Difference between revisions of "Optical lithography"

From LNF Wiki
Jump to navigation Jump to search
Line 1: Line 1:
 
{{lead rewrite}}
 
{{lead rewrite}}
{{duplication|dupe=General lithography}}
+
{{missing information|photoresist tone}}
 
{{Infobox technology
 
{{Infobox technology
 
|image =
 
|image =
Line 32: Line 32:
  
 
==Methods of Operation==
 
==Methods of Operation==
 +
{{confusing|section}}
 
The ability to focus an image into the sample is proportional to the distance from the focal plane (depth of focus), and the amount of diffraction of the light. Both of these parameters are proportional to the wavelength of the light. The amount of diffraction is proportional to the wavelength, therefore to resolve finer features, shorter wavelengths are required. However, with shorter wavelengths the depth of focus is also lower, minimizing the amount of topology on the surface that is acceptable.
 
The ability to focus an image into the sample is proportional to the distance from the focal plane (depth of focus), and the amount of diffraction of the light. Both of these parameters are proportional to the wavelength of the light. The amount of diffraction is proportional to the wavelength, therefore to resolve finer features, shorter wavelengths are required. However, with shorter wavelengths the depth of focus is also lower, minimizing the amount of topology on the surface that is acceptable.
  
 
There are a series of steps that are common to all types of optical lithography
 
There are a series of steps that are common to all types of optical lithography
#Surface cleaning
+
#Sample preparation
#Dehydration
+
#*Surface cleaning
#Adhesion promoter
+
#*Dehydration
#resit spinning
+
#*Adhesion promoter
#Soft bake
+
#Photoresist application and soft bake
 
#Exposure
 
#Exposure
 
#Post exposure bake (PEB) (necessary with some resists)
 
#Post exposure bake (PEB) (necessary with some resists)
#Develop
+
#Development
 
#Hard bake (necessary with some resists)
 
#Hard bake (necessary with some resists)
#Descum
+
#Plasma descum
 +
 
 +
===Sample preparation===
 +
{{main|Lithography processing#Sample preparation}}
 +
Prior to photoresist application and exposure, the sample should be [[Cleaning|cleaned]] and free of [[Lithography processing#Dehydration bake|moisture]]. Additionally, an [[Lithography processing#Adhesion promoter|adhesion promoter]] such as [[HMDS]] may be applied.
 +
 
 +
===Photoresist application===
 +
{{main|Lithography processing#Photoresist application}}
 +
Once the sample is prepared, photoresist is applied to the sample. This is most commonly achieved by spinning it on as a liquid and then baking the sample to remove the solvent. The thickness of the layer is determined by the speed at which it is spun. Spin curves and bake times and temperatures can be found on the [[photoresist]]s' datasheets.
 +
 
 +
It is also possible to apply photoresist using a spray-on tool or through {{em|what's it called when you dip the wafer in a tub of resist and slowly draw it out? I'm pretty sure that's a thing...}}, although these methods are not currently available at the LNF.
 +
 
 +
===Exposure===
 +
{{main|Lithography processing#Exposure}}
 +
After the photoresist is applied and baked, it is exposed to UV light to generate the desired pattern. The UV light causes a chemical reaction in the photoresist. In positive photoresist, the reaction makes the photoresist acidic, so that it will dissolve in a alkaline [[developer]] solution. With negative photoresist, the exposed polymer cross-links, making it impervious to the developer, which only removes the areas that are unexposed.
 +
 
 +
The exposure may be [[direct writing|directly]] written on the mask with a laser, or the entire wafer can be exposed through a [[mask]]. The latter is a much faster and more cost-effective process when multiple samples are desired. Mask exposure can further be divided into two categories: {{em|contact}} and {{em|projection}}
 +
 
 +
; Contact exposure
 +
Contact exposure involves placing the wafer in direct contact or very close proximity (less than 100{{nbsp}}μm) with the mask. This reduces diffraction through the mask to create a clear image in the photoresist. In this type of exposure, the pattern drawn on the mask will be directy transferred into the photoresist. Resolution is limited by the amount of diffraction and photoresist thickness. The majority of contact exposure tools in the LNF have a resolution of around 2{{nbsp}}μm.
 +
 
