Briefly describes
photolithography means that the mask version of the mask version is transferred to the substrate by means of a photoresist (also known photoresist) under illumination. technology. The main process is: First, ultraviolet light is irradiated through the mask version to the surface of the substrate attached to the photoresist film, causing a chemical reaction in the exposed area; then dissolved the exposure region or the unexposed region by developing techniques. Photoresist (formerly known as the positive photoresist, the latter is called negative photoresist), enabling the graphic on the mask version to the photoresist film; finally transferring the pattern to the substrate by etching technology.
Process
Two processes
Conventional lithography technique is ultraviolet light having a wavelength of 2000 to 4500 angstroms as an image information carrier, with photointed The etchant is the intermediate (image recording) medium to realize the transformation, transfer, and processing of the graphics, and finally transmit image information to a process of wafer (mainly reflections) or medium layer. On a broad sense, it includes two main aspects of light copying and etching processes.
1 Optocopying Process: The prefabricated device or circuit graphic is accurately passed to the pre-coated surface or dielectric layer according to the required position. The photoresist is thin layer.
Figure 2 Photolithography (2 photos)
2 etching process: Using chemical or physical methods, resist the resist The layered wafer surface or dielectric layer is removed, thereby obtaining a pattern that is fully consistent with the resist thin layer pattern on the wafer surface or dielectric layer. The functional layers of the integrated circuit are stereoscopic overlapping, and thus the photolithography process is always repeated multiple times. For example, a large-scale integrated circuit is to complete all of the passages of each layer of graphics through about 10 times. On the narrow sense, the photolithography process refers to only the optical copy process, that is, from 4 to 5 or from 3 to 5 process.Main flow
The main process of the optical copy process is shown in Figure 2:
Exposure system
Exposure mode
Common exposure The way the way is classified as follows:
The difference between contact exposure and non-contact exposure is that the relative relationship between the mask and the wafers is closely separated during exposure. The contact exposure has a high resolution, a large copy area, good copy precision, simple exposure device, convenient operation and high production efficiency. However, it is prone to damage and contaminated mask and the photosensitive rubber coating on the wafer, affecting the yield and mask life, and the increase in alignment accuracy is also limited. It is generally believed that the contact exposure is only suitable for discrete components and medium and small-scale integrated circuits.
Non-contact exposure mainly refers to projection exposure. In the projection exposure system, the mask pattern is imaged on the photosensitive layer via the optical system, and the mask is not in contact with the photosensitive rubber layer on the wafer, which does not cause damage and contamination, high yield, and the alignment accuracy is also high. Meet the requirements of high integration devices and circuit production. However, projection exposure is complex and technically difficult, so it is not suitable for the production of low-end products. Modern application is the most widely 1: 1 times total reflection scanning exposure system and X: 1 times to directly step-by-step repeated exposure system on wafers.
Introduction
Direct step-by-step repetition exposure system (DSW) The large scale integrated circuit requires high resolution, high-alone accuracy and large diameter wafer processing. Direct step-by-step repetition exposure systems are optical exposure systems developed to adapt to these mutual restrictions. The main technical features are:
1 using the like-plane segmentation principle to cover a single exposure area of the maximum chip area as a minimum imaging unit, thereby creating conditions for obtaining high resolution optical systems.
2 is used to repeat exposure with precision positioning control technology and automatic alignment techniques to achieve large area image transmission in combination, thereby meeting the actual requirements of the wafer diameter increasing.
3 shorten the image transfer chain, reduce the defects and errors caused by the process, and obtain a high yield.
4 adopts precision automatic focusing technology to avoid the effect of wafer deformation of the high temperature process on the quality of imaging quality.
5 Adopts the original automatic selection mechanism (library), not only, it is not only the improvement rate, but also a conventional exposure system capable of flexible production of multi-circuit combination.
This system is a precision complex light, machine and electricity system. It is divided into two categories on the optical system. One is a total refractive imaging system, which uses 1/5 ~ 1/10 reduction magnification, technology is mature; one is 1: 1 times refractive-reflection system, simple optical path, low requirements.
Photoresist
Photoresist, referred to as photoresist or resist refers to a polymer compound which can change the resistance after the light. The particle is divided into two categories.
1 a positive photoresist: The degradation reaction in the light receiving portion can be dissolved for the developer. The diagram of the non-exposed portion left is consistent with the mask. The positive resistance has the advantages of high resolution, insensitive to the standing wave effect, large exposure, low needle density and non-toxicity, and is suitable for the production of high intensive devices.
2 negative photoresist: The light receiving portion produces a cross-strand reaction, and the non-exposed portion is dissolved by the developer, and the graphics obtained are complementary to the mask. The adhesion of the negative resist and high sensitivity, and the development conditions are not strict, suitable for devices suitable for low intensity.
