The history and current status of photolithography
Latest update time：2020-11-29
Reads：
Source: The content comes from the public account "The World of Lithography", author: Lou Qihong, etc., thank you.
The rapid development of integrated circuits depends on the development of related manufacturing processes - photolithography technology, which is the highest precision processing technology that can be achieved so far.
The integrated circuit industry is the cornerstone of the modern information society. The invention of integrated circuits has greatly reduced the cost of electronic products and miraculously reduced their size. Take computers as an example. The world's first digital computer, which was born in 1946, weighed 30 tons and occupied an area of about 140 square meters. Integrated circuits connect electronic components such as transistors, resistors, and capacitors on small silicon wafers, making computers smaller, with lower power consumption and faster speed. Since the world's first planar integrated circuit came out in 1958, in just over 50 years, the rapid development of semiconductor and microelectronics technology has driven the rise of modern information technology. The development of integrated circuits is inseparable from the progress of its manufacturing process - photolithography technology.
The integrated circuit industry is the cornerstone of the modern information society. The invention of integrated circuits has greatly reduced the cost of electronic products and miraculously reduced their size. Take computers as an example. The world's first digital computer, which was born in 1946, weighed 30 tons and occupied an area of about 140 square meters. Integrated circuits connect electronic components such as transistors, resistors, and capacitors on small silicon wafers, making computers smaller, with lower power consumption and faster speed. Since the world's first planar integrated circuit came out in 1958, in just over 50 years, the rapid development of semiconductor and microelectronics technology has driven the rise of modern information technology. The development of integrated circuits is inseparable from the progress of its manufacturing process - photolithography technology.
The history of photolithography
Photolithography is a process technology that uses the principle of photochemical reaction and chemical and physical etching methods to transfer the pattern on the mask to the wafer. The principle of photolithography originated from photolithography in printing technology, which is to process and form micro-patterns on a plane. Photolithography is mainly divided into optical photolithography and particle beam photolithography according to the exposure light source (common particle beam lithography mainly includes X-ray, electron beam and ion beam lithography, etc.). Among them, optical photolithography is the most important photolithography technology at present, and its mainstream position will remain unshakable in the next few years.
The progress of photolithography technology has continuously reduced the feature size of devices and continuously improved the integration and performance of chips. Under the guidance of Moore's Law, optical photolithography has undergone changes in exposure methods such as contact/proximity, equal-magnification projection, reduced step projection, and step scanning projection. The wavelength of the exposure light source has developed from 436 nanometers (G line), 365 nanometers (Ⅰ line), to 248 nanometers (KrF), and then to 193 nanometers (ArF). The technology nodes range from 1.5 microns, 1 micron, 0.5 microns, 90 nanometers, 45 nanometers in 1978 to the current 22 nanometers. The development of integrated circuits has always been advancing with the continuous innovation of optical lithography technology.
The lithography machine (also known as the lithography system) is the key equipment of lithography technology. Its composition mainly includes lithography light source, uniform illumination system, projection lens system, mechanical and control system (including workpiece stage, mask stage, silicon wafer transmission system, etc.). Among them, the lithography light source is the core part of the lithography machine. With the continuous reduction in the size of integrated circuit devices, the continuous improvement of chip integration and computing speed, higher requirements are also placed on the exposure resolution of lithography technology. Optical resolution refers to the minimum feature size that can be imaged on a wafer. For optical projection lithography systems, the resolution is determined by the Rayleigh formula:
The progress of photolithography technology has continuously reduced the feature size of devices and continuously improved the integration and performance of chips. Under the guidance of Moore's Law, optical photolithography has undergone changes in exposure methods such as contact/proximity, equal-magnification projection, reduced step projection, and step scanning projection. The wavelength of the exposure light source has developed from 436 nanometers (G line), 365 nanometers (Ⅰ line), to 248 nanometers (KrF), and then to 193 nanometers (ArF). The technology nodes range from 1.5 microns, 1 micron, 0.5 microns, 90 nanometers, 45 nanometers in 1978 to the current 22 nanometers. The development of integrated circuits has always been advancing with the continuous innovation of optical lithography technology.