 +
; Projection exposure
 +
In projection exposure, a lens is placed between the mask and the wafer, which focuses the image on the surface of this wafer. This allows for contact-less lithography, which can be cleaner and easier. Additionally, the lens typically reduces the size of the image from the mask, allowing for improved resolution. The [[GCA AS200 AutoStep|projection exposure tool]] in the LNF has 5x reduction, so the features on the wafer will be 5 times smaller than those drawn on the mask. This tool has a resolution of 0.7{{nbsp}}μm.
 +
 
 +
===Post exposure bake===
 +
{{main|Lithography processing#Post exposure bake}}
 +
{{missing information|section|why a PEB is used}}
 +
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===
 +
{{main|Lithography processing#Development}}
 +
After exposure, the photoresist is placed in a developer solution which dissolves parts of the photoresist on the wafer. For positive photoresist, the areas that were exposed dissolve, and for negative photoresist, the areas that were un-exposed dissolve. For most standard resists, this is performed by soaking the sample in a [[:Category:Bases|alkaline]] solution, although some use [[:Category:Solvents|solvent]] based developers.  Check the photoresist datasheet to determine the recommended developer.
 +
 
 +
{{em|Optional alternative paragraph: The most commonly used developer is a highly diluted [[TMAH]] solution. The LNF recommends [[AZ 726]], a developer with the same concentration of TMAH as [[AZ 300]] plus surfactants to improve the uniformity of the developer during puddle developing. Other supported developers are listed in on the [[developer]] page. There are also solvent-based developers for specific resists, like [[SU-8]] and [[PMMA]].}}
 +
 
 +
===Hard bake===
 +
{{main|Lithography processing#Hard bake}}
 +
Some photoresists recommend hard-baking the resist after development. This will densify the resist, improve the adhesion to the surface, and make it more resistant to wet chemical etching. It will reduce the undercut of the resist during wet chemical etching. As a rough approximation, it reduces the undercut for an [[Shipley 1800|1800 series]] mask by 10–15%. Hard baking resist has been shown to have no effect or can be detrimental for [[RIE]] etching.
 +
 
 +
{{note|The hard bake is not recommended for certain resists. Please check the photoresist datasheet to determine if it is recommended.|reminder}}
 +
 
 +
{{em|Original text:
 +
 
 +
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.
 +
 
 +
{{note|For some photoresists, like [[SPR 220]], a hard bake should explicitly ''not'' be used, as it will reflow the resist and degrade the features.|error}}
 +
}}
 +
 
 +
===Plasma descum===
 +
{{main|Plasma ashing}}
 +
For many applications, a [[plasma descum]] step is performed after the lithography before further processing. This step typically consists of a short, low power [[oxygen]] plasma, which etches the photoresist a small amount (on the order of 20–30{{nbsp}}nm). The purpose of the descum is to remove any residue from the surface where the photoresist was developed, and to get rid of the "tail" that often occurs at the interface between the photoresist and the substrate, and improve the vertical profile of the features. A descum is strongly recommended before any [[RIE]] etching. The oxygen plasma can be replaced with a high power [[Argon]] plasma, which can be useful for etches where surface roughness and sidewall profile are critical.
 +
 
 +
Oxygen plasma treatment is also strongly recommended prior to [[wet etching]]. Photoresist is naturally [[Wikipedia:hydrophobic|hydrophobic]] and will repel water-based solutions, causing small features to not be etched. Exposure to oxygen plasma renders the surface hydrophilic and enables etching to occur.
 +
 
 +
{{em|Original text:
 +
 
 +
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 [[etching|etch]] or the adhesion of a [[PVD|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 [[plasma ashing|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.
 +
}}
  
 
==Figures of Merit==
 
==Figures of Merit==
Line 62: Line 123:
 
The majority of defects in optical lithography are user created errors.  It's necessary to pay close attention to '''every''' step of the process.  A glove finger print may not show up initially on the wafer until the wafer is etched.  A drop of acetone from the mist created by an acetone squirt bottle can destroy part of a pattern.  Often it's possible to reduce both particulate and defects by using an automated tool such as the [[ACS 200 cluster tool]] to remove as much of the human skill needed as possible.
 
The majority of defects in optical lithography are user created errors.  It's necessary to pay close attention to '''every''' step of the process.  A glove finger print may not show up initially on the wafer until the wafer is etched.  A drop of acetone from the mist created by an acetone squirt bottle can destroy part of a pattern.  Often it's possible to reduce both particulate and defects by using an automated tool such as the [[ACS 200 cluster tool]] to remove as much of the human skill needed as possible.
  
