What Is Stereolithography?

In the manufacture of integrated circuits, the technology of using optical-chemical reaction principles and chemical and physical etching methods to transfer circuit patterns to the surface of a single crystal or a dielectric layer to form an effective graphic window or functional pattern.

Lithography technology refers to the technology of transferring the pattern on the reticle to the substrate by means of photoresist (also called photoresist) under the action of light. The main process is: first, the ultraviolet light is irradiated to the surface of the substrate with a layer of photoresist film through the mask, causing the photoresist in the exposed area to chemically react; Photoresist (the former is called a positive photoresist, the latter is called a negative photoresist), so that the pattern on the mask is copied to the photoresist film; finally, the pattern is transferred to the substrate by etching technology.

Photoresist, referred to as photoresist or resist, refers to the

Gas phase bottom mold

2. Rotary baking glue

3.Soft baking

4. Alignment and exposure

5. Post-exposure baking (PEB)

6. Development

7. Hard film baking

8.Development inspection

Photolithography is a major process in the production of planar transistors and integrated circuits. It is a processing technique to open a mask (such as silicon dioxide) on the surface of a semiconductor wafer to perform localized diffusion of impurities.

As the current mainstream lithography technology, excimer lithography mainly includes: 248 nm KrF excimer laser technology with a feature size of 0.1 m; 193 nm ArF excimer laser technology with a feature size of 90 nm; and a feature size of 65 nm 193 nm ArF immersion technology (Immersion, 193i). Among them, 193 nm immersion lithography is the longest and most competitive of all lithography technologies, and it is also a research hotspot on how to further realize its potential. Conventional lithography technology uses air as the medium between the photoresist and the exposure lens, while immersion technology replaces air with a liquid medium. In fact, because the refractive index of the liquid medium is closer to the refractive index of the lens material of the exposure lens than the air medium, the lens aperture size and numerical aperture (NA) are equivalently increased, and the depth of focus (DOF) and exposure can be significantly improved. Process tolerance (EL), immersion lithography uses this principle to improve its resolution.

The first generation immersion lithography machine prototypes of the world's three largest lithography machine manufacturers ASML, Nikon and Cannon were all developed and improved on the basis of the original 193nm dry lithography machine, which greatly reduced the development cost and risk. Because the principle of immersion lithography system is clear and does not change much with the existing lithography technology, 193nm ArF excimer laser lithography technology has been widely used in semiconductor mass production below 65nm node; ArF immersion lithography technology is at 45nm node This is the mainstream technology for mass production.

In order to further advance the 193i technology to the 32 and 22nm technology nodes, lithography experts have been looking for new technologies. Before there is no better new lithography technology, double exposure technology (or double molding technology, DPT) ) Has become a hot spot of concern. ArF immersion double exposure technology has been considered by the industry as the most competitive technology for 32nm nodes; among lower 22nm nodes and even 16nm node technologies, immersion lithography technology also has considerable advantages.

The main challenges facing immersion lithography are: how to solve the problems of defects such as bubbles and pollution during exposure; research and development of photoresist with good compatibility with water and refractive index greater than 1.8; research and development refraction Optical lens materials and immersed liquid materials with large rates; and the expansion of effective numerical aperture NA. In response to these difficult challenges, scholars at home and abroad, as well as companies such as ASML, Nikon and IBM have done related research and put forward corresponding countermeasures. Immersion lithography machines will be developed towards higher numerical apertures to meet the requirements of smaller lithography line widths.

The traditional method to improve the resolution of lithography technology is to increase the NA of the lens or shorten the wavelength. Usually, the first method is to shorten the wavelength. As early as the 1980s, extreme ultraviolet lithography has begun theoretical research and preliminary experiments. The technology's light source is extreme far ultraviolet light with a wavelength of 11 to 14 nm. Its principle is mainly achieved by the extremely short wavelength of the exposure light source. The purpose of improving the resolution of lithography. Because all optical materials have a strong absorption of light at this wavelength, they can only take a reflective optical path. The EUV system is mainly composed of four parts, namely a reflective projection exposure system, a reflective lithographic mask, an extreme ultraviolet light source system, and a lithographic coating that can be used for extreme ultraviolet. The main imaging principle is that extreme far ultraviolet light waves with a wavelength of 10 to 14 nm are projected on a reflective mask through a periodic multilayer film mirror, and the extreme ultraviolet light reflected by the reflective mask is passed through a polygon mirror. The reduced projection system images the integrated circuit geometry on the reflective reticle into a photoresist on the surface of the silicon wafer to form a lithographic pattern required for integrated circuit manufacturing.

The current EUV technology uses an exposure wavelength of 13.5nm. Because of its short wavelength, all optical lithography does not need to use optical proximity correction (OPC) technology, so it can extend the lithography technology to technology nodes below 32nm . In September 2009, Intel demonstrated the 22 nm process wafer to the world for the first time, saying that it will continue to use 193nm immersion lithography and plan to cooperate with EUV and EBL exposure technology to extend the 193nm immersion lithography technology to 11nm process node. ^[3]