The lithography machine (also known as the lithography system) is the key equipment of lithography technology. Its composition mainly includes lithography light source, uniform illumination system, projection lens system, mechanical and control system (including workpiece stage, mask stage, silicon wafer transmission system, etc.). Among them, the lithography light source is the core part of the lithography machine. With the continuous reduction in the size of integrated circuit devices, the continuous improvement of chip integration and computing speed, higher requirements are also placed on the exposure resolution of lithography technology. Optical resolution refers to the minimum feature size that can be imaged on a wafer. For optical projection lithography systems, the resolution is determined by the Rayleigh formula:
R = k1λ/NA
In the formula, k1 is the process factor, k1 is 0.25 for a single exposure, λ is the wavelength of light, and NA is the optical numerical aperture of the projection objective.
It can be seen that there are three ways to improve optical resolution: one is to reduce the k1 value; the second is to increase the numerical aperture NA; the third is to reduce the wavelength. Among these ways, increasing the numerical aperture and shortening the exposure wavelength are achieved by changing the exposure equipment, while reducing the k1 factor is achieved through the improvement of process technology. For example, the resolution enhancement technology used in each stage of the projection exposure system mainly includes polarized light illumination, phase shift mask, off-axis illumination, etc.
Reducing the wavelength of the exposure light source is an important development trend of lithography technology and equipment. Over the past half century, with the development of lithography technology, the feature size has been reduced. In the 1960s, semiconductor chip manufacturers mainly used visible light as a light source. In the 1980s, lithography mainly used 436 nanometers (G line) and 365 nanometers (I line) generated by high-pressure discharge mercury lamps as light sources. Mercury lamps are widely used in stepper exposure machines to achieve a feature size of 0.35 microns. The application of 250-nanometer ultraviolet light radiated by a discharge mercury lamp has realized the need to reduce the wavelength of the lithography light source for the first time. However, as the technology node of integrated circuits develops towards the nanometer level, the light source of the lithography machine has also quickly developed from the mercury lamp light source in the near-ultraviolet band to the excimer laser in the deep ultraviolet band. The main light sources used range from KrF excimer laser 248 nanometer laser, ArF excimer laser 193 nanometer laser to F2 excimer laser 157 nanometer laser. When the wavelength of the light source develops to 157 nanometers, the development of 157-nanometer lithography technology is greatly restricted due to the limitations of photoresist and mask materials, low graphic contrast and other factors.
However, researchers have found that water, which can be used as an immersion liquid, is almost completely transparent to 193-nanometer light waves. After being filled with immersion liquid, the equivalent wavelength of the 193-nanometer light source is less than 157 nanometers, and the numerical aperture of the projection lens is also greatly improved. In addition, the 193-nanometer lithography machine technology is relatively mature, and developers need to focus on solving problems related to immersion technology. Therefore, the 193-nanometer light source using immersion technology to replace the 157-nanometer light source continues to be a research hotspot. By 2003, the 130-nanometer process with a wavelength of 193 nanometers had been mass-produced, such as the Pentium 4 chip at the time.
With the development of double patterning exposure technology, chip manufacturers represented by Intel have announced that they have officially abandoned the 157-nanometer lithography technology. From the 90-nanometer process to the future 45-nanometer process, they all rely on the 193-nanometer lithography technology. With the development of immersion lithography technology and resolution enhancement technology, the accuracy and performance of lithography have been continuously improved. In 2006, scientists from International Business Machines Corporation (IBM) announced that they used the 193-nanometer interference immersion lithography device NEMO to produce 29.9-nanometer lines, breaking the prediction of the 32-nanometer optical lithography limit. Using the ArF excimer laser with immersion technology, the lithography node has reached 22 nanometers, and it is possible to further reach the 16-nanometer node in the future. Through the continuous innovation of lithography technology, Moore's Law is still maintained.
Since the optional lithography exposure light source is limited, and each time a new exposure wavelength is changed, the mask pattern and photoresist materials of the lithography machine, the structure and materials of the projection lens and other systems need to be updated, the development of a lithography machine with a new wavelength requires high manpower and material costs, and requires the joint efforts of multiple countries and companies to succeed. Compared with 157-nanometer lithography technology, 193-nanometer immersion lithography technology does not require the development of new masks, lenses and photoresist materials. The 193-nanometer immersion lithography machine can even retain most of the components of the existing 193-nanometer dry lithography machine, and only needs to improve the design of some subsystems. The first generation of 193-nanometer immersion prototypes of the world's three largest lithography machine manufacturers, ASML, Nikon and Canon, were all developed and improved on the basis of the original 193-nanometer dry lithography machine, greatly reducing the cost and risk of research and development.
