The popularity of ASML's optical projection lithography machine has been long-lasting. With the attention attracted by the concepts of High NA EUV lithography machines and domestic lithography machines, various industry research reports have emerged one after another. In contrast, the track of electron beam lithography seems deserted.
In addition to the application of conventional scientific research directions, small-scale trial production, quantum chips are also the main application of electron beam lithography machines. The patterning of photomasks in photomask factories is the most important purpose of electron beam lithography at present, and its importance is no less than that of ASML's various types of lithography equipment.
Electron beam and light: Different paths are the same
The wave-particle duality of the electron itself determines that at higher energy, the higher frequency can be equivalent to a smaller wavelength. When the energy of the electron beam is, its equivalent wavelength is about 0.004 nm, which is much smaller than 13.5 nm of the EUV.
There is no doubt that electron beam lithography has better resolution.
The structure of electron beam lithography can be roughly divided into electron guns, vacuum systems, precision workpiece tables and motion systems, and data processing systems.
Source: 100kV Beam: JBX--, JEOL News 07.2000 Vol.35
The electron gun controls the generation of the electron beam, and focuses and projects the electron beam onto the substrate surface through the electromagnetic coil and the aperture, which acts as equivalent to the projection objective lens of an optical projection lithography machine. Unlike optical projection lithography, the electron beam needs to be rapidly deflected and shielded during the electron beam lithography process, so a high-speed beam gate is needed to control it.
The vacuum system maintains a high vacuum in the cavity through a molecular pump, thereby reducing the interference caused by gas molecules in the air to the electron beam. Ion pumps are used to maintain ultra-high vacuum in the lens barrel, reducing the charging effect caused by additional contaminants, causing unexpected deflection of the electron beam.
The precision workpiece table and the motion system control the movement of the substrate, realize accurate graphic splicing, and improve exposure efficiency. The mechanism of co-motion between the workpiece table and the beam gate used for advanced electron beam exposure is called write on fly, which takes into account the speed and accuracy of direct graphics writing to the greatest extent.
In the advanced mask graphics process, the original layout and data files are very large, with a capacity of even more than 500GB or even reaching the TB level. Therefore, data preparation and parsing (Data) requires a huge amount of computing power, so high-performance data processing systems are indispensable.
Compared with the output of 12-inch wafers of more than 270 pieces per hour for optical projection lithography machines, the efficiency of an electron beam lithography machine is much lower than that of a 6-inch mask without 6 to 12 hours. However, it is worth it to exchange for a photocopy mask for tens of thousands of exposure life in an optical projection lithography machine.
As one of the alternative technologies of the early next-generation lithography technology (NGL, Next), electron beam lithography machines were also first used in wafer exposure. With the advancement of Moore's Law, its characteristic of direct writing without masks is used to replace laser direct writing to produce masks.
From deformation to clone: the path to electron beam development
In the 1970s, East Germany Zeiss invented the first commercial electron beam lithography machine for mankind. In the 1990s, after the merger of the two Germans, East-West Germany Zeiss was merged into Carl Zeiss, and the department of the electron beam lithography machine was split into Jena Optics and independent. Later, after being acquired by Leica, it became independent and became the current one.
From the perspective of technological development, in order to improve output, large beam current has always been the development direction of technology. The other direction is the beam spot control of electron beams, which have undergone the development process of Gaussian beams, deformation beams to multiple beams, and their output speed and accuracy have been greatly improved.
Source: Current status and prospects for the development of electron beam lithography equipment, Liang Huikang & Duan Huigao
The beam spot size of the Gaussian beam (Beam) cannot be adjusted by changing and adjusting, and raster scanning is mainly used in the exposure process. Its mechanism is simple, without the need for complex control of the aperture, and the switching control of the beam gate is relatively simple.
The deformation beam (VSB) can be controlled by the aperture so that the beam spot size can be changed, so that the exposure efficiency can be improved leaps and bounds. Vector scanning can also greatly improve exposure efficiency, but the control requirements for the aperture, beam gate and electron beam deflection are high.
Source: Institute of Semiconductor, Chinese Academy of Sciences
Multi-electron beams/multibeams divide the electron beam into tens or even tens of thousands of beams through the aperture array, and control them through the array beam gate to realize direct write exposure of multiple electron beams in different areas of the substrate, greatly improving the writing speed. Taking the MBMW-101 of IMS as an example, the number of cocoa-programmed electron beams can reach beams (arrays).
Source: Current status and prospects for the development of electron beam lithography equipment, Liang Huikang & Duan Huigao
Just as ASML's EUV lithography machine fails to enter the mainland market, IMS's multi-electron beam lithography machine cannot enter the mainland Chinese market, which is also one of the important reasons for restricting mainland wafer fabs from entering efficient and low-cost advanced chip manufacturing.
Compared with ASML's EUV lithography machine, the industry has obviously insufficient attention to multi-electron beam lithography machine.
City on the Top of the Mountain: Who will climb?
The development process of electron beam lithography machines is the history of the development of scanning electron microscopes. The technical themes are closely related to scanning electron microscopes. The industry leaders of electron beam lithography machines are almost all technical masters in the field of scanning electron microscopes.
As mentioned above, although Zeiss invented the earliest commercial electron beam lithography machine, it eventually divested its related business. In the field of wafer exposure, Germany and Raith and the Netherlands still have a place, while in the photomask graphics market, the track appears much narrower.
On the one hand, due to the condition that the graphic light mask is oriented towards the industrial market, the application is single and the market space is limited, and it is impossible to accommodate too many players. Several companies that entered the early share have been divided up.
In the mainland market, electron beam lithography machines used for mask patterning have completely entered the era of deformation beams. Among them, Japanese electronic JEOL has a high market share in the mature process market, while both Japanese occupy the high-end market. In the global market, Austria's IMS debuted at its peak, directly entered the multi-bubble market, and received investment from Intel. Among the world's advanced processes, IMS has an absolute advantage. It is worth mentioning that IMS's multi-bubble direct writing device also had the opportunity to enter the Chinese market in its early years, and eventually missed the opportunity for well-known reasons.
The research and development and marketization of domestic electron beam lithography equipment have begun, but it has not yet penetrated into the market for mask patterning. At present, several companies in China can provide commercial electron beam lithography machines with a resolution of 20-50nm. The main users are currently colleges and universities. With the rapid changes in the geopolitical situation, entering the graphic market of light masks can be said to be a set goal and a realistic demand from the client.
As mentioned above, electron beam lithography machines rely on a series of technologies related to scanning electron microscopes. Therefore, if domestic equipment wants to develop and grow better, it must rely on the development and support of local high-end precision instruments. With this process and application, it can only be implemented based on hardware. As a precondition, advanced scanning electron microscope is a path that cannot be bypassed!
With the rapid development of the mainland AI and consumer electronics markets and demand, the demand for domestic advanced processes has shown explosive growth. A large number of advanced photocapsules are like horns in the throat, so domestic electron beam lithography machines have a long way to go and are urgent.