==Automated batch equipment==
+
==Equipment==
{{see also|ACS 200 cluster tool}}
+
===Automated batch equipment===
 
+
{{Hatnote|Equipment: [[ACS 200 cluster tool]]}}
==Sample preparation==
+
{{expand section}}
===Sample cleaning===
 
{{main|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 N<sub>2</sub> 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 [[Plasma ashing|oxygen plasma]] is another good alternative.
 
 
 
====Equipment====
 
* [[YES-CV200RFS(E)]] - [[plasma ashing|oxygen plasma]] cleaning system
 
* [[CL200 Megasonic Cleaner]] - aggressive [[wet cleaning]] system
 
 
 
===Dehydration bake===
 
{{main|Lithography processing#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===
 
===Adhesion promoter===
{{main|Lithography processing#Adhesion promoter}}
+
{{Hatnote|Equipment: [[Image Reversal Oven]]
{{details|Vapor prime|HMDS application}}
+
{{expand section}}
  
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.
+
===Photoresist application===
 
 
====Equipment====
 
* [[YES-310TA]] - Dedicated vapor prime and image reversal oven
 
* [[ACS 200 cluster tool]] - automated spinner and developer for 4" and 6" wafers
 
 
 
==Photoresist spinning==
 
{{main|Lithography processing#Photoresist application}}
 
 
 
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===
 
 
* Automated batch processing tools
 
* Automated batch processing tools
 
** [[ACS 200 cluster tool]] - 4" and 6" only
 
** [[ACS 200 cluster tool]] - 4" and 6" only
Line 107: Line 141:
 
** [[CEE 100CB photoresist spinner]] - fully manual spinner for photoresist and other polymers
 
** [[CEE 100CB photoresist spinner]] - fully manual spinner for photoresist and other polymers
  
===Soft Bake===
+
===Exposure===
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==
 
{{main|Lithography processing#Exposure}}
 
 
 
The LNF offers several types of exposure, explained in more detail on the [[Lithography processing#Exposure|lithography processing]] page.  There are several contact aligners, one projection stepper, as well as direct write capabilities.
 
 
 
===Equipment===
 
 
*Contact exposure
 
*Contact exposure
 
**[[MA-BA-6_Mask-Bond_Aligner|MA/BA-6 Mask/Bond Aligner]] - 4" and 6" wafers with backside alignment capability
 
**[[MA-BA-6_Mask-Bond_Aligner|MA/BA-6 Mask/Bond Aligner]] - 4" and 6" wafers with backside alignment capability
Line 125: Line 151:
 
*Direct write exposure
 
*Direct write exposure
 
**[[Heidelberg µPG 501 Mask Maker]] - mainly for [[mask making]] but can also be used on individual samples
 
**[[Heidelberg µPG 501 Mask Maker]] - mainly for [[mask making]] but can also be used on individual samples
 +
[imageright|Photolithography exposure.|{UP(Public.Lithography)}Photoresist-small.jpg]
  
==Post exposure bake==
+
===Development===
{{main|Lithography processing#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==
 
{{main|Lithography processing#Developing}}
 
 
 
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 [[:Category:Bases|basic]] solution, although some use [[:Category:Solvents|solvent]] based developers.  Check the photoresist datasheet to determine the recommended developer.
 
 
 
===Equipment===
 
 
* Automated batch processing tools
 
* Automated batch processing tools
 
** [[ACS 200 cluster tool]] - 4" and 6" only, [[MF 300]] and [[MF 319]]
 
** [[ACS 200 cluster tool]] - 4" and 6" only, [[MF 300]] and [[MF 319]]
Line 145: Line 162:
 
* Beaker developing
 
* Beaker developing
 
** [[Base Bench 63]] - useful for developing thick photoresist like [[KMPR]]
 
** [[Base Bench 63]] - useful for developing thick photoresist like [[KMPR]]
 
==Hard Bake==
 
{{main|Lithography processing#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.
 
 
{{note|For some photoresists, like [[SPR 220]], a hard bake should explicitly ''not'' be used, as it will reflow the resist and degrade the features.|error}}
 
 
==Plasma Descum==
 
{{main|Plasma ashing#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 [[etching|etch]] or the adhesion of a [[PVD|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 [[plasma ashing|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.
 