193 nm Excimer Laser Source for Photolithography
High-end lithography machines have the characteristics of high numerical aperture, high throughput, high critical dimension control performance and low operating cost, which require the lithography light source to have corresponding laser performance. High-quality lithography light sources require narrow laser spectrum width, high wavelength and energy stability, high average power and laser repetition rate. At present, the 193-nanometer ArF excimer laser uses immersion technology to reach the 22-nanometer lithography node and extend to the 16-nanometer node. It has become the mainstream light source for high-end lithography machines.
Excimer laser is the most powerful laser light source in the ultraviolet band. It is a kind of ultraviolet discharge gas laser with a pulse width of tens of nanoseconds. Excimer is an excited dimer with excited state binding and ground state dissociation. Its characteristic is that the ground state is unstable and generally decomposes into free particles within the vibration relaxation time. Its excited state appears in the form of binding and is relatively stable, and decays in the form of radiation. Therefore, excimer laser has the characteristics of high gain.
Excimer lasers already have relatively mature commercial products abroad. Cymer and Coherent in the United States and Gigaphoton in Japan are the main suppliers of excimer lasers for lithography. At present, pre-ionized discharge pumped excimer lasers can achieve high repetition rate, high power, and narrow line width laser output. Based on ArF excimer lasers, ASML, Nikon, Canon USA and other companies have developed commercial lithography systems. Since the discovery of the Xe2 excimer laser with a wavelength of 170 nanometers by Lawrence Livermore National Laboratory in the United States in 1972, 17 types of excimer laser oscillations have been obtained successively, and their spectra cover multiple wavelengths between 126 and 675 nanometers.
It is difficult for a single excimer laser cavity to achieve narrow spectral lines and highly stable, high-energy pulse output as a lithography light source. On the one hand, the same laser is required to work under the extreme conditions of narrow line width and high output energy at the same time. On the other hand, the degradation of ultraviolet optical components under high pulse energy will cause the life of narrow line width work to decrease. Studies have found that the dual-cavity structure is a good solution. One of the discharge cavities generates a seed pulse light source with narrow linewidth but low energy, and the other discharge cavity realizes the power amplification of the seed light source. Typical dual-cavity structures include the master oscillator power amplifier (MOPA) and the seed light injection locking system (ILS). In the MoPA structure, the linewidth narrowing optical element works at a lower repetition frequency, which reduces the photothermal effect and prolongs the life of the optical element. Secondly, the master oscillator only requires the generation of lower energy pulses, which makes it easier to obtain an extremely narrow linewidth spectrum and helps to prolong the life of the element. Represented by Cymer's xLA and xLR series, the seed light injection locking system is characterized by the seed light being amplified multiple times in the amplification cavity. Its main advantages are stable performance and low operating cost. Represented by ILS technology is the GT40A series ArF immersion lithography machine that Gigaphoton entered the market in 2004.
It is difficult for a single excimer laser cavity to achieve narrow spectral lines and highly stable, high-energy pulse output as a lithography light source. On the one hand, the same laser is required to work under the extreme conditions of narrow line width and high output energy at the same time. On the other hand, the degradation of ultraviolet optical components under high pulse energy will cause the life of narrow line width work to decrease. Studies have found that the dual-cavity structure is a good solution. One of the discharge cavities generates a seed pulse light source with narrow linewidth but low energy, and the other discharge cavity realizes the power amplification of the seed light source. Typical dual-cavity structures include the master oscillator power amplifier (MOPA) and the seed light injection locking system (ILS). In the MoPA structure, the linewidth narrowing optical element works at a lower repetition frequency, which reduces the photothermal effect and prolongs the life of the optical element. Secondly, the master oscillator only requires the generation of lower energy pulses, which makes it easier to obtain an extremely narrow linewidth spectrum and helps to prolong the life of the element. Represented by Cymer's xLA and xLR series, the seed light injection locking system is characterized by the seed light being amplified multiple times in the amplification cavity. Its main advantages are stable performance and low operating cost. Represented by ILS technology is the GT40A series ArF immersion lithography machine that Gigaphoton entered the market in 2004.
