What Is a Lithographer?
Lithographers are used in the manufacture of semiconductors, liquid crystal displays, and other products to depict patterns of circuits and pixels on substrates by irradiating light.
Because they use extremely intense light and require precise control of the stage, they are often large and cost in the hundreds of millions of dollars. Lithographers are very important in the manufacturing of semiconductors and LCDs because they determine the patterns of design data (CAD data). Various lithographer methods have been developed and adopted by various companies.
Usage of Lithographers
Lithographers are mainly used in semiconductor manufacturing and flat panel display (FPD) manufacturing, including liquid crystal displays (LCDs).
In the semiconductor manufacturing process, a silicon wafer is used as a substrate, and after forming an oxide film, etc., a photoresist (photosensitive material) is coated, and the coated surface is irradiated with intense ultraviolet light emitted from Lithographer through a photomask so that unwanted areas can be removed by etching, etc. Such a method using a lithographer is called photolithography.
In the LCD manufacturing process, a glass substrate is used, and several cycles of deposition, photolithography, and etching of thin films of metals and other materials are repeated.
On one substrate, pixel electrodes and switching elements (TFT elements, etc.) can be formed, and on the other substrate, color filters with the three primary colors of light (red, green, and blue) can be formed. By laminating both substrates and placing liquid crystal material between them, a panel for liquid crystal display is completed.
When selecting lithographers, it is necessary to fully discuss with the equipment manufacturer the type of light to be used in the exposure, the accuracy, and the precision of the stage before purchasing the equipment, as they are extremely expensive.
Principle of Lithographers
Exposure measures consist of a light source, deflection lens, photomask, focusing lens, stage, and a robot for transporting silicon wafers and other materials.
The lenses and photomasks are designed with extremely high precision, and the stage also operates with high precision. During operation, the exposure target is precisely fixed to the stage. During operation, the stage moves with each exposure, so that numerous patterns are depicted on the exposed object over the entire exposure area.
The intense light with a short wavelength emitted from the light source is directed by a deflecting lens and irradiated onto a photomask, which is the prototype for the circuit pattern. The light passing through the photomask is focused by a condenser lens to produce a very small circuit pattern on the exposed object.
Once the exposure is completed over the entire exposed area, the photomask is transported by a robot or other means. Some products are designed so that the exposure target is permeated by a liquid, allowing for more precise exposure.
Other Information on Lithographers
1. Lithographer Market Share
Lithographer manufacturing vendors for semiconductors are almost oligopolized by European and Japanese manufacturers, with Europe (84%) and Japan (14%) in 2018. In addition, the market for flat panel display (FPD) lithographers for liquid crystal displays (LCDs) is almost exclusively dominated by two Japanese manufacturers.
Lithographers for semiconductors are said to be the most precise machines in history, and the latest semiconductors have been miniaturized to the extent that the width of wiring on chips (process rule) is 3 to 5 nm.
The latest FPD lithographers have line widths of less than a few microns, and these are becoming thinner and larger year by year, and the equipment is becoming more precise and larger to achieve more beautiful, high-definition images.
2. About EUV Lithographers
Among semiconductor lithographers, EUV (extreme ultraviolet) lithographers are those that use extremely short wavelengths of light known as extreme ultraviolet (EUV).
Lithographers using ArF excimer lasers, which have been used in the past, are able to process finer dimensions that are difficult to process. Semiconductor miniaturization has been progressing in accordance with Moore’s Law (semiconductor integrated circuits become four times more highly integrated and functional in three years).
The development of reduced projection exposure technology called steppers, shorter exposure wavelengths, and immersion exposure technology has dramatically improved resolution. Miniaturization means that the minimum process size that can be burned onto a wafer becomes smaller, and the minimum process size R is expressed by the following Rayleigh’s equation.
R = k/λ/NA *k is a proportionality constant, λ is the exposure wavelength, and N.A. is the numerical aperture of the exposure optical system.
Lithographers have been able to achieve miniaturization by reducing k, λ, and NA through the development of various technologies, and EUV lithographers are considered to be a technology that can break through the limitations of the past by shortening the exposure wavelength, and have been mass-produced in recent years.
3. About FPD Lithographers
FPDs (flat panel displays) include liquid crystal displays, plasma displays, and organic electroluminescent (EL) displays, which can be seen in smartphones, tablet-type terminals, and flat-screen TVs for home use, as well as in every aspect of our homes and towns.
FPD lithographers are used to manufacture flat panel displays. In principle, they are the same as semiconductor manufacturing equipment, which irradiates light onto a photomask and exposes a circuit pattern on a glass plate through a lens to create an array.
In addition, color filters that produce images and video for displays are created and combined with the arrays to complete the display. Color filters are used to express the colors of images and video, and pigment-based color resist is applied to the glass, which is then exposed and developed.