 
==References==
 
 
  
 
==See also==
 
==See also==
Line 172: Line 171:
 
* [https://docs.google.com/document/d/1lwKiyFrUNtZ2j9MNi21j697glr_YwgbzE97o4q3xDRY/preview Lithography Handbook]
 
* [https://docs.google.com/document/d/1lwKiyFrUNtZ2j9MNi21j697glr_YwgbzE97o4q3xDRY/preview Lithography Handbook]
 
* [https://umich.box.com/s/buip2kslnb3ewvv9jewzmoi5hrvmgoaw Lithography Workshop June 12, 2015]
 
* [https://umich.box.com/s/buip2kslnb3ewvv9jewzmoi5hrvmgoaw Lithography Workshop June 12, 2015]
 +
* [[Wikipedia:Photolithography]]
  
 
[[Category:Lithography]]
 
[[Category:Lithography]]

Revision as of 14:48, 10 March 2016

Optical lithography
Technology Details
Technology Lithography
Equipment List of lithography equipment
This article is about optical (UV) lithography. For information on e-beam lithography, see Electron beam lithography.
For more details on optical lithography practices and common processes, see Lithography processing.

Optical lithography is the patterning of masks and samples with photoresist prior to other processing steps (e.g. deposition, etching, doping). There are a variety of lithography processes that are available in the LNF. The lab offer a general training session for lithography processing including details of process steps and the tools available. This session is required for authorization on several of the tools, but can be taken by anyone in the lab.

Selection of type of optical lithography

For optical lithography a physical pattern is required with clear and dark areas typically on a mask. Most often the mask is a glass plate with a UV opaque material on it such as chromium. There are two types of optical lithography utilized in clean room environments:

  1. Contact lithography places the glass mask in direct contact with the sample. This has some distinct advantages and disadvantages:
    • Because it is in direct contact with the photoresist, it is subject to picking up particles and transferring them to all subsequent wafers.
    • It is capable of patterning an entire wafer with a single exposure
    • Minimum features are larger than projection lithography
      • At LNF 2µm features
    • Registration is limited to what can be seen (power of the microscope)
      • At LNF 1µm alignment tolerance
  2. Projection lithography shines light through the mask, a set of lenses and projects this onto the substrate.
    • Mask stays cleaner, less susceptible to particulates
    • Many steppers have reduction in the optics allowing for definition of smaller features
      • At LNF 0.5µm minimum features, 0.2µm minimum alignment tolerance
    • Will focus on different parts of the wafer, eliminating problems with warped wafers
    • Especially with a reduction, limited in die size
      • At LNF 15mm x 15mm
    • More limited depth of focus (step height)

Methods of Operation

The ability to focus an image into the sample is proportional to the distance from the focal plane (depth of focus), and the amount of diffraction of the light. Both of these parameters are proportional to the wavelength of the light. The amount of diffraction is proportional to the wavelength, therefore to resolve finer features, shorter wavelengths are required. However, with shorter wavelengths the depth of focus is also lower, minimizing the amount of topology on the surface that is acceptable.

There are a series of steps that are common to all types of optical lithography

  1. Sample preparation
    • Surface cleaning
    • Dehydration
    • Adhesion promoter
  2. Photoresist application and soft bake
  3. Exposure
  4. Post exposure bake (PEB) (necessary with some resists)
  5. Development
  6. Hard bake (necessary with some resists)
  7. Plasma descum

Sample preparation

Prior to photoresist application and exposure, the sample should be cleaned and free of moisture. Additionally, an adhesion promoter such as HMDS may be applied.

Photoresist application

Once the sample is prepared, photoresist is applied to the sample. This is most commonly achieved by spinning it on as a liquid and then baking the sample to remove the solvent. The thickness of the layer is determined by the speed at which it is spun. Spin curves and bake times and temperatures can be found on the photoresists' datasheets.

It is also possible to apply photoresist using a spray-on tool or through what's it called when you dip the wafer in a tub of resist and slowly draw it out? I'm pretty sure that's a thing..., although these methods are not currently available at the LNF.

Exposure

After the photoresist is applied and baked, it is exposed to UV light to generate the desired pattern. The UV light causes a chemical reaction in the photoresist. In positive photoresist, the reaction makes the photoresist acidic, so that it will dissolve in a alkaline developer solution. With negative photoresist, the exposed polymer cross-links, making it impervious to the developer, which only removes the areas that are unexposed.