Linewidth Technology
The original spectrum width emitted by the discharge cavity is several hundred picometers, and such a wide spectrum bandwidth cannot meet the requirements of applications such as lithography. Taking the current mainstream lithography light source ArF excimer laser as an example, it is necessary to narrow the free-oscillating broadband spectrum of about 500 picometers to the sub-picometer level. Spectral bandwidth is an important factor affecting imaging capability and feature size. Due to the limitation of optical materials in the deep ultraviolet wavelength region, the projection prism of the ArF lithography system will inevitably produce chromatic aberration. The impact of sub-picometer spectral line broadening cannot be ignored. However, the chromatic aberration effect can be reduced by narrowing the spectral line width of the light source. In order to realize integrated circuit lithography at the 90-nanometer technology node, the line width of the laser pulse must reach the sub-picometer level. Secondly, while using immersion lithography to increase the numerical aperture, a narrower spectral width is required to match. Third, the narrow line width can reduce the sensitivity of the light source to the critical size, thereby improving the unevenness of the lithography pattern caused by the instability of the light source. Fourth, a lower k requires a narrower spectral line width to match. Therefore, in order to reduce the feature size of lithography and improve the efficiency of Raman scattering and the accuracy of fluorescence spectrum analysis, it is necessary to narrow the line width of the wider natural spectrum.
The lithography light source generally adopts a line width narrowing scheme combining a multi-prism beam expander and a large-size grating. The prism beam expander is used to separate wavelengths and maintain a small divergence angle. Usually, 2 to 4 prisms can achieve 20 to 40 times of optical beam expansion. The prism material is fused quartz or calcium fluoride with high transmittance in the ultraviolet band. The laser incident and exit surfaces of the prism are usually coated with anti-reflection coatings. The expanded light spot is projected onto the large-size grating, and the optical path of the prism group and the grating forms a Littrow structure. Considering the beam expansion rate, transmittance and prism anti-reflection requirements of the prism, the incident angle of the prism is usually set between 68 and 71 degrees. The large-size grating is usually a medium-step grating, and its larger blaze angle is conducive to the high-order dispersion and line width compression of the spectrum. The beam after beam expansion can also be incident on a high-reflection plane mirror first and then reflected on the grating. Rotating the high-reflection mirror can change the angle of incidence on the grating, thereby achieving tuning and stable control of the laser center wavelength.
In order to avoid energy loss caused by the strong absorption of ultraviolet laser by oxygen atoms in the atmosphere and to isolate the optical components from external pollution, optical components such as prism expanders, reflectors and large-size gratings are usually assembled in a closed cavity. In the lithography light source, such a cavity is called a line width narrowing module. When the lithography machine is working, a specific flow of high-purity nitrogen or helium is generally passed through the line width narrowing module. In addition to the
full width at half maximum (FwHM) of the peak, the spectral width of the laser should also be able to display the integral width of 95% of the spectral energy (E95). The size and stability of the E95 indicator is one of the important parameters of the lithography machine, which affects the imaging capability of the exposure system and the critical dimension (cD) control. The E95 of the latest models of Cymer and Gigaphoton is less than 0.35 picometers.
The lithography light source generally adopts a line width narrowing scheme combining a multi-prism beam expander and a large-size grating. The prism beam expander is used to separate wavelengths and maintain a small divergence angle. Usually, 2 to 4 prisms can achieve 20 to 40 times of optical beam expansion. The prism material is fused quartz or calcium fluoride with high transmittance in the ultraviolet band. The laser incident and exit surfaces of the prism are usually coated with anti-reflection coatings. The expanded light spot is projected onto the large-size grating, and the optical path of the prism group and the grating forms a Littrow structure. Considering the beam expansion rate, transmittance and prism anti-reflection requirements of the prism, the incident angle of the prism is usually set between 68 and 71 degrees. The large-size grating is usually a medium-step grating, and its larger blaze angle is conducive to the high-order dispersion and line width compression of the spectrum. The beam after beam expansion can also be incident on a high-reflection plane mirror first and then reflected on the grating. Rotating the high-reflection mirror can change the angle of incidence on the grating, thereby achieving tuning and stable control of the laser center wavelength.