Semiconductor devices and integrated circuits have put forward increasingly high requirements on photolithography techniques, requiring the amount of information that is required to pass the image in the unit area to be close to the limits of conventional optical. The common wavelength of photolithography is 3650 to 4358 angstroms, and the utility resolution is expected to be about 1 micron.
The principle of geometric optics allows the wavelength to extend downward to a far-ultraviolet wavelength of about 2000 angstroms, which is approximately 0.5 to 0.7 microns. In addition to the advanced exposure system, the micrometer graphic is highly exposed to the characteristics, film forming technology, development technology, ultra-clean environment control technology, etching technology, wafer flatness, deformation control technology, etc. Requirements. Therefore, the automation and mathematical modeling of the process process are two important research directions.
Basic step
1. Air phase bottom mold
2. Rotating bake
3. Soft Baking
< P> 4. Alignment and exposure5. After exposure, baking (PEB)
6. Development
7. Neijing Bake
< P> 8. Development checkPhotolithography
lithography is a major process in planar transistors and integrated circuit production. It is a mask (such as silica) on the surface of the semiconductor wafer to perform a processing technique for the domain diffusion of impurities.
Zonor photolithography
The excimer photolithography technique is used as the current mainstream photolithography technique, mainly including 248 nm KrF excimer laser technologies having a characteristic size of 0.1 μm; 193 NM Arf excimer laser technology (IMMersion, 193i) of characteristic size was 65 nm. Among them, 193 NM immersion photolithography is the most long and competitive in all lithography techniques, and how to further develop research hotspots. The medium between the traditional lithography of the photoresist and the exposure lens is air, while the immersion technology is converted to a liquid medium. In fact, since the refractive index of the liquid medium is more close to the refractive index of the exposure lens lens material, the lens diameter and numerical aperture (NA) can be significantly increased, and the focus depth (DOF) and exposure can be significantly increased. Catholic tolerance (EL), immersion lithography technology is using this principle to increase its resolution.
The world's three major photolithography producers ASML, NIKON and Cannon's first-generation immersion photolithography models are improved on the basis of the original 193nm dry lightning machine, which is greatly reduced. R & D costs and risks. Because the principle of the immersion lithography system is clear and the existing lithography is not changed, 193nm Arf excimer laser photolithography has been widely used in 65 nm or less; ARF immersion photolithography technology is 45 nm node The mainstream technology of large production.
In order to further advance 193i technology to the technical node of 32 and 22 nm, the photolithography experts have been looking for new technologies, and there is no better new photolithography technique before, two exposure techniques (or Two forming techniques, DPT) becomes a hot spot for people. Arf immersion two exposure techniques have been the most competitive technology of 32nm nodes; in lower 22 nm nodes or even 16 nm node technology, the immersion photolithography technology has considerable advantages.
The challenges faced by the immersion photolithography include: How to solve the problem of defects such as bubbles and pollution generated in the exposure; R & D and water have good compatibility and refractive index greater than 1.8 light Intensive problems; optical lens materials and immersion liquid materials with large refractive index; and expansion of effective numerical aperture Na values. The needle challenges these difficulties, and the country's internal experts have met-related research and proposes corresponding countermeasures in countries with advances in countries and ASML, Nikon and IBM. The immersion photolithography will be developed toward higher numerical aperture to meet smaller lightning width requirements.
Conventional method of ultraviolet photolithography
to increase lithography technology resolution is to increase the Na or shrinkage of the lens, and the first method of normal first is to shorten the wavelength. As early as the 1980s, extreme UV photolithography has begun the theoretical research and preliminary experiment, the light source of this technology is extremely far-violet light having a wavelength of 11 to 14 nm, and the principle is mainly used with a short wavelength of the exposure source. To improve the purpose of lithography. Since all optical materials have strong absorption of the wavelength of the wavelength, only reflective optical paths can be taken. The EUV system is mainly composed of four parts, namely reflective projection exposure systems, reflective photoresist, extreme ultraviolet light source systems, and photolithographic coatings that can be used for ultraviolet. Its main imaging principle is extremely long ultraviolet light wavelength of 10 to 14 nm. The periodic multilayer film mirror is projected onto the reflective mask plate, and the ultraviolet light wave reflected by the reflective mask is composed of a plurality of mirrors. The reduced projection system, projection the integrated circuit geometry on the reflective mask is imaged into the photoresist of the surface of the silicon film forms the exciting pattern of the integrated circuit manufacturing.
Currently the exposure wavelength adopted by EUV technology is 13.5 nm, since it has such a short wavelength, there is no need to use optical neighboring effect correction (OPC) technology in all lithography, so it can Techniques extend to technology nodes below 32 nm. In September 2009, Intel showed 22 NM process wafers to the world, saying continued to use 193nm immersion photolithography technology, and planned with EUV and EBL exposure technology to extend 193 nm immersion photolithography technology to 15 and 11nm process node.