The exposure may be directly written on the mask with a laser, or the entire wafer can be exposed through a mask. The latter is a much faster and more cost-effective process when multiple samples are desired. Mask exposure can further be divided into two categories: contact and projection

Contact exposure

Contact exposure involves placing the wafer in direct contact or very close proximity (less than 100 μm) with the mask. This reduces diffraction through the mask to create a clear image in the photoresist. In this type of exposure, the pattern drawn on the mask will be directy transferred into the photoresist. Resolution is limited by the amount of diffraction and photoresist thickness. The majority of contact exposure tools in the LNF have a resolution of around 2 μm.

Projection exposure

In projection exposure, a lens is placed between the mask and the wafer, which focuses the image on the surface of this wafer. This allows for contact-less lithography, which can be cleaner and easier. Additionally, the lens typically reduces the size of the image from the mask, allowing for improved resolution. The projection exposure tool in the LNF has 5x reduction, so the features on the wafer will be 5 times smaller than those drawn on the mask. This tool has a resolution of 0.7 μm.

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 photoresist is placed in a developer solution which dissolves parts of the photoresist on the wafer. For positive photoresist, the areas that were exposed dissolve, and for negative photoresist, the areas that were un-exposed dissolve. For most standard resists, this is performed by soaking the sample in a alkaline solution, although some use solvent based developers. Check the photoresist datasheet to determine the recommended developer.

Optional alternative paragraph: The most commonly used developer is a highly diluted TMAH solution. The LNF recommends AZ 726, a developer with the same concentration of TMAH as AZ 300 plus surfactants to improve the uniformity of the developer during puddle developing. Other supported developers are listed in on the developer page. There are also solvent-based developers for specific resists, like SU-8 and PMMA.

Hard bake

Some photoresists recommend hard-baking the resist after development. This will densify the resist, improve the adhesion to the surface, and make it more resistant to wet chemical etching. It will reduce the undercut of the resist during wet chemical etching. As a rough approximation, it reduces the undercut for an 1800 series mask by 10–15%. Hard baking resist has been shown to have no effect or can be detrimental for RIE etching.

The hard bake is not recommended for certain resists. Please check the photoresist datasheet to determine if it is recommended.

Original text:

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

Main article: Plasma ashing

For many applications, a plasma descum step is performed after the lithography before further processing. This step typically consists of a short, low power oxygen plasma, which etches the photoresist a small amount (on the order of 20–30 nm). The purpose of the descum is to remove any residue from the surface where the photoresist was developed, and to get rid of the "tail" that often occurs at the interface between the photoresist and the substrate, and improve the vertical profile of the features. A descum is strongly recommended before any RIE etching. The oxygen plasma can be replaced with a high power Argon plasma, which can be useful for etches where surface roughness and sidewall profile are critical.

Oxygen plasma treatment is also strongly recommended prior to wet etching. Photoresist is naturally hydrophobic and will repel water-based solutions, causing small features to not be etched. Exposure to oxygen plasma renders the surface hydrophilic and enables etching to occur.

Original text:

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.

Figures of Merit

Resolution

The minimum feature resolution is generally a direct result of the type of resist, thickness, exposure time and develop time.

Registration

Also referred to as alignment accuracy, is critical to ensure 2 patterns are properly registered to each other.

Thickness

When photoresist is used as a mask for etching it will also be etched (usually at a significantly slower rate). Therefore it is important to have enough thickness to last the length of the etch. Generally it is good to have a reasonable margin of safety, usually ~25-50% is ok. On the other hand it's easier to pattern smaller features in thinner resist.

Sidewall Angle

The sidewall angle of the photoresist is critical to many processes. Vertical sidewalls are necessary for etching where as an outwards sloping sidewall makes liftoff easier.

Defect Level

The majority of defects in optical lithography are user created errors. It's necessary to pay close attention to every step of the process. A glove finger print may not show up initially on the wafer until the wafer is etched. A drop of acetone from the mist created by an acetone squirt bottle can destroy part of a pattern. Often it's possible to reduce both particulate and defects by using an automated tool such as the ACS 200 cluster tool to remove as much of the human skill needed as possible.

Equipment

Automated batch equipment

Adhesion promoter

{{Hatnote|Equipment: Image Reversal Oven

Photoresist application

Exposure

[imageright|Photolithography exposure.|{UP(Public.Lithography)}Photoresist-small.jpg]

Development

See also

Further reading