In order to avoid energy loss caused by the strong absorption of ultraviolet laser by oxygen atoms in the atmosphere and to isolate the optical components from external pollution, optical components such as prism expanders, reflectors and large-size gratings are usually assembled in a closed cavity. In the lithography light source, such a cavity is called a line width narrowing module. When the lithography machine is working, a specific flow of high-purity nitrogen or helium is generally passed through the line width narrowing module. In addition to the
full width at half maximum (FwHM) of the peak, the spectral width of the laser should also be able to display the integral width of 95% of the spectral energy (E95). The size and stability of the E95 indicator is one of the important parameters of the lithography machine, which affects the imaging capability of the exposure system and the critical dimension (cD) control. The E95 of the latest models of Cymer and Gigaphoton is less than 0.35 picometers.
Spectrum stabilization technology
The wavelength jitter of high repetition rate pulses and the wavelength drift in a short time will cause the spectrum to be broadened. In order to reduce the exposure aberration caused by spectral changes, the wavelength measurement of the lithography light source must achieve high precision (relative wavelength) and accuracy (absolute wavelength). The relative wavelength measurement can be achieved by one or more etalons. This is because the width and spacing of the interference ring fringes formed by the laser passing through the etalon are related to the wavelength and line width of the laser. On the other hand, the determination of the absolute wavelength (wavelength calibration) can be achieved by comparing the measured relative wavelength with the atomic absorption line. Stable spectral bandwidth is particularly important for low-node lithography applications. Due to the chromatic aberration of the projection lens, the change of spectral bandwidth will cause defocus error, cause contrast loss and generate optical proximity error. In addition, the concentration of fluorine gas in the working gas of the laser cavity will also affect the spectral width of the laser. In the master oscillator-amplifier structure, the spectral width will change nearly linearly with the discharge interval time of the two cavities. Using this feature, the laser spectrum parameters can be detected online and the discharge interval time can be dynamically adjusted by using a closed-loop control system, thereby achieving short-term stable control of the spectrum. In the line width narrowing module, the spectrum of the narrow line width laser is also detected in real time, and the diffraction angle of the grating is dynamically adjusted to control the stability of the central wavelength and line width. The function of the beam uniformity technology lithography machine illumination system is to provide high uniformity illumination for the entire mask surface, and to improve the resolution of the lithography system and increase the depth of focus by controlling the exposure dose and realizing the off-axis illumination mode. The illumination system of high-resolution projection lithography has very high requirements for the wavelength, uniformity, and light intensity of the output light, among which the uniformity of the illumination is required to be 1.5%~1%. The quality of the illumination system directly affects the quality of projection lithography, and high uniformity illumination technology is the main key technology of the illumination system. In systems where the requirements for illumination uniformity are not very high, the illumination uniformity can be improved by adding a compensator. The principle of the compensator is to improve the uniformity of the light energy distribution by controlling the transmittance at various locations on the light-transmitting surface. In order to further improve the uniformity of the output light energy distribution, an optical homogenizer (or optical integrator) is usually used in the illumination system. A compound eye lens or a rod-shaped light guide rod is usually used as an optical homogenizer. The principle of improving uniformity is to divide the light beam into many small beams, so that the uniformity of each sub-beam is improved compared with the uniformity of the original beam, and then all the sub-beams are superimposed in space, so that the light energy distribution of each sub-beam is further compensated, thereby greatly improving the uniformity of light energy distribution.
When designing the optical path of the lighting system, the collimation system of the beam expansion should be designed first. Since the beam cross-section of the excimer laser is rectangular, the original rectangular spot of the excimer laser needs to be changed into a square distribution. A set of cylindrical beam expanders is required for beam expansion, and then a set of spherical beam expanders is used to expand the beam into a square spot of a suitable size, and then a lens array is used to obtain good lighting uniformity M. This is because the microlens array divides the laser beam with uneven energy distribution. Using the mathematical integration principle, it can be seen that the superposition of many thin beams can obtain lighting with relatively uniform energy distribution. Finally, the microlens array group must cooperate with the condenser group to obtain better illumination uniformity. Kohler illumination is usually used. When the front lens array of the microlens array group is imaged on the mask by the optical system behind it, the rear lens array should be imaged by the condenser group at the entrance pupil of the projection objective lens. This ensures both image uniformity and matching with the projection objective lens. At the same time, in order to match the entrance pupil of the projection system with the exit pupil of the illumination system, the exit pupil of the illumination system should be at infinity. At this time, the mask should be located at the rear focal plane of the condenser group. The rear group of the microlens array should be located at the front focal plane of the condenser group. Only in this way can the front group of the microlens array be imaged on the mask by the optical system behind it. In addition, for the condenser group, because the field of view and aperture angle are relatively small, the aberration can be better corrected with only two spherical lenses.
