processing. An oxygen plasma is another good alternative.

Equipment

Dehydration bake

Because photoresist is hydrophobic, a dehydration bake is necessary to remove all moisture from the surface of the wafer. This can be done simply by placing the wafer on a hotplate but may also be included as part of the vapor prime step, discussed in the next section.

Adhesion promoter

For more details on HMDS application, see Vapor prime.

To promote adhesion, HMDS is often applied to a sample prior to applying the photoresist. The recommended method of application is with a vapor prime process in one of the tools listed below. It can also be applied in liquid form and spun on the surface, similar to spinning photoresist, but this has been shown to be less effective.

Equipment

Photoresist spinning

The most common method of applying photoresist to a sample is by spinning it on as a liquid and then baking the sample to remove the solvent. There are a variety of tools that can be used to apply the photoresist depending on the size of your sample and type of photoresist used.

Equipment

Soft Bake

Most photoresists require a softbake to bake off the remaining solvents. For many processes on the ACS 200 cluster tool, this bake is included automatically after the spin step. For manual spinning, this should be performed on a hotplate at the temperature recommended by the photoresist datasheet.

Exposure

The LNF offers several types of exposure, explained in more detail on the Lithography page.

Post exposure bake

Some photoresists recommend or require a post exposure bake. Like the soft bake, this can be performed on a hotplate or in the ACS 200 cluster tool. Please check the photoresist datasheet to determine if this is recommended.

Development

After exposure, the sample should be developed to remove the desired pattern. For most standard resists, this is performed by soaking the sample in a basic solution, although some use solvent based developers. Check the photoresist datasheet to determine the recommended developer.

Equipment

Hard Bake

Some photoresists recommend a hard bake, performed after the development of the sample. This is often recommended prior to performing wet etching processes. Please check the photoresist datasheet to determine if a hard bake should be used.

For some photoresists, like SPR 220, a hard bake should explicitly not be used, as it will reflow the resist and degrade the features.

Plasma Descum

Prior to subsequent processes, a plasma descum is highly recommended. This will remove any residue left after development that may degrade the performance of an etch or the adhesion of a deposition (e.g. when performing a lift-off. Specifically for wet etching, it will also make the photoresist surface hydrophilic, which will ensure even etching by the chemical.

Equipment

For descum, typically, an oxygen plasma step is performed using the YES-CV200RFS(E). Some RIE equipment also can perform the descum step, often immediately before beginning the etch process.

See also

Other related wiki pages

References


Further reading