
Usage examples of Oleophobic Photoresist
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Basics of Oleophobic Photoresist and a Case Example
An oleophobic photoresist is made by adding the hydrophobicity (water repellency) and oleophobicity (oil repellency) of fluorine to the photoresist, which is used in the photolithography process for manufacturing electronic substrates, semiconductors, etc.
This oleophobic photoresist technology enables the fine processing required in manufacturing substrates of electronic devices which keep advancing, and also helps address issues in manufacturing. The technology offers the possibility of solving various other issues in manufacturing electronic devices.
This article introduces basic knowledge on oleophobic photoresists and a case example of using this technology.
01/What is an Oleophobic Photoresist?
An oleophobic photoresist is a photoresist, which is used in the photolithography process for manufacturing electronic substrates, semiconductors, etc., to which oleophobicity (oil repellency) has been added.
A photoresist enables arbitrary shapes to be formed by using photosensitivity. An oleophobic photoresist is achieved by applying oleophobicity to this photoresist. Such photoresists solve issues in manufacturing substrates for leading-edge electronic devices, etc. such as fine processing.
The photoresist and oleophobicity that are needed for an oleophobic photoresist, and their functions, are outlined below.
What is a photoresist?Its role in photolithography
What is a photoresist?Its role in photolithography
A photoresist is a photosensitive material that is used during the photolithography process in manufacturing electronic substrates, semiconductors, etc.
Photolithography is a technology to developing a photograph. After applying the photoresist on the substrate (wafer), it is developed by exposure to ultraviolet light (UV light), etc. via the photomask, which is a negative plate on which fine circuit patterns are drawn. It is also called lithography.
Two types of photoresist may be used, a positive resist or a negative resist. When a positive resist is used, the part subjected to pattern exposure via the photomask disappears after development. On the other hand, when a negative resist is used, the part subjected to pattern exposure remains.
The photoresist enables the exposure and development of fine patterns in photolithography.

Fig. 1: Photolithography process
After coating the photoresist on the substrate, it is pre-baked and exposed to UV light via the patterned photomask, followed by development, post-baking to complete the pattern transfer.
What is the oleophobic technology?The mechanism of repelling liquids
What is the oleophobic technology?The mechanism of repelling liquids
Perhaps the best known example of the oleophobic technology is frying pans that have undergone fluorine processing.
A drop of oil (liquid) dripped onto the surface of such a frying pan forms a ball shape and rolls because of the balance between the surface tension of the frying pan (solid) and the surface tension of the oil (liquid) and the interfacial tension between the oil and the frying pan.
The angle θ between the solid surface and the tangent from the point of contact of the liquid in this state is called wettability (angle of contact). This relationship is expressed by Young’s formula (Fig. 2). The wettability (angle of contact) changes when the surface (interfacial) tension in each of the terms in the formula changes. For example, the solid becomes less wettable if its surface tension (γS) is reduced, and repels liquids better. That is, oleophobicity involves reducing the surface tension of the solid.
To improve the oleophobicity, materials are often coated with an oleophobic agent, or a base material with a small surface tension is used for the solid itself.

Fig. 2: Wettability of a liquid on a solid surface

AGC Seimi Chemical Co., Ltd.:
http://www.seimichemical.co.jp/eng/product/fluoro/
Technologies and Materials of Hydrophobicity and Oleophobicity, CMC Publishing Co., Ltd.:
https://www.cmcbooks.co.jp/user_data/overseas.php

Usage examples of Oleophobic Photoresist
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02/Case example of applying the oleophobic photoresist technology in the manufacture of OLED displays
This section explains why the oleophobic photoresist technology became necessary in the manufacture of OLED displays, the issues that were solved, the required specifications, etc.
The OLED display is used as a case example of the oleophobic photoresist technology. It explains why the technology became necessary in the manufacture of OLED displays, the issues that were solved, the required specifications, etc. Please examine the possibilities of oleophobic photoresist based on this case example.
Why oleophobicity became necessary in the manufacture of OLED display panel
Why oleophobicity became necessary in the manufacture
of OLED display panel
The conventional methods of manufacturing OLED display panels are the white vapor deposition + color filter method and the RGB vapor deposition method. These manufacturing processes require large vacuum devices and fine masks. However, using these methods for larger displays involves extreme technical difficulties, as well as increased manufacturing cost due to low production efficiency, increased material cost due to low material utilization ratio, and environmental impact.
Meanwhile, the RGB printing method, which has been subject to research and development, reduces the processes of large vacuum devices and requires no fine mask. This enabled the mass production of medium-sized monitor displays, higher production efficiency, and lower production cost. JOLED Inc. launched a mass production line using the RGB printing method to produce a 32-inch display (OLEDIO™) in 2021.
JOLED Inc.:
https://www.j-oled.com/eng/technology/
JOLED Inc.:
https://www.j-oled.com/eng/press/20210329/
The oleophobic technology is essential in the RGB printing method.
Separate RGB ink application on a inkjet OLED display solved by the oleophobic technology
Separate RGB ink application
on a inkjet OLED display
solved by the oleophobic technology
In the RGB printing method, which is an efficient way of manufacturing OLED displays, luminescence materials are applied onto the RGB pixels inside the OLED display panel by inkjet.
An OLED uses organic compounds (inks) as the luminescence materials. There are also RGB pixels of width 10 to 30 μm and film thickness 1 to 2 μm aligned inside the panel, as shown in Fig. 3.
To prevent color mixing between adjacent pixels when ink is applied to the pixels as the luminescence material, the wall (bank) that separates the pixels must be oleophobic. In the photolithography process, a hydrophobic and oleophobic layer is formed only at the top part of the wall (bank) that separates the RGB pixels (see Fig. 4) to prevent color mixing.