The issue of beam energy utilization of the exposure system and the overall uniformity of the laser beam after passing through the projection system both require some quantitative evaluation indicators. For example, the main evaluation indicators for the uniformity of the excimer laser beam include processing window, energy fraction, flat top factor, etc.
When designing the optical path of the lighting system, the collimation system of the beam expansion should be designed first. Since the beam cross-section of the excimer laser is rectangular, the original rectangular spot of the excimer laser needs to be changed into a square distribution. A set of cylindrical beam expanders is required for beam expansion, and then a set of spherical beam expanders is used to expand the beam into a square spot of a suitable size, and then a lens array is used to obtain good lighting uniformity M. This is because the microlens array divides the laser beam with uneven energy distribution. Using the mathematical integration principle, it can be seen that the superposition of many thin beams can obtain lighting with relatively uniform energy distribution. Finally, the microlens array group must cooperate with the condenser group to obtain better illumination uniformity. Kohler illumination is usually used. When the front lens array of the microlens array group is imaged on the mask by the optical system behind it, the rear lens array should be imaged by the condenser group at the entrance pupil of the projection objective lens. This ensures both image uniformity and matching with the projection objective lens. At the same time, in order to match the entrance pupil of the projection system with the exit pupil of the illumination system, the exit pupil of the illumination system should be at infinity. At this time, the mask should be located at the rear focal plane of the condenser group. The rear group of the microlens array should be located at the front focal plane of the condenser group. Only in this way can the front group of the microlens array be imaged on the mask by the optical system behind it. In addition, for the condenser group, because the field of view and aperture angle are relatively small, the aberration can be better corrected with only two spherical lenses.
The issue of beam energy utilization of the exposure system and the overall uniformity of the laser beam after passing through the projection system both require some quantitative evaluation indicators. For example, the main evaluation indicators for the uniformity of the excimer laser beam include processing window, energy fraction, flat top factor, etc.
Liquid Immersion Technology
According to the Rayleigh formula, increasing the numerical aperture (NA) is an effective technical approach to improve lithography accuracy. The principle of immersion lithography is to fill the space between the projection lens of the lithography machine and the photoresist on the wafer with a high refractive index liquid, so that the numerical aperture is greater than 1.
For 193-nanometer lithography, the traditional dry lithography machine has air between the projection lens and the wafer, and its maximum effective numerical aperture is only 0.93. The refractive index of water at 193 nanometers is 1.44, and it has a high transmittance. During the exposure process, the substances dissolved in the water may be deposited on the lower surface of the last lens of the projection lens or on the photoresist, causing imaging defects, and the gas dissolved in the water may also form bubbles, causing light to scatter and refract. Therefore, the industry currently generally uses cheap, easy-to-obtain deionized and degassed pure water as the immersion liquid of the first generation of immersion lithography machines. Using water as the immersion liquid, a numerical aperture of 1.35 can be achieved, and the lithography node has reached 32 nanometers. In order to extend immersion lithography technology to 32 nanometers or even 22 nanometers, liquids with higher refractive indices are used instead of water as immersion liquids. Many companies are working on the research of second-generation immersion liquids and have found a variety of liquids with a refractive index of around 1.65. After the introduction of the second-generation immersion liquid, finding a projection objective lens bottom lens material with a high refractive index (>1.65) will become the key to further improve the numerical aperture.
Immersion lithography technology has shown great advantages and development potential, and a series of problems brought by immersion have also found corresponding countermeasures. Such as liquid temperature control, pressure measurement and control, bubble elimination, photoresist contamination caused by liquid immersion, and re-optimization of the optical system. Immersion lithography machines will continue to develop in the direction of larger numerical apertures. In the future, companies will use various second-generation immersion liquids and high-refractive-index bottom lens materials to build experimental platforms for exposure testing, analyze exposure defects, line width uniformity, liquid circulation, and the impact of liquid on imaging quality, find the best material, and design immersion lithography machines with higher numerical apertures on this basis to meet the challenges of smaller lithography line widths.
