Color TFT LCD Manufacturing Process

The Fundamentals of Color TFT LCD Production

The basic manufacturing process of color TFT LCDs and major Japanese component material manufacturers are illustrated in Figure 7-2. Compared with the STN LCD process, the color TFT LCD process is much more complex. This complexity arises because each pixel contains a TFT active switching element, requiring each step in the TFT fabrication process to be executed with precision. A burned LCD screen often results from imperfections in these intricate processes, highlighting the importance of strict quality control throughout production.

The manufacturing process of color TFTLCDs consists of several key stages: glass substrate engineering, array TFT formation engineering, color filter formation engineering, liquid crystal cell assembly engineering, and module assembly engineering. Each stage requires specialized equipment, precise environmental controls, and expert handling to prevent defects that could lead to a burned LCD screen or other display anomalies.

7.1.2.1 Glass Substrate Engineering

TFTLCDs require alkali-free (metal-free) glass substrates for production. In Japan, the main suppliers of glass substrates for TFTLCDs include Asahi Glass, NH Techno Glass, Corning (Coming), and Nippon Electric Glass, with Corning holding the largest market share. The glass substrates used in TFTLCDs are called white plate glass (as opposed to the blue plate glass used in STN and TN displays). Proper substrate selection is crucial, as impurities or imperfections in the glass can eventually lead to a burned LCD screen under prolonged use.

The glass substrate serves as the foundation for the entire display, so its quality directly impacts the performance and longevity of the final product. Even minor defects in the glass can propagate through subsequent manufacturing steps, potentially causing problems ranging from image distortion to a complete burned LCD screen failure. Manufacturers invest heavily in substrate inspection systems to detect and reject flawed materials before they proceed through the production line.

The thickness of TFTLCD glass substrates has decreased significantly over the years, from around 1.1mm to as thin as 0.4mm for some applications. This reduction saves material costs and makes displays lighter, but also increases handling challenges. Specialized equipment is required to transport and process these thin glass sheets without causing damage that could lead to a burned LCD screen or other defects in finished products.

7.1.2.2 Array TFT Formation Engineering

The array TFT formation process, also known as the patterning process, involves forming TFT elements and pixel electrodes on the glass substrate. For amorphous silicon (a-Si) TFTLCDs, which have become the mainstream technology, this process includes a series of steps such as deposition of amorphous silicon and various metal layers, photoresist coating, exposure, development, etching, and photoresist stripping. These steps are repeated 4 to 6 times (as shown in Figure 7-2), making this process quite similar to the manufacturing process of semiconductor DRAMs. Any misalignment or contamination during these repetitions can create weaknesses that may result in a burned LCD screen later in the display's lifecycle.

Film Deposition Process

The first step is the film deposition process. Thin films of metal, semiconductor, and insulating layers, with thicknesses ranging from 50 to 300nm, need to be formed on the cleaned glass substrate. Specifically, insulating films such as silicon oxide and nitride films, and a-Si semiconductor films are deposited using methods like PCVD in CVD equipment. The gate electrodes, source and drain electrodes, and pixel electrodes of the TFT are deposited using methods like magnetron sputtering in sputtering equipment. The quality of these thin films is critical – any irregularities can lead to current leakage or hotspots, which may eventually result in a burned LCD screen.

Deposition chambers must maintain extremely high vacuum levels and precise temperature controls to ensure film uniformity. Even minor fluctuations can create areas of higher resistance that generate excess heat during operation, increasing the risk of a burned LCD screen. Manufacturers use advanced in-situ monitoring systems to detect and correct any variations in the deposition process.

Photoresist Coating Process

The photoresist coating process involves applying a UV-sensitive photoresist uniformly onto the glass substrate surface using methods such as slit coating or spin coating. In Japan, major suppliers of photoresist include Clariant, Japan Synthetic Rubber, Shipley Far East, Tokyo Ohka Kogyo, and Nippon Zeon. Proper coating thickness and uniformity are essential, as uneven application can lead to patterning defects that might cause electrical anomalies or even a burned LCD screen in the final product.

The choice between slit coating and spin coating depends on the substrate size and production requirements. Slit coating is more efficient for large substrates, while spin coating can achieve higher uniformity for smaller panels. Both methods require precise control of photoresist viscosity and application speed to ensure consistent results. Any inconsistencies in photoresist thickness can lead to uneven exposure and development, creating potential weak points that may contribute to a burned LCD screen under prolonged use.

Photolithography Process

After the prebake process, which dries and heat-treats the photoresist, the photolithography process begins. This process includes sub-steps such as exposure, development, etching, and photoresist stripping. Exposure involves using an exposure device to irradiate the photoresist coated on the glass substrate surface with ultraviolet light through a patterned exposure mask, replicating circuit patterns corresponding to each pixel. In Japan, suppliers of photomasks include SK Electronics, Dai Nippon Printing, Toppan Printing, and HOYA. Precise alignment during exposure is critical – even minor misalignment can create electrical pathways that cause excessive current flow and potentially a burned LCD screen.

Following exposure, development is performed in a developer machine. After development comes the etching process, which removes unwanted portions of the film layers beneath the photoresist according to the developed circuit pattern, creating the desired structure. Currently, etching mostly uses dry processes, such as plasma etching in a reduced-pressure atmosphere through gas-phase reactions in plasma discharge. Improper etching parameters can create undercutting or incomplete material removal, both of which can lead to electrical faults and increase the risk of a burned LCD screen.

After the etching process is complete, the unwanted photoresist is removed in a stripper machine. Through these processes, the array TFT formation engineering is completed. On the other glass substrate, the color filter (CF) formation process is carried out, which is discussed in detail in section 7.1.3. Each completed array substrate undergoes rigorous inspection to identify any defects that could compromise performance or lead to issues like a burned LCD screen in the finished display.

The photolithography process is repeated multiple times, each with different masks to create the various layers of the TFT structure. Each iteration introduces new opportunities for defects, making process control and inspection critical at every stage. Automated optical inspection systems check for pattern defects, while electrical testing verifies proper functionality. Any substrates with defects that could potentially lead to a burned LCD screen or other failures are rejected to maintain quality standards.

The complexity of the array TFT formation process cannot be overstated. Each layer must be precisely aligned with the previous ones, and each material must maintain its properties throughout subsequent processing steps. The tiniest defect – a single particle, a pinhole in a film, or a misaligned pattern – can create a path for excessive current that may eventually result in a burned LCD screen. This is why manufacturers invest billions in advanced manufacturing facilities and continuously refine their processes to improve yields and product reliability.

As display technologies advance toward higher resolutions, faster response times, and lower power consumption, the array formation process becomes even more challenging. Finer feature sizes require more precise photolithography, while new materials like indium gallium zinc oxide (IGZO) demand different deposition and etching techniques. These advancements aim to improve display performance while also reducing issues like a burned LCD screen by creating more robust and uniform TFT structures.

Other Key Manufacturing Processes

Major Japanese Component Manufacturers

Japan has long been a leader in TFTLCD technology, with many companies specializing in critical components and materials. These manufacturers play a vital role in ensuring the quality and reliability of TFTLCD products, helping to minimize issues like a burned LCD screen through the supply of high-quality materials.

These Japanese manufacturers have developed specialized expertise in their respective fields, contributing to the global TFTLCD supply chain. Their commitment to quality helps ensure that display manufacturers can produce reliable products with minimal defects like a burned LCD screen. Many of these companies also invest heavily in research and development, driving innovation in display technology and manufacturing processes.