Fig. 3: RGB pixels on an OLED display substrate

Fig. 4: Cross-sectional drawing of RGB pixels on an OLED display substrate
Oleophobic photoresist that supports the RGB printing method for manufacturing OLED display panels
Oleophobic photoresist that supports
the RGB printing method
for manufacturing OLED display panels
For the oleophobic photoresist used in the RGB printing method, the hydrophobic and oleophobic layer must be formed only on the top part of the wall (bank) that separates the RGB pixels during the photolithography process.
The substrate with a hydrophobic and oleophobic layer formed after the photolithography process is sent to the process to apply the luminescence material (ink) inside the pixels by inkjet. It is possible to control the ink in this process as the luminescence material (ink) slides down and settles inside the pixel due to the oleophobic performance even when ink is dripped onto the hydrophobic and oleophobic layer at the top of the bank (see Fig. 5).

Fig. 5: Cross-sectional drawing of RGB pixels on an OLED display substrate, and the function of the hydrophobic and oleophobic layer in an oleophobic photoresist
Surface transfer property of fluorine, which is required in the oleophobic photoresist for inkjet OLED display panels
Surface transfer property of fluorine,
which is required in the oleophobic photoresist
for inkjet OLED display panels
A fluorine compound is used in the oleophobic photoresists for inkjet OLED displays. This is because fluorine has the properties of hydrophobicity and oleophobicity and surface transfer to the air interface. In particular, the surface transfer property is important for forming the hydrophobic and oleophobic layer only at the top part of the wall (bank) that separates the RGB pixels.
Fluorine is transferred to the surface due to its small Van der Waals force (intermolecular force) and small internal energy. While multiple compounds including fluorine component are mixed in the solvent in the oleophobic photoresist, the fluorine component separates from the other components due to the difference in Van der Waals force when the solvent is removed during the photolithography process. Since air has a small Van der Waals force similar to the fluorine component, the fluorine component, which has a relatively small internal energy compared to the other compounds, tends to move toward the air interface in order to stabilize the coating film (see Fig. 6).
This characteristic makes it possible to transfer the fluorine component to the surface selectively, thus forming an oleophobic photoresist with a hydrophobic and oleophobic layer only at the top part of the bank.

Fig. 6: Process of forming a hydrophobic and oleophobic layer at the top of the bank on a negative oleophobic photoresist
Specifications of oleophobic photoresist for inkjet OLED display panels
Specifications of
oleophobic photoresist
for inkjet OLED display panels
Requirements of photoresists for inkjet OLED display panels
- Contact AngleWater: 100°, xylene: 46°
- Thickness0.5〜2μm
- Resolution10μm
- Exposure wavelengthsi-line, ih-line, ghi-line

Usage examples of Oleophobic Photoresist
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Reasons for Choosing AGC
AGC has used the oleophobic technology in leading-edge device manufacturing processes and technological research.
We can propose customized products that suit the purpose, in addition to our lineup of standard products equipped with oleophobic performance.
Customized Products of AGC
We will make proposals according to the purpose of oleophobicity, such as electronic device manufacturing processes and coating on base materials. We have a solid track record in the fields of photoresists, various types of coating, microchannels, and biochips.
Standard Products of AGC
Our lineup of products with oleophobicity includes:
- ATX®Series
- CYTOP®
- SURECO®
Customized Products of AGC
AGC manufactures fluororesins from raw materials with excellent repellency.
We discuss with our customers, propose solutions to meet their performance requirements, and connect them to practical applications. We receive inquiries for applications in a wide range of fields, particularly the electronics (including nano-sized applications), life sciences, and automotive(mobility) industries.
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