Immersion lithography technology has shown great advantages and development potential, and a series of problems brought by immersion have also found corresponding countermeasures. Such as liquid temperature control, pressure measurement and control, bubble elimination, photoresist contamination caused by liquid immersion, and re-optimization of the optical system. Immersion lithography machines will continue to develop in the direction of larger numerical apertures. In the future, companies will use various second-generation immersion liquids and high-refractive-index bottom lens materials to build experimental platforms for exposure testing, analyze exposure defects, line width uniformity, liquid circulation, and the impact of liquid on imaging quality, find the best material, and design immersion lithography machines with higher numerical apertures on this basis to meet the challenges of smaller lithography line widths.
A new generation of extreme ultraviolet lithography light sources
Currently, semiconductor companies have entered the 10-nanometer process, but the physical limitations they face are getting higher and higher. Improving semiconductor processes requires new equipment. Extreme ultraviolet (EUV) lithography machines are the key to breaking through the 10-nanometer feature size and the subsequent 7-nanometer and 5-nanometer processes, and extreme ultraviolet light with a wavelength of 13.5 nanometers is likely to become the next generation of lithography light sources. Laser plasma extreme ultraviolet (LPP-EUV) light sources are currently considered to be the most promising high-power EUV lithography light sources due to their good power expansion capabilities.
Since extreme ultraviolet light with a wavelength of 10 to 14 nanometers is strongly absorbed in materials, its optical system must adopt a reflective form. LPP-EUv usually uses a high-power COZ laser beam to irradiate a droplet target (usually metal Sn) to generate plasma and radiate ultraviolet light. The reflective focusing system is then used to collect EUV radiation and project it onto the master. The EUv radiation reflected by the master causes the mask pattern to pass through a reflective imaging system and then shrink the projection image onto a silicon wafer coated with a resist. An important problem that limits the increase in EUv light source power is the removal of target material residues on the condenser. The Sn in these residues will cause the reflectivity of the mirror to decrease. In addition to the light source, EUv's technical challenges also include the manufacture of masks, precision optical systems and components.
At the 2016 International Society for Optical Engineering (SPIE) Advanced Lithography Technology Seminar, participants believed that although EUv technology has made great progress, it is still not suitable for mass production of semiconductors. ASML of the Netherlands and Gigaphoton of Japan are leading in the field of EUV light sources, and both have the ability to develop 250-watt EUV light sources. ASML has developed the NXE:33xOB commercial lithography light source, which will reach a power of 250 watts in 2016 and can mass produce 125 wafers per hour. In July 2016, Gigaphoton demonstrated a 250-watt LPP-EUV prototype with an efficiency of 4%. However, EUV, as the key to breakthroughs in new-generation semiconductor processes, has made less progress than expected. Samsung, Taiwan Semiconductor Manufacturing Company (TSMC) and Intel have basically agreed that the 5-7 nanometer node will be achieved around 2020. Each EUV lithography machine is worth $110 million, which is expensive but still favored by chip manufacturers. Samsung and TSMC are actively purchasing EUV lithography machines in order to use EUV processes at 7-10 nanometer nodes to increase density and reduce costs.
At the 2016 International Society for Optical Engineering (SPIE) Advanced Lithography Technology Seminar, participants believed that although EUv technology has made great progress, it is still not suitable for mass production of semiconductors. ASML of the Netherlands and Gigaphoton of Japan are leading in the field of EUV light sources, and both have the ability to develop 250-watt EUV light sources. ASML has developed the NXE:33xOB commercial lithography light source, which will reach a power of 250 watts in 2016 and can mass produce 125 wafers per hour. In July 2016, Gigaphoton demonstrated a 250-watt LPP-EUV prototype with an efficiency of 4%. However, EUV, as the key to breakthroughs in new-generation semiconductor processes, has made less progress than expected. Samsung, Taiwan Semiconductor Manufacturing Company (TSMC) and Intel have basically agreed that the 5-7 nanometer node will be achieved around 2020. Each EUV lithography machine is worth $110 million, which is expensive but still favored by chip manufacturers. Samsung and TSMC are actively purchasing EUV lithography machines in order to use EUV processes at 7-10 nanometer nodes to increase density and reduce costs.
