Photolithography in TFT-LCD Array manufacturing transfers each mask pattern into deposited films on the glass substrate. The same core cycle repeats for Gate metal, semiconductor, Source/Drain metal, passivation, and ITO layers.
Key Takeaways
- Photolithography is the repeated pattern-transfer engine of the TFT-LCD Array process.
- Positive photoresist is commonly used in TFT-LCD Array fabrication because exposed regions become soluble in developer and can be removed cleanly.
- Wet etching and dry etching are chosen according to film material and process requirements.
Step 1: Film Deposition
The process starts by depositing a thin film on the glass substrate. Metal films are commonly deposited by PVD sputtering, while nonmetal functional films are commonly deposited by CVD or PECVD equipment.
Step 2: Photoresist Coating
After deposition, the film is coated with photoresist. Photoresist systems include positive and negative types. Positive photoresist is commonly used in TFT-LCD Array fabrication because exposed regions become soluble in developer and can be removed cleanly.
Step 3: Exposure and Development
During exposure, ultraviolet light passes through the photomask and transfers the pattern to the coated photoresist. During development, the exposed part of positive photoresist dissolves in developer solution, leaving the designed resist pattern.
Step 4: Wet Etching or Dry Etching
Etching removes the film area not protected by photoresist. Etching is generally grouped into wet etching and dry etching. In general, wet etching is used for metal layers, while dry etching is used for nonmetal materials.
| Etching type | Typical target | Core mechanism |
|---|---|---|
| Wet etching | Metal film layers | Chemical solution reacts with and removes the exposed film. |
| Dry etching | Nonmetal film layers | Reactive plasma species react with the exposed film, and byproducts are removed by vacuum pumping. |
Step 5: Photoresist Stripping
After etching, the remaining photoresist is stripped from the glass substrate with chemical solution. The substrate is then ready for the next film deposition and mask cycle.
Process Role in the Full Array Flow
Photolithography connects every deposition step with the final TFT pattern. Each mask cycle defines which film areas remain, which areas are etched away, and how the next functional layer aligns with the previous structure.
Frequently Asked Questions
What is TFT photolithography?
TFT photolithography is the pattern-transfer process used to define films on the TFT-LCD Array substrate through photoresist coating, exposure, development, etching, and stripping.
What is the difference between wet etching and dry etching?
Wet etching uses chemical solution to remove exposed film, often metal layers. Dry etching uses plasma-generated reactive species and is commonly used for nonmetal films.
Why is positive photoresist used?
Positive photoresist is useful because the exposed region becomes soluble in developer, allowing the mask pattern to be transferred cleanly into the resist.
Technical References
The following industry references support the material properties, TFT backplane terminology, and process context used in this guide.
- Applied Materials: Amorphous Silicon
a-Si has long been a dominant active-matrix TFT-LCD semiconductor; its low mobility explains why oxide and LTPS are used for higher-performance backplanes. - AGC: Glass Substrates for TFTs (AN100)
TFT-LCD glass must be alkali-free, heat resistant, chemically stable, and dimensionally stable during array fabrication. - Nippon Electric Glass: Alkali-Free Glass Substrate OA-11
Alkali-free display glass uses very low alkaline oxide content and supports dimensional stability through TFT process temperatures. - SID / Wiley: Beyond Amorphous-Silicon TFTs
a-Si mobility is limited compared with newer high-mobility TFT materials, which helps explain material trade-offs in LCD backplane design.
Related Deep-Dive Guides
- Main TFT-LCD Array process guide
- TFT-LCD Array substrate structure
- 5-mask TFT-LCD Array process flow
- TFT-LCD Array materials
- Copper vs aluminum Gate electrodes
Related SuccessLCD Resources
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