Photolithography is a key technology to promote the development of integrated circuits and related industries. Ten years ago, a 512-megabyte memory stick cost several hundred yuan. Today, a memory stick of the same price can store 16 to 32 gigabytes. Today, the computing performance of a mid-range mobile phone exceeds that of a personal computer ten years ago, and is growing at the rate predicted by Moore's Law. The development of photolithography has greatly improved the computing speed and storage capacity of chips, and is also changing people's lives.
References: [1] Ma Jianjun. Historical evolution of optical lithography technology. Special Equipment for Electronic Industry, 2008, 37 (4): 28-32. [2] Zhang Haibo, Lou Qihong, Zhou Jun, et al. ArF excimer laser linewidth compression technology. Laser and Optoelectronics Progress, 2009, 46(12): 46-51. [3] Yu Yinshan, You Libing, Liang Xu, et al. Development of excimer laser technology. Chinese Laser, 2010, 37(9): 2253-2270. [4] Li Hongxia, Lou Qihong, Ye Zhenhuan, et al. Research on evaluation indexes of excimer laser beam uniformity. High Power Laser and Particle Beams, 2004, 16(6): 729-732. [5] Yuan Qiongyan, Wang Xiangchao, Shi Weijie, et al. Research progress of immersion lithography technology. Laser and Optoelectronics Progress, 2006, 43(8): 13-20. [6] Saito T, Ueno Y, Yabu T, et al. LPP-EUv light source for HVM lithog-raphy. Proc. SPIE10254, XXI International Symposium on High Power Laser Systems and Applications 2016, 2017. [7] Mizoguchi H, Nakarai H, Abe T, et al. Development of 25Ow EUv light source for HVM lithography. China Semiconductor Technology International Conference, y20i7: l-4.
References: [1] Ma Jianjun. Historical evolution of optical lithography technology. Special Equipment for Electronic Industry, 2008, 37 (4): 28-32. [2] Zhang Haibo, Lou Qihong, Zhou Jun, et al. ArF excimer laser linewidth compression technology. Laser and Optoelectronics Progress, 2009, 46(12): 46-51. [3] Yu Yinshan, You Libing, Liang Xu, et al. Development of excimer laser technology. Chinese Laser, 2010, 37(9): 2253-2270. [4] Li Hongxia, Lou Qihong, Ye Zhenhuan, et al. Research on evaluation indexes of excimer laser beam uniformity. High Power Laser and Particle Beams, 2004, 16(6): 729-732. [5] Yuan Qiongyan, Wang Xiangchao, Shi Weijie, et al. Research progress of immersion lithography technology. Laser and Optoelectronics Progress, 2006, 43(8): 13-20. [6] Saito T, Ueno Y, Yabu T, et al. LPP-EUv light source for HVM lithog-raphy. Proc. SPIE10254, XXI International Symposium on High Power Laser Systems and Applications 2016, 2017. [7] Mizoguchi H, Nakarai H, Abe T, et al. Development of 25Ow EUv light source for HVM lithography. China Semiconductor Technology International Conference, y20i7: l-4.
*Disclaimer: This article is originally written by the author. The content of the article is the author's personal opinion. Semiconductor Industry Observer reprints it only to convey a different point of view. It does not mean that Semiconductor Industry Observer agrees or supports this point of view. If you have any objections, please contact Semiconductor Industry Observer.
Today is the 2508th issue of content shared by "Semiconductor Industry Observer" for you, welcome to follow.
Recommended Reading
★ Will Applied Materials defeat ASML and return to the leading position in semiconductor equipment?
★ Intel’s strongest competitor in history is not AMD!
★ “Ice and Fire” in the Semiconductor Top List
Semiconductor Industry Observation
" The first vertical media in semiconductor industry "
Real-time professional original depth
Scan the QR code , reply to the keywords below, and read more
Storage｜Wafer ｜Lithography ｜FPGA｜Apple｜OLED｜RF｜Packaging and Testing
Reply
Submit your article
and read "How to become a member of "Semiconductor Industry Observer""
Reply Search and you can easily find other articles that interest you!
京公网安备 11010802033920号